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The long-term effect of Fe3O4 in activating persulfate to degrade refractory organic contaminants for groundwater remediation

Sa Xiao,Lina Zhang,Lian Zhou,Hua Zhong,Mark L Brusseau,Yan Li,Yake Wang,Guansheng Liu,Juntao Zhang

Highly reactive metal-based materials for persulfate activation have been intensively studied for treatment of groundwater contaminants. However, the long-term efficacy of the readily available metal-oxide additives, which can be more important for groundwater remediation practice, has received minimal attention. In this study, the results of preliminary experiments demonstrated that Fe 3 O 4 was superior to seven metal oxides (MnO, Fe 2 O 3 , MnO 2 , CuO, Cu 2 O, CoO, NiO) and zero-valent iron for activating persulfate to degrade 1,2-dichloropropane. Experiments were then conducted to examine the long-term effects of Fe 3 O 4 -activated persulfate degradation of four contaminants, i.e., 1,2-dichloropropane, 1,1,2-trichloroethane, 1,4-dioxane, and methyl tert -butyl ether (MTBE). The system achieved complete removal of the contaminants in approximately 72 h, which was contrasted to a removal efficiency less than 35 % in the absence of Fe 3 O 4 . Highly efficient use of persulfate for contaminant degradation was observed with insignificant production of soluble Fe before depletion of the contaminants. Production of sulfate radical (SO 4 •− ) and hydroxyl radical (HO • ) via surface reactions was likely the process responsible for the degradation. Ten and five cycles of 1,2-dichloropropane degradation experiments were conducted in deionized water and actual groundwater. These results suggested that the Fe 3 O 4 could retain 80 % of its original activation capacity after 5 cycles, but partial oxidation of Fe 3 O 4 eventually occurred. Production of some Cl-containing degradation-resistant intermediates from degradation of 1,2-DCP was observed and could be mitigated under specific conditions. The results show that Fe 3 O 4 has a long-term effect in activating persulfate for contaminant degradation, which is promising for applications such as permeable reactive barriers and nanoparticle injection for groundwater remediation.