Optimization and Mechanism Study on Destruction of the Simulated Waste Ion-Exchange Resin from the Nuclear Industry in Supercritical Water

Abstract

The optimization and mechanism for oxidation of the waste anion exchange resin from the nuclear industry in supercritical water were investigated. To achieve the maximum chemical oxygen demand (COD) and total nitrogen (TN) removal efficiencies, the response surface methodology (RSM) was employed to optimize four operating variables. Two quadratic polynomial models with satisfactory accuracy were established based on the experimental results. Under optimized conditions, the removal rates of the COD and TN could reach 99.91 and 36.02%, respectively. According to the identification of intermediates under different reaction conditions, a detailed degradation mechanism involving Huffman decomposition, depolymerization, oxidation, ring-opening, recombination, and finally oxidation to small molecules was proposed. As the quaternary ammonium falls off, the reaction mainly follows two routes. Phenols and amides were the main intermediates. The optimization and mechanism analysis would provide the theoretical basis and guidelines for the applications of supercritical water oxidation technology in the minimization and inorganic stabilization of radioactive waste.

Optimization and pathway study on destruction of the spent extraction solvent in supercritical water

“…16,17 In recent years, researchers have conducted comprehensive investigations on SCWO treatment of radioactive organic waste. Xu et al 18 investigated the optimization of the waste anion exchange resin from the nuclear industry in SCW. Under optimized conditions, the removal rates of the COD and TN could reach up to 99.91% and 36.02%, respectively.…”

Experimental investigation and thermomechanical performance evaluation of supercritical water oxidation of n‐dodecane/tributyl phosphate

“…The results showed that the chemical oxygen demand (COD) removal rate of the waste resin was 99.9%, and there were no radioactive nuclides in the waste gas. 21 Researchers have primarily focused on TBP regarding the challenging problem of radioactive organic liquid waste treatment generated from nuclear power plants and spent fuel reprocessing. Yang and Zhang found that the gaseous product of TBP degradation is CO 2 , while the liquid products include PO 3 -4…”

“…studied the degradation process of nuclear industry anion exchange resin in SCWO. The results showed that the chemical oxygen demand (COD) removal rate of the waste resin was 99.9%, and there were no radioactive nuclides in the waste gas 21 . Researchers have primarily focused on TBP regarding the challenging problem of radioactive organic liquid waste treatment generated from nuclear power plants and spent fuel reprocessing.…”

“…33 The reason is that when the initial concentration of the material is too high, a lot of unexpected intermediate products will be produced in the reaction degradation process, and the degradation of the intermediate products requires a large number of activated molecules, which makes the degradation of organic matter incomplete in a short time. 21 Besides, if the feed concentration is too high, it may increase the likelihood of secondary polymerization reactions occurring, resulting in byproducts such as coke and tar. 34 Therefore, according to the experimental results, limited by the oxidation capacity of the SCWO system, the feed with a material concentration of 4 wt% is the most suitable.…”

Supercritical water oxidation of phenol and process enhancement with in situ formed Fe2O3 nano catalyst

“…Generally, different oxidant including air, O 2 , and H 2 O 2 are applied into the superheated water during supercritical water oxidation (SCWO) that not only increase the operational cost but also enhance energy demand (500-700°C) (Huelsman andSavage, 2013, Zhang et al 2020a). However, the proper usage of catalysts could effectively improve the oxidant concentration and reactor energy demand without affecting the operational performance (Xu et al 2020). An appropriate catalyst not only improves the removal of chemical oxygen demand (COD) of the waste but also enhances the selectivity of phenols into CO 2 , CH 4 , and H 2 (Nadjiba et al 2017 (Abdpour and Santos, 2020, De Silva et al 2017, Huelsman and Savage, 2013.…”