Functionalized Dipicolinic Acid Derivatives as TALSPEAK-MME Stripping Agents

• Published in: Solvent extraction and ion exchange 2021-01, Vol.39 (1), p.18-37
• Main Authors: Uhnak, Nicolas E. F., Nash, Kenneth L.
• Format: Article
• Language: English
• Subjects: actinide; Dipicolinic Acid; lanthanide; Solvent Extraction; TALSPEAK
• ISSN: 0736-6299; 1532-2262
• DOI: 10.1080/07366299.2020.1815391

This work describes the results of an assessment of two derivatives of dipicolinic acid (DPA) as the actinide-selective stripping reagents in the combined HEH[EHP]/Cyanex-923 system, TALSPEAK-MME (mixed monofunctional extractants). One purpose of this investigation is to demonstrate probable advantages derived in phase-transfer kinetics by deploying dipicolinates as preorganized aminopolycarboxylate complexants in TALSPEAK-derived separation systems. The investigation is focused on the behavior of the lanthanides, Am, and selected transition metals (Zr, Mo, Pd, Ru, and Rh) in the extraction, solvent conditioning, and stripping steps. Solvent conditioning with glycine buffer solutions is shown to be effective for the removal of entrained HNO 3 while also managing Pd concentration prior to actinide stripping. The efficacy of the DPA derivative during the actinide-selective strip was assessed, focusing explicitly on the effects of pH and ligand concentration and evaluating the stripping kinetics. These ligands were shown to be highly selective for americium, producing in the TALSPEAK-MME platform separation factors comparable to commonly used actinide selective stripping agents for radiotracer Eu, Am, a trans-lanthanide series and selected transition metals. The stripping kinetics study revealed very rapid phase-transfer reactions, reaching equilibrium in less than 10 s on vigorous agitation. Further work will be required to address the possible contamination of the product by selected transition metals (such as Zr) during the stripping step.