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MEI Online: Commodities: Metallic Ores: Zinc: Latest News: August 23rd 2005


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:: Mintek Launches Zinc Bioleaching Project

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.




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