Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8850372 | Chemosphere | 2018 | 31 Pages |
Abstract
Naphthenic acids (NAs) are one of the constituents of concerns in oil sands process water (OSPW) because of their persistence and recalcitrance. Herein, we investigated the degradation of five model NA compounds by UV-activated persulfate (UV/persulfate) process under medium-pressure UV lamp irradiation at pH 8.0. UV/persulfate process showed higher degradation efficiency towards cyclohexanoic acid (CHA) compared to UV/H2O2 process under the same experimental conditions. CHA (0.39â¯mM) was completely removed within 30â¯min when 2â¯mM persulfate was used as oxidant, while more than 60â¯min were needed for the UV/H2O2 process. The removal of CHA decreased from 100% to 10% when 300â¯mM tert-butyl alcohol (TBA) was used as the scavenger, indicating that hydroxyl radical (OH) was responsible for the CHA degradation in the UV/persulfate process. Sulfate (SO4â) radicals reacted slowly with CHA in the UV/persulfate process with a second-order rate constant of kâ¯=â¯5.3â¯Ãâ¯107â¯Mâ1sâ1. Relative kinetics studies using binary mixtures of model NA compounds showed similar structure-reactivity to that under UV/H2O2 process. NAs with long carbon chain, cyclic ring, and aromatic ring were more reactive in the UV/persulfate process. The presence of high concentration of chloride ions dramatically inhibited the reaction. The OH radicals in the UV/persulfate process were generated by capturing OHâ in solutions, as evidenced by the decrease of the pH value from 8.0 to 2.8 before and after treatment, respectively, in a pure water matrix. Primary intermediate products (oxy-CHA, hydroxyl-CHA, and dihydroxyl-CHA) of UV/persulfate process were confirmed by UPLC-MS.
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Authors
Zhi Fang, Pamela Chelme-Ayala, Quan Shi, Chunming Xu, Mohamed Gamal El-Din,