Metal Recovery from Spent Samarium-Cobalt Magnets Using a Trichloride Ionic Liquid

Closed-loop process for selective leaching and recovery of palladium from spent auto-exhaust catalysts using iodotrihalide ionic liquids

The recovery of palladium from spent auto-exhaust catalysts (SAE-catalysts) is of great significance for resource sustainability. Herein, we proposed an efficient closed-loop leaching and recovery method for palladium from SAE-catalysts using iodotrihalide ionic liquids (ILs). Recovery design was explored aimed at green leaching and process simplification. Iodotrihalide ILs exhibited exceptional performance in terms of leaching efficiency (99.1%), selectivity (selectivity > 6.8 ×103) and reusability (over 6 cycles). The mechanism study revealed that excellent leaching performance was attributed to the redox and complexation. Additionally, the chemical reaction-controlled model was best suited to describe the leaching process. Notably, under the optimal conditions determined by the response surface methodology, a high-purity Pd(II) solution (purity > 99.8%) was obtained. More significantly, it was ideal for practical applications due to the low-viscosity (36.0 cP), mild (55 °C) and one-step leaching and recovery. In conclusion, this work provides an eco-friendly method for recovering palladium from SAE-catalysts with its non-high corrosiveness and low environmental impact.

Hydrocarbon Extraction with Ionic Liquids

Separation and reaction processes are key components employed in the modern chemical industry, and the former accounts for the majority of the energy consumption therein. In particular, hydrocarbon separation and purification processes, such as aromatics extraction, desulfurization, and denitrification, are challenging in petroleum refinement, an industrial cornerstone that provides raw materials for products used in human activities. The major technical shortcomings in solvent extraction are volatile solvent loss, product entrainment leading to secondary pollution, low separation efficiency, and high regeneration energy consumption due to the use of traditional organic solvents with high boiling points as extraction agents. Ionic liquids (ILs), a class of designable functional solvents or materials, have been widely used in chemical separation processes to replace conventional organic solvents after nearly 30 years of rapid development. Herein, we provide a systematic and comprehensive review of the state-of-the-art progress in ILs in the field of extractive hydrocarbon separation (i.e., aromatics extraction, desulfurization, and denitrification) including (i) molecular thermodynamic models of IL systems that enable rapid large-scale screening of IL candidates and phase equilibrium prediction of extraction processes; (ii) structure-property relationships between anionic and cationic structures of ILs and their separation performance (i.e., selectivity and distribution coefficients); (iii) IL-related extractive separation mechanisms (e.g., the magnitude, strength, and sites of intermolecular interactions depending on the separation system and IL structure); and (iv) process simulation and design of IL-related extraction at the industrial scale based on validated thermodynamic models. In short, this Review provides an easy-to-read exhaustive reference on IL-related extractive separation of hydrocarbon mixtures from the multiscale perspective of molecules, thermodynamics, and processes. It also extends to progress in IL analogs, deep eutectic solvents (DESs) in this research area, and discusses the current challenges faced by ILs in related separation fields as well as future directions and opportunities.

Noble Metals Dissolution Catalyzed by [AlCl4 -]-Based Ionic Liquids

Imidazolium-based ionic liquid mixtures with [NO₃]^- and [AlCl₄]^- anions were used as oxidizing agents for the dissolution of Au, Pd, and Pt metals under mild conditions. The thermodynamic reduction of [NO₃]^- to [NO] is catalyzed by [AlCl₄]^- anions and coupled with the oxidation process of noble metals. The developed ionic liquid system for dissolving Au can reactivate the Au⁰ formed in the deactivation process of the catalyst in vinyl chloride production. This demonstrates the relevance of the here-presented work for technical noble metal recycling.

