Effect of Zn2+ and its addition sequence on flotation separation of scheelite from calcite using water glass

Flotation separation of scheelite from calcite remains a challenge because of the presence of Ca active sites on both mineral surfaces and of their similar physicochemical characteristics. In this study, the effect of Zn2+ and its addition sequence on flotation separation of scheelite from calcite was investigated via micro-flotation experiments, zeta potential measurements, solution chemistry calculations, and X-ray photoelectron spectroscopy (XPS) tests. The Zn-water glass (a mixture of Zn2+ and water glass) exhibits a better selective depression effect on calcite than the water glass alone but is much less sensitive to scheelite flotation. However, when Zn2+ is added prior to the water glass, both scheelite and calcite are significantly depressed. The superior selective depression effect of Zn-water glass arises from the selective adsorption of the Zn-silicate polymer and Si(OH)4 on the calcite surface, while the significant non-selective depression effect of Zn2+ added prior to the water glass is due to the adsorption of the hydrophilic Zn species on both scheelite and calcite surfaces.