Effect of pH and diethyl dithiophosphate (DTP) treatment on chalcopyrite and tennantite surfaces observed using atomic force microscopy (AFM)

Abstract

Atomic force microscopy (AFM) has been used to observe the morphology and surface characteristics of chalcopyrite and tennantite treated at pH 4 and 9. Mineral treated with DTP at pH 9 was also observed. It was found that new surface “islands” were formed on the minerals after these treatments. The occurrence of these islands as a product of reaction was amplified with increasing treatment time. Adhesion force measurements revealed that the formation of islands under acidic conditions (pH 4) lowered the adhesion force value compared to that under alkaline conditions (pH 9), thus rendering the surfaces of the minerals more hydrophobic. A similar tendency was observed in the adhesion force value of minerals surface-treated with DTP at pH 9. This phenomenon arose as a result of a propensity for the formation of elemental sulfur or metal-deficient sulfur-rich species at pH 4 and DTP species at pH 9. The more hydrophilic surfaces of both minerals indicated by higher values of the adhesion force after treatment at pH 9 may be attributed to the occurrence of metal hydroxide moieties. From the morphology images and adhesion force, it is apparent that the coverage of islands on the surface of a mineral determines its hydrophobicity or hydrophilicity. Moreover, it also shows the relative reactivities of the minerals, with tennantite being more reactive than chalcopyrite. Furthermore, the microscopic observation by AFM was consistent with the macroscopic observations of contact angle and flotability studies.