Factors affecting the flotation recovery of molybdenite from porphyry copper ores

Investigations have been conducted to characterize the surface chemical and flotation properties of molybdenite in aqueous environments typical of those that exist in the copper circuits of plants which process porphyry copper ores. These investigations have revealed that molybdenite and quartz particles are negatively charged at the pH commonly used for bulk sulfide flotation, namely 11. While the adsorption of calcium ions reduces the magnitude of negative charge on molybdenite, the adsorption can reverse the surface charge on quartz particles when the calcium concentration in solution exceeds 1 × 10^-3 M. Heterocoagulation of molybdenite and quartz particles will thus be inevitable in solutions containing large amounts of lime and will impair the floatability of molybdenite. The deleterious effects of heterocoagulation can be somewhat overcome by an ultrasonic conditioning prior to flotation. Besides heterocoagulation, particle size is very critical for optimum molybdenite flotation. Coarse molybdenite particles (120 × 200 mesh) float extremely rapidly and completely without being influenced by heterocoagulation. The flotation of fine molybdenite particles (minus 200 mesh) is sensitive to particle size and heterocoagulation. Results of tests conducted to assess the effects of overgrinding of molybdenite have indicated that while there is no change in the crystal structure due to prolonged grinding, the floatability is significantly reduced due to the creation of very rough surfaces.