基于XAFS和DGT技术原位研究土壤铅在磷酸盐矿物相锁定和再活化的分子机理

Phosphate minerals has great application potential in remediation of lead (Pb) contaminated soils, but the long-term stability after remediation is still not clear. Therefore, it’s necessary to study thoroughly the micro-scale reaction mechanisms of phosphate minerals with Pb, build mathematical models for metal mobilization processes, and recognize quantitatively the risk factors controlling remobilization. In this project, technique of diffusive gradients in thin-films (DGT) will firstly be employed to evaluate the variation of Pb and P bioavailabilities during two years in soils applying phosphate minerals; secondly, synchrontron based X-ray absorption fine structure (XAFS) technique will be adopted to analyze the microstructure and Pb-atom occurrence forms in standards, of synthesized through reactions of phosphate minerals and Pb at various environmental conditions (pH, metal concentration and organic matter content), and typical soil samples; thirdly, DIFS (DGT Induced Fluxes in Soils) modelling and geochemical calculation will be further incorporated to the methodologies to obtain the sorption/desorption rates of Pb and P in remediated soils. The goals of this study are to 1) resolve at molecular level the microstructure of sequestered Pb by phosphate minerals; 2) quantify the remobilization risks of Pb after soil remediation; 3) provide fundamental scientific basis for remediation of heavy metal contaminated soils.

磷酸盐矿物在土壤铅污染修复领域具有较大应用潜力，然而修复后的长期活化风险尚不明确。因此有必要深入研究磷酸盐矿物锁定铅的微观反应机制，建立金属活化过程的数学模型和定量辨识再活化风险因子。本项目拟应用梯度扩散薄膜（DGT）技术测定施用磷酸盐矿物两年周期内污染土壤中铅和磷的生物有效性变化，并在此基础之上结合同步辐射X射线吸收精细结构光谱（XAFS）技术分析多种环境条件（如pH、浓度、有机质含量）下合成的磷酸盐矿物与铅反应产物标样以及典型土壤样品中亚稳态固定产物的微观结构及其铅原子的赋存位置。然后结合DIFS（DGT Induced Fluxes in Soils）模型、地球化学模拟计算获取施用磷酸盐矿物的土壤中铅和磷吸附/解吸动力学参数。期望实现：1）分子水平解析磷酸盐矿物锁定铅的反应产物的微观结构；2）量化施用磷酸盐矿物锁定土壤中铅的再活化风险；3）为治理土壤重金属污染提供科学依据。

磷酸盐矿物在土壤铅污染修复领域具有较大应用潜力，然而修复后的长期活化风险尚不明确。因此有必要深入研究磷酸盐矿物锁定铅的微观反应机制，建立金属活化过程的数学模型和定量辨识再活化风险因子。本项目对羟基磷灰石锁定铅等重金属的地球化学机制进行了模拟计算，探明了羟基磷灰石晶格中铅等重金属的取代特征；通过溶液化学和物质微观结构表征探究了磷酸盐矿物锁定铅等重金属的机制，明确了沉淀和表面吸附的主导作用；基于梯度扩散薄膜（DGT）技术和DIFS模型开发了评价修复后土壤中重金属长期稳定性的定量表征表征方法，提出了一种测量微界面有效态磷含量分布的方法；开展了典型铅锌矿区土壤重金属稳定性和生态效应研究，探索了矿物溶蚀和功能材料施加对土壤中铅等迁移性和稳定性的影响。研究结果明确了微界面解吸过程对磷酸盐矿物锁定和再活化铅等重金属的主导作用，为土壤重金属原位钝化材料的开发和长期稳定性评价提供科学依据。