Canadian indigenous researchers are extremely underrepresented in the field of chemical sciences, and so it is important that we as a community acknowledge some of the incredible work being done.
Chelsea Benally studies environmental chemical sciences and was the first indigenous woman to earn a PhD of engineering at the University of Alberta. Her work in chemical engineering focuses on using chemistry to treat the wastewater that is produced in the extraction of oil and natural gas from oil sands in Alberta.
Oil sand mining produces toxic wastewater that is released to local rivers in order for operations to continue, therefore, it is evident that finding a solution to treat these wastewaters before releasing them to the surrounding environment is imperative. Some of the compounds that contaminate these waters include naphthenic acids (NAs), polycyclic aromatic hydrocarbons (PAHs), and other organic species. Benally and her team are looking for sustainable methods to remove these contaminants from wastewater so it can be released to the environment without downstream complications.
Traditional methods to remove these compounds involve reactions such as the Fenton reaction; however, the conventional methods to this reaction have numerous limitations and drawbacks. Firstly, they require large volumes of peroxides such as H2O2 which pose both safety and stability issues. Next, they require a solution pH of around 3 when wastewaters are typically alkaline with a pH up to 9. And lastly, they require immense UV light presence, whereas ideal methods are capable of functioning under solar light. For these reasons, Benally et al. have turned to the photochemical reactions of ferricarboxlyate compounds to treat wastewaters.
The specific compound used was ferric citrate, which has been known to have a role in the photochemistry present in atmospheric and surface waters for almost 3 decades. It was proposed due to its presumed ability to function under alkaline pH and reactivity to solar light. What they found was that at a concentration of 0.2 g/L ferric citrate, PAHs were completely removed in wastewater treated with 1.5 hours of simulated solar light (Figure 1). Additionally, this occurred at a pH of 8.9 which is the native pH of these wastewaters.
Figure 1: Synchronous fluorescence spectra of wastewater treated by 0.2 g/L ferric citrate under different light exposure time. Three peaks are shown representing three different types of PAHs present in wastewater. All three PAHs were found to decrease under simulated solar light as time progressed.
Regarding the removal of NAs, they found that over 40% were degraded at a ferric citrate concentration of 0.3 g/L under simulated solar light for 1.5 hours. However, this is the degradation at pH 8.9, and as the solution pH is decreased the efficacy of NA removal is found to increase, reaching 100% degradation of NAs at pH 5 (Figure 2).
Figure 2: Degradation ratio of NAs in wastewater treated by 0.3 g/L ferrice citrate as a function of time exposed to a simulated solar light source.
Ultimately, Benally et al. have found an alternative to the traditional Fenton reaction where they can bypass many limitations and drawbacks by using ferric citrate. Using this method, scientists will be able to significantly reduce the percentage of contaminants in wastewater before releasing it back into the environment which is a step towards being more eco-friendly. While fossil fuel energy sources are by no means the future of sustainability, one cannot deny that they will continue to be present for years to come, and using techniques such as those proposed by Benally et al. will help significantly decrease the amount of toxic by-products released.
The finding of this work has been published in Chemical Engineering Journal: Zhijun, L.; Lingjun, M.; How, Z. T.; Chelme-Ayala, P.; Yang, L.; Benally, C.; El-Din, M. G. Treatment of oil sands process water by the ferric citrate under visible light irradiation. Chem. Eng. J. 2022, 429, 132419. https://doi.org/10.1016/j.cej.2021.132419
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