Preparations Of Functional Materials Based On Calixarene And Amidoxime Groups And Their Separation Preformances Of Metal Ions

Nuclear energy,as a kind of low-carbon,efficient and clean energy,has attracted widespread attention.With the development of nuclear industry,the demand for uranium resources is rising rapidly,and the uranium resources on land can not meet the needs of the nuclear industry.Therefore,the extraction of uranium from seawater,Saline Lake and other aqueous solution is of great significance.On the other hand,with the rapid development of nuclear industry,a large amount of nuclear wastewater containing lots of lanthanum and actinide metal ions is being produced.It is of great significance to enrich lanthanum and actinide metal ions from nuclear wastewater for the sustainable utilization of resources and environment security.Therefore,it is necessary to research on the separation and extraction of lanthanum and actinide metal ions from aqueous solution.Calixarene has the advantages of easily modified structure,good ion recognition ability,high radiation stability and thermal stability,so it has a good application prospect in the recognition and extraction of metal ions.Amidoxime functional group,which is copmosed of amino and oxime,has a unique chelation of uranyl ion and is widely used in the extraction towards uranyl ion.Although europium is a kind of lanthanide elements,it is often used for simulation of actinides because of their similar physical and chemical properties.And neodymium,as rare earth elements,has great practical application value in industrial production.In this work,Eu,Nd and U were selected as the extraction aim.Based on the performance of calixarene and amidoxime,six kinds of separation materials were prepared and investigated to evaluate the separation performances towards Eu(?),Nd(?) and U(?) in aqueous solution.Four kinds of different carboxylic acid modified calixarenes were chosen as the extractants and characterized by FT-IR,¹H NMR,and MS,respectively.The extraction behaviors of these different carboxylic acid modified calixarenes towards Eu(?) and Nd(?) were performed under different conditions,including p H,concentration of extractants and temperature.Carboxylic acid modified calix[6]arene(C6ACOOH)showed remarkably high extraction ability for Eu(?)and Nd(?).The thermodynamic parameters(enthalpy,entropy and Gibbs free energy)were determined.The extraction of Eu(?)with C6ACOOH occurred with a cation exchange reaction and this extraction reaction is an exothermic process.Kinetic studies of reactive extraction of Eu(?)with C6ACOOH were performed in a stirred cell.The value of mass-transfer coefficient of Eu(?) in chloroform was evaluated to be 3.35�10^-6 m/s.The Hatta number was calculated and observed to vary in the range of 3.80�10^-4-9.10�10^-4.The effects of stirring speed,the phase volume ratio and species concentration on the initial extraction rate and Hatta number,demonstrate that the reaction is a very slow chemical reaction process occurring at the bulk of the organic phase.The rate constants of forward and backward reactions were determined,respectively.In order to improve the selective extraction capacity of calixarene towards uranyl ion,a novel calixarene derivative,amidoxime group modified calix[8]arene(C8A-AO) was synthesized from the nitrile group modified calix[8]arene(C8A-CN),and then the nitrile group was changed into amidoxime group by treating with hydroxylamine under alkaline solution.And the products were characterized by NMR,FT-IR,FE-SEM,XPS and TG.The prepared C8A-AO was applied to adsorb U(VI)in low concertration uranium solution,less than 1 mg/L.Effects of pH,contact time,initial concentration,and temperature on the sorption of U(VI)on C8A-AO were investigated.The adsorption efficiency of U(?) on C8A-AO reached more than 95%in neutral solution.The results showed the adsorbent C8A-AO had an excellent distribution coefficient(K_d)when the initial uranium concentration was less than 1mg/L.Besides,the adsorption results revealed that the kinetics of U(?) adsorption followed pseudo-second-order model and the adsorption isotherm fitted well with Langmuir model.The results of thermodynamic parameters showed that the adsorption process of U(?) was spontaneous,feasible and endothermic.Furthermore,the excellent selective adsorption capability of U(?) in simulated seawater suggested that C8A-AO was a potential adsorbent for recovery of U(?) from seawater.Based on activated carbon fibers(ACFs),amidoxime-grafted activated carbon fibers(ACFs-AO),was prepared using a chemical grafting method and tested for the efficient removal of uranium from aqueous solution.The sorbent was characterized using XPS,FE-SEM,elemental analysis,TGA and BET.The effects of p H,contact time,initial concentration,and temperature on the sorption of U(?) were investigated.The sorption of U(?) on ACFs-AO obeyed pseudo-second-order model and Langmuir isotherm.The sorption capacity of ACFs-AO for U(?)(about 191.6 mg/g)was much higher than that of activated carbon fibers(ACFs)(about 70.52 mg/g),which was mainly attributed to surface complexation between U(VI)and the amidoxime group on ACFs-AO.Additionally,the thermodynamic parameter results showed that the sorption process of U(?) was spontaneous,feasible,and endothermic.Moreover,ACFs-AO adsorbed U(?) selectively in an aqueous solution containing competitive ions,and was regenerated and reused efficiently.Based on the comparison of pH of the solution and the XPS spectra of ACFs-AO before and after the adsorption of U(?),it can be concluded that the uranyl ions were adsorbed onto ACFs-AO through the complexation of U(?) with both the amine and hydroxyl groups of the amidoxime groups.The findings of this work indicate that ACFs-AO could be a promising sorbent for the effective removal of U(?) from aqueous solution.This study on the preparation and seperation performances of these novel and effective materials for the research on the separation of Eu(?),Nd(?)and U(?) from aqueous solution provides experimental data and credible theoretical foundation.It will promote the development of the work on effective separation towards lanthanide actinides in nuclear industry.