OZ Minerals recently set out to contribute to the acceleration of responsible metal production by the copper industry through the Ingenious Extraction innovator challenge, the outcomes of which have just been published. The in-depth document explores potential extraction methods and technologies, specifically utilising concentrate leaching techniques that can perform economically at scale. It also outlines the next steps that will be taken based on the momentum created through the challenge and how this supports OZ Minerals in the achievement of producing clean, value–adding products in a transparent manner.
The miner states: “Copper is an essential ingredient in the transition to a low carbon future. Electric vehicles will replace combustion vehicles, with the average EV containing 83 kg of copper. Renewable energy solutions including solar and wind will replace coal and gas, with a standard wind turbine containing up to 4.7 t of copper. Copper is the best non–precious conductor of electricity and heat and will therefore play an essential role in the transition to green technologies…it is widely accepted that the average ore grades in copper mines are steadily reducing. As the ore grades have dropped, mines have become larger in order to maintain profitability, creating greater pressure on energy, water and land use resources. The mining industry will need to respond to the challenge of creating a sustainable supply of responsibly produced raw materials against this backdrop of falling ore grades.”
It adds: “With this global context in mind, OZ Minerals has aspirations to produce clean, value adding products in partnership with our customers in a transparent manner, to emit zero scope 1 emissions and strive to systematically reduce scope 2 and 3 emissions. OZ Minerals is also striving to minimising water use and consume and produce in a way that generates net zero waste. These aspirations are the key drivers of the Ingenious Extraction challenge.”
Some 260 participants from 40 countries took part in this challenge through the incubator, creating long–lasting and valuable industry networks. From this group, Think & Act Differently selected seven teams as finalists. Each team proposed new and innovative extraction systems with potential for economic recovery of metals from copper concentrate. Various experiments were funded to validate the performance of these processes. OZ Minerals will continue development of a number of promising technologies. The BIOX technology, now part of Metso Outotec, which uses bacteria to leach copper and cobalt minerals, is currently undergoing pilot testing and will soon be the subject of a feasibility study. A ferric chloride system is being tested further, with the intention of moving to pilot testing and prefeasibility later in 2022. Thiocyanate and GlyCat systems for gold recovery are also being tested further and will be incorporated into future pilot programs.
For a typical commercial concentrate leach and electrowinning process, the majority of costs come from reagents (~30% operating expense (OPEX)), power (~30% OPEX) and electrowinning cells (~25% capital expense (CAPEX)). The costs for power for on–site leaching treatment is high, with electrowinning of copper using approximately 8 times the power of the competing electrorefining process (used in conjunction with smelting), in addition to labour costs and project execution. The costs for reagents can include oxygen supply for leaching and lime or limestone for neutralisation of acid and precipitation of iron. In addition, costs for cyanide for gold recovery can be significant and is exacerbated by the need for cyanide destruction prior to residue disposal. Finally, conventional electrowinning of copper operates at low current density, thereby requiring a large number of electrowinning cells, resulting in high capital costs.
As such, the high costs of reagents, power and electrowinning cells are a key barrier to the commercial adoption of concentrate extraction systems for OZ Minerals. As such, the primary focus of the challenge was to identify new processes that could demonstrate a material reduction in these costs, while maintaining metal recovery rates equivalent to the incumbent systems.
Looking at the background of the seven finalists and their work with OZ Minerals in more detail:
Clean&Recover – replace electrowinning stage with electrodialysis
Clean&Recover, led by CEO Luke Berry, has a mission to capture value from mining waste streams and clean the treated output to a high standard. Their product offerings centre around cleaning solids from waste water and treatment of acid mine drainage. This opportunity aims to investigate electrodialysis as a method for direct metal separation and recovery from acidic solutions by formation of metal hydroxide precipitates. Electrodialysis is the process by which metal ions present in a feed solution are precipitated from solution using electricity, rather than chemicals. Clean&Recover designed an experiment to determine if copper and cobalt could be selectively separated and recovered from an acidic solution based on the different pH’s at which they typically precipitate from solution. The experimentation consisted of precipitating two synthetic leach solutions: a copper solution and a mixed copper/cobalt solution. To test the precipitation of copper, an artificial copper sulphate solution was run through the Electrochemical Reactor (ECR). The copper was fully recovered from the acid solution by increasing the pH to 6.6. Separation of copper and cobalt precipitates was tested using a mixed copper/cobalt solution. Based on experiment results, 99% of copper and 9% of cobalt coprecipitated at pH 5.9, while the remaining 91% of cobalt in the solution precipitated by increasing the pH to 9.5. The main barrier to Clean&Recover’s ECR technology was developing the ECR further to reduce the energy required to raise sufficiently the pH of the solution. Overall, the ECR technology demonstrated success in the full recovery and separation of copper and cobalt hydroxides from leach solutions. Testing was conducted at Clean&Recover’s pilot plant. Further testing and process improvements are proposed to improve the energy efficiency of the process. Improvements are available in areas including optimising the cathode, anode, membrane, flow turbulence, power supply, configuration of cells in series, cell residence time, flowrate and process kinetics.
