Kinetics and Mechanistic Aspects of As(III) Oxidation by Aqueous Chlorine, Chloramines, and Ozone:  Relevance to Drinking Water Treatment

Abstract

Kinetics and mechanisms of As(III) oxidation by free available chlorine (FAC-the sum of HOCl and OCl-), ozone (O3), and monochloramine (NH2Cl) were investigated in buffered reagent solutions. Each reaction was found to be first order in oxidant and in As(III), with 1:1 stoichiometry. FAC-As(III) and O3-As(III) reactions were extremely fast, with pH-dependent, apparent second-order rate constants, k''app, of 2.6 (+/- 0.1) x 10(5) M(-1) s(-1) and 1.5 (+/- 0.1) x 10(6) M(-1) s(-1) at pH 7, whereas the NH2Cl-As(III) reaction was relatively slow (k''app = 4.3 (+/- 1.7) x 10(-1) M(-1) s(-1) at pH 7). Experiments conducted in real water samples spiked with 50 microg/L As(III) (6.7 x 10(-7) M) showed that a 0.1 mg/L Cl2 (1.4 x 10-6 M) dose as FAC was sufficient to achieve depletion of As(III) to <1 microg/L As(III) within 10 s of oxidant addition to waters containing negligible NH3 concentrations and DOC concentrations <2 mg-C/L. Even in a water containing 1 mg-N/L (7.1 x 10(-5) M) as NH3, >75% As(III) oxidation could be achieved within 10 s of dosing 1-2 mg/L Cl2 (1.4-2.8 x 10(-5) M) as FAC. As(III) residuals remaining in NH3-containing waters 10 s after dosing FAC were slowly oxidized (t1/2 > or = 4 h) in the presence of NH2Cl formed by the FAC-NH3 reaction. Ozonation was sufficient to yield >99% depletion of 50 microg/L As(III) within 10 s of dosing 0.25 mg/L O3 (5.2 x 10(-6) M) to real waters containing <2 mg-C/L of DOC, while 0.8 mg/L O3 (1.7 x 10(-5) M) was sufficientfor a water containing 5.4 mg-C/L of DOC. NH3 had negligible effect on the efficiency of As(III) oxidation by O3, due to the slow kinetics of the O3-NH3 reaction at circumneutral pH. Time-resolved measurements of As(III) loss during chlorination and ozonation of real waters were accurately modeled using the rate constants determined in this investigation.

A green approach towards simultaneous remediations of chromium(VI) and arsenic(III) in aqueous solution

“…As depicted in Fig. S2, an increase in the fractions of As(III) as H 2 AsO 3 À , HAsO 3 2À and AsO 3 3À was present at pH > 9.0, which were expected to be stronger nucleophiles than As(OH) 3 [27]. In this case, H 2 O 2 can be the primary reagent instead of Å OH for As(III) oxidation, whereas ionic As(III) species exerted negligible influence on As(V) formation at pH < 8.5, since fractions of these species are very small (<5 Â 10 À6 ).…”

Arsenic Chemistry

“…As discussed further in Chapter 7, As(III) oxidation in water may be enhanced with radiation (Hug et al, 2001), electrochemical methods (Arienzo et al, 2002;Licht and Yu, 2005; Maldonado-Reyes, Montero-Ocampo and Solorza-Feria, 2007), a variety of chemical oxidants (Hug and Leupin, 2003;Dodd et al, 2006), and/or bacteria (Ehrlich, 2002;Anderson et al, 2002;De, 2005), 684. Effective chemical oxidants for arsenic in water include: chlorine (Cl 2 ), ozone (O 3 ), sodium hypochlorite (NaOCl), chlorine dioxide (ClO 2 ), potassium permanganate (KMnO 4 ), iron(VI) compounds (such as K 2 FeO 4 ), and manganese (oxy)(hydr)oxides (Foster, 2003), 58; (Bissen and Frimmel, 2003;Licht and Yu, 2005;Dodd et al, 2006;Dutta et al, 2005), 1827; (Tournassat et al, 2002;Tani et al, 2004), 6618; (Manning et al, 2002;Clifford and Ghurye, 2002), 231; (Thirunavukkarasu et al, 2005). …”

Inorganic arsenic speciation by electroanalysis. From laboratory to field conditions: A mini-review

“…The following oxidants can be used: KMnO 4 , ozone, chlorine or hypochlorite [9,19 and refs. therein], where ozone is the fastest of those at pH > 8 [124]. Photochemical oxidation of acid samples also results in oxidation of all the forms of arsenic to As(V) [12,91,118,125,126].…”