Development course of separating rare earths with acid phosphorus extractants: A critical review

The highly selective green colorimetric detection of yttrium ions in biological and environmental samples using the synergistic effect in an optical sensor

A new eco-friendly method for creating an optical sensor membrane specifically designed to detect yttrium ions (Y3+) has been developed. The proposed sensor membrane is fabricated by integrating 4-(2-arsonophenylazo) salicylic acid (APASA), sodium tetraphenylborate (Na-TPB), and tri-n-octyl phosphine oxide (TOPO) into a plasticized poly(vinyl chloride) matrix with dimethyl sebacate (DMS) as the plasticizer. In this sensor membrane, APASA functions dually as an ionophore and a chromoionophore, while TOPO enhances the complexation of Y3+ ions with APASA. The composition of the sensor membrane has been meticulously optimized to achieve peak performance. The current membrane exhibits a linear dynamic range for Y3+ ions from 8.0 × 10-9 to 2.3 × 10-5 M, with detection and quantification limits of 2.3 × 10-9 and 7.7 × 10-9 M, respectively. No interference from other potentially interfering cations and anions was observed in the determination of Y3+. The membrane showed strong stability and a swift response time of about 3.0 minutes, with no signs of APASA leaching. This sensor is highly selective for Y3+ ions and can be renewed by treating it with 0.15 M HNO3. It has been effectively applied to measure Y3+ in nickel-based alloys, as well as in biological and environmental samples.

A sustainable strategy for targeted extraction of thorium from radioactive waste leachate based on hydrophobic deep eutectic solvent

In this work, the new hydrophobic deep eutectic solvents (HDESs) based on 2-hexyldecanoic acid (HDA) as a hydrogen bond donor (HBD) were used to selectively enrich trace Th from radioactive waste leach solution. These HDESs are characterized by low toxicity, bio-friendliness, low viscosity and sufficient hydrophobicity. Compared with Al, Mg, Ca and RE, HDESs exhibited exceptional selectivity for Th extraction, along with high loading capacity, easy stripping and stable reusability. The mechanism of Th extraction by the HDES is a cation exchange reaction. Based on the thymol (TL):HDA (1:3) HDES, a short flow closed-loop recovery process of Th in the leach solution of radioactive waste residue was developed. After a single-step extraction, the extraction percentage (E%) of Th exceeded 98.0%, while the E% of other elements was less than 0.14%. After stripping, the concentration of Th in the concentrated solution reached 2.16 × 103 mg/L with a purity of 74.2%, which could be directly used for subsequent purification. By adjusting the pH to 4.00, the raffinate was used as a feed solution for RE elements recovery. The HDES-based extraction strategy for Th is simple, safe, efficient and environmentally friendly, providing a new idea for the recovery of radioactive waste residues.

Highly efficient removal of rare earth elements by two-dimensional titanium carbide nanosheets as impacted via water chemistry

The separation and recycling of rare earth elements (REEs) are very important owing to the high demand, limited resource, specific usages, and environmental issues. In this work, two-dimensional Ti3C2Tx MXene was introduced to remove REEs (Nd(III) and La(III)) from water, and its physicochemical properties were conducted by HRTEM, SEM-EDS, XRD, FTIR, and XPS. Various parameters, such as initial pH, REEs initial concentration, contact time, and temperature, were investigated by batch experiment, respectively. Furthermore, the adsorption kinetic and isotherm were examined to analyze the adsorption behavior and adsorption mechanism. Nd(III) and La(III) have a good affinity with Ti3C2Tx MXene surface functional groups (-F, -OH, and containing oxygen groups). The maximum adsorption capacities of Ti3C2Tx MXene for Nd(III) and La(III) were 229.85 mg/g and 175.83 mg/g at T = 333 K, respectively. The adsorption data of Nd(III) on Ti3C2Tx MXene fitted well with the Freundlich isotherms model and pseudo-second-order kinetic model. However, the best fitting for La(III) adsorption on Ti3C2Tx MXene was described by both pseudo-first-order and pseudo-second-order model. Thermodynamic study of Nd(III) and La(III) adsorption on Ti3C2Tx MXene showed that the reaction was a spontaneous and endothermic process. These results indicated Ti3C2Tx MXene had a great potential in extracting REEs from an aqueous solution.

Spontaneous and Ion-Specific Formation of Inverted Bilayers at Air/Aqueous Interface

Developing better separation technologies for rare earth metals, an important aspect of a sustainable materials economy, is challenging due to their chemical similarities. Identifying molecular-scale interactions that amplify the subtle differences between the rare earths can be useful in developing new separation technologies. Here, we describe the ion-dependent monolayer to inverted bilayer transformation of extractant molecules at the air/aqueous interface. The inverted bilayers form with Lu³⁺ ions but not with Nd³⁺. By introducing Lu³⁺ ions to preformed monolayers, we extract kinetic parameters corresponding to the monolayer to inverted bilayer conversion. Temperature-dependent studies show Arrhenius behavior with an energy barrier of 40 kcal/mol. The kinetics of monolayer to inverted bilayer conversion is also affected by the character of the background anion, although anions are expected to be repelled from the interface. Our results show the outsized importance of ion-specific effects on interfacial structure and kinetics, pointing to their role in chemical separation methods.

Selective crystallization of dysprosium complex from neodymium/dysprosium mixture enabled by cooperation of coordination and crystallization

Designing a molecular-level Ln³⁺ separation system remains a challenge for developing next-generation separation methodologies. Herein, we report crystallization-based Nd³⁺/Dy³⁺ separation using a tripodal Schiff base ligand. Highly selective crystallization of the Dy³⁺ complex was enabled by cooperation between the coordination and crystallization processes.

