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

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

Ionic Liquid Technology for the Separation of Rare Earths

Ionic liquids possess some interesting properties for solvent extraction experiments such as a negligible volatility, a low flammability and high structure tuneability. Moreover, their ionic structure and metal complex solvation power is totally different from apolar aliphatic or aromatic solvents. Even though ionic liquids are considered as safer and more environmentally friendly alternatives for traditional organic diluents, they have one main disadvantage which is their slower extraction kinetics due to the higher viscosity and mass transport of this kind of solvents. In the last years, the supply of rare earths and NdFeB magnets has been under a constant pressure due to a cheaper production process of China resulting in a quasi-monopoly and its strong export. Therefore, the recovery of rare-earths from end-of-life materials such as NdFeB magnets becomes strategically very interesting as it reduces the rare-earth supply dependency on China. In the first results part of this PhD dissertation, the basic extractant trihexyl(tetradecyl)phosphonium in combination with chloride and nitrate anions is used to separate some main transition metals from the rare earths present in NdFeB or SmCo magnets. The process is based on a salting-out procedure by using high concentrations of salt or acid in the aqueous phase. The most promising process was tested on a real NdFeB magnet, which was first roasted and leached selectivily to remove the iron. Than, the remaining transition metals were removed by solvent extraction with trihexyl(tetradecyl)phosphonium chloride in the presence of 3.5 M of NH4Cl in the aqueous phase. Afterwards, the rare earths were precipitated by the addition of oxalic acid and calcinated. In this way, a highly pure mixture of the rare-earth oxides was produced which can be used directly as starting material for the production of NdFeB magnets. The processes are operated in that way that they minimize the amount of waste streams and the amount of chemicals consumption. Moreover, the ionic liquid or even aqueous phases are reused to obtain a closed and environmentally friendly process. The second part of this PhD dissertation focuses on the use of the ionic liquid betainium bis(trifluoromethylsulfonyl)imide for the extraction of metals. An innovative process, increasing the reaction and extraction rate by reducing the ionic liquid phase viscosity during the extraction process, is worked out. In this method, called homogeneous liquid-liquid extraction, the aqueous/ionic liquid mixture is heated above its critical temperature, at which one homogeneous phase is formed. Afterwards, the mixture is cooled and two phases are reformed. In this way, mixing and reaction between the metal and the extractants occurs at molecular scale in the homogeneous state, whereas phase and metal separation can be achieved by cooling down and obtaining twonbsp; The ionic liquid betainium bis(trifluoromethylsulfonyl)imide, in combination with trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide and water was used as well for a triphasic extraction system. In this triphasic system, three different metals (Sc(III), Y(III) and Sn(II)) can be separated in one single step, a separation that cannot be achieved when working with the conventional two phases.nrpages: 182status: publishe

Ionic liquid technology for metal separation and NdFeB magnet recycling

The most often used ionic liquids for metal extraction and separation studies contain fluorinated anions such as [Tf2N] or [PF6]. These ionic liquids are chosen for solvent extraction systems because they are lowly viscous and hydrophobic. They have also several disavantages: fluorinated anions are expensive, toxic and they have a high persistency in nature. Anions such as [Tf2N] or [PF6] have weakly coordination abilities, so they have to be used as diluents for extractants. Dilution has the consequence that it is not possible to work with concentrated metals streams. In addition, ion exchange can occur in order to obtain change neutrality, in which the anion or cation are lost into the aqueous phase. Non-fluorinated hydrophobic ionic liquids containing cations such as tetraalkyl ammonium or tetraalkyl phosphonium can be used as well in solvent extraction systems. The anion of the ionic liquid can be chosen deliberatively and dilution is often not necessary. Moreover, they are cheaper and have a lower persistency. These ionic liquids are often not considered for metal extraction because they are highly viscous resulting in slow extraction kinetics and a larger energy inputs. However, one often forgets that the viscosity of an ionic liquid in a solvent extraction systems not only depends on its structure but also on the solubility of water in the ionic liquid. Therefore, the difference in viscosity compared to the traditional fluorinated ionic liquids can be surprisingly small. An overview of the work published on extraction of metal ions with non-fluorinated ionic liquids will be given in this presentation. A comparison between the fluorinated and non-fluorinated ionic liquids will be presented with special attention for toxicity, viscosity, coordinating ability and water solubility of the two types of ionic liquids. It will be shown that non-fluorinated ionic liquids can be interesting alternatives for fluorinated ionic liquids.Oral presentation given by Tom Vander Hoogerstraetestatus: publishe

Metal Quantifications by TXRF in Solution with Large Matrices

Oral presentation by Tom Vander Hoogerstraetestatus: publishe

Determination of halide impurities in ionic liquids by total reflection X-ray fluorescence (TXRF)

Poster presented by Tom Vander Hoogerstraetestatus: publishe

Homogeneous Liquid–Liquid Extraction of Rare Earths with the Betaine—Betainium Bis(trifluoromethylsulfonyl)imide Ionic Liquid System

Several fundamental extraction parameters such as the kinetics and loading were studied for a new type of metal solvent extraction system with ionic liquids. The binary mixture of the ionic liquid betainium bis(trifluoromethylsulfonyl)imide and water shows thermomorphic behavior with an upper critical solution temperature (UCST), which can be used to avoid the slower mass transfer due to the generally higher viscosity of ionic liquids. A less viscous homogeneous phase and mixing on a molecular scale are obtained when the mixture is heated up above 55 °C. The influence of the temperature, the heating and cooling times, were studied for the extraction of neodymium(III) with betaine. A plausible and equal extraction mechanism is proposed in bis(trifluoromethylsulfonyl)imide, nitrate, and chloride media. After stripping of the metals from the ionic liquid phase, a higher recovery of the ionic liquid was obtained by salting-out of the ionic liquid fraction lost by dissolution in the aqueous phase. The change of the upper critical solution temperature by the addition of HCl or betaine was investigated. In addition, the viscosity was measured below and above the UCST as a function of the temperature