Bioleaching of Rock Phosphate by Aspergillus niger

Abstract

Bioleaching process is based on the ability of microorganisms (bacteria and fungi), to transform solid compounds resulting in soluble and extractable elements, which can be recovered. The main objective of the present study is to characterize the solubilization of phosphorus and uranium from rock phosphate with Aspergillus niger. An appreciable amount of uranium was also determined in the rock sample (0.012 % U₃O₈). XRD data indicated the presence of flourapatite [Ca₂(PO₄)₃F] as the main source of phosphorus. Other accessory minerals like biotite, muscovite, gypsum, aluminium oxide, trona, orthoclase, diopside and albite, etc. were estimated in the sample. The fungal strains of Aspergillus niger produced citric acid and oxalic acid during fermentation of glucose which resulted in a drastic drop in initial pH of the growth medium. During bioleaching studies of rock phosphate, the dissolution of phosphorus, uranium and other metal ions was observed in shake flasks leaching studies. Solubilization of these metal ions was apparently attributed to pH dependant. The SEM-EDX analysis of rock phosphate revealed that a significant amount of phosphorus, calcium, silicon and oxygen was present in the rock-matrix.