Industrial practice and the biology of leaching of metals from ores The 1997 Pan Labs Lecture |
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Authors: | D E Rawlings |
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Institution: | (1) Department of Microbiology, University of Cape Town, Rondebosch, 7700, South Africa, ZM |
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Abstract: | Biomining processes have been used successfully on a commercial scale for the recovery of metals, the most important of which
are copper, uranium and gold. These processes are based on the activity of chemoautolithotrophic bacteria which are able to
use either iron or sulfur as their energy source and which grow in highly acid conditions. In general, low-rate dump and heap
leaching processes are used for copper recovery while the biooxidation of difficult-to-treat gold-bearing arsenopyrite ores
is carried out commercially in highly aerated stirred tank reactors. Because of the high levels of bacterial activity required,
limitations in the growth rate of the microorganisms which were not apparent in low-rate processes have become an important
factor. A key to the commercialization of the gold-bearing arsenopyrite biooxidation process was the development of a rapidly-growing,
arsenic-resistant bacterial consortium. The empirical technique of mutation and selection in a continuous-flow system was
used to improve the ability of the bacteria to decompose the ore. This approach resulted in a dramatic initial enhancement
in growth rate but a plateau in improvement of performance has been reached. Further advances will require a more direct approach
based on an understanding of the underlying physiological mechanisms and an application of the tools of molecular biology.
Considerable advances have been made in our understanding of the molecular biology of Thiobacillus ferrooxidans. However much less is known about the other biomining bacteria. Recent studies using 16S rRNA analysis techniques have indicated
that T. ferrooxidans may play a smaller role in continuous flow stirred tank biomining processes than was previously thought.
Received 20 November 1997/ Accepted in revised form 2 March 1998 |
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Keywords: | : biomining bioleaching biooxidation ore decomposition Thiobacillus Leptospirillum |
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