A review of water re-use in flotation

Abstract

Increasing use of recycle water in flotation often has negative effects on recovery and grade. These have been traced to the accumulation of dissolved compounds, inorganic and organic, which alter the chemistry of the system. Some examples from industrial experience with complex sulphide and non-sulphide ores are discussed. In complex sulphide systems the loss in selectivity and recovery can be traced to one or a combination of the following factors: residual xanthates and their oxidation products dixanthogens which adsorb unselectively on most sulphides; residual sulphides which cause undesirable depression; metallic ions like Cu ++, Fe ++, Pb ++ which cause inadvertant activation; and alkaline earth metal ions which may activate the nonsulphide gangue. The adverse effect observed in nonsulphide systems have been discussed in terms of: residual flotation agents including carboxylate collectors, alkyl sulphates and amines all of which reduce selectivity by their relatively unselective adsorption characteristics; and Ca ++ and Mg ++ ions which increase the positive surface charge of the minerals and affect the action of flotation agents functioning by electrostatic mechanism. A number of wastewater treatment techniques which may be applicable to recycle water in flotation are discussed. These include physical adsorption methods using active carbon, coal or bentonite clay or mineral slimes, biological oxidation of organics, removal of ionic species by ion exchange resins, and relatively new techniques like reverse osmosis and atmospheric freezing. Potential applications of each of the techniques are discussed.