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The Tiris project is located in Mauritania a country with a well established mining industry. The 1.25 Mtpa mine and process plant has been designed to take full advantage of these unusual characteristics whilst providing a low capital cost and rapid project development and construction. The Tiris mineralisation allows for rejection of 85-90% of ore mass as barren rejects through a simple beneficiation process. To optimise the material transport, a modular transportable beneficiation circuit located close to the resources was incorporated. The trucks will have a transport distance of around one to two km to the beneficiation stage and slurried product will be pumped to the processing plant.
This paper will delve into some important testwork a process plant design for a transportable modular front end plant will have to be moved twice. Given that this will stop production until all the plant systems and utilities are re-connected and re-commissioned, a highly planned shutdown will be required. An allowance of four weeks to shift the beneficiation circuit each time has been made in the mine schedule.
A common question raised by mine managers is why do we need geometallurgy, what are the costs and the benefits?. Geometallurgy is an interdisciplinary field that integrates geology, mining and metallurgy. Its purpose is to create predictive models for metallurgical behaviour before the ore is extracted. The aim is to fundamentally improve understand of resource economics across the project. Geometallurgy is a proven strategy for effective ore characterisation and improved prediction of process variability and can be used to enhance economics and reduce risk. Geometallurgy can optimise the life of a project.
Implementing geometallurgy requires planning and developing a database and inputting this into ore block models that display the distribution of key metallurgical parameters throughout the orebody that support metallurgical process modelling and add value to the planning and optimization process. A geometallurgical modeling and approach can directly reduce the risks in production stages, such as meeting the production targets. Geometallurgy acts on both consequences and likelihood axes in reducing the risk. This paper will delve into some important case studies where geometallurgy has made breakthroughs in mine function and continues to be developed today, fostering innovation and productivity.
Previous studies found that a conventional crush–grind–float process was not economically viable for this large, low-grade copper deposit due to ore hardness and low grade, which would require high grinding energy and therefore high capital and operating costs. However, new technologies such as ore sorting, high pressure grinding rolls (HPGR), and coarse particle flotation (CPF) can significantly reduce energy consumption, which is typically the largest processing cost. For example, CPF can achieve around 80% recovery at particle sizes of ~500 microns, reducing grinding requirements. Sensor-based ore sorting can also pre-concentrate ore by rejecting waste early, reducing processing volumes and improving feed grades.
Another option is heap leaching, which is well suited to large, low-grade deposits. Advances such as HPGR crushing, catalysed chemistry, and bacterial leaching at ~60°C can improve leach performance and overcome chalcopyrite passivation. Heap leaching generally has lower capital and operating costs than whole-ore flotation. Additional benefits may come from removing fines and roasting a pyrite–copper concentrate to produce acid on site, supporting the leach process and lowering costs.
Progress is being made with reducing reliance on carbon in the resource sector in Australia and reducing green house gases (GHG). The progress is greater for new projects rather than retrofitting changes to older existing projects. This sector is crucial to Australia’s standard of living. Energy is typically the single largest cost input for these projects. The options available for GHG reduction in the mining and metal industry include using renewable energy such as wind or solar, hydrogen, ammonia, reforestation, CO2 capture and storage, biological solutions and initiatives towards energy reduction, waste heat recovery and reducing energy use.
At the same time energy efficiency initiatives are being implemented. The resource sector has an important role to play in reducing global emissions. The mining industry may have difficulty in wide-scale electrification according to experts, however, with access to massive infrastructure and equipment, the mining industry may be able to harness naturally occurring capability in carbon capture and storage with relative ease, and researchers are currently exploring circular mining economy which has great promise.
Based on ISO 14064-1 the industry has started to measure their carbon footprint and this has benefits of compliance, improvement in reduction, cost savings and improved corporate reputation. A number of case studies are cited where this has been successfully employed.
The rotary kiln electric arc furnace (RKEF) technology consists of three main stages, viz: drying of nickel ore in a rotary dryer (RD), reduction of moisture content in a rotary kiln (RK) and smelting of nickel ore to produce crude FeNi in an electric furnace (EF). To support operations, the smelter is equipped with a coal fired power plant and supporting facilities, including: seawater intake and discharge facilities. The main facilities are drying, rotary kiln reduction, the electric arc furnace to produce ferronickel ingots and slag. Historically these plants operated in Russia, Macedonia, Brazil and China however recently there has been a rapid expansion of RKEF plants in Indonesia.
For nickel sulphide concentrates Outokumpu Flash smelting, Inco or Noranda smelting has been used. Converting was done separately but over time the Flash Smelters were modified to produce matte with hydrometallurgical processing of the matte. More recently Chinese Bottom Blown Furnaces have been developed for smelting base metals including nickel. Going forward all of these smelting processes face challenges with their carbon footprint particularly RKEF.
This paper will look at a number of recent projects.
The very high current gold price is resulting in waste dumps from 20 years ago being processed with new technology to recover gold by heap leaching. The crush size sensitivity of these ores has meant that finer crushing and agglomeration was required to achieve a high gold recovery. High Pressure Grinding Rolls (HPGR) is a newcomer to grinding circuits and offers energy savings, lower media wear and recovery gains which make it hard to resists compared to conventional grinding circuits. In addition the use of ore sorting and gravity pre concentration techniques are discussed to demonstrate how low grade gold heap leach flowsheets are changing.
Laboratory small scale and pilot testing and scaleup is well established and reliable. From an operational aspect the ability to change operating pressures and screen apertures offers significant operational flexibility not offered by a SAG mill. In addition the rolls life has greatly increased due to innovation and change out times have shortened. The reliability of HPGR has been shown to be higher than SAG mills. The importance of agglomeration and percolation testing to achieve high gold recoveries is also discussed. Successful HPGR applications started with cement clinker and then hard iron ores, gold ores, copper ores and now lithium projects. Recent applications are cited and discussed in detail including operating history.
Decarbonisation represents a long term threat to the Western Australian iron ore exporters. The global steel industry is starting to convert to green steel. This is very evident in Sweden. The DR process requires +67% iron much higher than Western Australian iron ore grades currently. Therefore some post mining beneficiation will be required for Western Australian ores. In terms of DR plants there are options such as MIDREX, Circored, Corex or Finmet that can be considered. These may be initially based on natural gas and steam reforming to produce grey hydrogen.
Others are pursuing carbon capture technologies but these look difficult. In the longer term green hydrogen based on solar or wind energy will be required however the cost of producing the hydrogen is currently too high. There are other process options being developed by Neosmelt/BHP/Bluescope Steel and Posco with their HyREX process. Electrowinning of iron is also under investigation
A large low grade gold ore deposit of 0.4 g/t cannot be processed in a conventional carbon in leach (CIL) plant because of the low grade and poor economics despite today’s record gold prices. The first step was to look at the likely beneficiation options that could be used to develop a technical and commercially viable process flowsheet. On account of the large size of the potentially exploitable orebody, a number of options such as ore sorting, gravity gold recovery, coarse particle flotation and heap leaching were evaluated in order to develop a potential process flowsheet.
High purity alumina (HPA) is a processed premium non-metallurgical alumina product characterised by its purity level i.e. 99.99% (4N), 99.999% (5N). The market price, application, and performance of HPA varies widely according to its degree of purity. High purity alumina is a form of aluminium oxide (Al2O3) with growing use in LED lighting and coating on the ceramic cathode separator sheets in lithium ion batteries. This paper describes a study on producing high purity alumina from feldspar to produce HPA and potash for use as a fertiliser. The project was positive for a number of reasons. High potassium extraction >99% was achieved in the alkali leach using sodium hydroxide as the leaching agent and full dissolution of the alkali leach residue was achieved with hydrochloric and sulphuric acid. The potential to produce a high purity alumina product via a complex but promising emerging process was assessed. The potential to extract potassium as potassium sulphate to add value to the project was also demonstrated with the testwork |
This paper describes a study on producing high purity quartz to meet the tight specification required by modern day high efficiency solar panels, lighting and fibre optics. The market specification is four and even five nines. The market for high purity silica to be used in solar panels is growing rapidly due to the growth in renewable energy applications. The processing of quartz is the key step to adding value. These unit processes include primary crushing, scrubbing. Attrition and magnetic separation, flotation and acid leaching followed by hot chlorination. The grinding of quartz requires specialist equipment because of the hardness and extreme abrasion. No increase in iron can be tolerated. Chemical refining is very effective. Critical impurities are aluminium, iron, sodium, potassium, lithium, titanium, zircon, calcium and magnesium. During the hot chlorination process at 1,200 C in a chlorine hydrogen chloride gas atmosphere. Only specialist companies can achieve this step and the danger of releasing any gas outside the vessel is very serious. Microelectronic components are created by chemically fabricating wafers of semiconductors such as silicon to obtain the desired transport of electrical charge and control of the current. The high purity quartz market for >99.97% is a highly secretive and specialised market. High purity quartz is used to make silicon metal. Silicon metal has been designated a Strategic Mineral by the European Commission and by the US Department of justice. This paper describes the laboratory testwork undertaken to produce a high purity quartz pre cursor material from an Australian ore source. |
Magnetic separation is the standard route to produce concentrates. Salt roasting to extract vanadium followed by water leaching has been the standard processing route for many years and this locks up the titanium in a glass phase. The cost of suitable sodium salts, availability of capital and increasing energy costs and energy availability are critical factors in determining the viability of aspiring vanadium producers. Alternatively smelting of concentrate to produce pig iron and titanium slag is also used where the vanadium can be recovered in a slag from the pig iron. In this paper, factors influencing the recovery of vanadium are reviewed and emerging processing trends explored particularly hydrometallurgical. The work done to produce titanium rich concentrates exploiting differences in magnetic susceptibility and new hydrometallurgical routes to produce separate vanadium, titanium and iron oxide products are discussed. The new understanding that the vanadium might be locked in the lattice spinel with iron but it can be effectively leached with high recoveries using catalytic chemistry. The growing demand for vanadium electrolyte in Redox Flow Batteries now adds another value added product which can assist vanadium project economics. The important aspects of the processing of titaniferous magnetites have been condensed from the literature, published works, company websites, our own testwork and personal communication covering a range of titaniferous magnetites. Reference is made to a number of historical projects and future projects covering traditional process flowsheets and new technology process flowsheets such as TIVAN where titanium pigment, iron oxide and vanadium pentoxide are recovered.
Australia had its failures with first generation HPAL plants such as Murrin Murrin, Cawse and Bulong. The second generation plants such as Goro and Ravensthorpe were also problematic. Current nickel prices are at an all time low and even sulphide nickel projects have closed. At the same time Indonesia has built three third generation HPAL projects and is planning seven more on Sulawesi.The usual phases of development, najmely feasibility, approval, construction and commissioning have taken place in record time.In Australia we have a number of HPAL projects in the pipeline but banks are negative on funding and the projects are stalled. Australia has larger reserves of lateritic nickel but we cant compete with Indonesia. This paper looks at why the Indonesians are successful with their HPAL plants and whats holding back plants being developed in Australia. Why have the Indonesians been able to ramp up to capacity in less than 12 months compared to an average of more than five years in the west. |
This paper describes the current best practice and critical steps of developing metallurgical testplans and the final important step to process design of a circuit. No two deposits are the same and developing testplans that address the geology and ore domains is a complex task. Sample selection, and ore characterisation to understand the metallurgical response of an ore is only the start. Invariably testplans need to be updated based on results received. The testwork needs to be considered as a project with the scope of work, schedule, cost, quality, safety and environment the new norms required. It needs to be managed using the best project management knowledge available. The data interpretation of the results is the most difficult part and requires personnel skilled in the art as well as benchmarking and discussing with vendors and reference to existing projects. Project Failure Analysis often highlights where gaps in knowledge existed and the interpretation of the metallurgical results was deficient. In some cases this may require piloting of the process to improve process confidence, reduce risks and provide engineering data. Often this is all summarised in a Metallurgical Summary Report. Process Design is the final step and has its own challenges with regards to not being too conservative but ensuring the design is functional and operable. A number of examples are provided highlighting the lessons learned. |
The global market for lithium products is very attractive with the supply of raw materials falling behind the emerging demand growth in markets such as China. This paper examines the growing number of lithium conversion plants to produce battery grade lithium hydroxide or carbonate. These are complex chemical plants with very high capital costs. For several conversion projects, the feasibility study projected CAPEX and OPEX had been far exceeded during the development. Projects ramp up had been slow, taking around twenty-four to thirty-six months to achieve the requisite battery grade (4N) specifications of the products as well as plant throughput and reliability. This paper references several projects—without identifying them—and lessons learned. Several projects made mistakes and bad decisions with fast tracking and efforts to reduce capital resulting in poor quality equipment; all of which have led to increase in operating costs. Whilst generally, the ore preparation including the acid roasting and leaching steps, which are standard technologies, have proven to be operable, the multi-stage crystallisation and re-leaching steps are proving to be problematic. The softening in lithium prices during 2023 has exacerbated some of these problems. Mergers and takeovers in the industry are occurring. In the longer term, a strengthening of the prices will see a different industry emerge.
Ionic adsorption clays (IAC) are formed by natural weathering of rare earth (RE) bearing minerals and the subsequent adsorption of the rare earth elements (REEs) onto the clay surface. They can be leached from these regolith-hosted clays using only dilute ammonium sulphate solution. Generally, the costs for extracting from such deposits are economic with very low processing costs. It is thus an attractive process if applicable. A testwork organised by iTech Minerals at a commercial laboratory to extract the REEs from a clay sample achieved minimal extraction. iTech contacted METS and a metallurgical testwork programmed was developed and executed. It consisted of ore beneficiation, REE extraction by ion exchange desorption, sulfuric acid baking followed by water leaching, hydrochloric acid leaching and their combinations. The work revealed that the material was not an ionic clay but beneficiation by simple screening resulted in almost doubling of the REE grade while also producing a kaolin by-product. Leaching with hydrochloric acid, yielded an average of 87% extraction of the REEs including more than 90% of the neodymium, while allowing also almost complete recycle of the unconsumed acid. Clearly, these would have a substantial positive impact on the CAPEX and OPEX of its application.
There exists a third class of rare earth (RE) ores, which are called ionic clays. They are typically found in southern China and other subtropical areas. They are formed by the chemical weathering of rare earth elements (REE)-containing parent rocks, resulting in the formation and mobilization of REE ions, which are then adsorbed onto the clay particles and hence, the class name.
The Caralue Prospect in South Australia was initially established as a high purity kaolin prospect following identification of thick intervals of bright white kaolin—close to surface—in several historical drill holes. A 2022 drilling program undertaken by iTech identified significant REEs, in the kaolin rich intervals, over a large area. The Caralue Bluff Prospect has an exploration target of 110-220 Mt @ 635-832 ppm TREO and 19-22% Al2O3. This exploration target is based on 80 drill holes, from a total program of 260 holes, across an area of approximately 12km x 12km, as reported by iTech on 18 August 2022, “Exploration Target Defined at Caralue Bluff”). Significantly, it remains open in multiple directions allowing for possible expansion. The REE mineralisation is rich in key magnet REEs namely neodymium, praseodymium, dysprosium and thulium (Nd-Pr-Dy-Tb) averaging 25% of the REE basket.
