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In this article Part II, we consider the application of ienaic modeling for solvent extraction of rare earths in the case of the mixed DMDOHEMA/HDEHP extractant system. The system exhibits a synergistic extraction effect depending on the acid concentration and the extractant mole fraction, as demonstrated in the experimental article Part I. In this work, we directly compare experimental findings with theoretical predictions of the droplet model. The model considers the effective free energy of transfer as a combination of competing molecular forces, but contrary to previous micelle models that focus only on the dominant stoichiometry, it allows calculations of free energies of every possible spherical aggregate. The resulting image of the extraction process is that different behaviors can be obtained depending on the acidity and mole fraction of extractants, which are associated with different aggregation regimes in a complex free energy landscape of the system. Nevertheless, self-assembly is tuned by the extraction of all solutes, and not only the target metal cations. [ABSTRACT FROM AUTHOR]

Efficient formulations used in hydrometallurgy are often based on synergistic action of two oil-soluble extractants at an optimized mole fraction. In this series of two papers, we describe the N,N'-dimethyl-N,N'-dioctylhexylethoxymalonamide (DMDOHEMA)/di(2-ethylexyl) phosphoric acid (HDEHP) system, and how expression of the synergistic effect varies with acidity, using the three common representations: distribution ratios, yields, and free energies of transfer. The experimental results are detailed in this first part (Part I) with the so-called supramolecular approach, which considers the reverse micelle-like aggregates formed by the lipophilic extractant molecules. It shows that no specific aggregation state is observed at the maximum of synergism and antagonism. Besides, the critical aggregation concentration that characterizes the micellization free energy appears to follow some synergistic trends but cannot explain how acid tunes synergism to antagonism of this mixed system. Based on these results, Part II proposes a theoretical model based on the ienaic approach to interpret acid effect on synergism and antagonism. [ABSTRACT FROM AUTHOR]

In the context of the separation of uranium and plutonium from spent fuel allowed by N,N -dialkylamides, three regioisomers of N,N -di(2-ethylhexyl) butyramide (DEHBA or ββ) and the diastereopure isomers of N -(2-ethylhexyl)- N -(oct-3-yl)butyramide (EHOBA or αβ) were synthesized to assess their extraction performance and to study the mechanisms at the origin of the differences observed between the stereo- and regioisomers. The N,N -dialkylamides showed differences in extraction, with a greater effect of regio- than stereoisomerism. A mechanistic study at both the molecular and supramolecular scales was initially applied to explain these effects. X-ray absorption and UV-vis spectroscopy showed that uranium is extracted by a UO 2 (NO 3 ) 2 L 2 complex, which is not very sensitive to steric hindrance, while plutonium is extracted by two complexes, Pu(NO 3 ) 4 L 2 and Pu(NO 3 ) 6 (HL) 2 , which are differently affected by stereo- and regioisomerism. Investigations at the supramolecular scale also showed that Pu(NO 3 ) 4 L 2 complexes are disadvantaged by the bulkiness of the extractants, while Pu(NO 3 ) 6 (HL) 2 is favored by the preformation of larger supramolecular aggregates.

Silica-based porous liquids (PLs) are innovative and versatile liquid materials with a high potential, although their application is often restricted to gas sorption. In this work, we propose to evaluate their potential to extract metals. For this goal, we have adapted their synthesis to provide PLs functionalized with thiols that are expected to chelate metallic contaminants, such as lead. As the accessibility of liquids and metals to the PL's porous network is one of the key points for their application, we developed an original small-angle neutron scattering experiment to verify that the PL is permeable to polar liquids. Then, preliminary extraction tests have successfully been carried out, with an extraction of lead cations by complexation on one-third of accessible thiol groups. This work demonstrates that the extraction of metal species by a PL is possible and opens many perspectives for optimization.

Developing greener hydrometallurgical processes implies offering alternatives to conventional solvents used for liquid-liquid extraction (LLE) of metals. In this context, it is proposed to substitute the organic phase by a hydrophobic silica-based porous liquid (PL). Two different sulfonated hollow silica particles (HSPs) are modified with various polyethoxylated fatty amines (EthAs) forming a canopy that provides both the targeted hydrophobicity and liquefying properties. This study shows that these properties can be tuned by varying the number of ethylene oxide units in the EthA: middle-range molecular weight EthAs allow obtaining a liquid at room temperature, while too short or too long EthA leads to solid particles. Viscosity is also impacted by the density and size of the silica spheres: less viscous PLs are obtained with small low-density spheres, while for larger spheres (c.a. 200 nm) the density has a less significant impact on viscosity. According to this approach, hydrophobic PLs are successfully synthesized. When contacted with an aqueous phase, the most hydrophobic PLs obtained allow a subsequent phase separation. Preliminary extraction tests on three rare earth elements have further shown that functionalization of the PL is necessary to observe metal extraction., (© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.)

This study presents a comprehensive investigation of the aggregation behavior of a malonamide extractant molecule ( N , N '-dimethyl, N , N '-dioctylhexylethoxymalonamide (DMDOHEMA)) in three different solvents, including two piperidinium- and (trifluoromethylsulfonyl)imide-based ionic liquids (1-ethyl-1-butylpiperidinium bis(trifluoromethylsulfonyl)imide ([EBPip + ][NTf 2 - ]) and 1-ethyl-1-octylpiperidinium bis(trifluoromethylsulfonyl)imide ([EOPip + ][NTf 2 - ])) and n -dodecane. By combining polarizable molecular dynamics simulations and small-angle X-ray scattering experiments, we extensively investigated the arrangement of supramolecular assemblies of the extractant molecules. Our results showed that the insertion of the alkyl chains of the extractant molecules into the apolar domain of [EOPip + ][NTf 2 - ] has a significant impact on the aggregation behavior of the extractant molecules, leading to the formation of smaller aggregates having a higher dispersion compared to other solvents. These findings provide new insights into the physicochemical properties of this type of system and are crucial in designing more effective solvents for rare earth metal extraction.

