Water-soluble Schiff base-actinyl complexes and their effect on the solvent extraction of f-elements

• Published in: Dalton transactions : an international journal of inorganic chemistry 2016-01, Vol.45 (39), p.15415-15426
• Main Authors: Hawkins, Cory A, Bustillos, Christian G, May, Iain, Copping, Roy, Nilsson, Mikael
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Cations; Complexation; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Ligands; Mathematical analysis; Raw materials; Schiff bases; Solvent extraction
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c6dt01357k

Conventional solvent extraction of selected f-element cations by bis(2-ethylhexyl)phosphoric acid (HDEHP) yields increased extraction from aqueous to organic solution along the series Np( v ) < Cm( iii ) < Eu( iii ) < U( vi ), with distribution ratios all within two orders of magnitude. However, in the presence of the water-soluble tetradentate Schiff base ( N , N ′-bis(5-sulfonatosalicylidene)-ethylenediamine or H 2 salenSO 3 ), selective complexation of the two actinyl cations (Np( v ) and U( vi )) resulted in an extraction order of Np( v ) < U( vi ) < Eu( iii ) < Cm( iii ). The extraction of neither Cm( iii ) or Eu( iii ) by HDEHP are significantly impacted by the presence of the aqueous phase Schiff base. Despite observed hydrolytic decomposition of H 2 salenSO 3 in aqueous solutions, the calculated high conditional stability constant ( β 11 = 26) for the complex [UO 2 (salenSO 3 )] 2− demonstrates its capacity for aqueous hold-back of U( vi ). UV-visible-NIR spectroscopy of solutions prepared with a Np( vi ) stock and H 2 salenSO 3 suggest that reduction of Np( vi ) to Np( v ) by the ligand was rapid, resulting in a pentavalent Np complex that was substantially retained in the aqueous phase. Results from 1 H NMR of aqueous solutions of H 2 salenSO 3 with U( vi ) and La( iii ), Eu( iii ), and Lu( iii ) provides additional evidence that the ligand readily chelates U( vi ), but has only weak interactions with trivalent lanthanide ions. Conventional solvent extraction of neptunyl( v ), Cm( iii ), Eu( iii ) & uranyl( vi ) by bis(2-ethylhexylphosphoric acid (HDEHP) can be altered through introduction of an actinyl selective hold-back complexant.