Key Lab of Integrated Regulation and Resource Development on Shallow Lakes, Ministry of Education, College of Environment, Hohai University, Nanjing, 210098, China.
The National Key Laboratory of Water Disaster Prevention, Hohai University, Nanjing 210098, China; College of Hydrology and Water Resources, Hohai University, Nanjing, 210098, China.
Environ Pollut. 2024 Nov 1;360:124623. doi: 10.1016/j.envpol.2024.124623. Epub 2024 Jul 26.
Hydrogel adsorbents are promising tools for reducing heavy metals' bioavailability in contaminated soil. However, their practical feasibility remains limited by the low stability, inefficient removal efficiency, and potential secondary pollution. Optimizing the adsorption operation and the functional properties of hydrogel adsorbents could eliminate this method's drawbacks. Herein, three innovative in-situ remediation strategies for Pb/Cu-contaminated soil were adopted based on the concept of novel TEMPO-cellulose (TO-NFCs)/lignin/acrylamide@MIL-100(Fe) nanocomposite hydrogel adsorbent (NCLMH). Characteristic analyses revealed ideal Pb/Cu adsorption mechanisms by swelling, complexation, electrical attraction, and ion exchange via carboxyl/hydroxyl/carbonyl groups and unsaturated Fe(III) sites on ANCMH besides FeOOH formation. The highest maximum theoretical adsorption capacities of Pb(II) and Cu(II) on ANCMH were 416.39 and 133.98 mg/g, under pH 6.5, governed by pseudo-second-order/Freundlich models. Greenhouse pot experiments with contaminated soils amended with two-depth layers of 0.5% NCLMHs (SA@NCLMH) displayed a decline in Pb and Cu bioavailability up to 85.9% and 74.5% within 45 d. Soil column studies simulating continuous water soil flushing coupled with NCLMH layers, instead of conventional extractant fluids, and connected to NCLMH-sand column as purification unit (CF@NCLMH) achieved higher removal rates for Pb, and Cu of 89.5% and 77.2% within 24 h. Alternatively, conducting multiple-pulse soil flushing mode (MF@NCLMH) gained the highest Pb and Cu removal of 96.5% and 85.4%, as the water flushing-stop flux events allowed adequate water movement/residence period, promoting Pb/Cu desorption-adsorption from soil to NCLMH. Also, the NCLMH-sand column conducting and easy separation of the stable/reusable NCLMHs prevented the potential secondary pollution. Interestingly, the three remediated soils reached the corresponding regulation of the permissible limits for Pb and Cu residential scenarios in medium-to-heavily agricultural polluted soils, alleviating the Pb/Cu bioaccumulation and phytotoxicity symptoms in cultivated wheat, especially after MF@NCLMH treatment. This study introduces promising alternative remediation strategies with high sustainability and feasibility in acidic-to-neutral heavy metal-contaminated agricultural soil.
水凝胶吸附剂是降低污染土壤中重金属生物有效性的有前途的工具。然而，其实际可行性仍然受到低稳定性、低效去除效率和潜在二次污染的限制。优化吸附操作和水凝胶吸附剂的功能特性可以消除该方法的缺点。在此，采用了三种基于新型 TEMPO-纤维素（TO-NFCs）/木质素/丙烯酰胺@MIL-100（Fe）纳米复合水凝胶吸附剂（NCLMH）概念的新型原位修复策略来修复 Pb/Cu 污染土壤。特征分析表明，通过肿胀、络合、静电吸引和离子交换，除了 FeOOH 形成之外，羧基/羟基/羰基和不饱和 Fe（III）位点还可以理想地吸附 Pb/Cu。在 pH 值为 6.5 时，ANCMH 对 Pb（II）和 Cu（II）的最大理论吸附容量分别为 416.39 和 133.98mg/g，符合准二级/Freundlich 模型。在温室盆栽实验中，用两层 0.5%的 NCLMH（SA@NCLMH）对污染土壤进行改良，在 45d 内，Pb 和 Cu 的生物有效性下降了 85.9%和 74.5%。模拟连续水土壤冲洗并与 NCLMH 层结合而不是传统提取液，并与 NCLMH-砂柱连接作为净化单元（CF@NCLMH）的土壤柱研究，在 24h 内实现了对 Pb 和 Cu 的更高去除率，分别为 89.5%和 77.2%。或者，进行多次脉冲土壤冲洗模式（MF@NCLMH）可获得最高的 Pb 和 Cu 去除率，分别为 96.5%和 85.4%，因为水冲洗停止通量事件允许足够的水运动/停留时间，促进 Pb/Cu 从土壤中解吸-吸附到 NCLMH。此外，NCLMH-砂柱的运行和稳定/可重复使用的 NCLMH 的易于分离防止了潜在的二次污染。有趣的是，在进行 MF@NCLMH 处理后，三种修复土壤均达到了中重度农业污染土壤中 Pb 和 Cu 居住场景的相应规定限值，缓解了小麦种植中 Pb/Cu 的生物积累和植物毒性症状。本研究为酸性到中性重金属污染农业土壤引入了具有高可持续性和可行性的有前途的替代修复策略。
