基于双改性膨润土的竖向屏障阻控有机-重金属复合污染物的机理和性能研究

Organic and heavy metal combined contamination is a universal condition in chinese urban industrial contaminated sites. Such combined contamination leads to a severely deteriorated containment performance of soil-bentonite vertical cutoff wall, whereas current modified bentonites are unable to effectively enhance the containment performance. This proposal aims to investigate hydrophobic organic cation and hydrophilic polymer composite-modified bentonite and its application to soil-bentonite vertical cutoff walls. The following key issues are addressed by laboratory experiments and theory analyses: (1) measure the changes in the interlayer structure of montmorillonite, characteristic functional groups, surface charge property, and bond water content of bentonites created by hydrophobic organic cation and hydrophilic polymer composite modification. The resulting changes of these properties are used to interpret main modification mechanisms of the modified bentonite; and therefore, to establish an optimization method for the modification technology. (2) conduct analysis of the physical and chemical interaction mechanism among modifying materials, bentonite, and combined contaminants. The analysis helps to understand the elution behavior of modifying material from the soil-bentonite backfill due to hydraulic permeation and/or combined contamination, and to optimize modified bentonite content in the backfill. (3) assess the enhanced effects of the containment performance due to bentonite modification via flexible-wall permeability test, chemico-osmotic test, and theoretical calculation. The internal connections between key migration parameters and contact angle of solid-liquid interface, soil particle surface properties, soil microstructure are elucidated to reveal the enhancement mechanisms. The overall results from this proposal are able to facilitate providing scientific basis for the safety evaluation of vertical barriers. In addition, it can be expected that the outcome of this project can promote the development of environmental risk control technologies for industrial contaminated sites.

我国城市工业污染场地广布的有机-重金属复合污染严重影响土-膨润土竖向阻隔屏障的安全服役。现有膨润土改性技术难以有效提升复合污染作用下屏障的阻控性能。项目以疏-亲水聚合物双改性膨润土竖向屏障材料为研究对象，通过室内试验与理论分析，拟解决以下关键问题：①研究改性膨润土层间结构、特征官能团、颗粒表面带电与结合水特性，揭示双改性机理，建立改性工艺遴选分析方法；②查明改性材料-膨润土-污染物间物理及化学相互作用机理，明晰水力渗透与复合污染作用下屏障中改性材料抗溶脱行为，建立屏障材料掺比优化方法；③通过柔性壁渗透和土柱化学渗透试验及理论计算，定量评价改性作用对服役性能的增强效果，阐明复合污染作用下污染物关键运移参数与颗粒表面状态、孔隙分布特征、微观结构间内在关联，揭示改性效果增强的机理。研究成果可为土-膨润土竖向屏障安全服役的理论评价体系提供重要的科学依据，促进我国工业污染场地的环境风险阻控技术发展。

我国城市工业污染场地广布的有机-重金属复合污染严重影响土-膨润土竖向阻隔屏障的安全服役。现有膨润土改性技术难以有效提升复合污染作用下屏障的阻控性能。项目以疏-亲水聚合物双改性膨润土竖向屏障材料为研究对象，通过室内试验与理论分析，解决以下关键问题：①揭示双改性机理，建立改性工艺遴选分析方法；②查明改性材料-膨润土-污染物间物理及化学相互作用机理；③通过柔性壁渗透和理论计算，定量评价改性作用对服役性能的增强效果，揭示改性效果增强的机理。重要结果如下：（1）相同苯酚浓度条件下CMC改性膨润土的膨胀指数较母土测定结果高1.5至2.5倍。同一孔隙比范围内，改性作用使膨润土渗透系数降低一个数量级。研究范围内，聚合物分子量和取代度未显示对膨胀指数和渗透系数的影响规律；（2）相同条件下CMC改性膨润土膨胀和防渗性能相对最优，而CTMAB-CMC改性则有效削弱苯酚溶液对膨胀指数和渗透系数的影响程度；（3）CMC改性作用有效增强回填材料在自来水中的防渗性能，有机改性剂CTMAB 的加入未显著影响回填材料的渗透系数，高浓度苯酚污染作用下，CMC改性作用有效降低回填材料的渗透系数，较未改性母土测试结果降幅为67%。对高风险有机污染地块开展竖向阻隔工程时，回填材料中CMC改性膨润掺量推荐使用9.6%。（4）CMC改性提升化学相容性的主因有：（a）聚合物水凝胶对膨润土颗粒间的大孔隙具有堵塞作用；（b）特征基团（羧酸根、羧基）与苯酚的酯化反应等相互作用，以及苯酚与水凝胶中水分子的氢键作用阻碍苯酚迁移，从而减轻其对压缩蒙脱石黏土矿物双电层的不利影响。（4）CTMAB阳离子对苯酚的分配作用是改性膨润土化学相容性增强的主因。透射电子显微镜观测显示，苯酚溶液未显著影响改变两种改性膨润土的微观结构，CTMAB-CMC改性膨润土分散程度优于CMC改性膨润土。研究成果为土-膨润土竖向屏障安全服役的理论评价体系提供重要的科学依据，促进我国工业污染场地的环境风险阻控技术发展。

内容获取失败，请点击重试