2 research outputs found
Understanding the solution behavior of minor actinides in the presence of EDTA(4-), carbonate, and hydroxide ligands
Understanding the solution behavior of minor actinides in the presence of EDTA(4-), carbonate, and hydroxide ligand
Understanding the Solution Behavior of Minor Actinides in the Presence of EDTA<sup>4–</sup>, Carbonate, and Hydroxide Ligands
The aqueous solution
behavior of An<sup>III</sup> (An = Am or Cm) in the presence of EDTA<sup>4–</sup> (ethylenediamine tetraacetate), CO<sub>3</sub><sup>2–</sup> (carbonate), and OH<sup>–</sup> (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 [AnÂ(EDTA)Â(CO<sub>3</sub>)]<sup>3–</sup><sub>(aq)</sub>, (where An = Am<sup>III</sup> or Cm<sup>III</sup>), 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 [AnÂ(EDTA)]<sup>−</sup><sub>(aq)</sub> species. The carbonate
ion is expected to bind as a bidentate ligand and replaces two coordinated
water molecules in the [AnÂ(EDTA)]<sup>−</sup><sub>(aq)</sub> complex. In a 1:1 Am<sup>III</sup>/EDTA<sup>4‑</sup> binary
system, luminescence spectroscopy shows that the number of coordinated
water molecules (<i>N</i><sub>H<sub>2</sub>O</sub>) decreases
from ∼8 to ∼3 as pH is increased from approximately
1 to 10. This is likely to represent the formation of the [AmÂ(EDTA)Â(H<sub>2</sub>O)<sub>3</sub>]<sup>−</sup> species as pH is raised.
For a 1:1:1 Am<sup>III</sup>/EDTA<sup>4–</sup>/CO<sub>3</sub><sup>2–</sup> ternary system, the <i>N</i><sub>H<sub>2</sub>O</sub> to the [AmÂ(EDTA)]<sup>−</sup><sub>(aq)</sub> 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 [AnÂ(EDTA)Â(CO<sub>3</sub>)]<sup>3–</sup><sub>(aq)</sub> species. As pH is further
increased from approximately 10 to 12 in both systems, there is a
sharp decrease in <i>N</i><sub>H<sub>2</sub>O</sub> 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., [AmÂ(EDTA)Â(OH)]<sup>2–</sup><sub>(aq)</sub> and/or AmÂ(OH)<sub>3(s)</sub>)