Eawag, Swiss Federal Institute of Aquatic Science and Technology , Ueberlandstrasse 133, CH-8600 Duebendorf, Switzerland.
Environ Sci Technol. 2014 May 6;48(9):5154-62. doi: 10.1021/es500804g. Epub 2014 Apr 21.
Reactions of ferrate(VI) during water treatment generate perferryl(V) or ferryl(IV) as primary intermediates. To better understand the fate of perferryl(V) or ferryl(IV) during ferrate(VI) oxidation, this study investigates the kinetics, products, and mechanisms for the reaction of ferrate(VI) with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) and self-decay of ferrate(VI) in phosphate-buffered solutions. The oxidation of ABTS by ferrate(VI) via a one-electron transfer process produces ABTS(•+) and perferryl(V) (k = 1.2 × 10(6) M(-1) s(-1) at pH 7). The perferryl(V) mainly self-decays into H2O2 and Fe(III) in acidic solution while with increasing pH the reaction of perferryl(V) with H2O2 can compete with the perferryl(V) self-decay and produces Fe(III) and O2 as final products. The ferrate(VI) self-decay generates ferryl(IV) and H2O2 via a two-electron transfer with the initial step being rate-limiting (k = 26 M(-1) s(-1) at pH 7). Ferryl(IV) reacts with H2O2 generating Fe(II) and O2 and Fe(II) is oxidized by ferrate(VI) producing Fe(III) and perferryl(V) (k = ∼10(7) M(-1) s(-1)). Due to these facile transformations of reactive ferrate(VI), perferryl(V), and ferryl(IV) to the much less reactive Fe(III), H2O2, or O2, the observed oxidation capacity of ferrate(VI) is typically much lower than expected from theoretical considerations (i.e., three or four electron equivalents per ferrate(VI)). This should be considered for optimizing water treatment processes using ferrate(VI).
高铁酸盐（VI）在水处理过程中的反应会生成过铁（V）或高铁（IV）作为主要的中间产物。为了更好地了解高铁酸盐（VI）氧化过程中过铁（V）或高铁（IV）的命运，本研究考察了高铁酸盐（VI）与 2,2'-偶氮-双（3-乙基苯并噻唑啉-6-磺酸）（ABTS）的反应动力学、产物和机制，以及高铁酸盐（VI）在磷酸盐缓冲溶液中的自衰变。高铁酸盐（VI）通过单电子转移过程氧化 ABTS 生成 ABTS（•+）和过铁（V）（在 pH 7 时，k = 1.2×10(6) M(-1) s(-1)）。在酸性溶液中，过铁（V）主要通过自衰变生成 H2O2 和 Fe（III），而随着 pH 的增加，过铁（V）与 H2O2 的反应可以与过铁（V）的自衰变竞争，并产生 Fe（III）和 O2 作为最终产物。高铁酸盐（VI）自衰变通过两电子转移生成高铁（IV）和 H2O2，初始步骤是限速步骤（在 pH 7 时，k = 26 M(-1) s(-1)）。高铁（IV）与 H2O2 反应生成 Fe（II）和 O2，而 Fe（II）被高铁酸盐（VI）氧化生成 Fe（III）和过铁（V）（k = ∼10(7) M(-1) s(-1)）。由于这些反应性高铁酸盐（VI）、过铁（V）和高铁（IV）向反应性较低的 Fe（III）、H2O2 或 O2 的转化非常容易，因此观察到的高铁酸盐（VI）的氧化能力通常远低于理论预期（即，每摩尔高铁酸盐（VI）三或四个电子当量）。在使用高铁酸盐（VI）优化水处理工艺时，应考虑这一点。
