Surface chemical studies on sphalerite and galena using Bacillus polymyxa: I. Microbially induced mineral separation

Abstract

The interaction of sphalerite and galena with cells of Bacillus polymyxa was investigated through adsorption, electrokinetic, flotation, and flocculation studies. Adsorption experiments indicated that a higher amount of the cells was adsorbed onto galena compared to sphalerite. The adsorption density of the cells onto galena was almost independent of pH while that onto sphalerite was found to continuously decrease with increasing pH. The adsorption isotherms of the bacterial cells on galena and sphalerite exhibited Langmuirian behavior. Electrokinetic measurements showed that the negative electrophoretic mobilities of the cells were reduced in magnitude in proportion to the time of interaction with either sphalerite or galena. Similar trends were observed in the cases of sphalerite and galena after interaction with the cells. However, the magnitude of the reduction in the electrophoretic mobilities was found to be greater for galena than for sphalerite. Flotation tests revealed that galena was almost completely depressed after interaction with the cells both in the absence and in the presence of the collector. In contrast, the addition of collector and activator to sphalerite, which was initially interacted with the cells, restored the floatability at and beyond pH 8.5. Selective flotation tests on a synthetic mixture of galena and sphalerite confirmed that sphalerite could be preferentially floated from galena, which was depressed by the bacterial cells. Selective flocculation tests further demonstrated that galena could be flocculated from sphalerite, which was dispersed in the presence of cells of B. polymyxa at pH 9-9.5.