Ferrate (Fe(VI)) and Fe2+/peroxydisulfate (Fe2+/PDS) oxidation process are widely applied to treat a wide range of organic contaminants. However, only limited efforts were dedicated to understand the roles of reactive iron species, i.e., Fe(V)/Fe(IV). Using methyl phenyl sulfoxide (PMSO), carbamazepine, and caffeine as probe compounds, it was revealed that Fe(VI) was less reactive than what we expected and Fe(V)/Fe(IV) were the major active oxidants responsible for contaminants oxidation during Fe(VI) oxidation. In the Fe2+/peroxydisulfate (Fe2+/PDS) process, Fe(IV) and sulfate radical/hydroxyl radical were generated and the major oxidizing intermediate changed from Fe(IV) to sulfate radical/hydroxyl radical with an increase of the PDS/Fe(II) molar ratio at pH 3.0. Fe(IV), sulfate radical, and hydroxyl radical were all involved in this process at pH 3.0–6.5, but their available amounts that contributed to abating organic contaminants decreased with an increase in pH. Furthermore, Fe(IV), sulfate radical, and hydroxyl radical contributed differently to abating different organic contaminants because of the different reactivities of these oxidizing oxidants toward different organic contaminants. Compared to sulfate radical and hydroxyl radical, Fe(IV)/Fe(V) are more selective and have lower oxidation activity, but their steady-state concentrations are much greater. Therefore, the oxidation processes with Fe(IV)/Fe(V) as major oxidants have greater selectivity than the traditional advanced oxidation processes.

Generation and contributions of reactive iron species in ferrate (Fe(VI)) and Fe2+/peroxydisulfate oxidation processes

ACS Spring Meeting 2021

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