Microbially-assisted dissolution of minerals and its use in the mining industry
D. E. Rawlings
Department of Microbiology, University of Stellenbosch,
Private Bag X1,
Stellenbosch 7602, South Africa
Abstract: Biomining is currently used successfully for the commercial-scale
recovery of metals such as copper, cobalt, and gold from their ores.
The mechanism of metal extraction is mainly chemistry-driven and is
due to the action of a combination of ferric and hydrogen ions, depending
on the type of mineral. These ions are produced by the activity of chemolithotrophic
microorganisms that use either iron or sulfur as their energy source
and grow in highly acidic conditions. Therefore, metal extraction is
a combination of chemistry and microbiology. The mixture of organisms
present may vary between processes and is highly dependent on the temperature
at which mineral oxidation takes place. In general, relatively low-efficiency
dump and heap irrigation processes are used for base metal recovery,
while the biooxidation of difficult-to-treat gold-bearing arsenopyrite
concentrates is carried out in highly aerated stirred-tank reactors.
Bioleaching reactions, the debate as to whether the
reactions are direct or indirect, the role of microorganisms, and the
types of processes by which metals are extracted from their ores are
described. In addition, some new processes under development and the
challenges that they present are discussed.
*Plenary lectures presented at the Inaugural Conference for the Southern and Eastern Africa Network of Analytical Chemists (SEANAC), Gaborone, Botswana, 7-10 July 2003. Other presentations are published in this issue, pp. 697-888.
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