Some recent advances in the bioprocessing of bauxite

This paper describes some of the important microbiological and engineering challenges in scaling up biobeneficiation of bauxite. A soil bacterium Paen ibacillus polymyxa was recently shown to selectively remove calcium and iro n impurities from low grade bauxite (< 50% Al), for abrasive and refractory applications. respectively. An industrial scale formulation of Bromfield m edium (called ISF-2), based on cane sugar and tap/mine water, is developed to successfully culture P. polymyxa under septic conditions. The culture is found to be efficient in removing calcium from bauxite ore, carried out as cascade operations in total recycle slurry reactors. In cascade leaching e xperiments with pre-grown culture, calcium removal was observed to occur so lely by indirect mechanism in an initial rapid phase lasting few minutes, f ollowed by a gradual phase comprising of direct attack as well as indirect mechanisms. An alternative mechanism of indirect leaching is proposed based on solubilisation of accessible calcium in the culture metabolite, up to a saturation solubility limit. The saturation solubility theory gives an exp lanation for the need to perform cascade experiments, and also successfully predicts the possibility of pulse leaching experiments. Some of these rece nt advances are likely to enable successful commercialisation of bauxite bi obeneficiation. <(c)> 2001 Elsevier Science B.V. All rights reserved.