Commercial Processes of Metal Recovery,Heap Reactor Technology,Stirred Tank Reactor Technology,Ammonia,Oxidation of Sulphides,Ferrooxidans

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Home >> Industrial and Microbial Biotechnology >> Microbes and Microbial Genomics for Industry >> Commercial Processes for Metal Recovery

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Commercial processes for metal recovery.
Following two technologies are available for microbe mediated mineral degradation for metal recovery:

(a) Heap-reactor technology. In this technology, low grade ore is piled up in a heap, which is sprayed with a leaching solution containing Fe³⁺,(SO₄)^2- and At. ferooxidans (the sulphates provide an acidic medium for the growth and activity of the microbe, and Fe³⁺ brings about oxidation of sulphides). The leach solution containing the soluble metal sulphates (produced due to Fe³⁺, involving microbial activity) is drained and sent for metal recovery. The remaining leachate flows into an open pond and is used again for spraying the heap, after getting recharged due to oxidation of Fe²⁺, into Fe³⁺ and sulphide into sulphate.

Mining of copper with bacteria

Different Steps Involved in Mining of Copper with Bacteria

Heap technology has been in operation for years in countries including USA, Peru, Chile, Cyprus, and Australia, and has been mainly used for the treatment of copper ores, although it can also be used for the treatment of gold bearing ores, before recovering gold through cyanidation. Heap reactors are cheaper and suitable for treatment of lower grade ores, but are less efficient (also more difficult to inoculate, and inadequately aerated), so that the process takes months rather than days.

(b) Stirred-tank reactor technology. In this technology, a finely ground mineral concentrate/ ore along with the inorganic nutrients (ammonia and phosphate-containing fertilizers) is added to the first tank. The suspension flows through a series of tanks, where mineral decomposition takes place within days rather than in weeks or months needed in heap reactors.

However, stirred reactors need high capital investment and also high running cost (since it requires a low pulp density of ~20%), so that only for high value minerals, its use may be justified. Despite this, many stirred reactors are being used commercially in South Africa, Australia, Ghana, Peru, Uganda and China. Most of these stirred-tank reactors are used for extraction of gold ores, making use of BIOX^® process of GFL/Biomin Technologies, South Africa (GFL = Gold Fields); the only other technologies used are Mintek-Bac Tech technology used in Beaconfield plant in Australia and Laizhou plant in China and the BRGM (Bureau de Recherches Geologiques et Minieres) technology used in Uganda (Kases).

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