Understanding the stabilization mechanism of bitumen-coated fine solids in organic media from non-aqueous extraction of oil sands

Abstract

Considerable amounts of fine solids retained in the bitumen product have been a challenging issue impeding the industrial application of the non-aqueous extraction (NAE) of oil sands ore. The undesired stable suspension of bitumen-coated fine solids in the bitumen-solvent mixture is generally considered as the origin of solid migration to the NAE bitumen. In this work, two advanced nanomechanical techniques, i.e., colloidal probe atomic force microscope (AFM) and quartz crystal microbalance with dissipation (QCM-D), were utilized to unravel the stabilization mechanism of fine silica solids in organic solvents, including cyclohexane, heptane and the mixed solvents. The adsorbed bitumen layer on the silica surfaces exhibited a swelling behavior in cyclohexane-rich solvent, giving rise to strong repulsion between the fine silica solids. Addition of heptane to the organic media could notably weaken the inter-particle repulsion by causing the shrink and collapse of bitumen layer. The degree of adsorption of bitumen layer on the silica surfaces could be significantly enhanced by slightly decreasing volume fraction of cyclohexane (φc) in the mixed solvents but could be inversely inhibited as φc was smaller than the asphaltene precipitation onset. The stability of bitumen-coated silica solids in organic solvent was also examined via sedimentation tests. It was found that the settling efficiency could be markedly enhanced by decreasing φc in surrounding solvent. Our results provide useful insights into the stabilization mechanism of fine solids in NAE bitumen, with important implications for developing effective and economical strategies of removing fine solids from the NAE bitumen product.