长期冻融作用下固化改性高浓度重金属污染土工程特性劣化效应及机理研究

Cement stabilized/solidified (S/S) heavy metal-contaminated soil is one of the most commonly technologies adopted for the remediation of contaminated sites. The interaction mechanisms among stabilizing agents, heavy metals and soils are complicated. The freeze-thaw cycles are considered to be the most important abiotic process acted on soil system in seasonal frozen-thawing area. However, literature work has not clearly explained the influence of freeze-thaw on engineering properties and environmental behavior of cement-based s/s heavy-metal-contaminated soils. Based on the characters of frozen-thawing cycles in north area, the soil samples collected from. And then, in order to investigate the influence of freeze-thaw cycles on the unconfined compressive strength (UCS), compressibility behavior, hydraulic conductivity, chemical forms and other environmental behavior of cement-based s/s heavy-metal-contaminated soils, the freeze-thawing cycles treatments, soil test, toxicity characteristic leaching procedure (TCLP) and sequential extraction procedures were employed. Based on the research on the response of physical and chemical properties to freeze-thawing cycles and the soil profile features of scanning electron microscope (SEM) ， Fourier transforms infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR)and Three-Dimensional Excitation Emission Matrix(3DEEM) will be observed before and after the freeze-thawing cycles treatments. After then, the changes of the construction of S/S and binding characteristic among stabilizing agents, heavy metals metal molecular and soils grain will be investigated. Furthermore, the findings will be used to reveal the mechanism of the influence of freeze-thawing cycles on the mechanical property and environmental behavior of cement-based S/S heavy-metal-contaminated soils. The research results will provide scientific basis for remediation of heavy metal contaminated site and preventing and controlling of heavy metal pollutant in seasonal freezing area.

水泥基固化剂封闭是近年重金属污染土壤修复治理的主要技术手段之一。固化剂-重金属-土间的相互作用受外部环境影响显著，机理复杂。季节性冻融作用是我国季节性冻融区广泛存在的作用于土壤系统的重要非生物营力，但其对固化污染土长期工程特性和稳定性状的影响尚未明确。项目根据冻融区土壤冻融特征，在前期研究基础上以某污染场地土壤为试验材料，结合长期冻融交替、室内土工试验、毒性浸出试验、淋滤试验及形态分析等方法，揭示长期冻融交替作用对水泥基材料固化重金属污染土强度、压缩性、渗透性及重金属赋存形态和再溶出特征等工程力学和环境行为的影响；结合土壤理化性质对长期冻融的响应及SEM\FTIR\3DEEM图谱特征分析冻融前后土壤结构及固化剂-土-重金属间结合特征的变化，从宏-微-细观多层次揭示长期冻融交替对固化重金属污染土工程特性和环境行为的影响机理。为季节性冻融区重金属污染场地修复治理和污染物安全控制提供理论依据。

水泥基固化/稳定化技术（S/S）是目前治理重金属污染土的主流技术方案，但修复效果受众多环境因素影响。冻融循环作为一种重要外营力，其对固化/稳定化重金属污染土工程特性的影响值得深入研究。本项目以水泥基材料固化/稳定化高浓度单元素（Pb）及复合元素（Pb-Zn-Cd）重金属污染土为研究对象，通过室内土工试验，阐明了长期冻融交替环境下固化污染土工程特性（强度、变形、渗透性）的劣化规律；通过毒性浸出试验、淋滤试验、重金属赋存形态分析等方法，揭示了经长期冻融作用下固化污染土中重金属元素再溶出特性及迁移规律；利用CT扫描、X射线衍射（XRD）、能量色散X射线光谱仪（EDS）、扫描电子显微镜（SEM）以及傅里叶变换红外光谱（FTIR）等分析测试手段，揭示了长期冻融循环作用影响固化高浓度重金属污染土的工程特性及环境行为的细微观机理。研究成果可为我国广大季节性冻土地区的重金属污染场地固化/稳定化修复及安全再利用提供重要科学依据和理论支撑。