Lanthanide and actinide extractions with cobalt bis(dicarbollide) ion derivatives covalently bonded to diglycolyl diamide platform

The separation of minor actinides from high-level waste (HLW) remains a difficult problem. A wide series of compounds based on two cobalt bis(dicarbollide) ions [(1,2-C2B9H10)(1′,2′-C2B9H11)-3,3′-Co(III)]− (1) covalently bonded to a diglycolyl amide platform via diethyleneglycol connectors was prepared by reaction of the diglycolic acid dichloride with various ammonium derivatives of the ion 1 with the aim to develop new class of extractants for trivalent radionuclides from acidic waste solutions. The extractants of general formulation [{(N,N-(8-CH2-CH2O)2-1,2-C2B9H10)(1′,2′-C2B9H11)-3,3′-Co)(N,N′-R)NCOCH2}2-O]Na2 differed in substitution on the amidic nitrogen (by e.g. butyl-, hexyl-, octyl-, t-octyl-, dodecyl-, benzyl-groups). Compounds were characterized by combination of 11B, 1H and 13C NMR spectroscopy, ESI-MS, HPLC, and TLC RF. The purity of all species was better than 98%. Most of the compounds proved to be very efficient extraction agents and enabled effective extraction of europium(III) and americium(III) from nitric acid solutions. The recovery of the trivalent radionuclides from the loaded organic phase was possible by using ammonium citrate or even better by using solution of ammonium citrate and ammonium DTPA (diethylenetriamine pentaacetate).