Effect of Fe(II) as assistant depressant on flotation separation of scheelite from calcite

The preparation of high-grade schleelite concentrates from calcite containing ores despite significant research progress remains an important commercial challenge. In this study, Fe(II) was selected as an assistant depressant and combined with sodium silicate (SS) to improve the flotation separation of scheelite from calcite. Micro-flotation experiments of the individual minerals and artificially mixed minerals using oleic acid as a collector were conducted to evaluate the selective depression effect of the SS/Fe(II) depressant (the mixture of SS and Fe(II)). The results showed that the depressant mixture had a better selective depression effect on calcite than SS alone, and the optimum mass ratio of SS to ferrous sulphate was 4:1. Flotation tests using ore from a commercial mine showed that a concentrate with a WO3 grade of more than 62% and recovery greater than 89% could be achieved using SS/Fe(II) as the depressant. The depression mechanism of the SS/Fe(II) was investigated in detail using zeta potential measurements and X-ray photoelectron spectroscopy. The results showed that silicate species are more likely to adsorb on the surface of calcite and produce a selective depression effect. The improved depression effect could be attributed to the Fe(II), which not only increased the adsorption of the silicate species on the calcite surface, but also improved the formation of polymeric silicate species.