Integrated Process for Treatment of Plutonium Oxalate Supernatants in Evaporator: Combining Mn 2+ -Catalysed Oxalate Destruction and HCHO-Mediated Denitration with Volume Reduction

Conventional removal of oxalate from plutonium oxalate supernatant is typically carried out through oxidation using potassium permanganate, followed by neutralization with hydrogen peroxide. While effective, this approach results in the generation of large quantities of secondary solid waste and a significant increase in solution volume, posing challenges for downstream waste management. In the present study, an advanced and integrated process strategy is proposed, which combines Mn²+-catalysed oxalate destruction with formaldehyde-mediated denitration, followed by in-situ concentration through evaporation within a single pot-type reactor. This integrated methodology eliminates the need for additional reagents apart from trace levels of Mn²+ catalyst and leads to a substantial reduction (approximately 80–90%) in secondary solid waste generation compared to conventional practices. Laboratory-scale experiments were conducted to determine key process parameters such as residence time and steady-state oxalate concentration, and the results were systematically compared with predictions from a Continuous Stirred Tank Reactor (CSTR) model. The strong agreement between experimental observations and model predictions validates the robustness and applicability of the CSTR framework. Model analysis further indicates that, for a recovery (RA) cycle evaporator, operation with 0.005–0.010 M Mn²+ enables near-complete oxalate destruction (residual oxalate ≤ 0.008 M) along with effective volume reduction, offering directly scalable parameters for industrial deployment.