Initial testwork organised by Itech Minerals at a commercial laboratory achieved zero recovery. Itech contacted METS and a metallurgical testwork programmed was developed and executed resulting in eighty seven percent (87%) leaching recovery of the REEs. In addition, process optimisation resulted in a reduced OPEX and CAPEX. At the same time a kaolin product was produced as a by-product.
This paper describes a study on processing monazite. Monazite which was previously waste is now an economically significant source of rare earths. The mass composition and percentage basket price is important comparing monazite and xenotime to other minerals. The minerals are highly liberated and produce high grade concentrates. The key steps to processing include cracking, impurity removal and producing a mixed rare earth carbonate product. With cracking we have a choice of caustic conversion or acid bake. Both routes result in a separation of phosphates. The final purification is best done using complex solvent extraction circuits to produce 99.9% REE product.
Monazite is stable and the uranium and thorium are in equilibrium however when processing a state of disequilibrium exists and the radioactive waste needs to be disposed of at a facility such as Tellus near Kalgoorlie in Western Australia.
The key risks, OPEX, CAPEX and project scale are discussed.
The rare earth industry is currently undergoing an unprecedented resurgence driven by the electric vehicle revolution. Each rare earth orebody is different but invariably consists of several rare earth elements that need to be recovered for the process to be economically viable. This necessitates the use of multi-unit processes and the need to deal with complex chemistries. Thus, the process flowsheet, which can become extremely complex, is project specific. So, it is common to limit production to mixed rare earth carbonate products but still requires numerous testwork to optimise, rendering the development timeframe to take around six years at best. |
Significant advances in bacterial leaching of copper sulfide ores has been achieved and laboratory scale testing method for developing a commercial application has been established. Copper recoveries of up to 80% over 120 days is achievable. The success or otherwise of any project is determined by the ore type, testwork required, interpretation of testwork results, ore preparation prior to stacking, and agglomeration requirements. The critical issues that can make or break an operation include bacterial health maintenance, heap temperature control, adequacy of drainage, pad porosity and saturation, and pipe work and irrigation rates. These will be discussed in this paper.
Ultra Fine Grinding (UFG) has been employed for processing refractory gold ores for many years. Environmental considerations have been a large driver for its adoption. Laboratory testwork, pilot trials and operations have improved the gap between UFG and other alternate technologies making it more attractive as a technology choice. In addition, there are a number of equipment types. This paper describes the development of UFG in Australia and overseas as well as different media and reducing the power consumption. The mill selection has proven difficult because of the lack of uniformity among vendors with regard to test methods and sizing of the equipment. Media selection has moved from low-cost silica sand to alumina beads and the advantages of not contaminating the product and media size is a critical determinant of specific energy. There is a divergence of opinion on the benefit of close circuiting with cyclones and overcoming cyclone blockages. Issues of thickening low-density pulp to 50% solids are discussed. Capital and Operating costs are also discussed, and reference is made to laboratory scale and final operating performance.
The gold at the Harbour Lights Mine in Western Australia occurs principally in pyrite and arsenopyrite minerals, rendering it inaccessible to direct cyanidation. Bulk froth flotation produces a low weight concentrate with high recoveries of sulfides and gold. Several concentrate processing options such as roasting, pressure oxidation, bacterial leaching, ultra fine grinding and nitro catalysed decomposition as well as smelting were all tested but proved problematic owing to either mineralogy or environmental issues. The gold in the pyrite is particulate and can be recovered by simple cyanidation after regrind to P80 20 microns. So, the concept that was developed was to separate pyrite and arsenopyrite and export the arsenopyrite concentrate containing gold in solid solution. After investigating several alternatives, a novel flotation process was developed to separate the concentrate into pyrite and arsenopyrite rich fractions. Potassium permanganate was used to achieve a separation by controlling the redox during flotation. The pyrite fraction was finely ground, and cyanide leached, while the arsenopyrite was treated off-site. The plant operated for several years but had to close pending a large capital cost required to allow underground mining. Following on from the work for another project, a number of oxidants namely sodium hypochlorite (NaClO), potassium permanganate (KMnO4), potassium dichromate (K2Cr2O7), and hydrogen peroxide (H2O2) were tested to promote the separation of pyrite (FeS2) from arsenopyrite (FeAsS) by flotation. Hydrogen peroxide provided the best selectivity but cost was an issue. |
Metal prices have declined in real terms, and this makes it more difficult over time to bring new projects into production. They also require better researched and optimised projects with more robust economics. The impact of a reduced carbon footprint will present enormous challenges across the industry. The introduction of renewables has begun, and energy is usually the biggest cost for resource projects. Innovation and the introduction of new technology will be a major challenge required to succeed and overcome some of these issues. Australia’s record of technology innovation in the gold industry, for example, has been brilliant by any standards. Energy is a major cost for processing minerals and the comminution processes we use are inefficient and large consumers of energy. The development of new grinding technologies is long overdue. There will be an increasing trend to hydrometallurgical processing and a decline in pyrometallurgical processes. The tougher environmental constraints being placed on new projects will mean that some projects will not be allowed on environmental grounds. Exploration activities and will be curtailed in sensitive areas and even excluded altogether. Water is going to become a scarce resource and access is going to be difficult with an emphasis on conservation and re-use. Mine Closure is starting at the study stage and the accepted standards are even higher than before. Social and Political issues are impacting on new projects like never before. The common cry “not in my back yard” makes it more difficult to win hearts and minds and gain acceptance for new projects. Mining companies will be called on more and more to provide schools, hospitals and services where governments fail to do so particularly in impoverished areas. Mining projects are only now starting to implement sustainability policies and understand the full impact of such policies including a greater role for recycling. The mining industry could become a global leader in sustainable development. The industry has in the past demonstrated a willingness to better understand and resolve difficult issues at the local level.
Magnetite ores can be used to produce very high-grade concentrates that are suitable feed for the direct reduction process route, but the high sulfur content of the concentrates causes substantial environmental issues. Processing of high sulfur magnetite ore is therefore increasingly problematic for the industry. Generally, the industry demands a concentrate with <0.05% sulfur and <2% silica. This paper reports the outcomes of a work to produce a concentrate with the requisite low sulfur content from a sulfur rich magnetite ore. The main findings may be summarised as follows: If the sulfur is present in magnetite as monoclinic pyrrhotite, it can be beneficiated using magnetic separation and hence, discarded. X-ray diffraction and Qemscan analyses revealed that the magnetite was liberated at P80 30 microns and associated with maghemite, pyrrhotite, carbonates and hematite with very low amounts of chalcopyrite, sphalerite and arsenopyrite. Sulfur removal using flotation was the first stage of investigation and this required flash flotation in the grinding stage followed by column flotation of the initial concentrate to generate the final concentrate. At the same time, it was observed that oxidation of the pyrrhotite had a negative effect on its flotation requiring copper sulphate to activate it. Bioleaching and concentrate leaching were also considered and achieved over 90% sulfur recovery but were deemed unsuitable owing to the production of highly reactive wastes and high CAPEX. Reference is made to a number of operating magnetite producers and how they manage the sulfur in feed.
Introduction:
The current challenges faced by the resource sector are enormous, with the investment required and changes needed to take place in a relatively short time staggering. This sector is crucial to Australia’s standard of living, and how we manage the transition will have long term outcomes. This paper identifies potential technologies for carbon dioxide abatement from the mining and metal industries with special reference to the Australian Resources Sector. Activities such as mineral processing, hydrometallurgy and smelting are very energy intensive and have historically relied on fossils fuels which produce Green House Gases (GHG). There are many new resource projects under development with a significant GHG footprint. These projects are receiving feedback from financial institutions and banks that they need to reduce their GHG footprint to obtain funding. An analysis and quantification of the potential GHG reduction of carbon sinks and sequestration options for the mining and metal industry indicates there are no easy solutions and they all come with significant capital cost implications. This paper includes indicative cost estimates for different options that are currently available. The options available for GHG reduction in the mining and metal industry include using renewable energy such as wind or solar, hydrogen, ammonia, reforestation, CO2 capture and storage, biological solutions and initiatives towards energy reduction, waste heat recovery and reducing energy use. The message being received from government, regulators and financial institutions is that whilst there will be a transition phase, “greenwashing” will not be acceptable longer term. This paper concludes with a number of actual project examples and recommendations resulting from a number of studies.
Metal prices have declined in real terms, and this makes it more difficult over time to bring new projects into production. They also require better researched and optimised projects with more robust economics. The impact of a reduced carbon footprint will present enormous challenges across the industry. The introduction of renewables has begun and energy is usually the biggest cost for resource projects. Innovation and the introduction of new technology will be a major challenge required to succeed and overcome some of these issues. Australia’s record of technology innovation in the gold industry, for example, has been brilliant by any standards. Energy is a major cost for processing minerals and the comminution processes we use are inefficient and large consumers of energy. The development of new grinding technologies is long overdue. There will be an increasing trend to hydrometallurgical processing and a decline in pyrometallurgical processes. The tougher environmental constraints being placed on new projects will mean that some projects will not be allowed on environmental grounds. Exploration activities and will be curtailed in sensitive areas and even excluded altogether. Water is going to become a scarce resource and access is going to be difficult with an emphasis on conservation and re-use. Mine Closure is starting at the study stage and the accepted standards are even higher than before. Social and Political issues are impacting on new projects like never before. The common cry “not in my back yard” makes it more difficult to win hearts and minds and gain acceptance for new projects. Mining companies will be called on more and more to provide schools, hospitals and services where governments fail to do so particularly in impoverished areas. Mining projects are only now starting to implement sustainability policies and understand the full impact of such policies including a greater role for recycling. The mining industry could become a global leader in sustainable development. The industry has in the past demonstrated a willingness to better understand and resolve difficult issues at the local level.
The green revolution using wind generators and solar cells to produce low cost energy will require batteries to store this renewable energy. The vanadium redox flow battery (VRFB) is one type of electrochemical energy storage devices ideally suited to storage of such power. The battery operates by reduction oxidation chemical reactions in liquid vanadium electrolyte (VE) which flow through the battery during charge and discharge.
The study has also looked at the possible technologies that can be used for VE production from vanadium pentoxide, ammonium meta vanadate or pregnant liquor solution. Based on the technology study it was found that various methods could be used to produce VE with different options showing different levels of complexity and CAPEX/OPEX. Different electrolyte production methods demonstrated that many different reducing agents could be used and the purity of the feedstock would greatly affect the number of purification stages required. It was found that sulfuric acid would be the recommended solvent due to the best combination of vanadium-ion solubilities and redox-couple reversibility for redox flow cell applications. The specifications for VE varied depending on the VRFB manufacturer or electrolyte producer. Nonetheless,
it seems to be a trend towards higher purity electrolytes. Two options were selected as the more promising options based on the options study and they were
1) Option 1: VE production using SO2 as the reducing agent
2) Option 2: VE production by electrolysis
The two options were further assessed and then ranked based on the product quality, plant capability, economics, environmental impacts, and metallurgical risks. The ranking is preliminary in nature based on a qualitative review given the available information, experience, and vendor feedback.
Titaniferous magnetite deposits are a significant source of vanadium for use in high strength steel alloying and other chemical applications as well as producing titanium slag for the chloride production of titanium pigment. The mineralogy of the deposits varies markedly and the ore characteristics strongly influence the process route selected and the metallurgical outcomes. Characterisation of the ores reveals the presence of magnetite, ilmenite and other unique vanadium minerals such as spinel hematite and goethite with variable degrees of weathering along with weathered products of the host rock. The standard processing route was to crush, grind and magnetically recover a concentrate for salt roasting to produce a soluble vanadate.
Ore beneficiation is practised to generate an iron-based mineral concentrate containing much of the vanadium with low combined silica and alumina levels of 4%. Typical processing problems encountered are fine liberation size, potential over grinding of the magnetite, and variable response to magnetic separation as a result of the weathering profile. Beneficiation options are restricted, and generally focused on producing a combined iron and titanium rich concentrate, containing vanadium due to the fact that ilmenite, magnetite and their products of weathering are magnetic and have similar specific gravities making their separation difficult. The ilmenite usually contains up to 0.5% levels of vanadium, making its separation from the iron minerals containing higher levels of up to 3% vanadium highly desirable. Magnetic separation is the standard route to produce concentrates. Salt roasting to extract vanadium followed by water leaching has been the standard processing route for many years and this locks up the titanium in a glass phase. The cost of suitable sodium salts, availability of capital and increasing energy costs and energy availability are critical factors in determining the viability of aspiring vanadium producers. Alternatively, smelting of concentrate
to produce pig iron and titanium slag is also used, where the vanadium can be recovered in a slag from the pig iron. In this paper, factors influencing the recovery of vanadium are reviewed and emerging processing trends explored. The work done to produce titanium rich concentrates exploiting differences in magnetic susceptibility and new hydrometallurgical routes to produce separate vanadium, titanium and iron
oxide products are discussed. The growing demand for vanadium electrolyte in Redox Flow Batteries now adds another value added product, which can assist vanadium project economics. The important aspects of the processing of titaniferous magnetites have been condensed from the literature, published works, company websites, our own
testwork and personal communication covering a range of titaniferous magnetites. Reference is made to a number of historical projects and future projects covering traditional process flowsheets and new technology process flowsheets such as TIVAN, where titanium pigment, iron oxide and vanadium pentoxide are recovered.
The world’s steel industry contributes seven to nine percent of global greenhouse gas emissions. This is principally from blast furnaces, basic oxygen steelmaking, sintering and pelletising. The push to reduce carbon emissions will see a change, where green high-grade magnetite with ≥68% Fe grade becomes the preferred feedstock for the steel industry, over the lower grade hematite. This will necessitate changes to flowsheets to remove carbon footprint. The magnetite concentrates would command a premium in price. The largely hematite Pilbara iron ores are most at risk with this change. The global steel industry faces massive technical challenges to transition a zero-carbon footprint. Both blue and green hydrogen may have a role to play in this transition. Examples of new technologies to produce higher grade magnetite concentrates and the options for steel mills to move away from conventional blast furnace operations are discussed. These include hydrogen reduction, MIDREX, CIRCORED, HYL, PERED and others. Carbon capture and storage are possible options but are not yet a commercial alternative. Biomass is not an alternative as it still has a carbon footprint. Hydrogen reduction of iron ores circa 62% iron is possible but requires magnetic separation to remove silica and alumina to achieve ≥68% iron. For Pilbara hematite ores, this is one solution going forward. Hydrogen is more explosive than natural gas, requiring nitrogen purging at start up and shutdown, representing a significant operating risk. Its transport and storage is a challenge, as it causes embrittlement of steel. Ammonia has been suggested as alternative.
Hydrometallurgy is brilliant technology able to recover metals from low grade and complex ores. This involves the unit operations of leaching, purification and extraction. It has become increasingly more popular due to the decreased capital costs and lower energy requirements than alternative technologies.
The advent of battery minerals where product specifications call for four or even five nine purity has challenged our methodologies with purification. Solvent extraction, precipitation and crystallisation are discussed. Reference is made to manganese, lithium and titanium pigments.
Participants will gain a better understanding of the difficulties of achieving these low levels.
