Surface chemical studies on sphalerite and galena using Bacillus polymyxa: II. Mechanisms of microbe-mineral interactions

Abstract

Biodissolution tests reveal the release of lead/zinc species from galena/sphalerite, respectively, while biosorption experiments confirm interaction of cells of Bacillus polymyxa (B. polymyxa) with the metal ions of interest. The amount of exo-polysaccharides is found to be the highest in the case of galena-interacted cells, followed by the Bromfield medium-grown cells while the sphalerite-interacted cells have the least, based on ruthenium red adsorption studies. In contrast, the sphalerite-interacted cells assay the highest amount of protein while the galena-interacted cells have the lowest amount, on a comparative basis. The adsorption of xanthate onto galena is found to be diminished in the presence of the cells whereas the xanthate adsorption density for activated sphalerite is unaffected in the pH range 9-11. Additionally, the cell surface hydrophobicity tests confirm that the sphalerite-interacted cells are more hydrophobic relative to the galena-interacted cells. FTIR spectroscopic data lend support to the higher adsorption density of the cells onto galena vis-à-vis sphalerite. The higher exo-polysaccharide and lower protein contents together with the hydrophilic nature of the galena-interacted cells could be the contributing factors to the selective flocculation and depression of galena. In a similar manner, the higher protein and lower exo-polysaccharide contents as well as the greater hydrophobicity of the sphalerite-interacted cells favor its floatability and dispersion.