Evaluation of phosphate thermodynamic properties for spent electrolyte recycle

Adaptation of the phosphate conversion technique was undertaken and evaluated for application to the recycle process of the spent electrolyte generated from metal electrorefining process. In order to confirm the conversion behaviors of fission product (FP) chlorides to the phosphates, conversion experiments were carried out for some alkali metal, alkaline earth metals and rare-earth elements and their results were compared with that of thermodynamic calculations of previous study [I. Amamoto, H. Kofuji, M. Myochin et al., in: Proceedings of Global 2007, Boisi, Idaho, USA, 2007]. Among these elements, rare-earth chlorides were converted into phosphates and Cs was not, according to the prediction by the calculation. As for alkaline earth metals, their equilibrium constants were nearly 1 based on the results of the calculations, the conversion reactions were difficult to occur. In addition, it was clarified that phosphates were thermally unstable, easily to decompose at higher temperature, through the measurements of their heat flow and vapor pressure.