Bacterial oxidation

Bacterial oxidation is a bio-hydrometallurgical process developed for pre-cyanidationtreatment of refractorygoldoresor concentrates. The bacterial cultureis a mixed culture of Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirillum ferrooxidans. The bacterial oxidationprocess comprises contacting refractory sulfideROM ore or concentrate with a strain of the bacterial culture for a suitable treatment period under an optimum operating environment. The bacteria oxidise the sulfide minerals, thus liberating the occluded gold for subsequent recovery via cyanidation.

Under controlled continuous plant conditions, the number of bacterial cells and their activity is optimised to attain the highest rate of sulfide oxidation. The bacteria require a very acidic environment(pH1.0 to 2.0), a temperatureof between 30 and 45 °C, and a steady supply of oxygenand carbon dioxidefor optimum growth and activity. The unusual operating conditions for the bacteria are not favourable for the growth of most other microbes, thus eliminating the need for sterility during the bacterial oxidationprocess. Due to the fact that organic substances are toxic to the bacteria, they are non-pathogenic and incapable of causing disease. The bacteria employed in the process do not, therefore, pose a health risk to humans or any animals.

The bacterial oxidation of iron sulfidemineralsproduces iron(III) sulfateand sulfuric acid, and in the case of arsenopyrite, arsenic acidis also produced. The arsenic is removed from the liquor by co-precipitation with the iron and sulfate in a two stage neutralisationprocess. This produces a solid neutralisation precipitatecontaining largely calcium sulfate, basic iron(III) arsenateand iron(III) hydroxide. The iron(III) arsenate is sufficiently insoluble and stable to allow the neutralisation product to be safely disposed of on a slimes dam. The neutralisation liquor, purified to contain an acceptable level of arsenic, can be re-used in the milling, flotation or bacterial oxidation circuits.

See also

• Economic geology
• Geomicrobiology

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It uses material from the http://en.wikipedia.org/wiki/Bacterial+oxidation Wikipedia article Bacterial oxidation.