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Abstract

Bitumen extraction processes in the oil sands involve interactions between minerals and bitumen. Aggregation can occur during hydrotransport as well as during the bitumen extraction processes. To counteract this and to promote the liberation of bitumen, several lignosulfonate polymers that may adsorb on the solids and improve dispersibility were investigated for their effect on the wettability of a bitumen surface, as the bitumen should remain hydrophobic and able to attach to air bubbles. Three lignosulfonates of differing chemical characteristics such as anionicity and molecular weight were tested at different concentrations and pH to determine their effect on the wettability of the bitumen surface. Lignosulfonate polymers are a byproduct of the wood pulp industry and were chosen due to their abundance, proven dispersant capability and non-toxic nature. Dynamic contact angle measurements using the captive bubble method were carried out on bitumen-coated slides. The initial contact angle as the air bubble touched the surface, the maximum contact angle reached with time, as well as the contact angle evolution rate were measured for each condition. For these three polymers, the hydrophobicity of the bitumen was only mildly reduced in that initial and maximum contact angles were not affected in a major way. Differences were found mainly by the rate at which an air bubble was able to thin and break the intervening water layer and advance across the surface of the bitumen. The level of anionicity combined with the molecular size were determined to be factors to consider. A smaller molecule which is able to more densely pack on the surface, combined with lower anionicity to minimize electrostatic repulsion between the polymer and the bitumen was determined to be a better choice of dispersant. The effects of ionic strength and calcium ions were also tested and found to not markedly influence the wettability in the concentration range tested.