Extraction of uranium(VI) with diamides of dipicolinic acid from nitric acid solutions

Three structural isomers of diamides of dipicolinic acid ( N , N ′-diethyl- N , N ′-ditolyl-dipicolinamide, EtTDPA) with varying position of the methyl group on the tolyl ring have been synthesized and investigated on extractability toward U(VI). The polar diluent FS-13 was used, and distribution ratios of U(VI) were studied as a function of nitric acid, ligand, and lithium nitrate concentrations. Extractability of uranium was shown to increase with increased concentration of nitrate and ligands. Infrared spectra of organic extraction phases indicate that nitric acid is coextracted as part of the neutral metal-ligand complex with U(VI) and EtTDPA through hydrogen bonding with the carbonyl group in the amide moiety.