Adsorption Of U(Ⅵ),Eu(Ⅲ) And Th(Ⅳ) On Magnetic Bamboo Carbon Fiber Composites Activated By Phosphoric Acid

With the rapid development of nuclear industry,the nuclear industry system is also facing the key problems such as radioactive wastewater treatment.In the process of nuclear fuel cycle,a large amount of radioactive waste water will be produced.This kind of waste water must be strictly treated before it is allowed to be discharged into the environment.Among various treatment methods,adsorption method has the advantages of high efficiency,simplicity,economy and environmental protection.Activated carbon is widely used in water purification and decontamination.Bamboo fiber has pore structure.The specific surface area of activated carbon prepared is large,and it has been widely concerned because of its simple preparation technology and economic.In this paper,europium（Ⅲ）elements,which are commonly used in the simulation of trivalent actinides and lanthanides,and U（VI）and Th（Ⅳ）as target pollutants,are selected as the target pollutants.The bamboo charcoal fibers are activated by phosphoric acid by high temperature pyrolysis method.Then,the traditional hydrothermal method is used to prepare magnetic phosphoric acid activated bamboo carbon fiber（MABCP）by using ferrous sulfate and iron trichloride as the source of iron.The effects of solid-liquid ratio,p H,ionic strength,time and temperature on the adsorption of U（VI）,Eu（III）and Th（IV）on MABCP were investigated and discussed.The samples were characterized by SEM,FT-IR,bet and XRD.The micro morphologies of the composites before and after adsorption were analyzed by different adsorption models.The conclusions are as follows:（1）The morphology of MABCP is typical of carbon fiber layer structure,and the spherical body on the surface is composed of Fe₃O₄ microspheres,and the magnetic spheres on the layered structure agglomerate after absorption.By analyzing XRD,MABCP has good crystallinity,while some characteristic peak intensity of MABCP adsorbed Eu（Ⅲ）,U（VI）and Th（Ⅳ）changes,mainly because of the increase of diffraction peak strength due to the agglomeration of magnetic spheres.XPS analysis showed that MABCP successfully adsorbed the adsorbate on the material,and the functional groups of MABCP were well preserved after adsorption by FT-IR.（2）The adsorption of U（VI）,Eu（III）and Th（IV）by MABCP was significantly affected by p H;The adsorption of U（VI）and Eu（III）was not dependent on the background ionic strength,and the adsorption was inhibited at low p H;Th（IV）can inhibit the adsorption at high background ion strength,because thorium ion is easy to hydrolyze,and the higher the concentration of background ion in the solution,the higher the background ion concentration is,the more inhibited the adsorption,because high ion strength will compete with the adsorption target ion in the adsorption process.（3）Under different experimental conditions,when the concentration of Eu（III）is 10mg/L,m/v=1 g/L and p H=5.5,the adsorption rate of Eu（Ⅲ）by MABCP is 93.2%,and the adsorption capacity is 23.08 mg/g;the concentration of U（VI）is 10 mg/L,m/v=1 g/L,p H=6.0,the adsorption rate can reach 91.83%,and the theoretical maximum adsorption capacity is 83.8 mg/g.When the initial concentration of Th（Ⅳ）is 10 mg/L,m/v=1 g/L and p H=3.0,the adsorption rate of Th（Ⅳ）is 89.1%,and the theoretical maximum adsorption capacity is 28.44 mg/g.（4）Through the dynamic analysis of MABCP to U（VI）,Eu（Ⅲ）and Th（Ⅳ）,they all conform to the quasi second-order kinetic model,and the chemical adsorption is the main reaction.The results show that the reaction is influenced by the diffusion of particles,liquid film diffusion or external energy exchange.Through thermodynamic analysis,the adsorption of U（VI）,Eu（Ⅲ）and Th（Ⅳ）by MABCP is in good agreement with Langmuir isotherm model,Freundlich isotherm model and D-R isotherm model.It is shown that the reaction is mainly based on surface monolayer adsorption,and multi-layer adsorption is the auxiliary if irregular.In the process of adsorption of U（VI）,Eu（Ⅲ）and Th（Ⅳ）,△G⁰<0and△H⁰>0,the adsorption of these three different nuclides is a spontaneous and endothermic reaction.