Bio-modulation of galena and sphalerite surfaces using Thiobacillus thiooxidans

The interaction of Thiobacillus thiooxidans (T. thiooxidans) with sphalerit e and galena has been investigated through adsorption, electrokinetic, and flotation studies. The amount of T. thiooxidans cells adsorbed onto galena and sphalerite is found to be almost independent of pH. However, a greater amount of cells is adsorbed onto galena compared to sphalerite. The adsorpt ion isotherms of T, thiooxidans onto both galena and sphalerite exhibit Lan gmuirian behaviour. Electrokinetic measurements reveal that the isoelectric points (iep) of galena and sphalerite are located around pH 2, while that of T. thiooxidans is around pH 3. The isoelectric points of the minerals ar e shifted to higher pH values after interaction, consequent to bacterial ce ll attachment. indicating specific adsorption. Additionally, the electropho retic mobilities are found to become less negative as a function of time af ter bacterial interaction. Such a trend is also followed in the case of the cells after interaction with the minerals for different time intervals. On a comparative basis, the cells after interaction with sphalerite are less negative vis-a-vis those after interaction with galena. The flotation recov ery of sphalerite. beyond 1 h of interaction with T. thiooxidans cells is n ot affected but galena is totally depressed in the presence of T. thiooxida ns cells. in the pH range 5-11. The differential flotation tests on a synth etic mixture of galena and sphalerite reveal that sphalerite can be selecti vely floated from galena in the presence of. thiooxidans. (C) 2001 Elsevier Science B.V, All rights reserved.