聚磷基分散剂改性膨润土竖向工程屏障阻隔高风险重金属污染物的机理和性能研究

Soil-bentonite slurry-trench cutoff walls are extensively used as engineered barriers for the purpose of controlling migration of heavy metals from contaminated groundwater to surroundings. Bentonite modification is an important approach to enhance servicing performance of soil-bentonite cutoff walls when exposed to high risk heavy metals and cyclic drying and wetting processes. This proposal aims to investigate polyphosphate-modified bentonite and its application to soil-bentonite cutoff walls. The following key issues are addressed by laboratory experiments and theory analyses: (1) measure changes of functional group, microstructure, and surface charge of bentonite after modification with polyphosphate dispersants. The changes of these properties are used to interpret main modification mechanisms of polyphosphate dispersants modified bentonite; (2) conduct modified fluid loss tests and evaluate chemical compatibility of modified soil-bentonite cutoff wall backfills with concentrated heavy metal solutions. Based on the test results, optimization of polyphosphate modification technology is established; (3) combine microscopic analyses of backfills and chemical speciation of heavy metals in the pore fluid of backfills to understand the hydraulic containment performance improved by polyphosphate modification, and (4) conduct numerical analysis to assess how soil-modified bentonite cutoff walls can contain heavy metals in contaminated groundwater. Parametric studies are performed to evaluate effects of wall thickness, keyed-in depth, wall-aquitard contact conditions, and local wall defects on servicing performance. All parameters are obtained from laboratory tests. The overall results of this proposal can facilitate systematic assessment of servicing performance of soil-bentonite vertical cutoff walls under sensitive conditions. In addition, it is expected that the outcome of this project can yield theoretical basis for the application of vertical barriers in industrial contaminated sites.

土-膨润土竖向工程屏障广泛用于工业污染场地的防渗阻隔。高风险重金属污染、地下水位变动所致干湿交替作用的敏感环境下，膨润土改性是确保屏障安全服役的有效方法。本项目以聚磷基分散剂改性的竖向工程屏障为研究对象，通过室内试验和理论分析，拟解决以下关键科学问题：①系统研究改性膨润土的微观结构、特征官能团和表面带电特性，揭示聚磷基分散剂对膨润土的改性机理；②通过改进滤失试验，查明屏障材料在高风险重金属暴露环境下的化学相容性，建立改性的优化分析方法；③分析屏障材料的微观结构和重金属形态特征，揭示聚磷酸分散剂改性作用对防渗性能的增强机理；④综合柔性壁渗透试验、土柱化学渗透试验和数值模拟，明确敏感环境下重金属通过屏障材料运移参数的演化规律，进而定量评价典型工况下工程屏障的服役性能。研究成果可完善土-膨润土竖向工程屏障防渗阻隔性能研究的理论评价体系，为提高我国污染场地处理技术水平提供重要的科学依据和理论。

本项目按计划从聚磷基分散剂改性膨润土机理研究、改性膨润土竖向工程屏障材料掺量优化研究、改性膨润土竖向工程屏障材料化学相容性研究、改性膨润土竖向工程屏障材料阻隔性能研究四各方面开展，完成了本项目主要研究目标。主要研究进展与成果包括：（1）系统查明了改性膨润土的微观结构、特征官能团和表面带电特性，揭示了聚磷基分散剂对膨润土的改性机理；（2）建立了改性膨润土及竖向阻隔屏障材料的优化分析方法；（3）明确了重金属等污染物作用下六偏磷酸钠改性屏障材料渗透系数以及运移参数的演化规律。研究成果可完善土-膨润土竖向工程屏障防渗阻隔性能研究的理论评价体系，为提高我国污染场地处理技术水平提供重要的科学依据和理论。本项目发表了标注本项目资助的学术论文42篇，申请/授权专利19项，编写了3部行业标准以及2部专著，培养了2名博士以及5名硕士。基于项目成果获2022年中国岩石力学与工程学会科学技术一等奖（排2），2020年湖北省科技进步一等奖（排3），2020年环境保护科学技术二等奖（排7），2020年Acta Geotechnical Best Paper Award以及2019年Canadian Geotechnical Journal Fredlund Award等奖项。