Thallium(I) Oxidation by Permanganate and Chlorine: Kinetics and Manganese Dioxide Catalysis

Abstract

The oxidation of the toxic heavy metal thallium­(I) (Tl­(I)) is an efficient way to enhance Tl removal from water and wastewater. However, few studies have focused on the kinetics of Tl­(I) oxidation in water, especially at environmentally relevant pH values. Therefore, the kinetics and mechanisms of Tl­(I) oxidation by the common agents KMnO4 and HOCl under environmentally relevant pH condition were explored in the present study. The results indicated that the pH-dependent oxidation of Tl­(I) by KMnO4 exhibited second-order kinetics under alkaline conditions (pH 8–10) with the main active species being TlOH, while the reaction could be characterized by autocatalysis at pH 4–6, and Mn­(III) might also play an essential role in the MnO2 catalysis. Furthermore, a two-electron transfer mechanism under alkaline conditions was preliminarily proposed by using linear free energy relationships and X-ray photoelectron spectroscopy (XPS) analysis. Distinctively, the reaction rate of Tl­(I) oxidation by HOCl decreased with increasing pH, and protonated chlorine might be the main active species. Moreover, the Tl­(I)-HOCl reaction could be regarded as first order with respect to Tl­(I), but the order with respect to HOCl was variable. Significant catalysis by MnO2 could also be observed in the oxidation of Tl­(I) by HOCl, mainly due to the vacancies on MnO2 as active sites for sorbing Tl. This study elucidates the oxidation characteristics of thallium and establishes a theoretical foundation for the oxidation processes in thallium removal.

Kinetics of Thallium(I) Oxidation by Free Chlorine in Bromide-Containing Waters: Insights into the Reactivity with Bromine Species

“…For kinetics experiments of Tl­(I) oxidation by HOCl under the influence of Br – , 30 μM (6 mg/L) Tl­(I) and Br – at desirable concentrations (0–50 μM/0–4 mg/L) were simultaneously spiked into solutions containing 5 mM (262 mg/L) HOCl at t = 0 to start the reactions. Aliquots of each sample (1.0 mL) were periodically withdrawn at specific time intervals and then quenched in a DMSO solution for Tl­(III) production measurement using an ABTS method . All reactions proceeded with constant magnetic stirring.…”

“…Our previous study indicates that the oxidation rate constants during chlorination decreased with increasing pH . Apart from solution pH, Tl­(I) speciation could also affect Tl­(I) oxidation kinetics due to the different reactivities of Tl + and TlOH­(aq) . Tl + is the predominant Tl­(I) species and the TlOH­(aq) dominance shift occurs at pH 13.2…”

“…Because Tl­(III) is less mobile and more easily separated from aqueous solutions in the form of (hydr)­oxide precipitates, − the oxidation of Tl­(I) to Tl­(III) is considered as a practical way for Tl removal in water and wastewater (WW) treatment . Tl­(I) oxidation to form Tl­(III) needs strong oxidizing conditions, ,− and chlorine (HOCl) was able to efficiently oxidize Tl­(I) over a wide pH range. ,, The oxidation kinetics of Tl­(I) by HOCl was highly dependent on solution pH. Our previous study indicates that the oxidation rate constants during chlorination decreased with increasing pH .…”

“…Tl­(I) oxidation to form Tl­(III) needs strong oxidizing conditions, ,− and chlorine (HOCl) was able to efficiently oxidize Tl­(I) over a wide pH range. ,, The oxidation kinetics of Tl­(I) by HOCl was highly dependent on solution pH. Our previous study indicates that the oxidation rate constants during chlorination decreased with increasing pH . Apart from solution pH, Tl­(I) speciation could also affect Tl­(I) oxidation kinetics due to the different reactivities of Tl + and TlOH­(aq) .…”

Oxidation process and kinetics of bromothymol blue by alkaline permanganate

“…By adding the requisite amount of reagent powder to doubly distilled water, a stock solution of BTB was formed 32, 33 . A stock solution of KMnO 4 (BDH) as described elsewhere was prepared, stored, and standardized 34–36 . All other reagents were of analytical grade, and their solutions were prepared by dissolving in doubly distilled water 37–39 .…”