Investigation Of Sorption Of U (Ⅵ) On Modified Clay

Here, three kind of nature clays (bentonite, montmorillonite and halloysite) wereselected as the basic adsorption materials which are rich in our country. The three claymaterials were modified by taking physical and chemical methods, and using infraredspectroscopy, X-ray diffraction, scanning electron microscopy, potentiometric titratorand other testing methods to characterize them. Radionuclide U (VI) ions adsorptionperformance was investigated by using a static test batch of these materials, anddiscussed the influence of adsorption time, adsorbent concentration, pH, ionic strength,plus the impact of electrolyte ions, humic acid and other factors. What’s more, theadsorption isotherms and adsorption thermodynamics of these three materials werealso studied. The experimental results are as follows:①The results indicated that the sorption of U(VI) on the bentonite was stronglydependent on pH and ionic strength. When pH <6.5, the sorption of U(VI) on thebentonite increased with increasing pH, whereas the sorption of U(VI) on bentonitedecreased with increasing pH at pH>6.5. The presence of humic acid (HA) enhancedthe sorption of U(VI) on bentonite obviously at low pH while reduced U(VI) sorptionon bentonite at high pH values. The enhancement of U(VI) sorption on HA-bentonitehybrids at low pH was attributed to the strong surface complexation of surfaceadsorbed HA with U(VI) on bentonite surface.Whereas the decrease of U(VI) sorptionon bentonite at high pH was attributed to the formation of free HA-U(VI) complexesin solution. The Langmuir and Freundlich models were applied to simulate thesorption isotherms of U(VI) at three different temperatures of298,318and338K,respectively. The thermodynamic parameters (i.e., H0, S0and G0) calculated fromthe temperature dependent sorption isotherms indicated that the sorption process ofU(VI) on bentonite was an endothermic and spontaneous process.②β-cyclodextrin (CD) was grafted onto montmorillonite/iron oxides to prepare anovel magnetic CD/MMT/iron oxide composite by low-temperature plasma technology.The sorption irreversibility was attributed to inner-sphere binding of U(VI) onCD/MMT/iron oxide surface sites. The thermodynamic parameters indicated that thesorption of U(VI) on CD/MMT/iron oxide was an endothermic and spontaneous process. The CD/MMT/iron oxide can be potentially used as a cost-effective materialfor the purification of actual U(VI)-bearing effluents.③Graphene oxide (GO) was bind to the halloysite nanotubes by using a new chemicalmethod composite and the novel materials were used to investigate its impact on theadsorption U(VI). The results showed that the pH value of the adsorption behavior ofU(VI) on the composite impact is obvious. U(VI) is adsorbed on HNTs/GO compositeswithin4hours to reach equilibrium; At at pH <3.52, the ionic strength is increasedadsorption inhibition; when at pH>3.52, the influence of ionic strength on theadsorption can ignored. Through the study of adsorption isotherm data at differenttemperatures, and the application of Langmuir and Freundlich models to simulate theirdata, the results showed that the adsorption behavior of U(VI) on the compositematerial is an endothermic and spontaneous process.