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Presentation Overview:
Presentation Overview:
The Haib Copper Project is a large copper-molybdenum porphyry located in the Karas region of southern Namibia. The main mineralised hosts at the Haib deposit are quartz feldspar porphyry and feldspar porphyry rock. The principle ore material at Haib deposit is chalcopyrite with minor constituents being bornite, chalcocite and various green copper oxides. The Haib deposit features an indicated resource of 456.9 MT at 0.31% copper grade. The plant design proposed for the Haib Copper Project will use 3 crushers and an ore sorting system. The process is designed for a 90% availability, processing over 23,000 tonnes of ore per day (at a 8.5 Mtpa scenario) at a strip ratio of waste: ore of 2:1. For the recovery of copper from the Haib copper deposit, ore heap leaching was considered for all options in recovering copper. The primary reason for the selection of heap leaching is due to the vast scale of the orebody and the low-grade nature of the ore. Previous work that was conducted on the Haib Copper Project suggested that a conventional method featuring a crush-grind-float and sale of copper concentrate method is not economically feasible due to the hardness and low grade of the ore, which would require a significant amount of energy for grinding. Bacterial leaching at 60 °C overcomes the passivation of chalcopyrite and pyrite in the ore generates acid for leaching. The costs associated with heap leaching compared to a whole ore floatation circuit are considerably lower. The development of an alternate flowsheet where the -106 micron fines are removed from the heap feed and processed separately over time is described including the key advantages.
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This paper focusses on the use of dense media and flotation of hard rock spodumene ores to produce concentrates that meet market specification. The paper describes laboratory testing and the difficulties of reproducing these results at plant scale. Whilst laboratory testwork indicates that lithium can be recovered and impurities removed spodumene flotation at plant scale can be challenging due to reagent optimisation, grind size, water quality and the presence of slimes. In addition the activation of quartz and feldspar by iron salts introduced during grinding. In addition the debate over open or closed circuit flotation is considered.
The Feasibility Study CAPEX and OPEX for a number of projects were never achieved. The Feasibility Study was bare bones and fast track and in a number of respects would not qualify as a Feasibility Study. Project Ramp up was slow at 12-18 months due to grade problems and water issues and plant reliability.
This paper references a number of projects and lessons learned. A number of projects made mistakes and bad decisions with fast tracking and efforts to reduce capital, poor quality equipment all of which has increased operating costs. The softening in lithium prices during 2020 and funding issues finally resulted in several companies going into Administration.
Going forward we can see an industry struggling to survive and being very innovative which argues well for the future. We are seeing mergers and takeovers and in the longer term a strengthening of prices which will see a different industry emerge.
Merrill Crowe preceded Carbon In Pulp (CIP) technology and is now only used for very high-grade gold projects or where the silver to gold ratio exceeds ten to one. CIP technology is generally more efficient and cost effective for lower grade ores whereas Merrill Crowe is superior for high grade silver ores.
Gravity processes are not as efficient for high silver ores as for gold. Metallic silver or electrum can be recovered at modest recoveries whereas acanthite (Ag2S) exhibits poor gravity recovery even with centrifugal concentrators.
Leaching of high silver ores requires significantly higher cyanide (>1500 ppm) and oxygen levels and extended leach times (>72 hours). Usually, the recovery is lower than for gold.
The adsorption capacity needs to be higher for high grade silver ores with a larger inventory of carbon and more carbon movement. Carbon activity and solution loss become more critical with a general requirement for more adsorption stages in order to achieve equilibrium.
Silver elutes first from the carbon and at a lower temperature. These conditions are at odds with the gold elution. Generally, operations optimise to maximise gold recovery from the carbon. The silver cyanide complex (Ag(CN)2–) is less stable than gold cyanide (Au(CN)2–) and breaks down at the lower temperature and forms metallic silver which remains on the carbon. This has a negative impact on carbon activity and hence solution loss.
Where high silver values are present during electrowinning, the cathodes can be washed with high pressure water and the electrowon gold and silver comes off very easily. In addition, high sludging of the cell is not uncommon as the dendrites are loosely held. Some designs exploit this feature in self-sludging cells.
Conventional processing of silver-bearing materials containing gold group metals involves smelting the material to bullion and purification of the silver by electro refining, along with recovery of gold and platinum group metals from the slimes generated by the electro refining process. An alternative process has been developed that allows extraction of the silver from such residues using a combination of chloride and nitrate chemistry. An advantage of the process is the production of very high-purity silver. A number of examples are cited with the good design aspects highlighted.
Spirals have been the backbone of mineral sands plants since 1943. The Reflux Classifier invented by Kevin Galvin at the University of New South wales has the potential to offer greater efficiency and simpler flowsheets with lower capital costs. This would be a transformational technology change if it is taken up by the industry.
The Reflux Classifier incorporates a “laminar high shear rate” mechanism, which represents the latest in fine particle gravity based separation technology. The lamella section enhances the efficiency/capacity of the Reflux Classifier, producing a more compact, higher efficient separation unit when compared to competing fine coal and mineral processing equipment such as spirals, up-current classifiers and teeter bed separators. Recently FL Smidth has launched its modular Reflux Classifier plant, which is suitable for fines gravity separation applications.
Recent piloting and applications are cited and discussed in detail including operating history.
The metallurgical heart of the majority of copper oxide processes is the heap leaching operation. Fresh low grade sulfide ores is a far greater challenge. The success of this unit operation is so important that operators need to understand the ramifications of their decisions or non-decisions and how they could affect the downstream processing. Heap leaching is an operation that can be described as a scientific art whereby principles of science can be used to guide experienced personnel in attaining their goals. Recent advances have been made based on better understanding the ore characteristics. The success of a heap leach operation, or otherwise, is dependent upon a number of factors, notably:
Other issues:
The heap leaching of sulfide ores, including chalcopyrite, via enhanced bacterial leaching is discussed.
The world is moving to de carbonise however with a long history of using coke. How realistic and economically viable is this change to hydrogen? Many countries are moving to zero emissions by 2050. How quickly could this change and what will the new proposed hydrogen based steelworks look like? The challenge to produce massive production of hydrogen under economically acceptable conditions is a formidable challenge. Can iron ores be reduced in a shaft furnace operated with hydrogen only?
Regarding kinetics, reduction with hydrogen is definitely faster. Several research and development innovation projects have been started that will confirm the viability of this breakthrough and environmentally friendly ironmaking process.
Dr Andrew Forrest, Chairman of FMG in the Boyer Lecture said it was no longer a pipedream, because enterprising businesses around the world, such as Thyssenkrupp in Germany and Japan’s Nippon Steel, were already figuring out the technology. Also Dr Forrest hailed green hydrogen as the key to slashing emissions and halting global warming. This paper will look at ironmaking including the energy needed, the economics and hybrid options based on renewable hydrogen from solar or wind electricity.
The Rover deposit consists of magnetite with free gold and bismuthinite and copper which are well liberated plus cobaltite and pyrite. The magnetite is likely to mill autogenously.
The ore is amenable to gravity gold with recovery ranging from 50% to 60%. Conventional tabling of the concentrate is required rather than intensive leaching because of the negative impacts of cyanide on flotation.
A bulk flotation to recover copper, bismuth and cobalt is the best option rather than selective staged flotation. The copper and cobalt concentrate will be pressure leached and processed via solvent extraction to produce a clean copper and separate cobalt product.
The products from the project will be gold ore bullion from both gravity and CIL processing. A clean copper product will be sold as copper containing bismuth is not saleable. A bismuth concentrate will be produced and this will contain minor copper. A clean cobalt product will be produced.
Eight flowsheets were considered before finalising on a preferred flowsheet.
The basis of design is for an underground crusher and a coarse ore stockpile on the surface. An autogenous mill will grind the ore in close circuit with cyclones to a P80 product size of 75 microns. A Knelson concentrator will be used to recover gravity gold.
The cyclone overflow will be subjected to bulk flotation. The tailings will be thicken and processed by CIL to recover gold and these tailings processed using magnetic separation to recover a clean magnetite product for coal washing use.
The bulk concentrate will be reground and separated into copper/cobalt pyrite and a bismuth concentrate for sale. There are two options here either to depress the copper or depress the bismuth which requires further testwork.
Copper cannot be sold with bismuth in it due to severe penalties. Smelters find it difficult to remove bismuth from copper. This presents a technical challenge.
The copper concentrate will be pressure leached and processed by solvent extraction to produce a clean copper product and separate cobalt product. The bismuth residue will be combined with the bismuth concentrate.
The infrastructure is very good with road and rail access plus water and a gas pipeline close by. The town of Tennant Creek will provide support services and a commercial airport with regular flight services.
The project is small and lends itself to modular design and fabrication offsite. A number of engineering deliverables are required to facilitate this. A work programme going forward is recommended.
High Pressure Grinding Rolls (HPGR) is a newcomer to grinding circuits and offer energy savings, lower media wear and recovery gains which make it hard to resists compared to conventional grinding circuits.
The laboratory small scale and pilot testing is well established and reliable. Scale up and design predictability is reliable. From an operational aspect the ability to change operating pressures and screen apertures offers significant operational flexibility not offered by a SAG mill. In addition the rolls life has greatly increased due to innovation and change out times have shortened. The reliability of HPGR has been shown to be equal to SAG mills.
Successful applications started with cement clinker and then hard iron ores, gold ores and now lithium projects. Recent applications are cited and discussed in detail including operating history.
The metallurgical testwork for a new gold project indicated acceptable settling rates and filtration rates. The equipment was sized accordingly and the plant constructed. Subsequently commissioning of the thickening and filtration for dry stacking of tailings indicated serious deficiencies with the design and a much lower throughput achievable.
The throughput was some thirty percent of design and cash flow considerations were that the project throughput was restricted by poor performance of the thickeners and tailings filtration acting as a bottleneck
METS was commissioned with the task of increasing filtration throughput and removing the bottleneck.
For the thickeners new flocculants were evaluated, changes to the flocculant dilution and increasing the thickener underflow pump speeds. An additional filter feed storage tank was installed to allow for short term filter shutdowns.
With the two belt filters various flocculants, guar and diatomaceous earth were evaluated. We also evaluated more permeable filter cloths. The single biggest improvement achieved was with the use of coagulants.
This paper describes how the task was tackled and what steps were taken to finally achieve design throughput.
The Bald Hill lithium project failed in late 1999 and we were asked by a Client to look at the project and see why this occurred. The project development and operation is not a good story. It is a classic fast track project failure with a number of poor decisions made. A number of projections of costs were made but never achieved. There was no information provided on the low grade, lower recovery and very high operating costs in the Australian Stock Exchange (ASX) announcements. The focus on reporting was on the increasing production and the quality of the concentrate. The fast track approach meant the best outcomes were not achieved.
The feed grade (0.8 -0.90% Li2O) is low compared to Talison Greenbushes, Mt Marian, Pilbara Minerals, Altura lithium projects. The project does not benchmark well against other lithium producers in Western Australia because of low recovery, high operating costs and low feed grade. The by-product tantalum product is a positive.
The Feasibility Study CAPEX and OPEX were never achieved. The Feasibility Study was bare bones and fast track and in a number of respects would not qualify as a Feasibility Study. Ramp up was slow at 12 months due to grade problems and water issues and plant reliability. The Feasibility Study indicated a 12 month payback on capital in reality the project has only ever incurred losses.
The project made a number of mistakes and bad decisions with fast tracking and efforts to reduce capital which has increased operating costs. The softening in lithium prices and funding issues finally resulted in the company going into Administration.
The nickel-copper-cobalt sulphide deposits at Lynn Lake were mined continuously between 1954 and 1976 (in that time processing more than 20 million tonnes), and it was one of Canada’s major nickel mining centres of its time. Substantial resources remain and further extensive drill defined mineralisation also exists within the mining centre. The feasibility of selling a bulk concentrate is not considered economical on the basis that the value of either copper or nickel is not reimbursable when selling to a nickel or copper smelter. When considering that the economics of selling a bulk concentrate is poor, it is clear that this option would not be economical. There are limited smelters or facilities who could process this concentrate. This paper describes the testwork undertaken to produce separate copper and nickel concentrates and flowsheet options including downstream processing.
This is an example of modern metallurgy delivering a major technical breakthrough, producing separate high-value and high-purity nickel and copper concentrates. This work will enable the determination of value for the large historical mining centre, at a time when there is an expectation of future increased demand for metals.
The Australian mining industry has been based on high cost diesel fired power stations for power supply. The mining industry is leading the way in renewables and a change that has not been well recognised. The business case for renewables in mining which has been underwritten by Rio Tinto’s Weipa project and Sandfire Resources Solar Project is being followed by a Gold Mine which will serve as a blueprint for other companies to deploy similar off-grid energy solutions helping to decarbonise the mining sector. The renewable Gold Mine hybrid microgrid will consist of five wind turbines delivering 18 MW, a 10,000 panel 4 MW solar farm and a 13 MW Battery Energy Storage System underpinned by a 16 MW gas engine power station. This renewable microgrid is expected to provide 60% of the energy required by the project.
The demand for high purity battery grade lithium carbonate has exceeded even the most optimistic predictions. The lithium-ion battery sector is one of the fastest growing and largest consumers of lithium. This paper focusses on the use of dense media separation and flotation of hard rock spodumene ores to produce concentrates that meet market specification. The paper describes laboratory testing and the difficulties of reproducing these results at plant scale. Whilst laboratory testwork indicates that lithium can be recovered and impurities removed, spodumene flotation at plant scale can be challenging due to reagent optimisation, grind size, water quality and the presence of slimes. In addition, the activation of quartz and feldspar by iron salts introduced during grinding can be experienced. The metallurgy of lithium ores is very ore specific depending on lithology and the lithium silicate minerals are generally refractory. Physical concentration using dense media separation and flotation with magnetic separation is commonly followed by hydrometallurgical process routes for the concentrates. The current dense media separation and flotation circuit regimes are invariably complex and producers loathe divulging their technical know-how. The industry has gone from euphoria and unprecedented optimism for new projects to one of pessimism in a few short years. With the much lower lithium prices we now find the new producers are struggling to survive financially.
Lithium is found in granitic pegmatites in commercial concentrations. Lithium ores of major
economic importance are spodumene (Li2O.Al2O3.4SiO2), lepidolite (3LiF.K2.2Al2O3).7SiO2), ambylgonoite (Li.Al.F.PO4), petalite (LiAlSi4O10,), zinnwaldite (KLiFeAl(AlSi3)O10(OH,F)2) and brines (Li.Na.PO4). Spodumene because of its abundance is the most important source of lithium. Due to its lithium content spodumene is an important source of feed in producing lithium hydroxide. The lithium hydroxide is used in the lithium-ion batteries.
Lithium can be extracted by acid roasting at 1050 centigrade in rotary kilns. The alpha spodumene is converted to beta spodumene. This is the traditional route however we now have a number of new processes. Amongst these are the Eli process, Nemaska process, SiLeach process, L-Max process and the Outotec alkaline leach process plus some other patented processes. This paper reviews the processes available and discusses issues with process plants in China.
