Adsorption of hydrolyzable surfactants: effect of precipitation on adsorption of oleate on hematite

Abstract

Adsorption of surfactant at the solid-liquid interface plays a governing role in many separation techniques including the concentration of mineral values by flotation. Good correlation has been obtained between collector adsorption and flotation recovery in a number of mineral-surfactant systems. However, several investigators have not found this to be the case in the hematite-oleate system. We have shown that precipitation and complexation reactions in solution contribute significantly to oleate abstraction. When these are taken into account, pH-dependent adsorption density (under flotation conditions) does show the same trend as flotation recovery. Equilibrium abstraction and adsorption are examined and evidence for specific contribution from dissolved mineral species to surfactant depletion is found. Unexpectedly, a strong effect of S/L ratio on adsorption density has been identified indicating that measured precipitation is underestimated. A method of data handling is suggested to extract adsorption density from total depletion, eliminating the effect of the presence of the mineral bed. Adsorption density is found to be quite low, less than 1 % surface coverage. To explain the high hydrophobicity at such low adsorption, a mechanism involving two-point attachment is proposed.