弱磁场与阴离子对零价铁去除水中As(III)的协同作用机制研究

The coexisting ion present in water is an important factor that determining the reactivity and longevity of zero-valent iron (ZVI). On the other hand, upon exposure to a magnetic field, the movement of these charged ions would be affected by either the Lorentz force or magnetic gradient force. Previous studies have evidenced that the introduction of a weak magnetic field (WMF) can significantly enhance the corrosion of ZVI and thereby induce an improvement in contaminants removal. However, regarding to the mechanism of the WMF effect, it is not quite clear now and more research are thus needed. Moreover, with a magnetic field the major anion effects on ZVI reactivity may be quite different from without, while no relevant comparative tests have been conducted, to the best of our konwledge. Given that, we first propose that there may be coupled effects of WMF and anions on the ZVI performance, where the co-existing anions may play important roles in supporting or stimulating the WMF effect. Accordingly, in this project, As(III) will be seclected as the model pollutant by using its sequestration rate as a metric of ZVI reactivity influenced by anions in the presence of WMF. The main objectives of this study are, therefore, to compare the effects of major anions on the ZVI reactivity toward As(III) with and without WMF by batch and column tests; to investigate the possible coupled effects of anions and WMF on ZVI reactivity via the migration of ions (including anions and Fe2+) and the generation/transformation of corrosion products. This project will not only offer a better understanding of the relationship between anions and ZVI reactivity but also provide some insights into how the WMF-enhacing effect works.

水中共存离子是影响零价铁反应活性及其长效运行的重要因素。磁场作用下，零价铁体系中的各带电离子会因洛伦兹力或磁场梯度力而发生迁移运动。最新研究证实外加弱磁场可显著加快零价铁的腐蚀进而提高其对污染物的去除效果，然而弱磁场这一加速作用的机制目前尚不十分明确。弱磁场与阴离子间可能存在协同作用，其有望为深入探索弱磁场在零价铁除污染过程中的作用机制提供一个突破口。因此，本课题拟以As(III)为目标污染物，通过间歇实验考察弱磁场条件下水中常见阴离子对零价铁反应活性的影响特性，并系统地研究弱磁场和阴离子共存时，固液界面阴离子、顺磁性Fe2+离子的迁移运动规律以及零价铁腐蚀产物生成、演变过程，从而揭示弱磁场与阴离子对零价铁腐蚀除污染的协同作用。本课题的实施将进一步明确共存离子与零价铁反应活性的关系，并为利用弱磁场来提高或维持零价铁反应活性提供深入的理论依据。

零价铁是土壤/地下水修复及工业废水处理中常用的环境功能材料，然而受制于自身较低的反应活性，其进一步推广应用受到了阻碍。因此本研究以提高零价铁的反应活性为目标，基于零价铁铁磁性及化学反应体系电荷平衡理论，系统研究了弱磁场与阴离子对零价铁去除污染物的协同作用效能与机理。研究结果发现，弱磁场可显著提升零价铁去除水中包含As(III)在内的多种污染物的反应活性，且阴离子的存在对这一促进作用能否产生至关重要。弱磁场与阴离子的协同强化作用与阴离子的种类密切相关，其中硫酸根离子的作用效果最为突出。磁场梯度力是弱磁场强化零价铁去除污染物的主要作用机制，其能驱动顺磁性亚铁离子的定向迁移，从而引起非均匀腐蚀；而阴离子是亚铁离子迁移的 “载体”，其能中和亚铁离子定向迁移所积累的正电荷，进而维持亚铁离子的持续迁移。