膨润土系竖向隔离墙阻滞重金属污染物运移的机理及性能研究

Soil-bentonite (SB) vertical cutoff wall is widely used in the remediation of contaminated land. Literature work shows that the concentration of calcium and potassium ion concentration can considerably change the permeability and semi-permeable membrane behavior of SB cutoff wall backfills. In the contaminated lands, due to diffusion and advection, heavy metals will transport and then interact with SB cutoff backfills. However, very limited study addresses the engineering properties and semi-permeable membrane behavior of cutoff wall backfills when subjected to heavy metal contaminants. .In this proposal, the lead and cadmium are selected as target contaminants. Laboratory test and theoretical analysis are conducted to solve following scientific problems: i) to investigate the consolidation and compressibility characteristics of SB cutoff wall backfills exposed to the attack of heavy metals. The mechanisms and crucial controlling factors are discussed through investigation of physical and microstructural properties; ii) to understand factors controlling semi-permeable membrane behavior of SB cutoff wall backfills by 1-dimensional chemico-osmosis test using a rigid-wall apparatus. The intrinsic relationship between heavy metal concentration and membrane efficiency coefficient is established; iii) to investigate hydraulic properties and semi-permeable behavior of SB cutoff wall backfills amended with zeolite and sodium carbonate agents. The mechanism of modification and feasible dosage of the agents are discussed through permeability and chemico-osmosis tests and physical indices; iv) to investigate the containment performance of SB cutoff wall with laboratory model test and numerical simulation, with and/or without the consideration of coupling of chemico-osmosis, advection, and diffusion. The effects of of width and depth of SB cutoff wall on the containment performance are illustrated through lab test and numerical analysis. .The expected results will considerably improve the current theory for evaluating performance of SB vertical cutoff wall, and provide important scientific evidence and solid theoretical support for advocating isolation remediation technique in the contaminated lands of China.

膨润土系竖向隔离墙广泛应用于工业污染场地修复领域。现有研究尚未探明重金属污染物对隔离墙半透膜效应的影响规律及作用机理。本项目以黏土-膨润土类型的隔离墙材料和典型重金属污染物铅和镉为研究对象，通过室内试验和理论分析，拟解决如下关键问题：①探讨在重金属污染物作用下，隔离墙材料的固结压缩特性变化规律，结合物理特性及微观特征，揭示隔离墙材料工程特性的变化机理；②通过土柱化学渗透试验，阐明隔离墙材料半透膜效应的控制因素，建立金属离子浓度与膜效率系数的内在关联；③通过室内模型试验并结合数值模拟，定量评价考虑半透膜效应与对流-扩散-弥散共同作用下，隔离墙阻滞重金属污染物运移的工作性能；④研究改性膨润土系隔离墙材料的防渗特性和半透膜效应，查明改性机理并提出改性剂合理掺量。研究成果可完善现有膨润土系竖向隔离墙性能的理论评价体系，为提高我国污染场地的隔离修复设计水平提供重要的科学依据和理论支撑。

膨润土系竖向隔离墙广泛应用于工业污染场地修复领域。现有研究尚未探明重金属污染物对隔离墙半透膜效应的影响规律及作用机理。本项目以黏土-膨润土类型的隔离.墙材料和典型重金属污染物铅和镉为研究对象，通过室内试验和理论分析，解决了以下关键科学问题：①研究了在重金属污染物作用下，隔离墙材料的压缩特性变化规律，并结合物理特性及微观特征，揭示了隔离墙材料工程特性的变化控制机理；②通过柔性壁和刚性壁渗透试验、土柱化学渗透试验，明确了重金属污染物作用下隔离墙材料的渗透系数演变规律，对比分析了复合重金属污染物、单一重金属污染物作用下隔离墙材料的有效扩散系数、阻滞因子和半透膜效应的变化规律，建立了金属离子浓度与膜效率系数的内在关联；③开展了室内模型试验，模拟当与底部土层接触不良时隔离墙阻滞重金属污染物运移的工作性能；④研发了无机和有机改性材料，通过固结压缩、柔性壁渗透试验，明确了改性膨润土系隔离墙材料的化学相容性，查明了改性机理并筛选了有效的改性剂。研究成果可完善现有膨润土系竖向隔离墙性能的理论评价体系，为提高我国污染场地的隔离修复设计水平提供重要的科学依据和理论支撑。