THE ROLE OF POLYOXYETHYLENE ALKYL ETHERS IN APATITE FLOTATION AT FOSKOR, PHALABORWA (SOUTH-AFRICA)

Batch flotation tests were conducted on a foskorite ore to elucidate t he role of polyoxyethylene alkyl ethers (PAE) in the fatty acid (FA) f lotation recovery of apatite at Foskor, Phalaborwa. Only those PAE wit h a narrow distribution of relatively short oxyethylene chain lengths are effective in promoting apatite recoveries. Adsorption and microflo tation studies were conducted on apatite and calcite (gangue mineral) with PAE, FA, and depressants to further elucidate the role of PAE in the flotation process. It is proposed that PAE and FA form a mixed mic elle in solution, 'protecting' the FA from 'hard water' ions in soluti on. More PAE are adsorbed on apatite than on calcite, causing less dep ressant to be co-adsorbed on apatite. For PAE with longer oxyethylene chain lengths, their higher adsorption levels on apatite prevent parti cle-bubble contact, due to strong repulsive hydration forces associate d with the predominance of oxyethylene head groups on the mineral surf ace. This favours the flotation of calcite where less PAE are adsorbed . For PAE with shorter oxyethylene chain lengths, the depressant effec t is less pronounced, and the floatability of apatite is enhanced due to the absorption of more FA and less depressant than on calcite.