Chen Long, Yu Huilin, Wang Xingrun, Zhu Hongtao
Beijing Key Lab for Source Control Technology of Water Pollution, College of Environmental Science and Engineering, Beijing Forestry University, Beijing 100083, China; Engineering Research Center for Water Pollution Source Control & Eco-remediation, College of Environmental Science and Engineering, Beijing Forestry University, Beijing 100083, China.
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
Sci Total Environ. 2024 May 1;923:171538. doi: 10.1016/j.scitotenv.2024.171538. Epub 2024 Mar 6.
Chromium (VI) in soil poses a significant threat to the environment and human health. Despite efforts to remediate Cr contaminated soil (Cr-soil), instances of re-yellowing have been observed over time. To understand the causes of re-yellowing as well as the influence of overdosed chemical reductant in remediating Cr-soil, experiments on excess reducing agent interference and soil re-yellowing mechanisms under different extreme conditions were conducted. The results show that the USEPA method 3060A & 7196A combined with KSO oxidation is an effective approach to eliminate interference from excess FeSO reducing agents. The main causes of re-yellowing include the failure of reducing agents, disruption of soil lattice, and interactions between manganese oxides and microorganisms. Under various extreme conditions simulated across the four seasons, high temperature and drought significantly accelerated the failure of reducing agents, resulting in the poorest remediation effectiveness for Cr-soil (91.75 %). Dry-wet cycles promoted the formation of soil aggregates, negatively affecting Cr(VI) removal. While these extreme conditions caused relatively mild re-yellowing (9.46 %-16.79 %) due to minimal soil lattice damage, the potential risk of re-yellowing increases with the failure of reducing agents and the release of Cr(VI) within the lattice. Prolonged exposure to acid rain leaching and freeze-thaw cycles disrupted soil structure, leading to substantial leaching and reduction of insoluble Cr, resulting in optimal remediation effectiveness (94.37 %-97.73 %). As reducing agents gradually and the involvement of the water medium, significant re-yellowing occurred in the remediated soil (51.52 %). Mn(II) in soil enriched relevant microorganisms, and the Mn(IV)-mediated biological oxidation process was also one of the reasons for soil re-yellowing.
土壤中的六价铬对环境和人类健康构成重大威胁。尽管人们努力修复受铬污染的土壤（铬污染土壤），但随着时间的推移，仍观察到土壤重新变黄的情况。为了解重新变黄的原因以及过量化学还原剂对铬污染土壤修复的影响，开展了不同极端条件下过量还原剂干扰及土壤重新变黄机制的实验。结果表明，美国环境保护局方法3060A和7196A结合重铬酸钾氧化是消除过量硫酸亚铁还原剂干扰的有效方法。重新变黄的主要原因包括还原剂失效、土壤晶格破坏以及锰氧化物与微生物之间的相互作用。在模拟四季的各种极端条件下，高温和干旱显著加速了还原剂的失效，导致铬污染土壤的修复效果最差（91.75%）。干湿循环促进了土壤团聚体的形成，对六价铬的去除产生负面影响。虽然这些极端条件由于土壤晶格破坏最小而导致相对较轻的重新变黄（9.46%-16.79%），但随着还原剂的失效和晶格内六价铬的释放，重新变黄的潜在风险增加。长时间暴露于酸雨淋溶和冻融循环会破坏土壤结构，导致大量不溶性铬的淋溶和还原，从而产生最佳的修复效果（94.37%-97.73%）。随着还原剂逐渐耗尽和水介质的参与，修复后的土壤中发生了显著的重新变黄（51.52%）。土壤中的锰（II）富集了相关微生物，锰（IV）介导的生物氧化过程也是土壤重新变黄的原因之一。
