Surface Chemistry Features in the Hot Water Processing of Utah Tar Sand

Abstract

The hot water processing of Utah tar sand involves two important steps in the process sequence, phase disengagement (digestion) and phase separation (flotation). Inasmuch as phase separation is accomplished by flotation, the hydrophobic/hydrophilic balance at the surface of the bitumen droplets was studied in conjunction with the system's solution chemistry and the results correlated with the flotation response. Contact angle measurements of solvent extracted bitumen revealed a moderate hydrophobic character; however, air bubble attachment at the surface of bitumen obtained from a hot water concentrate was difficult and required long induction times. These results suggest that the phase separation by flotation is dependent on air bubble entrapment by bitumen droplets rather than attachment due to surface hydrophobicity. In addition, identification of surface functional groups and components solubilized during hot water digestion was attempted using IR and NMR spectra. Strong absorption peaks at 1708 cm⁻¹, 2920 cm⁻¹, and 2855 cm⁻¹ for the solubilized components together with NMR spectra indicate the presence of dissolved paraffinic carboxylates, the amount of which increased as the digestion pH was increased. Potentiometric titration of the water soluble constituents indicated an acid dissociation constant of pK_a = 5 which would be expected for such carboxylate species. This phenomenon appears to account, in part, for the polar bitumen surface and the hydrophilic character of the digested bitumen. These and other results indicate that phase disengagement during digestion and bitumen hydrophobicity may be mutually exclusive effects and reinforce the notion that flotation separation is achieved by entrapment of air bubbles in the viscous bitumen droplets. Finally, the surface chemistry associated with phase disengagementhas been considered to alimited extent. It appears from preliminary experiments that phase disengagement by digestion involves the actual chemical attack of the silica surface layers by the hot alkaline solution which allows the release of the quartz particles from the bitumen phase.