Abstract for presentation at Chemeca 2007

In the flotation of copper sulphide minerals such as chalcopyrite, low copper concentrate grades are often the result of iron sulphide gangue minerals, such as pyrite and pyrrhotite, misreporting to the copper concentrate. In this study, we have increased the number of methods that can be used to reduce copper activation of iron sulphide minerals and to selectively depress iron sulphide flotation. It was found that addition of thiol collectors during grinding could reduce chalcopyrite oxidation/dissolution and therefore copper activation of iron sulphide minerals. Control of the concentration of collector additions during grinding and conditioning is critical in order to optimize both the iron sulphide rejection and copper sulphide flotation. We have also found that thioglycolic acid (TGA) is a strong complexant of copper hydroxide species in solution and on the pyrite surface, and therefore can be used during grinding to reduce copper activation of iron sulphide minerals. If copper activation cannot be prevented during grinding, reagents (with hydrophilic groups) have to be added to reduce the overall surface hydrophobicity of the iron sulphides. We have found that TGA removes surface copper hydroxides before collector can adsorb onto them, zinc hydroxide (zinc sulphate addition) and sulphite ions adsorb on the pyrite surface, oxygen gas (high Eh) and hydroxide ions (increase in pH) promote the formation of iron oxide/hydroxide. The efficacy of these methods has been optimized by controlling the pulp conditions and by a better knowledge of the mechanism of action of the reagents involved in these methods.