Zinc Extraction from Iranian Low Grade Complex Zinc-Lead Ore by Two Native Microorganisms: Acidithiobacillus ferrooxidansand Sulfobacillus

A mesophilic iron oxidizing bacterium, Acidithiobacillus ferrooxidans, has been isolated (33°C) from a typical chalcopyrite copper concentrate of the Sarcheshmeh Copper Mine in the region of Kerman located in the south of Iran. In addition, a thermophilic iron oxidizing bacterium, Sulfobacillus, has been isolated (60°C) from the Kooshk Lead and Zinc Mine near the city of Yazd in the center point of Iran. Variation of pH, ferrous and ferric concentration on time and effects of some factors such as temperature, cell growth, initial ferrous concentration and pH on bioleaching of low grade complex zinc-lead ore obtained from Kooshk Lead and Zinc Mine near the city of Yazd in the center of Iran were investigated. Bioleaching experiments were carried out in 500 ml shake flask containing 250 ml of the medium, 5% (v/v) inoculum and 2% (w/v) of low grade ore. Control bioleaching tests were carried out with ore sterilized, 250 ml of the medium without inoculum by the addition of 5 ml of 0.5% (v/v) formaline in ethanol. The results indicate that the efficiency of zinc extraction is dependent on all of the mentioned variables; especially temperature and initial ferrous concentration have more effect than other factors for these microorganisms. In addition, results show that the maximum Zn recovery was achieved using a thermophilic culture. Copper dissolution reached 58% with Sulfobacillus while it was 51% with Acidithiobacillus ferrooxidans at pH=1.5, initial Fe2+ concentration=7000 and 9000 mg/lit for mesophilic and thermophilic strains respectively, after 30 days.

Keywords:

bioleaching , Acidithiobacillus ferrooxidans , Solfobacillus , low grade ore , sulfide mineral , zinc recovery