Impact of Peroxydisulfate in the Presence of Zero Valent Iron on the Oxidation of Cyclohexanoic Acid and Naphthenic Acids from Oil Sands Process-Affected Water

Large volumes of oil sands process-affected water (OSPW) are produced during the extraction of bitumen from oil sands in Alberta, Canada. The degradation of a model naphthenic acid, cyclohexanoic acid (CHA), and real naphthenic acids (NAs) from OSPW were investigated in the presence of peroxydisulfate (S₂O₈^2–) and zerovalent iron (ZVI). For the model compound CHA (50 mg/L), in the presence of ZVI and 500 mg/L S₂O₈^2–, the concentration decreased by 45% after 6 days of treatment at 20 °C, whereas at 40, 60, and 80 °C the concentration decreased by 20, 45 and 90%, respectively, after 2 h of treatment. The formation of chloro-CHA was observed during ZVI/S₂O₈^2– treatment of CHA in the presence of chloride. For OSPW NAs, in the presence of ZVI alone, a 50% removal of NAs was observed after 6 days of exposure at 20 °C. The addition of 100 mg/L S₂O₈^2– to the solution increased the removal of OSPW NAs from 50 to 90%. In absence of ZVI, a complete NAs removal from OSPW was observed in presence of 2000 mg/L S₂O₈^2– at 80 °C. The addition of ZVI increased the efficiency of NAs oxidation by S₂O₈^2– near room temperature. Thus, ZVI/S₂O₈^2– process was found to be a viable option for accelerating the degradation of NAs present in OSPW.