Preparation Of Functional ?-cyclodextrin Modified Copolymer And Evaluation Of The Adsorption And Regeneration Properties Of Uranium And Thorium

Based on the background of uranium and thorium recovery from seawater and high discharge waste liquid,adsorption method has been widely discussed on account of?cost-effectively?and?environmentally friendly?.Various adsorbents have been investigated extensively in order to minimize the usage of costly or avoiding the use of other expensive and complex treatment technologies.Four kinds of?-cyclodextrin/maleic anhydride-co-acrylonitrile-co-maleic anhydride copolymer??-CD/MAH-co-AN-co-MAH?with different ratios of raw materials were synthesized and got the amidoxime-functionalized products of the copolymers.The chemical structure,thermal stability,and mechanical strength were evaluated by means of Fourier transform infrared spectra?FTIR?,scanning electron microscopy?SEM?,X-ray Diffraction?XRD?,thermal gravity analysis?TGA?techniques.And then the adsorption performance and mechanism of U???and Th???onto the adsorbent were also investigated.At the same time,the structure of the material and the change of functional groups after adsorption and desorption experiments can be observed by these characterization methods.By batch adsorption experiments to explored the adsorption performance and mechanism of U???,Th???.The experimental results showed that the maximum adsorption capacity of U???adsorption onto the material before and after amidoxime was 0.24 g/g and 0.75 g/g,respectively.And the maximum adsorption capacity of Th???adsorption onto the material before and after amidoxime was 0.37 g/g and 0.35 g/.Experimental results indicated that the copolymer showed the best adsorption performance while the raw material ratio of?-CD,MAH and AN was 1:18:18,which was due to its optimized support structure and the presence of amidoxime groups.The adsorption of U?VI?on?-CD/MAH-co-AO-co-MAH was strongly dependent on pH and positive ions in the following order:K⁺>Mg²⁺>Na⁺,however,the presence of different concentrations of Na⁺and negative ions?i.e.ClO₄^-,Cl^-and NO₃^-ions?increases the ionic strength of the solution without affecting the efficiency of uranium adsorption.The adsorption process fitting results indicated that the adsorption followed the Langmuir isotherm model and the maximum adsorption capacity was 0.75 g/g at pH 4.0.The E value obtained from D-R model was 8.47 kJ/mol approving that the process of adsorption was mainly controlled by chemical ion-exchange,which is related to the strong complexing action between U???and AO groups.The highest correlation coefficient value?R²=0.9996?of pseudo-second-order kinetics model close to 1,which indicated that the process of adsorption was chemisorption controlled by the rate-limiting step.Dynamic fitting results implied that the valence forces between the U???ions and?-CD/MAH-co-AO-co-MAH through sharing or exchanging of electrons.The equilibrium of U???adsorption on adsorbent is reached within 50 min,which makes the adsorbent have a strong ability of regeneration,and be helpful to reduce the processing cost.The electron-donating ability of amidoximate is stronger than that of carboxyl,which is due to the bond lengths of U=O bonds for U adsorption onto the carboxyl-based adsorbents are shorter than those for the U adsorption onto the amidoximate-based adsorbents.In addition,the regeneration performance was investigated by varying the concentration of eluent,temperature and contact time.Under the desorption condition of 0.10 M HNO₃,the adsorbents can be reused 12 times,in the case that the adsorption capacity was not significantly reduced.The functionalized copolymer exhibits high selectivity under circumstance of other co-existing ions is present in the solution.