磁场强化硫化改性零价铁快速去除亚硒酸盐的效能和机理研究

Zero valent iron (ZVI) has been shown to remove a wide variety of contaminants from water. However, passivation has become an obstacle of applying ZVI for contaminants removal either in permeable reactive barrier or in industrial wastewater treatment. In order to solve this problem, sulfide modified Zero valent iron (S-ZVI) synergy with magnetic field were proposed to improve the reactivity of ZVI. In our previous study, it was found that sulfide modified zero valent iron increased the removal rate of selenite than ZVI, and magnetic field accelerated this process further. However, the kinetics and mechanisms of sulfide modified zero-valent iron remove selenite in the presence of magnetic field were still unexplored. Therefore, selenite (Se(IV)) will be selected as the model pollutant in this project. A series of sulfide modified zero valent iron was synthesized by changing the S and Fe mole ratio. The performance of this material for Se(IV) removal was tested by comparison with pure ZVI with or without the presence of magnetic field, and the mechanisms are elucidated based on SEM, XRD, XPS,EXAFS and experimental results. This study will not only offer a simple and effective method of activating ZVI but also intrigue the broader applications of ZVI assistance with magnetic field on field-scale remediation.

本课题针对零价铁易钝化导致反应活性差的问题，提出将零价铁表面覆盖导电子能力强的铁硫化物进行改性，并利用绿色环保的磁技术进行强化来提高其反应活性。申请人前期研究中发现硫化改性可以明显加速零价铁的腐蚀速率，且磁场对该过程有一定的强化作用，但其动力学影响规律和加速机理尚不清晰。因此本项目拟选择毒性较强的亚硒酸盐为目标污染物，制备一系列不同硫铁摩尔比的改性零价铁，在磁场的作用下研究其快速去除亚硒酸盐的动力学过程，对操作条件进行优化；同时设计连续流实验装置，实现磁场强化硫化改性零价铁连续去除亚硒酸盐的过程；利用EXAFS/XPS/XRD等技术探明表面硫化改性加速零价铁去除污染物的关键结构特性，明晰该体系去除亚硒酸盐过程中亚硒酸盐的去除机理及腐蚀产物的生成和演变规律。本项目预期成果将为零价铁的活化提供新的方向，进而推动磁场强化零价铁体系在水处理及环境修复领域的应用。

本课题针对零价铁易钝化导致反应活性差的问题，提出将零价铁表面覆盖导电子能力强的铁硫化物进行改性，并利用绿色环保的磁技术进行强化来提高其反应活性。结果表明零价铁的粒径为30μm、S/Fe摩尔比为1:80、溶液pH=5、S-ZVI投加量为0.75g/L、磁场强度为20mT时、磁场对硫化改性零价铁去除Se(IV)的促进作用最明显。水中常见共存离子Cl-、PO43-、SO42-、Mg2+和Ca2+对反应有促进作用，而NO3-、SiO32-、CO32-对反应有抑制作用，磁场在各种离子存在的条件下对反应均有促进作用。此外，磁场可将反复使用5次的S-ZVI的Kobs提高2.57-5.83倍。为明确磁场强化S-ZVI在柱反应器中连续去除Se(IV)的动力学过程，研究开展了连续流实验，当进水流速为1rpm时，柱子穿透时间为50.1h，进水流速越慢越利于Se(IV)的去除。同时发现S-ZVI与石英砂混合均匀填充比分层填充更有利于Se(IV)的去除，且适量添加活性炭可以提高Se(IV)的去除能力；利用XPS和XANES谱等表征手段发现Se(IV)被S-ZVI通过还原和吸附的方式去除，反应后的S-ZVI部分被氧化为纤铁矿和Fe2O3。综上所述，磁场和硫化改性可以有效的提高零价铁去除Se(IV)的反应活性。在此基础上，项目又进一步拓展了磁场强化以零价铁为基础的类Fenton体系去除染料和内分泌干扰物的研究，同时利用生物炭负载纳米铁去除Se(VI)，并研究纳米铁负载前后对微生物的毒性作用。经过大量研究发现，以零价铁为基础的污染物治理技术具有较好的应用前景。