Temperature

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Temperature and bioleaching

Temperature affects leaching kinetics. In cold environments, temperature becomes a limiting factor during heap leaching. Primary copper sulfides (for example chalcopyrite) do not leach well except at elevated temperatures.

Commercial biooxidation started with using mesophiles to oxidise refractory gold ores (BIOX process). But at the high temperatures required for efficient bioleaching of sulfide minerals such as chalcopyrite, mesophiles won't thrive. Biological leaching is limited to the temperature limits of microorganisms that are capable of oxidizing metal sulfides or oxidizing ferrous to ferric iron. Therefore thermophiles are considered as a means to improve the mineral sulfide oxidation rates, and to reduce the costs associated with the provision of cooling for this exothermic process. The major focus of research and development is heap leaching of chalcopyrite by thermophiles. [1]

Some examples of microorganisms capable of oxidizing ferrous, metal sulfides, and elemental sulfur in environments above 60° C. include: Acidianus brierleyi, Acidianus infernus, Metallosphaera sedula, Sulfolobus acidocaldarius, Sulfolobus BC, and Sulfolobus metallicus. However, there are also other extreme thermophiles that can grow and leach metal sulfides at temperatures above about 60° C. Thermophilic organisms, which grow at temperatures higher than 60° C., achieve much greater rates of mineral dissolution when compared with moderate thermophiles, which grow in the range of 40-60° C., and mesophiles, which grow in the temperature range of 10-40° C.

However, the high temperature required for rapid leaching of chalcopyrite, as well as other hypogenic copper sulfides, increases the mass transfer limitations of oxygen and carbon dioxide in the system. This in turn has placed severe limitations on the pulp density that can be used in stirred tank processes due to the high oxygen requirements of the thermophiles and the oxidation reaction occurring on the surface of the chalcopyrite during leaching.

[2]


Psychrotolerant acidophiles may be useful in order to pre-warm a heap.

References

  1. M.E. Clark, J.D. Batty, C.B. van Buuren, D.W. Dew and M.A. Eamon, Biotechnology in minerals processing: Technological breakthroughs creating value, Hydrometallurgy, Vol.83 No.1-4, 2006
  2. http://www.freepatentsonline.com/US20070264703.html
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