Recovery of Rare Earth Elements from NdFeB Magnets by Chlorination and Distillation

A sustainable separation concept for large-scale recycling of NdFeB magnets under atmospheric pressure was developed by utilizing a combination of two separation concepts known from the literature: (I) selective pre-separation by in situ chlorination and evaporation of ground oxidized NdFeB material and (II) subsequent distillation for high-purity recovery of all recyclable chlorinated material components, especially its Rare Earth Elements (REEs). Theoretically, simplified estimations of the time conversion curves at 1173 K, 1273 K, and 2000 K of a single particle resulted in the idea of realizing chlorination in some kind of combustion chamber, fluidized bed, or continuous combustion chamber. After chlorination, all non-volatile components, such as REE chlorides, are condensed out of the vapor phase in a single-stage phase separator. For subsequent fine separation by distillation (1292–1982 K for Rare Earth Chlorides and 418–867 K at 2500 kPa for boron and zirconium chloride recovery), simplified simulations were performed in a total-reflux column under ideal phase equilibrium conditions to show the estimated minimum separation effort. Using two composition examples from the literature, high-purity separation of the major Rare Earth Chlorides within a twelve-stage distillation column as a residual heavy boiling product has been demonstrated to be potentially technically feasible.

Sorption Preconcentration and Analytical Determination of Cu, Zr and Hf in Waste Samarium–Cobalt Magnet Samples

We developed a method of sorption determination via the atomic emission of Cu, Zr and Hf metals in the waste of samarium–cobalt magnets. This method was based on the preconcentration of impurities using S- and N-containing heterochain sorbents, with further determination of the analytes via inductively coupled plasma atomic emission spectrometry (ICP-OES). Different sorbents such as PED (polyethelendiamine), TDA (polythiodimethanamine), PhED (N-phenylpolyethediamine) and PTE (polythioether) were tested for Ti, Cu, Zr, Nb and Hf extraction. The PTE sorbent ensured the maximum extraction of the analytes (recovery 60% for Ti, 80% for Nb, 95–100% for Cu, Zr and Hf) and thus was selected for further research. Additionally, various acidities of chloride solution (0.01–1 M HCl) were investigated for metal sorption. Under the optimised sorption conditions, trace impurities of Cu, Zr and Hf were determined using ICP-OES with a relative standard deviation of less than 5%. The obtained results were confirmed by the added–found method and cross-method experiments. The detection limits (DLs) were 1.5, 2, 0.15, 2 and 0.75 µg/L for Ti, Cu, Zr, Nb and Hf, respectively. The proposed method can be successfully used for the determination of various microelements in other waste REE-magnetic materials.

Microwave Digestion and ICP-MS Determination of Major and Trace Elements in Waste Sm-Co Magnets

In this article, inductively coupled plasma mass-spectrometry (ICP-MS) and inductively coupled plasma optical-emission spectrometry (ICP-OES) were used for the development of an analytical procedure for analysis of the waste of Sm-Co magnets. Experimental parameters related to microwave digestion processes and acid concentrations were optimized. Microwave digestion was carried out in mixtures of HF, HCl, HNO3 and H2SO4. The complete dissolution of the samples occurred in the system: 10 mL H2O, 2 mL HNO3, 10 mL HCl and 1 mL H2SO4. The dependence of the matrix effect on the ICP-MS analysis of waste Sm-Co magnets was studied and optimal instrumental parameters were investigated (nebulizer gas flow, sampling depth and potential at the extractor lens). The optimal conditions were a nebulizer gas flow of 0.85–0.90 L/min, a sampling depth of 101, potential at the extractor lens of −400 V and a sample flow rate of 50 rpm. A recovery test and inter-method experiments were performed to verify the accuracy of the proposed method.

Solvent-driven fractional crystallization for atom-efficient separation of metal salts from permanent magnet leachates

This work reports a dimethyl ether-driven fractional crystallization process for separating rare earth elements and transition metals. The process has been successfully applied in the treatment of rare earth element-bearing permanent magnet leachates as an atom-efficient, reagent-free separation method. Using ~5 bar pressure, the solvent was dissolved into the aqueous system to displace the contained metal salts as solid precipitates. Treatments at distinct temperatures ranging from 20–31 °C enable crystallization of either lanthanide-rich or transition metal-rich products, with single-stage solute recovery of up to 95.9% and a separation factor as high as 704. Separation factors increase with solution purity, suggesting feasibility for eco-friendly solution treatments in series and parallel to purify aqueous material streams. Staged treatments are demonstrated as capable of further improving the separation factor and purity of crystallized products. Upon completion of a crystallization, the solvent can be recovered with high efficiency at ambient pressure. This separation process involves low energy and reagent requirements and does not contribute to waste generation.

Rare earth elements are essential to electrified infrastructure and clean energy production. Here, authors show reagent- and energy-efficient separation of lanthanides from secondary feedstock using dimethyl ether-driven fractional crystallization.

