Electrochemical characteristics of pyrrhotite and its implication to flotation

The difficulties in the flotation separation of complex sulfide ores are well known, but the principles behind the complex behaviors of polysulfide ores are still not well understood. The copper-nickel Duluth gabbro is a prime example of such a complex ore. These ores must be ground to fine sizes for efficient liberation which require long grinding time and thereby not only accelerate the galvanic interactions between sulfide minerals and grinding media, but also accelerate the galvanic interactions between different sulfide minerals themselves. These electrochemical interactions significantly affect the flotation behaviors of sulfide minerals. It is important, therefore, to develop a comprehensive mechanism for better understanding of galvanic interactions that are expected to occur in the processing of complex sulfide ores.; Pyrrhotite is commonly associated with nickel, copper, and platinum. Its electrochemical characteristics and flotation response strongly influence the recoveries of both the base metals and platinum group metals (PGM). In this investigation, the mechanism of cathodic decomposition reactions on pyrrhotite was studied by using cyclic voltammetry, surface analysis and ac impedance techniques. The electrochemical reactions, the reaction products and the pyrrhotite/solution interface were characterized. A series of micro-flotation tests was performed for correlating the electrochemical data with the flotabilities of pyrrhotite. The kinetic parameters of electrochemical reactions occurring on pyrrhotite surface were determined, and compared with those on chalcopyrite surface for correlation with their flotation behaviors.; The cathodic decomposition reactions occurring on pyrrhotite were shown to be more complex than those on chalcopyrite. The surface alterations resulted through both oxidation and reduction reactions significantly affected the flotation separation of complex sulfide ores. Such a mechanism may be useful for interpreting the flotation behaviors of sulfide minerals in general. The potential applications of this study are to the effective separation of copper-nickel ores, the maximizing PGM recoveries, and the minimizing the environmental impact from residual sulfides in flotation tailings.