| Ion exchange resin is a polymer that can exchange ions with a contact medium,which is insoluble in the medium and only the relevant ions in resin can exchange with the medium.Ion exchange resins are commonly used in the nuclear fuel cycle,radioactive waste liquid treatment,etc.With the development of the nuclear industry,more and more radioactive waste resins need to be treated urgently.The long-term temporary of waste resins is prone to radiolysis and produce explosive gases,which brings potential safety hazards for the environment and society.Therefore,it is urgent to propose an appropriate method for waste resin treatment.Compared with methods such as pyrolysis,solidification,and incineration for treating waste resin,molten salt oxidation has the advantages of high oxidation efficiency,large volume reduction ratio,and less acid gas generation.In this paper,ZG-ANR-50 cation resins were used as the experimental object,and the conditions for molten salt oxidation were selected.The destruction process of cation exchange resins and Sr containing cation exchange resins,as well as the effect of Sr on their destruction process were researched.The damage process of mixed resin and mixed exchange resin containing Sr,as well as the influence of Sr on their damage process were studied.In this paper,the cation resins were tested by thermogravimetric analysis under N2 and air atmospheres,respectively.It was found that the oxidization of resins in air had an extra weight loss peak than that in N2 atmosphere.The products obtained by molten salt oxidation of resins were tested by infrared and gas chromatography.It was found that the extra weight loss process was amorphous carbon being oxidized to CO2.Then,the parameters of the oxidation process of cation resin were explored.Cationic resins were subjected to molten salt oxidation at different rates of air(0 m L/s,1.5 m L/s,3 m L/s,4.5 m L/s).The oxidation efficiency,volume reduction ratio,and sulfur interception rate were comparative studied.The oxidation residue and waste salt were studied,and the optimal air rate was determined.The further exploration of oxidation time(0.5 h,1 h,1.5 h,2 h)under the optimal air rate conditions was conducted to obtain the on the optimal oxidation time.It was found that when the air rates were 3 m L/s and 4.5 m L/s,the temperature was 800℃,and the oxidation time was 2 h,the oxidation efficiency could reach 99.50%,the reduction ratio could reach over3.70,and the retention rate of S element could reach 73.4%.The above results were all meet the technical requirements for molten salt oxidation of waste resins.Considering the actual operating cost of the process,the experimental conditions were selected as air rate of 3 m L/s and time of 2 h.Secondly,based on the optimal experimental parameters,the effect of Sr on the resin oxidation process was explored by the comparative research of the cation resins and Sr containing cation exchange resins.Two types of resins were oxidized at different temperatures for 2 h,and their oxidation products and oxidation efficiency were compared and analyzed.Combining thermogravimetry,XPS and infrared tests,it was found that the addition of Sr element affected the decomposition process of functional groups in cation resins,and the decomposition of sulfonic acid groups changed from two steps to one step.In addition,the termination temperature of functional group decomposition in cation resin is advanced due to the participation of Sr element.The results obtained by infrared carbon-sulfur and XPS analyses were showed that Sr element inhibited the resin oxidation before the ternary carbonate melts,while promoted the resin oxidation after ternary carbonate melts.The promotion effect mainly reflected in the reduction of sulfur bond formation by the addition of Sr element.By the tests of ICP and XPS,the carbonate had a strong ability to trap Sr element and acid gases,and Sr and S elements could promote each other.At the same time,under the optimal conditions,the mixed resin and the mixed exchange resin containing Sr was oxidated in ternary carbonate at different temperatures,and the effect of Sr on the oxidation process of mixed resin was explored.In the mixed resin,the functional groups of the anion resin decomposed before the functional groups of the cation resins.The addition of Sr element made the termination temperature of the decomposition of anionic functional groups delayed by 10℃.The effect of Sr element on the oxidation of the mixed resin is mainly reflected in the decomposition part of the cation exchange resins,where the decomposition of the sulfonic acid group changes from two steps to one step and reduces the generation of sulfur bonds.This result is consistent with the impact on the oxidation process of the cation resin.The decomposition of functional groups in anion exchange resins produced nitrates,which promote the oxidation of the resin and the absorption of acidic gases produced by the oxidation of resin. |
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