| It is regarded as a promising environmental remediation technology by using zero valent iron(ZVI) for the treatment of contaminants. As the reduction of contaminants by iron is a surface-mediated reaction, nanoscale zerovalent iron (NZVI) with larger specific surface area show higherreactivity on removing contaminants. However, NZVI is susceptible to aggregation due to thecolloidal property and intrinsic magnetic interaction. Meanwhile, NZVI can also be easily oxidizedand be poor in stability. So the removal ability of contaminants by NZVI can be clearly decreased.Therefore, it is of great importance to prepare supported NZVI with high reactivity and stability byusing suitable supporting materials, which can help to promote the real application of NZVI inenvironmental remediation.In comparison with other supports, the modified bentonites are advantageous due to theirparticular properties of adjustable structure and functions, as well as pH buffering effect. In thisthesis, according to the properties of target contaminants, the modified bentonites supported NZVIwere prepared with different surface zeta potential by suitable methods and they were used for thetreatment of various contaminants. Namely, the positively-charged hydroxo-Al(III)-bentonite-supported NZVI (NZVI/Al-bent) was used to remove anionic inorganic contaminants such asSe(VI)(that is SeO42-), and the negatively-charged Na+-bentonite-supported NZVI(NZVI/Na-bent) was used to remove cationic inorganic contaminants such as Ni(II)(that is Ni2+). The NZVIand supported NZVIs were characterized with TEM, XRD and BET techniques. Combining thebatch with advanced analysis methods (such as AAS, X-ray photoelectron spectroscopy (XPS), X-ray Absorption Fine Structure (XAFS)), the reaction process of Se(VI) and Ni(II) removal byNZVI/Al-bent, NZVI/Na-bent and NZVI systems was studied. The change of contaminantcompositions and pH in the reaction systems, the iron concentration released into the solutions,surface compositions of reaction product, and microenvironment of main elements on solidreaction product were all investigated. The difference of reaction kinetics and reusability of Se(VI)and Ni(II) by NZVI and supported NZVIs was compared. The synergetic effect of modifiedbentonites in the removal of contaminants by NZVI was studied from the micro level.The main research results included that:(1) The modifided bentonites (Na-bent and Al-bent) asthe carrier of NZVI could effectively prevent it from aggregation, and improve the removal efficiency on contaminants by supported NZVIs. In addition, the carrier also has a buffering effectfor the pH in the solution.(2) The removal efficiency of Se(VI) and Ni(II) by NZVI/Al-bent and NZVI/Na-bent.is notonly much higher than that by NZVI containing the same amount of iron, but also superior to thesum of reduction by NZVI plus adsorption by Na-bent and Al-bent, respectively. This indicates thegood synergetic effect between NZVI reduction and modifided bentonite adsorption.(3) The kinetic studies suggested that the removal of Se(VI) and Ni(II) by NZVI, NZVI/Al-bent and NZVI/Na-bent are surface reaction and can be fitted well to the L-H model. The reactionrate was positively related to the adsorption of Se(VI) and Ni(II) on NZVI, NZVI/Al-bent andNZVI/Na-bent. Namely, the negatively-charged NZVI/Na-bent showed higher removal ofcationic Ni(II), while the positively-charged NZVI/Al-bent showed higher removal of anionicSe(VI).(4) XPS and XAFS analysis results showed that the modified bentonites can transfer part ofthe corrosion products from iron surface to bentonites, which help to increase the reactivity ofNZVI. |
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