Cs~+ Loading Of Zeolite 4A In Electrolytic Refining Waste Salt And Its Solidification

The waste salt produced by spent fuel dry reprocessing contains chlorides of various fission products.Because zeolite 4A has good cation exchange performance and a sodalite structure with Cl^-to hold chlorides,using zeolite 4A to load the fission products in the waste salt for solidification treatment has attracted widespread attention.In order to purify waste salts and reduce the amount of radioactive waste disposal,in this work,zeolite 4A was used to support Cs⁺in waste salts,and the Cs⁺loaded zeolite 4A was made into glass-ceramic waste forms at high temperature.The leaching property of glass-ceramic waste forms was explored.The main research contents are as follows:（1）The Cs⁺loaded zeolite 4A was studied in Li Cl-KCl molten salts.It was found that the Cs⁺content in zeolite 4A increased slightly with increasing temperature at below 600℃.However,at 600℃,the crystal structure of zeolite 4A collapsed.When the mass ratio of salt to zeolite is in the range of 5:1～15:1,the Cs⁺content in zeolite was relatively close,while the Cs⁺content was low at 3:1 and 20:1.The Cs⁺content in the zeolite increases with the increase of the concentration of Cs Cl.The lattice parameters of zeolite 4A before and after loading Cs⁺were calculated by XRD.It was found that lattice shrinkage occurred,indicating that in addition to loading Cs⁺,ion exchange appeared between Li⁺from in molten salts and Na⁺.The influence of Li⁺on lattice parameters was greater than that of Cs⁺.（2）The Cs⁺loaded zeolite 4A was studied in solid Li Cl-KCl waste salt.The Cs⁺content of zeolite 4A increased with increasing temperature.When the temperature was close to the eutectic point of Li Cl-KCl,the Cs⁺content of zeolite 4A was slightly higher than that obtained in molten waste salt.The Cs⁺content in zeolite 4A increased with the increase of Cs Cl content in the waste salt.When Cs Cl content was higher than 4 wt.%,the influence of Cs Cl content on the Cs⁺content in zeolite 4A began to weaken.It is found that the Cs⁺content in zeolite 4A had a higher Cs⁺content when zeolite 4A has a smaller particle size.It was found that lattice shrinkage occurred,indicating that in addition to loading Cs⁺,ion exchange appeared between Li⁺from in molten salts and Na⁺.The influence of Li⁺on lattice parameters was greater than that of Cs⁺.（3）Iron borophosphate glass and borosilicate glass were prepared.Glass powder was used as a binder and Cs⁺loaded zeolite 4A was blended at 800℃to prepare a glass ceramic waste form.The structural properties of glass ceramic with different mass ratios of iron borophosphate glass/zeolite were studied.The results showed that there was almost no glass phase and a large number of pores in glass ceramic.With the addition of zeolite 4A,the hardness of glass ceramic increased and the color gradually turned red.The crystal phase formed by Cs⁺is Cs₄Al₄Si₂₀O₄₈.After 28 days of immersion in 90℃deionized water,the normalized leaching rate of Cs⁺in waste form prepared at mass ratio of 3:1,1:1,1:3 was found to be 9.38×10^-4 g m^-2 d^-1,5.20×10^-5 g m^-2 d^-1 and 1.44×10^-6 g m^-2 d^-1.The structural properties of glass ceramic with different borosilicate glass/zeolite ratios have been studied.The results showed that when waste form was prepared in the mass ratio（glass/zeolite）of 3:1 and 1:1,there is a glass phase in the waste form,while the mass ratio in 1:3,there is almost no glass phase,and there are a lot of pores.The formed crystal phase related to Cs⁺in waste form was found to be Cs Al Si₂O₆.After being immersed in 90℃deionized water for 28 days,the normalized leaching rates of Cs⁺in waste form prepared in the mass ratio of 3:1,1:1,1:3 were found to be 3.10×10^-5 g m^-2 d^-1,2.18×10^-4g m^-2 d^-1 and 2.32×10^-4 g m^-2 d^-1.Comparing the two glass ceramic,the iron borophosphate waste form with a glass/zeolite mass ratio of 1:3 has the lowest normalized leaching rate of Cs⁺.