Unraveling the interaction of hydroxylamine and Fe(III) in Fe(II)/Persulfate system: A kinetic and simulating study

Hydroxylamine showed an outstanding performance on enhancing the oxidation of pollutants in Fe(II) involved advanced oxidation processes, while the detailed reaction schemes have not been fully revealed. Specific functions of hydroxylamine in the oxidation of benzoic acid with Fe(II)/persulfate (PDS) system were explored. With the addition of hydroxylamine, degradation kinetics of benzoic acid deviated from both two-stage kinetics and pseudo first order kinetics, but could be interpreted well with binomial regression analysis. Degradation rate constant (k_obs) of benzoic acid was calculated and showed the same variation trend with [hydroxylamine][Fe(III)]²/([Fe(II)][H⁺])², the value of which was changed during reaction processes. A detailed kinetic model for simulating the degradation profile of benzoic acid with hydroxylamine acceleration was proposed for the first time and indicated that interactions of hydroxylamine and Fe(III) were fast equilibrium reactions, which was a dominant factor influencing the oxidation kinetics of benzoic acid in Fe(II)/hydroxylamine/PDS system. Comparative study showed that when 1.4 mM of ascorbic acid was added into Fe(II)/PDS system, degradation kinetics of benzoic acid was similar to that enhanced by hydroxylamine. However, when 0.6 mM or 1.0 mM of ascorbic acid was added, oxidation kinetics still presented as the two-stage profile. Kinetic simulations indicated that Fe(II) was produced slower from Fe(III)-ascorbic acid complexes than that with hydroxylamine, which caused the difference in oxidation kinetics. This study could improve our understanding about the effect of hydroxylamine and other reductants in promoting pollutants elimination in Fe(II)/PDS system.