Hard-Soft Interactions in Solvent Extraction with Basic Extractants: Comparing Zinc and Cadmium Halides

Solvent extraction is often applied to separate and purify metals on an industrial scale. Nevertheless, solvent extraction processes are challenging to develop because of the complex chemistry involved. For basic extractants, much of the chemical behavior remains poorly understood due to the conditions far from thermodynamic ideality. To elucidate the extraction mechanism, we studied the speciation and extraction of zinc(II) and cadmium(II) from chloride, bromide, and iodide media by using a basic extractant consisting of a trioctylmethylammonium cation and, respectively, a chloride, bromide, or iodide anion. These systems were specifically selected to increase the understanding of the less-studied bromide and iodide media and to focus on the effect of hard-soft interactions on solvent extraction systems. It was observed that, in general, a metal is more efficiently extracted when its hydration in the aqueous phase is lower and its stabilization in the organic phase is higher. In the investigated systems, these conditions are obtained by forming metal complexes with a lower charge density by coordinating the right number of halide anions and by selecting a halide with a lower charge density. In the organic phase, the stability of the metal complex can be increased by forming strong metal-anion bonds and by decreasing the water content. These insights might be of interest in the development and optimization of separation schemes for metals.

Synthesis, Crystallization, and Electrochemical Characterization of Room Temperature Ionic Liquid Bromidostannates(II/IV)

Ionic liquids (IL) are valuable in a variety of applications due to their high electrochemical stability and physical properties. Using the cation 1-methyl-3-octylimidazolium, [OMIM]⁺, the bromidostannate RTIL [OMIM][Sn^+IIBr₃], "undercooled melt" [OMIM][Sn^+IVBr₅], and IL [OMIM]₂[Sn^+IVBr₆] were synthesized. The uncommon solid state structure of [SnBr₅]^- was elucidated in the form of its RTIL salt. Additionally, the IL based on tribromine-monoanion [OMIM][Br₃] was used to dissolve metallic Sn, selectively resulting in the formation of [SnBr₃]^- as confirmed by Raman spectroscopy. Subsequent cyclic voltammograms (CV) of [SnBr₃]^- confirmed the deposition potential of metallic Sn and renewal of the polybromide [Br₃]^-. The RTIL bromidostannates were stable compounds, making a selective electrochemical investigation of the deposition of metallic Sn(0) to Sn(+II)/Sn(+IV) redox process possible, via conductance and CV measurements. The CVs of the RTILs and of solutions in propylene carbonate had the redox couples of Sn(0)/[Sn^+IIBr₃]^-/[Sn^+IVBr₅]^-.

Oxidative Dissolution of Metals in Organic Solvents

Dissolution of metals in organic solvents is relevant to various application fields, such as metal extraction from ores or secondary resources, surface etching or polishing of metals, direct synthesis of organometallic compounds, and separation of metals from other compounds. Organic solvents for dissolution of metals can offer a solution when aqueous systems fail, such as separation of metals from metal oxides, because both the metal and metal oxide could codissolve in aqueous acidic solutions. This review critically discusses organic media (conventional molecular organic solvents, ionic liquids, deep-eutectic solvents and supercritical carbon dioxide) for oxidative dissolution of metals in different application areas. The reaction mechanisms of dissolution processes are discussed for various lixiviant systems which generally consist of oxidizing agents, chelating agents, and solvents. Different oxidizing agents for dissolution of metals are reviewed such as halogens, halogenated organics, donor-acceptor electron-transfer systems, polyhalide ionic liquids, and others. Both chemical and electrochemical processes are included. The review can guide researchers to develop more efficient, economic, and environmentally friendly processes for dissolution of metals in their elemental state.

