(186d) Kinetics of PFAS Mineralization in Subcritical Water with Alkaline Additives

Despite their widespread use in diverse industrial and consumer products, perfluoroalkyl and polyfluoroalkyl substances (PFASs), including perfluorocarboxylic acids (PFCAs) and perfluorosulfonic acid (PASAs), present considerable health hazards. Conventional decomposition or removal techniques for PFASs, typically effective at low concentrations, struggle against high-concentration contaminant scenarios. Hydrothermal mineralization offers a promising avenue, characterized by faster reaction rates and enhanced recovery of halide ions in aqueous solutions. However, the literature is scant on its efficacy and the complete recovery of fluorine atoms/ions, with a detailed examination of its reaction kinetics across varied conditions have yet to be conducted.

This investigation focuses on the mineralization of PFCA and PFSAs with chain lengths from C4 to C10 in aqueous NaOH solutions under subcritical water conditions. Our results indicate that defluorination rates conform to second-order kinetics, influenced by the concentrations of both OH⁻ and the fluorinated entities. The length of carbon chains highly affects the defluorination rate and the longest carbon-chain PFCA perfluorodecanoic acid (C10) presented the lowest mineralization rate among all PFCA studied. Reaction mechanism consistent with the kinetic data was developed, revealing that the nucleophilic substitution reactions are likely the major PFAS mineralization pathways. Our findings contribute valuable insights into the mechanisms and kinetics of hydrothermal treatment, steering us toward more efficient solutions for the pressing issue of PFAS contamination in the environment.