Kinetics of Oxidation of Arsenite by Various Manganese Dioxides

Abstract

Three Mn dioxides—birnessite, cryptomelane, and pyrolusite—were examined for their ability to deplete the concentration of As(III), a highly toxic pollutant, in solution. The depletion [oxidation of As(III) to As(V) and sorption of As(III)] of As(III) by all three Mn dioxides follows first‐order kinetics. The rate constants for the depletion of As(III) by birnessite and cryptomelane at 298 K are 0.267 and 0.189 h−1, respectively. On the other hand, the depletion rate of As(III) by pyrolusite is much slower: the rate constant at 298 K is 0.44 × 10−3 h−1. This difference in the rate of depletion is largely attributed to the crystallinity and specific surfaces of the Mn dioxides. Pyrolusite is highly ordered and has a low specific surface of 0.8 hm2/kg (7.9 m2/g); conversely, birnessite and cryptomelane are poorly crystalline and have relatively high specific surfaces of 27.7 and 34.6 hm2/kg (277 and 346 m2/g), respectively. The energies of activation for the depletion of As(III) by the Mn dioxides range from 26.0 to 32.3 kJ/mol. The reaction appears to be predominantly diffusion‐controlled. The ability of the Mn dioxides to sorb As(III) and As(V) appears to be related to the specific surface and the point‐of‐zero charge of the oxides. The data indicate that, after the systems have reached equilibrium with respect to the sorption of total As, the depletion of As(III) by the oxides is still progressing. This is apparently because of the one‐to‐one relationship between the amount of As(III) depleted and the amount of As(V) appearing in solution.

Effect of soil microorganisms on arsenite oxidation in paddy soils under oxic conditions

“…Mn oxides are common soil minerals with a high capacity to oxidize heavy metals and metalloids including As(III) (Post 1999). The effective oxidation of As (III) by synthetic Mn oxides such as birnessite (δ-MnO 2 ) has been reported (Oscarson et al 1981(Oscarson et al , 1983. However, 4…”

“…Although As(III) specifically adsorbs to iron (hydr)oxides (Dixit and Hering 2003), it is generally accepted that ferric iron [Fe(III)] in soils does not oxidize As(III) significantly. Manganese oxide minerals (Mn oxides) are another important minerals, since they readily oxidize As(III) to As(V) (Oscarson et al 1983). Although Mnoxides are effective oxidants, the rate of As(III) oxidation decreases with time due to blocking of surface reactive sites by reaction products such as As(V), Mn(II) and possibly Mn(III) (Lafferty et al 2010a(Lafferty et al , 2010b.…”

Arsenic(III) Oxidation and Arsenic(V) Adsorption Reactions on Synthetic Birnessite

“…This investigation was designed to link the findings of previous work (18)(19)(20)(21) with new information derived from EXAFS spectroscopy.…”

Arsenic(III) Remediation from Contaminated Water by Oxidation and Fe/Al Co-Precipitation

“…Oscarson et al [27] found that the oxidation of As(III) by birnessite, cryptomelane, and pyrolusite obeyed the first-order rate law with the rate constants at 298 K being 0.267, 0.189 and 0.44 × 10…”

“…However, Chen and Fang [28] reported that the oxidation rate of As(III) by MnO 2 was rapid initially followed by a firstorder kinetics with respect to As(III) concentration. The activation energies for the oxidation reaction by the MnO 2 were measured to be in the range 26.0 -32.3 kJ/mol [27]. The oxidation process was reported to be limited by diffusion of the reactant As(III) to or the reaction products away from the surface [27][28][29].…”