Efficient removal of fission product thulium by electrolytic refining and high temperature adsorption of molecular sieves to achieve the purification and reuse of waste salt

In the process of pyroprocessing after spent fuel, the recycling of molten salt and electricity consumption are an important factor that restricts the cost of post-treatment. The implementation of high-temperature electrolysis and adsorption techniques can significantly enhance the extraction rate of Tm. This approach effectively addresses the issue of low current efficiency when ion concentration is low, resulting in reduced electricity expenses and facilitating the recycling of waste salt. In this paper, the electrochemical reduction and oxidation process of Tm(III) and In(III) were investigated on a tungsten (W) electrode at 773 K in the molten salts of LiCl-KCl. The findings suggest that the reaction process observed was a reversible, diffusion-controlled process. In-Tm alloys were synthesized using galvanostatic/potentiostatic electrolysis on W electrode in a LiCl-KCl-InCl3-TmCl3 melt. The electrolysis process resulted in a Tm extraction rate of approximately 93.86 % from the In electrode. Subsequently, the removal of Tm (III) using 5A molecular sieve was investigated. Through the utilization of molecular sieves in high-temperature adsorption, the elimination rate can exceed 99.50 %, resulting in a significant enhancement in the purification of waste salt. The predominant adsorption mechanism was determined to be chemical (specifically ion exchange), as evidenced by the application of pseudo-first-order, pseudo-second-order, and intraparticle diffusion model of Weber-Morris.