Separation of Lanthanoid Phosphates From the Spent Electrolyte of Pyroprocessing

This study is carried out to make the pyroprocessing hold a competitive advantage from the viewpoint of environmental load reduction and economical improvement. As one of the measures is to reduce the volume of the high-level radioactive waste, the phosphate conversion method is applied for removal of fission products from the melt as spent electrolyte in this paper. Though the removing target elements in the medium are alkali metals, alkaline earth metals and lanthanoid elements, only lanthanoid elements and lithium form the insoluble phosphates by reaction with Li₃PO₄ or K₃PO₄. Therefore, as the first step, the precipitation experiment was carried out to observe the behaviours of elements which form the insoluble precipitates as double salts other than simple salts. Then the filtration was experimented to remove lanthanoid precipitates in the spent electrolyte using Fe₂O₃-P₂O₅ glass system as a filtlation medium which is compatible material with the glassification. The result of separation of lanthanoid precipitates by filtration was effective and attained almost 100%.