Department of Chemical and Environmental Engineering, University of California at Riverside, Riverside, California92521, United States.
Environ Sci Technol. 2023 Nov 28;57(47):18433-18442. doi: 10.1021/acs.est.2c05324. Epub 2023 Jan 31.
In drinking water distribution systems, the oxidation of zerovalent chromium, Cr(0), in iron corrosion scales by chlorine residual disinfectant is the dominant reaction to form carcinogenic hexavalent chromium, Cr(VI). This study investigates inhibitive corrosion control strategies through adjustments of chemical water parameters (i.e., pH, silicate, phosphate, calcium, and alkalinity) on Cr(VI) formation through oxidation of Cr(0) by free chlorine under drinking water conditions. The results show that an increase in pH, silicate, alkalinity, and calcium suppressed Cr(VI) formation that was mainly attributed to in situ surface precipitation of new Cr(III) solids on the surface of Cr(0), including Cr(OH), Cr(SiO), CrPO, Cr(CO), and CrCa(CO). The Cr(III) surface precipitates were much less reactive with chlorine than Cr(0) and suppressed the Cr redox reactivity. The concentration of surface Cr(III) solids was inversely correlated with the rate constant of Cr(VI) formation. Adding phosphate either promoted or inhibited the Cr(VI) formation, depending on the phosphate concentration. This study provides fundamental insight into the Cr(VI) formation mechanisms via Cr(0) oxidation by chlorine and the importance of surface precipitation of Cr(III) solids with different corrosion control strategies and suggests that increasing the pH/alkalinity and addition of phosphate or silicate can be effective control strategies to minimize Cr(VI) formation.
在饮用水分配系统中，氯残留消毒剂氧化铁腐蚀层中的零价铬（Cr(0)），是形成致癌六价铬（Cr(VI)）的主要反应。本研究通过调整化学水参数（即 pH 值、硅酸盐、磷酸盐、钙和碱度），在饮用水条件下，通过自由氯氧化 Cr(0)，考察了抑制腐蚀控制策略对 Cr(VI)形成的影响。结果表明，pH 值、硅酸盐、碱度和钙的增加抑制了 Cr(VI)的形成，这主要归因于 Cr(0)表面原位沉淀新的 Cr(III)固体，包括 Cr(OH)、Cr(SiO)、CrPO、Cr(CO)和 CrCa(CO)。与 Cr(0)相比，Cr(III)表面沉淀物与氯的反应性要小得多，从而抑制了 Cr 的氧化还原反应性。表面 Cr(III)固体的浓度与 Cr(VI)形成的速率常数呈反比。添加磷酸盐会促进或抑制 Cr(VI)的形成，这取决于磷酸盐的浓度。本研究深入了解了通过氯氧化 Cr(0)形成 Cr(VI)的机制，以及不同腐蚀控制策略下 Cr(III)固体表面沉淀的重要性，并表明提高 pH 值/碱度以及添加磷酸盐或硅酸盐可以是一种有效的控制策略，以最大程度地减少 Cr(VI)的形成。
