Role of hydrophobic solids in the stability of oil sands fine tailings

Abstract

Hydrophobic solids are known to occur in the fine tailings produced during bitumen extraction at both the Syncrude and Suncor oil sands plants. Removal of these solids, and associated residual bitumen, produces changed settling behaviour and subsequent dewatering of the remaining tailings. In this work a fractionation scheme has been developed that allows this hydrophobic component to be separated selectively from fine tailings. Two types of particulate solids, both having considerably higher organic carbon contents than the bulk tailings solids, have been identified. In one fraction the solids are completely hydrophobic (HPS), whereas the particles in the other fraction exhibit intermediate wetting characteristics (BWS). Each fraction represents ∼ 1.5–2 wt% of the total tailings. The solids have been characterized by particle size distribution, XPS and elemental, including heavy metal, analyses. Both fractions are capable of forming a flocculated structure by an agglomeration process involving residual bitumen and naphtha in amounts typically found in tailings ponds. Measurement of the change in sediment volume for the agglomerated fractions has been used to investigate this process. Results for both fractions show a significant increase in the final sediment volume after agglomeration. The increase in sediment volume implies the formation of a flocculated structure. Such a structure could enhance tailings stability by reinforcing the ultrafine solids gel network also present in tailings.