Electroreduction of oxygen on copper-containing sulfide minerals

The state of the surface of and the oxygen electroreduction on the naturally occurring minerals bornite, chalcopyrite, and chalcosine are studied in borate buffer solutions using X-ray photoelectron spectroscopy, cyclic voltammetry, and the rotating disk electrode technique. The surface of the minerals in an oxygen-containing atmosphere is covered with compounds of copper and iron in the highest oxidation states, and the oxygen electroreduction occurs on these compounds. Electrocatalytic activity of sulfide minerals during cathodic polarization is presumably due to the participation in the oxygen electroreduction reaction of redox centers, i.e. ions of Fe(II) in bornite and chalcopyrite, and ions of Cu(I) bonded with the sulfide sulfur in each of the minerals.