The nickel-copper-cobalt sulphide deposits at Lynn Lake were mined continuously between 1954 and 1976 (in that time processing more than 20 million tonnes), and it was one of Canada’s major nickel mining centres of its time. Substantial resources remain and further extensive drill defined mineralisation also exists within the mining centre. The feasibility of selling a bulk concentrate is not considered economical on the basis that the value of either copper or nickel is not reimbursable when selling to a nickel or copper smelter. When considering that the economics of selling a bulk concentrate is poor, it is clear that this option would not be economical. There are limited smelters or facilities who could process this concentrate. This paper describes the testwork undertaken to produce separate copper and nickel concentrates and flowsheet options including downstream processing.
This is an example of modern metallurgy delivering a major technical breakthrough, producing separate high-value and high-purity nickel and copper concentrates. This work will enable the determination of value for the large historical mining centre, at a time when there is an expectation of future increased demand for metals.
The Bald Hill lithium project failed in late 1999 and we were asked by a Client to look at the project and see why this occurred. The project development and operation is not a good story. It is a classic fast track project failure with a number of poor decisions made. A number of projections of costs were made but never achieved. There was no information provided on the low grade, lower recovery and very high operating costs in the Australian Stock Exchange (ASX) announcements. The focus on reporting was on the increasing production and the quality of the concentrate. The fast track approach meant the best outcomes were not achieved.
The feed grade (0.8 -0.90% Li2O) is low compared to Talison Greenbushes, Mt Marian, Pilbara Minerals, Altura lithium projects. The project does not benchmark well against other lithium producers in Western Australia because of low recovery, high operating costs and low feed grade. The by-product tantalum product is a positive.
The Feasibility Study CAPEX and OPEX were never achieved. The Feasibility Study was bare bones and fast track and in a number of respects would not qualify as a Feasibility Study. Ramp up was slow at 12 months due to grade problems and water issues and plant reliability. The Feasibility Study indicated a 12 month payback on capital in reality the project has only ever incurred losses.
The project made a number of mistakes and bad decisions with fast tracking and efforts to reduce capital which has increased operating costs. The softening in lithium prices and funding issues finally resulted in the company going into Administration.
Following the discovery of a major gold resource, discussions with the regulator introduced restrictions on how the ore could be processed. The regulatory requirements necessitated that no arsenic was allowed to migrate into the environment. In addition, iron arsenate was not considered sufficiently stable to exist within the environment, and it was mandated that arsenopyrite, which contained the gold, could not be chemically changed.
Testwork was undertaken to develop a flowsheet that would maximise gold recovery from an ore containing 3 g/t Au and high levels of arsenic.
Treatment of the sulphide ore involves gravity separation, flotation, and cyanide leaching. A gravity concentrate is recovered within the grinding circuit before the ore is subjected to froth flotation. The concentrate from the flotation circuit is then treated to produce an arsenopyrite-rich bulk concentrate. The bulk concentrate is then subjected to ultrafine grinding, ahead of cyanide leaching.
This paper follows the development path and lessons learned through this case study, particularly in maximising recovery over time.
Titaniferous magnetite hard rock deposits are common throughout the world. Previously they have been processed to recover vanadium using the standard salt roast process however the economics based on vanadium alone are marginal because of high capex and opex.
New Zealand Steel and others have produced vanadium slag by iron reduction and smelting of iron sands.
Of recent times various groups have endeavoured to produce titanium pigment and vanadium from these ores using hydrometallurgical process routes. The technical challenges are significant. However the potential to produce titanium pigment from these ores is approaching technical and commercial feasibility.
This paper looks at the methods used and process routes being considered for various of potential projects.
METS reviewed extensive reports detailing design and operability choices made during the historical operation of the Bottle Creek Gold Project, which ultimately led to the closure of the plant. Extensive identification and evaluation of the past mistakes and advances in gold processing technology and mineralogical assessment since the 1980’s improve confidence in ensuring that the same mistakes would not be repeated. A number of opportunities were identified for improvement on the historical project.
Significant improvements in mineral characterisation techniques now provide more comprehensive insight into the factors that shape process selection and design, including mineral identification, gold association and grain size. In the past, technological limitations restricted the quality of information obtainable during both project development and project operation; such limitations contributed to the issues experienced within the Bottle Creek project.
There were issues with the comminution section of the plant, mostly arising from high variability within the deposit. Semi-Autogenous (SAG) milling would likely eliminate these issues, which was initially trialled at Bottle Creek, however proved ineffective due to the soft nature of the oxide ore processed at the beginning of the project. Since the 1980’s, huge advances in SAG milling equipment design and operation have been made.
The high silver content of the ore was one of the largest oversights for the project. High silver loading on the carbon significantly decreased the economic viability of the project due to increased stripping costs following the conventional carbon-in-pulp (CIP) circuits. Seeking a process flowsheet that is tolerant to high silver levels, such as the Merrill-Crowe process, would have been a more viable option.
This paper summarises new testwork and project developments, including the establishment of a commercial flowsheet.
Copper and gold have similar cyanide metallurgy depending on the nature of the minerals present. The processing of gold copper and copper gold ores can be highly problematic, site specific and the process selection is dependent on ore grade, mineralogy, acid leach behaviour, cyanide chemistry, product saleability and environmental considerations. The production of a copper gold concentrate is also an option where the copper is of a marketable grade. In some situations the flotation tailings may be subject to cyanide leaching if technically and commercially viable. The general effects of copper on cyanide leaching chemistry are increased cyanide and lime consumption and decreased dissolution rates for gold and silver. The severe fouling of carbon, high solution losses and even re-precipitation of gold can occur. Recent advances in cyanide recovery and producing saleable copper products have changed the flowsheets available for such problematic ores. There are a number of technologies and new methods now available. |
Western Australian iron ore was originally exported as Direct Shipping Ore, or DSO, primarily from Mt Tom Price and Mt Whaleback. It was at these sites that the earliest beneficiation plants were established, by Pilbara Iron and BHP respectively.
FMG also does some beneficiation of iron ores, improving iron grades through de-slime processes.
Two pellet plants- one in Dampier and the other in Cape Lambert- operated within Western Australia for a number of years, but closed during the oil crisis of the 1980’s.
Rio Tinto oversaw the HIsmelt process in Kwinana for a number of years, but ceased operation in 2011.
Two magnetite processing operations – one, the Sino Iron Project, in Cape Preston, and the other in Karara, in the mid-west – have both struggled to achieve design specifications for a number of years.
The Roy Hill Project, recently undertaken by the Hancock Prospecting Group, also includes some beneficiation.
This paper examines the future for downstream processing and value adding opportunities for iron ore within Western Australia, and whether, technically or commercially, there exists an opportunity for value adding. The Pilbara contains vast resources of low grade iron ores and significant resources of natural gas. Previously , iron ore unit prices were low, and, since the Brazilian tailings dam failures export volumes and prices from Australia have improved significantly.
Qemscan allows characterisation which provides better ore characterisation. There has been development of scalping units for low grade deposits and improved spirals (CT). The use of reflux classifiers have also found unique applications.
Optimisation of wet concentrators through modelling and simuation including modelling of specific units. The development of novel analytical techniques using heavy liquid separations from samples around the concentrator.
The optimisation of dry plants is a critical area where products are made and final specification is achieved. The innovations with magnetic and electrostatic separators is discussed.
The option to leach iron from low grade copper concentrates could reduce transport costs and significantly improve the saleability of the concentrate. In addition, it reduces smelting costs and can remove undesirable impurities. The trend to produce cleaner and higher grade copper concentrates is very appealing to the smelters. A recent copper project came on line and there were three serious deficiencies which were not identified in the Feasibility Study. This came as a surprise and resulted in a number of projects to investigate ways of rectifying the problems in the shortest timeframe possible and using minimal new capital. The first serious issued not identified when commissioning was the lower than expected copper recovery, which was 70% compared to a predicted recovery of 80% to 87% in the Feasibility Study. This required investigating new flotation reagents and incorporating controlled potential sulphidisation. The second serious issue overlooked is the presence of significant amounts of talc minerals (insol) in the ore which are naturally floatable. This leads to lower concentrate grade and attempts to remove the talc resulted in lower copper recovery. Smelters have limits on the amount of talc in concentrate because it produces viscous slags and difficulties for the smelter. It also incurs higher transport costs. The third serious issue not identified in the Feasibility Study was the high arsenic reporting to the concentrate. Arsenic is a penalty element for smelters and at levels exceeding 0.3% the smelters may reject the concentrate. Arsenic is a problem environmentally for copper smelters and penalties apply when it is high. This paper describes the options for penalty element removal and suitability to incorporate into the modified flowsheet. It also highlights where the geometallurgy was not properly addressed and how these surprises could have been avoided.
Pyro metallurgical and hydrometallurgical processing for nickel laterites has been implemented on a commercial scale for many deposits. High pressure acid leaching (HPAL) has experienced many issues since its development and suffers from issues such as operability, high acid consumption, environmental complexities, low availabilities and high maintenance requirements.
The production of ferronickel by reduction smelting (RKEF) is an attractive alternative to this process which also produces a highly desirable product in ferronickel. Ferronickel has a minimum nickel content of 15% and contains considerably less phosphor and sulfur per tonne of nickel than nickel pig iron (NPI). The production of ferronickel from nickel laterites is reviewed and compared to alternative nickel laterite processing options.
Lithium production is dominated by brines and the hard-rock minerals such as spodumene, petalite, lepidolite and amblygonite. With lithium batteries powering the lithium mining sector the commercial development of lower grade resources is gaining traction. Lithium clays are a large low grade source of lithium and cannot be processed by standard hard-rock processes. The poor beneficiation characteristics and high energy requirements of these processes are not economically feasible. Recent research and advances into the extraction of lithium from clays has resulted in new projects advancing towards production. Acid leaching is particularly promising although there is also considerable merit to roasting lithium clays in the presence of gypsum.
Impurity elements that are leached from the lithium clay are of particular importance to processing as they can have a significant impact on the viability of producing a high purity lithium carbonate product. Recent advancements in lithium clay processing technologies have improved the selective extraction of lithium over impurity elements. Progress has also been made on the separation of impurity elements after they are dissolved in solution.
Recent advances in the extraction of lithium from clays are discussed here with a focus on hydrometallurgical processing and purification of the leach solution.
Traditional pyro metallurgical processing of copper ores is not economical for the extraction of copper from remote large low-grade copper deposits. For low grade sulphide deposits the ore is typically beneficiated by sulphide flotation to produce a low grade concentrate for sale to smelters. Beneficiation for large low grade deposits is challenging and often it is not economically viable to sell a low grade flotation concentrate to smelters.
Also the technology options for processing low grade copper are reviewed and recent advancements in ore-sorting technology are discussed. The practicality of hydrometallurgical upgrading of low grade copper concentrates on site to produce a 60% copper concentrate for shipment to smelters is also discussed.
As an alternative development option the advent of new hydrometallurgical processing has transformed the copper industry making low grade oxide and sulphide ores economical to mine. Heap leaching is now a well-established process for copper ores and the development of bacteria capable of breaking down sulphides has made the process applicable to sulphide ores when it was previously only feasible for oxide ores. The bacterial breakdown of sulphides is also advantageous as acid is generated in the process.
The treatment of gold ores is dependent on the mineralogy and is unique to each deposit. Free milling gold is gold that can be recovered by concentrating methods without resorting to roasting, pressure leaching or chemical treatment. Refractory gold ores are ores that have gold associated with sulphides, carbonaceous matter or gold in solid solution with other minerals. Refractory ores require pre-treatment steps to liberate gold for the cyanidation step. Gold ores may also be double refractory. Double refractory gold is associated with both sulphides and carbonaceous matter. Typical free milling gold circuits consist of a gravity concentration process which typically has low recovery but produces a high grade ‘heavy’ concentrate and a low grade ‘lighter’ fraction. The low grade fraction is processed by carbon in pulp/carbon in leach (CIP/CIL) circuits and the high grade fraction is processed through an intensive leaching process. For refractory sulphide ores an additional process step is required to improve the availability of gold for cyanide leaching. There are a number of process technologies capable of this of which several are discussed here. This paper summarises the various technologies that can be applied in the treatment of gold ore from free milling gold to double refractory gold with a focus on recovery of free milling and mildly refractory gold ores.
This paper focusses on the use of flotation of hardrock spodumene ores to produce concentrates that meet market specification. The paper describes laboratory testing and the difficulties of reproducing these results at plant scale. Whilst laboratory testwork indicates that lithium can be recovered and impurities removed spodumene flotation at plant scale can be challenging due to reagent optimisation, grind size, water quality and the presence of slimes. In addition the activation of quartz and feldspar by iron salts introduced during grinding.
In addition the debate over open or closed circuit flotation is considered.
It is common to use mechanical scrapers and the use of cationic and anionic collectors, frothers and regulators is described including de slime. The presence of mica which is platy poses a number of problems with de lamination and contaminating the final spodumene concentrate.
The current flotation circuit regimes are invariably complex and producers loathe to divulge their know how. Grinding to maximise the generation of cleavage planes on spodumene grains can improve flotation performance and lithium recovery. In addition reagent Vendors have demonstrated improvements in selectivity over other aluminosilicate minerals and operators restricting sale of their proprietary reagent to other competitors.
The beneficiation of goethitic and limonitic iron ores is difficult with current technology and new technologies are required to exploit these lower grade ores which respond poorly to beneficiation.
Coarse goethitic samples can responded well to gravitational beneficiation methods, however coarse processing of limonite-bearing ores is not a practical option due to insufficient upgrade and high formation of slimes. Magnetic separation at high gauss appears to have potential for fine materials. Higher recoveries can be achieved if calcination is utilised, although penalty elements remain a concern.
The coarse fraction of goethite-bearing material appears to be well suited to gravity methods, although the fine processing required additional development. Alternative fine processing methods should also be pursued, including:
This paper highlights where success was achieved and the unresolved issue of dealing with the large mass of low grade iron ore slimes which responded poorly to beneficiation.
The discovery of a new lead zinc exploration project dictated some early sighter testwork in order to justify further exploration drilling and underpin possible project development.
Ore characterisation including head assays, assay by size and mineralogy and heavy liquid separation to evaluate dense media pre-concentration.
Sequential vs bulk flotation and reagent optimisation to achieve high grade lead and zinc concentrates. Grind size optimisation and reagent depressant options were investigated.
Flash flotation and column flotation were considered and a basic flowsheet and engineering undertaken.
This paper covers the initial testwork through to flowsheet development and potential project development.
Tailings projects are usually marginal and high risk. This paper reviews three tailings projects which were studied. Firstly involves a visit to the Data Room where the data has been collected, and Due Dilige nce (DD) of that information, followed by a written report. Once the site visit and the DD have been completed, the gaps are identified, to determine the work that must still be done to produce all the documentation required for the various scopes of work necessary to consider development.
This interpretation will result in the delivery of the process design criteria (PDC) document, which is used to produce the process flow diagram (PFD) for the new tailings project. A mass balance for the project is the next stage and all these documents result in a process description.
The process design documents are used to prepare a mechanical equipment list (MEL) that is the basis of the project Capex, and the Capex and the mass balance are used to produce the project Opex. The work described previously is utilised to produce the project cash flows, internal rates of return (IRR) and net present value (NPV) calculations which will be used for scenario analysis of the project, which are the fundamental documents and calculations required to attract potential funders of the project.
