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:: Mintek Launches Major Bioleach R&D Projects
Mintek, in association with partners from industry and other research organisations, has embarked on two major consortium-based bioleaching R&D programmes.
The first programme is aimed at extending existing tank-bioleaching technology, which has already been commercialised for refractory gold and demonstrated for copper sulphides, to the processing of zinc concentrates. The second involves the development of an improved inoculation technique for bio-assisted heap leaching operations processing copper sulphides.
The two programmes, which together are worth R9 million over two years, are being funded by the Biotechnology Partnership and Development (BioPAD) initiative.
Zinc concentrates are conventionally treated by the roast-leach-electrowinning (RLE) process. Many plants have excess electrowinning capacity, and the successful development of a bioleaching route would enable existing facilities to expand their output without installing additional roasters. A further advantage would be the ability to accept a broader range of concentrates, including those unsuitable for roasting - for example, those with high copper levels.
Mintek's research partners in this programme are the Department of Chemical Engineering at the University of Cape Town, which is providing kinetic and mechanistic data, and the CSIR's Food, Biological and Chemical Technologies (Bio/Chemtek) unit, which is investigating bacterial sulphur metabolism.
Provided that a bacterial culture with a sufficiently high tolerance to zinc can be developed, leaching can proceed to a high concentration, and zinc electrowon directly from the leachate. Mintek has already developed a method for electrowinning zinc from relatively low-grade bioleach solutions.
Alternatively, a low-zinc solution could be produced and upgraded by a solvent extraction step prior to electrowinning. It will be important to limit the extent of sulphur oxidation to S0 instead of S042- in both scenarios, since this will greatly reduce the requirements for aeration and acid neutralisation - which are the two major operating costs in bioleaching.
The second R&D programme will focus on a unique and effective inoculation technology that is aimed at shortening start-up times, leading to faster copper extraction and increased recoveries. This will substantially improve the economic performance of copper sulphide heap-bioleaching operations.
There are currently nine heap-leach operations world-wide processing copper sulphide ores, with an annual production of US$1.3 billion worth of copper metal, and this figure is set to rise to more than US$2 billion within a few years. Heap leaching has a potential cost advantage of at least 10-15 US cents per pound of copper - around 10 per cent of the current copper price - compared with the conventional process.
In sulphide heap leaching, the reaction is catalysed by iron- and sulphur-oxidising bacteria that have to be specifically introduced into the heap. However, with current practice, it is extremely difficult to obtain an adequate bacterial population, and this has resulted in start-up problems and below-optimum performance at most sulphide operations. As a result, the anticipated cost improvements have not been fully realised.
The work will be conducted in partnership with Mineral Energetics, a private South African company that was established in 2002 to develop and commercialise new technologies in the mining and related fields. Mineral Energetics has rights to the patent upon which the proposed technology is based, and Mintek's Biotechnology Division will act as the technology development partner. Both organisations will contribute to the commercialisation of the technology.
The consortium has a separate co-operation agreement with a major international resources company, which will provide a site for field testing the technology.
Biotechnology Partnership and Development (BioPAD) is a regional innovation centre established under the auspices of the Department of Science and Technology and its National Biotechnology Strategy, with the aim of establishing a sustainable biotechnology industry in South Africa, BioPAD funds a portfolio of multi-institutional projects, focusing on agricultural, industrial, mining and environmental applications for biotechnology - areas that are strategically important for South Africa and for the region. Apart from the granting function, SioPAD also seeks to strengthen the links between innovators, entrepreneurs and incubators, with the aim of obtaining the right mix of technical and business expertise so that research outcomes an be rapidly commercialised.
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