Bioleaching of Zn(II) and Pb(II) from Nigerian sphalerite and galena ores by mixed culture of acidophilic bacteria

Zn(II) and Pb(II) from Nigerian sphalerite and galena ores were bioleached by a mixed culture of acidophilic bacteria. The influences of pH and ferric ion on the bioleaching rates of sphalerite and galena were examined. The result shows that pH 2.1 and 2.7 are favourable for the leaching of Zn(II) and Pb(II) from sphalerite and galena, respectively. It was observed that the use of agarose-simulated media caused cells to excrete exopolymers containing ferric ions which enhanced oxidation. The oxidation equilibrium for sphalerite and galena took 3 and 4 d, respectively. About 38.3% sphalerite and 34.2% galena were leached within 1 d and approximately 92.0% Zn(II) and 89.0% Pb(II) were recovered in 5 d, respectively. The unleached residual products were examined by X-ray diffraction for sphalerite, revealing the presence of elemental sulphur(S), zinc sulphate (ZnSO(4)) and few traces of calcium aluminate (Ca(3)Al(2)O(6)). The XRD pattern also indicates the presence of elemental sulphur (S), lead sulphate (PbSO(4)) and few traces of itoite [Pb(S,Ge)(O,OH)(4)] and cobalt lead silicate [Pb(8)Co(Si(2)O(7))(3)] in the unleached galena ore.