Studies on bitumen–silica interaction in surfactants and divalent cations solutions by atomic force microscopy

Abstract

Abstract Synergistic effects of surfactants and divalent metal ions on bitumen–silica interaction were investigated in various pH solutions by using atomic force microscope (AFM). Zeta potential measurements were carried out and the extended DLVO theory was employed to interpret the bitumen–silica interaction behaviors. The AFM force measurements showed that the presence of cationic surfactant of dodecyltrimethylammonium chloride (DTAC) caused a strong long-range attractive force and high adhesive force, which were considerably reduced as divalent metal ions of Ca2+ or Mg2+ added in the acid solutions. However, the long-range repulsive force changed to attractive force compounded with a relative high adhesion when both the anionic surfactant of sodium dodecylbenzene sulfonate (SDBS) and divalent metal ions of Ca2+ or Mg2+ presented in the alkaline solution. Mechanism on bitumen–silica interaction behaviors at various conditions was discussed. It was suggested that changes of surface wettability arising from the adsorption of surfactants on silica and bitumen surfaces were responsible for the variation of the bitumen–silica interactions. The preferential adsorption of the divalent metal ions of Ca2+ or Mg2+ on silica and bitumen surfaces acted as either a barrier to prevent the cationic surfactants from adsorbing or a bridge to anchor the anionic surfactants. The generation of the hydrophobic attraction between bitumen and silica was supported by the extended DLVO theory. It is believed that the findings in this work have a guideline of controlling the oilsands processing condition to obtain a high bitumen recovery and good froth quality.