Counter-current extraction of uranium and lanthanides from simulated high-level waste using N,N,N′,N′-tetraoctyl diglycolamide

Amide-decorated reusable C18 silica-packed columns for the rapid, efficient and sequential separation of lanthanoids using reversed phase-high performance liquid chromatography

The current work focuses on the sequential separation of trivalent lanthanides (except Pm3+) using modified C18 silica-packed supports through the reversed-phase high-performance liquid chromatography (RP-HPLC) technique. In the current research, four indigenously synthesized amphiphilic aromatic triamide derivatives, namely N1, N1, N3, N3, N5, N5-hexa(alkyl) benzene-1,3,5-tri carboxamide (alkyl = butyl, hexyl, octyl, and decyl), were employed as column modifiers. The results show that the separation of Ln3+ can be achieved systematically (< 12 min) by tuning the modifiers' functional group and hydrophobic chain and fine-tuning the column modification procedure and separation parameters. The chromatographic studies revealed that the use of 0.168 mmol of N1, N1, N3, N3,N5, N5-hexa(hexyl)benzene-1,3,5-tricarboxamide (HHBTA) coated column and 0.419 mmol of N1, N1, N3, N3, N5, N5-hexa(octyl) benzene-1,3,5-tricarboxamide (HOBTA) modified columns offered excellent separation for the lanthanoids, using 0.1 M α-hydroxyisobutyric acid (HIBA), as mobile phase. The separated lanthanoids were quantified by post-column derivatization reaction (after the separation process) using Arsenazo (III) as the post-column reagent by integrating with a UV-Visible detector fixed at 655 nm (λmax). A systematic study on the influence of various analytical features, such as the effect of the modifier's chain length and its concentration, mobile phase composition and pH, was performed and optimized for achieving the best separation protocols.

Separation of vanadium, tungsten and molybdenum from spent SCR catalysts solution by solvent extraction with primary amine N1923

The large accumulation of spent selective catalytic reduction (SCR) catalysts cause waste of resources and environmental pollution. In this study, an efficient method is proposed to separate vanadium (V), molybdenum (Mo), and tungsten (W) from the leachate of hydrometallurgical treated spent SCR catalysts. First, V and W could be preferentially extracted by acidified primary amine N1923 and left Mo in the raffinate, then V and W were stripped selectively by sulfur acid and ammonia solution, respectively, leading to the separation of V, Mo, and W. Optimized experimental conditions were achieved as Initial pH of 6.7, phase ratio O/A of 1, contact time of 4 min and the concentration of primary amine N1923 was 10 % (v/v), under which V and W were extracted as high as 99.91 % and 96.86 % for the two-stage counter-current extraction, respectively, limiting Mo co-extraction to 5.84 %. The stripping ratio of V and W were up to 95.34 % and 95.50 % with sulfuric acid and ammonia, respectively and the organic phase was remained to recycle. The mechanism and process of extraction were analyzed using the slope method and the FT-IR spectra. In addition, the equations for the stripping of V and W with sulfuric acid and ammonia were deducted. Compared to traditional solvent extraction and chemical precipitation, this one-step-extraction-two-steps-stripping process shorten steps and is more efficient to separate three metals ions of V, Mo and W.

Unique transport behaviour of Am(III)/Eu(III) ions across a supported liquid membrane containing a TREN-based diglycolamide dendrimer ligand

Appropriately functionalized dendrimers are exotic ligands and are expected to give rise to better extraction/transport results than the corresponding monofunctional ones. Diglycolamide- (DGA) based dendrimers and their transport studies are rarely reported. Transport of Am(III) and Eu(III) was studied across a PTFE- (polytetrafluoroethylene) based flat sheet supported liquid membrane containing a tris(2-aminoethyl)amine (TREN) dendrimer ligand containing six DGA pendent arms (termed as TREN-G1-DGA) in 5% isodecanol modified n-dodecane. The transport results were compared with those of the monofunctional ligand TODGA (N,N,N′,N′-tetra-n-octyl diglycolamide). In case of a 5.75 × 10−4 M TREN-G1-DGA solution, Am(III) transport was slower than that of Eu(III) under identical conditions. In case of TREN-G1-DGA the role of acid on the metal ion transport was less important than that while using TODGA as a carrier. However, a nitric acid medium is much more suitable for metal ion transport than a mixture containing sodium nitrate as the major component. Insight into the extraction and transport of the Eu(III) complexes was obtained from luminescence spectroscopic studies.

