A novel secondary process aid (SPA), sodium citrate (NaCit), recently has been applied in oil sand extraction industries. It was discovered that adding sodium citrate as a secondary process aid with sodium hydroxide (NaOH) enhanced the bitumen recovery of both good and poor processing ores. In this study, we investigated the synergetic effect of sodium citrate and sodium hydroxide on the bitumen liberation. A quartz crystal microbalance with dissipation (QCM-D) was applied to estimate the bitumen liberation from the silica surface in the presence of NaOH only, NaCit only, and their mixture (1:1 molar ratio). It was observed that the degree of bitumen liberation (DBL) increased when the concentration of chemical aids increased. More importantly, the combination of NaCit with NaOH showed the highest DBL. The colloidal interactions between bitumen and silica measured with an atomic force microscope (AFM) indicated that adding NaCit into the solution reduced the adhesive force between bitumen and silica. Meanwhile, the adhesive forces became negligible with addition of NaOH and the 1:1 mixture of NaOH and NaCit. Zeta potential results indicated that the combined addition of NaOH and NaCit led to a more negatively charged surface of both bitumen and silica. A stronger repulsive force between bitumen and silica surfaces resulted in a weaker adhesion between bitumen and silica, leading to the efficient detachment of bitumen from silica surfaces, which in turn increased the degree of bitumen liberation. The possible mechanism of the synergistic effect of NaOH and NaCit on modifying the surface properties of bitumen and silica is elucidated in this study.

The detachment of bitumen from sand grains in oil sands processing is known as bitumen liberation. In this study, a quartz crystal microbalance with dissipation (QCM-D) was applied to study the bitumen liberation process under various process conditions. Bitumen was coated on the surface of silica sensors to simulate the oil sands ore. By recording the change of frequency and dissipation of the coated sensor, QCM-D allows for a real-time quantitative analysis of the bitumen detachment process. The effects of solid wettability, solution pH, and operation temperature on bitumen liberation were investigated using QCM-D. The effects of different solution pH values and temperatures on bitumen liberation were conducted with untreated hydrophilic silica sensors. It was found that the degree of bitumen liberation (DBL) was improved from 32 to 98% when the solution pH was increased from 7.8 to 11, indicating the importance of solution pH in the water-based bitumen extraction process. An increasing temperature enhanced not only the degree of bitumen liberation but also the rate of bitumen detachment. The DBL from a hydrophobic silica surface was about 1.2% at pH 11.5 and 22 °C, which is much lower than the hydrophilic silica surface. QCM-D is a powerful tool in studying the bitumen liberation from both hydrophobic and hydrophilic surfaces.

The dynamic displacement of heavy oil from solid surfaces by water plays a significant role in the oil recovery process. In this work, a bitumen–water–quartz system was applied to study the effect of sodium citrate (Na3Cit) and calcium ions (Ca2+) on the dynamic displacement of bitumen from quartz surfaces. It was found that the addition of Ca2+ slowed down the bitumen displacement rate and generated daughter droplets during the receding process. In contrast, the presence of Na3Cit not only accelerated the displacement of bitumen from quartz surfaces but also led to a smaller water contact angle at the end of the experiments. Moreover, Ca2+ ions were chelated by the added Na3Cit, which counterbalanced the detrimental effect of Ca2+ on the bitumen displacement. The reduced interfacial tension of the bitumen–water interface and the increased negative charges on both bitumen and silica surfaces by Na3Cit were considered as the reasons for the improved bitumen displacement process. To better understand the underlying physics, both the hydrodynamic (HD) model and the molecular kinetic (MK) model were employed to analyze the dewetting dynamics of heavy oil from quartz surfaces under the effect of Ca2+ and Na3Cit.

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