Utilization of Citric Acid to Improve the Depressive Efficiency of Sodium Silicate on the Flotation of Calcite and Fluorite

As a common depressant of calcite and fluorite, sodium silicate presents the disadvantages of large dosage and incomplete depression effect. Improving the depression effect of sodium silicate on calcite and fluorite, reducing the amount of sodium silicate in mineral processing is of great industrial and economic importance. In this manuscript, a novel reagent scheme is proposed that adding a small amount of citric acid (CA) can greatly improve the depression effect of sodium silicate on calcite and fluorite. The flotation results suggest that the CA concentration to be added is 4 × 10 −4 mol/L and the sodium silicate concentration is 5 × 10 −3 mol/L; the recoveries of calcite and fluorite reach 0.9% and 1.1%, suggesting the two minerals have been depressed, completely. Theoretical analysis results indicate that the addition of CA dissolves calcium ions of the calcite and fluorite surface and decreases the calcium activation sites on the mineral surface. Then, the addition of sodium silicate adsorbs on the remaining calcium sites on the calcite and fluorite surfaces, further preventing the collector adsorbed on the mineral surfaces. DFT calculation further proves the depression mechanism of mixed depressant that sodium silicate is easy to adsorb on the surface of calcite and fluorite surfaces, while citric acid is difficult to adsorb on the surface of calcite and fluorite surfaces.