The metallurgical heart of the majority of copper oxide processes is the heap leaching operation. Fresh low grade sulfide ores is a far greater challenge.The success of this unit operation is so important that operators need to understand the ramifications of their decisions or non-decisions and how they could affect the downstream processing. Heap leaching is an operation that can be described as a scientific art whereby principles of science can be used to guide experienced personnel in attaining their goals. Recent advances have been made based on better understanding the ore characteristics. The success of a heap leach operation, or otherwise, is dependent upon a number of factors, notably:
Other issues:
The heap leaching of sulfide ores, including chalcopyrite, via enhanced bacterial leaching is discussed.
The demand for high purity battery grade lithium carbonate has exceeded even the most optimistic predictions. The lithium-ion battery sector is one of the fastest growing and largest consumers of lithium. Lithium-ion batteries have superior energy density, are more efficient and environmentally friendly than traditional acid batteries and the cost is falling based on innovation and technical development.
Lithium ores of major economic importance are spodumene (Li2O.Al2O3.4SiO2), lepidolite (3LiF.K2.2Al2O3).7SiO2), ambylgonoite (Li.Al.F.PO4), petalite (LiAlSi4O10,), zinnwaldite (KLiFeAl(AlSi3)O10(OH,F)2) and brines (Li.Na.PO4). Spodumene because of its abundance is the most important source of lithium.
The metallurgy of lithium ores is very ore specific depending on lithology and the lithium silicate minerals are generally refractory. Physical concentration using dense media and flotation with magnetic separation is common followed by hydrometallurgical process routes for the concentrates.
Some of the project metallurgical pitfalls identified at the Finance Due Diligence stage could have been avoided if a systematic checklist unique to lithium projects had been put in place during the Feasibility Study stage. Currently the proposed hard rock lithium projects are very profitable but future oversupply predictions could dampen the outcomes.
Australia is a major world producer of zircon currently supplying 45% of the world’s production. A number of these resources are high in radioactivity (uranium & thorium) and this makes them commercially unattractive and more difficult to market.
Zircon is used for foundry sand, refractories, ceramics and glazes and zirconium chemicals. There are radiation limits on the sale and transport of zircon in countries such as China.
This has created a challenge to reduce the radioactivity and greatly improve the marketability of the product. There are a number of patents and proprietary technologies available for reducing radioactivity in zircon. A number of these options were tested and results were mineralogically controlled and the efficiency varied depending on the source of the zircon sand.
In addition there were issues with OPEX and design of process plants to achieve such reductions. Whilst a number of companies have evaluated a number of these technically challenging process options, no commercial plants have been built to date.
The option to leach iron from what is a low grade copper concentrate could reduce transport costs and make the saleability of the concentrate much better. In addition it reduces smelting costs and can remove undesirable impurities. OZ Minerals are proposing to do this for their Prominent Hill copper concentrate increasing the grade from 37 to 55-60% Cu. The trend to cleaner and higher grade copper concentrates is very appealing to the smelters.
For remote projects where transport costs are significant this represents a significant opportunity to reduce costs.
CuFeS2(s) + CuSO4(aq) → CuS(s) + FeSO4(aq)
3 CuFeS2(s) + 6 CuSO4(aq) + H2O → 5 Cu1.8S(s) + 3 FeSO4(aq) + H2SO4
6 CuS(s) + 3 H2O → 5 Cu1.8S(s) + 4 H2SO4
Metallurgical testwork completed on HQ core samples from the Cobalt Ridge Project
Testwork objective was to build on the promising results from the sighter RC testwork
Testwork focused on recovering cobalt, copper and gold
Testwork split into three stages:
The demand for high purity battery grade lithium carbonate is expected to grow significantly in the near term. The lithium-ion battery sector is one of the fastest growing and largest consumers of lithium.
Lithium-ion batteries have superior energy density, are more efficient and environmentally friendly than traditional acid batteries and the cost is falling based on innovation and technical development.
Lithium batteries need the following inputs:
Titaniferous magnetite hard rock deposits are common throughout the world. Previously they have been processed to recover vanadium using the standard salt roast process however the economics based on vanadium alone are marginal. Of recent times various groups have endeavoured to produce titanium pigment and vanadium from these ores using hydrometallurgical process routes. The technical challenges are significant. However the potential to produce titanium pigment from these ores is approaching technical and commercial feasibility.
Carbon Capture and Storage (CCS) prevents large amounts of carbon dioxide (CO2) being released into the atmosphere. Global Emissions of CO2 from fossil fuels and cement production in 2015 was estimated to be 36.3 billion tonnes. Australian emissions for 2015 were estimated to be 535.7 million tonnes of CO2 equivalent, with the mineral resource sector producing an estimated 12% of this. The resource sector produces carbon dioxide from power stations, smelting operations, transportation and cement plants. Australia also exports large tonnages of coke and coal which contribute to global CO2 production. The continuing reliance on fossil fuels is likely to remain strong, especially in developing countries where a significant percentage of the population does not have access to electricity; it is estimated that 16% of the global population does not have access to electricity.
CCS is a viable option for significantly reducing emissions from large emission sources such as smelters and power stations. This paper looks at the technical options for resource companies and examples of projects under development.
An Option Study was commissioned to look at the best technology and minimum size required for a new proposed copper smelter.
Copper smelting has evolved over time, with a number of process routes culminating in the development of the Outokumpu Flash Smelter (Flash), which was one of the most significant developments of the twentieth century. Subsequently, this Flash process has been improved over time. Other process developments have been the Ausmelt submerged lance smelting, the Mitsubishi continuous smelting, slag cleaning and blister copper production. Another innovation was the Noranda top smelting, and more recently, the Chinese bottom blowing furnaces that have been commissioned in China.
With regards to selecting a new copper smelter process, energy considerations and copper and precious metals recovery are critical, as well as environmental considerations. This paper outlines the findings of a recent study where the difficult technical decision of either going with Flash or considering bottom blowing had to be resolved. A site visit was arranged to some of the largest Chinese smelters and the findings taken into account for the options Study.
Australia is a major world producer of zircon currently supplying 45% of the world’s production. A number of these resources are high in radioactivity (uranium & thorium) and this makes them commercially unattractive and more difficult to market.
Zircon is used for foundry sand, refractories, ceramics and glazes and zirconium chemicals. There are radiation limits on the sale and transport of zircon in countries such as China.
This has created a challenge to reduce the radioactivity and greatly improve the marketability of the product. There are a number of patents and proprietary technologies available for reducing radioactivity in zircon. A number of these options were tested and results were mineralogically controlled and the efficiency varied depending on the source of the zircon sand.
In addition there were issues with OPEX and design of process plants to achieve such reductions. Whilst a number of companies have evaluated a number of these technically challenging process options, no commercial plants have been built to date.
Tests have shown that there is a clear relationship between the amount of titanium in a titanomagnetite concentrate and the recovery of vanadium in an oxidizing salt roast-water leach. The vanadium recovery decreases as the amount of titanium in the ore increases. Similarly, in a reduction roast, as reduction conditions become more intense, the acid extraction of vanadium from the calcine decreases.
Scanning electron microscope analysis of tests samples showed that unleached vanadium, from salt roast-water leach residues, was associated with silicate gangue and high titanium oxides.
Reductive roasting to produce metallic iron redistributes the vanadium into the titanium oxide lattice making the vanadium more refractory to salt roasting and acid leaching.
There was initial excitement at finding a new gold ore body. It was decided to carry out sighter tests on the ore before launching into a major drilling programme. Subsequently exploration drill core samples were prepared and tested in the laboratory to establish if the ore was free milling. The results for the cyanide leach gold recoveries were very poor on a high grade primary sulphide ore of 6.2 g/t Au with no silver. Subsequent mineralogy showed the ore to be a characteristic pyrite, carbonaceous refractory gold ore (double refractory). This was a very disappointing finding but useful in that large amounts of money were not spent drilling a problematic gold ore.
A small scale gravity and flotation test programme was developed to produce a concentrate with the majority of the gold. This also failed with most of the gold remaining in the tailings. At this stage exploration was curtailed until an economic process could be developed. An ICP scan also showed variable levels of antimony.
The Client then requested a Desktop Study be undertaken with minimal laboratory testwork looking at Pressure Oxidation (POX), roasting, ultra-fine grinding, graphite passivation and consideration of any new technologies that might be applicable to this type of ore. The subsequent Study highlighted how difficult these double refractory gold ores are to process and highlighted some recent technology developments may be applicable.
The demand for high purity battery grade lithium carbonate is expected to grow significantly in the near term. The lithium-ion battery sector is one of the fastest growing and largest consumers of lithium. Lithium-ion batteries have superior energy density, are more efficient and environmentally friendly than traditional acid batteries and the cost is falling based on innovation and technical development.
Lithium ores of major economic importance are spodumene (Li2O.Al2O3.4SiO2), lepidolite (3LiF.K2.2Al2O3).7SiO2), ambylgonoite (Li.Al.F.PO4), petalite (LiAlSi4O10,), zinnwaldite (KLiFeAl(AlSi3)O10(OH,F)2) and brines (Li.Na.PO4). Spodumene because of its abundance is the most important source of lithium.
The metallurgy of lithium ores is very ore specific depending on lithology and the lithium silicate minerals are generally refractory. Physical concentration using dense media or flotation is common followed by hydrometallurgical process routes. The hydrometallurgical difficulties specifically managing impurities is ore specific and often means that some lithium ores are not economic. At the same time some lithium ores contain valuable by products which can enhance the project economics if saleable products can be produced.
Mineralogy of gold ores has played an increasingly important role in process metallurgy and flowsheet development. The development of Qemscan in particular has been a quantum leap forward compared to optical mineralogy with respect to representivity and the information provided. This is particularly so with refractory gold and complex metallurgy pre and post various treatments
At the early stage of project development the nature and occurrence of the gold minerals and the host rock is very informative with regards to process characteristics. The presence of cyanicides and carbonaceous materials can be predicted based on the mineralogy. Liberation and locking is particularly important and Qemscan is particularly good at this looking at thousands of particles and providing this information.
Using mineralogy on mill products pre and post gravity and tailings is very informative in optimising the process metallurgy. For the tailings diagnostic leaching in association with the mineralogy may result in significant improvements. An example of techniques used at one gold project is cited where the future ore was characterised as not being refractory a very important outcome. In addition it was demonstrated that the ore was not grind sensitive and throughput could be increased with no loss of gold recovery. This was a significant finding with positive economic outcomes resulting.
The demand for high purity battery grade lithium carbonate is expected to grow significantly with the development of electric motorcycles, cars and other devices. The mining and processing of spodumene, lepidolite Lithium ores of major economic importance are spodumene (Li2O.Al2O3.4SiO2), lepidolite (3LiF.K2.2Al2O3).7SiO2), ambylgonoite (Li.Al.F.PO4), petalite (LiAlSi4O10,), zinnwaldite (KLiFeAl(AlSi3)O10(OH,F)2) and brines (Li.Na.PO4). Spodumene because of its abundance is the most important source of lithium. Also by product metals such tin, tantalum and caesium or phosphates can be produced.
This involves a number of challenges in order to achieve a high grade and recovery with minimal impurities.
The concentrate is then processed through the traditional sulphuric acid route and the challenges involved in achieving battery grade lithium carbonate are discussed. In addition, the advantages and disadvantages of building a lithium carbonate plant in Australia or China are discussed. Also new and novel technology is discussed with respect to ensuring high purity lithium and minimising waste acid issues.
This paper was based on a copper project where the high talc and arsenic came as a complete surprise. This resulted in studies to develop options to mitigate the impact on the project. Smelters prefer clean copper concentrates. Talc is undesirable because it forms viscous slags and reduces productivity. Arsenic on the other hand has become a serious issue because it forms toxic arsenic trioxide which is environmentally and occupational health issues which are unacceptable and difficult to remove from off gas. Arsenic and talc attract penalties and for arsenic if greater than 0.3% the concentrate will be rejected.
As a result of these limitations a number of technologies and solutions have been developed to reduce arsenic and talc levels in concentrates or processing the concentrates using hydrometallurgy. In addition hydrometallurgical options have been developed.
Clay minerals can cause nightmares with Mineral Processing because of the inherent difficulties of processing high clay gold ores.
These clay minerals typically form in near surface geological environments due to weathering, particularly above the natural water table, sedimentation and digenesis and are common in hydrothermally altered rocks.
Understanding the geology, mineralogy and correctly selecting representative samples of the ore to be processed is critical in getting the mineral processing right. Clays have the potential if not recognised to destroy project economics. Testing at an early stage of representative ore samples is critical.
The presence of clays in hard rock comes as a surprise if not fully understood. Similarly waste dilution from country rock containing clay can adversely affect the process. There are some solutions which assist in processing ores but do not negate all of the difficulties.
The presence of clays has a major influence on the process selection and equipment used in the final flowsheet.
The industry has paid a heavy price on a number of projects where the clay was not recognised or the process plant was based on a hard rock design which later proved to be totally unsuitable. Trying to mitigate the impact of clay on the process if the percentage of clay in the feed cannot be controlled is a mineral processing challenge.
Reference is made to two specific gold projects where wet sticky clay ores caused processing difficulties.
The demand for high purity battery grade lithium carbonate is expected to grow significantly in the future. The mining and processing of spodumene involves a number of challenges in order to achieve a high grade and recovery with minimal impurities. This paper discusses the value adding beneficiation step of processing spodumene and challenges. This spodumene concentrate is then processed through the traditional sulphuric acid route and the challenges involved in achieving battery grade lithium carbonate are discussed. In addition, the evolving new alternative process routes are listed as options for consideration. The lithium-ion battery sector is one of the largest consumers of lithium, currently estimated to be at approximately 26% of total global lithium demand. Originally used in computing and mobile communication devices, lithium-ion batteries are being increasingly used to power electric bicycles (e-bikes), vehicles and mass energy storage devices. Lithium-ion batteries have superior energy density, are more efficient and environmentally friendly than traditional acid batteries. |
For phosphate projects where commercial uranium concentrations pervade through the ore body, it is both commercially attractive and necessary to produce a phosphate product that is free of radioactivity. This paper discusses a recent phosphate project containing uranium, based in Africa, and the lessons learned during the project development. The presence of uranium necessitated evaluating a number of flowsheet options, followed by mineralogy to understand the nature and occurrence of the uranium minerals.
This was followed up by a series of sighter tests, including assay by size, heavy liquid separation and preliminary flotation and acid leaching with uranium shake tests. The testwork highlighted the high degree of variability within the ore body and the difficulty of achieving acceptable flotation grade and recovery. The low uranium and phosphoric acid price and the complexity of the ore resulted in the Client shelving the project until such time as prices recovered and the project economic viability improved. While the resource was very large, it was considered that the metallurgical effort required would be substantial with no guarantee of success.
Magnetite ore bodies require crushing and grinding with significant energy costs in processing and the capital costs are significantly higher than for direct shipping ores (DSO). Overseas, the mining and processing of magnetite ores has a long history of production. This raises the question as to why the new magnetite projects have been so problematic and also whether there is a future for the long list of potential magnetite projects in Australia.
The quality of the magnetite concentrate product is superior to most DSO products and the magnetite contains energy benefits when converted to hematite in sintering or pelletising. The industry’s hopes have been dashed and questions are being raised as to the financial viability of such projects.
