Optimal floc structure for effective dewatering of polymer treated oil sands tailings

Abstract

Synthetic polymeric flocculants such as anionic polyacrylamides are widely used for dewatering mature fine tailings (MFT) generated from oil sands mining operations. Many studies have investigated the effects of polymer properties on dewatering efficiency. However, only a few studies have investigated the reasons for effective dewatering at optimum dosages from the perspective of understanding changes in the internal and external microstructure of the floc. In MFT, clay solids are dispersed in brine (along with trace amounts of bitumen) and are known to have a house-of-card like microstructural arrangement due to electrostatic stabilization. In this study, we investigated why there is maximum dewatering in the specific polyacrylamide (PAM) polymer-MFT system at optimum dosage. To understand this, we investigated the morphological changes in the house-ofcards microstructure in terms of porosity and floc density when flocculated at different polymer dosages as well as the corresponding floc strength, size, and re-flocculation tendencies. SEM imaging results showed that at the optimum dosage of 1000 ppm the internal floc microstructure had two different characteristic zones of reduced porosity and open channels, respectively, indicating that this arrangement could have led to an effective squeeze-out of water from the pores. Focused Beam Reflectance Microscopy results indicated that optimum dosage leads to effective dewatering due to flocs formed in the size range of 10–50 μm and 50–150 μm having reduced re-flocculation tendencies. Optimum dosage resulted in the least number of flocs and the reduction of flocs in the size range of 10–50 μm and < 10 μm was maximum while the corresponding increase of flocs in the size range of 50–150 μm was maximum as compared to other dosages. Additionally, the flocs at optimum dosage did not change in number for a given size range of flocs even after 1-hour stirring indicating strong floc formation. These observations are specific for the particular pairing and could form a basis for investigating other polymer-tailing systems.