THE LEADER VOLUME 17 • NUMBER 7
Ingenious extraction
Editorial Director Paul Moore BSc ( Hons ), MSc Email : paul @ im-mining . com
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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 .
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 .
Clean & Recover , led by CEO Luke Berry , looks to replace the electrowinning stage with electrodialysis using an Electrochemical Reactor ( ECR ). Overall , the ECR technology demonstrated success in the full recovery and separation of copper and cobalt hydroxides from leach solutions ; further testing & process improvements are proposed .
The Curtin University and Mining & Process Solutions ( MPS ) team have developed leaching processes using glycine , an amino acid . Four specific processes were tested : Oxidation ( sulphur removal ), GlyAmm ( copper removal ), GlyCat ( gold and silver removal ) and GlyLeach ( cobalt removal ). Further testing is suggested for the four processes to optimise the extractive abilities & demonstrate them at a larger , continuous scale . From MPS , Ivor Bryan is the Managing Director and from Curtin , Professor Jacques Eksteen is the co-inventor of the tech .
A team from tfgMM Strategic Consulting & TP McNulty & Associates including Krishna Parameswaran , Terry McNulty & David Robertson proposed & tested roasting & water leaching with sulphate electrowinning . 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 .
DCS Technical Ltd led by Founder Dave Sammut has a concentrate treatment system based on halide leaching . It designed & tested a prototype EW cell that took a novel approach to production and handling of the crystalline dendritic ‘ tree ’ structure characteristic of halide copper electrowinning . 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 .
Ray Shaw is the Director of Minetometal , researching the use of alkaline chloride-based leaching chemistry . Results confirmed the process is technically viable , as demonstrated by the production of copper oxide crystals ready for reduction . 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 producing sulphuric acid and / or elemental sulphur . The next steps are to investigate metal purity , cobalt recovery , and leach residue cyanidation for gold extraction .
Wenying Liu is an Associate Professor at The University of British Columbia looking at the use of acidic ferric chloride media and thiocyanate as opposed to sulphate in the copper-gold concentrate leaching process . Reactor tests showed very high copper extraction ( over 98 %). Gold extraction exceeded 90 % in the presence of thiocyanate . 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 .
Finally , BIOX , now owned by Metso Outotec , refers to a concentrate leaching process that utilises bacteria , followed by solvent extraction and electrowinning to produce copper cathode from copper concentrate . Joe Seppelt is the BIOX team lead within OZ Minerals . Small scale experimentation has confirmed that very high extractions are possible . Current work is focused on replicating these experiments in a larger pilot plant to support a feasibility study .
Paul Moore Editorial Director paul @ im-mining
JULY 2022 | International Mining 3