An efficient approach for the treatment of radioactive waste perfluoropolyether lubricants via a synergistic effect of thermal catalysis and immobilization

Abstract

Perfluoropolyether (PFPE) lubricants are a kind of high-molecular polymer with many excellent properties. However, the use of PFPEs in the nuclear industry can lead to partial decomposition and carrying radionuclides, resulting in a large amount of radioactive waste PFPE lubricants annually. Moreover, radioactive waste PFPE lubricants are difficult to be effectively treated due to their high stability, the risk of possible leakage of radionuclides, and hypertoxic fluorine-containing by-products. In this study, without any precedent, a strategy of MnO₂-catalyzed decomposition and Na₂CO₃-immobilized conversion was proposed for PFPE lubricant decomposition and fluorine immobilization simultaneously based on the Lewis acid-base and oxygen vacancies concept. A high fluorine conversion efficiency of 95.4% was achieved. Meanwhile, the mechanism of decomposition suggested that MnO₂ mainly provided Lewis acid sites and attacked the (basic) fluorine or oxygen atoms in PFPE molecules. The decomposition of PFPE chains was proceed down and volatile fluorine-containing gas was released by partial electron transfer, intramolecular disproportionation reaction, and unzipping fashion. Subsequently, gas by-products could be further oxidized and then immobilized into fluoride salts by carbonate solid absorbents. Overall, this study provides a simple, safe, and potentially practical strategy for the harmless conversion of refractory fluorinated organic wastes, especially perfluoropolymers.