Dissolution behavior of precious metals and selective palladium leaching from spent automotive catalysts by trihalide ionic liquids

The dissolution behavior of the precious metals gold, platinum, rhodium and palladium in the trihexyl(tetradecyl)phosphonium trihalide ionic liquids [P66614][Cl3], [P66614][Br3], [P66614][IBr2] and [P66614][I3] was investigated. The highest dissolution rates were observed for the trichloride ionic liquid [P66614][Cl3] and this system was investigated in more detail. The effects of the trichloride concentration in the ionic liquid and temperature were studied, reaching higher leaching rates at higher trichloride conversions and increased temperatures. The stability of the trichloride anion at these elevated temperatures was studied by Raman spectroscopy. It was found that the trichloride anion decomposed during leaching at higher temperatures, showing the requirement to store these reactive compounds in sealed and cool environments, shielded from light. The optimal leaching conditions were applied for the recovery of palladium from ceramic monolith powder, obtained from end-of-life automotive catalysts. The catalyst powder was contacted with the ionic liquid [P66614][Cl3] and the metal concentrations in the ionic liquid were monitored. The trihalide ionic liquid allowed a more selective leaching of palladium compared to other metals present at very high concentrations in the monolith structure, like magnesium. The relative ratio of palladium over magnesium increased by two orders of magnitude compared to the original catalyst composition. The effect of the contact time between the catalyst powder and the ionic liquid on the metal concentrations in the leachate was investigated, but no significant improvement in the selectivity was observed.

Chromatographic separation of rare earths from aqueous and ethanolic leachates of NdFeB and SmCo magnets by a supported ionic liquid phase

The separation of rare-earth elements (REEs) from other components of end-of-life NdFeB and SmCo magnets was investigated by column chromatography. A carboxylic-acid functionalized supported ionic liquid phase (SILP) was studied as a stationary phase. The magnets were firstly leached with a dilute aqueous or ethanolic hydrochloric acid solution at room temperature. Leaching of REEs from a NdFeB magnet was similarly efficient with both lixiviants, but the REEs were more efficiently leached from a SmCo magnet with the ethanolic lixiviant. The SILP exhibited a high affinity towards trivalent cations of REEs, which were successfully recovered from the aqueous and ethanolic leachates of magnets. Divalent cations of iron and cobalt, which were the major components of the acidic aqueous leachates of magnets, were rejected by the SILP. Iron and cobalt were present as negatively charged chloro complexes in the ethanolic leachates of magnets, and were not recovered by the cation-exchanging SILP. A versatile column chromatography method is developed, suitable for the separation of REEs from iron and cobalt, either from aqueous or ethanolic leachates of permanent magnets.

Conductivity and Redox Potentials of Ionic Liquid Trihalogen Monoanions [X3 ]- , [XY2 ]- , and [BrF4 ]- (X=Cl, Br, I and Y=Cl, Br)

The ionic liquid (IL) trihalogen monoanions [N2221 ][X3 ]- and [N2221 ][XY2 ]- ([N2221 ]+ =triethylmethylammonium, X=Cl, Br, I, Y=Cl, Br) were investigated electrochemically via temperature dependent conductance and cyclic voltammetry (CV) measurements. The polyhalogen monoanions were measured both as neat salts and as double salts in 1-butyl-1-methyl-pyrrolidinium trifluoromethane-sulfonate ([BMP][OTf], [X3 ]- /[XY2 ]- 0.5 M). Lighter IL trihalogen monoanions displayed higher conductivities than their heavier homologues, with [Cl3 ]- being 1.1 and 3.7 times greater than [Br3 ]- and [I3 ]- , respectively. The addition of [BMP][OTf] reduced the conductivity significantly. Within the group of polyhalogen monoanions, the oxidation potential develops in the series [Cl3 ]- >[BrCl2 ]- >[Br3 ]- >[IBr2 ]- >[ICl2 ]- >[I3 ]- . The redox potential of the interhalogen monoanions was found to be primarily determined by the central halogen, I in [ICl2 ]- and [IBr2 ]- , and Br in [BrCl2 ]- . Additionally, tetrafluorobromate(III) ([N2221 ]+ [BrF4 ]- ) was analyzed via CV in MeCN at 0 °C, yielding a single reversible redox process ([BrF2 ]- /[BrF4 ]- ).

Process Flowsheet Development for Separation of Sm, Co, Cu, and Fe from Magnet Scrap

A complete process flowsheet to recover metal values from Sm₂Co₁₇-type magnet scrap was investigated. The magnet scrap was leached in chloride medium at pulp density of 2% (w/v) under the optimum conditions of 15% (v/v) HCl and 5% (v/v) H₂O₂ at 70 °C for 3 h, which yielded 98.5% Sm and 99% Co extractions. The full factorial Design of Experiment technique was adopted for the optimization of leaching conditions. Sm was selectively separated from the leach liquor as precipitated double salt using Na₂SO₄. The precipitated double sulfate was later converted to Sm-oxalate, which was subsequently calcined to produce pure Sm₂O₃. Following Sm separation, Fe was removed through precipitation by raising the pH to 3.0. For Cu and Co recovery, solvent extraction techniques using LIX 84I and Na-CYANEX 272, respectively, were followed. The McCabe-Thiele diagrams for extraction as well as stripping were presented for both Cu and Co.

