Li Qi, Zhang Xiaoming, Zheng Junhao, Qin Jingxi, Ou Chunyu, Liao Qi, Si Mengying, Yang Zhihui, Yang Weichun
School of Metallurgy and Environment, Central South University, Changsha 410083, PR China.
School of Metallurgy and Environment, Central South University, Changsha 410083, PR China; Chinese National Engineering Research Centre for Control & Treatment of Heavy Metal Pollution, Changsha 410083, PR China.
J Hazard Mater. 2024 Jan 5;461:132530. doi: 10.1016/j.jhazmat.2023.132530. Epub 2023 Sep 12.
The slow release of Cr(VI) from chromium ore processing residue-contaminated soil (COPR-soil) poses a significant environmental and health risk, yet advanced remediation techniques are still insufficient. Here, the slow-release behavior of Cr(VI) in COPR-soil is observed and attributed to the embedded Cr(VI) in the lattice of vaterite due to the isomeric substitution of CrO for CO. A citric acid-aided mechanochemical approach with FeS/ZVI as reductive material was developed and found to be highly effective in remediating COPR-soil. Almost all Cr(VI) in COPR-soil, including Cr(VI) embedded in the minerals, are reduced with a reduction efficiency of 99.94%. Cr(VI) reduction kinetics indicate that the Cr(VI) reduction rate constant in the presence of citric acid was 4.8 times higher compared to its absence. According to the Raman spectroscopy, X-ray diffraction (XRD), and Electron Probe X-ray Micro-Analyzer (EPMA) analysis, the reduction of Cr(VI) embedded in vaterite was mainly attributed to the citric acid-induced protonation effect. That is, under the protonation effect, the embedded Cr(VI) could be released from vaterite through its phase transformation to calcite, whose affinity to Cr(VI) is low. While the reduction of released Cr(VI) could be promoted due to the complexation of citric acid with disulfide groups on FeS/ZVI. The results of long-term stability tests demonstrated that the remediated COPR-soil exhibited excellent long-term stability, which may also be associated with improved utilization of available carbon and electron donors by the Cr(VI) reducing bacteria (Proteobacteria)-dominated microbial community in the presence of citric acid, thereby promoting to establish a stable reducing microenvironment. Collectively, these findings will further our understanding of the reduction remediation of COPR-soil, especially in the case of Cr(VI) embedded in minerals.
铬矿加工残渣污染土壤（COPR土壤）中六价铬的缓慢释放带来了重大的环境和健康风险，但先进的修复技术仍显不足。在此，观察到COPR土壤中六价铬的缓慢释放行为，并将其归因于由于CrO对CO的异构取代，六价铬嵌入球霰石晶格中。开发了一种以FeS/ZVI作为还原材料的柠檬酸辅助机械化学方法，发现该方法在修复COPR土壤方面非常有效。COPR土壤中的几乎所有六价铬，包括嵌入矿物中的六价铬，都被还原，还原效率为99.94%。六价铬还原动力学表明，存在柠檬酸时六价铬的还原速率常数比不存在时高4.8倍。根据拉曼光谱、X射线衍射（XRD）和电子探针X射线微分析仪（EPMA）分析，嵌入球霰石中的六价铬的还原主要归因于柠檬酸诱导的质子化效应。也就是说，在质子化效应下，嵌入的六价铬可以通过球霰石向方解石的相变从球霰石中释放出来，方解石对六价铬的亲和力较低。而释放的六价铬的还原由于柠檬酸与FeS/ZVI上的二硫基团络合而得到促进。长期稳定性测试结果表明，修复后的COPR土壤表现出优异的长期稳定性，这也可能与在柠檬酸存在下以六价铬还原细菌（变形菌门）为主的微生物群落对有效碳和电子供体的利用率提高有关，从而促进建立稳定的还原微环境。总的来说，这些发现将加深我们对COPR土壤还原修复的理解，特别是在矿物中嵌入六价铬的情况下。
