Fundamentals of secondary process aids in oil sands extraction
R Manica and BL Xiang and TZ Bai and MN Ashani and JQ Li and MD Li and ZQ Zhang and QX Liu, CANADIAN JOURNAL OF CHEMICAL ENGINEERING, 100, 2682-2706 (2022).
The application of sodium citrate (Na(3)Cit) as a secondary process aid (SPA) in combination with caustic (NaOH) was found to significantly improve the recovery and froth quality in oil sands extraction. Over the past several years, our group has been investigating the benefits of the combined application of Na(3)Cit and NaOH in oil sands extraction and the fundamental science involved. This review summarizes the recent developments and understandings based on experimental observations and theoretical analysis. Experimental techniques used to investigate different sub-steps and the fundamental science involved in bitumen extraction are also discussed. Both the ideal system and the process water system are considered. Generally, the results show that the combined addition of Na(3)Cit and NaOH has a synergistic effect on enhancing the bitumen recovery, especially benefitting the bitumen liberation and coalescence, and preventing slime coating. The key fundamentals behind those benefits are Na(3)Cit chelating with metal cations in the extraction system and adsorbing on different interfaces. Therefore, the more negative zeta potential of bitumen, silica, clay, and air bubble was observed. The increased electrostatic repulsion and reduced adhesion are the main reasons for Na(3)Cit enhancing bitumen liberation. Through de-activating the divalent cations in the bulk, Na(3)Cit eliminates slime coating and potentially helps bitumen droplets coalesce. Meanwhile, Na(3)Cit breaks asphaltene aggregates and lowers the interfacial tension of the bitumen/water interface by removing the metal-bridge between surfaces-active species contained in bitumen. The findings of this study provide a better understanding of the use of processing aids for the bitumen extraction process.
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