Study of plasma off-gas treatment from spent ion exchange resin pyrolysis

Effects of Temperature and Sulfuric Acid and Iron (II) Concentrations on the Efficacy of Decontamination of Spent Ion-Exchange Resins Containing Hematite

The effect of H2SO4 and FeSO4 concentrations and temperature on the efficacy of decontamination of spent ion-exchange resins was estimated. The study was performed on model spent ion-exchange resins purposefully contaminated with hematite and Co-57 radionuclide. It was found that an increase in solution temperature up to 50 °C and the addition of FeSO4 increases the efficacy of decontamination of spent ion-exchange resins by 1 M and 2 M H2SO4 solutions by 1–2 orders of magnitude, whereas the decontamination factor value here is >103. Since under static conditions, the secondary adsorption of Co-57 was observed, the extra washing of ion-exchange resins by 3 M solution of NaNO3 is required. Decontamination under dynamic conditions excludes the secondary adsorption of Co-57, so that the necessity of the extra stage of washing can be skipped. Under dynamic conditions, the consumption of a solution of the composition H2SO4 (1 mol/L) + FeSO4 (0.2 mol/L) is 1.5-fold lower in comparison with the 2M solution of H2SO4 at compatible values of the decontamination factor. Such an approach enables reduction in the volume of secondary waste and the equipment corrosion due to the decrease in H2SO4 concentration.

Co-pyrolysis of spent radioactive ion exchange resin and manganese dioxide: Decrease the decomposition temperatures of functional groups

With the development of the nuclear industry and clean energy, spent radioactive ion exchange resin has become a major concern that needs to be solved urgently. In this study, the mixed resin (sulfonic aid and quaternary ammonium polystyrene beads, 1:2, v/v) is co-pyrolyzed with manganese dioxide in a tube furnace, selecting argon as the reaction atmosphere. Manganese dioxide exhibits unique catalytic and oxidative activity, and a low mass remaining efficiency of 34.14% is obtained under low heating temperature of 300 ℃. The required decomposition temperatures of functional groups and benzene are decreased by approximately 100 ℃, and that of polymer chain is decreased by 130 ℃. The TGA analysis shows the decomposition temperature rule of functional groups and base polymer. The FT-IR spectra and XPS analysis reveal the bridging effects of manganese sulfonate and sulfide group. The SEM diagrams prove that the two processes including depolymerization and reunion could be found in co-pyrolysis. The XRD analysis indicates manganese dioxide undergoes the reduction path of MnO₂→Mn₃O₄→MnO, and MnS is formed with the decomposition of manganese sulfonate. The possible mechanism of solid-phase reaction is proposed to explain the promotion of manganese dioxide on co-pyrolysis.

Hydrothermal oxidation of pre-dissolved resorcinol-formaldehyde resins as a new approach to safe processing of spent cesium-selective organic ion-exchangers

Here we report a new approach to predisposal processing of spent resorcinol-formaldehyde resins (RFR) selective to cesium radionuclides via dissolution and hydrothermal oxidation (HTO) with the mineralization efficiency above 85%. Using a combination of potentiometric and colloid titration, we have shown that dissolution of RFR by consecutive treatment with nitric acid and sodium hydroxide solutions at optimal concentrations of 3-5 mol/L and 1 mol/L, respectively, yields colloid solutions of partially depolymerized and oxidized RFR. The efficiency of HTO of resorcinol and RFR solutions with hydrogen peroxide was investigated in a flow-type stainless steel reactor in the temperature range 165-250 °С and at linear flow rates of 1-3 cm/min. It was demonstrated that HTO allowed efficient resorcinol mineralization using hydrogen peroxide at H₂O₂: resorcinol molar ratios above 10 at 195 °С and a linear flow rate of 2 cm/min. Due to the colloidal nature of organics in RFR solution, its efficient decomposition occurred at higher temperature or molar excess of the oxidizer as compared to resorcinol, but in both cases HTO was the most efficient in acidic media yielding acetic acid as the main oxidation resistant product.

Pyrolysis and High Performance Plasma Treatment Applied to Spent Ion Exchange Resins

Treatment and conditioning of spent ion exchange resins from nuclear facilities is a complex process that not only should contemplate obtaining a stable product suitable for long-term storage and/or disposal, but also have to take into account the treatment of secondary currents generated during the process. The combination of low temperature pyrolysis treatment and high performance plasma treatment (HPPT) of the off-gas generated could be a novel solution for organic matrix nuclear wastes with economic and safety advantages. In the present work, results of lab scale studies associated with the pyrolysis off-gas characterization and the performance and operating parameters influence on the removal of model compounds in a laboratory-scale flow reactor, using inductively coupled plasma under subatmospheric conditions, are shown. The pyrolysis off-gas stream was largely characterized and the evolution of main compounds of interest as function of temperature process was established. The results of plasma assays with the model compound demonstrate a high destruction and removal efficiency (>99.990%) and a good control over the final gas products. First results of a bench scale arrangement combining both processes are presented and bode well for the application of this combined technology.