Electrodeposition of lanthanides from ionic liquids and deep eutectic solvents

Lanthanides belong to the most important raw materials and are highly demanded in high-tech industry. Low-temperature electrochemical deposition of lanthanides and lanthanide-based alloys for recycling and obtaining functional materials can provide a real alternative to the currently used high-temperature electrolysis of molten salts. The review summarizes the advancements in the field of electrodeposition of lanthanides from organic ionic systems, such as ionic liquids and deep eutectic solvents. The growing interest in these ionic systems is due to their excellent physicochemical properties, in particular non-volatility, thermal and electrochemical stability. The review also discusses further prospects and potential of the electrochemical approach for obtaining lanthanide-containing advanced materials.

The bibliography includes 219 references.

In Situ Synthesis and Applications for Polyinterhalides Based on BrCl

The use of neat BrCl in organic and inorganic chemistry is limited due to its gaseous aggregate state and especially its decomposition into Cl2 and Br2 . The stabilization of BrCl in form of reactive ionic liquids via a novel in situ synthesis route shifts this equilibrium drastically to the BrCl side, which leads to safer and easier-to-handle interhalogenation reagents. Furthermore, the crystalline derivatives of the hitherto unknown [Cl(BrCl)2 ]- and [Cl(BrCl)4 ]- anions were synthesized and characterized by single-crystal X-ray diffraction (XRD), Raman and IR spectroscopy, as well as quantum chemical calculations.

Construction of Ternary Iodine-Bromine-Chlorine Octahalides

A series of five ternary octanuclear iodine-bromine-chlorine interhalides, [I₂ Br₂ Cl₄ ]^2- (1), [I₃ BrCl₄ ]^2- (2), [I₄ Br₂ Cl₂ ]^2- (3), [I₂ Br₄ Cl₂ ]^2- (4) and [I₃ Br₃ Cl₂ ]^2- (5), have been rationally constructed in two steps. Firstly, addition of a dihalogen (ICl or IBr) to the triaminocyclopropenium chloride salt [C₃ (NEt₂ )₃ ]Cl forms the corresponding trihalide salt with [ICl₂ ]^- or [BrICl]^- anions, respectively. Secondly, addition of a half-equivalent of a second dihalogen, followed by crystallization at low temperature, gives the corresponding octahalide: addition of Br₂ and IBr to [ICl₂ ]^- gives 1 and 2, respectively, whereas addition of I₂ , Br₂ and IBr to [BrICl]^- gives 3, 4 and 5, respectively. The five octahalides were characterized by X-ray crystallography and far-IR spectroscopy.

From Polyhalides to Polypseudohalides: Chemistry Based on Cyanogen Bromide

Pseudohalogens are defined as molecular entities that resemble the halogens in their chemistry. While our understanding of polyhalogen chemistry has increased over the last years, research on polypseudohalogen compounds is lacking. The pseudohalogen BrCN possesses a highly pronounced σ-hole at the bromine side of the molecule, inducing strong halogen bonding. This allows the synthesis and characterization of new polypseudohalogen anions, as shown by the single-crystal X-ray diffraction of [PNP][Br(BrCN)] and [PNP][Br(BrCN)₃ ]. Both the nearly linear anion [Br(BrCN)]^- and the distorted pyramidal anion [Br(BrCN)₃ ]^- were characterized by Raman spectroscopy and quantum-chemical calculations. The behavior of the polypseudohalogen compounds in solution and as room-temperature ionic liquids (RT-ILs) using the [NBu₄ ]⁺ cation was studied by ¹³ C and ¹⁵ N NMR spectroscopy. These types of ILs are capable of dissolving elemental gold and offer themselves as promising compounds in metal recycling.

Ionic liquids with polychloride anions as effective oxidants for the dissolution of UO2

Polychloride ionic liquids can not only successfully dissolve UO₂, but also raise the chlorine efficiency.