Sequestration of tetravalent neptunium from acidic feeds using diglycolamide-functionalized dendrimers in a room temperature ionic liquid: extraction, spectroscopic and electrochemical studies

Extraction of Np(iv) was studied using RTIL containing two poly(propyleneimine) based dendrimer ligands from HNO3 solutions. Studies of the extracted complexes were also carried out by Vis-NIR and cyclic voltammetry.

Highly efficient diglycolamide-functionalized dendrimers for the sequestration of tetravalent actinides: solvent extraction and theoretical studies

Two DGA-functionalized dendrimers were used for the extraction and bonding computations of tetravalent actinide ions Np⁴⁺ and Pu⁴⁺ from HNO₃ medium.

Two novel extraction chromatographic resins containing benzene-centered tripodal diglycolamide ligands: Actinide uptake, kinetic modeling and isotherm studies

Two novel extraction chromatographic resins (EC), termed as RL-1 and RL-2, were prepared by impregnating two benzene-centered tripodal iglycolamide ligands (Bz-T-DGA) containing different spacer groups where the ligands are termed as L-1 and L-2, respectively. They were employed for the uptake of actinide and fission product ions, viz. Am³⁺, Eu³⁺, UO₂²⁺, Np⁴⁺, Pu⁴⁺, Sr²⁺, and Cs⁺, from acidic feeds. Weight distribution coefficient (K_d) values were measured by the batch method and the loaded metal ions were back extracted using a 0.01 M EDTA solution at pH 4. Kinetic modeling of the sorption data of Am(III) on both resins suggested pseudo-second order rate kinetics with rate constants of 1.68 × 10^-6 and 2.47 × 10^-6 g/cpm.min for the resins containing L-1 and L-2, respectively. Sorption isotherm studies indicated the Langmuir monolayer chemisorption phenomenon with Eu(III) experimentally determined saturation uptake capacities of 6.02 ± 0.11 and 5.49 ± 0.14 mg per g of RL-1 and RL-2 resins, respectively. As the batch uptake study results appeared encouraging, column studies were also carried out using both resins. The resin reusability data indicated a marginal change in the K_d values for the RL-1 resin up to three repeat runs beyond which a steady decrease of the K_d value was seen. On the other hand, in the case of RL-2 a steady decrease in the K_d values was observed for three repeat runs beyond which there was marginal change.

Evaluation of two aza-crown ether-based multiple diglycolamide-containing ligands for complexation with the tetravalent actinide ions Np4+ and Pu4+: extraction and DFT studies

Two multiple diglycolamide (DGA)-containing extractants where the DGA arms are tethered to the nitrogen atoms of two aza-crown ether scaffolds, a 9-membered aza-crown ether containing three ‘N’ atoms (L_I) and a 12-membered aza-crown ether containing four ‘N’ atoms (L_II), were evaluated for the extraction of the tetravalent actinide ions Np⁴⁺ and Pu⁴⁺. The tripodal ligand with three DGA arms (L_I) was relatively inferior in its metal ion extraction properties as compared to the tetrapodal ligand with four DGA arms (L_II) and Pu⁴⁺ ion was better extracted than Np⁴⁺ ion with both the ligands. A solvation extraction mechanism, where species of the type ML(NO₃)₄ are extracted, was found to be operative for both the ligands involving both the tetravalent actinide ions. While the extraction of the metal ions increased with the feed nitric acid concentration up to 4 M, a sharp decline in the extraction was seen after that. Quantitative extraction (>99%) of the actinide ions was observed with L_II from 4 M HNO₃, suggesting the possible application of the ligands for actinide partitioning of high-level waste. The structure and the composition of the complexes were optimized by DFT computations.

Two multiple diglycolamide (DGA)-containing aza-crown ether ether-based extractants were evaluated for the extraction of the tetravalent actinide ions Np⁴⁺ and Pu⁴⁺.

