Long chain alkyl pyridinium salts have been used as collectors for the flotation of chalcopyrite and copper-activated sphalerite. For the ores tested in this study, these reagents have demonstrated improved selectivity and recovery in comparison to conventional xanthates. The best flotation results, in terms of both grade and recovery, were achieved with cetyl pyridinium chloride (CpCl). A distinct advantage of using CpCl instead of a conventional xanthate, such as sodium isopropyl xanthate (NaIpX), is that the kinetics of flotation are much faster. This may be explained by the reduction in the negative ζ-potential of the sulfide mineral upon adsorption of cetyl pyridinium ions, which, in turn, minimizes the electrostatic component of the disjoining pressure of the wetting film. CpCl has also demonstrated a remarkable selectivity despite the fact that both chalcopyrite and the silicious gangue minerals present in the ore are negatively charged. This may be explained by the premise that cetyl pyridinium ions adsorb more strongly on chalcopyrite than on the gangue. Analysis of the adsorption isotherms established for chalcopyrite and quartz supports this view. Several possible mechanisms have been suggested to explain the 'high affinity' type of adsorption observed in the CpCl-chalcopyrite system. / Master of Science