Interaction-determined extraction capacity between rare earth ions and extractants: taking lanthanum and lutetium as models through theoretical calculations

Extractant plays an important role in the separation and purification of rare earth elements (REEs), whereas, extraction performance is the most effective tactic to evaluate whether an extractant is complete...

Study on Phenanthroline Carboxamide for Lanthanide Separation: Influence of Amide Substituents

Phenanthroline carboxamide compounds are promising for lanthanide intra-series separation. This paper presents a study on the effect of structure modification of phenanthroline carboxamides on the extraction of the whole lanthanide series. The study consists of theoretical calculations, extraction experiments of the 14 stable lanthanides, and extended X-ray absorption fine structure (EXAFS) analyses of Nd and Dy complexes. Tridentate monocarboxamides and tetradentate dicarboxamides show different trends in series extraction, although both preferentially extract the light lanthanides. The amide substituents, although not directly coordinating the metal ions, were also found to impact the distribution ratio, most probably due to a modification in the internal polarity of the molecules. This latter effect, if extrapolated to other nitrogen-based ligands such as pyridines or triazines, can be used to further fine-tune extractants for a process improvement.

Synthesis of Phosphonated Carbon Nanotubes: New Insight into Carbon Nanotubes Functionalization

Carbon nanotubes were successfully functionalized for the first time in a free radical phosphonylation reaction. Three synthetic protocols were proposed. Carbon nanotubes and diethylphosphite reacted in the presence of known radical initiator, such as azobisisobutyronitrile, single electron oxidant-Mn(OAc)3, or under UV radiation. The functionalized material was fully characterized by means of spectroscopic methods, together with microscopic, surface area and thermogravimetric analyses. UV-illumination was found to be the most effective approach for introducing phosphonates onto carbon nanotubes. X-ray photoelectron spectroscopy analysis showed 6% phosphorus in this sample. Moreover, the method was performed at room temperature for only one hour, using diethylphosphite as a reactant and as a solvent. The functionalized carbon nanotubes showed an improved thermal stability, with a decomposition onset temperature increase of more than 130 °C. This makes it very promising material for flame retarding applications.

Kinetics Study of Solvent and Solid-Phase Extraction of Rare Earth Metals with Di-2-Ethylhexylphosphoric Acid

The kinetic features of solvent and solid-phase extraction of yttrium and iron (III) from simulated and industrial phosphoric acid solutions are revealed. Di-2-ethylhexylphosphoric acid (D2EHPA) was used as a liquid extractant, and D2EHPA-containing Levextrel resin—a co-polymerization product of styrene and divinylbenzene in the presence of D2EHPA—was used as a solid-phase extraction agent. Significant dependence of yttrium extraction rate constant on the stirring rate was revealed using the formal first-order kinetic equation. The data obtained characterizes a diffusion-limited process with an activation energy of 16.2 ± 1.3 kJ/mol. Temperature increase during the iron (III) extraction process leads to a changeover of a rate-limiting stage from kinetic to diffusion, accompanied by drop of activation energy from 40.0 ± 1.4 to 11.4 ± 1.2 kJ/mol. Effective separation of elements at the extraction stage is possible at temperatures of 283–300 K under non-equilibrium conditions of the ferric ions transport from aqueous to organic phase. This condition ensures a high yttrium–iron separation coefficient of 23.2 in 1.5–2 min. Extraction kinetics by Levextrel resin are described by Fick’s second law equation, which establishes the laws of diffusion in the solid grain of the organic phase with an activation energy of 18.5 ± 2.0 kJ/mol.

Metal extraction from a deep eutectic solvent, an insight into activities

The solvent extraction of gold, palladium, technetium, indium and rhenium from both mixtures of a deep eutectic solvent with aqueous salt solutions and of two different aqueous salt solutions has been performed. Initially using gold and then the other metals the solvent extraction results were interpreted using an activity coefficient/function equation (specific ion interaction theory). The most important presented result is the addition of a new term to the specific ion interaction theory equation. Using the new model it will be possible to make predictions of the behaviour of a solvent extraction system where one of the liquid phases is a mixture of aqueous salts and the deep eutectic solvent.

Characterization of the ALSEP Process at Equilibrium: Speciation and Stoichiometry of the Extracted Complex

We have determined the identity of the complexes extracted into the ALSEP process solvent from solutions of nitric acid. The ALSEP process is a new solvent extraction separation designed to separate americium and curium from trivalent lanthanides in irradiated nuclear fuel. ALSEP employs a mixture of two extractants, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) and N,N,N',N'-tetra(2-ethylhexyl)diglycolamide (TEHDGA) in n-dodecane, which makes it difficult to ascertain the nature of the extracted metal complexes. It is often asserted that the weak acid extractant HEH[EHP] does not participate in the extracted complex under ALSEP extraction conditions (2-4 M HNO₃). However, the analysis of the Am extraction equilibria, Nd absorption spectra, and Eu fluorescence emission spectra of metal-loaded organic phases argues for the participation of HEH[EHP] in the extracted complex despite the high acidity of the aqueous phases. The extracted complex was determined to contain fully protonated molecules of HEH[EHP] with an overall stoichiometry of M(TEHDGA)₂(HEH[EHP])₂·3NO₃. Computations also demonstrate that replacing one TEHDGA molecule with one (HEH[EHP])₂ dimer is likely energetically favorable compared to Eu(TEHDGA)₃·3NO₃, whether the HEH[EHP] dimer is monodentate or bidentate.