零价铁-生物炭复合材料对地下水中硝酸盐的去除

Nitrate removal from groundwater by zero-valent iron-biochar composites

为了解决我国日益严重的地下水中硝酸盐污染问题,采用液相还原法制备了零价铁-生物炭复合材料(ZVI-BC)。研究了不同制备条件对ZVI-BC合成的影响,并通过X射线衍射(XRD)、电子扫描显微镜(SEM)、透射电镜(TEM)和X射线光电子能谱(XPS)对优选制备条件下所合成的复合材料进行了表征分析。在严格控制厌氧环境的基础上,考察了初始pH、初始硝酸盐浓度、复合材料投加量和反应温度对复合材料去除水中硝酸盐效率的影响,并从动力学、氮平衡等方面初步探讨了零价铁-生物炭复合材料还原硝酸盐的途径。结果表明:复合材料的优选制备条件为聚乙烯吡络烷酮K30(PVP)作溶剂、ZVI∶BC=1∶0.1,通过对在优选制备条件下得到的零价铁-生物炭复合材料的SEM表征,发现成链状连接的零价铁颗粒负载在层状分布的生物炭表面,其对硝酸盐具有良好的去除效果;初始硝酸盐浓度越大,则反应初期硝酸盐去除速率越慢,硝酸盐的去除率越低;硝酸盐去除率随复合材料投加量的增加而有所升高;反应体系中的pH对复合材料降解硝酸盐的影响不大;反应体系的温度越高,硝酸盐去除速率越快;硝酸盐去除过程不能单纯的使用反应级数来表示,硝酸盐反应的最终产物主要为氨氮。生物炭负载零价铁有效的减少了零价铁的团聚,进一步促进了硝酸盐的去除,在地下水硝酸盐的去除中具有良好的应用前景。

In order to solve the problem of increasingly serious nitrate pollution in groundwater of China,zerovalent iron-biochar composites(ZVI-BC)were prepared by liquid phase reduction.The effects of different preparation conditions on the synthesis of ZVI-BC were studied,and the composites synthesized under the optimal preparation conditions were characterized by X-ray diffraction(XRD),electron scanning microscope(SEM),transmission electron microscope(TEM)and X-ray photoelectron spectroscopy(XPS).Under the strictly anaerobic environment condition,the effects of initial pH,initial nitrate concentration,composite dosage and reaction temperature on the removal efficiency of nitrate in water were investigated.The ways of reducing nitrate by zero-valent iron-biochar composites were preliminarily discussed from the aspects of kinetics and nitrogen balance.The results show that the preferred preparation conditions of the composites were following:polyvinylpyrrolidone K30(PVP)as solvent and ZVI∶BC=1∶0.1.The SEM images of the composites obtained under the optimized preparation condition showed that the zero-valent iron particles with chain-like connection were loaded on the surface of biochar with lamellar distribution structure,having a good removal performance for nitrate.The higher the initial concentration,the slower the nitrate removal rate at the initial stage of the reaction,the lower the nitrate removal rate.The removal rate of nitrate increased with the increase of composites dosage.The pH of the reaction system had slight effect on nitrate removal by the composites,and the higher the temperature of the reaction system,the faster the nitrate removal rate.The nitrate removal process could not be simply expressed by the use of reaction series,and ammonia nitrogen was the main final product of nitrate reaction.Biochar loaded with zero-valent iron could effectively reduce the agglomeration of zero-valent iron and further promote the removal of nitrate,which has a good application prospect in the removal of nitrate from groundwater.