Efficiency of Copper Bioleaching of Two Mesophilic and Thermophilic Bacteria Isolated from Chalcopyrite Concentrate of Kerman-Yazd Regions in Iran

A mesophilic iron oxidizing bacterium, Acidithiobacillus ferrooxidans, has been isolated (33\degree C) from a typical chalcopyrite copperconcentrate of the Sarcheshmeh Copper Mine in the region of Kerman located in the south of Iran. In addition, a thermophilic iron oxidizing bacterium, Sulfobacillus spp., has been isolated (60\degree C) from the Kooshk Lead and Zinc Mine near the city of Yazd in the mid-west region of Iran. The variation of pH, ferrous and ferric concentration and cell growth on the time and effects of some factors, such as temperature and initial ferrous concentration, on the bioleaching of chalcopyrite concentrate obtained from Sarcheshmeh Copper Mine, were investigated. Bioleaching experiments were carried out batch wise using 5% (v/v) inoculum and 2% (w/v) of concentrate. The control tests were conducted using the sterilized concentrate and without the inoculum. The results obtained showed the importance of the influence of all the tested variables on the efficiency of the copper bioleaching. The effects of temperature and initial ferrous iron concentration were found to be considerable. Maximum copper recovery was obtained when the thermophilic culture had been used. Copper dissolution reached up to 80\% using Sulfobacillus spp., while this value was 72% when Acidithiobacillus ferrooxidans was used at pH = 1.5. The initial Fe^2+ concentrations for the tested mesophilic and thermophilic strains were 7 and 9 g/L, respectively. The test duration was 30 days.