Regeneration of the ionic liquid tetraoctylammonium oleate after metal extraction

Abstract

Ionic liquids (ILs) have been presented as suitable candidates for metal extraction in the hydrometallurgy. It has already been proven that they have an adjustable selectivity towards metal ions. However, industrial applications of ILs are limited due to their high price.Therefore, regeneration of ILs is necessary. In this study the regeneration of the fatty acid based IL tetraoctylammonium oleate was investigated, because in a previous study we obtained excellent metal salt extraction efficiencies with this benign IL. Several methods for regeneration were investigated, i.e. electro-deposition and chemical regeneration. Electrodeposition turned out to be unfeasible for this IL. Chemical regeneration showed that the metal ions (Zn, Co and Mn) can be selectively back-extracted, so that metals can also be separated from each other in this step. The best stripping solution was aqueous sodium oxalate, which allowed the IL to be immediately reused.

Water‐Based Synthesis of Hydrophobic Ionic Liquids [N8888][oleate] and [P666,14][oleate] and their Bioprocess Compatibility

“…[28] The N 8888 cation was demonstrated to be less viscous than asymmetrical ammonium branched cations. [26] Furthermore, complete regenerationo f[ N 8888 ][oleate] was demonstrated in metal extraction, [29] which is am ajor challenge for affinity-separation applications. [30] The P 666,14 cation was selected because it showed the best performance in previous extraction experiments.…”

Ionic Liquid-Based Process Development for Cobalt Recovery from Aqueous Streams

“…The majority of previous studies show that strong acids and strong bases are able to remove a wide variety of metal ions from a loaded ionic liquid [10,11,[18][19][20][21][22][23][24][25][26][27][28]. However, the main drawback of these regeneration solutions is that they do not allow direct re-use of the ionic liquid because strong acids protonate ionic liquids and strong bases form emulsions [18]. In the context of the above mentioned four process criteria, strong acids and bases are often used to merely investigate the extraction process on a lab-scale without considering the consequences for the overall process.…”

“…For this study, [P 8888 + ][Oleate -] was selected for Co 2+ extraction because it 1) consists of a natural hydrophobic anion and a hydrophobic cation which is assumed to minimize the losses to the aqueous phases, 2) has the ability to selectively extract transition, rare earth, alkaline earth and alkaline metals depending on the pH and composition of the feed [18], and 3) has a relatively low viscosity at room temperature (200 mPa.s) thus eliminating either the need of a hydrophobic solvent to dilute the IL [29,30] and the need for high(er) temperatures during operation.…”

“…In earlier studies, using phosphonium and ammonium-based ionic liquids with the same functionalized anion oleate, sodium oxalate was used as a regeneration solution in both cyclic and continuous experiments. The regeneration efficiency was below 25% in the cyclic experiments (5 cycles) and below 80% in continuous mode (180 minutes) [9,18]. Huang et al also used sodium oxalate for the regeneration of their acid-base coupling bifunctional ionic liquid, applied for rare earth element separation [31].…”

“…Huang et al also used sodium oxalate for the regeneration of their acid-base coupling bifunctional ionic liquid, applied for rare earth element separation [31]. Even though the metal regeneration efficiency was higher than in the studies of Parmentier et al, [18] it took at least two days to reach a regeneration efficiency of 90-100% [31]. In the present contribution, Na 2 CO 3 has been used instead of sodium oxalate as it is more environmentally friendly, more than ten times cheaper and results directly in the formation of a marketable product (i.e., CoCO 3 (s)), which is mainly used as a catalyst and in ceramic pigments.…”