Reverse flotation separation of talc from molybdenite without addition of depressant: Effect of surface oxidation by thermal pre-treatment

The excellent inherent floatability of talc and molybdenite makes them very difficult to be separated in the flotation process. To conquer the problem, for the first time, an attempt was made to separate molybdenite and talc by calcining the ores under the air condition before flotation separation. Micro-flotation test results showed that the natural floatability of molybdenite vanished after thermal pretreatment at above 400 °C. In contrast, for that of talc, it barely changes. A satisfying flotation separation effect of molybdenite and talc in either mixed minerals or molybdenite-talc bulk concentrate was achieved through the thermal pretreatment method. The results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis indicated that the surface of molybdenite underwent dramatical oxidation after thermal treatment at 400 °C. The formation of MoO3 and reduction in sulfur content on the surface of molybdenite were proposed to result in the poor floatability of molybdenite after thermal treatment.