SURFACE AND INTERFACIAL-TENSION OF THE WHITEROCKS BITUMEN AND ITS RELATIONSHIP TO BITUMEN RELEASE FROM TAR SANDS DURING HOT-WATER PROCESSING

The surface tension of bitumen recovered from Whiterocks tar sand was determined to be 23.6 m Nm-1 at 20-degrees-C and 20.5 m Nm-1 at 60-degrees-C using the Wilhelmy plate technique. The effect of aqueous phase composition on interfacial tension was examined. In the case of pH variation, a maximum interfacial tension of 11-15 m Nm-1 was obtained between pH = 4.8 and pH = 8.7. Increasing the concentration of sodium tripolyphosphate to 0.05 M at pH = 9 lowered the interfacial tension to gamma(BW) < 2 m Nm-1. Samples of the Whiterocks tar sand were immersed in alkaline solutions (pH = 8.0-11.5) and mechanisms of bitumen separation from mineral grains were observed through a microscope. It was observed that the bitumen release from tar sand may be stimulated by a change in the bitumen-water (BW) interfacial tension as can be accomplished by varying the concentration of hydrogen ions and/or sodium tripolyphosphate. Thus, in addition to bitumen viscosity considerations, interfacial tension plays an important role in the hot water processing of tar sands. Effective separation of bitumen from Whiterocks bitumen in hot water experiments was obtained for the bitumen-water interfacial tension of less than 2-3 m Nm-1, although satisfactory bitumen recovery was still observed for larger interfacial tensions, up to about 7 m Nm-1.