Interaction forces between bitumen and clay minerals in oil sands liberation process at different solution environments

Global oil sands resources are abundant, and their effective development can help alleviate the global petroleum shortage. However, fine clay minerals and metal cations significantly reduce the liberation efficiency of oil sands. To elucidate the mechanisms behind the difficulty in liberating bitumen, the chemical structures, microscopic morphologies, and elemental compositions of bitumen and clay minerals were systematically characterized, using Fourier-transform infrared spectroscopy, contact angle, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction methods. Additionally, the atomic force microscopy colloidal probe technology was employed to investigate the interaction forces between bitumen and typical clay minerals (silica, kaolinite, illite, and montmorillonite) at different solution environments. The results showed that the adhesion forces (≥14.3 nN) between clay minerals and bitumen were higher than that (7.9 nN) between silica and bitumen in distilled water. Furthermore, the presence of metal cations increased both adhesion forces and jump-out distances between the minerals and bitumen. Divalent cations, with their higher charge, had a greater impact on adhesion forces than monovalent cation due to stronger electrostatic interactions with negatively charged substrates. In particular, the interactions between montmorillonite and bitumen were most significantly affected by divalent cations, with adhesion force and jump-out distance reaching 44.6 nN and 80 nm in a 10 mM CaCl2 solution. The presence of fine clay minerals and metal cations led to bitumen surface coverage, reducing liberation efficiency. These findings provide insights into the mechanisms underlying the difficulty in liberating bitumen from oil sands, providing theoretical insights for efficient bitumen extraction from oil sand ores in industrial applications.