Effect of energy source and leaching method on bio-leaching of rock phosphates by Acidithiobacillus ferrooxidans

The effects of energy source and leaching method on improving the bio-leaching of rock phosphates by Acidithiobacillus ferrooxidans CK were investigated. The dissolution of rock phosphates by strain CK in response to ferrous iron and elemental sulfur as the sole and mixed energy source was studied in a series of bio-leaching experiments without and with pre-cultivation of the microorganism. The mixture of ferrous iron and sulfur was found to be optimal for bio-leaching of rock phosphates. Bio-leaching of rock phosphates with pre-grown culture was observed to be enhanced significantly in comparison to that obtained without pre-cultivation under the condition of the same energy source. The presence of rock phosphates exerts a negative effect on bacterial oxidative activity. Phosphorous solubilization from rock phosphates relies on protons to proceed. The enhanced bio-leaching of rock phosphates coincided with the increased generation of gypsum crystals and the decreased formation of jarosite precipitates due to the relatively lower pH values achieved by the simultaneous release of protons from the precipitation of ferric ions and bio-oxidization of sulfur when both energy sources were available as well as the delayed addition of ore samples under pre-grown culture leaching.