Direct analysis of metal ions in solutions with high salt concentrations by total reflection x-ray fluorescence

Total reflection X-ray fluorescence (TXRF) is becoming more and more popular for elemental analysis in academia and industry. However, simplification of the procedures for analyzing samples with complex compositions and residual matrix effects is still needed. In this work, the effect of an inorganic (CaCl2) and an organic (tetraalkylphosphonium chloride) matrix on metals quantification by TXRF was investigated for liquid samples. The samples were spiked with up to 20 metals at concentrations ranging from 3 to 50 mg L^–1 per element, including elements with spectral peaks near the peaks of the matrix elements or near the Raleigh and Compton scattering peaks of the X-ray source (molybdenum anode). The recovery rate (RR) and the relative standard deviation (RSD) were calculated to express the accuracy and the precision of the measured element concentrations. In samples with no matrix effects, good RRs are obtained regardless of the internal standard selected. However, in samples with moderate matrix content, the use of an optimum internal standard (OIS) at a concentration close to that of the analyte significantly improved the quantitative analysis. In samples with high concentrations of inorganic ions, using a Triton X-100 aqueous solution to dilute the sample during the internal standardization resulted in better RRs and lower RSDs compared to using only water. In samples with a high concentration of organic material, pure ethanol gave slightly better results than when a Triton X-100–ethanol solution was used for dilution. Compared to previous methods reported in the literature, the new sample-preparation method gave better accuracy, precision, and sensitivity for the elements tested. Sample dilution with an OIS and the surfactant Triton X-100 (inorganic media) or ethanol (organic media) is recommended for fast routine elemental determination in matrix containing samples, as it does not require special equipment, experimentally derived case-dependent mathematical corrections, or physicochemical removal of interfering elements

Recovery of scandium( iii ) from diluted aqueous solutions by a supported ionic liquid phase (SILP)

The adsorption of scandium from diluted, acidic solutions by a supported ionic liquid phase (SILP) was investigated, as part of a process for recovery of scandium from bauxite residue (red mud). Both dry impregnation and covalent linking were studied for the SILP preparation. The SILP betainium sulfonyl(trifluoromethanesulfonylimide) poly(styrene-co-divinylbenzene) [Hbet–STFSI–PS–DVB] was prepared by covalent linking of the ionic liquid to the resin and this resulted in an adsorbent suitable for scandium recovery. For a chloride feed solution, the effects of pH, contact time, adsorption capacity, desorption, reusability of adsorbent and the influence of Fe(III), Al(III) and Ca(II) on the Sc(III) adsorption were studied. The adsorption of Sc(III) from nitrate and sulfate feed solution under optimal conditions was studied as well. The adsorption kinetics followed a pseudo-second order kinetic model. Equilibrium studies at room temperature showed that the experimental data could be well fitted by the Langmuir isotherm model. The stripping of Sc(III) from the loaded SILP was achieved with 1 M sulfuric acid. The SILP was stable and could be reused for seven adsorption/desorption cycles without significant losses in its adsorption efficiency for Sc(III)

Selective recovery of indium from iron-rich solutions using an Aliquat 336 iodide supported ionic liquid phase (SILP)

Selective recovery of valuable metals from secondary (waste) sources is essential for better resource efficiency. However, low-grade waste streams typically have complex and variable compositions and low concentrations of valuable metals. Therefore, development of novel technologies, able to deal with these complex and variable waste streams, is necessary. In this work, we present a process for the separation and purification of indium from iron-rich matrix solutions making use of a supported ionic liquid phase (SILP). The SILP used in this study was synthesized by impregnating AmberliteXAD–16N with the iodide form of the quaternary ammonium salt Aliquat336. The SILP was characterized by infrared spectroscopy, elemental analysis, density, specific surface area and porosity and it was tested for the selective recovery of indium. Adsorption was preceded by the addition of an excess of iodide anions to the solution, to form indium iodide species, which were extracted to the ionic liquid of the SILP. A high selectivity for indium over iron could be achieved because iron iodide species are not stable in aqueous medium. The reaction kinetics and several adsorption parameters, including anion concentration, adsorbent mass, stripping and reusability of the adsorbent were investigated, using synthetic binary iron-indium solutions containing iron in large excess in comparison with indium, as is typically the case in low-grade ores or industrial process residues. Finally, the developed indium recovery process was validated on a real leachate of goethite residue. A pure indium solution of 49mg·L–1 was obtained with an indium-over-iron mass ratio of 7.9 and a selectivity factor equal to 5400

