Study On Mechanism Of Kaolinite Adsorbing Of Th(?)

Uranium is the main raw material for nuclear energy development.In the process of uranium mining,some of the uranium ore and the radionuclides contained in it diffuse into the environment and have an impact on ecology and human health.Adsorption of radioactive waste water is currently a more mature treatment method.Kaolinite has the characteristics of low price,large specific surface area and good adsorption performance,making it an important material for adsorption research.This paper mainly studies the adsorption mechanism of kaolinite for Th(IV),from two aspects: first-principles calculations and experiments.In theory,the first-principles method models kaolinite and performs global relaxation optimization.Choose the approximate method of GGA-PBE,the cutoff can be 450 e V,the K point is 4×4×2,and Gaussian widening is used for calculation.After optimization,the stable kaolinite crystal lattice parameters are(a=5.1569 ?,b=8.9544 ?,c=7.3277 ?,?=91.8800°,?=105.2778°,?=89.7645°),and the lowest energy is obtained from them The adsorption surface-001 surface.Then,adsorption models of three different adsorption sites(top position,bridge position,and hole position)of kaolinite(001)adsorbing Th(IV)was created.By calculating the density of states and the differential charge density,electronic properties and adsorption energy explain the adsorption mechanism of adsorption.In terms of experiments,the batch static experiment method was used to study the effect of Th(IV)on the adsorption conditions of kaolinite,and the kinetic and thermodynamic models were fitted.The results showed that:(1)Comparing the results of simulation and XRD characterization,it is shown that kaolinite is easily cracked from the 001 surface to form a stable interface,in which the SiO(001)surface is negatively charged,and Th(IV)ions are more easily adsorbed on this surface.SEM results show that the surface of kaolinite does adsorb Th(IV)in the solution.(2)The static experiment results show that the initial p H,temperature,time,solid-toliquid ratio and initial Th(IV)concentration of the solution all affect the adsorption performance of kaolinite.Binding experiments and simulation results of adsorption rate increases as the p H increases,mainly because of kaolinite cleavage surface 001 and negatively charged surface enhancement.When the p H is 3.0 ? 4.0,it is the equipotential of kaolinite at this time,so it has little effect on adsorption.(3)Comparing the results of first-principles and kinetic and thermodynamic model fitting,it shows that the adsorption is a spontaneous surface monolayer adsorption based on chemical adsorption.The law of adsorption energy for Th(IV)at different adsorption sites of kaolinite is: hole site adsorption energy(-426.1580 k J/mol)<bridge site adsorption energy(-321.3870 k J/mol)<top site adsorption energy(-222.4040 KJ/mol);The charge transfer number of Th is: hole site adsorption>bridge site adsorption>top site adsorption.That is,the greater the charge transfer number of Th,the greater the bond energy,the more stable the system of kaolinite adsorption of Th(IV),and the lower the adsorption energy.(4)The simulation results of lattice parameters and electronic properties show that kaolinite is an insulator mineral with a band gap of 5.002 e V before adsorption.After adsorption,the kaolinite 001-Th(IV)system will exhibit metallic behavior.Metal bonds between Th atoms.A pseudo-energy gap will be generated at the Fermi level to enhance the structural stability of the adsorption system.(5)The total electron density of states after adsorption moves to the lower energy direction,and the characteristic energy peak of Th is added.The p orbitals of Th will form bonds with the 2p orbitals of O and Si to form Th-O and Th-Si bonds.The energy range of the orbitals for bonding is-9 e V to Fermi level and-25 e V to-20 e V.