Precipitation Method Was Used To Removal Of La(Ⅲ),Sr(Ⅱ) And Ba(Ⅱ) From Electrorefining Waste Salts And Its Solidification

Nuclear power has obvious advantages in sustainable development and low carbon economy.With the widespread use of nuclear energy,radioactive waste continues to accumulate.At present,the electrorefining in molten salts is considered as one of the promising spent fuel reprocessing technologies in the nuclear fuel closed cycle.However,rare earth elements and radioactive fission products continue to accumulate in the molten salt during electrorefining of spent fuel,which seriously hinders the recovery of actinides.In order to recycle molten salt and reduce the amount of high-level radioactive waste disposal,the fission products must be removed from the molten salt.Therefore,in this work,La（Ⅲ）,Sr（Ⅱ）and Ba（Ⅱ）were precipitated and separated from Li Cl-KCl molten salt.Meanwhile,the precipitate was heated with the glass material to produce waste form,so as to achieve the recycling of molten salt and disposal of high-level radioactive waste.（1）The Gibbs free energy changes for the precipitation reaction of LaCl₃,SrCl₂ and BaCl₂with the precipitant were calculated thermodynamically.The feasibility of removing La（Ⅲ）,Sr（Ⅱ）and Ba（Ⅱ）from waste salt was confirmed by phosphate precipitation combined with carbonate precipitation methods.Adding Na₃PO₄ to Li Cl-KCl-LaCl₃ molten salt,adding K₂CO₃to Li Cl-KCl-SrCl₂ molten salt,adding K₂CO₃ to Li Cl-KCl-BaCl₂ molten salt,can achieved the purpose of removing a single nuclide and purifying the waste salt.At the same time,it is found that with the increase of precipitator,the removal rate can be increased to about 99%.Na₃PO₄was firstly added to the waste salt and the sediment was obtained.XRD result indicated that of the sediment is La PO₄.Then Na₂CO₃ was added into the waste salt,and the sediment was obtained.XRD result of the sediment showed that the formation of Sr CO₃ and Ba CO₃.The concentration La（Ⅲ）,Sr（Ⅱ）and Ba（Ⅱ）in supernatant salt was analyzed by ICP-AES,The removal rates of La（Ⅲ）,Sr（Ⅱ）and Ba（Ⅱ）in molten salt were 92.5%,82.7%and 81.6%,respectively.The purpose of purifying the molten salt was achieved.（2）The precursor of Ba_0.6Sr_0.4Ti O₃ was firstly prepared for glass ceramic waste form and precursor was characterized.The sodalite was prepared by heat treatment of Na Cl and 4A zeolite,and the decomposition temperature of sodalite to form nepheline was preliminary studied.It is found that sodalite prepared by heat treatment of Na Cl and 4A zeolite at 500°C can partially decompose to produce a small amount of nepheline at 950°C,and XRD result of sodalite prepared at 950℃by heat treatment did not observe the diffraction peaks related to nepheline,which confirmed the sodalite was more conducive to further glass ceramic.Then,the borosilicate glass was synthesized and characterized by XRD and infrared spectroscopy.No obvious crystal peak was observed in the XRD diffraction peaks,which met the design requirements for glass.Borosilicate glass ceramic waste form was prepared at high temperature using different proportions of borosilicate glass,4A zeolite,salt-containing lanthanum phosphate precipitation,and barium strontium titanate ceramic crystals.The density and leaching rate of glass ceramic were determined,and the density was found to be between 3.2～4g cm^-3,and the standard leaching rate of the three elements was found in the order of 10^-7;The SEM results of the glass ceramic before and after leaching revealed that the particle size did not change significantly,and the surface of the particle was slightly etched,which met the basic requirements of glass ceramic.（3）The iron phosphate glass was synthesized,and it was characterized by XRD and infrared spectroscopy.No obvious crystal peak was observed in XRD diffraction peaks,which met the design requirements for glass.Iron phosphate glass ceramic waste form was prepared at high temperature using different proportions of iron phosphate glass,4A zeolite,salt-containing lanthanum phosphate precipitation,and barium strontium titanate ceramic crystals.The density and leaching rate of glass ceramic were determined,and the density was found to be between2～4 g cm^-3.The standard leaching rates of the three elements in glass ceramic prepared at embedding rate of 30%,40%and 50%were found in the order of 10^-7,and the difference of standard leaching rates in glass ceramic prepared at embedding rate of 10%and 20%was found,the order of magnitude was 10^-7～10^-4.The SEM results of the glass ceramic before and after leaching revealed that the particle size did not change significantly,and the surface of the particle was slightly etched,which met the basic requirements of glass ceramic.