Bacterial Oxidation

The use of the bacteia Thiobacillus ferrooxidans is very well known in the lixiviation of sulphurs of copper since, at least, forty five years ago. Nonetheless, its application to refractory minerals of gold is very recent.publications of works performed in the United States, Canada, South Africa and the former Soviet Union exist, some of which compare costs and benefits of the different alternatives existent, recommending the bacterial oxidation as the most adequate from the technical-economical point of view.

The lixiviation is performed in agitated reactors with the addition of air, nutrients and CO2 to the temperature of 30°C to 40°C, one concentration of solids between 15% to 20%, and a time of residence which varies between one and six days. For the type of attack which it produces it is possible to recuperate an 85% of the gold with an oxidation of only the 60%. In the case of a pilot plant of the Equity Silver Mines, the recuperation increased from 10% to 70-75%. The only disadvantage is the low velocity of reaction. It is known of three plants which use this alternative in the world. One in South Africa (Fairview Mine), another in Zimbabwe, and the third in Snow Lake, Canada.

In Cimm,comparissons have been performed between the different alternatives available and arep resently working, in conjunction with El Indio, in the evaluation of the bacterial oxidation of refractory re-washings through tests in collumns.