MPS & Curtin University – glycine leaching and sulphate electrowinning
The Curtin University and Mining and Process Solutions (MPS) teams have been commercial partners since 2014. Curtin University has extensive research facilities at their Bentley and Kalgoorlie campus, while MPS is an independent company that operates a development laboratory in Perth with a principal focus of commercialising glycine based leaching systems. From MPS, Ivor Bryan is the Managing Director and from Curtin University, Professor Jacques Eksteen is the co–inventor of the glycine leaching technology. The Curtin University and MPS team have developed leaching processes using glycine, an amino acid. When used in an alkaline environment, it is selective for base and precious metals including copper, cobalt and gold. This process notably does not take iron and magnesium into solution, which simplifies downstream metal extraction process. This process operates within a low intensity alkaline system in low to modest temperatures, with no exotic materials required and where by–products are non– toxic. The glycine mixture is further not chemically consumed during the process, allowing it to be recycled, contributing to material circularity. The Curtin University team seeks to investigate whether alkaline leach and sulphate electrowinning can achieve a high extraction of copper and select precious metals. MPS and Curtin University performed a detailed mineralogical analysis of the Carrapateena concentrate followed by a large number of extraction tests. Extraction of the value metals was performed on the as–received concentrate and a pre–oxidised concentrate. Copper, gold, iron and sulphur in products were determined using liquid and solid sample analysis. In this experiment, four specific processes were tested: Oxidation (sulphur removal), GlyAmmTM (copper removal), GlyCatTM (gold and silver removal) and GlyLeachTM (cobalt removal). Further testing is suggested for the four processes mentioned above to optimise the extractive abilities of each process and to demonstrate the process at a larger, continuous scale. Process integration of the sub–processes is required and metal recovery from solution and purification needs to be integrated.
DCS Technical – halide leaching and chloride electrowinning
DCS Technical led by Founder Dave Sammut is a boutique consultancy that works with Australian minerals, waste recycling and general scientific industries. Hydrometallurgy consulting is one of their core services with specific application to the minerals and waste sectors. DCS Technical’s concentrate treatment system is based on halide leaching, a promising alternative to conventional sulphate–based practices. Halide leaching offers significant economic benefits in CAPEX and OPEX cost savings due to reductions in the plant size required for atmospheric leaching and energy usage for electrowinning, along with the use of inexpensive reagents. This technology is able to minimise the environmental impact of copper concentrate processing. Specifically, it operates within a closed loop system where zero liquid wastes and gases are emitted and avoids the use of toxic reagents and produces environmentally stable solid residues. This is not a new technology. It has been in development for over 30 years and is close to commercialisation. A$50 million have been invested in chloride–based hydrometallurgical extraction technology by Australian companies Dextec Ltd and Intec Ltd. In 1998 to 2000 and 2003, pilot and demonstration scale plants (~1 t per day) were operated. However, issues arising from the removal of crystalline copper dendrites during the electrowinning stage have prevented the technology from progressing further. The Intec Process electrowinning (EW) cell required substantive modifications, maintenance and repairs. This was attributable to the complicated cell design, which included vertically arranged sawtooth cathodes and a bulky wiper mechanism. DCS Technical’s halide electrowinning technology aims to reconfigure the halide leaching EW cell and prove commercial feasibility. DCS Technical designed and tested a prototype EW cell to determine if it could improve the previous Intec Process design and continuously recover copper metal directly from cuprous halide electrolyte. The prototype EW cell took a novel approach to the production and handling of the crystalline dendritic ‘tree’ structure that is characteristic of halide copper electrowinning. This new prototype performed strongly under testing, and demonstrated its potential to reduce operational costs, maintenance and handling. Overall, the results suggest that the combination of halide extractive metallurgy and the DCS Technical EW cell system offer the possibility of direct copper recovery on site at recovery levels at or above those of commercial smelting processes. To validate long term performance of DCS Technical’s EW cell and conversion rates, a pilot scale operation should be conducted for 6–12 months of continuous operation.
