Zeta potential study of the oxidation of copper sulfide minerals

The zeta potential of the copper sulfide minerals, chalcocite, covellite, c halcopyrite, bornite, enargite and tennantite was measured as a function of pH and oxidising conditions. The changes in zeta potential observed in thi s study are consistent with the presence of a copper hydroxide layer coveri ng a metal-deficient sulfur-rich surface and with the extent of this copper hydroxide coverage increasing with oxidation conditions. The existence of these surface species and their percentage were also confirmed by X-ray pho toelectron spectroscopy. Analysis of the zeta potential data revealed that during the acid titration of the minerals, dissolution of the surface coppe r hydroxide layer occurs at pH values less than 8 while during the base tit ration, precipitation of copper hydroxide on the mineral surface is observe d at pH values higher than 6. Hysteresis between the zeta potential acid an d base titration curves was only observed in oxidising conditions and is at tributed to the dissolution of the minerals at acidic pH values. The follow ing ranking for the oxidation of these minerals is obtained: chalcocite > t ennantite > enargite > bornite > covellite > chalcopyrite. (C) 1999 Elsevie r Science B.V. All rights reserved.