Add time:08/16/2019         Source:sciencedirect.com

CHALCOPYRITE (cas 1308-56-1) is the most abundant but also the most recalcitrant copper sulfide mineral in leaching processes. The reasons for its refractory character are passivation and/or its semi-conductive properties. In our study chalcopyrite was hydrometallurgically processed via chemical leaching, electrochemical leaching, bioleaching and electrobioleaching in 2 l stirred tank laboratory experiments. Both biotic leaching treatments were more successful than both abiotic leaching experiments, however, overall the copper recovery was low due to the recalcitrant character of chalcopyrite. Various electrochemical techniques such as cyclic voltammetry, potentiodynamic polarization and electrochemical impedance spectroscopy were applied to investigate the differences in surface properties of the residues. Potentiodynamic polarization and cyclic voltammetric studies showed that any kind of leaching resulted in increased dissolution resistance and surficial redox inactivation compared to unprocessed chalcopyrite. However, if chalcopyrite was continuously in direct contact to the cathodic working electrode its surface was activated and showed even the highest oxidation currents which implicates increased leachability. Thus, at the surface of such chalcopyrite particles the mineral was converted into readier leachable minerals such as chalcocite. Additionally, electrochemical impedance spectroscopy (EIS) was carried out in the presence of ferrous and ferric iron. It turned out that surface activation via ferrous iron was not observed. In contrast, ferric iron led to successive passivation over time. The charge transfer resistance was the lowest for unprocessed and surface reduced chalcopyrite and the highest for chemically and electrochemically leached sulfide mineral. The findings of this comparative, electrochemical study support that passivation takes place to larger extend during abiotic leaching (chemical and electrochemical leaching) compared to biotic leaching (bioleaching and electrobioleaching).

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