Separation of rare earths and other valuable metals from deep-eutectic solvents: a new alternative for the recycling of used NdFeB magnets

Deep-eutectic solvents (DESs) are used as a promising alternative to aqueous solutions for the recovery of valuable metals from NdFeB magnets. A deep-eutectic solvent based on choline chloride and lactic acid (molar ratio 1 : 2) was used for the leaching of rare earths and other metals from NdFeB magnets. A process for the separation of Fe, B and Co from Nd and Dy in the deep-eutectic solvent was developed by using the ionic liquid tricaprylmethylammonium thiocyanate (Aliquat 336 SCN, [A336][SCN]) diluted in toluene (0.9 M). The extraction parameters were optimized and stripping of B was efficiently carried out by HCl, while EDTA was employed for the recovery of Fe and Co. The separation of Nd and Dy was assessed by using two different types of extractants, a mixture of trialkylphosphine oxides (Cyanex 923) and bis(2-ethylhexyl) phosphoric acid (D2EHPA). Based on the distribution ratios, separation factors and the ease of subsequent stripping, Cyanex 923 was chosen as the most effective extractant. The purified Dy present in the less polar phase was easily recovered by stripping with water, while the Nd present in the deep-eutectic solvent was recovered by precipitation stripping with a stoichiometric amount of oxalic acid. Nd2O3 and Dy2O3 were recovered with a purity of 99.87% and 99.94%, respectively. The feasibility to scale up this separation process was corroborated by a setup of mixer-settlers and highlighted by the possibility to fully recover and reuse the deep-eutectic solvent and the less polar phases employed in the extractions. The new proposed system based on a deep-eutectic solvent combined with traditional organic extraction phases presented higher selectivities and efficiencies than the analogous aqueous system. Extended X-ray absorption fine structure (EXAFS) was employed to elucidate the different mechanisms for extraction of Co and Fe from the deep-eutectic solvent and from an aqueous solution

Split-anion solvent extraction of light rare earths from concentrated chloride aqueous solutions to nitrate organic ionic liquids

Despite its benefits, the extraction of rare earths (REEs) from chloride solutions with neutral or basic extractants is not efficient, so that separation is currently carried out by using acidic extractants. This work aims to improve this process by replacing the conventional molecular diluents in the organic phase by ionic liquids (ILs) which contain coordinating anions. The extraction of La(III), Ce(III) and Pr(III) from concentrated chloride solutions was tested with a quaternary ammonium and a phosphonium nitrate IL extractant. Dissolution of a trialkylphosphine oxide neutral extractant (Cyanex 923) in the nitrate ILs changed the preference of the organic phase from lighter to heavier REE and increased the overall extraction efficiency and the loading capacity of the organic phase. An increase of the CaCl2 concentration in the feed solution resulted in higher extraction efficiencies, due to a lower activity of water and hence to a poorer hydration of the REE ions. In that respect, chloride ions were not coordinating to the REE ion after extraction from concentrated chloride solutions. To achieve selectivity, one should fine-tune the loading by varying the CaCl2 and/or Cyanex 923 concentrations. Adjustment of the CaCl2 concentration in the feed and stripping solutions is essential for the separation of mixtures of REE. However, and unlike in the case of acidic extractants, no control of equilibrium pH is required. The split-anion extraction offers the possibility to separate mixtures of REEs in different groups without having to change the chloride feed solution. It leads to safer and environmentally friendlier extraction processes by (1) using solvents that are not volatile, not flammable and do no accumulate static electricity, (2) consuming no acids or alkali, (3) easy stripping with water and (4) avoidance to create nitrate-containing effluents

Structural and Luminescence Properties of Silica-Based Hybrids Containing New Silylated-Diketonato Europium(III) Complex

