Impact of calcium and gypsum on separation of scheelite from fluorite using sodium silicate as depressant

The impact of calcium and gypsum on separation of scheelite from fluorite using sodium silicate as depressant was investigated by micro-flotation tests, X-ray photoelectron spectroscopy (XPS), zeta potential measurements and solution chemical analysis. The flotation results confirmed that sodium silicate exhibited certain selective inhibition on fluorite. According to the XPS results, silicate could adsorb on fluorite surface, but not on scheeltie in DI water. When treated in calcium solution and gypsum saturated solution, silicate could adsorb on both mineral surfaces. Zeta potential results showed that sodium silicate could shift the fluorite zeta potential obviously, while reduce the scheelite zeta potential a little in DI water. The similar change law of scheelite and fluorite zeta potential could be obtained in the presence of calcium ion, which was mainly contributed to the adsorption of calcium silicate formed in solution. The presence of calcium ion in solution would decrease the selectivity of sodium silicate, and obviously inhibit the floatability of scheelite and fluorite. The inhibition exists varying degrees of difference in gypsum saturated solution.