Bacterial solubilization of phosphorus from phosphate rock containing sulfur-mud

Bacterial solubilization of phosphorus (P) from phosphate rock with acidophilic iron- and sulfur-oxidizing bacteria (Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans) was carried out in shake flasks leaching experiments. Phosphate rock sample was supplemented with sulfur-mud (a waste of sulfuric acid manufacturing plant) containing significant amounts of elemental sulfur (S-0) and greigeite (Fe3S4, cubic) as an energy substrate for these acidophilic bacteria. Bacterial oxidation of sulfur and sulfur mineral was an acid-generating system. Biologically generated sulfuric acid (H2SO4) was produced which dissolved P from phosphate rock due to acid attack on fluorapatite mineral Ca-5(PO4)(3)F) present in rock matrix. The dissolution of P from phosphate rock was mainly attributed to the concentration of bacterially produced sulfuric acid in the leaching medium. A. ferrooxidans and A. thiooxidans solubilized significant amounts of P in bioleaching process. The mixed culture of these bacteria solubilized higher amounts of P (70.2% P2O5) at 10% pulp density during 40-days of leaching as compared with pure culture alone. The maximum P solubilzation rate of 564.8 mg P2O5 L-1 d(-1) was achieved in leach solution inoculated with mixed culture. The dissolution of P was found to be pH-dependant phenomenon. (C) 2010 Elsevier B.V. All rights reserved.