Effect of grinding media-chalcopyrite interaction on the self-induced flotation of chalcopyrite

Abstract

US Bureau of Mines research to understand the surface chemical mechanisms of flotation showed that galvanic interactions between grinding media and chalcopyrite influence the self-induced floatability of chalcopyrite in simulated process water. Galvanic interactions were characterized by several electrochemical techniques, including rest potential, combination potential, and polarization measurements. Chalcopyrite floatability was similar from a synthetic chalcopyrite-quartz mixture and a natural ore, and floatability was dependent on the electrochemical conditions in grinding, conditioning, and flotation stages. Nitrogen-purged and open-to-air atmospheres in grinding, conditioning, and flotation were investigated for chalcopyrite ground with high-carbon and stainless-steel media. For grinding with high carbon steel in a nitrogen-purged atmosphere, low grinding solution pH was detrimental to chalcopyrite recovery at constant flotation pH. As grinding solution pH was increased, chalcopyrite floatability was enhanced as a result of lower galvanic interaction during grinding in higher pH solution. Electrochemical measurements substantiated that high-carbon steel was passivated at higher pH. When the mineral was ground with high-carbon steel in the presence of air, chalcopyrite flotation was not significantly affected by grinding solution pH. This was consistent with chalcopyrite and high-carbon steel electrochemical polarization measurements which were not significantly affected by pH changes in the presence of air. Stainless steel was more easily passivated than high-carbon steel, and chalcopyrite floatability was significantly higher after air or nitrogen-purged grinding with stainless-steel media. Increased chalcopyrite floatability was observed with more positive flotation pulp potentials. For given grinding conditions, the type of flotation gas had a strong effect on recovery, and flotation with air yielded higher chalcopyrite recovery than flotation with nitrogen. For the natural ore, chalcopyrite was depressed while molybdenite was floated with nitrogen, and chalcopyrite was subsequently recovered by flotation with air.