| Natural clay minerals are often used as adsorbent in environmental pollution controllingbecause of its advantages of high specific surface area, abundant reserves, low prices and thestability of the physical and chemical properties. The application of clay minerals in the fieldof environmental remediation will create huge beneficial effect in economy and society. Inorder to improve the adsorption performance of natural clay minerals, numerous literatureshave studied different modification methods to improve the properties of clay minerals suchas pore size, specific surface area, thermostability and chemical activity. So the developmentof new, efficient and low-cost adsorption materials through different modification methodshas attracted widespread attention. Based on the review of the properties, modificationmethods and the applications of montmorillonite and vermiculite, the dissertation includedfollowing contents:1. Ethylamine modified montmorillonite (Ethyl-Mt) and ethylamine modifiedvermiculite (Ethyl-VER) were prepared with natural calcium montmorillonite (Ca-Mt) andvermiculite (VER) by ion exchange method. In order to examine the influence of ethylamineto the crystal structure and surface properties of Ca-Mt and Ethyl-Mt, the materials werecharacterized by the methods of X-ray diffraction spectra (XRD), Fourier transform infraredspectra (FTIR), BET analysis, scanning electron microscopy/energy disperse spectroscopy(SEM&EDS) and zeta potential analysis. The results showed that the layered structure ofmontmorillonite has not been destroyed during the modification process, and the specificsurface area was increased from71.15to154.17m2g-1. At the same time, Ethyl-Mt possessedmore negative charge than Ca-Mt, which suggests that the modification improved the surfaceproperties and adsorption performance of montmorillonite.The layered structure ofvermiculite collapsed and striped slightly. The octahedral cations of vermiculite weregradually leaching during the modification process, which lead to the increasing specificsurface area and pore volume.2. The adsorption performance of Ethyl-Mt and Ca-Mt were evaluated by Cs+adsorption experiments consideringthe influencing factors such as initial solution pH, contact time, initialCs+concentration, temperatureand coexistence cations. The results demonstrated that Cs+adsorption on Ethyl-Mt and Ca-Mt could achieve balance within30min. The maximumadsorption capacity of Ethyl-Mt and Ca-Mt were80.27and60.03mg g-1, respectively. ThePseudo-second-order model and Langmuir adsorption isotherm could describe well the Cs+adsorption on Ethyl-Mt and Ca-Mt and the adsorption process was spontaneous exothermicreaction. Furthurmore, Cs+adsorption capacity decreased slightly with the increase intemperatures and an optimal adsorption pH range of4-10was obtained. Coexisting cations inthe solution could significantly inhibit the Cs+adsorption, and the extent of inhibition wasrelated with the charge and chemical properties of coexisting cations. The analyses combiningcharacterization results with adsorption data revealed that the removal mechanisms of Cs+onCa-Mt mainly involved ion-exchange.At the same time, electrostatic interaction and channelinterception also played a role on the Cs+adsorption on Ca-Mt. While the mechanisms of Cs+adsorption on Ethyl-Mt also involved ligand adsorption in addition to the above effect.3. The adsorption properties of Ethyl-VER and VER were studied through Cs+adsorptionexperiments. The results suggested that the maximum uptake of Cs+of vermiculite increasedfrom56.92to78.17mg g-1after modification, and the adsorption process was in accordancewith Langmuir adsorption isotherm. The Pseudo-second-order could describe well the Cs+adsorption on Ethyl-VER and VER with an equilibrium time of30min, and the adsorptionrate of Ethyl-VER was greater than that of VER. The adsorption thermodynamics researchindicated that the adsorption process was spontaneous exothermic reaction. Coexistence ofcations and small molecule organic acid significantly inhibited the Cs+adsorption. Theinhibitory effect was connected with the charge of cations and the number of organicfunctional groups oforganic acids.In addition, the concentration and properties of coexistingcations and small molecule organic acids could significantly affect the degree of inhibition. |
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