Thermoresponsive Starch for the Flocculation of Oil Sands Mature Fine Tailings.

The reclamation of land and recovery of water from tailing ponds created during bitumen extraction from oil sands is a major technical and environmental challenge. In the current study, thermoresponsive hydroxybutylated (HB) corn starch (HB-CS) and potato starch (HB-PS), with lower critical solution temperatures (LCSTs) ranging from 36 to 45 °C, were examined as flocculants for oil sands mature fine tailings (MFT). The ability of different doses of the HB-CS and HB-PS to flocculate 2 and 10 wt % MFT, prepared by diluting 35 wt % MFT in tap water, in terms of the initial settling rate (ISR), supernatant turbidity (ST), sediment solids content (SSC), and water recovery (WR), was examined at temperatures below and above their LCSTs. The thermoresponsive HB-CS and HB-PS were good flocculants of MFT, and their thermoresponsive behavior was essential for optimal results in that they were considerably more effective in several aspects at temperatures above their LCSTs than below. In terms of ISRs, the HB-PS was a considerably better flocculant than the HB-CS, and this was especially so with the 10 wt % MFT. With the HB-PS, the ISR was lower when using diluted MFT prepared with tap water as opposed to simulated oil sands process water.

Thermoresponsive hydroxybutylated starch nanoparticles.

Starch nanoparticles (SNPs) have been explored as promising new environmentally friendly materials for over a decade. On the other hand, thermoresponsive SNPs, which have potential novel applications in medicine, food and composites, have not yet been reported. Here we report the preparation and characterization of thermoresponsive SNPs. Hydroxypropyl (HP) and hydroxybutyl (HB) starch nanoparticles (SNPs) were prepared with molar substitution (MS) values of 0.90-2.10 and 0.48-1.85 respectively, and examined for thermoresponsivity in water. None of the HPSNPs were thermoresponsive up to 70 °C. HBSNPs having MS values of 1.29-1.85 were thermoresponsive with cloud point (Tc) values ranging from 33 to 52 °C. The Tc decreased with increasing MS. The Tc did not change significantly between concentrations from 5 to 50 g/L though from 5-0.5 g/L, the transmittance curves were broader and the Tc increased by 2.2 °C. The hydrodynamic diameter (Dh) of the HBSNPs increased significantly at temperatures above their Tc as determined by dynamic light scattering. The presence of kosmotropic salts decreased the Tc while NaI, a chaotropic salt, increased the Tc. In general, Tc values decreased in alcohol-water mixtures in comparison to water alone. The ability of the alcohols to cause a decrease in the Tc increased with increasing hydrophobicity of the alcohols.