Recovery of Scandium(III) from Aqueous Solutions by Solvent Extraction with the Functionalized Ionic Liquid Betainium Bis(trifluoromethylsulfonyl)imide

The ionic liquid betainium bis­(trifluoromethylsulfonyl)­imide [Hbet]­[Tf₂N] was used for the extraction of scandium from aqueous solutions. The influence of several extraction parameters on the extraction efficiency was investigated, including the initial metal concentration, phase ratio, and pH. The extraction kinetics was examined, and a comparison was made between conventional liquid–liquid extraction and homogeneous liquid–liquid extraction (HLLE). The stoichiometry of the extracted scandium complex was determined with slope analysis. Scandium­(III) is extracted as a complex with zwitterionic betaine in a 1:3 stoichiometry, with three bis­(trifluoromethylsulfonyl)­imide counterions. Upon extraction of scandium­(III), proton exchange occurs and three protons are transferred to the aqueous phase. Scandium is an important minor element present in bauxite residue (red mud), the waste product that results from the industrial production of alumina by the Bayer process. To evaluate the suitability of [Hbet]­[Tf₂N] for the selective recovery of scandium­(III) from red mud leachates, the extraction of other metals present in the leachates (La­(III), Ce­(III), Nd­(III), Dy­(III), Y­(III), Fe­(III), Al­(III), Ti­(IV), Ca­(II), Na­(I)) was considered. It was shown that the trivalent lanthanide ions, yttrium­(III) and the major elements aluminum­(III), titanium­(IV), calcium­(II), and sodium­(I), are all poorly extracted, which is advantageous for the selective recovery of scandium­(III) from red mud. Iron­(III) showed an extraction behavior similar to that of scandium­(III). Scandium recovery was examined from a multielement rare-earth solution. Scandium could be separated from the other rare-earth elements by extraction with [Hbet]­[Tf₂N] and subsequent scrubbing of the loaded ionic liquid phase to remove coextracted metal ions. The extracted scandium was recovered from the ionic liquid phase by using back-extraction with hydrochloric acid or precipitation stripping with oxalic acid

Overview of the Effect of Salts on Biphasic Ionic Liquid/Water Solvent Extraction Systems: Anion Exchange, Mutual Solubility, and Thermomorphic Properties

Hydrophobic (water-immiscible) ionic liquids (ILs) are frequently used as organic phase in solvent extraction studies. These biphasic IL/water extraction systems often also contain metal salts or mineral acids, which can significantly affect the IL trough (un)­wanted anion exchange and changes in the solubility of IL in the aqueous phase. In the case of thermomorphic systems, variations in the cloud point temperature are also observed. All these effects have important repercussions on the choice of IL, suitable for a certain extraction system. In this paper, a complete overview of the implications of metal salts on biphasic IL/water systems is given. Using the Hofmeister series as a starting point, a range of intuitive prediction models are introduced, supported by experimental evidence for several hydrophobic ILs, relevant to solvent extraction. Particular emphasis is placed on the IL betainium bis­(trifluoromethylsulfonyl)­imide [Hbet]­[Tf₂N]. The aim of this work is to provide a comprehensive interpretation of the observed effects of metal salts, so that it can be used to predict the effect on any given biphasic IL/water system instead of relying on case-by-case reports. These prediction tools for the impact of metal salts can be useful to optimize IL synthesis procedures, extraction systems and thermomorphic properties. Some new insights are also provided for the rational design of ILs with UCST or LCST behavior based on the choice of IL anion

Solvent Extraction of Scandium(III) by an Aqueous Biphasic System with a Nonfluorinated Functionalized Ionic Liquid

The use of ionic liquids (ILs) as solvents for extraction of metals is a promising development in separation science and technology; yet, the viscosities of ionic liquids (ILs) can be so high that long reaction times are required to reach the equilibrium state. An aqueous biphasic system (ABS) consisting of the nonfluorinated carboxyl-functionalized phosphonium IL [P₄₄₄C₁COOH]Cl and a 16 wt % NaCl solution is described. The IL-rich phase of the aqueous biphasic system has a very low viscosity, in comparison to the pure IL [P₄₄₄C₁COOH]­Cl. This system has excellent extraction properties for scandium. Different extraction parameters were investigated, including contact time and metal loading. The influence of the pH on the solubility of the IL cation in the water-rich phase was determined via quantitative ¹H NMR. The stripping of scandium with oxalic acid from the IL phase was also investigated. A plausible extraction mechanism is proposed where three IL cations are deprotonated to form zwitterionic compounds that can coordinate scandium­(III) ions

