- Bacterial oxidation
Bacterial oxidation (BIOX) is a biohydrometallurgical process developed for pre-
cyanidation treatment ofrefractory gold ores or concentrates. Thebacterial culture is a mixed culture of "Thiobacillus ferrooxidans ", "Thiobacillus thiooxidans " and "Leptospirillum ferrooxidans ". The bacterialoxidation process comprises contacting refractorysulfide ROM 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 viacyanidation .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 veryacidic environment (pH 1.0 to 2.0), atemperature of between 30 and 45 °C, and a steady supply ofoxygen andcarbon dioxide for optimum growth and activity. The unusual operating conditions for the bacteria are not favourable for the growth of most othermicrobes , thus eliminating the need for sterility during the bacterialoxidation process. Because 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 sulfide minerals producesiron(III) sulfate andsulfuric acid , and in the case ofarsenopyrite ,arsenic acid is also produced. The arsenic is removed from the liquor bycoprecipitation with the iron and sulfate in a two stageneutralisation process. This produces a solid neutralisationprecipitate containing largelycalcium sulfate , basiciron(III) arsenate andiron(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.ee also
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Economic geology
*Geomicrobiology External links
* [http://wiki.biomine.skelleftea.se/wiki/index.php/Biooxidation Biooxidation, BioMineWiki]
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