重金属污染土壤原位钝化修复的稳定性及其影响机理

In situ immobilization was the most promising remediation technology for the heavy metals contaminated soils with low or moderate pollution concentration in our country. The stability of heavy metal immobilization was the key to the successful application of this technique. The surface-modified nano-particle black carbon, bentonite and modified bentonite by organics will be used as passivation materials for the remediation of heavy metals contaminated soils. This project investigates the chemical and biological stability of heavy metal immobilization on the surface of three materials and evaluates corresponding influence factors by the incubation experiments. The microstructure for the immobilization processes of heavy metals on different materials will be probed with X-ray absorption fine structure spectroscopy for clarifying the immobilization mechanism. The influence of rhizosphere on heavy metal fractionations, migration and transformation will be investigated by rhizosphere experiment and the rhizosphere DOM composition and interactions between DOM and heavy metals will be analyze with the modern instrumental analysis. The purpose of this project is to clarify the release mechanism of heavy metals from solid phase to liquid phase in soil caused by the rhizosphere DOM. The characteristics of this project: 1). taking the complexity of soil-microbial-plant system into account, we firstly investigate the immobilization stability of heavy metals on multiple materials, evaluate corresponding influence factors and explicit the environment risk of this technique; 2). we will reveal the immobilization micro-mechanism of heavy metals on different immobilization materials and obtain theory basis for the application of this technology; 3). taking the interactions between the rhizosphere DOM and heavy metals as the breakthrough point, we will reveal the release mechanism of heavy metals from solid phase to liquid phase in soil caused by the rhizosphere DOM and thus improve the immobilization theory for heavy metal contaminated soils remediation.

以代表性有机、无机、有机-无机复合钝化材料为例，通过培养实验研究其对重金属钝化的化学、生物学稳定性。通过模拟实验，用Ｘ射线吸收精细结构光谱（XASF）等手段，研究重金属在钝化材料上和土壤中作用的微观结构、影响因素等，阐明其对重金属的钝化稳定性机理。通过根际微区实验，研究根际DOM对重金属形态、迁移转化的影响，借助现代仪器分析手段，研究根际DOM结构特征和根际DOM与重金属配合作用，阐明其对重金属钝化稳定性的影响机制。 本项目特点：首先，充分考虑土壤-微生物-植物系统及相互作用的复杂性，研究不同钝化材料钝化稳定性及影响因素，为判断该技术的环境风险提供依据。其次，借助现代仪器分析手段，从微观结构揭示不同钝化材料对重金属的钝化机理。再者，以根际DOM与重金属配合作用为研究突破点，从分子水平揭示根际DOM对重金属钝化稳定性影响机制。为重金属污染土壤钝化修复提供理论依据。

重金属钝化修复技术施入土壤的钝化材料吸附重金属后，残留于土壤中。因此，钝化材料本身及吸附重金属的稳定性是该项技术成功应用的关键。本项目以黑碳（BC）与膨润土为例，通过模拟实验、根际微区实验等，借助现代仪器分析，研究不同钝化材料对重金属钝化稳定性机理及其影响因素、根际DOM对土壤重金属钝化稳定性影响机理等。为重金属污染土壤钝化修复技术提供理论依据。主要结论如下：. （1）从材料的表面特性、分子形态、微观结构分析， BC与膨润土对Cu2+和Cd2+的钝化是以静电吸附、离子交换和微孔捕获为主，改性后以螯合作用为主。改性前吸附活化能Ea＜20 kJ•mol-1，以物理吸附为主，改性后Ea＞40 kJ•mol-1，以化学吸附为主。钝化材料吸附的Cu2+和Cd2+以H2O、CaCl2和EDTA逐级解吸，显示改性前以物理作用为主，改性后以螯合作用为主。. （2） pH为4.47~8.16的5种土壤，添加改性纳米黑碳（MBC），与对照相比，土壤DTPA-Cd下降了33.22%~64.46%，土壤pH越高，MBC对Cd的钝化效果越好。添加MBC，种植Cd耐受植物黑麦草、超积累植物红叶菾菜和印度芥菜，土壤DTPA-Cd含量分别降低了12.80%、1.30%和5.22%。黑麦草根际有效态Cd含量比非根际显著降低了8.9%。在MBC应用于Cd污染土壤修复时，应避免种植超积累植物。. （3）红叶菾菜根际/非根际DOM含量高于黑麦草，添加MBC后大大减小了两种植物根际/非根际DOM含量的差异。三维荧光光谱显示两种植物根际/非根际DOM中类富里酸＞类腐殖酸＞类蛋白；施加MBC后，类富里酸荧光强度显著降低，类蛋白荧光强度显著增加。预示着MBC对DOM有吸附作用，且对DOM中不同组分吸附性能不同。. （4）观察植物根尖超微结构，发现BC和MBC在植物细胞壁聚集。BC和MBC对带正电的大单囊胞（GUV+）的破坏作用远大于带负电的大单囊胞（GUV-）。随着BC和MBC浓度增高，暴露时间增长，其对GUV+损害作用增强。高浓度暴露10min出现囊泡皱缩，观察到磷脂碎片、颗粒聚积等现象，低浓度暴露4h 才出现上述现象，且MBC的损害作用大于BC。颗粒粒径、表面带电性、浓度、暴露时间是纳米材料对植物细胞影响的关键因素。