Pipeline transport is commonly used in the oil sand industry to convey crushed oil sand ores and tailings. Bitumen residues in the oil sand tailings can be a threat to the environment that separating them from tailings before disposal is crucial. However, low bitumen concentration in the tailings slurry and the complex transport characteristics of the four-phase mixture make the process difficult. This study establishes an Eulerian-Eulerian CFD model for an industrial-scale oil sand tailings pipeline. A comprehensive sensitivity analysis was conducted on the selection of carrier-solid and solid-bitumen drag models. The combination of small and large particle sizes (i.e., 75 & 700 μm) and bitumen droplet size (i.e., 400 μm) provided good agreement with field data in velocity profiles and pressure drop. The validated model was subsequently extended to investigate the influence of the secondary phase (i.e., bitumen droplets and bubbles) on flow characteristics in a tailing pipeline. The investigation covered a range of bitumen droplet size (100-400 μm), bitumen fraction (0.0025-0.1), bubble size (5-1000 μm), and bubble fraction (0.0025-0.3) and their influences on the velocity, solids, and bitumen distribution are revealed. For an optimum bubble size of 500 μm, a maximum recovery of 59% from the top 50 % and 83 % from the top 75 % of the pipe cross-section was obtained. The present study demonstrates the preferential distribution of bitumen and provides valuable insight on bitumen recovery from an industrial-scale tailings pipeline.

Bitumen residues in oil sand tailings ponds create greenhouse gas emissions and threaten the ecosystem. However, it is technically challenging to recover bitumen residues from tailing slurries with high solid contents. This study investigates a novel concept of microbubble-enhanced bitumen recovery during hydrotransport in a laboratory-scale pipeline loop. Our results revealed that bubbles had a positive impact on bitumen recovery. Furthermore, bitumen recovery efficiency increases significantly when the temperature increases up to 52 °C. The recovery efficiency was even higher from the addition of CO 2 bubbles compared to air bubbles. The generation of microbubbles enabled the recovery of 61% bitumen from an extremely low initial fraction of 0.2 wt % at a solid content of 50 wt %. Our work demonstrated an effective combination of bubbles and operational conditions for separating bitumen effectively from highly concentrated tailings. The approach may be also valuable for reducing the environmental impact of other industrial waste slurries.

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Recent developments in ultrafine bubble generation have opened up new possibilities for applications in various fields. Herein, we investigated how substances in water affect the size distribution and stability of microbubbles generated by a common nanobubble generator. By combining light scattering techniques with optical microscopy and high-speed imaging, we were able to track the evolution of microbubbles over time during and after bubble generation. Our results showed that air injection generated a higher number of microbubbles (<10 μm) than CO2 injection. Increasing detergent concentration led to a rapid increase in the number of microbubbles generated by both air and CO2 injection and the intensity signal detected by dynamic light scattering (DLS) slightly increased. This suggested that surface-active molecules may inhibit the growth and coalescence of bubbles. In contrast, we found that salts (NaCl and Na2CO3) in water did not significantly affect the number or size distribution of bubbles. Interestingly, the presence of oil in water increased the intensity signal and we observed that the bubbles were coated with an oil layer. This may contribute to the stability of bubbles. Overall, our study sheds light on the effects of common impurities on bubble generation and provides insights for analyzing dispersed bubbles in bulk.

Removing bitumen from oil-sands tailings reduces greenhouse gas emission during waste disposal. However, it is technically challenging to efficiently recover bitumen residual in tailing slurries with high solid contents, due to the tiny fraction of bitumen and complicated composition in the tailings. This work focuses on microbubble-enhanced bitumen recovery in a flow of artificial tailings that consisted of 50 wt% solids, 0.2 wt% bitumen and 49.8 wt% process water. Using a laboratory\textendash scale transport pipeline loop, we show that several operation conditions had a positive impact on the efficiency of bitumen recovery, including bubble formation from intensified cavitation, the addition of gas integrated with cavitation, or increasing the temperature up to 52 C. The efficiency of bitumen recovery was even higher from the addition of CO_{2} bubbles compared to air bubbles. Under optimal conditions, more than 61 % bitumen was recovered from an extremely initial fraction of 0.2 wt% with the generation of microbubbles. This work provides guideline in finding an effective combination of operational conditions for bitumen separation from hydrotransported real tailings containing high solid content. The same approach may be also applicable for cleaning of oil contaminated slurries.