Oxidation of synthetic and natural samples of enargite and tennantite: 1. Dissolution and zeta potential study

The oxidation of synthetic and natural samples of tennantite and enargite i s compared by measuring the dissolution and the zeta potential of these min erals. The changes in zeta potential with pH and oxidizing conditions are c onsistent with the presence of a copper hydroxide layer covering a metal-de ficient sulfur-rich surface and with the extent of this copper hydroxide co verage increasing with oxidation conditions, Analysis of the zeta potential data reveals that during the acid titration of the minerals, dissolution o f the surface copper hydroxide layer occurs at neutral pH values, whereas p recipitation of copper hydroxide on the mineral surface is observed during the base titration. Hysteresis between the zeta potential acid and base tit ration curves is only observed in oxidizing conditions and is attributed to the dissolution of copper from the mineral lattice at acidic pH values. Ar senic does not appear to contribute to the mineral oxidation; in particular , its dissolution is much less than that of copper. This study has shown th at in alkaline conditions the natural samples of tennantite and enargite ox idize more than the synthetic samples and tennantite oxidizes more extensiv ely than enargite.