Abstract: Most of secondary copper sulfides are associated with pyrite in the nature. Pyrite's over-dissolution in bioleaching can lead to acid-iron imbalance in the leaching system. Based on the atom orbit and molecular theory, the electrochemical dissolution mechanism of pyrite is analyzed and it is considered that redox potential is the key factor influencing the pyrite dissolution. Tests on pure pyrite by sulfuric acid leaching, ferric sulfate leaching and Leptospirillum are made. The results validate that when there are no bacteria, the redox potential will be basically lower than 700mV and the pyrite is hardly dissolved, with an iron leaching rate lower than 10%. When there are bacteria, the redox potential can be raised to higher than 800mV, speeding up the pyrite dissolution, with the iron leaching rate as high as 67%.

Key words: Pyrite, Bioleaching, Redox potential, Leaching rate