Study On System Screening And Oxidation Process Of Molten Carbonate Oxidation Mixed Ion Exchange Resin

Nuclear energy stands out among green new energy due to its clean and efficient advantages.With the continuous development of the nuclear industry,radioactive waste has gradually increased.Among them,radioactive waste resin is the main component of medium and low-level radioactive waste and its treatment and disposal have attracted widespread attention.There are many treatment methods such as incineration,solidification,pyrolysis,etc.Among them,the molten salt oxidation treatment technology has the advantages of high oxidation efficiency and adsorption of acid gases.The molten salt oxidation system was screened,and the damage process of mixed resin and the effect of doping Sr on its damage process was studied in this article.ZG-ANR-50 cation exchange resin and ZG-ANR-140 anion exchange resin were used as experimental objects.Among the three molten salt systems Li₂CO₃-Na₂CO₃,Li₂CO₃-K₂CO₃,and Li₂CO₃-Na₂CO₃-K₂CO₃,the ternary salt system has higher oxidation efficiency,volume reduction ratio and sulfur interception rate than the binary salt system.Carbonate played a catalytic role in the process of resin oxidation and the activity of catalyst was generally related to its fluidity on the surface.Therefore,the melting point was a key factor in choosing a suitable molten salt system.In the system with different ratios of resin and molten salt（1:1,1:2,and 2:1）.The larger the proportion of carbonate,the more obvious the oxidation effect（DRE 99.99%）.But the corresponding resin volume reduction ratio was not high.and the oxidation effect was not obvious when the carbonate content was less.In summary,Li₂CO₃-Na₂CO₃-K₂CO₃ ternary salt system,the ratio of resin to molten salt 1:1 was more conducive to molten salt oxidation.Through modern analysis and testing methods such as thermogravimetric analysis,infrared analysis,SEM,XPS,XRD,and C-S analysis,it was found that the destruction process of the mixed resin could be divided into five stages:（1）The destruction of the quaternary ammonium functional group（-N（CH₃）₃OH）.（2）The destruction of the sulfonic acid group（-SO₃H）:a part of which was removed from the hydroxyl group and converted to a sulfone group（-SO₂-）continues to exist,and a part was decomposed and converted into SO₂ to escape.（3）The sulfone group（-SO₂-）was continuously destroyed and transformed into a sulfur bond（-S-）structure which was more difficult to oxidize.（4）The destruction of the resin styrene skeleton.（5）Continuous oxidation of resin skeleton residue.Molten salt system has a good adsorption effect on the acid gas produced by decomposition,and it existed stably in the waste salt in the form of nitrate,sulfate,etc.The presence of nitrate promotes the S element produced by resin destruction to be fixed in the molten salt in a more stable form.The resin doped with metal Sr element was used to simulate mixed resin.The oxidation process of the resin was promoted by the addition of Sr.The destruction process of the simulated mixed resin was basically the same as that of the original resin.The presence of metal Sr in the resin will not have a great influence on the destruction order of the functional groups and skeleton in the mixed resin.The carbonate molten salt system has a good retention effect on the metal Sr element,and the retention rate was up to 98.51%.And the Sr element existed in the molten salt in various forms such as strontium nitride,strontium sulfide,and strontium carbonate.Compared with the oxidation time,the oxidation temperature have a greater impact on the oxidation process of the simulated mixed resin.