Although the raffinate salt contains very low concentrations of actinides, it still needs to be treated at the ‘zeolite column’ process to remove LFP ele­ments, by ion exchange with structural elements of zeolite or by occlusion of chloride molecules in the 3-dimensional cage structures of zeolite. Figure 10.7 shows the equilibrium absorption characteristics of alkali metal chlo­rides, alkaline-earth chlorides and lanthanide chlorides in zeolite-4A at temperatures ranging from 400 °C to 450 °C (Tsukada, 2008). As the figure shows, the amount of absorption depends on the fraction of the element in the salt and on the valence of the element. At the same equivalent fraction of approximately 0.1, the amount of lanthanide elements loaded is about twice that of alkali metal elements, while the amount of alkaline-earth ele­ments loaded is about 1.5 times that of alkali metal elements. Though further study is still needed to gain detailed absorption behaviours, it is clear that zeolite-4A works as a potential absorbent of LFP from LiCl-KCl eutectic salt. To use zeolite as an LFP absorbent, a continuous system with a zeolite column is preferable from the point of view of efficiency; however, a batch-type system with a zeolite bed is also possible. Whichever system is employed, the LFP-loaded zeolite still needs further treatment to form

10.7

Absorption characteristics of alkali metal chloride, alkaline-earth chloride and lanthanide chloride in zeolite 4A.

acceptable waste because a certain amount of free salt containing LFP adheres to the surface of the zeolite.