A new betadiketonate ligand displaying a trimethoxysilyl group as grafting function and a diketone moiety as complexing site (TTA-Si = 4,4,4-trifluoro-2-(3-trimethoxysilyl)propyl)-1-3-butanedione (C4H3S)COCH[(CH2)3Si(OCH3)3]COCF3) and its highly luminescent europium(III) complex [Eu(TTA-Si)3] have been synthesized and fully characterized. Luminescent silica-based hybrids have been prepared as well with this new complex grafted on the surface of dense silica nanoparticles (28 (+/-3 nm) or on mesoporous silica particles. The covalent bonding of Eu(TTA-Si)3 inside the core of uniform silica nanoparticles (40 (+/- 5 nm) was also achieved. Luminescence properties are discussed in relation to the europium chemical environment involved in each of the three hybrids. The general methodology proposed allowed high grafting ratios and overcame chelate release and tendency to agglomeration, and it could be applied to any silica matrix (in the core or at the surface, nanosized or not, dense or mesoporous) and therefore numerous applications such as luminescent markers and luminophors could be foreseen

Luminescence tuning of MOFs via ligand to metal and metal to metal energy transfer by co-doping of 2∞[Gd2Cl6(bipy)3]*2bipy with europium and terbium

The series of anhydrous lanthanide chlorides LnCl3, Ln=Pr–Tb, and 4,4'-bipyridine (bipy) constitute isotypic MOFs of the formula 2∞[Ln2Cl6(bipy)3]*2bipy. The europium and terbium containing compounds both exhibit luminescence of the referring trivalent lanthanide ions, giving a red luminescence for Eu3+ and a green luminescence for Tb3+ triggered by an efficient antenna effect of the 4,4'-bipyridine linkers. Mixing of different lanthanides in one MOF structure was undertaken to investigate the potential of this MOF system for colour tuning of the luminescence. Based on the gadolinium containing compound, co-doping with different amounts of europium and terbium proves successful and yields solid solutions of the formula 2∞[Gd2-x-yEuxTbyCl6(bipy)3]*2bipy (1–8), 0≤x, y≤0.5. The series of MOFs exhibits the opportunity of tuning the emission colour in-between green and red. Depending on the atomic ratio Gd:Eu:Tb, the yellow region was covered for the first time for an oxygen/carboxylate-free MOF system. In addition to a ligand to metal energy transfer (LMET) from the lowest ligand-centered triplet state of 4,4'-bipyridine, a metal to metal energy transfer (MMET) between 4f-levels from Tb3+ to Eu3+ is as well vital for the emission colour. However, no involvement of Gd3+ in energy transfers is observed rendering it a suitable host lattice ion and connectivity centre for diluting the other two rare earth ions in the solid state. The materials retain their luminescence during activation of the MOFs for microporosity

Highly Luminescent Salts Containing Well-Shielded Lanthanide-Centered Complex Anions and Bulky Imidazolium Countercations

In this paper, we report on the syntheses, structures, and characterization of four molten salts containing imidazolium cations and europium(III)- or terbium(III)-centered complex anions. In the complex anions, the lanthanide centers are wrapped by four pseudodiketonate anionic ligands, which prevent them from contacting with high-frequency oscillators and allow them to show intense characteristic europium(III) or terbium(III) emission, small line widths, high color purity, high quantum yields (30−49%), and long decay times (\u3e2 ms)

Rare-earth-containing magnetic liquid crystals

Rare-earth-containing metallomesogens with 4-alkoxy-N-alkyl-2- hydroxybenzaldimine ligands are reported. The stoichiometry of the complexes is [Ln(LH)3(NO3)3], where Ln is the trivalent rare-earth ion (Y, La, and Pr to Lu, except Pm) and LH is the Schiff base. The Schiff base ligands are in the zwitterionic form and coordinate through the phenolic oxygen only. The three nitrate groups coordinate in a bidentate fashion. The X-ray single- crystal structures of the nonmesogenic homologous complexes [Ln(LH)3(NO3)3], where Ln = Nd(III), Tb(III), and Dy(III) and LH = CH3OC6H3(2-OH)CH=NC4H9, are described. Although the Schiff base ligands do not exhibit a mesophase, the metal complexes do (SmA phase). The mesogenic rare-earth complexes were studied by NMR, IR, EPR, magnetic susceptibility measurements, X-ray diffraction, and molecular modeling. The metal complexes in the mesophase have a very large magnetic anisotropy, so that these magnetic liquid crystals can easily be aligned by an external magnetic field