Abstract

Water quality affects the flotation recovery of minerals and their separation. Mining-process waters become saturated with soluble salts after contact with minerals (oxidation and dissolution) during crushing, classification and flotation. Inorganic species, such as metal ions but also carbonate and sulphate ions, may have a positive or negative effect on mineral flotation. As sulphate ions are always found in high concentrations in process waters, their effects on the flotation of copper, molybdenum and zinc sulphides were investigated in single minerals and ores experiments with complementary mineral surface analysis and particle-bubble detachment studies. It was found that molybdenite flotation was more depressed than chalcopyrite flotation by the presence of sulphate ions in water as a result of increased surface oxidation which decreased particle-bubble attachment. Similar results were obtained in the flotation of two copper ores; however, the grade of chalcopyrite and molybdenite was much lower as a result of increased recovery of unwanted or gangue minerals (e.g., sphalerite, pyrite and quartz).