Amylopectin-graft-hydrolyzed-poly(methyl acrylate) (AP-g-H-PMA) Flocculants for the Treatment of Oil Sands Tailings

Abstract

The extraction of bitumen from the Alberta oil sands reserves has long been a major economic contributor to the Canadian society, but the impact this industry has had on the environment has raised concerns worldwide. The main problems are how to reclaim the area and reduce the number of tailings ponds. A major obstacle is how to treat the stable suspensions of fine particles that constitute the mature fine tailings (MFT). Synthetic polymer flocculants commonly used in the industry are limited by their shear degradability and possible environmental impact. Natural polymers are more shear stable and ecofriendly, but they do not perform as well as synthetic polymers. This thesis explores the flocculation and dewatering performance of a family of natural amylopectin-graft-hydrolyzed-poly(methyl acrylate) (AP-g-H-PMA) flocculants on MFT. Free radical graft polymerization was used to chemically graft methyl acrylate chains to amylopectin backbones, followed by alkaline hydrolysis. Several grades of the graft copolymer, with different graft lengths and densities, were produced following a central composite design of experiments and tested on 10 wt.% MFT suspensions. The flocculants were characterized by Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (1H and 13C NMR), helium-ion microscopy (HiM), and thermogravimetric analysis (TGA). After hydrolysis, the products were again analyzed by FTIR and field flow fractionation (FFF). The synthesis parameters influencing graft length, graft density, and flocculant dosage affected the flocculation performance significantly. Generally, AP-g-H-PMA flocculants with longer and fewer grafts led to higher initial settling rates (ISR) and faster capillary suction times (CST), especially at high dosages, but produced supernatants with slightly higher turbidities. When optimum dosages were used, AP-g-H-PMA outperformed both of its homopolymers (AP and H-PMA), as well as a commercial anionic polyacrylamide (A-PAM).