Am(III) separation from acidic solutions by diamides of dipicolinic acid

The separation of minor actinides from high level liquid waste (HLLW) belongs to the principal challenges of advanced nuclear fuel treatment. We studied in this work several diamides of dipicolinic acid for direct separation of trivalent actinides from post-PUREX raffinate. The N,N′-diethyl-N,N′-di-meta-tolyldipicolinamide, Et(m)TDPA, exhibited the highest Am(III) extraction ability and sufficient Am(III)/Eu(III) selectivity (SFAm/Eu ≥ 5) from all tested derivatives. Am(III) and Eu(III) extraction with the Et(m)TDPA into solvents of different polarities was studied in detail. The extraction abilities of extractants dissolved in polar nitro- or fluorinated solvents were significantly higher than those in less or low polar solvents like hexyl methyl ketone, 1-octanol, chloroform, toluene, etc. Et(m)TDPA in nitrobenzene provided selective separation of americium from lanthanides (SFAm/Ln > 5) and from the majority of other fission products (SF > 150) present in model PUREX raffinate. The co-extraction of some undesirable elements as Zr and Pd was significantly suppressed by addition of oxalic acid and HEDTA to the raffinate solution.