A comparison of Savage River, Project Magnet, Citic Pacific and Kurara is used to understand the differences between the projects and why some are more successful than others.
The White Dam gold project is located in South Australia, approximately 95 kms west of Broken Hill, with a total resource of 10.12 Mt containing 338,000 ounces of gold. The project was operated by Polymetals and Exco Resources. The proposal was for a dump leach project, and based on the high risk and short life of the project, the bank sought external Due Diligence in order to arrive at a funding decision.
This was a complex Due Diligence exercise, particularly deciding what the likely overall gold recovery would be based on column tests. Furthermore, there was a potential process risk with cyanide soluble copper in addition to the normal dump leach issues. Dump leaching being a quantum leap carries a higher risk than heap leaching where the ore is crushed. In addition, there was little experience in Australia with dump leaches.
This paper describes the process that was undertaken so funding could be provided, and discusses the final project performance compared to what was predicted.
Troy Resources acquired the Karouni Gold Project in Guyana, South America in 2014 and immediately proceeded to a Pre-Feasibility Study and project implementation. The study considered two open pit mines feeding a conventional carbon in leach (CIL) gold plant with a capacity of 1Mtpa. The study assumed a total of 2.61 million tonnes of ore with an average grade of 3.84 g/t gold with a recovered gold production of 303,526 ounces over a three year mine life.
The project development involved drilling metallurgical test holes, securing second-hand major pieces of equipment where suitable, and arranging shipping to Guyana. The remote location meant logistical considerations were paramount. The plant consists of conventional two-stage crushing with single stage ball milling and a gravity circuit. The tailings circuit includes DETOX.
The extremely high rainfall presented challenges with water management and the necessity to dispose of clean water to the environment. The DETOX was also mandatory due to the highly sensitive environment and past history in the area. The criticality of this meant that in the design, any cyanide in the tailings would precipitate in a plant shutdown.
Lessons were learned and the project has been both profitable and successful for Troy Resources in a new operating location. In addition, the project has created jobs, delivered royalties and brought new skills into an area where previously there was little current mining activity.
Australia is a major world producer of zircon currently supplying 45% of the world’s production. A number of these resources are high in radioactivity (uranium & thorium) and this makes them commercially unattractive and more difficult to market.
Zircon is used for foundry sand, refractories, ceramics and glazes and zirconium chemicals. There are radiation limits on the sale and transport of zircon in countries such as China.
This has created a challenge to reduce the radioactivity and greatly improve the marketability of the product. There are a number of patents and proprietary technologies available for reducing radioactivity in zircon. A number of these options were tested and results were mineralogically controlled and the efficiency varied depending on the source of the zircon sand.
In addition there were issues with OPEX and design of process plants to achieve such reductions. Whilst a number of companies have evaluated a number of these technically challenging process options, no commercial plants have been built to date.
The increasing global concerns and new environmental regulations regarding the transportation and destruction of cyanide have led to a renewed interested in recovering cyanide and copper from gold processing operations. Resins are particularly well suited to the recovery of copper cyanide, and can be applied to cyanide in solutions or pulp. The process uses a strong base resin technology to extract free cyanide radicals as well as metal-cyanide complexes from gold tailings. The process offers a number of important benefits including:
There is mounting pressure on the gold industry to ban the use of cyanide in more jurisdictions around the world. Cyanide recovery using resins is a far more acceptable solution to banning its use. The increased cost of cyanide also dictates that recovery is preferable to destruction.
The industry places a high value on good quality water for processing iron ores. Minimising its use with conservation and recycling are the norm.
Where groundwater is used, sustainability and recharge rates matching extraction is mandatory for licenses to be maintained. Transporting water over long distances and the need for reverse osmosis is becoming more common for iron ore projects because the water is usually poor quality and high in chlorides. Product specifications impose limits of chlorides in iron ores. Some projects are capacity limited because of water supply. Water is also used for dust suppression, camps and slurry transport of product.
This paper also looks at options, strategies, unit operations, water accounting and system analysis for iron ore resource projects where large quantities of water are required.
Clay minerals can cause nightmares with mineral processing because of the inherent difficulties of processing high clay ores. Understanding the geology, mineralogy and correctly selecting representative samples of the ore to be processed is critical in getting the mineral processing right. Testing at an early stage of representative ore samples is critical. The presence of clays in hard rock comes as a surprise if not fully understood. Similarly waste dilution from country rock containing clay can adversely affect the process. The presence of clays has a major influence on the process selection and equipment used in the final flowsheet. The materials handling issues in bins, stockpiles and conveying will also be addressed. For high clay ores Tunra type testing to determine rill angles, angles of repose and materials handling characteristics is a must. Only apron feeders are effective feeders with high clay ores. The use of stockpiles is not possible because of increased incidence of rat holing and the difficulties getting the ore to flow in a stockpile or bin is extreme. Conveying is also difficult, requiring the use of belt washing stations plus increased tracking issues. Scrubbing of ores to remove fines and clay is commonly used. This requires scrubbing tests and sizing of the scrubbers. |
Safe design begins in the concept development phase of a process plant when choices are made about the overall design and its details. The safety of a design can be enhanced prior to design and construction if a risk management approach is adopted.
Personal safety is paramount and the designer has a Duty of Care. A safe design approach begins in the conceptual and planning stages with an emphasis on making choices about design, materials used and methods of manufacture or construction to enhance the safety of the finished process plant. Specific issues such as noise, dust, volatiles, chemicals, heat, fire and explosion, HAZOP, HAZID, plant layout, waste disposal and ventilation will be discussed.
The design function is influenced by a range of parties at varying stages of the design process, as well as during the lifecycle of the structure. They include:
Pipelines are a common mode for transport of liquid hydrocarbons and there are significant benefits with such systems. This includes onshore and offshore pipelines. The products transported include concentrates, crude oil, petroleum products, water, LPG, natural gas and tar sands.
The stages of a pipeline project are the Concept stage followed by the Feasibility stage and thereafter the basic Engineering followed by full Detailed Design stage. There are a number of major codes and standards that apply to the design. In addition there is a variety of software packages used in such designs. The route selection is a critical initial stage followed by material selection and corrosion control, including wall thickness, stress analysis and design factors.
Thereafter valves, fittings and P&IDs including pumps and compressors with major engineering deliverables are incorporated into the final design process. The installation, testing and commissioning will be discussed including examples of such installations.
Australia has the potential to be the world’s top uranium producer however development of new uranium projects has slowed throughout the world.
The crisis at the Fukushima nuclear plant in Japan after the tsunami killed off the world’s appetite for nuclear energy and with it the price for yellowcake – making it so low that most projects other than Insitu Leach (ISL) are not viable. A number of projects are on hold waiting for the uranium price to improve.
This paper addresses the three options of uranium mining and its associated processing options including their long term sustainability in the current climate considering political implications of mining uranium ores.
Australia has the potential to be the world’s top uranium producer however development of new uranium projects has slowed particularly in Australia.
The crisis at the Fukushima nuclear plant in Japan after the Tsunami killed off the world’s appetite for nuclear energy and with it the price for yellowcake – making it so low that most projects other than Insitu Leach (ISL) are not viable. A number of projects are on hold waiting for the uranium price to improve.
The long awaited improvement in price has not materialised. A radical approach has been used to try and develop economically viable uranium projects.
This paper addresses the three options of uranium mining and its associated processing options including their long term sustainability in the current climate considering political implications of mining uranium ores. It considers mineralogy of ore and gangue, ore sorting, possible process routes and key drivers plus the potential for by products.
Reference is made to a number of current operating plants and their key differences.
The primary objectives of an independent mineral processing project technical due diligence review are:
It is an essential part of the technical due diligence review that the independent engineer identifies and reviews the inputs and assumptions that underpin the project financial model.
Following the independent engineer’s assessment, a “signed off” model will be agreed and will form the basis for a lending institution base case model, which will be used by the third party company in its assessment of the project.
The final technical report should be self-contained and reasonably comprehensive so that it can be read without unnecessary recourse to source documents. The report should be internally consistent with regard to the integration of the specific areas of review (geology, mining, processing, infrastructure, environment, etc.).
The executive summary should outline all of the key risks and their materiality in relation to financing this project.
It is very disappointing to see the results of resource project failures where this could have been prevented. We see so often that we worry about why these fundamental technical mistakes are being repeated.
Common issues are-non representative testing, new technology, failure to recognise the mineralogy and variability, skipping stage gate studies, failure to run “what happens if scenarios”, failure to recognise materials handling issues, failure to undertake a reasonableness check, failure to apply lessons learnt, not recognising good ore and bad ore, inability to blend ores, recognising the level of complexity processing ore.
There is now a new generation of mobile crushing and screening plant systems available which have been developed based on the motivation of reducing truck haulage. Newly designed mobile crushing and screening plant systems have the advantages of mobility, flexibility, economy and reliable performance, making this system very appealing for small to medium sized projects or projects where a number of resources are separated by distance. A brief review of the past history and experience with transportable crushing plants provides an insight into some of the issues with transportable plants in mineral processing. A closer look at a simple model based on exploiting small but high grade ore bodies suggests the concept has merit, however there are many more engineering, logistics, legal, technical and management aspects which have limited the application of such a concept in the resource sector. This paper explores the concept in detail and endeavours to analyse the preferred commodities and scenarios under which the concept could be used and the economic and logistical limitations for iron ore. The paper also looks at the risk assessment criteria to be applied in selecting the type of resource projects where the model could be applied successfully. Other aspects considered in this paper are the project planning requirements, technical and economic feasibility, bankability, and operability. Reference is made to the operating experience of contractors at a number of sites and feedback from the resource companies as managers of the projects.
This paper conducts a review of the current state of the technology and flotation equipment including equipment suppliers and sites significant technical changes. Flotation cells have increased in size over the last thirty years and there have been significant changes in cell layout, technology and design. The key factors for sizing and equipment selection is the ore character based on flotation testwork and plant experience. The retention time required at each stage is also a key factor discussed. The change from square Hough trough cells to cylindrical tank cells up to 600 m in size has been game changing. The recovery of a flotation cell relates directly to the amount of air added to the cell. Optimising reagent chemical use has provided great insights into flotation performance.
Flash flotation cells, column cells, Jameson cells, unit cells, improved metallurgical performance, internal launders, etc. in stream analysis are all developments worthy of mention. Advances in modelling, simulation and control optimisation are bringing benefits to the industry. Examples of large flotation cell installations and related issues are also outlined.
Clay minerals can cause nightmares with mineral processing. These clay minerals typically form in near surface geological environments due to weathering, particularly above the natural water table, sedimentation and digenesis and are common in hydrothermally altered rocks. Clay minerals associated with alteration is referred to as Argillic alteration. The extremely small particle size, usually <2 microns (sometimes coarser or finer) and with the very high specific surface area, these clay minerals are highly reactive and respond to changes in the processing environment. Understanding the geology, mineralogy and correctly selecting representative samples of the ore to be processed is critical in getting the mineral processing right. Clays have the potential, if not recognised, to destroy project economics. Testing at an early stage of representative ore samples is critical. The presence of clays in hard rock comes as a surprise if not fully understood. Similarly waste dilution from country rock containing clay can adversely affect the process. There are some solutions which assist in processing high clay ores but do not negate all of the difficulties. The presence of clays has a major influence on the process selection and equipment used in
the final flowsheet. The industry has paid a heavy price on a number of projects where the clay was not recognised or the process plant was based on a hard rock design which later proved to be totally unsuitable. Trying to mitigate the impact of clay on the process, if the percentage of clay in the feed cannot be controlled, is a mineral processing challenge.
The history of mill liners has evolved over time and this paper tracks the changes and development of liner technology. It provides an overview of the primary types of liners, the design and the materials of construction. The design of a mill liner is driven by application, materials of construction, casting technology and handling issues. The choice of solid steel, grid liners, rubber or composites and magnetic liners is based on many factors.
The methods used for monitoring wear and predicting eventual change out time are many and varied. The contribution of discrete element modelling (DEM) analysis in predicting wear profile is discussed.
Mill trajectory and DEM software programs are used with great effect to predict the effect of lifter height, face angle, high low lifters or mill speed. In the field, trial and operational experience, is used or improvements/design concepts at one operation are applied to another. Broken lifters, accentuated wear and other problems can be better understood using hardess testing, chemical analysis and photo micrograph analysis of pearlitic or martensitic structure along with fracture face observations form part of typical root cause analysis. However given correct and sound liner and lifter, feed and discharge design media selection, and materials of construction, the majority of premature liner or bolting failure is normally attributed to incorrect operational methods such as excessive high ball to feed ratio, incorrect mill speed relating to lifter ball throw, incorrect media selection, “tramp” material entering the mill charge from upstream or recirculating process and understanding the specific mill operation in question.
It is hoped that this paper will benefit mill operators who are faced with challenges of improving wear life and at the same time optimizing mill throughput and performance.
| More and more gold plants around the world are being required by law to destroy cyanide in tailings. This paper evaluates the options and what influences the process selection for cyanide destruction and recovery. The cost effectiveness, comparison of common detoxification methods with advantages and disadvantages are explored. This paper also looks at the safety and hazards of cyanide and explores various cyanide degradation methods so as to make it safe to people and the environment upon disposal. Fundamental aspects of the International Code for Cyanide Management are covered, and highlighted are references to all major Australian bodies who are consulting on the management of cyanide. Case studies are examined so as to illustrate major hazards and mitigations that may occur and be implemented in gold processing operations. The various environmental issues pertaining to the usage of cyanide, including the effects on wildlife, monitoring procedures and strategies undertaken to prevent and control any risks due to exposure to the environment will be discussed. Treatment procedures, and methods, for cyanide poisoning are also briefly covered as well as standard transport and storage procedures for the handling of cyanide. |
The processing of gold copper and copper gold ores can be highly problematic, site specific and the process selection is dependent on ore grade, mineralogy, acid leach behaviour, cyanide chemistry, product saleability and environmental considerations. The production of a copper gold concentrate is also an option where the copper is of a marketable grade. In some situations the flotation tailings may be subject to cyanide leaching. The general effects of copper on cyanide leaching chemistry are increased cyanide and lime consumption and decreased dissolution rates for gold and silver. The severe fouling of carbon, high solution losses and even re-precipitation of gold can occur.
The Paulsens gold deposit in the Pilbara region of Western Australia was discovered by CRA in 1998. In 2001, St Barbara Mines Limited (St Barbara) made a successful takeover offer for Taipan Resources NL and then began an update of the previous Bankable Feasibility Study (BFS) undertaken by Minproc Limited. This paper describes the history of the metallurgical testwork, plant design and initial development to optimise a project with complex metallurgical process characteristics and manage the risks. The Paulsens ore is preg robbing, has cyanide soluble copper and nickel and is highly sulphidic. The ore is relatively hard and requires a very fine grind size of P80 53 microns. The metallurgical challenges have been met for this complex ore and the process flowsheet included aspects not commonly associated with a typical gold plant.
Geometallurgical mapping of the global ore body to understand the variability of cyanide soluble copper and nickel as well as potential problems from preg robbing waste was undertaken to assess the risks and suitability of the proposed flowsheet. Concurrently, the mine schedule could be optimised to manage the levels of copper and nickel in the feed by understanding the copper behaviour with respect to block modelling.
