The leaching of semiconductors (GaN, GaAs and InAs) and LEDs in a nonvolatile tribromide ionic liquid and the selective recovery of gallium, indium and arsenic from this ionic liquid was investigated. In order to prevent the formation of the highly toxic arsine (AsH 3 ), usually formed when leaching metal arsenides with acids, the hydrophobic trihalide ionic liquid tributyldecylphosphonium tribromide [P 44410 ][Br 3 ] was used to oxidatively leach the semiconductors, avoiding arsine formation. After leaching, a selective stripping procedure was applied to remove and recover the arsenic, gallium and indium. Arsenic and gallium could be stripped using NaBr solutions and pure water respectively, while indium was removed from the ionic liquid phase via precipitation stripping with a NaOH solution. A mechanistic study was performed to explain this difference in stripping behavior. A flowsheet was proposed and finally, the procedure was applied to real LEDs.

Within the framework of metal separations and solvent extraction, chloride media are among the most studied systems. Bromide and iodide media have received much less attention, but can allow a different selectivity during the extraction. In present research, the extraction behavior of several precious and base metal ions, i.e. Pt(IV), Pd(II), Rh(III), Au(III), Cu(II), Fe(III) and Ni(II), from the different halide media was explored using the undiluted ionic liquid Aliquat 336 chloride and its bromide and iodide analogues. A single-step separation of Pt(IV) and Pd(II) from Fe(III) and Ni(II) was possible in the iodide system, but it was found to be incompatible with Au(III) and Cu(II). The chloride and bromide media showed potential for the separation of Au(III), Pd(II), Fe(III) and Cu(II), and their performance was subsequently compared. Fe(III) and Cu(II) were easily separated from Au(III) and Pd(II) via an extraction at low acid concentration followed by scrubbing with water for both systems. However, the stripping showed superior characteristics for the bromide system, where Pd(II) could be recovered using a 0.2 mol L -1 ammonia solution and Au(III) using 1.0 mol L -1 sodium sulfite. The proposed method for the separation of Au(III), Pd(II), Fe(III) and Cu(II) can be relevant for the recycling of waste electric and electronic equipment or analytical applications. The results highlight the importance of considering halides other than chloride as both the extraction and stripping properties of the system can be changed.

The synthesis of ionic liquids (ILs) usually involves two steps: (i) quaternization of a precursor followed by (ii) a salt metathesis reaction to introduce the desired anion. A consequence of the second step is that most ILs still contain some amount of the initial anion, often chloride. In this work, wavelength dispersive X-ray fluorescence (WDXRF) spectrometry is presented for the direct measurement of chlorides in ILs. The WDXRF settings were optimized, and the system was calibrated for the detection of chloride in several analogues of the commercially available IL Aliquat 336, [A336]­[X] (with X = I–, Br–, NO3 –, or SCN–). The Cl Kα intensity showed excellent linearity for samples with a conversion >0.80 (approximately Cl < 8000 ppm). Synthetic quality control samples showed that the instrumental error and deviations induced by the calibration procedure were small with maximum values of 1 and 5%, respectively. Detection and quantification limits depended strongly on the matrix (i.e., anion system and dilution) but were relatively low: 42–191 and 127–578 ppm Cl, respectively. Compared with other analytical techniques used for this purpose, the strengths of WDXRF include its ease of use, rapid measurements, the near absence of sample preparation steps, and versatility in terms of anion systems and chloride concentration range.

Following the initial cation formation, the synthesis of ionic liquids (ILs) often involves an anion-exchange or metathesis reaction. For hydrophobic ILs, this is generally performed through several cross-current contacts of the IL with a fresh salt solution of the desired anion. However, if a large number of contacts is required to attain an adequate conversion, this procedure is not economical because of the large excess of the reagent that is consumed. In this study, the metathesis of an IL, Aliquat 336 or [A336][Cl], to ILs with other anions ([A336][X] with X = HSO 4 – , Br – , NO 3 – , I – , and SCN – ) was studied in a continuous counter-current mixer-settler setup. McCabe–Thiele diagrams were constructed to estimate the required number of stages for quantitative conversion. Significantly higher IL conversions were achieved, combined with reduced reagent consumption and waste production. This improvement in efficiency was most pronounced for anions placed low in the Hofmeister series, for example, HSO 4 – , Br – , and NO 3 – , which are difficult to exchange. The performance of the counter-current experiments was compared with the conventional multistep cross-current batch process by calculating the reaction mass efficiency (RME) and the environmental factor (E-factor). The RMEs of the cross-current experiments were notably smaller, that is, 38–78% of the values observed for the counter-current experiments. The E-factors of the counter-current experiments were a factor of 2.0–6.8 smaller than those of the cross-current experiments. These sustainability metrics indicate a highly efficient reagent use and a considerable, simultaneous decrease in waste production for the counter-current IL metathesis reactions.

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