Flotation of phosphatic material containing carbonatic gangue using sodium oleate as collector and sodium silicate as modifier

Abstract

The effect of sodium silicate as a depressant for calcite is examined in the flotation of phosphatic material containing calcite and siliceous gangue using sodium oleate as collector. Maximum flotation of apatite occurs at pH 8, whereas the pH at which calcite floats best varies with particle size. At pH 8 and 9, sodium silicate depresses calcite to some extent beyond 1500 g/t (2·10 −3 M), and the depression is more pronounced at higher pH but the recovery of apatite is correspondingly low at these pH values. Selective action of silicate on calcite surfaces can be seen from the analysis of pulp liquid. However, for the pH range 7–11 and at any sodium silicate concentration, no significant selectivity between apatite and calcite is achieved. The influence of oleate concentration, pH and the concentration of sodium silicate on the flotation behaviour are discussed in detail.