Tian Hailong, Wang Xuehui, Pan Rubin, Qin Jialu, Xu Nuo, Huang Xianfeng
National and Local Joint Engineering Research Center for Ecological Treatment Technology of Urban Water Pollution, School of Life and Environmental Science, Wenzhou University, Wenzhou, 325035, China.
Environ Sci Pollut Res Int. 2023 May;30(22):62733-62743. doi: 10.1007/s11356-023-26594-1. Epub 2023 Mar 22.
Cr(III)-organic complexes are stably presented in tanning, electroplating, and other industrial wastewaters, and their safe and efficient removal remains a current challenge. Available oxidation processes can remove Cr(III) complexes but readily result in highly toxic Cr(VI) accumulation. Herein, negligible Cr(VI) accumulation was achieved during photo-oxidation of Cr(III) complexes using a simple strategy of decreasing dissolved oxygen (DO). At the DO concentration of 5.0 mg·L or less, the in-process formation of intermediate Cr(VI) was totally abated by in situ formed reductive species, and total Cr was reduced from 9.0-11.0 mg·L to below 1.0 mg·L. A complete curtailment of Cr(VI) was observed after 30-60 min at pH 6.0-9.0. Increasing Cr(III)-EDTA concentration and decreasing pH value facilitated the in situ reduction of intermediate Cr(VI). Based on the identification of intermediates and additional Cr(II) and quenching experiments, the possible key species involved in intermediate Cr(VI) reduction were the photogenerated Cr(II) and some C-centered radicals from Cr(III)-EDTA decomplexation, and the possible mechanisms of Cr(III)-EDTA decomplexation and intermediate Cr(VI) reduction were thus proposed. The process also showed efficient treatment on other Cr(III) complexes (citrate, oxalate, and tartrate) and realistic Cr(III) complexed wastewater. This study would provide an insignificant Cr(VI)-accumulated alternative for efficient and safe removal of Cr(III) complexes from contaminated water.
Cr(III)有机络合物稳定存在于制革、电镀及其他工业废水中，其安全高效去除仍是当前面临的挑战。现有的氧化工艺可去除Cr(III)络合物，但易导致剧毒的Cr(VI)积累。在此，通过降低溶解氧(DO)的简单策略，在Cr(III)络合物的光氧化过程中实现了可忽略不计的Cr(VI)积累。在DO浓度为5.0 mg·L或更低时，原位形成的还原物种完全抑制了中间产物Cr(VI)的生成，总Cr含量从9.0 - 11.0 mg·L降至1.0 mg·L以下。在pH 6.0 - 9.0条件下，30 - 60分钟后观察到Cr(VI)完全消除。增加Cr(III)-EDTA浓度和降低pH值促进了中间产物Cr(VI)的原位还原。基于中间体的鉴定以及额外的Cr(II)和猝灭实验，提出了参与中间产物Cr(VI)还原的可能关键物种为光生Cr(II)和Cr(III)-EDTA解络合产生的一些C中心自由基，并由此提出了Cr(III)-EDTA解络合和中间产物Cr(VI)还原的可能机制。该工艺对其他Cr(III)络合物(柠檬酸盐、草酸盐和酒石酸盐)及实际含Cr(III)络合物废水也显示出高效处理效果。本研究将为从污染水中高效安全去除Cr(III)络合物提供一种几乎无Cr(VI)积累的替代方法。
