Continuous bio-hydrometallurgical extraction of zinc from a bulk lead-zinc flotation concentrate on a pilot scale

The high interlock between the fine particles of sphalerite and galena in some parts of the Goushfil mine (Isfahan, Iran) ore has significantly reduced the flotation efficiency. According to the acceptable capability of bioleaching in the recovery of metals from the complex mineralogical resources, the feasibility of zinc extraction from a low-grade (34% Zn) bulk flotation concentrate was investigated. The applied concentrate was processed using a large-scale continuous bioleaching system, including three 50 l stirred bioreactors in series. After 15 days, 83% of zinc was recovered by implementing a mixed culture of moderately thermophile bacteria at pH = 1.8 and 15% solid content. In the next stage, 83% of the accompanying iron impurity was removed from the leachate by jarosite precipitation. Then, about 99.9% of zinc was gained by solvent extraction using 25% saponified D2EHPA at pH = 3.5, O/A = 1 at two steps. Consequently, bioleaching, in combination with bulk flotation, can be successfully applied to recover zinc from the complex lead-zinc ore of the examined deposit.