School of Environmental Science and Engineering, Shandong University, Qingdao 266237, China.
School of Environmental Science and Engineering, Shandong University, Qingdao 266237, China; Shandong Key Laboratory of Environmental Processes and Health, Shandong University, Qingdao 266237, China; Shandong Key Laboratory of Water Pollution Control and Resource Reuse, Shandong University, Qingdao 266237, China.
J Hazard Mater. 2023 Jun 15;452:131282. doi: 10.1016/j.jhazmat.2023.131282. Epub 2023 Mar 23.
Flocculation is a traditional and effective method to remove Cr from wastewater, but the addition of flocculants inevitably leads to secondary pollution. In this study, Cr flocculation was induced using hydroxyl radical (•OH) (•OH flocculation) generated in an electro-Fenton-like system, achieving total Cr removal of 98.68% at initial pH = 8 within 40 min. The obtained Cr flocs showed significantly higher Cr content, lower sludge yield, and good settling properties compared to alkali precipitation and polyaluminum chloride flocculation. •OH flocculation behaved like a typical flocculant, introducing electrostatic neutralization and bridging. The mechanism proposed that •OH could overcome the steric hindrance of Cr(HO) and combine with it as an additional ligand. Then Cr(III) was proved to undergo multi-step oxidation to form Cr(IV) and Cr(V). After these oxidation reactions, •OH flocculation took precedence over Cr(VI) generation. As a result, Cr(VI) didn't accumulate in solution until •OH flocculation was completed. This work provided a clean and eco-friendly strategy for Cr flocculation instead of flocculants and extended the application of advanced oxidation processes (AOPs), which is expected to enrich existing strategies of AOPs towards Cr removal.
絮凝是去除废水中 Cr 的传统且有效的方法，但添加絮凝剂不可避免地会导致二次污染。在这项研究中，使用电芬顿类似体系中生成的羟基自由基（•OH）（•OH 絮凝）诱导 Cr 絮凝，在初始 pH=8 下 40 分钟内实现了 98.68%的总 Cr 去除率。与碱沉淀和聚合氯化铝絮凝相比，所得 Cr 絮体具有更高的 Cr 含量、更低的污泥产率和良好的沉降性能。•OH 絮凝表现出典型的絮凝剂行为，引入了静电中和和桥接作用。提出的机制表明，•OH 可以克服 Cr(HO) 的空间位阻并与之结合作为附加配体。然后证明 Cr(III)经历了多步氧化，形成 Cr(IV)和 Cr(V)。在这些氧化反应之后，•OH 絮凝优先于 Cr(VI)的生成。因此，直到•OH 絮凝完成，Cr(VI)才在溶液中积累。这项工作为 Cr 絮凝提供了一种清洁环保的策略，而不是使用絮凝剂，并扩展了高级氧化工艺（AOPs）的应用，有望丰富现有的 AOPs 去除 Cr 的策略。
