Role of Caustic Addition in Bitumen-Clay Interactions

Coating of bitumen by clays, known as slime coating, is detrimental to bitumen recovery from oil sands using the warm slurry extraction process. Sodium hydroxide (caustic) is added to the extraction process to balance many competing processing challenges, which include undesirable slime coating. The current research aims at understanding the role of caustic addition in controlling interactions of bitumen with various types of model clays. The interaction potential was studied by quartz crystal microbalance with dissipation monitoring (QCM-D). After confirming the slime coating potential of montmorillonite clays on bitumen in the presence of calcium ions, the interaction of kaolinite and illite with bitumen was studied. To represent more closely the industrial applications, tailings water from bitumen extraction tests at different caustic dosage was used. At caustic dosage up to 0.5 wt % oil sands ore, a negligible coating of kaolinite on the bitumen was determined. However, at a lower level of caustic addition, illite was shown to attach to the bitumen, with the interaction potential decreasing with increasing caustic dosage. Increasing concentration of humic acids as a result of increasing caustic dosage was identified to limit the interaction potential of illite with bitumen. This fundamental study clearly shows that the critical role of caustics in modulating interactions of clays with bitumen depends upon the type of clays, guiding the multi-billion dollar oil sands industry to identify clay type as a key operational variable.