Rate of Bitumen Film Transfer from a Quartz Surface to an Air Bubble as Observed by Optical Microscopy
The rate of bitumen transfer from a bitumen-coated quartz plate to a gas bubble surface in aqueous alkaline solutions was recorded photographically. During bitumen spreading, a bulk layer followed the formation of thin bitumen films (precursor films). The bulk layer spread at the bubble surface with a velocity of about one order of magnitude less than the velocity of the precursor film. The energy of activation for spreading of the bulk layer varied from about 66 to 123 kJ/mol depending on the stage of bitumen spreading but remained constant at about 105 kJ/mol for the precursor film. Results are discussed with respect to fundamental issues associated with flo t a t i o n r e c o v e ry of heavy oils.
Application of thermodynamics to the athabasca tar sands
Significant changes in the interfacial areas often accompany transformations in highly dispersed systems containing oil, water, solid and gas phases. When such changes in area are considered, interfacial tension expressions diametrically opposed to the conventional criteria for oil spreading or de-wetting may result. Further modifications in the energetics criteria are obtained when the electrical contributions to the free energy of the system (resulting from the adsorption of ionic surfactants) are included.
Flocculation properties of some water-soluble cationic copolymers toward silica suspensions: A semiquantitative interpretation of the role of molecular weight and cationicity through a “patchwork” model
Abstract Cationic polyelectrolytes of various molecular weights and cationicities were tested as flocculant of silica suspensions. We examined the sedimentation rate, the clarification and the height of the sedimented bed in connection with some operative conditions (stirring), some physicochemical measurements (adsorption isotherms, electrokinetic potential), and the characteristics of the flocculant ( M w , cationicity). The experimental results cannot be explained in classical terms of the interparticular bonding theory. But assuming that macromolecules in flocculation conditions are independently adsorbed, in a thin charged layer on the surface of particles (“patch” model) we first calculated the probability for two vicinal particles to be attractive and second, the mean value of attraction according to the various relative positions of the two facing particles. These two local effects are connected respectively with the efficiency of the clarification (turbidity of the supernatant) and the flocculation rates. Experimental data, especially the influence of flocculant molecular weight and cationicity on flocculation, agree with the proposed model.