Separation of trivalent lanthanides and actinides by extraction chromatography

One of the most critical steps in the Partitioning and Transmutation strategy is the separation of the lanthanides and actinides that are present in nuclear waste streams. Since these elements are chemically very alike the separation of these elements is nearly impossible through the use of conventional techniques. Extraction chromatography seems to offer several advantages over the use of liquid-liquid extraction. Therefore it was decided to apply this technique for the lanthanide/actinide separation. CMPO, a powerful extractant for both the lanthanides and concerned actinides was loaded onto porous silica particles and was tested with regards to the lanthanide/actinide separation. To improve the poor selectivity of CMPO for this separation, water soluble complexing agents were added to the extraction chromatographic system. Experiments were carried out to examine the influence of the different complexing agents on the distribution of the lanthanides and actinides between the resin and the aqueous phase. Six different complexing agents participated in the experiments, but none was found to be satisfactory. In highly concentrated nitric acid media most complexing agents were unable to form complexes with metal ions. In dilute nitric acid solutions only dipicolinic acid seemed to be capable of retaining metal ions from the resin. Unfortunately dipicolinic acid tends to show very little distinction between lanthanides and actinides. Because of this fact no separation factor larger than 1.5 was found as a result of the experiments.