黏土改性材料修复农田土壤镉铅污染的微观机理、效应及稳定性研究

In-situ immobilization is an extremely promising remediation technique due to its simple operation and rapid response, especially for the large area heavy metal polluted agricultural fields in China. However, the current immobilization reagents should be improved for better performance, meanwhile the microscopic remediation mechanisms were not clear and the studies regarding their environmental risk and long term stability were rare. The microscopic mechanisms were the essential of remediation effect, selectivity and stability. The stability was a critical factor affecting the practical utilization. In this project, the modified clay with independent intelligent property mercapto functionalized sepiolite was selected as remediation material. The remediation effect, microscopic mechanisms and stability were investigated by sorption in solutions, pot trials and field demonstration experiments. The microscopic mechanism were identified by X-ray absorption fine structure spectroscopy and micro X-ray fluorescence analyses combined with isothermal titration calorimetry. Rice and rape were selected as model plants to elucidate the remediation effects in soil-plant system and the effect of modified clay on soil environmental quality including the nutrients, trace elements and basic properties. The remediation stability were studied by column leaching by stimulated acid rain, freeze-thawing cycle and consecutive two-year field demonstration. This project can provide technical support for new remediation materials and the theoretical fundamental for the practical application.

土壤重金属原位钝化修复技术具有修复速率快、操作简便的优点，特别适宜于我国大面积中低度重金属复合污染农田。而现有一般钝化材料负载重金属容量较低，修复效率受限，而且修复微观机理尚不明确，环境影响及长期稳定性研究较少。微观机理是决定修复效应、选择性与稳定性的根本因素；稳定性是影响实际应用的关键因素。本项目以自主知识产权的黏土改性材料巯基修饰海泡石作为修复材料，通过吸附、土培、盆栽和田间示范实验，研究其修复农田土壤镉铅污染的微观机理、效应及稳定性特征。通过X射线吸收精细结构光谱和微区X射线荧光分析，结合等温滴定微量热技术，研究其钝化重金属的微观机理；以水稻和油菜为模式作物，研究其对土壤-植物系统重金属污染的修复效应及其对养分、微量元素等土壤环境质量的影响；通过模拟酸沉降、冻融交替和连续示范时间变异性实验研究钝化修复稳定性特征。本研究可为发展高效、实用、安全的重金属污染土壤钝化修复技术提供科学依据。

土壤重金属原位钝化修复技术具有修复速率快、操作简便的优点，特别适宜于我国大面积中低度重金属复合污染农田。而现有一般钝化材料负载重金属容量较低，修复效率受限，而且修复微观机理尚不明确，环境影响及长期稳定性研究较少。微观机理是决定修复效应、选择性与稳定性的根本因素；稳定性是影响实际应用的关键因素。本项目以自主知识产权的黏土改性材料巯基修饰海泡石作为修复材料，通过吸附、土培、盆栽和田间示范实验，研究其修复农田土壤镉铅污染的微观机理、效应及稳定性特征。钝化剂是决定农田土壤重金属污染钝化效应的关键因素，本研究探索出一种新型高效钝化剂巯基海泡石。巯基海泡石在应用剂量0.1–0.3%模式下显著降低糙米镉含量65.4–77.9%，其钝化修复效率比传统的pH调节类钝化剂显著增加。单一及连续浸提土壤有效态镉含量均证实了巯基海泡石具有显著的钝化效应，同时可以增强土壤颗粒对镉的吸附固定，从而进一步减少其生物有效性。巯基海泡石对土壤pH以及零电荷点无显著影响，对于有效态铜锌含量以及碱解氮和有效钾含量均无明显副作用，具有良好的环境友好兼容性。巯基海泡石还可以增强总抗氧化能力、增加非蛋白巯基，从而缓解镉对水稻根系的胁迫与毒害。本研究证实了巯基海泡石可以作为新型高效钝化剂，其修复机理有待于进一步深入研究。巯基坡缕石在应用剂量0.1%-0.3%的情况下就可以显著降低2个不同品种的水稻糙米和秸秆镉含量，同时显著降低根际土与非根际土中DTPA浸提有效态镉含量，由此可以确认巯基坡缕石是水稻土镉污染高效钝化剂。两个品种水稻的根际土与非根际土，在施用巯基坡缕石后pH并未有明显升高或降低，但是其zeta电位均有明显降低，表明巯基坡缕石增强了土壤颗粒对镉的吸附固定。巯基坡缕石增强了水稻根系中POD活性，显著缓解了镉对根系的胁迫。本研究可为发展高效、实用、安全的重金属污染土壤钝化修复技术提供科学依据。