Abstract
A supported ionic liquid phase (SILP) was developed to selectively recover germanium from iron-rich aqueous solutions. The SILP was synthesised by impregnating Amberlite XAD-16N with Aliquat 336, a mixture of quaternary ammonium salts. Characterisation was performed using elemental analysis, infrared spectroscopy, specific surface area, porosity and density measurements. Adsorption was preceded by the addition of citrate anions to the iron-rich aqueous solutions, to form germanium(IV) citrate complexes, which were extracted to the ionic liquid layer of the SILP. The reaction kinetics and several adsorption parameters, including pH, anion concentration and adsorbent mass, were investigated using synthetic single-element germanium solutions. The coordination of germanium(IV) to the citrate ligands was elucidated using Extended X-ray Absorption Fine Structure (EXAFS). Subsequently, the optimal adsorption parameters were tested on a multi-element solution with elemental concentrations resembling those of a leachate of goethite residue from the zinc industry. A high selectivity for germanium over iron could be achieved. Finally, the stripping and the reusability of the SILP were studied. A germanium solution of 44 mg·L−1 was obtained with a germanium-over-iron mass ratio of 39. This corresponds to a selectivity factor equal to 34 400, demonstrating the high potential of the reported process.
Highlights
One of the key factors of resource efficiency is to treat ‘waste’ as a source of raw materials [1]
As a consequence of the viscous or water-soluble organic phase, issues may arise from poor phase separation with the aqueous phase. These issues could be solved by coating a small layer of ionic liquid onto a solid support, thereby creating a supported ionic liquid phase (SILP)
We studied the selective recovery of germanium from iron-rich solutions using citrate complexation and subsequent adsorption onto a SILP, consisting of Aliquat 336 impregnated onto a solid support, Amberlite XAD-16N
Summary
One of the key factors of resource efficiency is to treat ‘waste’ as a (secondary) source of raw materials [1]. These issues could be solved by coating a small layer of ionic liquid onto a solid support, thereby creating a supported ionic liquid phase (SILP) As a consequence, both the advantages of solvent extraction using ionic liquids (i.e., high selectivity and tunability) and adsorption chromatography (i.e., ease of phase separation and ability to treat large volumes of low-concentrated solutions) are combined [23]. A solvent-impregnated resin (SIR) system, based on the extractant di-(2-ethylhexyl)phosphoric acid (D2EHPA), has been studied to recover germanium, but very high acid concentrations ([H+] ≥ 6 mol·L−1) were needed to obtain full germanium recovery [28,29]. We studied the selective recovery of germanium from iron-rich solutions using citrate complexation and subsequent adsorption onto a SILP, consisting of Aliquat 336 impregnated onto a solid support, Amberlite XAD-16N. In addition to the synthesis and characterisation of the SILP, we report the parameter optimisation experiments performed on aqueous germanium-containing solutions, both single-element germanium solutions and synthetic mixtures simulating the composition of a real goethite leachate
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