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Electrochemical aspects of the aqueous oxidation of copper sulphides Etienne, Arlette


The Cu-S binary system was subjected to electrochemical studies at temperatures below 100°C in acid solution. Three types of electrochemical experiments were conducted: a) Measurements of electromotive force were made on the galvanic cell, Cu | 0.1 M CuSO₄, 0.1 M H₂SO₄ | Cu[sub y]S across the Cu-S system (y variable). The range of copper activity corresponding to the zone of stability of digenite (~ Cu[sub 1.8]S) was accurately determined. From these measurements and the existing thermodynamic data on covellite (CuS), the standard free enthalpy of formation of digenite (~ Cu[sub 1.8]S) and djurleite (Cu[sub 1.965S]) was calculated. b) Copper sulphides were grown on a copper anode from an acidic solution saturated with H₂S at constant current. The thickening: of the copper sulphide film was accounted for by electrolytic transport in the scale. The diffusion coefficient of cuprous ions in low chalco-cite (Cu₂S) and low digenite (~ Cu[sub 1.8]S) was calculated from the slope of the electrode potential versus time relationship. c) Galyanostatic polarization of rotating disk anodes of digenite and covellite was studied at 55°C in 0.1 M CuSO₄-0.1 M H₂SO₄ solutions. The resistances arising during the anodic dissolution of these sulphides were assessed from the dependence of the electrode potential on time and current density. The above polarization experiments were correlated with the electrolysis of copper matte anodes and the leaching experiments in acidic ferric solutions described in the literature.

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