Effect of an alkyl substituent and spacer length in benzene-centered tripodal diglycolamides on the sequestration of minor actinides

Three benzene-centered tripodal diglycolamide (Bz-T-DGA) ligands, where diglycolamide (DGA) moieties are tethered to the central benzene ring through a methylene spacer and having either a hydrogen atom (LI) or an isopentyl group (LII) attached to the N-atom, and DGA moieties attached via an ethylene spacer and having an isopentyl group attached to the N-atom (LIII), were studied for their complexation and extraction abilities towards trivalent actinides and lanthanides. The distribution ratio of Am(iii) and Eu(iii) with 1 mmol L-1 ligand in 5% iso-decanol/n-dodecane followed the order: LII > LIII > LI. The substitution of the H atom with the isopentyl group on the N-atom of the DGA moieties resulted in two orders of magnitude enhancement in the extraction ability of the ligand. On the other hand, increase in the spacer length between the benzene ring and the DGA moieties resulted in several fold reduction in the extraction ability of the ligand. Spectroscopic studies with Eu3+ ions in acetonitrile also confirmed the metal/ligand complex formation constant in the order: LII > LIII > LI. Luminescence decay lifetimes of Eu3+/ligand complexes confirmed the absence of water molecules and that all the primary coordination sites of the metal ion are occupied by the ligands.

Application of a functionalized ionic liquid extractant tributylmethylammonium dibutyldiglycolamate ([A336][BDGA]) in light rare earth extraction and separation

A type of functionalized ionic liquid extractant, tributylmethylammonium dibutyldiglycolamate ([A336][BDGA]), was synthesized, and its extraction ability of light rare earth elements, namely, La(III), Ce(III), Pr(III) and Nd(III), wascompared with that of other functionalized ionic liquid extractants, including tributylmethylammonium dioctyldiglycolamate and diglycolic amide extractants N,N,N,N-tetrabutyl-3-oxapentane-diamide (TBDGA) and N,N,N,N-tetraoctyl-3-oxapentane-diamide (TODGA). The study of extraction behavior indicated that the ionic liquids exhibited better extraction properties than the amides under lower acidity conditions. The effects of the pH and concentration of the extractant on the extraction behavior of [A336][BDGA] on light rare earths were determined. A separation strategy of mixed light rare earths was investigated by means of extraction chromatography using [A336][BDGA] as the stationary phase. As a result, nearly pure La(III), Ce(III), Pr(III) and Nd(III) were obtained, respectively. A new strategy of separating mixed light rare earths was established by means of extraction chromatography. The stationary phase of [A336][BDGA] was used in this strategy. The four rare earths elements, La(III), Ce(III), Pr(III) and Nd(III), achieved baseline separation.

Studies on adsorption of rare earth elements from nitric acid solution with macroporous silica-based bis(2-ethylhexyl)phosphoric acid impregnated polymeric adsorbent

For the adsorption and recovery of rare earth elements from aqueous nitric acid, solid-phase extraction resins were prepared by impregnating and immobilizing of bis(2-ethylhexyl)phosphoric acid extractant into the macroporous silica-based polymeric (SiO2-P) particles. It was found that bis(2-ethylhexyl)phosphoric acid/SiO2-P had higher adsorption distribution coefficient for heavy rare earth elements than for light rare earth elements. The adsorption capacity of Gd(III) was observed to be 0.315 mmol g−1 by bis(2-ethylhexyl)phosphoric acid/SiO2-P in 0.1 M HNO3 at 298 K, which increased slightly when increasing temperature from 298 to 323 K. The adsorption isotherms of Gd(III) matched well with the Langmuir and Freundlich models. The obtained thermodynamic parameters (ΔHo and ΔGo) showed that the adsorption of Gd(III) by bis(2-ethylhexyl)phosphoric acid/SiO2-P was a spontaneous and exothermic process. This study also evaluated the chemical stability of bis(2-ethylhexyl)phosphoric acid/SiO2-P treated with nitric acid at different temperatures and demonstrated that bis(2-ethylhexyl)phosphoric acid/SiO2-P had considerable stability against nitric acid and heat.

Minimizing the aggregation of diglycolamide reverse micelles in the n-dodecane phase with bis-(2-ethylhexyl)phosphoric acid “reactive” phase modifier

“Reactive“ phase modifiers enhance the extraction of trivalent metal ions through synergism and prevent third phase formation.