tfgMM Strategic Consulting & TP McNulty & Associates – roast & water leaching and sulphate electrowinning
This team comprises three experienced metallurgists with a dream of resurrecting and modernising an old commercial process for leaching roaster “calcine” for the recovery of copper, cobalt, gold and silver. Krishna Parameswaran has a doctorate in metallurgy from the Pennsylvania State University and has over 30 years’ experience at ASARCO LLC. He is now President of tfgMM Strategic Consulting. Terry McNulty has a Doctorate in Metallurgical Engineering from Colorado School of Mines. Terry has over 25 years in various research, operating and management positions at The Anaconda Company, Kerr–McGee Chemical, and Hazen Research. Over 30 years ago, he founded TP McNulty and Associates, a global consulting firm. David Robertson has a doctorate in Metallurgical Engineering from the University of New South Wales. He taught at Imperial College in London and later at the University of Missouri at Rolla where he was also Director for Center of Pyrometallurgy. Their proposed process entails the selective roasting of copper concentrates to convert copper and cobalt to their water soluble forms (sulphates and oxy–sulfates), which then undergo solvent extraction and conventional sulphate electrowinning to recover copper. Cobalt is precipitated as a commercial product. A fluidised bed roasting test was completed to produce a calcine containing copper sulphate, copper oxide, copper oxy–sulphate and haematite. The leach extractions using pH 1 solution conditions were 97% for copper and 82% for cobalt. The experiment demonstrated adequate copper and cobalt extraction. Further testing and process refining is suggested.
Minetometal – ammonium and ammonium chloride leaching and metal precipitation
Ray Shaw is the Director of Minetometal, a boutique consulting company within the industrial minerals and metals industry. Their primary offerings are targeted towards mineral processing, copper and zinc hydrometallurgy, and smelting processes. This opportunity relates to the use of alkaline chloride-based leaching chemistry for copper concentrates. Numerous acid sulphate processes have been developed but are not commonly used for concentrates at a commercial scale. Alternative chemical reactions can be applied at each of the three key stages to achieve the same outcome at lower economic and environmental cost. Firstly, ammonia–ammonium chloride leaching is used instead of sulphate leaching, which offers the benefit of being able to process concentrates from difficult ores. Secondly, crystallisation and thirdly direct hydrogen reduction are replacements for solvent extraction and electrowinning that eliminate the need for an additional neutralisation process whilst minimising carbon dioxide emissions. These chemical reactions have been studied extensively over the past 50 years. However, a single process combining these and applying them to the treatment of copper concentrate has not yet been explored. This has created an opportunity to develop an integrated end–to–end flowsheet. Minetometal has developed a conceptual ammonia–ammonium chloride leaching, crystallisation and direct reduction process and are working to prove its feasibility for niche applications. Minetometal conducted experiments to determine the basic plant design and a preliminary economic study on the potential CAPEX and OPEX reductions. Supporting test work included the investigation of copper solubility, lime roasting, leaching, oxidation and crystallisation. Based on these results, Minetometal firmed up on sections of the flowsheet (MTM Process) that consisted of three stages: leaching, crystallisation and direct reduction. During the leaching stage, Minetometal proposed two options to oxidise copper sulphide: roasting or direct leaching. Roasting exposed the concentrate to temperatures of 680°C prior to leaching with water and ammonia and ammonia–ammonium chloride. Alternatively, direct leaching was completed at 90°C, in which oxygen was injected in the ammonia–ammonium chloride leach. Results confirmed that copper can be selectively extracted under both these conditions. The crystallisation stage involved precipitating copper crystals from the pregnant liquor with hydrolysis to remove any residual chloride. The hydrogen reduction stage is a well–known process, and the program did not extend to carrying out that step. Results confirmed that the Minetometal process is technically viable, as demonstrated by the production of copper oxide crystals ready for reduction and an alkaline residue suitable for gold recovery by cyanidation. The sulphur is dumped in the residue as gypsum, rather than produce sulphuric acid and/or elemental sulphur. These would incur extra CAPEX and face potential issues with purity and marketing. The iron reports as inert haematite. The next steps are to investigate metal purity, cobalt recovery, and leach residue cyanidation for gold extraction.
