The effect of switchable additives on colloidal interactions found in oil sands as measured by chemical force spectrometry

Abstract

After oil sands separations, settling of clays from aqueous tailings can be promoted by additives such as Ca2+ salts. However, if the liberated water is then recycled, these same additives in the water interfere with bitumen recovery in the separator. Therefore, we have tested CO2-triggered switchable additives to see whether they can switch back and forth between a form that is suitable for the separation stage and a form that promotes tailings ponds settling. CO2-triggered switchable additives can reversibly change water chemistry merely by introduction and removal of CO2, a benign trigger. Here, the effects of CO2-mediated switchable additives on colloidal interactions found in model oil sands were studied by chemical force spectrometry. Self-assembled monolayers of 12-phenyldodecanethiol and 12-mercaptododecanoic acid were used to chemically modify gold-coated atomic force microscope tips. These were subsequently used to study the adhesion force between the modified tips and the minerals silica and mica. The adhesion between the tips and the mineral substrates was studied in aqueous solutions of varying pH and divalent cation concentration and in the presence of cationic switchable additives of varying surfactant potency, both in the presence and in the absence of CO2. In the presence of CO2, the best additive promotes attractive forces, while in the absence of CO2, the forces are repulsive. These results are discussed in the context of the mechanism of colloidal interactions in an oil sands system.