Bioleaching of apatite rich low grade Indian uranium ore

Abstract

Uranium ore from Narwapahar Mines, UCIL contains 0?047% U 3 O 8 with some refractory minerals and high apatite (5%) results in a maximum 78% recovery through conventional processing at UCIL, with a fairly high consumption of sulphuric acid and pyrolusite, and loss of uranium as uranium phosphate. To avoid usage of non-ecofriendly oxidants, obviate the influence of phosphate and improve the overall process output of uranium, an alternate extraction technology using microbial isolate(s) is elucidated in this study. A.ferrooxidans isolated from Narwapahar mine water was used in bioleaching of uranium from this apatite rich low grade uraninite ore. Optimum uranium biorecovery of 96% is achieved at 10% pulp density (w/v), pH 1.7 and 35degC in 40 days with the fine particles of <45micron size. Under the optimum condition at pH 1.7, rise in redox potential is recorded to be 594–708 mV in 40 days. Bioleaching of uranium seems to follow the indirect mechanism of leaching with the involvement of Fe(III) biogenically generated by Acidithiobacillus ferrooxidans (A. ferrooxidans). Uranium recovery was also examined using another mesophilic isolate of Leptospirillum ferrooxidans (L. ferrooxidans) which showed 98% uranium leaching at 40degC, which shows the possibility of improving the kinetics of the process. The high R2 values in the temperature range (298–308 K) indicated uranium dissolution by the chemical reaction occurring at the ore surface with Fe(III) generated biogenically, with Ea value of 28.3 kJ/mol. The mechanism of uranium bioleaching is also elucidated with X-ray diffraction phase identification of the leach residues with time, followed by observing the surface morphology through SEM at varying temperatures.