Synthesis and evaluation of novel water-soluble ligands for the complexation of metals during the partitioning of actinides

Abstract

Different types of water-soluble ligands were synthesized and their capability was evaluated by solvent extraction studies to complex trivalent actinides and suppress their extraction by a strong lipophilic ligand, such as TODGA. The back extraction efficiency of hydrophilic diglycolamide (DGA) derivatives with a varying number of ethylene glycol groups, or containing sodium acetate moieties on the amidic nitrogen shows a decrease in back-extraction efficiency with increasing number of ethylene glycol units on the amidic nitrogen at various pH values of the aqueous phase. Among the PQS donating ligands only the ligand with a malonamide backbone exhibits a high reverse extraction efficiency, although, with no selectivity for americium. Within the water-soluble tripodal ligands, i.e. the amide derivatives of nitrilotriacid with N,N-dimethyl and N,N-bis(hydroxyethyl) moieties, the first one shows a pronounced selectivity for Am(III) over Eu(III), with a maximum separation factor of 11.1, while the latter one more efficiently complexes the radionuclides in the aqueous phase with a maximum separation factor of 5. Isothermal microcalorimetry experiments of the complexation of Eu(III) by a selected series of ligands confirm the observed trend in the back extraction properties.

High selective extraction for thorium(IV) with NTAamide in nitric acid solution: Synthesis, solvent extraction and structure studies

“…In spite of this, their selectivities are not high enough for thorium separation over either uranium or rare earth [23,24]. In order to improve the selectivity, a kind of amides derived from aminopolycarboxylate ligands, such as ethylenendiamine tetraacetic acid (EDTA), nitrilotriacetic acid (NTA) and diethylenetriamine pentacetic acid (DTPA), have been explored for actinides separation [25][26][27]. Among them, those based on NTA with special tripod structure were paid more attention.…”

Liquid–Liquid Extraction of Actinides from Nitric Acid Feeds Using Two Hexa-n-alkylnitrilotriacetamides

“…N,N,N',N',N",N"-hexa-n-octylnitrilotriacetamide (HONTA, Figure 1c) are alternative 'green' CHON type ligands where three acetamide groups are appended onto a central nitrogen atom to form a tripodal ligand structure with both hard (O) and soft (N) donor atoms. Though the extractant was first reported by Iqbal et al [18,19] a subsequent study by Sasaki et al, used HONTA solutions in n-dodecane and indicated selective extraction of Am and Cm with respect to lanthanides at lower nitric acid concentrations. [20] They also reported high extraction of Pu and other relevant fission product elements such as Mo, Tc, and Pt group metals.…”

Palladium-catalyzed cross-coupling of various phosphorus pronucleophiles with chloropyrazines: synthesis of novel Am(iii)-selective extractants

“…The lipophilic ligands are typically used to extract f-block elements from highly acidic radioactive waste solutions, while the water-soluble complexants are applied to strip metal ions back. 25 Pyridine-based ligands, picolinamides for instance, are known to lose their extraction ability significantly at a pH < 3, due to protonation of the pyridine nitrogen. 25 Pyrazine will be less acid sensitive, since the pyrazine nitrogen ( pK b , pyrazine = 13.8) is much less basic than that of pyridine ( pK b , pyridine = 8.8).…”