Synergistic effect of water layer and divalent metal ions in a model oil sand on bitumen liberation from solids surface

In this work, we offer a direct evidence to illustrate the synergistic effect of water layer and divalent metal ions in oil sands on bitumen liberation from solids surface. A model oil sand was constructed by coating bitumen on the glass surface with a water layer containing divalent metal ions inserted between them. The bitumen liberation behaviors were investigated by placing the model oil sands in various pH solutions. It was found that the water layer facilitated the bitumen liberation, while the presence of Ca2+ or Mg2+ in the water layer played a different role on the bitumen liberation depending on the solution pH. It was believed that the variation of the bitumen liberation was attributed to the changes of surface wettability arising from the adsorption of natural surfactants on the solids and bitumen surfaces. The preferential adsorption of Ca2+ or Mg2+ on the solids and bitumen surfaces acted as either a barrier to disturb the cationic surfactants adsorbing or a bridge to anchor the anionic surfactants. The findings in this work are important for understanding the bitumen liberation behaviors and give a guideline of how controlling the water chemistry when processing the oil sands by water-based bitumen extraction processes.