Cadmium (Cd) pollution in soil has attracted more attention recently for its high toxicity and easy accumulation in crops. This study aims to investigate the mechanisms governing the transport behavior of Cd, and to simulate and predict the long-term migration of Cd in different paddy soil layers. Therefore, a layer-by-layer (LBL) model based on the geochemical model PHREEQC was developed. A dual-porosity finite difference method was applied to model the two-region diffusion process. The solute transport parameters were obtained by field measurement, literature review, or inversely estimation using PHREEQC based on the experimental results. Modeling and experimental results both indicate that different mechanisms (cation exchange reaction, preferential flow, etc.) control the transport and vertical distribution of Cd. The prediction results show that only the surface soil (< 0.3 m) would pose the risk of Cd²⁺ pollution. The coupled LBL model could correctly simulate the migration of Cd under near-field conditions.

土壤中的镉（Cd）污染由于其高毒性和易于在农作物中积累而引起了越来越多的关注。这项研究旨在探讨控制Cd迁移行为的机制，并模拟和预测Cd在不同水稻土层中的长期迁移。因此，建立了基于地球化学模型PHREEQC的逐层（LBL）模型。应用双孔隙度有限差分法对两区域扩散过程进行建模。溶质运移参数是通过实地测量，文献综述或根据实验结果使用PHREEQC进行反估计而获得的。建模和实验结果均表明，不同的机制（阳离子交换反应，优先流动等）控制Cd的迁移和垂直分布。²⁺污染。耦合的LBL模型可以正确模拟Cd在近场条件下的迁移。