Invited for this month's cover is the collaborating group of Dr Guilhem Arrachart and Dr Stéphane Pellet-Rostaing at Institut de Chimie Séparative de Marcoule (ICSM). The cover picture shows a person going uranium fishing thanks to the use of bis-catecholamide materials. These materials have shown interesting performance for the recovery of uranium in saline environments such as seawater. More information can be found in the Research Article by G. Arrachart, S. Pellet-Rostaing, and co-workers., (© 2023 Wiley-VCH GmbH.)

Efficient and selective extractions of precious and critical metal ions such as Au(III) and Pd(II) were investigated using zirconia nanoparticles surface modified with different organic mono- and di-carbamoyl phosphonic acid ligands. The modification is made on the surface of commercial ZrO 2 that is dispersed in aqueous suspension and was achieved by optimizing the Bronsted acid-base reaction in ethanol/H 2 O solution (1:2), resulting in inorganic-organic systems of ZrO 2 -L n (L n : organic carbamoyl phosphonic acid ligand). The presence, binding, amount, and stability of the organic ligand on the surface of zirconia nanoparticles were confirmed by different characterizations such as TGA, BET, ATR-FTIR, and 31 P-NMR. Characterizations showed that all the prepared modified zirconia had a similar specific surface area (50 m 2 .g -1 ) and the same amount of ligand on the zirconia surface in a 1:50 molar ratio. ATR-FTIR and 31 P-NMR data were used to elucidate the most favorable binding mode. Batch adsorption results showed that (i) ZrO 2 surface modified with di-carbamoyl phosphonic acid ligands had the highest adsorption efficiency to extract metals than mono-carbamoyl ligands, and (ii) higher hydrophobicity of the ligand led to better adsorption efficiency. The surface-modified ZrO 2 with di-N,N-butyl carbamoyl pentyl phosphonic acid ligand (ZrO 2 -L 6 ) showed promising stability, efficiency, and reusability in industrial applications for selective gold recovery. In terms of thermodynamic and kinetic adsorption data, ZrO 2 -L 6 fits the Langmuir adsorption model and pseudo-second-order kinetic model for the adsorption of Au(III) with maximum experimental adsorption capacity q max = 6.4 mg.g -1 .

Surfactants aggregate in water into micelles, and these micelles incorporate organic substances to solubilize them. Hydrotropes are compounds that increase the solubility of hydrophobic substances in water without this form of aggregation. Decreasing the chain length of the classical surfactant Aerosol OT (AOT) from C8 to C5 results in a molecule with intermediate properties. Molecular dynamics simulations and surface tension measurements are performed on this short chain derivative of AOT. This compound shows high solubility and at the same time progressive weak aggregation. The hydration of head groups hinders significant plunging into a hydrophobic core, which leads to well defined liquid chain nanodomains. The transition to bicontinuous aggregates is in the concentration range of 1 mol L -1 . The sulfonate group of the head groups (placed at the water interface of worm-like aggregates) rather than the aggregate-aggregate interaction is responsible for the unusual small angle X-ray scattering pattern.

The nanoscale organization of some classes of ionic liquids is responsible for their singular properties. In this paper, we use polarizable molecular dynamics simulations and small-angle X-ray scattering to probe the structure of two piperidinium- and (trifluoromethylsulfonyl)imide-based ionic liquids ([EBPip + ][NTf 2 - ] and [EOPip + ][NTf 2 - ]) that differ in the alkyl chain length of their cation. The X-ray scattering intensities calculated numerically, from the radial distribution functions, are in excellent agreement with the experimental data. The analysis of the different contributions of the X-ray scattering data allowed us to highlight the correlations responsible for the low q peak observed for the long-chain alkyl cations. New angular analyses showed that anions were more likely to align with alkyl chains as their size increased, inducing angular correlation between anions at larger distances. They also showed that the long alkyl chains of the cations aligned more with each other than the short ones. These more aligned alkyl chains induce a smaller volume of the apolar microdomains compared to the well-studied imidazolium-based ionic liquids, leading to the smaller correlation distance for piperidinium-based ionic liquids.

Rare-earth elements (REEs) are involved in most high technology devices and have become critical for many countries. The progress of processes for the extraction and recovery of REEs is therefore essential. Liquid-solid extraction methods are an attractive alternative to the conventional solvent extraction process used for the separation and/or purification of REEs. For this purpose, a solid-phase extraction system was investigated for the extraction and valorization of REEs. Ion-exchange resins were synthesized involving the condensation of terephthalaldehyde with resorcinol under alkaline conditions. The terephthalaldehyde, which is a non-hazardous aromatic dialdehyde, was used as an alternative to formaldehyde that is toxic and traditionally involved to prepare phenolic ion-exchange resins. The resulting formaldehyde-free resole-type phenolic resins were characterized and their ion-exchange capacity was investigated in regard to the extraction of rare-earth elements. We herein present a promising formaldehyde and phenol-free as a potential candidate for solid-liquid extraction REE with a capacity higher than 50 mg/g and the possibility to back-extract the REEs by a striping step using a 2 M HNO 3 solution.