Optimizing Permanganic Acid Production: Effects of Temperature on Stability

Area of Science:

• Nuclear Engineering
• Materials Science
• Radiochemistry

Background:

• Nuclear metallic structures accumulate radioactive contaminants on oxide layers, primarily chromium (III) oxide (Cr₂O₃).
• Effective decontamination is crucial for reducing radiation exposure during nuclear industry maintenance and dismantling.
• Permanganic acid (HMnO₄) is a potential oxidizing agent for dissolving these problematic oxide layers.

Purpose of the Study:

• To synthesize permanganic acid (HMnO₄) for dissolving oxide layers on nuclear metallic structures.
• To investigate the kinetics of chromium oxide dissolution using HMnO₄ under varying concentrations and temperatures.
• To evaluate the decomposition of HMnO₄ using oxalic acid (H₂C₂O₄) for post-treatment applications.

Main Methods:

• HMnO₄ synthesized via ion exchange using AmberLite IRN97 H resin and potassium permanganate (KMnO₄).
• Dissolution kinetics studied at HMnO₄ concentrations (240-1920 ppm) and temperatures (30-80 °C).
• HMnO₄ decomposition analyzed using oxalic acid (H₂C₂O₄) at 80 °C with varying molar ratios.

Main Results:

• Optimized HMnO₄ synthesis achieved high acidity (pH~1.6) and low potassium (<0.1 ppm).
• Increased HMnO₄ concentration significantly enhanced chromium dissolution (up to 31% in 33 h); lower temperatures improved efficiency.
• Effective HMnO₄ decomposition required H₂C₂O₄/HMnO₄ molar ratio > 2.75, but Mn²⁺ yields were limited (<55%).

Conclusions:

• Permanganic acid is a viable agent for dissolving chromium oxide layers in nuclear decontamination.
• Dissolution is favored by higher acid concentration and lower temperatures, with concentration being dominant at short times.
• H₂C₂O₄ can decompose HMnO₄, but limitations in reduction efficiency necessitate further investigation for safe waste management.