Studies on the separation of minor actinides from high-level wastes by extraction chromatography using novel silica-based extraction resins

To develop an advanced partitioning process by extraction chromatography us ing a minimal organic solvent and compact equipment to separate minor actin ides such as Am and Cm from nitrate acidic high-level waste (HLW) solution, several novel silica-based extraction resins have been prepared by impregn ating organic extractants into the styrene-divinylbenzene copolymer, which is immobilized in porous silica particles (SiO2-P). The extractants include octyl(phenyl)-N, N-diisobutylcarbamoylmethylphosphine oxide (CMPO), di(2-e thylhexyl)phosphoric acid (HDEHP), and bis(2,4,4-trimethylpentyl)dithiophos phinic acid (Cyanex 301). Compared to conventional polymer-matrix resins, t hese new types of extraction resin are characterized by rapid kinetics and significantly low pressure loss in a packed column. The results of separation experiments revealed that trivalent actinides and lanthanides can be separated from other fission products, such as Cs, Sr, and Ru in simulated HLW solution containing concentrated nitric acid by ext raction chromatography using a CMPO/SiO2-P resin-packed column. Satisfactor y separation between Am(III) and a macro amount of lanthanides from simulat ed HLW solution with pH 4 was achieved by using a newly purified Cyanex 301 /SiO2-P resin. However, the Am(III) separation was very sensitive to the pu rity of Cyanex 301, and the improvement of its stability is an important ta sk for practical utilization.