典型土壤中Cr(VI)的吸持规律与迁移特征及基准定值的关键参数研究

Determination of the rational soil environmental criteria values is the basis for investigation, assessment and remediation of contaminated sites. At present, the research of calculation model and parameters of soil criteria by migration to groundwater pathway at home and abroad is still at the exploratory stage. Cr(VI) will be selected as the research object because it has dramatic solubility and mobility. The sorption rules of Cr(VI) on the 13 typical soil samples will be investigated to find the main factors influencing the distribution coefficients (Kd). The relationship between Kd and the main soil attributes (pH, Eh, organic matter, cation exchange capacity, soil particle composition and mineral type) will be analyzed, and the regression model will be used to estimate the Kd values through the combined effect of soil attributes. The migration characteristics of Cr(VI) in saturated and unsaturated soils will be studied through soil column leaching experiment and numerical simulation method, and the parameters including permeability coefficient, dispersity and retardation factor will be obtained. The conceptual model of Cr(VI) migration will be established, including soil leaching and transport processes in the aeration zone and aquifers. The dilution and attenuation factor (DAF) with different groundwater depth and soil types will be determined by the model. Then the computation model of soil criteria by migration to groundwater pathway will be suggested, and the soil criteria values and key parameters assignment in typical soils will be determined. This study will provide scientific basis for determination of soil environmental criteria with different kinds of soil types and properties.

土壤环境基准的制定是开展污染场地调查、评估与修复工作的基础，当前以保护地下水为目标的土壤环境基准计算模型及参数体系研究尚处于早期探索阶段。已开展的相关研究中很少考虑污染物在包气带和含水层中的输移过程及机理，如何考虑污染物的迁移特征来推导保护地下水的土壤基准值计算模型并获取关键参数是当前亟需解决的科学问题。本项目针对重金属中迁移性较强的Cr(VI)，采用静态吸附实验研究我国13种典型土壤中Cr(VI)的吸持规律，分析pH、Eh、CEC、有机质含量、土壤颗粒组成、矿物类型等参数对Cr(VI)分配系数（Kd）的影响，建立Kd与主要参数的回归预测方程。结合土柱淋滤实验与数值模拟技术，研究Cr(VI)在饱和与非饱和土壤中迁移特征，获取渗透系数、弥散度、阻滞因子等参数。建立Cr(VI)经土壤淋溶、包气带输移、到达含水层全过程的迁移转化模型，获取不同地下水埋深及土层类型的Cr(VI)稀释衰减因子（DAF），建立我国典型土壤中保护地下水的土壤环境基准推导模型及方法，确定土壤环境基准值及关键参数赋值范围，为构建考虑土壤类型和土壤性质差异的环境基准体系提供科学依据。

土壤环境基准的制定是开展污染场地调查、评估与修复工作的基础，当前以保护地下水为目标的土壤环境基准计算模型及参数体系研究尚处于早期探索阶段。本项目针对重金属中迁移性较强的Cr(VI)，采用静态吸附实验研究我国13 种典型土壤中Cr(VI)的吸持规律，分析pH、Eh、CEC、有机质含量、土壤颗粒组成、矿物类型等参数对Cr(VI)分配系数（Kd）的影响，建立Kd 与主要参数的回归方程。利用Freundlich和Langmuir等温吸附曲线对Cr(VI)的吸附特征进行统计拟合。计算了不同土壤中Cr(VI)的最大吸附量及Cr(VI)的分配系数，不同土壤中Cr(VI)的最大吸附量与分配系数大小基本满足：红壤>黑土>水稻土>潮土。通过土壤参数与Cr(VI)分配系数（Kd）的相关性分析，识别出影响土壤中Cr(VI)分配系数的关键参数为pH、粘粒含量、阳离子交换量（CEC）、有机质（SOM）、游离铁（Fed）、游离锰（Mnd）。结合土柱淋滤实验与数值模拟技术，研究Cr(VI)在饱和与非饱和土壤中迁移特征，获取渗透系数、弥散度、阻滞因子等参数。建立Cr(VI)经土壤淋溶、包气带输移、到达含水层全过程的迁移转化模型，获取不同地下水埋深及土层类型的Cr(VI)稀释衰减因子（DAF），建立我国典型土壤中保护地下水的土壤环境基准推导模型及方法，确定土壤环境基准值及关键参数赋值范围，为构建考虑土壤类型和土壤性质差异的环境基准体系提供科学依据。研究结果可为我国土壤及地下水污染调查、风险评估与修复等工作提供参考依据。