University of British Columbia – ferric chloride & thiocyanate leaching and sulphate electrowinning
Wenying Liu is an Associate Professor in the Department of Materials Engineering at The University of British Columbia. Since joining the Hydrometallurgy Chair within the Department of Materials Engineering in 2015, Wenying has been undertaking research in developing sustainable hydrometallurgical technologies for extraction of metals from ores and investigating fundamental processes involved in contaminant release from mine wastes. This opportunity relates to the leaching of copper–gold concentrate, specifically the use of acidic ferric chloride media and thiocyanate as opposed to sulphate in the leaching process. In many of the conventional sulphate leaching processes, sulphides undergo oxidation to form sulphate. This produces large amounts of acid and residue. As a result, in the neutralisation stage, lime is required to treat the acid generated by this process. In the residue disposal stage, the gypsum waste by–product needs to be disposed of. Furthermore, gold must then be recovered in the cyanidation stage, which involves the use of cyanide in the leach solution. These stages in the current sulphate leaching process impose significant economic and environmental costs for the treatment of copper–gold concentrates. The University of British Columbia team have proposed a process that eliminates the need for these additional stages, thereby avoiding the associated economic and environmental impact. Specifically, their solution is to replace the traditional acidic sulphate media with acidic ferric chloride and use thiocyanate to extract gold. This is intended to enable the leaching of copper–gold concentrates under acidic conditions. The use of acidic chloride reduces freshwater consumption as saline water can be used, and minimises mine water discharge. The use of chloride based leaching for copper and thiocyanate for gold recovery has three benefits: eliminating the residue disposal stage as gypsum is no longer created as a waste by–product, eliminating the neutralisation stage by avoiding the use of lime and the associated carbon dioxide emitted in its production. Lastly, eliminating the cyanidation stage as cyanide is no longer required to extract gold. While there are numerous benefits, the use of acidic ferric chloride and thiocyanate to leach copper–gold concentrate is still in development and requires extensive testing. The UBC team conducted an experiment to confirm proof of concept, with the aim to show high copper and gold extraction with negligible sulphur oxidation. To test this, the team conducted numerous reactor leaching tests to study the effect of key process variables on copper and gold extraction efficiency. The outcomes of these tests show very high copper extraction (over 98%). Gold extraction exceeded 90% in the presence of thiocyanate. The elemental sulphur yield exceeded 93% confirming low sulphate generation rates. Further testing is required with the next phase of work
being scoped. This includes further investigations to test the oxidation of ferrous to ferric by air to oxygen–enriched air, gold extraction on activated carbon and solvent extraction of copper.
BIOX – bacteria leaching and sulphate electrowinning
BIOX refers to a concentrate leaching process that utilises bacteria, followed by solvent extraction and electrowinning to produce copper cathode from copper concentrate, in addition to gold/silver doré and cobalt. This technology is owned by Metso Outotec and has been in commercial operation for over 30 years, with 13 successful plants commissioned globally. BIOX has been utilised in multiple plants and has proven to produce copper cathode, cobalt and nickel, depending on the concentrate and treatment conditions. Joe Seppelt is the BIOX team lead and is an Operations Manager within OZ Minerals. This opportunity relates to the leaching of copper concentrate to produce copper cathode utilising bacteria, then solvent extraction and electrowinning. The BIOX technology uses a 2–stage atmospheric tank leach utilising medium temperature mesophile and high–temperature thermophile cultures that extract copper and other metals into solution. Nutrients, acid liquor and air are added to assist the reaction. The leached solids are washed, thickened and neutralised. The solids go into a cyanide leach circuit for gold and silver recovery. Next, acidic liquor is clarified and goes into a 2–stage copper solvent extraction process to produce a strong electrolyte for copper recovery in the electrowinning stage. Overall, this process produces copper cathode, gold/silver doré and cobalt precipitate. The BIOX technology has been used in commercial applications (particularly for gold) for over 30 years and has been utilised in 13 plants, including the world’s first commercial bioleaching plant to treat nickel sulphide concentrate in Finland (2015). However, critical areas need to be investigated to determine its suitability in commercial application at an existing site. These factors include economic viability (both CAPEX, OPEX and potential trade–offs), operational resilience (including risk management) and any potential impacts of site–specific conditions. In addition, bacteria require careful temperature control and may be impacted by power outages. Both are risks that will require careful engineering and operational controls to ensure successful implementation. OZ Minerals has been investigating BIOX concentrate leaching since 2019. Test work for continuous leaching is almost complete, as is the solvent extraction and electrowinning testing with 3 cathodes produced and currently being sampled. Development of additional scope is ongoing (eg gold and silver leaching). Small scale experimentation has confirmed that very high copper, cobalt, gold and silver extractions are possible. Current work is focused on replicating these small scale experiments in a larger pilot plant in order to generate engineering data to support a feasibility study. On completion of the pilot plant campaign it is expected that a feasibility study will be undertaken to confirm the capital and operating cost for a commercial scale plant.