Radiation-induced effects on the extraction properties of hexa-n-octylnitrilo-triacetamide (HONTA) complexes of americium and europium.

The candidate An(iii)/Ln(iii) separation ligand hexa-n-octylnitrilo-triacetamide (HONTA) was irradiated under envisioned SELECT (Solvent Extraction from Liquid waste using Extractants of CHON-type for Transmutation) process conditions (n-dodecane/0.1 M HNO3) using a solvent test loop in conjunction with cobalt-60 gamma irradiation. The extent of HONTA radiolysis and complementary degradation product formation was quantified by HPLC-ESI-MS/MS. Further, the impact of HONTA radiolysis on process performance was evaluated by measuring the change in 243Am and 154Eu distribution ratios as a function of absorbed gamma dose. HONTA was found to decay exponentially with increasing dose, affording a dose coefficient of d = (4.48 ± 0.19) × 10-3 kGy-1. Multiple degradation products were detected by HPLC-ESI-MS/MS with dioctylamine being the dominant quantifiable species. Both 243Am and 154Eu distribution ratios exhibited an induction period of ∼70 kGy for extraction (0.1 M HNO3) and back-extraction (4.0 M HNO3) conditions, after which both values decreased with absorbed dose. The decrease in distribution ratios was attributed to a combination of the destruction of HONTA and ingrowth of dioctylamine, which is capable of interfering in metal ion complexation. The loss of HONTA with absorbed gamma dose was predominantly attributed to its reaction with the n-dodecane radical cation (R˙+). These R˙+ reaction kinetics were measured for HONTA and its 241Am and 154Eu complexes using picosecond pulsed electron radiolysis techniques. All three second-order rate coefficients (k) were essentially diffusion limited in n-dodecane indicating a significant reaction pathway: k(HONTA + R˙+) = (7.6 ± 0.8) × 109 M-1 s-1, k(Am(HONTA)2 + R˙+) = (7.1 ± 0.7) × 1010 M-1 s-1, and k(Eu(HONTA)2 + R˙+) = (9.5 ± 0.5) × 1010 M-1 s-1. HONTA-metal ion complexation afforded an order-of-magnitude increase in rate coefficient. Nanosecond time-resolved measurements showed that both direct and indirect HONTA radiolysis yielded the short-lived (<100 ns) HONTA radical cation and a second long-lived (µs) species identified as the HONTA triplet excited state. The latter was confirmed by a series of oxygen quenching picosecond pulsed electron measurements, affording a quenching rate coefficient of k(3[HONTA]* + O2) = 2.2 × 108 M-1 s-1. Overall, both the HONTA radical cation and triplet excited state are important precursors to the suite of measured HONTA degradation products.

Theoretical Elucidation of Am(III)/Cm(III) Separation Mechanism with Diamide-type Ligands Using Relativistic Density Functional Theory Calculation.

We elucidated the separation mechanism between Am(III) and Cm(III) ions by using two different types of diamide ligands, diglycolamide (DGA) and alkylated diamide amine (ADAAM), by means of the density functional theory technique and electron density analysis. The molecular geometries and formation reactions of the metal-ligand complexes were modeled by using [M(DGA)3]3+ and [M(ADAAM)(NO3)3(H2O)]. We successfully reproduced Cm(III) selectivity over Am(III) with DGA and Am(III) selectivity over Cm(III) with ADAAM. Furthermore, we analyzed the bonding properties between the metal ion and the diamide-type ligands by using model complexes, [M(DGA)3]3+ and [M(ADAAM)(NO3)3(H2O)], and revealed the differences in terms of the bond dissociation energy and the metal 5f orbital participation in the covalency between the Am(III) and the Cm(III) complexes. It was suggested that the differences were key factors to understand the Am(III)/Cm(III) selectivity.

Effects of Diluents on the Separation of Minor Actinides from Lanthanides with Tetradodecyl-1,10-phenanthroline-2,9-diamide from Nitric Acid Medium.

To investigate the effective separation of actinides (Ans) from lanthanides (Lns), single-stage batch extraction experiments were performed with a novel extractant, tetradodecyl-1,10-phenanthroline-2,9-diamide (TDdPTDA) with various diluents such as 3-nitrobenzotrifluoride (F-3), nitrobenzene, and n-dodecane for Am, Cm, and Lns. The extraction kinetics with TDdPTDA was rapid enough to perform continuous extraction experiments using mixer-settler extractors. The slopes of the distribution ratio versus the TDdPTDA concentration and the distribution ratio versus the nitric acid concentration were similar for F-3 and nitrobenzene systems, but different from the n-dodecane system. These differences were attributed to the characteristics of the diluents. This study revealed high distribution ratios of Am (DAm) and Cm (DCm) for TDdPTDA, with the high separation factors (SFs) of Am from Lns enough for their separation.

Direct Temperature-Swing Extraction of Rare-Earth Elements from Acidic Solution Using the Hydrophobic Interactions of Poly(N-isopropylacrylamide) with Diglycolamide-typed Ligands.

The phase transition-based gelification phenomenon of poly(N-isopropylacrylamide) [poly(NIPAAm)] has great potential in developing new waste-free extraction processes. In this study, we realized the direct and complete temperature-swing extraction of all trivalent rare-earth (RE) ions from a multi-component nitric acid solution onto a poly(NIPAAm) gel as chelate complexes with hydrophobic diglycolamide-typed ligands. Moreover, we elucidated that the extractabilities are affected by not only the coordination ability of the ligands with RE ions but also by the hydrophobic interaction between the poly(NIPAAm) and the ligands.

High-Performance Alkyl Diamide Amine and Water-soluble Diamide Ligand for Separating of Am(III) from Cm(III).

Alkyl diamide amine (ADAAM), a new high-performance reagent with a simple structure, was examined for the mutual separation of Am(III) and Cm(III). The combination of ADAAM and N,N,N',N'-tetraethyldiglycolamide (TEDGA) as a masking agent shows selectivity for Am(III) over Cm(III) in highly acidic media with separation factors of up to 41.

The separation mechanism of Am(iii) from Eu(iii) by diglycolamide and nitrilotriacetamide extraction reagents using DFT calculations.

Relativistic density functional calculations were applied to study the separation behaviors of the Am(iii) ion from the Eu(iii) ion by diglycolamide (DGA) and nitrilotriacetamide (NTA) ligands in order to understand the difference in the separation mechanism of their reagents. The complexation reaction was modeled on the basis of previous experimental studies. The calculated energies based on stabilization by complex formation at the ZORA-B2PLYP/SARC level predicted that the DGA reagent preferably coordinated to the Eu(iii) ion when compared with the Am(iii) ion. In contrast, the NTA reagent selectively coordinated to the Am(iii) ion when compared with the Eu(iii) ion. These results reproduced the experimental selectivity of DGA and NTA ligands toward Eu(iii) and Am(iii) ions. Mulliken's population analyses implied that the difference in the contribution of the bonding property between the f-orbital of Am and donor atoms determined the comparative stability of Eu and Am complexes.

Highly Practical and Simple Ligand for Separation of Am(III) and Eu(III) from Highly Acidic Media.

A new, high-performance, highly practical, simple reagent called alkyl diamide amine (ADAAM) was examined for the separation of Am(III) and Eu(III). ADAAM has three donor atoms, one soft N-donor atom and two hard O-donor atoms, on a central frame. The combination of soft and hard donor atoms affords a tridentate that ensures remarkable extraction ability and selectivity of Am(III) and Eu(III) from highly acidic media (1.5 M HNO3) with a separation factor up to 25.