Multifunctional Alginate–Sulfonate–Silica Sphere-Shaped Adsorbent Particles for the Recovery of Indium(III) from Secondary Resources

A straightforward procedure was developed for the synthesis of surface-modified organic–inorganic hybrid adsorbent materials derived from alginate. Sphere-shaped particles were produced by gravitational droplet coagulation and chemically modified by soaking in a solution of the silica precursor tetramethyl orthosilicate (TMOS) and the functionalized organosilane (3-mercaptopropyl) trimethoxysilane (MPTMS). Upon oxidation of the thiol groups by hydrogen peroxide, sulfonic acid groups were obtained, homogeneously distributed over the hybrid polymer matrix. Three different particle sizes (2.2, 2.8, and 3.5 mm in diameter) were made to evaluate differences in material properties and the corresponding adsorption behavior. The alginate–sulfonate–silica (ASS) particles were characterized by Raman spectroscopy, optical microscopy, and scanning electron microscopy. The specific surface area, porosity, mechanical strength, and chemical composition were determined. Subsequently, the functionalized materials were examined for the recovery of indium from secondary resources. Adsorption of indium­(III) was first investigated in batch mode from single-element solutions to evaluate adsorption parameters such as kinetics and adsorption capacity and from a binary metal solution of gallium­(III) and indium­(III) and a simulated leachate of a zinc refinery residue to investigate the selectivity. The adsorbent particles showed a high adsorption capacity and selectivity for indium­(III). They showed hardly any affinity for the major elements in the leachate, such as cadmium­(II) and zinc­(II). By using the multifunctional spheres as the stationary phase in a gravitationally eluted chromatography column, it was shown that the valuable minor elements, indium­(III) and gallium­(III), could be separated from the major elements present in the feed solution

Homogeneous Liquid–Liquid Extraction of Metal Ions with a Functionalized Ionic Liquid

Binary mixtures of the ionic liquid betainium bis­(trifluoromethylsulfonyl)­imide and water show an upper critical solution temperature. This solvent system has been used to extract metal ions by phase-transition extraction, using zwitterionic betaine as extractant. The system is efficient for the extraction of trivalent rare-earth, indium and gallium ions. This new type of metal extraction system avoids problems associated with the use of viscous ionic liquids, namely, the difficulty of intense mixing of the aqueous and ionic liquid phases by stirring

Ethylenediaminetriacetic Acid-Functionalized Activated Carbon for the Adsorption of Rare Earths from Aqueous Solutions

A novel and low-cost ethylenediaminetriacetic acid-functionalized activated carbon (EDTA-AC) was synthesized by anchoring <i>N</i>-[(3-trimethoxysilyl)­propyl]­ethylenediaminetriacetic acid (TMS-EDTA) to oxidized activated carbon (AC). Material characterization was done by FTIR and Raman spectroscopy, TGA, N₂ physisorption, SEM and the Boehm titration method, the latter being used to determine the amount and type of oxygen functional groups present in carbon samples. EDTA-AC was tested for the adsorption and separation of rare-earth ions from aqueous solutions, in order to evaluate the feasibility of using this material for the recovery of rare earths from industrial wastewater, tailings and electronic waste, like batteries, magnets and lamp phosphors. The maximum adsorption capacity of EDTA-AC was derived for Nd­(III) by constructing an adsorption isotherm and fitting the data to the Langmuir adsorption model. A kinetic and thermodynamic study were performed by varying the contact time and the temperature and plotting the corresponding adsorption data to the pseudo-second-order kinetic model and the Van’t Hoff equation, respectively. The affinity of EDTA-AC for each of the lanthanide ions was determined and from binary mixtures of La/Ni, Sm/Co, Eu/Y and Dy/Nd, the highest selectivity was observed for the (heavy) rare earths. The adsorbed metal ions could be recovered and the adsorbent regenerated by treatment with a dilute solution of HCl, thus showing the (large-scale) potential of EDTA-functionalized AC for the recovery of rare earths from aqueous waste streams

