Key Laboratory of Intelligent Health Perception and Ecological Restoration of Rivers and Lakes, Ministry of Education, Hubei University of Technology, Wuhan, 430068, Hubei Province, China.
Key Laboratory of Intelligent Health Perception and Ecological Restoration of Rivers and Lakes, Ministry of Education, Hubei University of Technology, Wuhan, 430068, Hubei Province, China; Innovation Demonstration Base of Ecological Environment Geotechnical and Ecological Restoration of Rivers and Lakes, School of Civil Engineering, Architecture and Environment, Hubei University of Technology, Wuhan, 430068, Hubei Province, China.
J Environ Manage. 2024 Dec;371:123167. doi: 10.1016/j.jenvman.2024.123167. Epub 2024 Nov 2.
Electroreduction of Cr(VI) coupled with in-situ precipitation of Cr(III) on the cathode is a promising method for removing Cr(VI) from wastewaters. However, the influence of coexisting anions in wastewaters on the electrochemical removal process remains unclear. This study investigated the impact of common inorganic anions, including nitrate (NO), chloride (Cl), phosphate (PO) and sulfate (SO), on the electrochemical removal processes of Cr(VI). The results indicated that HCrO was directly electrochemically reduced to Cr, and the OH generated through electro-mediated water reduction could complex with Cr, thereby transforming Cr into chromium hydroxide (Cr(OH)) coated at cathode. Coexisting anions would partially penetrate the alkaline Cr(III) complexes, inhibiting the formation of Cr(OH) passivation layer and promoting the electroreduction of Cr(VI), whose penetration ability followed the order of SO > PO > Cl > NO. Both the inhibitory effect on Cr(III) precipitation and promoting effect on Cr(VI) reduction were intensified with increasing concentrations of these anions in the range of 1-100 mmol L. Accordingly, after electrolysis of 10 mg L Cr(VI) at an initial pH of 3.0 and -0.2 V (vs. Ag/AgCl), the highest electrochemical reduction ratio of Cr(VI) (99.9%) was achieved in the presence of 100 mmol L SO, while the total Cr removal ratio was minimal (3.3%). In contrast, the presence of NO at 1 mmol L resulted in a nearly lowest reduction ratio of Cr(VI) (92.9%), with the maximum total Cr removal ratio (92.8%). These findings provide new insights into the electrochemical removal mechanisms of Cr(VI) in complex solution environments.
六价铬在阴极上的电化学还原与原位沉淀是一种从废水中去除六价铬的有前途的方法。然而，废水中共存阴离子对电化学去除过程的影响尚不清楚。本研究考察了常见无机阴离子（包括硝酸盐（NO ）、氯化物（Cl ）、磷酸盐（PO ）和硫酸盐（SO ））对 Cr(VI)电化学去除过程的影响。结果表明，HCrO 在阴极上直接电化学还原为 Cr，而通过电介导水还原生成的 OH 可与 Cr 络合，从而将 Cr 转化为在阴极上覆盖的铬氢氧化物（Cr(OH) ）。共存阴离子会部分穿透碱性 Cr(III)络合物，抑制 Cr(OH)钝化层的形成并促进 Cr(VI)的电还原，其穿透能力的顺序为 SO ＞PO ＞Cl ＞NO 。随着这些阴离子浓度在 1-100 mmol·L 范围内从 1 增加到 100 mmol·L，对 Cr(III)沉淀的抑制作用和对 Cr(VI)还原的促进作用均增强。因此，在初始 pH 为 3.0 和-0.2 V（相对于 Ag/AgCl）下电解 10 mg·L 的 Cr(VI)后，在 100 mmol·L 的 SO 存在下，Cr(VI)的电化学还原率最高（99.9%），而总 Cr 去除率最低（3.3%）。相比之下，在 1 mmol·L 的 NO 存在下，Cr(VI)的还原率最低（92.9%），总 Cr 去除率最高（92.8%）。这些发现为复杂溶液环境中 Cr(VI)的电化学去除机制提供了新的见解。
