包气带中重金属污染物迁移转化机理研究

Vadose zone is a zone that heavy metals must pass when transported to groundwater, and it is also a natural barrier for groundwater. Vadose zone is characterized by unsaturated and preferential flow. Up to now the research on heavy metals pollution in vadose zone focused on the interaction between soil and heavy metals. However, preferential flow and unsaturated flow were scarcely considered. The dynamic characteristics of adsorption-desorption and dissolution-precipitation of typical heavy metals will be investigated by static adsorption and dynamic leaching tests. The migration of heavy metals in unsaturated soil will be investigated by unsaturated soil column penetration tests. The influence of preferential flow on the migration of soluble heavy metals and co-migration of colloid-heavy metals complexes will be investigated by solute breakthrough experiments. A two-domain model will be used to simulate and further investigate the migration of heavy metals. The hydrogeochemistry mechanism of heavy metals migration in vadose zone will be revealed. This program is helpful to pollution control of soils and groundwater. At the same time, this research is of scientific significance in revealing the process of heavy metals migration in vadose zone and promoting the intersection of Hydrogeology and Environmental Engineering.

包气带是地表重金属进入地下水的必经途径，也是地下水免受污染的天然屏障，地表包气带土体处于非饱和状态，且存在优先流通道。当前对包气带重金属污染的研究集中在土壤与重金属相互作用上，考虑包气带非饱和特征及优先流作用的研究很少。本项目选取易迁移的铬、砷和易吸附的铅、镉作为典型重金属，通过静态吸附和动态淋滤试验研究重金属的吸附-解吸动力学特征和溶解-沉淀转化机理，通过非饱和渗透-扩散试验和土柱瞬态淋滤试验研究重金属在非饱和土中扩散、弥散和吸附-解吸机理，通过优先流溶质出流试验研究包气带优先流对溶解态重金属及胶体—重金属共迁移的影响，建立大孔隙与基质中胶体—重金属共迁移数值模型进一步分析包气带重金属迁移规律，揭示包气带重金属迁移转化的水文地球化学作用机理。研究成果对土壤和地下水污染防治具有积极的现实意义，对于探讨包气带中重金属污染物的迁移过程、促进土中污染物运动特征的多学科综合研究具有重要科学意义。

工农业生产活动排放的重金属污染物通过地表进入地下造成污染，地表包气带土体处于非饱和状态，且存在动植物活动、干湿循环等作用形成的污染物迁移优先通道。本项目基于地表土非饱和且存在优先流的物理本质，选取以阳离子形式存在于土中的铅和镉、以阴离子基团形式存在的铬和砷作为典型重金属，通过一系列试验揭示重金属在土中的迁移和转化机理。进行吸附试验研究了四种典型重金属在粉质黏土中吸附的规律和机制；通过稳态非饱和土柱对流-扩散试验，研究了非饱和土中有效扩散系数、吸附量、弥散度、渗透系数随含水率的变化规律；通过土柱穿透试验揭示了优先流条件下重金属迁移以及胶体-重金属共迁移规律；进行玻璃珠柱出流试验研究了土中可溶性有机质对胶体-重金属共迁移的影响规律；研究了溶质迁移过程中的弥散度取值规律；基于铬、砷等重金属在不同价态下具有不同毒性和移动性的特点，研究了铬和砷在固化稳定化土体中的迁移转化机理；针对变价重金属铬，探讨了环境中氧化还原电位和pH变化对固化体中铬迁移转化的影响。研究成果有助于揭示重金属在地表土中迁移转化的地球化学作用机理，对于土壤和地下水污染防治具有积极现实意义。结合本项目共发表论文17篇，其中SCI收录7篇，EI收录10篇。