Shaping of Alginate–Silica Hybrid Materials into Microspheres through Vibrating-Nozzle Technology and Their Use for the Recovery of Neodymium from Aqueous Solutions

The vibrating-nozzle technology is very interesting to very easily and very rapidly produce industrial amounts of functional microspheres. The technology was used to make hybrid alginate–silica microspheres by droplet coagulation. The microspheres were formed starting from suspensions of sodium alginate, and coagulation occurred in an aqueous solution of calcium ions. To enhance the mechanical properties of the alginate raw material, it was combined with two different silica sources: tetramethyl orthosilicate (TMOS) and commercial silica powder. The two different batches of alginate–silica microspheres were fully compared with regard to their morphology, composition, shrinking behavior, and stability in acidic conditions. It was shown that the incorporation of an inorganic matrix resulted in a material with a better stabilized porous structure and a higher resistance in an acidic environment. Both are important when functional particles are designed to be used for adsorption of metal ions, either as a stirred suspension or as a stationary phase in a chromatographic column. A study of the adsorption performance was conducted in batch mode for neodymium­(III), a representative element for the group of critical rare-earth elements. The effect of stripping (desorption) on the adsorption performance and reusability was also investigated. The functional alginate–silica microspheres show a sustainable character

Synthesis of Poly‑<i>p</i>‑phenylene Terephthalamide (PPTA) in Ionic Liquids

Several ionic liquids (ILs) were tested for their suitability to synthesize the aramid polymer poly-<i>p</i>-phenylene terephthalamide (PPTA) in an attempt to diminish the dependence on the toxic <i>N</i>-methylpyrrolidone (NMP) that is currently used in industry. The room-temperature IL 3-methyl-1-octylimidazolium chloride ([C₈MIM]­[Cl]) showed the highest promise as, with this medium, the polycondensation reaction proceeds with a mechanism similar to how it occurs in the solvent mixture of NMP with CaCl₂. With this IL, PPTA polymer with an inherent viscosity of 1.95 dL/g was obtained in a low-temperature polycondensation reaction. This is the highest reported molecular mass of PPTA to date that was obtained by polymerization in an ionic liquid. An extended X-ray absorption fine structure (EXAFS) and solid-state NMR spectroscopic study showed that [C₈MIM]­[Cl] and the current industrial solvent of NMP and CaCl₂ show similar characteristics when it comes to the synthesis of PPTA

Low-Temperature Oxidation of Fine UO₂ Powders: Thermochemistry and Kinetics

The thermochemical behavior of low-temperature oxidation in fine UO₂ powders has been investigated by simultaneous thermogravimetric analysis and differential scanning calorimetry. The evaluation of the thermochemical and kinetic data reveals a complex interplay between different mechanisms. The initial reaction concerns the rapid chemisorption of oxygen gas onto the surface of UO₂ grains, having an activation energy of only 13.1 ± 0.6 kJ mol^–1. The subsequent oxidation at temperatures between 40 and 100 °C occurs first at the surface via a field-assisted mechanism, which progresses via domain growth into the bulk. At more elevated temperatures, thermally activated diffusion becomes the dominant mechanism

Selective Uptake of Rare Earths from Aqueous Solutions by EDTA-Functionalized Magnetic and Nonmagnetic Nanoparticles

Magnetic (Fe₃O₄) and nonmagnetic (SiO₂ and TiO₂) nanoparticles were decorated on their surface with <i>N</i>-[(3-trimethoxysilyl)­propyl]­ethylenediamine triacetic acid (TMS-EDTA). The aim was to investigate the influence of the substrate on the behavior of these immobilized metal coordinating groups. The nanoparticles functionalized with TMS-EDTA were used for the adsorption and separation of trivalent rare-earth ions from aqueous solutions. The general adsorption capacity of the nanoparticles was very high (100 to 400 mg/g) due to their large surface area. The heavy rare-earth ions are known to have a higher affinity for the coordinating groups than the light rare-earth ions but an additional difference in selectivity was observed between the different nanoparticles. The separation of pairs of rare-earth ions was found to be dependent on the substrate, namely the density of EDTA groups on the surface. The observation that sterical hindrance (or crowding) of immobilized ligands influences the selectivity could provide a new tool for the fine-tuning of the coordination ability of traditional chelating ligands