The effect of sodium hydrosulfide on molybdenite flotation as a depressant of copper sulfides

Abstract

Depressing copper sulfides using sodium hydrosulfide (NaHS) in the flotation of molybdenite is a common practice. However, the effect of NaHS on the flotation of molybdenite is not clear despite a number of studies. In this study, the effect of NaHS concentrations which depressed the flotation of chalcopyrite on the flotation of molybdenite of different particle sizes was investigated. It was found that molybdenite flotation was promoted at a low NaHS concentration. A high NaHS concentration only reduced the flotation kinetics slightly without affecting the final flotation recovery. The effect of NaHS on the flotation of smaller molybdenite particles was more significant. Cryo-XPS analysis was then carried out to understand the underpinning mechanism. It was evident that the flotation behavior of molybdenite in the presence of NaHS was determined by the reactions of NaHS on the edge plane surface of molybdenite. At a low NaHS concentration, NaHS adsorbed on the edge plane surface and formed hydrophobic species such as elemental sulfur and polysulfide. At a high NaHS concentration, the hydrophobic species disappeared with more HS− adsorbed. At both low and high NaHS concentrations, NaHS did not adsorb on the basal plane surface of molybdenite which remained its surface hydrophobicity.