Study On The Removal Of Soluble Cr(VI) By Using Zero-valent Iron Composite Supported By Surfactant Modified Zeolite

Surfactant modified zeolites(SMZ) and zero velant iron(ZVI) powder have be intercepted in the PRB to restore the groundwater contaminated by hexavalent chromiun(Cr(VI)). Combing the SMZ and ZVI, based on the adsorption ability of SMZ and the reducibility of ZVI, would synthesis an enhanced composite used for the removal of Cr(VI).The key points to gain such kind of composite are as following: 1) Solving the depleting of ZVI as water flow passes. It had been proved that the small particle size of the ZVI powder, the more active it will be. So it will pass across the pores in the basement material in PRB when the size of the selected ZVI powder is too small. 2) Holding the adsorption capability of SMZ. In the process of preparing the composite, it is hard to avoid inducing any chemicals which can react with the surfactant, which would make SMZ lose its ability. Considering for these problems, the sol-gel reaction between the aliginate and CaCl2 was for the immobilization of ZVI powder and the HDTMA-Br was used as the surfactant for natural zeolite in this thesis.The composite was prepared to determine whether the problems above have been solved. Scanning electron microscopy showed that ZVI powder was uniformly immobilized on the surface of the SMZ. The composite reacted with Cr(VI) was analyzed by X-ray photoelectron spectrometry(XPS), and the results revealed that there are both Cr(VI) and Cr(III) in the surface of the composite, which proved that composites combined the strong reductive quality of ZVI and superior adsorption of SMZ.Lab scale experiment was used to test the capability of the composite for removing Cr(VI). It showed that the process of Cr(VI) removal by the composite can be expressed in a pseudo second order model. The changing trend of qe and k was opposite. The composite with a 5.4% iron content showed better performance: its qe was 0.96mg/g, and k was 0.011g/(mg?h). And it still showed good performance when the concentration of Cr(VI) was 70mg/L. It has a qe of 1.29mg/g, and a k of 0.0094g/(mg?h). Using the Langmuir isotherm to fit the data from the Cr(VI) adsorption by composite got a maximum adsorption capacity of 2.49mg/g. Furthermore, higher removal efficiency was obtained at pH lower than 7.Cr(VI) treatment efficiency was test by column experiment under various chemicals condition. The column experiment proved that the induced Cl- at the time that adding CaCl2 to transform the alginate could react with HDTMA-Br and change to HDTMA-Cl. And the HDTMA-Cl could also have ion exchange with Cr(VI) and remove it, it had little influent on the treatment effect.By exploiting the sol-gel reaction between the alginate and CaCl2, an enhanced composite used for the removal of Cr(VI) was prepared. Iron powder was immobilized outside the composite, which solve the depleting of ZVI. And the adsorption ability of SMZ was hold by the composite at the same time.