Mechanism of collector adsorption in fluorite flotation

Fluorite is a strategically important mineral. Commercial deposits of fluorite are widespread throughout the world and its availability is essential to industry.1 The method of concentrating fluorite depends on the final application. Whereas a metallurgical-grade fluorite is obtained by gravity and magnetic separation methods, flotation is the major concentration process for the production of acid-grade fluorite. Selective flotation of fluorite from calcite presents many problems because the two minerals have the same cation, Ca++, in their crystal lattices. As a consequence of their similar physical and chemical surface properties anionic collectors float calcite alongside fluorite, and the depressants used for calcite also inhibit the flotation of fluorite. In the separation of fluorite from calcite by flotation various fatty acids (especially, oleic acid and sodium oleate), oleic acid emulsions with petroleum sulphonates, different mixtures of fatty acids, tall oils, alkyl amino-bis-methylene phosphoric acids, alkyl sulphonates, mixtures of oleic and naphtenic acids and amines are used as collectors. Various regulating agents, such as sodium silicate, sodium silicate–metal salt combinations, phosphates, tannic acid, quebracho, starches and sodium ligno-sulphonates, are used to depress calcite and to increase selectivity.2–5 The adsorption of collectors and depressants is largely controlled by the charge at the particle surface. The results produced by different investigations differ considerably and vary widely with minerals of different origin. The investigations reported here were undertaken with the aim of providing an electrophoretic and infrared spectroscopic characterization of fluorite and calcite as a basis for further flotation studies and for controlling the adsorption of electrolytes by exploiting differences in the surface charge.