Studies on bitumen-silica interaction in aqueous solutions by atomic force microscopy

The forces between spin-coated bitumen on a silica wafer and a silica particle in aqueous solutions were measured with an atomic force microscope. The effect of solution pH, salinity, divalent ion addition, and temperature on the interaction/adhesion forces was studied. The results showed that higher solution pH and temperature and lower salinity and calcium concentration resulted in a system of a stronger long-range repulsive force and a weaker adhesive force, which is favorable for bitumen detachment from the silica surface and the subsequent stabilization. The long-range interaction forces between bitumen and silica can be well described with the classical Derjaguin-Landau-Verwey-Overbeek theory, suggesting that the electrostatic forces play a dominant role in abitumen-silica colloidal system. The best-fitted Stern potentials of bitumen and silica were in excellent agreement with the corresponding zeta potential values measured independently using an electrophoresis technique. An additional repulsive force was observed at a relatively short separation. This additional repulsion can be attributed to a polymer-like steric force. The implication of the interaction forces measured by atomic force microscopy was confirmed by zeta potential distribution measurements. The quantitative description of bitumen/silica interaction provided fundamental insights into the bitumen extraction mechanism in a water-based system for bitumen extraction from oil sands and justified the industrial use of caustics.