One of the primary objectives of the project was to study the initial response of a uranium ore to In-Situ Leaching (ISL). This was achieved through a tailored testwork program with a stage-wise approach. The results of each stage were analysed before proceeding to the next step.
The amenability of the sample(s) to ISL hydrometallurgical processing was studied (acid and alkaline), to allow the development of an optimised process flowsheet. This will permitted the modelling of capital and operating costs as well as cash flow related to the predicted recovery determined by the testwork.
The project began with a review of the historical test data. The gap in the historical metallurgical testwork was clearly identified and recommendations for any further testwork made.
QEMSCAN mineralogical investigation identified the main uranium bearing minerals. It also provides a comprehensive analysis of the liberation and locking characteristics of the uranium bearing minerals and the associated gangue minerals to highlight any potential issues in leaching.
Head assay of the drill core to match with the lithology of the hole and twin holes was carried out. Bottle roll leach tests gave an indication on the relative rate and amount of uranium extracted and relative consumption of oxidant as a function of leach solution. This also enabled the determination of the extent of any gangue materials leaching.
The next stage of testing, the column leach test was designed to simulate field condition more closely than the bottle roll test, which allows permeability and hydraulic conductivity be measured.
Preliminary investigation also would be conducted to study the response of the leach liquor to purification by solvent extraction and ion exchange.
Pilot scale testing, involving well field hydrology and leach tests will follow after the specific issues encountered during bottle roll and column leach tests are resolved. In here, the well plan injection and recovery pattern will be investigated.
The advantages and disadvantages of ISL are outlined. Unless the metallurgy has been demonstrated there are significant risks which could be fatal flaws to the ISL project. Key findings of the study are outlined.
Beneficiation of low grade ores is the process of increasing the grade of a mineral through unit operations that remove and separate the waste (or gangue) material from the valuable mineral that can then be used for further processing or direct use. Important factors when deciding upon a beneficiation program are the feed grade, mass yield and the metal recovery. As lower grade ores are being processed beneficiation is a critical process. How predictive is laboratory test work for “as built” operating projects?
Beneficiation includes all or some of the available unit operations to produce a beneficiation flow sheet i.e. associated unit operations including but not limited to optical sorting, radiometric sorting, crushing and screening, coarse cobbing, jigging, dense media separation (DMS), spirals, magnetic separation, flotation, thickening, filtering and drying. Reference to specific projects and the approach developed in formulating a beneficiation flow sheet and a comparison of difficult and simple beneficiation flow sheets are cited.
The QEMSCAN system is the third generation of automated mineral analysis systems that began with the QEM*SEM at CSIRO 30 years ago (Butcher et al. 2000). It is now a successful commercial instrument with 39 instruments in operation around the world. Back Scattered Electrons (BSE) and Energy Dispersive (EDS) X-Ray spectra are used to create digital mineral images with mineral identification occurring online. Low-count EDS spectra are used preferentially to BSE brightness, allowing minerals to be accurately identified by chemical composition. Individual minerals or groups of similar compositions are identified by comparison to a comprehensive mineral database incorporated into the QEMSCAN software.
Optical mineralogy and Scanning Electron Microscopy has is a metallurgists’ tool for determining the ore process mineralogy and delivering a better flowsheet. These techniques have limitations, provide limited information and sometimes fail to provide representative information.
In contrast, QEMSCAN provides information on the nature and occurrence of all mineral species present plus the liberation characteristics, looking at thousands of particles in the sample presented. Some of the data presented includes:
It can also be used on concentrates, polished sections or drill core. This is a significant improvement in ore characterisation providing lithology, mineralogy, liberation, ore grade and porosity from a sample. Theoretical grade-recovery curves can be created to be mineralogically limited from QEMSCAN analysis which, when compared with metallurgical results, are valuable in evaluating whether liberation or chemical selectivity is driving flotation performance.
A number of case study examples are given where the QEMSCAN had a significant bearing on future project development at an early stage of exploration and mine development.
| Clay minerals can cause nightmares with Mineral Processing because of the inherent difficulties of processing high clay ores. These clay minerals typically form in near surface geological environments due to weathering, particularly above the natural water table, sedimentation and diagenesis and are common in hydrothermally altered rocks. Clay minerals associated with alteration is referred to as Argillic alteration. The extremely small particle size, usually <2 microns (sometimes coarser or finer) and with the very high surface area these clay minerals are highly reactive and respond to changes in the processing environment. |
Silver and gold bearing ore from the Troy Resources NL Casposo Gold-Silver Project, located within the San Juan Province of Argentina contains a complex mix of gold, silver, electrum and silver sulphides in the ore. Casposo is a typical low sulphidation epithermal style gold–silver deposit where mineralisation is hosted within rhyolite – andesite flows and breccias. Veins are typically banded quartz–chalcedony colloform – crustiform banded with quartz – carbonate infill. Mineralisation is associated with an assemblage consisting of quartz, chalcedony, adularia, calcite, illite, sericite and trace sulphides. Gold and silver occur as electrum, native silver, sulfosalts and silver sulphides. This paper presents a case study that describes the process selection, development and engineering of a tailored process plant for the recovery of gold and silver from this ore. The original feasibility study, modelling, metallurgical testwork and engineering studies are outlined. The final flowsheet was based on minimising capital cost, operability, recovery and minimising technical risk. The process flowsheet uses the traditional Merrill Crowe route because of the high silver to gold ratio in the feed and achieves maximum gold and silver recovery while providing a common facility for future ore body treatment.
As the resources sector becomes tougher with rising costs and cyclical metal prices, mining companies need to continue to reduce their costs and do more with less. Many new resource projects fail to come in under or on budget based on Feasibility Studies. Particularly, capital expenditure (CAPEX) proves difficult to achieve for resource projects. A number of resource projects have failed because of aggressive plant CAPEX cost cutting resulting in projects with no surge capacity and are unable to achieve design throughput. In addition, the plants are not operable because of the omissions. In recent times many businesses have also experienced the “costs” of simply implementing aggressive operating “cost cutting” measures as a strategy for solving business performance problems. This paper looks at technology driven, employment related, luxury cuts, department cuts and restructuring cuts. In the past companies used an incremental approach based on the use of past budget information as an integral part of the budget construction process going forward. The use of performance reports and Management Information Systems (MIS) is examined along with the role of continuous improvement in achieving
sensible cost cutting.
The Iron Road Limited Central Eyre Iron Project (CEIP) area, located on the Eyre Peninsula of South Australia, covers extensive Archaean iron formations that occur as coarse-grained magnetite-bearing gneiss. The cumulative strike length, estimated from aeromagnetic data, is at least 95 km.
The project is located in a grain growing area 185 km west of the existing iron ore and steel making operations of OneSteel at Whyalla. A narrow gauge railway built to transport agricultural products to the deep-water port of Port Lincoln, 175 km to the south, traverses the project area. A number of well-serviced rural townships are located nearby. Current activities include resource expansion drilling, extensive metallurgical test work, community consultation and a Pre-Feasibility Study (PFS) that commenced in April 2010.
The PFS has encompassed the Central Eyre Iron Project, comprising the three significant iron occurrences (Warramboo, Kopi and Hambidge) and was completed in early 2011. Extensive testwork programmes and metallurgical modelling confirmed viable process options for the project, using simple off the shelf processing technology.
Pre-concentration by coarse cobbing yielded promising results, and is the key to reducing not only the capital expenditure but also the operating cost, in particular the power cost, which is the highest operating cost component of a magnetite beneficiation plant. The ore is also amendable to High Pressure Grinding Rolls (HPGR) processing. This offers a potential for further reduction of the energy requirements.
Testwork also confirmed that a high grade blast furnace quality concentrate (~68% Fe) can be produced at a relatively coarse grind (P80 106 µm).
The classic method of recovery of gold and silver from cyanide solution was Merrill Crowe until the introduction of Carbon In Pulp (CIP) in the 1970’s. The CIP process indicated savings in CAPEX. This meant that lower grade ores could be economically treated than otherwise would have been the case. Soluble losses from CIP plants are lower than Merrill Crowe and the process is less vulnerable to impurities such as sulphides, arsenates in the leach liquor. The CIP process is more robust and forgiving than Merrill Crowe. Until recently for very high grade feeds Merrill Crowe was far superior to CIP and a clear choice. However, the trends toward the application of EMEW cells, ion exchange resins and hybrid plants are changing the way we might look at Merrill Crowe in the future for high grade gold and more particularly high silver feeds. The problem with direct electrowinning is that cell efficiency drops with solution tenor. The high grade gravity ILR pregnant solution may be able to be treated separately with direct electrowinning and save on zinc dust. Similarly the CCD overflow could be electrowon to save zinc. Solutions above 1,000 ppm silver for metallic silver to plate out and around 300 ppm for powder to be deposited on the cathode are required. The EMEW powder cell design incorporates 200 mm dia tube that acts as the cathode and has a stainless steel anode fitted. Solution is pumped through at high velocity and the powder is drained to a filter using a cycle timed PLC. The use of resins and IXEW (ion exchange followed by electowinning) hybrid circuits and Resin In Pulp (RIP) are also being considered, but as a retrofitted design based on piloting in an existing plant in order to minimise process risk.
The development of metallurgical projects involves high risks and high returns. There is a high degree of uncertainty. Minerals need to be extracted into concentrates or metal products. Design metallurgists are
specialists in mineral processing who undertake test work and flow sheet development and use the
principles of chemistry, physics and mathematics to achieve successful operating projects. Metallurgy is not an exact science and knowledge, experience and skill with interpreting results plays a significant role in developing successful projects. Project statistics show that only 50 per cent of projects turn out as predicted and there are many reasons for this. The common belief that a bankable feasibility study (BFS) guarantees success is flawed. Even quantitative risk analysis will not eliminate inherent risks or make up for some of the common metallurgical errors. There are many complex sulfide gold ores, uranium, nickel, tantalum, vanadium etc which can be problematic. Refractory gold ores and refractory uranium ores are further examples. Even beneficiating iron ores is not as simple as it first appears. Floating fresh sulfides, while generally straight forward, the range of liberation sizes, optimised reagent regimes and problems with weathered ore can be challenging. Metallurgical problems result from different objectives, common mistakes and incorrect interpretation or no interpretation of results. Experience has shown that unless these mistakes are identified and understood they are likely to be repeated.
Gold is showing quite a surge in price and interest of late. While everyone is trying to cash in with the current high price, there are some issues to be aware of when evaluating a gold deposit. Mineralogy is the most important characteristic as it drives the whole process route. Free, coarse metallic gold is easily treated as opposed to complex sulphides. Gold tellurides or gold locked in arsenopyrite these are commonly known as refractory deposits, require fine grinding and oxidative
techniques to expose the gold.
Head assays are important in terms of ore value (gold and silver), however trace elements like copper, nickel, zinc and mercury are also important to track and be aware of. High levels of coarse, free gold are particularly difficult to sample and can create sampling and representivity issues. Bulk leaches or screen fire assays technique may be of consideration. The ore characterisation is very important. Ores may range from highly weathered oxides through to fresh primary sulphides, with a transition material in between. Each ore type may require a significantly different process to treat efficiently. Comminution deals with crushing and grinding to the target size to liberate or expose the gold so it can be extracted. Selecting the correct crushing and milling circuit for a particular ore, or range of ores, is critical for the success of the project.
Leach extraction will determine the overall recovery and success of the project. The use of leaching enhancers (PbNO3, O2, peroxide) may be required in the presence of some reactive sulphide ore types to promote the leaching kinetics. Reactive sulphides (arsenopyrite, pyrrhotite, marcasite) can consume oxygen from the slurry, which is essential for gold leaching reaction. Once gold has been dissolved it needs to be adsorbed onto carbon before it can be electro won and smelted into doré bullion. Cyclic or Sequential Carbon Loading is required to determine the loading capacity and rate. This test can also highlight potential issues with competing ions (Cu, Ni, and Zn) or fouling potential (organic oxalate and humates) which may impact on the amount of carbon required to recover that amount of gold leached.
Tailings characterisation is required to maximise the amount of tailings that can be contained in a tails dam. Sulphide ore types may require acid generation and acid neutralising capacity tests to ensure acid mine drainage issues do not occur within the tailings dam. Water source is important, especially when using hyper-saline water. The water will buffer at a
lower pH than is optimum for cyanide leaching (typically from 8.5 – 9.0). As well as resulting in high lime consumption, the formation of HCN in the leaching process requires careful management from an operational OHS. The high lime usage may also create scale (CaCO3 and CaSO4) formation which will need to be managed in the circuit.
These important issues, if not addressed at an early stage, may cause critical problems during the processing of the gold ores being evaluated. Some examples will be presented where issues were not addressed and problems occurred.
| The Marvel Loch Operations (MLO) plant was treating ores from up to six MLO sources and in addition needed to blend externally sourced ores with its own ores. This presented a metallurgical accounting dilemma, which was subsequently addressed by the design, implementation and testing of an automatic sampling system. The MLO automatic sampler was well designed and has been the subject of previous internal and external reviews. The sampling action is fully automated and the unit is essentially self cleaning particularly when sampling primary ores. The purpose of this paper is to document the rationale behind the design, the specific details of the sampling station, its use for ore purchase purposes and an assessment of the sampling system to meet the needs of the operator. |
Merrill Crowe preceded Carbon In Pulp (CIP) technology and is now only used for very high grade gold projects or where the silver to gold ratio exceeds ten to one. CIP technology is generally more efficient and cost effective for lower grade ores whereas Merrill Crowe is superior for high grade silver ores.
Gravity processes are not as efficient for high silver ores as for gold. Metallic silver or electrum can be recovered at modest recoveries whereas acanthite (Ag2S) exhibits poor gravity recovery even with centrifugal concentrators.
Leaching of high silver ores requires significantly higher cyanide (>1500 ppm) and oxygen levels and extended leach times (>72 hours). Usually the recovery is lower than for gold.
The adsorption capacity needs to be higher for high grade silver ores with a larger inventory of carbon and more carbon movement. Carbon activity and solution loss become more critical with a general requirement for more adsorption stages in order to achieve equilibrium.
Silver elutes first off the carbon and at a lower temperature. These conditions are at odds with the gold elution. Generally, operations optimise to maximise gold recovery from the carbon. The silver cyanide complex (Ag(CN)2) is less stable than gold cyanide (Au(CN)2) and breaks down at the lower temperature and forms metallic silver which remains on the carbon. This has a negative impact on carbon activity and
hence solution loss.
Where high silver values are present during electrowinning, the cathodes can be washed with high pressure water and the electrowon gold and silver comes off very easily. In addition high sludging of the cell is not uncommon as the dendrites are loosely held. Some designs exploit this feature in self sludging cells.
The gold electrode potential is -0.63 volts and for silver -0.45 volts. This means the silver will preferentially plate out of solution before the gold, slowing the electrowinning process. In addition there is more metal to electrowin and more cell capacity is required.
