Study on the Degradation of Gelled Tributyl Phosphate Combined with DFT Calculations in a Ternary Li2CO3-Na2CO3-K2CO3 Molten Salt System

With the rapid development of the global nuclear industry, substantial amounts of radioactive tributyl phosphate (TBP) have accumulated during the PUREX process. Prolonged accumulation poses significant environmental risks. Therefore, this study proposes an efficient molten salt oxidation (MSO) method for the treatment of gelled TBP. Comprehensive thermal analysis data indicate that the oxidation process of gelled TBP primarily consists of three stages. The composition of the waste salts after the MSO process was analyzed using X-ray diffraction spectroscopy. Fourier transform infrared spectroscopy revealed that the primary functional groups in gelled TBP were progressively degraded with increasing temperature. Scanning electron microscopy clearly illustrated the decomposition process of gelled TBP. X-ray photoelectron spectroscopy results identified the predominant forms of residual substances. The generated exhaust gas was analyzed using gas mass spectrometry and chromatography. Additionally, through DFT calculations of TBP, the possible reaction mechanism of TBP in the molten salts was deduced. In the molten state, carbonate can effectively absorb P₂O₅ and eventually form stable NaPO₃, which is the reason for the 94.90% retention rate of phosphorus element. During the experimental process, the degradation rate of gelled TBP reached as high as 99.99%. The MSO method proposed in this study shows great potential for the treatment of liquid organic waste.