Deep investigation on different effects of Cl in transformation of reactive species in Fe(II)/NHOH/PDS and Fe(II)/NHOH/HO systems.

Hydroxylamine (NHOH) has been verified to efficiently strengthen pollutants oxidation in Fe(II)/peroxydisulfate (PDS) and Fe(II)/HO systems. However, the different effects of hydroxylamine salts types were rarely recognized. Herein, the effects of two commonly used hydroxylamine salts (i.e. NHOH·HCl and (NHOH)·HSO) on oxidation kinetics and reactive species composition were compared in Fe(II)/PDS and Fe(II)/HO systems for the first time. Pseudo first order kinetics could only describe benzoic acid (BA) oxidation well in Fe(II)/NHOH/HO system, which was related to the different concentration changes of Fe(III) determined by [Formula: see text] . Hydroxylamine salts types influenced not kinetic rules, but reaction rates of target compounds. The empirical reaction rate constant of BA in Fe(II)/NHOH·HCl/PDS system was 141.5% of that in Fe(II)/(NHOH)·HSO/PDS system under the same concentration of NHOH (1.4 mM), while the apparent reaction rate constant in Fe(II)/NHOH·HCl/HO system was 68% of that in Fe(II)/(NHOH)·HSO/HO system. This opposite effect resulted from the differences in primary reactive species compositions and their interactions with Cl. Reactive species identification indicated that Cl would decrease the contribution of ferryl ion (Fe(IV)) and transform sulfate radical (SO) to hydroxyl radical (·OH) in Fe(II)/NHOH/PDS system, while it competitively consumed the only reactive species ·OH in Fe(II)/NHOH/HO system. This study highlights the importance of reductants types on strengthening Fenton oxidation and offers a reference for reasonable construction of the relevant systems.