Bitumen spreading and formation of thin bitumen films at a water surface

Abstract

Bitumen spreading at gas bubble surfaces was observed through a stereoscopic microscope for Whiterocks oil sand samples submerged in alkaline solutions. This phenomenon was also observed for model systems where air bubbles were placed at the surface of a bitumen-coated quartz slide. Finally, the film pressure for bitumen films spreading at the aqueous phase surface was measured as a function of pH with the Wihelmy plate technique. It was found that a balance of interfacial tensions in all these systems favors spreading of the bitumen at the gas bubble surface because of a positive spreading coefficient. Filming occurs by the initial advancement of a thin film, the “bitumen film precursor”. This bitumen film precursor reduces the surface tension of the aqueous phase, and as a consequence, affects the driving force (spreading coefficient) for spreading. At room temperature, the gas bubble surface is covered by the bitumen film precursor during the first few seconds of contact between the phases. Subsequently, in a matter of minutes the bubble is enveloped by the bitumen film. Although thermodynamic conditions favor envelopment of the gas bubble by bitumen, several discontinuities in the thickness of the thin films (bitumen film precursors) were observed with a microscope. For oil sand systems, fine mineral particles with hydrophobic properties further complicate the spreading of bitumen over the gas bubble surface and promote the formation of bitumen islands.