The lanthanide fission products are not separated from the high-level waste in established plants and are planned to be disposed to a geologic repository in a vitrified waste form (Chapters 6 and 7). Advanced reprocessing studies are emphasizing development of processes for recovery of the trivalent actinides (Chapter 11). Most of the actinide recovery processes being con­sidered include an initial separation of the combined trivalent actinides and lanthanide fission products, followed by a process to partition the lan­thanides from the actinides. Examples include the combination of TRUEX — TALSPEAK processes (Fig. 8.3) developed in the United States and the DIAMEX-SANEX processes developed in France. Both combinations are dependent on the use of poly-amino-poly-carboxylate complex agents, together with buffering agents that permit precise control of pH in the process solutions. Following the actinide-lanthanide separation, another process is required to remove the complex agents from the product solu­tions. A group separation is obtained but with varying separation factors for the different lanthanide elements, as indicated in Table 8.5.23

If a separation of the individual lanthanide elements is needed, a multi­stage chromatographic separation process using pressurized ion exchange, strong complex agents, and precise pH control would need to be employed.24 These could be operated using either elution chromatography from an ammonium-form cationic resin or displacement cationic-exchange methods

8.3

that utilize a “barrier” metal, such as zinc or nickel. The barrier ion blocks elution of elements that form weaker complexes than the ion being eluted. Large systems of this type have been operated for rare earth recovery.