Optimization of operating parameters and rate of uranium bioleaching from a low-grade ore

In this study the bioleaching of a low-grade uranium ore containing 480 ppm uranium has been reported. The studies involved extraction of uranium using Acidithiobacillus ferrooxidans derived from the uranium mine samples. The maximum specific growth rate (mu(max)) and doubling time (t(d)) were obtained 0.08 h(-1) and 8.66 h, respectively. Parameters such as Fe2+ concentration, particle size, temperature and pH were optimized. The effect of pulp density (PD) was also studied. Maximum uranium bio-dissolution of 100 +/- 5 % was achieved under the conditions of pH 2.0, 5 % PD and 35 degrees C in 48 h with the particles of d(80) = 100 mu m. The optimum concentration of supplementary Fe2+ was dependent to the PD. This value was 0 and 10 g of FeSO4 center dot 7H(2)O/l at the PD of 5 and 15 %, respectively. The effects of time, pH and PD on the bioleaching process were studied using central composite design. New rate equation was improved for the uranium leaching rate. The rate of leaching is controlled with the concentrations of ferric and ferrous ions in solution. This study shows that uranium bioleaching may be an important process for the Saghand U mine at Yazd (Iran).