Bioleaching phosphorus from fluorapatites with acidophilic bacteria

Abstract

Currently known high grade easily-acquirable phosphate rock reserves are depleting. The objective of this study was to evaluate the potential application of bioleaching technology to the recovery of phosphorus from different phosphate ore materials, and isolate indigenous phosphorus-solubilising bacterial strains from them. In the bacterial enrichment and isolation experiments no growth was detected in the medium designed for acidophiles. Heterotrophic phosphorus solubilising isolates were enriched from the fluorapatite concentrate, and all four isolates were most closely related to Burkholderia fungorum. Bioleaching of phosphorus from low grade fluorapatite ore containing 8.2% P2O5 and from fluorapatite concentrate containing 29.8% P2O5 was carried out in shake flasks. Supplemental elemental sulphur was added as an energy source for acid generation. Mixed and pure acidophilic bacterial cultures consisting of iron- and/or sulphur-oxidizing bacteria Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans were used in the experiments. These acidophiles are commonly used in bioleaching of sulphide minerals, but their application to phosphorus solubilisation has until now been limited. Phosphorus leaching was shown to be a pH-dependent phenomenon. Phosphorus bioleaching yields of up to 97% and 28% were obtained in 21d for low grade fluorapatite ore and concentrate, respectively, in solutions with a 1% solid content. With adaptation, the bacterial mixture was acclimated to suspensions with a 10–30% solid content. These results indicate a potential for the application of bioleaching to phosphorus extraction of low grade materials.