Bio-chemical leaching of kaolinite-hematite-boehmite type bauxite ore

Low grade bauxites of Severo-Onezhsky and Sredne-Timansky deposits of Russia have been evaluated for their amenability towards bioleaching. Two microbial isolates of Bacillus genera have been isolated in Zak medium and enriched to conduct leaching experiments of bauxites. The bacteria are chosen due their specific ability to secrete exo-polysaachrides (EPS), which is believed to be very beneficial in dissolution-cum-flocculation of aluminosilicates. The microbes have been able to leach nearly 50% alumina and nearly 10-35% SiO2 and Fe2O3. Chemical leaching experiments with citric and oxalic acids on bauxite leaching result in a maximum extraction of aluminum to be nearly 39% at elevated concentrations of leaching agents and 2-8 hours residence time.