Fabrication Of Functionalized Boron Nitride And Mesoporous Silica And Studies On Their Adsorption Performance For Uranium And Thorium

Rare earths are commonly accompanied by uranium(U)and thorium(Th)via lattice substitution due to their similar chemical structures.The radioactivity of U and Th can not only cause pollution of environment and rare earth product,but also harm to human health during rare earths production.Hence,the separation of U and Th from rare earths becomes more important.Although solvent extraction is a major technique to remove U and Th from rare earths,it suffers from various problems such as the formation of third phase,complex process and disposal of large-scale organic solvent.Using economic and efficient solid-phase adsorption could overcome these drawbacks.This thesis synthesized solid-phase adsorbent by functionalization of mesoporous silica and boron nitride for separation of U and Th from rare earths.1.A fibrous hierarchically porous silica(F-SiO2)was prepared first,and then functionalized by diamide phenanthroline group(DP)to obtain solid-phase adsorbent F-SiO2-DP.F-SiO2-DP exhibits ultrafast adsorption kinetics for U(?)and Th(?)adsorption,which can reach equilibrium within 10 min.The adsorption of U(?)and Th(?)on F-SiO2-DP fits the pseudo-second-order kinetic model well.The adsorption isotherms U(?)and Th(?)on F-SiO2-DP fits Langmuir model well.The maximum adsorption capacity of U(?)(pH=5.0)and Th(?)(pH=3.8)are 416 and 277 mg/g,respectively.The hierarchically porous structure endows F-SiO2-DP faster adsorption kinetics and adsorption capacity compared with unimodal mesoporous silica like MCM-41 functionalized with DP.Higher temperature can facilitate the adsorption of U(?)and Th(?)on F-SiO2-DP.The selectivity coefficient of U(?)and Th(?)over rare earths is all larger than 9,indicating that F-SiO2-DP possesses excellent and selective adsorption performance for U(?)and Th(?).2.The irradiation stability of F-SiO2-DP was investigated in aqueous and 3 mol/L HNO3 under y-ray irradiation.One of the reasons of decrease of adsorption capacity of U(?)and Th(?)on y-irradiated F-SiO2-DP was caused by the reaction between solvated electrons induced y irradiation and functional group on F-SiO2-DP surface.The reaction rate constant between solvated electrons and DP is 1.0×109 L/(mol s)by the pulse radiolysis experiment of DP.The F-SiO2-DP still has excellent and selective adsorption performance for U(?)and Th(?)after y irradiation.3.Boron nitride was co-modified by dopamine and APTES to obtain solid-phase adsorbent BN@PDA+APTES.The adsorption of U(?)and Th(?)on boron nitride obviously increased after modification.The equilibrium time of U(?)and Th(?)are 60 and 30 min respectively.The adsorption of U(?)and Th(?)on BN@PDA+APTES fits the pseudo-second-order kinetic model well.The adsorption of U(?)and Th(?)on F-SiO2-DP fits Langmuir model well.The maximum adsorption capacity of U(?)(pH=5.0)and Th(?)(pH=3.8)are 110 and 83 mg/g respectively.Higher temperature can facilitate the adsorption of U(?)and Th(?)on BN@PDA+APTES.This original achieves of this dissertation are as following:1.The separation performance of U(?)and Th(?)from rare earths by adsorbent F-SiO2-DP based on hierarchically mesoporous silica was investigated.The hierarchically mesoporous structure endows F-SiO2-DP faster adsorption kinetics and adsorption capacity compared with unimodal mesoporous silica like MCM-41.Moreover,F-SiO2-DP possesses a good simultaneously selective adsorption performance for U(?)and Th(?)from rare earth.2.The reaction between DP and solvated electrons in octanol was studied by pulse radiolysis technique.One of the reasons of decrease of adsorption capacity of U(?)and Th(?)on y irradiated F-SiO2-DP was the reaction of solvated electrons induced y irradiation and functional group on F-SiO2-DP surface.3.Boron nitride was co-modified by dopamine and APTES for investigating the adsorption of U(?)and Th(?).There was almost no adsorption of U(?)and Th(?)on pristine boron nitride,but the equilibrium adsorption capacity of U(?)and Th(?)increased largely after modification of boron nitride.In this work,two novel adsorbents(F-SiO2-DP and BN@PDA+APTES)were successfully prepared,which can achieve efficient adsorption for uranium and thorium.The research results can provide theoretical references for separation of uranium and thorium from rare earths,together with separation of uranium and thorium from radioactive waste liquids.