In situ electrochemical characterization of natural pyrite as a galvanic catalyst using single-particle microelectrode technique in ferric sulfate solutions

Ferric reduction on the surface of pyrite, a major factor governing the overall kinetics of pyrite-assisted leaching of chalcopyrite in sulfate solutions, is investigated. In order to study the effect of pyrite on chalcopyrite leaching, four different pyrite samples were used in the leaching process. A single-particle microelectrode technique was employed to investigate the electrochemical and semiconducting properties of different pyrite samples by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy, and Mott–Schottky methods in a solution containing 0.5 mol/L sulfuric acid, 0.005 mol/L ferric sulfate, and 0.005 mol/L ferrous sulfate. During leaching, differences were observed in the behavior of different pyrite samples. CV showed a difference in the magnitude of the ferric reduction reaction peaks. An equivalent analog circuit was used to model the impedance spectra, which led to the conclusion that pyrite samples with lower charge transfer resistance are better catalysts for ferric reduction. Mott–Schottky analysis was used to quantify variations in some semiconductive and electrical properties of pyrite samples from different geographical locations.