title: Investigation of the impact of organic solvent type and solution pH on the extraction efficiency of naphthenic acids from oil sands process-affected water.
abstract: Naphthenic acids (NAs) from oil sand process-affected water (OSPW) were liquid-liquid extracted using six organic solvents (n-pentane, n-hexane, cyclohexane, dichloromethane, ethyl ether, and ethyl acetate) at three pHs (2.0, 8.5, and 12.0). The NAs exist in ionic (ions) and non-ionic (molecules) forms in the water phase depending on their dissociation constants and the solution pH. Results showed the extractability of NA molecules depends on the solvent polarity and the extractability of NA ions on the water solubility in solvent. The organic solvent type and solution pH were found to not only impact the extracted amounts of each NA species, but also the NAs distribution in terms of molecule carbon number and hydrogen deficiency. Overall, it is concluded that ethyl ether can be used as an alternative to dichloromethane (DCM) given their similar extraction efficiencies and extracted NA profiles. This is important since DCM is known to have metabolic toxicity and transitioning to the safer ethyl ether would eliminate laboratory DCM exposures and risk to human health. Despite the higher extraction efficiency of NAs at pH 2.0, extraction at pH 12.0 could be useful for targeted extraction of low-concentration nonpolar organic compounds in OSPW. This knowledge may assist in the determination of the specific NAs species that are known to have chronic, sub-chronic and acute toxicity to various organisms, and the potential targeting of treatment to these NAs species.
authors.affiliation: Department of Civil and Environmental Engineering, 7-285 Donadeo Innovation Centre for Engineering, University of Alberta, Edmonton, Alberta, T6G 1H9, Canada.
authors.forename: Rongfu
authors.initials: R
authors.lastname: Huang
authors.affiliation: Department of Civil and Geological Engineering, College of Engineering, University of Saskatchewan, Engineering Building, 57 Campus Dr., Saskatoon, SK, S7N 5A9, Canada.
authors.forename: Kerry N
authors.initials: KN
authors.lastname: McPhedran
authors.affiliation: Department of Civil and Environmental Engineering, 7-285 Donadeo Innovation Centre for Engineering, University of Alberta, Edmonton, Alberta, T6G 1H9, Canada.
authors.forename: Nian
authors.initials: N
authors.lastname: Sun
authors.affiliation: Department of Civil and Environmental Engineering, 7-285 Donadeo Innovation Centre for Engineering, University of Alberta, Edmonton, Alberta, T6G 1H9, Canada.
authors.forename: Pamela
authors.initials: P
authors.lastname: Chelme-Ayala
authors.affiliation: Department of Civil and Environmental Engineering, 7-285 Donadeo Innovation Centre for Engineering, University of Alberta, Edmonton, Alberta, T6G 1H9, Canada. Electronic address: mgamalel-din@ualberta.ca.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Gamal El-Din
mesh_terms: D002264:Carboxylic Acids / Q000302:isolation & purification*; D002853:Chromatography, Liquid; D006863:Hydrogen-Ion Concentration; D059625:Liquid-Liquid Extraction; D013058:Mass Spectrometry; D061329:Oil and Gas Fields / Q000737:chemistry*; D012996:Solutions; D012997:Solvents / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*
chemical_list: D002264:Carboxylic Acids; D012996:Solutions; D012997:Solvents; D014874:Water Pollutants, Chemical; C046170:naphthenic acid
keywords: Liquid–liquid extraction; Naphthenic acids; Oil sands process-affected water (OSPW); Ultra-performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOFMS)