The electrochemistry and kinetics of the oxidative dissolution of chalcopyrite in ammoniacal solutions: Part I – Anodic Reactions

The oxidative dissolution of chalcopyrite in aqueous solutions is an electrochemical process. Such processes can be evaluated as coupled anodic and cathodic reactions using electrochemical techniques. The chalcopyrite dissolution reaction has been studied in ammonia-ammonium sulphate solutions using potentiostatic and potentiodynamic methods. Anodic current densities in the vicinity of the mixed potential have been found to increase with an increase in total ammonia (NH₃ + NH₄ ⁺) from 1 M to 3 M, and the order of reaction was found to be 1st order with respect to ammonia. The reaction was found to be zero order with respect to [OH⁻] at a pH between 9 and pH 10. An analysis of the Tafel slopes suggested an average charge transfer coefficient of 0.61. The rate controlling step was concluded to be a single electron transfer reaction, which supports the formation of a copper depleted intermediate surface that is rapidly oxidised in subsequent electron transfer reactions. The anodic sweeps and constant potential tests did not support the formation of a passivating surface deposit on the oxidising chalcopyrite surface.