Abstract
Complexation of Np(v) with N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA) was studied in aqueous solution (I = 1.0 mol L-1 NaClO4, t = 25 °C) by spectrophotometry, microcalorimetry and Extended X-ray absorption fine structure (EXAFS) spectroscopy. Equilibrium constants for the formation of three complexes, NpO2L2-, NpO2(HL)-, and (NpO2)2(OH)2L26-, were determined to be (6.91 ± 0.06), (4.28 ± 0.03) and -(4.93 ± 0.03), respectively. The enthalpies of complexation were determined to be -(8.0 ± 2.0) kJ mol-1 for NpO2L2- and -(2.2 ± 2.0) kJ mol-1 for NpO2(HL)-. Thermodynamic data of the complexation of Np(v) with HEDTA were compared to those of Np(v) with other aminopolycarboxylic acids, gaining insight into the possible coordination modes of the complexes. The EXAFS studies provided further structural information on those modes. In both NpO2L2- and NpO2(HL)- complexes, HEDTA coordinates to Np(v) in a tridentate mode through two oxygens of two carboxylic groups and one nitrogen of the amine group. In the (NpO2)2(OH)2L26- complex, two Np(v) atoms are bridged by two hydroxides and each HEDTA maintains the tridentate coordination mode.
| Original language | English |
|---|---|
| Pages (from-to) | 114916-114926 |
| Number of pages | 11 |
| Journal | RSC Advances |
| Volume | 6 |
| Issue number | 115 |
| DOIs | |
| State | Published - 2016 |
Funding
This work was supported by the Fuel Cycle Research and Development (FCR&D) Thermodynamics and Kinetics Program, Office of Nuclear Energy, the U.S. Department of Energy under Contract Number DE-AC02-05CH11231 at Lawrence Berkeley National Laboratory. L. R. Martin acknowledges the support from DOE NE FCR&D Thermodynamics and Kinetics program, under DOE Idaho Operations Office Contract DE-AC07-05ID14517 while preparing this manuscript. The EXAFS data were collected at Stanford Synchrotron Radiation Laboratory (SSRL). SSRL is a user facility operated for the U.S. DOE by Stanford University.