Studies on the uptake of Am(III) and Eu(III) on ionic liquid modified polystyrene-divinyl benzene

Imidazolium bis(2-ethylhexyl)phosphate ionic liquid was anchored on a polystyrene-divinylbenzene (PS-DVB) copolymer and the product (R-Im-DEHP) was studied for the extraction of Am(III) and Eu(III) from dilute nitric acid medium to examine the feasibility using the anchored adsorbent for their mutual separation. The effect of various parameters such as the duration of equilibration, concentration of nitric acid, europium ion, and diethylenetriaminepentaacetic acid (DTPA) in aqueous phase on the distribution coefficient (K d) of Am(III) and Eu(III) was studied. The distribution coefficient of Am(III) and Eu(III) decreased with increase in the concentration of nitric acid. Rapid extraction of metal ions in the initial stages of equilibration followed by the establishment of equilibrium occurred within 4 h. The data on the rate of uptake of Am(III) and Eu(III) were fitted into pseudo-first order and pseudo-second order rate equation. The extraction isotherm was fitted to Langmuir and Freundlich adsorption models and the apparent europium extraction capacity was determined. The mechanism of extraction was elucidated and the conditions needed for efficient separation of Am(III) from Eu(III) was optimized using DTPA. The study indicated the possibility of using R-Im-DEHP for the separation of Eu(III) from Am(III) with high separation factors.

Effect of pKa on the extraction behavior of Am(III) in organo phosphorus acid and diglycolamide solvent system

A combination of neutral and acidic extractant has been proposed for the single-cycle separation of trivalent actinides from high-level liquid waste (HLLW). The nature of acidic extractant in the combined solvent formulation plays a profound role in deciding the extraction and stripping of trivalent actinides. Therefore, the extraction behavior of Am(III) in a solution of tetra-bis(2-ethylhexyl)-diglycolamide (TEHDGA) and acidic extractant (HA) was studied from nitric acid medium. The acidic extractants chosen were bis(2-ethylhexyl)phosphoric acid (HDEHP), bis(2-ethylhexyl)phosphonic acid (PC88A) and bis(2,4,4-trimethylpentyl)phosphinic acid (CYANEX-272) whose pKa values were 3.24, 4.51 and 6.37, respectively. The distribution ratio of Am(III) was measured as a function of various parameters such as concentration of nitric acid, TEHDGA, HA etc. The data were compared with those obtained in individual solvent systems namely 0.1 M TEHDGA/n-DD and HA/n-DD. Slope analysis of the extraction data indicated the synergic participation of both TEHDGA and HDEHP in the extraction of Am(III) at all acidities. However, antagonistic effect was observed at lower acidity when TEHDGA was mixed to PC88A or CYANEX-272 present in n-DD. Accordingly, a suitable mechanism has been proposed for the extraction of Am(III) at all acidities using these combined solvent formulation. Studies with fast reactor simulated high level liquid waste indicated that extraction of Am(III) was accompanied by co-extraction of lanthanides and unwanted metal ions such as Zr(IV), Mo(VI), Y(III) and Pd(II). However, addition of trans-1,2-diaminocyclohexane-N,N,N,N′-tetraaceticacid (CyDTA) reduced the extraction of unwanted metal ions. Batch extraction and stripping studies indicated the possibility of using 0.1 M TEHDGA+0.25 M HDEHP in n-dodecane for the single cycle separation of Am(III) from FR-SHLLW.

Unique selectivity reversal in Am3+–Eu3+ extraction in a tripodal TREN-based diglycolamide in ionic liquid: extraction, luminescence, complexation and structural studies

A unique selectivity reversal in metal ion extraction was seen in DGA-TREN vis-à-vis T-DGA.

Diglycolamide-Based Solvent Systems in Room Temperature Ionic Liquids for Actinide Ion Extraction: A Review

This review article gives a comprehensive account of the extraction of actinide ions using room temperature ionic liquid-based solvent systems containing diglycolamide (DGA) or functionalized DGA extractants. These extractants include multiple DGA-functionalized ligands such as tripodal DGA (T-DGA) and DGA-functionalized calix [4]arenes (C4DGA). Apart from metal ion extraction behaviour, other important features of the ionic liquid-based solvent systems such as separation behaviour, luminescence spectroscopic results, thermodynamics of extraction and radiolytic stability of the ionic liquid-based solvents are also reviewed. Results from studies on DGA-functionalized task-specific ionic liquids (TSIL) are also included in this review article.