Role of water chemistry in oil sands processing

Interaction forces between colloidal particles/droplets are central to the fundamental understanding of various processes involved in many disciplines such as biotechnology, pulp industry, and mineral processing. In this study, the role of water chemistry in oil sands processing was investigated from perspective of colloidal interactions of solid-bitumen and sand-clay.The stability of oil sand tailings against sedimentation and consolidation is, on the other hand, attributed to colloidal interactions of the mineral components, such as silica-clay interactions. In this study, the AFM colloidal probe method was used for the first time to quantitatively investigate anisotropic surface charge properties of mica, a 2:1 phyllosilicate. A surface element integration (SEI) method was used to extend DLVO calculations to account for the effect of surface roughness on the measured forces. This work explored how the anisotropic surface charge properties of the clay influence the silica-clay colloidal interactions in aqueous solutions, and determined the surface charge properties of both clay basal plane and edge surfaces directly from measured colloidal forces. A novel method was developed to prepare clay edge surfaces by a microtome cutting technique while the basal plane was obtained by cleavage. The direct force measurements verified the anisotropic surface charge properties of the basal plane and edge surfaces. The long-range forces between silica probe and mica basal plane were monotonically repulsive within pH range of 5.6-10. Through fitting the measured force profiles with the DLVO theory, the surface potentials of muscovite basal plane were determined to be pH insensitive over the pH range of 5.6-10. The fitted surface potentials showed a good agreement with values from the literature, thereby confirming that clay basal planes have permanent surface charge due to lattice cation substitution. In the case of edge surfaces, the forces were repulsive at pH 10, which decreased with decreasing pH, and changed to be attractive at pH 5.6, confirming that the charge of edge surface is pH-dependent. Considering the random roughness of the prepared edge surface, DLVO-SEI methodology was extended to the calculation of colloidal forces of rough surfaces. From the best fit of the measured force profile with the theory, the surface potentials of the muscovite edges were derived. The point of zero charge of the muscovite edge surface was estimated to be pH 7-8. This innovative study might open doors for more extensive studies of anisotropic clay surface properties for several scientific and engineering applications.The role of divalent cations (calcium and magnesium) and bicarbonate ions, which constitute the major inorganic chemical species of interest in industrial process water (PW) used in oil sands processing, i.e., in bitumen extraction, was studied. The impact of both natural surfactants and a model anionic surfactant SDS (sodium dodecyl sulfate), on bitumen-silica interactions in aqueous media in the context of bitumen recovery from oil sands was also investigated. Atomic force microscope (AFM) colloidal force measurements, zeta-potential distribution measurements, Denver cell flotation tests, as well as other complementary chemical and surface characterization techniques were used. The results showed that divalent cations increased sand-bitumen adhesion and slime coating, posing challenges to bitumen extraction. However, bicarbonate ions present in the industrial PW were demonstrated to be good process aids in buffering extraction slurry pH, precipitating calcium ions from the extraction PW, and decreasing solid-bitumen adhesion. The presence of natural surfactants or SDS could alleviate the negative impact of divalent cations on sand-bitumen interactions and thus facilitate bitumen liberation.