Effect of divalent cations and surfactants on silica-bitumen interactions

In oil sands processing, the separation of bitumen from sand grains is controlled by interfacial interactions between the bitumen and the sand. In this study, the effects of calcium and magnesium cations, surfactants, and their combination on the sand- bitumen interactions and consequently on bitumen liberation were investigated. Surface forces between silica and bitumen in industrial- plant process water and in water containing calcium and magnesium in amounts equivalent to those found in the plant process water were directly measured using an atomic force microscope. Zeta potential measurements were carried out for silica, bitumen, and their mixture to study the coagulation behavior between silica and bitumen. It was found that divalent cations are detrimental to bitumen liberation from sand grains because they decrease the long- range repulsive force and increase the adhesion force between silica and bitumen. On the other hand, surfactants were found to facilitate bitumen liberation by reducing silica- bitumen adhesion.