Dewatering Oil Sands Tailings with Degradable Polymer Flocculants

We synthesized hydrolytically degradable cationic polymers by micellar radical polymerization of a short-chain polyester macromonomer, polycaprolactone choline iodide ester methacrylate (PCL₂ChMA) with two polyester units, and used them to flocculate oil sands mature fine tailings (MFT). We evaluated the flocculation performance of the homopolymer and copolymers with 30 mol % acrylamide (AM) by measuring initial settling rate (ISR), supernatant turbidity, and capillary suction time (CST) of the sediments. Flocculants made with trimethylaminoethyl methacrylate chloride (TMAEMC), the monomer corresponding to PCL_nChMA with <i>n</i> = 0, have improved performance over poly­(PCL₂ChMA) at equivalent loadings due to their higher charge density per gram of polymer. However, MFT sediments flocculated using the PCL₂ChMA-based polymers are easier to dewater (up to an 85% reduction in CST) after accelerated hydrolytic degradation of the polyester side chains. This study demonstrates the potential of designing cationic polymers that effectively flocculate oil sands tailings ponds, and also further dewater the resulting solids through polymer degradation

Structure Modifications of Hydrolytically-Degradable Polymer Flocculant for Improved Water Recovery from Mature Fine Tailings

Variants of the partially hydrolytically degradable cationic macromonomer polycaprolactone choline iodide ester methacrylate (PCL₂ChMA) have been synthesized to assess the effects of structure on the performance of the resulting polymers in the flocculation of mature fine tailings (MFT) that are a byproduct of bitumen extraction from oil sands. Neither the substitution of PCL with poly­(lactic acid) (PLA) units or replacement of the methacrylate functionality with acrylate greatly affected the ability of the resulting cationic flocculants to settle and separate the sediments in diluted MFT suspensions, as the synthesized polymers have similar structures and charge densities. The higher degradation rates of the PLA-based materials, however, led to faster compaction of the MFT sediment, as quantified by the amount of water released from the flocculated materials over time. Over 50% compaction was observed in MFT samples ranging between 2 and 20 wt % held for either 5 days at 50 °C or for 12 weeks at room temperature, whereas no significant amount of water was released from sediment flocculated with a comparable nondegradable cationic polymer or with high molecular-weight nonionic poly­(acrylamide). The results demonstrate the potential of these LA-based cationic degradable polymers for dewatering of oil sands MFT or other flocculated sediments