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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.

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