Surface chemical studies on galena and sphalerite in the presence of Thiobacillus thiooxidans with reference to mineral beneficiation

Adsorption and electrokinetic studies were carried out to examine the surface chemical changes on galena and sphalerite before and after interaction with Thiobacillus thiooxidans (T. thiooxidans). The adsorption density of bacterial cells onto the two sulphide minerals was found to be independent of pH, although an increased number of cells was adsorbed onto galena compared to sphalerite. The adsorption isotherms of the cells with respect to the two minerals conform to the Langmuir equation. Zeta potential measurements revealed that the isoelectric points of the sulphide minerals were shifted to higher pH values after bacterial interaction, suggestive of specific adsorption. Both the sulphide minerals as well as the cells became less electronegative as a function of time after interaction with each other. Selective flotation and flocculation studies highlighted that galena could be separated from sphalerite after bacterial interaction. These tests confirmed that galena was depressed while sphalerite was made hydrophobic after interaction with the cells. Fourier transform infrared spectroscopic studies provided evidence in support of hydrogen bonding for the mineral-cell adsorption process. Possible mechanisms of interaction between galena/sphalerite and the cells of T. thiooxidans are discussed.