定量化研究重金属镉在碱性土壤中的迁移对我国北方水土资源环境的保护具有重要意义。本文以保守性溶质Cl-作为参照，以饱和土柱中开展的镉（Cd2＋）在3种土壤、2种输入浓度条件下的室内易混合置换实验为模拟对象，运用连续时间随机游动（Continuous Time Random Walk，CTRW）理论，模拟Cl-和Cd2＋在几种特定实验条件下的运移动态。模拟值与实测值的对比显示，无论是保守性溶质cl一还是重金属Cd2＋，CTRW理论都能够较好地拟合它们在不同实验条件下的穿透行为，较完整地刻画出它们在供试土壤中出流液浓度的动态过程。相对于保守性示踪剂仅受到物理非平衡条件的影响，同一土柱中的重金属镉的运移同时还受到化学非平衡条件的影响，因而导致了镉与示踪剂所对应的CTRW参数的差异。本文对CTRW理论在重金属运移行为模拟中的应用，既是对该理论模拟重金属镉在水土环境中迁移的有效性的评价，同时也在一定程度上为深化对CTRW中参数物理意义的理解，特别是为进一步加深对这些参数与非平衡条件之间的关系的理解提供了重要的参考依据。%Quantitative study of the transport behavior of the heavy metal cadmium in alkali soils has great significance for the preservation of the soil-water environment in North China. This study demonstrates the application of Continuous Time Random Walk （CTRW） theory to fit the breakthrough curves（BTCs） from miscible displacement of cadmium through three soils of different textures for two input concentrations of each soil, in which Cl-is used as the tracer. Results show that the theoretical solutions are consistent with the experimental measurements, indicating that the CTRW approach convincingly captures the full evolution of Cl-and Cd2＋ under all experimental conditions herein. Unlike the BTCs of tracer Cl- which only undergoes physical nonequilibrium, the Cd2＋ is subject to both physical and chemical nonequilibrium, which results in a discrepancy in the CTRW parameters for cadmium and Cl- under the same column conditions. Applications of CTRW theory to describe transport of cadmium not only validate the effectiveness of such theory in modeling of heavy metal cadmium, but also shed light on the physical meaning of the CTRW parameters, particularly provide deeper understanding of the relationship between these parameters and the nonequilibrium conditions.
展开▼
