Probing the Interaction Forces between Bitumen-Coated Mineral Surfaces with Implications for the Removal of Fine Solids from Oil Product: Effect of Solvent

Considerable amounts of fine solids retained in the bitumen product have been a significant challenge hindering the commercialization of nonaqueous extraction (NAE) of bitumen from oil sands. Understanding the surface interaction between bitumen-coated fine particles and the suspension stability in NAE bitumen products is essential for developing suitable solutions to remove these undesired particles. In this work, the adsorption behaviors of bitumen on a model clay surface (i.e., molecularly smooth mica surface) in organic solvents (i.e., cyclohexane and cyclohexane-heptane mixtures) were systematically investigated using a surface force apparatus (SFA). Furthermore, the interaction forces between bitumen-coated mica surfaces were directly measured in different organic solvents to reveal the stabilization mechanism of fine solids during the NAE process. It was found that the solvent type and adsorption time significantly affect the adsorption behavior of bitumen on mica surface and regulate the interaction forces between bitumen-coated mica surfaces, which in turn have an impact on the stability of suspended fine solids in solvents. In cyclohexane or cyclohexane-rich solution, a thin layer of bitumen (~5 nm) was quickly deposited on fresh mica surface within 5 minutes and gradually equilibrated to form a soft layer after a long process (>40 minutes). Only pure repulsive force due to steric repulsion was measured between the adsorbed layers, which led to a stable suspension of fine solids in solvents. In contrast, the presence of heptane caused the bitumen to rapidly (<20 minutes) form a compact packing adsorption layer, and a weak adhesive force (<5 mN/m) was measured between the bitumen-coated surface during the separation process. The adhesive force could be mainly brought by the interpenetration of long hydrocarbon chains or the conformation change of the organic network in both solution and substrate surface, which could lead to aggregation and settling of fine solids. Our SFA results provide valuable insights into the adsorption behavior of bitumen onto mineral surfaces and the interaction mechanism of bitumen-coated mineral surfaces in organic media, with important implications for the removal of fine solids from oil products.