Recovery of Hydrocarbons From Froth Treatment Tailings of Oil Sand Bitumen Processing

Bitumen is separated from surface-mined oil sand ore in a warm water extraction process that produces bitumen froth typically containing 60 wt% bitumen, 30 wt% water, and 10 wt% mineral solids. The water and solids are then removed from the froth by solvent dilution followed by gravitational settling. If light alkanes are used as the solvent in the froth treatment process, some of the asphaltenes in the bitumen are precipitated and form aggregates with solids and water droplets. These aggregates quickly separate from the diluted bitumen phase leaving very clean diluted bitumen. After solvent recovery, the asphaltenes, water, and mineral solids are discharged as froth treatment tailings.

The asphaltenes contained in the tailings constitute valuable hydrocarbons that, if recovered, could be useable as coker feed or paving material. We conducted investigations of the feasibility of recovering asphaltenes from the tailings. Two methods were tested – solvent extraction and agglomeration. In solvent extraction, aromatic solvent is mixed with froth treatment tailings to dissolve the asphaltenes followed by centrifugation to remove the mineral solids and water. The experimental results demonstrated that more than 90% of the asphaltenes in the tailings can be recovered. The recovered asphaltenes contain only a small fraction of mineral solids and might be usable as coker feed. In agglomeration, the tailings are agitated at elevated temperature (80°C) causing the asphaltene particles to form large agglomerates that separate from the tailings to give an asphaltene-rich sediment phase and tailings that are almost asphaltene-free. The agglomerates still contain significant fractions of mineral solids and water and require further treatment.