土壤微观环境对胶体协同核素污染物运移的影响机理及模拟

Radionuclide transport and risk analysis in subsurface and related control factors are important since radionuclides in environments are related to human health, and more and more people realize their significance. A lot of studies found that soil colloids are important for radionuclide transport in soil and groundwater. Soil heterogeneity and unsaturated flow are widely spread in natural environments. They are the key factors of affecting contaminant and colloid transport, and are the long-term and difficult problems for hydrologists and soil scientists. Radionuclides can move through colloid facilitated transport. Because soil heterogeneity and unsaturated flow condition in fields are very common, complex soil environments are widely spread, are extremely important for contaminant transport and remediation, and are the key factors of applying the parameters from laboratory to field scale. It is still unclear for the mechanism of soil microenvironment effect on colloid facilitated radionuclide transport. This project will attempt to do colloid facilitated radionuclide transport experiments under complex soil microenvironments, use X-ray computed tomography to observe soil structure, and combine numerical modeling with experimental data. The soil microenvironments in the experiments include soil heterogeneity and unsaturated flow conditions. The data will provide the basis for exploring the mechanism of colloid facilitated radionuclide transport under complex soil environments and develop related models to describe related phenomena. It is expected that the results from this study will be helpful for preventing colloid facilitated radionuclide into groundwater.

放射性核素在地下环境中的运移规律和风险评价以及影响核元素迁移的因素等基础问题越来越受到全社会重视。大量研究发现土壤胶体是影响核素在土壤和地下水中迁移的重要因素。自然界普遍的土壤存在着非均质性和非饱和流，它们是影响与制约污染物和胶体迁移的根本原因，也是长期困扰水文地质学家和土壤学家的难题。大量的研究发现核素可以随土壤胶体穿越非饱和带进入地下含水层。由于土壤的非均质性和非饱和流场引起土壤环境非常复杂，而这种复杂土壤环境对胶体协同污染物迁移的机制还不清楚。因而，本课题针对土壤非均质性和非饱和流问题，应用激光计算机断层扫描技术获取非均质土壤微观结构，通过室内结构土柱和非饱和土柱模拟野外复杂土壤微观环境，结合胶体迁移模型，来研究改变土壤微观环境对胶体协同核素污染物的迁移影响。本项目有助于揭示胶体协同的核元素污染地下水的发生机制，扩展纳米修复材料在环境治理和修复中的实际应用。

自然界普遍存在的非均质性和非饱和流是影响与制约溶质和胶体迁移的根本原因，也是水文地质领域最活跃的研究方向之一。本课题针对土壤非均质性和非饱和流问题，通过室内不同结构柱实验和相关模型，结合激光计算机断层扫描技术，研究了复杂土壤微观环境对胶体协同核素污染物的迁移影响。研究结果表明：（1）优先流通道可以加速氧化石墨烯的迁移。优先水流通道与周围介质的接触面积越大，氧化石墨烯的穿透量更低且具有更强的拖尾现象。层状结构的交界面处是氧化石墨烯滞留的一个主要区域；（2）高岭石、腐殖酸和高岭石/腐殖酸增强了铀在非均质介质中的移动性。铀的移动性在高岭石/腐殖酸存在时最高，在高岭石单独存在条件下最低。腐殖酸和高岭石/腐殖酸存在的条件下，快水流通道中释放出的铀比慢水流通道中更多。腐殖酸-高岭石胶体对铀迁移的促进作用在粗砂中比细砂中作用更强；（3）当入流液为铀时，离子强度对铀在均质和非均质介质中铀的迁移几乎没有影响。氧化石墨烯促进了铀在均质和非均质介质中的移动。在低离子强度条件下，铀的移动性在通入阶段显著增强，并且介质的非均质性进一步促进了吸附态铀的迁移。在高离子强度条件下，铀的移动性在通入阶段显著减弱，而在淋洗阶段有大量滞留的的吸附态铀释放出来；（4）当入流液中存在高岭石、腐殖酸或腐殖酸-高岭石时，高岭石和腐殖酸可以促进铀移动，并且其促进作用随着饱和度的降低而降低。溶液中存在高岭石、腐殖酸或腐殖酸-高岭石时，在饱和度为60%条件下，铀在快水流通道中的淋洗量均比慢水流通道中多。而铀在慢水流通道中的淋洗量均很小且无明显差别。当饱和度为40%时，铀在淋洗阶段只出现了一个由快水流通道淋出的淋洗峰，并没有出现慢水流通道淋洗出现的第二个淋洗峰。项目发表学术论文10篇，其中SCI论文7篇，培养博士生1名和硕士生3名。