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 (S0) 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 Ca5(PO4)3F) 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.