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Study On The Synthesis Of ZIT Composite By Molten Salt And Immobilization Of Lanthanide Element La

Posted on:2022-01-17Degree:MasterType:Thesis
Country:ChinaCandidate:Y H FuFull Text:PDF
GTID:2481306353484374Subject:Chemical Engineering and Technology
Abstract/Summary:PDF Full Text Request
In the recovery and reuse process of spent fuel,the waste salt after electrolytic reduction and electrorefining is rich in lanthanide oxide precipitation,and these waste oxides need to be effectively treated.The ZIT(Zinc Titanate)composite developed by the Korea Institute of Atomic Energy has become a potential option for the treatment of lanthanide oxides due to its large loading factor,high durability and low processing temperature.However,there are few reports about ZIT matrix at home and abroad,and there is no research on curing mechanism and process.The simulated waste La2O3 was treated with ZIT matrix here,and the main contents are as follows:The ZIT matrix material Zn2TiO4 was prepared by the molten salt synthesis method.The effects of different molten salt systems,reaction temperature,zinc-titanium ratio of raw materials and holding time on the structure and morphology of the product were studied respectively.Compared with the experimental results,it was determined that Zn O and TiO2were used as raw materials according to the molar ratio of zinc to titanium was 1.2:1.The optimum synthesis conditions of Zn2TiO4 were maintained at 1000?in Na Cl-KCl(molar ratio1:1)for 4 h.It was proved that the molten salt promoted the reaction of the Zn O-TiO2 system by the three zinc titanates,Zn2Ti3O8,Zn TiO3 and Zn2TiO4,coexisting at the lowest temperature of 700?.The growth mechanism of Zn2TiO4 in molten salt was discovered following the Ostwald ripening mechanism.Using Zn2TiO4,Ca HPO4,SiO2,B2O3 and La2O3 as raw materials,a high-temperature sintering method was applied to prepare ZIT ceramic materials with La PO4 monazite phase as the main structure.The analysis results of the formation process showed that the dehydration process of the raw materials occurred below 200?,La PO4 and Zn2SiO4 were generated at 800and 1000?respectively.In the range of room temperature to 1200C,the morphology of the raw material gradually changed from powder to block,and the flatness and density of the sample surface gradually increased.ZIT samples with different La2O3 loading factors were prepared,and the results showed that the ZIT materials with 30 wt.%La2O3 loading maintained the internal structure,morphology and good stability of physical and chemical properties.The existing crystal phases are mainly Zn2SiO4,La PO4 and TiO2.The density of ZIT material with20 wt.%La2O3 loading was about 3.56 gcm-3.After soaking in deionized water for 28 days,the leaching rate of La was 4.7510-6 gm-2d-1.Using V2O5 as an additive into ZIT composite,it was found that V2O5 can reduce the experimental temperature of Zn2TiO4 converting to Zn2SiO4 and inhibit the production of Al6Si2O13 in the immobilized body.V could enter the Zn2TiO4 lattice to replace Zn or Ti.After the crystal lattice,the lattice distortion caused the increase of the activation energy of the crystal lattice,thereby accelerating the conversion reaction of Zn2TiO4 to Zn2SiO4.At the same time,the low melting point of V2O5 promoted the process of dissolution,diffusion and precipitation of surrounding particles.The density and chemical stability tests showed that the density of the sample with 10 wt.%V2O5 substituted was 3.72 gcm-3,and the leaching rate of La on the 28th day was 810-6 gm-2d-1.The experimental results showed that the higher density ZIT composite with V2O5 substituted were successfully prepared by the high-temperature sintering method.
Keywords/Search Tags:Molten salt synthesis method, Zn2TiO4, Ceramic immobilization, ZIT composite, LaPO4
PDF Full Text Request
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