污染物在黏土中的非线性扩散特性

针对溶质运移测试中运移参数提取困难、方法不统一的现状,基于溶质在土粒上的质量分数,定义了一个新的非线性吸附模型；推导了非线性吸附情况下溶质运移的控制方程,并用最小二乘法原理编制运移参数的反演程序；用一维土柱静态扩散法测试Pb(Ⅱ)在高岭土柱中的扩散特性,用非线性吸附模型成功提取出运移参数.结果表明：非线性扩散理论比线性扩散理论能更好地解释实验现象；Pb(Ⅱ)在高岭土/水之间的吸附特性近似符合Freundlich模型；Pb(Ⅱ)在高岭土柱中的扩散系数为0.086 8～0.105 8 cm2/d,且呈现出随着溶质体积浓度的减小而增大的非线性；土柱扩散法测得Pb(Ⅱ)在高岭土柱中的单层吸附容量为0.001 77～0.002 36,明显小于Batch法所得的吸附容量；高岭土作为Pb(Ⅱ)的屏蔽材料是可行的,但增加土样的干密度会降低土样吸附污染物的能力.

Nonlinear diffusion behavior of pollutant in clay column

The reported methods to extract parameters for solute transport analysis are hard to handle with inconsistent test procedures. A new model with regard to the nonlinear adsorption behavior was defined on the basis of mass percent of solute on the soil particles. The relevant governing equations were deducted and a code to predict the solute transport parameters using backward analysis method was developed under a least square principle. The new method was verified by testing the diffusion behavior of Pb(Ⅱ) in Kaolin column. The results showed that the nonlinear diffusion theory could better explain the experimental phenomena than the linear diffusion theory. The adsorption of Pb(Ⅱ) on Kaolin appeared fitting Freundlich model with predicted adsorption capacity at 0.001 77～0.002 36. The diffusion coefficient of Pb(Ⅱ) in Kaolin which was determined to be in the range of 0.086 8～0.105 8 cm2/d decreased with increasing solute concentration. Kaolin was found applicable in barring the diffusion of Pb(Ⅱ) in spite that the adsorption capacity toward pollutant would be decreased with increasing dry density.