Production and Application of Different Waste-derived Sustainable Materials for the Removal of Naphthenic Acids Related to Oil Sands Process Water
Creators: An, Zhexuan
Publisher: name: University of Alberta Library
Year: 2024

<p>Oil sands process water (OSPW) is generated in a large volume during the bitumen extraction process from the oil sands. Naphthenic acids (NAs) are recalcitrant compounds that contribute to the toxicity of OSPW, which need effective treatment before being released into the environment. In the meantime, various undervalued waste materials and by-products from industry are facing a continuous accumulation problem. This study applied different waste-derived materials and evaluated their potential for OSPW remediation, including petroleum coke to remove the acid extractable fraction (AEF) in real OSPW, and coarse sand tailing, peat mineral mix, and wood waste-based biochar, to remove or degrade model NAs. All the assessed results contribute as an essential insight for the further practical implementation of real OSPW remediation.<br>
Firstly, a large-scale field pilot study was conducted to examine the feasibility and effectiveness of residual waste petroleum coke (PC) as an adsorbent for OSPW treatment. The quality of treated OSPW was evaluated as a function of residence time in the PC deposit under natural climatic conditions. The results indicated the AEF adsorption by PC followed a pseudo-second order (PSO) kinetics with overall removal efficiency of over 80%. The dissolved organic carbon (DOC) decreased by about 50% after 4 weeks of retention in the PC deposit. In addition, treated OSPW exhibited no acute toxic response in the whole effluent toxicity testing. This field pilot study proved that PC adsorption is a potentially commercially viable technology for OSPW treatment.<br>
Secondly, the adsorption behavior of NAs on coarse sand tailings (CST) and peat-mineral mix (PMM) was assessed. Both CST and PMM are leftovers of oil sands industry operations in Alberta and are readily available at the mining site. In this study, mono-compound and mixture solutions of NAs were applied to evaluate the removal efficiency and adsorption performance. The adsorption of dodecanoic acid (DDA) on CST and PMM followed PSO kinetics and intra-particle diffusion (IPD) model. The isotherm of DDA adsorption was best fitted with the Freundlich model for both materials. At equilibrium, the adsorption capacity of PMM for DDA (2.4 mg/g) was higher than CST (0.05 mg/g). The competing adsorption of different NAs was observed in the mixture solution where NAs with longer chain structures showed more competition capacity. The predominant adsorption mechanism for NAs on CST and PMM was identified as hydrophobic interaction. PMM could be a potential alternative material for NAs removal due to the better performance of removing most of the NAs in 96 h from the mixture solution. <br>
Finally, biochar ZnO (BC/ZnO) composites were synthesized using wood waste with different ZnO content and applied under simulated solar light for the photocatalytic degradation of NAs. The best experimental conditions were determined as 0.5 g/L BC/30%ZnO and 4 h of solar irradiation time, achieving 93.7% degradation of cyclohexanecarboxylic acid (CHA) following a pseudo-first order (PFO) kinetics. BC, with a porous structure and roughened surface, acted as an excellent platform for ZnO particles, as well as an electron reservoir to inhibit the recombination of photogenerated electron-hole pairs. Hydroxyl radicals (•OH) were identified to play the dominant role in CHA degradation, and the enhanced photocatalytic performance of the BC/30%ZnO composite was proved by more •OH species detected by EPR measurements compared to synthesized ZnO (Syn-ZnO). The composite showed good reusability and stability after 4 successive cycles of use. Moreover, for the first time, BC/30%ZnO composite was applied for the simultaneous removal of a complex mixture of 8 NAs with significantly different chemical structures. A competition tendency was observed in which NAs with S atom, as well as large, branched, and cyclic NAs showed a better degradation performance, finally reaching a total NAs degradation efficiency of more than 95% after 6 h solar irradiation. The excellent performance of BC/ZnO composite under solar light, as well as its good reusability and stability, make the composite a sustainable approach for OSPW remediation.<br>
This research provides valuable insight into developing and applying eco-friendly and effective alternatives for OSPW remediation. At the same time, it enhances the understanding of different waste-derived materials and highlights the possible future applications. More importantly, the outcomes are essential contributions that can be meaningful guidance for pursuing sustainable development by promoting economically feasible waste material management and environmental remediation.</p>