title: Understanding the solution behavior of minor actinides in the presence of EDTA4-, carbonate, and hydroxide ligands.
abstract: The aqueous solution behavior of An(III) (An = Am or Cm) in the presence of EDTA(4-) (ethylenediamine tetraacetate), CO3(2-) (carbonate), and OH(-) (hydroxide) ligands has been probed in aqueous nitrate solution (various concentrations) at room temperature by UV-vis absorption and luminescence spectroscopies (Cm systems analyzed using UV-vis only). Ternary complexes have been shown to exist, including [An(EDTA)(CO3)](3-)(aq), (where An = Am(III) or Cm(III)), which form over the pH range 8 to 11. It is likely that carbonate anions and water molecules are in dynamic exchange for complexation to the [An(EDTA)](-)(aq) species. The carbonate ion is expected to bind as a bidentate ligand and replaces two coordinated water molecules in the [An(EDTA)](-)(aq) complex. In a 1:1 Am(III)/EDTA(4-) binary system, luminescence spectroscopy shows that the number of coordinated water molecules (N(H2O)) decreases from ~8 to ~3 as pH is increased from approximately 1 to 10. This is likely to represent the formation of the [Am(EDTA)(H2O)3](-) species as pH is raised. For a 1:1:1 Am(III)/EDTA(4-)/CO3(2-) ternary system, the N(H2O) to the [Am(EDTA)](-)(aq) species over the pH range 8 to 11 falls between 2 and 3 (cf. ~3 to ~4 in the binary system) indicating formation of the [An(EDTA)(CO3)](3-)(aq) species. As pH is further increased from approximately 10 to 12 in both systems, there is a sharp decrease in N(H2O) from ~3 to ~2 in the binary system and from ~2 to ~1 in the ternary system. This is likely to correlate to the formation of hydrolyzed species (e.g., [Am(EDTA)(OH)](2-)(aq) and/or Am(OH)(3(s))).
authors.affiliation: Centre for Radiochemistry Research, School of Chemistry, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
authors.forename: Tamara L
authors.initials: TL
authors.lastname: Griffiths
authors.forename: Leigh R
authors.initials: LR
authors.lastname: Martin
authors.forename: Peter R
authors.initials: PR
authors.lastname: Zalupski
authors.forename: John
authors.initials: J
authors.lastname: Rawcliffe
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Sarsfield
authors.forename: Nick D M
authors.initials: ND
authors.lastname: Evans
authors.forename: Clint A
authors.initials: CA
authors.lastname: Sharrad