An investigation of the flotation minimum in the oleate flotation of hematite under alkaline conditions

Over the years there have been a number of instances describing a minimum in the flotation recovery of hematite in the alkaline pH region when oleate is used as the collector. These cases usually coincide with the use of a commercial oleate sample containing other fatty acids and/or salts as the collector. It is the purpose of this paper to provide experimental data involving the effects of pH on the flotation of a natural hematite sample using two collectors containing oleate and compare these data to changes in surface tension and bubble characteristics of aqueous oleate systems also as a function of pH. The main aim of this paper is to highlight and address this difference in hematite flotation behaviour with oleate solution characteristics and develop a better understanding of these interactions. It is proposed that this flotation minimum is associated with a reduction in both contact angle and bubble-particle flotation rate constant under these conditions, even though the surfactant solution chemistries would suggest that flotation should still be strong in this region.