Extraction of Lanthanoids with Diamides of Dipcolinic Acid from Nitric Acid Solutions. II. Synergistic Effect of Ethyl-Tolyl Derivates and Dicarbollide Cobalt

New ethyltolyl-substituted derivatives of dipicolinic acid, N,N-diethyl-N',N'-ditolyl diamides (DPA) have been synthesized and evaluated for their extraction capability toward americium and lanthanides. These diamides were studied as a stand-alone extractant in conjunction with a polar solvent FS-13 (trifluoromethylphenyl sulfone) as well as in an extraction mixture in conjunction with the synergistic extractant chlorinated cobalt dicarbollide and FS-13. The effect of the ortho-, meta-, and para position of the methyl group on the tolyl ring of the N,N'-diethyl-N,N'-ditolyl-diamide (EtTDPA) was investigated. Data on the extraction ability of different diamides of dipicolinic acid show that the Et(o)TDPA has the most promising properties because it has the best balanced selectivity between the heavy and light lanthanoids.