Oxidation of Cr(III)-Fe(III) Mixed-Phase Hydroxides by Chlorine: Implications on the Control of Hexavalent Chromium in Drinking Water.
Oxidation of Cr(III)-Fe(III) Mixed-Phase Hydroxides by Chlorine: Implications on the Control of Hexavalent Chromium in Drinking Water.
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DOI：
10.1021/acs.est.7b06013
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发表时间：
2018-07-17
影响因子：
11.4
通讯作者：
Liu H
中科院分区：
文献类型：
--
作者：
Chebeir M;Liu H
铬（Cr）作为一种无机污染物在饮用水中的存在被广泛报道。Cr的一个来源是其作为Cr（III）-Fe（III）氢氧化物，即FexCr（1-x）（OH）3（s），在饮用水分配系统的含铁腐蚀垢中的积累，其中x表示Fe（III）摩尔含量，通常在0.25和0.75之间变化。本研究探讨了饮用水中作为残留消毒剂的氯氧化FexCr（1-x）（OH）3（s）无意中生成六价铬Cr（VI）的动力学，并研究了Fe（III）含量和饮用水化学参数（包括pH、溴化物和碳酸氢盐）对Cr（VI）生成速率的影响。数据表明，在Fe（III）的摩尔含量的增加导致化学计量的Cr（VI）的产量和Cr（VI）的形成率显着下降，主要是由于氯衰变引起的Fe（III）的表面网站。碳酸氢盐的增加提高了Cr（VI）形成的速率，这可能是由于Fe（III）-碳酸根表面络合物的形成减缓了与氯的清除反应。溴离子的存在显著加速了氯对FexCr（1-x）（OH）3（s）的氧化，这是由于溴离子作为电子穿梭的催化作用。较高的溶液pH值在6和8.5之间减缓了氯对Cr（III）的氧化。这些研究结果表明，含铬的铁腐蚀产物在饮用水分配系统中的氧化转化可以导致在水龙头处发生Cr（VI），并且丰富的铁，以及仔细控制pH值、碳酸氢盐和溴化物水平可以辅助控制Cr（VI）的形成。
The occurrence of chromium (Cr) as an inorganic contaminant in drinking water is widely reported. One source of Cr is its accumulation in iron-containing corrosion scales of drinking water distribution systems as Cr(III)–Fe(III) hydroxide, that is, FexCr(1–x)(OH)3(s), where x represents the Fe(III) molar content and typically varies between 0.25 and 0.75. This study investigated the kinetics of inadvertent hexavalent chromium Cr(VI) formation via the oxidation of FexCr(1–x)(OH)3(s) by chlorine as a residual disinfectant in drinking water, and examined the impacts of Fe(III) content and drinking water chemical parameters including pH, bromide and bicarbonate on the rate of Cr(VI) formation. Data showed that an increase in Fe(III) molar content resulted in a significant decrease in the stoichiometric Cr(VI) yield and the rate of Cr(VI) formation, mainly due to chlorine decay induced by Fe(III) surface sites. An increase in bicarbonate enhanced the rate of Cr(VI) formation, likely due to the formation of Fe(III)-carbonato surface complexes that slowed down the scavenging reaction with chlorine. The presence of bromide significantly accelerated the oxidation of FexCr(1–x)(OH)3(s) by chlorine, resulting from the catalytic effect of bromide acting as an electron shuttle. A higher solution pH between 6 and 8.5 slowed down the oxidation of Cr(III) by chlorine. These findings suggested that the oxidative conversion of chromium-containing iron corrosion products in drinking water distribution systems can lead to the occurrence of Cr(VI) at the tap, and the abundance of iron, and a careful control of pH, bicarbonate and bromide levels can assist the control of Cr(VI) formation.
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