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

Abstract

The oxidation of thallium [Tl­(I)] to Tl­(III) by chlorine (HOCl) is an important process changing its removal performance in water treatment. However, the role of bromide (Br–), a common constituent in natural water, in the oxidation behavior of Tl­(I) during chlorination remains unknown. Our results demonstrated that Br– was cycled and acted as a catalyst to enhance the kinetics of Tl­(I) oxidation by HOCl over the pH range of 5.0–9.5. Different Tl­(I) species (i.e., Tl+ and TlOH­(aq)) and reactive bromine species (i.e., HOBr/BrO–, BrCl, Br2O, and BrOCl) were kinetically relevant to the enhanced oxidation of Tl­(I). The oxidation by free bromine species became the dominant pathway even at a low Br– level of 50 μg/L for a chlorine dose of 2 mg of Cl2/L. It was found that the reactions of Tl+/BrCl, Tl+/BrOCl, and TlOH­(aq)/HOBr dominated the kinetics of Tl­(I) oxidation at pH < 6.0, pH 6.0–8.0, and pH > 8.0, respectively. The species-specific rate constants for Tl+ reacting with individual bromine species were determined and decreased in the order: BrCl > Br2 > BrOCl > Br2O > HOBr. Overall, the presented results refine our knowledge regarding the species-specific reactivity of TI­(I) with bromine species and will be useful for further prediction of thallium mobility in chlorinated waters containing bromide.

Light- and H2O2-Mediated Redox Transformation of Thallium in Acidic Solutions Containing Iron: Kinetics and Mechanistic Insights

“…71 At higher pH values, however, hydrolysis accelerated the precipitation of Fe(III), 71 Although the reactivities of Tl(I) species (i.e, Tl + and TlOH (aq)) were different and may affect oxidation rates, Tl + was the predominant species over the examined pH range. 19 In addition, the pH effect on Fenton-like reactions was addressed by only adjusting the rate constants of reaction 9 while other reaction rate constants were held constant. As indicated by the sensitivity analysis (Text S8), reaction 9 plays the most important role among those reactions while ROS reactions have a negligible impact on the model fitting.…”

“…5,15−18 The existence of the two oxidation states allows Tl to undergo redox transformation, influencing its toxicity, reactivity, and mobility in natural waters. 11,16,19 Moreover, oxidation from Tl(I) to Tl(III) is also a critical process in water treatment since Tl is more readily removed as Tl(III) (hydr)oxides precipitate (log K sp = −45.2). 20 Therefore, a comprehensive understanding of Tl redox chemistry among species is critical for predicting both the geochemical speciation of Tl in natural aquatic systems and the removal potential in treatment processes.…”

“…As the most toxic regulated element in water, Tl is recognized to have a higher potential than lead (Pb), mercury (Hg), and arsenic (As) for causing chronic and acute poisoning in mammals. , Tl generally disperses at trace levels of <1 μg/L in nonpolluted natural waters . However, in waters affected by polluted sources of Tl, e.g., acidic mine drainages (AMDs), which are the primary sources for Tl emission into the environment, , elevated concentrations up to thousands of μg/L can be detected. , Tl mainly exists in thallous form (Tl­(I)) and thallic form (Tl­(III)). , Tl­(I) is predicted to predominate in the environment because it is more soluble, mobile, and thermodynamically stable than Tl­(III). , However, the transformation of Tl­(I) to Tl­(III) can occur due to some photochemical reactions , or microbiological activities, , resulting in considerable quantities of Tl­(III) over Tl­(I). ,− The existence of the two oxidation states allows Tl to undergo redox transformation, influencing its toxicity, reactivity, and mobility in natural waters. ,, Moreover, oxidation from Tl­(I) to Tl­(III) is also a critical process in water treatment since Tl is more readily removed as Tl­(III) (hydr)­oxides precipitate (log K sp = −45.2) . Therefore, a comprehensive understanding of Tl redox chemistry among species is critical for predicting both the geochemical speciation of Tl in natural aquatic systems and the removal potential in treatment processes.…”

Thallium accumulation and distribution in Silene latifolia (Caryophyllaceae) grown in hydroponics

“…Thallium (Tl) is one of the most toxic elements known to mankind (Lennartson 2015) and recently, it has been considered as an 'emerging pollutant' (Antoniadis et al 2019;Ma et al 2022;Wang et al 2021). Thallium toxicity is even greater than that of other well-known inorganic poisons such as arsenic (As), lead (Pb) and cadmium (Cd) (Liu et al 2020;Viraraghavan and Srinivasan 2011), and the element is listed as one of the US Environmental Protection Agency's 13 Priority Pollutants (Keith and Telliard 1979).…”

“…Thallium toxicity is even greater than that of other well-known inorganic poisons such as arsenic (As), lead (Pb) and cadmium (Cd) (Liu et al 2020;Viraraghavan and Srinivasan 2011), and the element is listed as one of the US Environmental Protection Agency's 13 Priority Pollutants (Keith and Telliard 1979). Thallium can exist in two different oxidation states (+ 1 and + 3), although in the environment thallous (+ 1) is predominant (Lennartson 2015;Ma et al 2022). Thallium toxicity in animals and humans is a consequence of its chemical similarity to K + (Mullins and Moore 1960).…”