Impact of fugitive bitumen on polymer-based flocculation of mature fine tailings

In bitumen recovery from oil sands, a percentage of the bitumen is lost to tailings. The effect of fugitive bitumen on fines settling and consolidation in tailings ponds remains controversial. In the current study, the settling performance of mature fine tailings (MFT) in response to flocculant addition was considered by studying MFT of varying bitumen content. Bitumen content in the MFT was adjusted by controlled removal of bitumen using a Denver flotation cell. The initial settling rate of flocculated MFT was observed to increase with decreasing bitumen content from 0.45 to 0.18wt%. A further reduction in bitumen content was found to dramatically decrease the settling rate of flocculated MFT. Such behaviour seems counterintuitive since the polymer flocculant was found to have a greater affinity for 'clean' surfaces (Al2O3) than for bitumen contaminated surfaces, as measured by quartz crystal microbalance with dissipation (QCM-D), which would predict a further increase in settling rate of flocculated MFT with decreasing bitumen content. The reduction in settling rate below a critical bitumen content is thought to result from selective removal of hydrophobic solids, since washing of untreated MFT with toluene is shown to significantly improve settling of flocculated solids. The current study confirms the use of flotation as a viable option to control MFT bitumen content and improve the settling rate of flocculated MFT.