Nonthermoresponsive and Thermoresponsive Cationic Starch for the Flocculation of Oil Sands Mature Fine Tailings

The mature fine tailings (MFT) in the massive tailing ponds created during bitumen extraction from oil sands must be dewatered before the land and water can be reclaimed. Here, we report the first studies employing cationic starch as a flocculant of MFT. Two types of cationic starch were examined: nonthermoresponsive cationic starches containing 2-hydroxypropyltrimethylammonium groups with molar substitutions of 0.02 (Cat0.02-St) and 0.2 (Cat0.2-St) and a thermoresponsive cationic starch containing both 2hydroxypropyltrimethylammonium groups and hydroxybutyl groups with molar substitutions of 0.02 and 2.0, respectively (Cat0.02-HB2.0St). These biopolymers were evaluated for their ability to flocculate 2 and 10 wt % MFT, in tap water and oil sands process water (OSPW), in terms of initial settling rate (ISR), supernatant turbidity (ST), sediment solids content (SSC), and water recovery (WR). All of the modified starches were capable of flocculating 2 wt % MFT in OSPW and tap water, though the ISR values were higher when using OSPW. Cat0.02-HB2.0-St exhibited higher ISR values than Cat0.02-St, was particularly effective when employed at a temperature (SO degrees C) above its lower critical solution temperature (LCST), in contrast to Cat0.02-St did not exhibit overdosing over the dose range examined, and had a very broad flocculation window. Cat0.02-St was unable to flocculate 10 wt % MFT at the highest dose tested (10 000 ppm), while in OSPW, 10 000 ppm of Cat0.2St was a good flocculant with an ISR of 17.1 m/h and an ST of 19 nephelometric turbidity units (NTU). With 10 wt % MFT in OSPW at 50 degrees C, 10 000 ppm of Cat0.02-HB2.0-St was very effective with an ISR of 34.9 m/h, an ST of 47 NTU, and an SSC of 64 wt % obtained after centrifugation of the flocculation sediment. At 50 degrees C, 10 000 ppm of Cat0.02-HB2.0-St did not perform as well as 1000 ppm of Magnafloc 1011, a commercial anionic polyacrylamide, in terms of ISR and WR but provided a cleaner supernatant and a higher final solids content after centrifugation of the flocculation sediment.