Oil sands tailings are the wastewater streams from heavy oil extraction processes in Canada. They are concentrated alkaline suspensions of fine clays (&gt; 30wt. %), water, and residual bitumen, that experience almost no sedimentation by gravity even after decades. Oil sands tailing ponds have already contaminated an area about 3 times the size of Manhattan, posing a serious environmental hazard in Canada. Making the problem worse, the unique physicochemical properties of oil sands tailings impede the efficient use of conventional polyacrylamide flocculants.<br/><br/>A possible solution is to tailor the properties of alternative polymer flocculants to optimize the flocculation and dewatering of these wastewater streams, such as copolymers of acrylamide and cationic diallyl dimethyl ammonium chloride. Using polymer reaction engineering tools and statistical design of experiments, we quantified the joint effect of copolymer average molecular weight and chemical composition on the treatment of industrial oil sands tailings samples by measuring their settling rate, supernatant turbidity, capillary suction time, and specific resistance to filtration. We also studied the impact of the width of the copolymer chemical composition distribution, caused by composition drift during free radical copolymerization in batch reactors.<br/><br/>Our results suggest that it is not possible to find a single flocculant microstructure optimize the criteria set out by all treatment metrics. The settling rate of the aggregates are influenced by both molecular weight and chemical composition averages, while dewatering, as measured by capillary suction time and filtration, are not a significantly influenced by the flocculant molecular weight. Moreover, we hypothesize that these conclusions are not unique to oil sands tailings, but may also apply to polymer flocculants used in wastewater treatment, paper making, or mineral processing.

Impact of polymer microstructure on flocculation and dewatering performance: Case of Canadian oil sands tailings

2019 Fall National Meeting

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