Quantitative assessment of the effect of pyrite inclusions on chalcopyrite electrochemistry under oxidizing conditions

The present paper quantifies the separate and combined effects of pyrite (FeS₂) inclusions, dissolved oxygen (0.001 mol/L) and ferric ion (0.01-0.05 mol/L) on the electrochemical behavior of chalcopyrite (CuFeS ₂) electrodes by means of potentiometry and linear sweep voltammetry. The experiments were carried out in 0.1 mol/L H₂SO₄ solutions at room temperature (26 ± 1 °C). Naturally associated pyrite-chalcopyrite electrodes were selected with the aims to better represent the sulfide association in the ore, thus minimizing the voltage losses across the mineral-mineral contact. The presence of ferric ion and oxygen was shown to increase in approximately 53% the mixed potential of CuFeS₂ electrodes; the dissolution current density increased up to 55 times. In the presence of these oxidants and pyrite (42% FeS₂ of the electrode surface), the mixed potential was further increased in 14%. For these mixed electrodes, the dissolution current density increased by a factor of approximately 2.6 and 2.2, respectively, in solutions containing 0.001 mol O₂/L and 0.05 mol Fe^{3 +}/L, and by 1.6 times in presence of both oxidants (0.001 mol O₂/L with 0.05 mol Fe^{3 +}/L). Therefore, more pronounced effect of pyrite inclusions on chalcopyrite oxidation rate was observed under the lower oxidizing conditions. The effects of the oxidants were described by electrochemical models. The galvanic effect of pyrite on the dissolution of this important sulfide was discussed by the kinetics of the half-cell reactions occurring in the pyrite-chalcopyrite coupling.