Maintaining Permeability for Continuous Mature Fine Tailings Dewatering

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Oil sands tailings dewater extremely slowly once they form the so-called "mature fine tailings" (MFT). The accumulated MFT volume is over 800 million cubic meters and counting. Over the last few decades the industry has developed a number of dewatering techniques (composite tailings, thickened tailings, in-line thickening/thin lift, centrifugation, filtration) to speed up the solid-liquid separation of the oil sands tailings. However, the performance of treatment is generally unsatisfactory, and the tailings could not be dewatered beyond ~55 wt% solids by mechanical means, making the target of >=75 wt% solids (required for reclamation) seem un-achievable. Our recent results show that the difficulty of dewatering the oil sands tailings could be attributed to the residual bitumen in MFT rather than the small size of the fine solids in the tailings. Our results show that an aqueous slurry of 35 wt% fine kaolinite (d50 = 4 µm) could easily filter to ~70 wt% solids using 50 g/t polyacrylamide (PAM) under 6 bar pressure. However, after blending in 3 wt% of the residual bitumen, the kaolinite slurry could only be filtered to ~60 wt% solids at >1,500 g/t PAM, behaving like MFT. Based on these results, we ask the question: are the typically used PAM flocculants the best in dealing with the residual bitumen? In the proposed project, we will answer this question and identify appropriate binders to alleviate the detrimental effect of the residual bitumen. The research techniques will include: 1) jar tests to evaluate the interaction of potential bitumen binders with residual bitumen isolated from MFT; 2) isothermal titration calorimetric (ITC) study to investigate the binding strength between residual bitumen and bitumen binders, and between fine solids and bitumen binders; 3) filter press tests of the MFT after treatment by the bitumen binders to observe the dewatering effect and the achieved cake % solids content; 4) micro computed tomography and cryogenic scanning electron microscopy to study the pore structures of the filter cake after the treatment, and to investigate the reasons for the poor and improved dewatering performances.