Extraction of some Hexavalent Actinide Ions from Nitric Acid Medium using Several Substituted Diglycolamides

Abstract

Several substituted diglycolamides, namely TPDGA, THDGA, TODGA, and TDDGA, were evaluated in a comparative study on the extraction of hexavalent actinide ions such as UO₂²⁺, NpO₂²⁺, and PuO₂²⁺ from nitric acid medium. The acid extraction constants (K_H) for the diglycolamides were determined to be 3.8 ± 0.6, 1.6 ± 0.1, 4.1 ± 0.4, and 1.4 ± 0.2 for TPDGA, THDGA, TODGA, and TDDGA, respectively. Though metal ion extraction generally increased with increasing the feed acid concentration, the nature of the extracted species changed with aqueous-phase acidity. While complexes of the type MO₂(NO₃)₂·nL (where L is the diglycolamide extractant and n is 1 and 2) were found to be extracted at 1 M HNO₃, the average number of ligand molecules associated with the complex decreased to ˜1 when the nitric acid concentration increased to 3 M. These results have great significance from the actinide separation point of view, as the actinides ions can be made virtually inextractable by adjusting their oxidation state. The thermodynamic parameters were also calculated, which indicated spontaneous reactions with large exothermicities.

Keywords:

• hexavalent actinides
• diglycolamides
• solvent extraction
• thermodynamics

ACKNOWLEDGMENTS

The authors thank Dr. A. Goswami, Head, Radiochemistry Division, for his keen interest and constant encouragement.