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

The interaction of sphalerite and galena with cells of Bacillus polymyxa wa s investigated through adsorption, electrokinetic, flotation, and flocculat ion studies. Adsorption experiments indicated that a higher amount of the c ells was adsorbed onto galena compared to sphalerite. The adsorption densit y of the cells onto galena was almost independent of pH while that onto sph alerite was found to continuously decrease with increasing pH, The adsorpti on isotherms of the bacterial cells on galena and sphalerite exhibited Lang muirian behavior. Electrokinetic measurements showed that the negative elec trophoretic mobilities of the cells were reduced in magnitude in proportion to the time of interaction with either sphalerite or galena, Similar trend s were observed in the cases of sphalerite and galena after interaction wit h the cells. However, the magnitude of the reduction in the electrophoretic mobilities was found to be greater for galena than for sphalerite. Flotati on tests revealed that galena was almost completely depressed after interac tion with the cells both in the absence and in the presence of the collecto r. In contrast, the addition of collector and activator to sphalerite, whic h 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 fr om galena, which was depressed by the bacterial cells. Selective flocculati on tests further demonstrated that galena could be flocculated from sphaler ite, which was dispersed in the presence of cells of B.polymyxa at pH 9-9.5 . (C) 2001 Academic Press.