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.