Department of Chemical and Environmental Engineering , University of California at Riverside , Riverside , California 92521 , United States.
Environ Sci Technol. 2018 Jul 17;52(14):7663-7670. doi: 10.1021/acs.est.7b06013. Epub 2018 Jul 6.
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, Fe Cr(OH), 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 Fe Cr(OH) 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 Fe Cr(OH) 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.
饮用水中铬（Cr）作为无机污染物的出现被广泛报道。Cr 的一个来源是其作为 Cr(III)-Fe(III) 氢氧化物积累在饮用水分配系统含铁腐蚀产物中，即 FeCr(OH)，其中 x 代表 Fe(III)摩尔含量，通常在 0.25 到 0.75 之间变化。本研究调查了作为饮用水残留消毒剂的氯通过氧化 FeCr(OH) 来诱发六价铬 Cr(VI)形成的动力学，并且研究了 Fe(III)含量以及饮用水化学参数（包括 pH 值、溴化物和碳酸氢盐）对 Cr(VI)形成速率的影响。数据表明，Fe(III)摩尔含量的增加导致化学计量 Cr(VI)产率和 Cr(VI)形成速率显著降低，主要是由于 Fe(III)表面点位引起的氯衰减。碳酸氢盐的增加会增强 Cr(VI)的形成速率，这可能是由于形成了 Fe(III)-碳酸盐表面络合物，减缓了与氯的清除反应。溴化物的存在显著加速了氯对 FeCr(OH)的氧化，这归因于溴化物作为电子穿梭体的催化作用。在 6 到 8.5 之间的较高溶液 pH 值会减缓氯对 Cr(III)的氧化。这些发现表明，饮用水分配系统中含铬铁腐蚀产物的氧化转化可能导致 Cr(VI)在龙头处出现，铁的丰度以及 pH 值、碳酸氢盐和溴化物水平的仔细控制可以有助于控制 Cr(VI)的形成。
