THE EFFECT OF SURFACE-POTENTIAL ON THE FLOTATION OF CHROMITE

The flotation of chromite from ''slime fraction'' of the gravity circu it of Kemi concentrator Finland was studied. The main gangue minerals are chlorite, tremolite and talc. Amines or fatty acid collectors are normally used for this sort of mineral composition. Theoretically, a s ufficient selectivity should be expected in the region where the surfa ce charge of chromite is opposite to that of the gangue minerals. The electrokinetic potential of the main components was determined as a fu nction of pH. The results showed that the region of selectivity lies a t a pH below three, where chromite is positively charged and the other components negatively. This suggest the use of an anionic collector. No selective region was found for chromite with negative surface charg e, excluding the use of amine collectors. Two commercial fatty acid co llectors, F2874 from Hoechst and AC825 from Cytec, were used in the ac tual flotation tests. Both are designed for low pH values. In an open circuit F2874 gave a concentrate around 95% of chromite with a recover y of 70%. The flotation was also found to favour the recovery of chrom ite particles with high chrome to iron ratio. The experiments showed a distinct abundance between the chromite surface charge and the select ivity as well as reversible adsorption-desorption behaviour. This conf irms the hypothesis of physical adsorption of fatty acids on chromite at low pH.