M. R. Samadzadeh Yazdi - Mining and Metallurgical Engineering Department, Mining Technologies Research Center (MTRC), Yazd University, Yazd, Iran
M. Abdollahi - Mineral Processing Division, Mining Engineering Department, Tarbiat Modares University, Tehran, Iran
S. M. Mousavi - Biotechnology Division, Chemical Engineering Department, Tarbiat Modares University, Tehran, Iran
A. Khodadadi Darban - Mineral Processing Division, Mining Engineering Department, Tarbiat Modares University, Tehran, Iran

Although bioleaching of chalcopyrite by thermophilic microorganisms enhances the rate of copper recovery, a high temperature accelerates iron precipitation as jarosite, which can bring many operational problems in the industrial processes. In this research work, the bioleaching of chalcopyrite concentrate by the thermophilic Acidianus brierleyi was studied, and the microbial growth, copper dissolution, iron oxidation, and jarosite precipitation were monitored in different initial pH (pHi) values. Bacterial growth was greatly affected by pHi. While the bacterial growth was delayed for ۱۱ days with a pHi value of ۰.۸, this delay was reduced to nearly one day for a pHi value of ۱.۲. Two stages of copper recovery were observed during all the tests. A high pHi value caused a fast bacterial growth in the first stage and severe jarosite precipitation in the later days causing a sharp decline in the bacterial population and copper leaching rate. The copper recoveries after ۱۱ days were ۲۵%, ۷۸%, ۸۴%, ۷۰%, ۵۶%, and ۳۹% for the pHi values of ۰.۸, ۱.۰, ۱.۲, ۱.۳, ۱.۵, and ۱.۷, respectively. Sulfur and jarosite were the main residues of the bioleaching tests. It was revealed that the drastic effect of jarosite precipitation on the microbial growth and copper recovery was mainly caused by the ferric iron depletion from solution rather than passivation of the chalcopyrite surface. A slow precipitation of crystalline jarosite did not cause a passive chalcopyrite surface. The mechanisms of chalcopyrite bioleaching were discussed.

Bioleaching, Chalcopyrite, Acidianus brierleyi, Initial pH, Iron oxidation, Jarosite precipitation