The effect of growth medium of Thiobacillus ferroxidans on pyrite flotation

The bacterium, Thiobacillus ferrooxidans, has been used for the depression of pyrite during the flotation separation of coal particles from associated minerals. However, the utilization of T. ferrooxidans as a regulator in the differential flotation of sulfide minerals is yet to be established. The conventional reagent used for pyrite depression is cyanide which is toxic and in many cases nonselective. The objective of the present investigation is to determine if T. ferrooxidans can be used for the selective depression of pyrite. In view of this objective T. ferrooxidans was grown in a variety of culture media to render bacteria with different surface properties such as contact angle and zeta potential. The passivity of pyrite surface due to sulfur coating, which is formed by the oxidation of the mineral, was examined using AC Impedance Spectroscopy. The influence of bacterial surface properties on adhesion and subsequent hydrophilic/hydrophobic balance of the pyrite mineral surface with regard to flotation recovery was examined. The flotation response of pyrite was interpreted in terms of surface modifications induced by the adsorption of bacteria.