Catalytic Oxidation Treatment of Radioactive Trioctylamine-Xylene Waste Liquids

　　This study investigates the catalytic oxidation treatment of radioactive trioctylamine-xylene (v/v = 20%/80%) organic waste liquid containing a transuranic nuclide using nano manganese dioxide (MnO₂) as the catalyst. The waste liquid exhibited an α-activity concentration with a total α-activity of 10⁸ Bq. Nano MnO₂ was selected for its cost-effectiveness, simple synthesis, and chemical stability. A cold test was conducted under optimized parameters (reactor temperature: 190 ± 20°C, feed rate: 87 mL/h, stirring speed: 30 rpm) to validate the process, achieving continuous operation for 90 hours. The results demonstrated that the primary products of catalytic oxidation were carbon dioxide, water, and trace small-molecule organics (e.g., benzene, toluene, ethylbenzene), with a mineralization rate exceeding 95%. Trioctylamine exhibited higher catalytic efficiency compared to xylene, likely due to its greater polarity, while the presence of ethylbenzene in exhaust gases indicated chemical reforming of xylene during oxidation.
　　Following cold test validation, the radioactive waste was successfully treated in a hot cell. Radiometric analysis revealed that 96.86% of transuranic nuclide was retained in catalyst residues, 1.95% adhered to reactor surfaces, and 1.06% remained in local ventilation systems. Airborne emissions accounted for less than 0.001% of the total activity, confirming the system’s effectiveness in preventing radionuclide dispersion. Exhaust gas analysis via gas chromatography-mass spectrometry (GC-MS) detected volatile organic compounds (VOCs) totaling 925.1 mg/m³, including benzene (25.38 mg/m³), toluene (17.97 mg/m³), and ethylbenzene (116.59 mg/m³), with minimal nitrogen oxides (NO: 0.05 mg/m³; NO₂: 0.52 mg/m³). Post-catalysis, the carbon content in the catalyst increased from 0.044% to 2.08%, suggesting residual organic deposition or elemental carbon formation.
　　The process achieved the critical objective of converting liquid radioactive waste into solid residues, enhancing storage safety. Post-treatment, the catalyst residues were immobilized using a glass matrix for interim storage. Error analysis attributed minor discrepancies to residual waste adhesion and analytical uncertainties, yet the overall transuranic nuclide retention efficiency reached 99.87%. Compared to conventional methods such as cementation or vitrification—which face challenges in volume expansion, leaching resistance, and compatibility with flammable organics—this catalytic oxidation process offers a viable alternative for managing medium-level radioactive organic wastes. The study underscores the technical feasibility of catalytic oxidation using nano MnO₂, aligning with regulatory requirements for radionuclide immobilization and environmental safety.