Conventional processing of silver-bearing materials containing gold group metals involves smelting the material to bullion and purification of the silver by electro refining, along with recovery of gold and platinum group metals from the slimes generated by the electro refining process. An alternative process has been developed that allows extraction of the silver from such residues using a combination of chloride and nitrate chemistry. An advantages of the process is the production of very highpurity silver. A number of examples are cited with the good design aspects highlighted
A successful ISL operation involves a multidisciplinary approach:
|
Gold rooms represent a high security area and preventing theft is a challenging task. Where gravity concentrates or high value unit intermediate products are present, particular and specific security procedures must be put in place. This paper describes the development and implementation which reflects best practice in gold room security. Procedures involving key holder systems, key locks, swipe cards and double locks preventing any one person having access to the gold room, including specific procedures for gravity gold concentrators, will be addressed. The use of monitoring and how to deal with alarms and potential hold ups will be reviewed. The use of cameras and archival DVD recorders is common in gold rooms.
The use of electronic surveillance, movement detectors, seismic monitors and the two person policy and gold room entry procedures are described, including how to deal with visitors. The importance of confidentiality regarding smelting and gold pick-up days, plus strategies employed to minimise storing large quantities of gold on site will be presented.
The role of metallurgical accounting in providing quality auditable information and the minimum standards of record keeping required is discussed. The role of the Gold Squad will be outlined. Regular auditing and risk analysis and several case studies are cited where security was deficient or improved.
Gravity gold recovery has been practiced for thousands of years, making it one of the oldest forms of mineral processing. Gold is 19 times heavier than water although the barren rock is generally only 2.7 times heavier. Any potential gold ore needs to be characterised to assess its amenability to a gravity recoverable gold (GRG) process based on well planned and executed test work. Scale up considerations need to be considered in designing a gravity circuit. The economic impact of
a gravity circuit should be justified based on the installed cost and likely benefits. Maximising gravity gold recovery results in a faster cash flow, lower operating cost per ounce and higher overall gold recoveries compared to the several weeks required to recover gold adsorbed onto carbon.
The advent of centrifugal concentrators such as the Knelson and Falcon, coupled with intensive leaching of concentrates (ILR), has revolutionised gravity gold circuit designs. Considerations associated with the sizing of the centrifugal machines and the percentage of the circulating load (bleed) that should be processed is discussed in this paper. The trends with gravity circuit layout, engineering, as well as optimum dumping cycles, are important areas which require close consideration. Key aspects of these are presented in this paper.
There are a number of circuit configurations to be considered, including the integration of different gravity concentrators. Other gravity process design considerations such as fewer modules, the effect of equipment size and enhancement of process efficiency using preconcentration, together with factors that affect OPEX and CAPEX are addressed.
Practical considerations of maintenance, security from theft, minimisation of risk and water balance considerations are discussed using different equipment and circuit configurations. The trend towards using gravity recovery in flotation plants is also reviewed. A number of examples are cited and good design aspects highlighted.
Metal prices have declined in real terms and this makes it more difficult over time to bring new projects into production. The Global Financial Crisis (G.F.C.) has had a major impact on the mineral industry with a sharp decline in commodity prices and profitability. Banks are more cautious lending to new resource projects. They also require better researched and optimised projects with more robust economics. There is little doubt some form of carbon tax will be increased and our energy sources will have to change.
Innovation and the introduction of new technology will be a major challenge required to succeed and overcome some of these issues. Australia’s record of technology innovation in the gold industry, for example, has been brilliant by any standards. Energy is a major cost for processing minerals and the comminution processes we use are inefficient and large consumers of energy. The development of new grinding technologies is long overdue. There will be an increasing trend to hydrometallurgical processing and a decline in pyrometallurgical processes.
The tougher environmental constraints being placed on new projects will mean that some projects will not be allowed on environmental grounds. Exploration activities and will be curtailed in sensitive areas and even excluded altogether. Water is going to become a scarce resource and access is going to be difficult with an emphasis on conservation and re-use.
Social and Political issues are impacting on new projects like never before. The common cry “not in my back yard” makes it more difficult to win hearts and minds and gain acceptance for new projects. Mining companies will be called on more and more to provide schools, hospitals and services where governments fail to do so particularly in impoverished areas.
Mining projects are only now starting to implement sustainability policies and understand the full impact of such policies. The mining industry could become a global leader in sustainable development. The industry has in the past demonstrated a willingness to better understand and resolve difficult issues at the local level.
Complex and refractory gold ores are problematic, metallurgically challenging and require higher CAPEX, higher operating costs and sometimes lower overall gold recovery. Finding simple free milling gold ores are likely to be less common going forward. Refractory ores include physically locked gold, chemically locked or preg robbing ores. The options currently available are flotation, roasting, ultra fine grinding, pressure oxidation and biological oxidation. These methods with their inherent advantages are discussed and new novel technology which may also be applied. Specific plants where the respective technologies have been applied are referenced. |
Feasibility Studies are vital for resource discovery to technically viable and profitable operation. The study levels and use on a stage gate process approach are typically Concept, Pre Feasibility, Feasibility and Definitive Studies. Each level must assess all aspects including Risk Analysis. The Study developed as a result describes a business opportunity and guides investment.
This paper considers Feasibility Studies and demonstrates their “Uses and Abuses”. A number of Case histories are discussed; common mistakes and lessons learned are presented. The paper outlines a framework for the conduct of Feasibility Studies and provides guidance to Minimum Standards and best practice.
Conclusions:
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Modern vibrating screens are being asked to operate at increasingly higher levels of performance. What are the critical factors to consider when sizing modern vibrating screens? An independent review of recent installations and applications
is presented.
The metallurgical heart of the majority of copper oxide processes is the heap leaching operation. The success of this unit operation is so important that operators need to understand the ramifications of their decisions or non-decisions and how they could affect the downstream processing.
Heap leaching is an operation that can be described as a scientific art whereby principles of science can be used to guide experienced personnel in attaining their goals. Its success or otherwise is dependent upon a number of factors, notably:
Although many of these factors or issues can be, and are, scientifically interpolated and used, their understanding alone does not guarantee a successful heap leaching operation. Some of the issues to be discussed that can make or break an operation could relate to:
These sorts of issues are generally personnel dependent and they have the capacity to inflict unknowing harm on the operations if they are not addressed adequately and in a timely manner. Finally, regardless of the scientific principles used for ore preparation, stacking and heap leaching, the success of this part of the project depends heavily on the personnel involved.
Introduction:
Beneficiation of magnetite is an integral part of the future of iron ore processing. Historically, the focus of Western Australian producers has been on exporting Direct Shipping Ore (DSO) namely hematite. The future for new DSO resources is limited so companies are changing their emphasis into processing the very large, undeveloped magnetite ores in Western Australia (WA), using beneficiation to produce shippable magnetite concentrates. These magnetite resources require higher cost processing techniques such as fine grinding and beneficiation to produce saleable concentrates. This distinct difference, from the DSO ores, has lead to the development of a number of new technologies.
This paper reviews:
There are no large rivers in Western Australia capable of supplying water for processing magnetite ores. If sea water is used there are severe corrosion issues and the requirement to wash the concentrates with potable water. If groundwater is used
there is a need to treat the water and sustainability is an issue for large projects because of potential drawdown of the aquifer.
If sea water is desalinated the cost of the water is high because of the power requirement. At the same time the necessity to conserve water has lead to flowsheets where all of the tailings have to be filtered to minimise the water requirement.
Managing the various water qualities and optimising water recovery and quality has resulted in optimising the water balance and issues meeting environmental obligations. Reverse flotation is a critical final step in reducing the silica level in the
final concentrate and requires good quality water.
The resource sector is conservative industry and people are resistant to change. The methods and procedures used to implement changes in process plants ultimately determine the success of such changes. The financial managers have a large say in where money is spent and the technical personnel must justify the cost and benefits for any expenditure. There are also others who believe it can’t be done-“we tried that”. Implementing change needs a ‘champion” who can assess the risks, plan,
define the objectives and scope, set the goals, determine the key performance indicators (KPIs) and stay focussed. This also requires preparing a budget and schedule and measuring against this. Contract management, reports and reviews are part of the implementation. Several case studies are given as examples of the implementation of process design changes to highlight the critical aspects involved.
Metallurgical accounting can be defined as the monitoring of the valuable metals from the time the ore is broken at the primary crusher until the time that we have the saleable products and residues. The overall purpose of metallurgical accounting is to provide management with up to date information that can be used to control mining and metallurgical operations. The decisions that are taken on the basis of the information that the metallurgical accounting system provides should result in improved control and, ultimately, increased revenue. The current state of accounting is a result of an extended evolutionary process and will continue as process plants become more sophisticated. Differences in mine “call factors” and grade control reconciliation can lead to frustration between the site’s geoscientists and its metallurgists leading to a level of distrust in the mill grade.
Metallurgical accounting is not included in sufficient detail in undergraduate courses and the acceptable industry standards have developed based on what is considered acceptable to industry personnel and consultants. There is now the AMIRA P754 Metal Accounting, Code of Practice and Guidelines handbook or reference manual. Computer based databases and spreadsheets have transformed tedious book keeping into an important management tool. Over time these standards have improved with developments in analytical procedures, weighing technology and sampling.
This paper provides anecdotal examples of problems and improvements observed over a number of years within the gold industry in Australia and overseas.
Beneficiation of minerals in general, is an integral part of the science of Mineral Processing, and the concept that this science encompasses are in large measure applicable to the field of iron ore beneficiation. In general the objective of beneficiation is to remove 1) unwanted minerals or 2) particles of unsuitable size or structure. Compared to the other extractive processes, it is relatively inexpensive. The future for Direct Shipping Ores (DSO) is limited and companies will be forced into processing lower grade ores and using beneficiation to produce shippable concentrates. This paper reviews:
Summary:
The single most striking feature of uranium process metallurgy is the diversity of minerals present and therefore the flowsheets adopted. As an interesting sideline, this diversity issue will limit the possibilities of toll milling to decrease CAPEX requirements and create viable projects – a common approach in gold and nickel. By their very nature, the numerous uranium and associated minerals in a deposit are exotic and complex. This creates a considerable challenge for metallurgists and process engineers as not only can the multiple uranium minerals behave very differently but their associated minerals can also pose considerable challenges to process design.
Uranium exists as vein ores, in sandstone, pegmatite’s, shales, lignite ores, gold ores and copper ores as well as some granites. The implications of mineral composition dictates how the ore will process. In addition the nature of the host rock or gangue can make extraction more difficult, increase reagent consumption or require pre treatment.
The most striking feature of uranium process metallurgy is the diverse range of minerals present. Creates considerable challenges for metallurgists and process engineers Uranium exists as vein ores, in sandstone, pegmatite’s, shales, lignite, gold and copper ores Mineral composition dictates how the ore will process; the nature of the host rock and gangue
minerals can make extraction more difficult Increasing demand in uranium, especially from China and India
Current Uranium projects: (In production stages)
and numbers of projects in the basic engineering and feasibility study phases Conventional flowsheet for Uranium processing Diversity in Uranium deposits in
Titaniferous magnetite deposits are a significant source of vanadium for use in high strength steel alloying and other chemical applications.
The mineralogy of the deposits varies markedly and the ore characteristics strongly influencing the process route selected and the metallurgical outcomes. Characterisation of the ores reveals the presence of magnetite, ilmenite and other minerals such as spinel hematite and goethite with variable degrees of weathering along with weathered products of host rock. The standard processing route is to crush, grind and magnetically recover a concentrate for salt roasting to produce a soluble
vanadate.
Ore beneficiation is practiced to generate an iron based mineral concentrate containing much of the vanadium with low silica levels of 2%. Typical processing problems encountered are fine liberation size, over grinding of the magnetite and
variable response to magnetic separation resulting from the weathering profile.
Beneficiation options are restricted, and generally focused on producing a combined iron and titanium rich concentrate containing vanadium due to the fact that ilmenite and magnetite and their products of weathering are magnetic and have similar specific gravities making their separation difficult. The ilmenite usually contains low levels of vanadium making its separation highly desirable from the iron mineralisation containing higher levels of vanadium.
Salt roasting of vanadium ores followed by water leaching has been the standard processing route for many years. The cost of suitable sodium salts, availability of capital and increasing energy costs and energy availability are critical factors in
determining the viability of aspiring vanadium producers. To date, only Windimurra has acquired full capital funding, secured energy and sodium salt supplies at suitable cost that enable the construction of the project. Low overall recoveries of vanadium to concentrate roasting at up to 1200C are critical cost issues.
In this paper, factors influencing the recovery of vanadium are reviewed and emerging processing trends explored. The important features of the processing of titaniferous magnetites have been condensed from the literature, published works,
company websites, our own work and personal communication.
Covering:
Conclusions:
Conclusions:
Conclusions:
Bench scale metallurgical ore characterisation test programmes are required because each ore body is unique even though there are typical process routes for metals contained in minerals.
The sample selection, representivity, sample size, cost and test methodologies under well controlled conditions are discussed hereafter including typical tests included in any programme.
Aspects of test programmes ranging from sighter tests through to full feasibility development programmes are discussed.
The development of the comminution, extraction and variability Testplans is a critical step in developing a flowsheet, predicting metal recoveries and for cash flow predictions. The progression from bench scale to pilot scale confirms the flowsheet and allows for material and energy balances, equipment selection and plant design.
A well designed metallurgical test programme minimises process risks associated with commercial development and provides a level of bankability.
Troy Resources NL acquired a 70% interest in the Mina Sertão gold project in Goias State, Brazil, in 2001 following a successful bid for the highly competitive international tender of a tenement package put out by Western Mining Corporation (WMC).
The Sertão deposit is located on cleared grazing land 380 kms west of Brasilia and is 30% owned by Amazonia Mineracao Ltda, a private Brazilian company. It is a small high-grade open-pittable orebody with a measured and indicated resource of 108,000 tonnes at a grade of 49.7 g/t for 172,500 ounces using a 2.0 g/t cut off.
Troy undertook the project management and development of the project while Amazonia managed the exploration activities and provided other services as required.
The project development involved drilling metallurgical test holes, scouring the world to locate an available and suitable second-hand plant, and arranging shipping to and reconstruction in Brazil.
The contracting strategy used by Troy was unusual in that Troy managed the subcontractors and consultants themselves including the engineering, procurement, construction and commissioning.
Entry into a country where the language and culture was significantly different as well as obtaining the necessary government approvals, including environmental and import permits, were all challenges for the management team. The tropical environment and logistics also had to be contended with.
The plant has some novel aspects including very high gold loadings, a DETOX circuit, and tailings filtration because a conventional tailings dam was not practical.
Lessons were learned and the project has been both profitable and successful for Troy and Amazonia. In addition, the project has created jobs, delivered royalties and brought new skills into an area where previously there was little mining activity.
The Paulsens gold deposit in the Pilbara region of Western Australia was discovered by CRA in 1998. In 2001 St Barbara Mines Limited (SBML) made a successful takeover offer for Taipan Resources and then began an update of the previous Bankable Feasibility Study (BFS) undertaken by Minproc Limited. This paper describes the history of the metallurgical testwork, plant design and initial development to optimise a project with complex metallurgical process characteristics.
The Paulsens ore is preg robbing, has cyanide soluble copper and nickel and is highly sulphidic. The ore is relatively hard and requires a very fine grind size of P80 53 microns. The metallurgical challenges have been met for this complex ore and the process flowsheet include aspects not commonly associated with a typical gold plant. The latest study changed the mining plan, utilised a second hand plant and improved the robustness of the project economics.