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Australasian Biotechnology, Vol. 11 No. 6, 2001, pp. 30-31 BIOTECHNOLOGY IN THE MINING INDUSTRY Straits Resources Limited And The Industrial Practice Of Copper Bioleaching In Heaps David John Readett Group Processing Manager, Straits Resources Limited, PO Box 1641, West Perth, WA 6872, Australia Code Number: au01072 Abstract The bioleaching of copper has been undertaken for centuries. However it has only been in the last 10 years that the technology has developed to a stage where it now contributes to a significant proportion of the world’s copper production. Straits Resources Limited managed the Girilambone Copper Operation - the world’s first stand-alone copper-mine heap-bioleach solvent-extraction-electrowinning (SX-EW) operation, and now also owns and operates the Nifty Copper Operation. Through the GCC operation the technique of heap-bioleach aeration was developed and is now being used by all major heap-bioleach operations around the world. Straits is continuing to develop its bioleach technology and next year is set to continue its ambitious R&D program to further develop the bioleaching of both chalcocite and chalcopyrite, and investigation of ecosystem rehabilitation in relation to mine closure. Copper Bioleaching History The industrial scale bioleaching of copper in heaps has had a chequered 400 year career. Over the past 20 years this technology has blossomed with annualised world copper production from the process increasing from 0.2% to approximately 8-10%. Bioleaching of copper in heaps was first recorded at the Rio Tinto mine in 17th century. The first modern industrialscale copper heap bioleach, producing 14,000tpa, commenced in 1980 at Lo Aguirre in Chile. The first stand-alone mine using copper bioleaching - solvent extraction - electrowinning was the Girilambone Copper Operation (managed by Straits Resources and commissioned 1993) in central NSW, Australia. Now of a total annualised world copper production of approximately 14 Mtpa, some 4-7% is realised by some form of bioleaching. The Process of Copper Bioleaching Copper heap bioleaching utilises naturally occurring mesophiles. The basic principles involve crushing of secondary copper sulphide (chalcocite) bearing ore to predetermined size distribution. Following crushing the ore is agglomerated with sulphuric acid and leach. The agglomerated ore is then ‘stacked’ to a height of 6-10m onto leach pads. A low-pressure aeration system is utilised to supply air at the base of the heap for the duration of the leaching cycle. The ore is allowed to cure for 1-6 weeks and then leached for 400 to 600 days with acidic leach liquor. Over this leaching period some 75 to 95% of the secondary copper sulphide minerals are leached. Further research is being targeted at increasing the chalcocite leaching rates utilising both mesophiles and thermophiles. The current technical hurdle being the control and manipulation of the temperature in an industrial-scale heap leach system. Straits Resources is currently pursuing START Grant funding for this element of their ongoing R&D effort. Straits Resources Limited Straits Resources Limited is Australia’s premier exponent of biotechnology in the mining Industry and currently operates two Copper Heap SX-EW operations in Australia with a total copper production capacity of 43,000 tpa. Under Straits management the Girilambone Copper Mine became the world’s first stand-alone mine biotechnology heap-leach - solvent extraction - electrowinning operation. A significant Research and Development program was undertaken as part of this operation to further the understanding and industrial application of biotechnology in the recovery of copper from secondary (chalcocite and covellite) and primary sulphide (chalcopyrite) minerals. The R&D conducted resulted in the discovery and development of aeration to allow for leach heaps to operate as bioreactors. This was a world first and was recognised by the AusIMM winning the Mineral Industry Operating Technique Award for ‘Forced aeration and heap management strategies for the leaching of secondary sulphide ores’. This technique has now been utilised by several other mining companies in Australia and around the world. (Note - a recent visit to Chile revealed that all of the major copper producers using bioleaching of copper were utilising the aeration technique developed at GCC.) Other significant developments include a ‘remining’ strategy to improve copper recovery from under-performing heaps, a two-stage leaching system and successfully implemented a novel ‘reverse’ two-stage leach. Research is ongoing at GCC on the potential for heap bioleaching of chalcopyrite applying the operational parameters for successful chalcocite leaching. To date, five chalcopyrite test heaps have been leached. The first test heap has achieved over 60% total copper recovery in 600 days with the best performing second generation heap achieving +40% total copper recovery in under 200 days. To date these heaps have delivered the recoverable copper in solution which has been processed successfully via SX-EW to produce cathode copper. Based on the company’s intellectual property, Straits Resources was able to purchase the Nifty Copper Operation (a mine heap-leach SX-EW operation) from WMC in 1998. Since then the operation has been expanded by 50% and the Life of Mine plan now extends out 9 years. Bioleaching trials have commenced at Nifty on chalcocite ore and initial results are favourable. As mentioned previously a significant R&D effort is being undertaken to further develop the bioleaching of the chalcocite ore and Federal Government START Grant funding is being sought. Straits Resources has also undertaken considerable R&D focusing on the downstream solvent extraction and electrowinning processes to ensure compatibility with the heap bioleach system. They have been instrumental in the co-development of both ‘in-settler’ coalescing systems, loaded organic coalescer systems (both now utilised by a number of Australian and international operations), semiautomated cathode flexing system and novel SX circuit configurations. Straits has also developed a significant understanding of the impact of bioleach on SX crud generation and transfer and control of impurity elements (iron, chloride and manganese). The final area of research and development undertaken by Straits has been the investigation of ecosystem rehabilitation in relation to mine closure. Significant resources are being expended on long-term testing of rehabilitation options for mining and heap-leach operations. Trial rehabilitation heaps has been undertaken and investigations into the adaptation of techniques utilised in USA. ANSTO have assisted also in development of suitable monitoring techniques. Nifty Copper Operation - Electrowinning. Copyright 2001 - AusBiotech The following images related to this document are available:Photo images[au01072f5.jpg] [au01072f2.jpg] [au01072f1.jpg] [au01072f3.jpg] [au01072f4.jpg] |
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