Extraction of americium (3), uranium (6) and plutonium (4) from nitric acid solutions with poly-(2-ethylhexyl)phosphonitrilic acid

Extraction properties of poly-(2-ethylhexyl)-phosphonitrilic acid (P2EHPNA) and di-(2-ethylhexyl)-phosphoric acid (D2EHPA) as to actinide elements in oxidation degrees (3), (4) and (6) are compared using as an example americium (3), uranium (6) and plutonium (4). It is found that P2EHPNA extracts trivalent actinides according to cation exchange mechanism with the formation of complexes MeX3(HX)sub(3n-3) and MeXsub(3)(HX)sub(2n-3), where HX-monomeric group of extractant. Exchange-solvate mechanism is not detected up to water phase acidity 8 mol/l. The constant of americium extraction is higher than for D2EHPA (approximately 108 times) which is explained by linear character of P2EHPNA polymers and possibility of polydentate coordination. During the extraction of tetra- and hexavalent actinides the contribution of cation exchange and exchange-solvate constituent becomes comparable and extraction ability of P2EHPNA is comparable with extraction ability of alkylphosphoric acids, D2EHPA in particular