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

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Kinetics of Thallium(I) Oxidation by Free Chlorine in Bromide-Containing Waters: Insights into the Reactivity with Bromine Species
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2021-11-22 , DOI: 10.1021/acs.est.1c06901
Chengxue Ma _{1,

2} , Haijun Cheng ₂ , Ruixing Huang ₂ , Yijie Zou ₁ , Qiang He ₁ , Xiaoliu Huangfu ₁ , Jun Ma ₂

Affiliation

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.

中文翻译：

含溴水中游离氯氧化铊 (I) 的动力学：对溴物质反应性的见解

氯 (HOCl) 将铊 [Tl(I)] 氧化为 Tl(III) 是改变其在水处理中去除性能的重要过程。然而，溴化物 (Br ^– ) 是天然水中的常见成分，在氯化过程中 Tl(I) 的氧化行为中的作用仍然未知。我们的结果表明，在 5.0-9.5 的 pH 范围内，Br ^{-被循环并充当催化剂以增强 HOCl 氧化 Tl(I) 的动力学。}不同的 Tl(I) 物质（即 Tl ⁺和 TlOH(aq)）和活性溴物质（即 HOBr/BrO ^-、BrCl、Br ₂ O 和 BrOCl）与 Tl(I) 的增强氧化具有动力学相关性. 即使在低 Br 条件下，游离溴物质的氧化也成为主要途径^-_{对于 2 mg Cl 2} /L的氯剂量，浓度为 50 μg/ L。发现 Tl ⁺ /BrCl、Tl ⁺ /BrOCl 和 TlOH(aq)/HOBr 的反应分别在 pH < 6.0、pH 6.0-8.0 和 pH > 8.0 时主导 Tl(I) 氧化的动力学。^{Tl +}与单个溴物种反应的物种特异性速率常数按以下顺序确定并降低：BrCl > Br ₂ > BrOCl > Br ₂ O > HOBr。总体而言，所呈现的结果完善了我们关于 TI(I) 与溴物种的物种特异性反应性的知识，并将有助于进一步预测铊在含溴化物的氯化水中的迁移率。

更新日期：2022-01-18

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