The role of polyoxyethylene alkyl ethers in apatite flotation at foskor, phalaborwa (South Africa)

Abstract

Batch flotation tests were conducted on a foskorite ore to elucidate the role of polyoxyethylene alkyl ethers (PAE) in the fatty acid (FA) flotation recovery of apatite at Foskor, Phalaborwa. Only those PAE with a narrow distribution of relatively short oxyethylene chain lengths are effective in promoting apatite recoveries. Adsorption and microflotation 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 micelle in solution, ‘protecting’ the FA from ‘hard water’ ions in solution. More PAE are adsorbed on apatite than on calcite, causing less depressant to be co-adsorbed on apatite. For PAE with longer oxyethylene chain lengths, their higher adsorption levels of apatite prevent particle-bubble contact, due to strong repulsive hydration forces associated with the predominance of oxyethylene head groups on the mineral surface. This favours the flotation of calcite where less PAE are adsorbed. For PAE with shorter oxyethylene chain lengths, the depressant effect is less pronounced, and the floatability of apatite is enhanced due to the absorption of more FA and less depressant than on calcite.