Extraction Using Bacteria The Basic Principles

Metal Extraction Using Bacteria The Basic Principles 

The bacteria utilized in metal-extraction processes are classified as autotrophic that is, they grow in the absence of organic materials, 

These bacterial reactions have been used commercially in the following three ways to extract metals from ores or concentrates  

The metal is extracted from the ore by the solubilizing action of the acid produced during bacterial growth. At the same time, insoluble metal sulfides are oxidized to soluble metal sulfates, either directly by the bacteria or indirectly by the action of the Fe(III) produced by bacterial oxidation of pyrite. Low-grade ores that cannot be economically extracted by conventional processes can be treated by this method, as described in Section IV. This process, which is usually described as bacterial leaching, has been carried out on an enormous scale for the extraction of copper. 

A more recent development involves the use of chemolithotrophic bacteria to solubilize sulfidic material which interferes with the normal chemical extraction process for a particular metal. A striking example is that of gold in refractory sulfidic ores, such as pyrite or arse-nopyrite, where gold recovery on cyanidation may be as low as 10-15% of the total gold present. Bacterial pretreatment of the concentrate to oxidize and solubilize the sulfide leads to enhanced recoveries of gold on cyanidation, often close to 100% of the total (Section V). 

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II, Metal Extraction Using Bacteria The Basic Principles... 

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