Regeneration of the ionic liquid tetraoctylammonium oleate after metal extraction

• Regeneration of the IL tetraoctylammonium oleate after metal extraction is studied.
• Zn, Co and Mn can be selectively recovered by chemical regeneration.
• Aqueous sodium oxalate is the best stripping agent allowing reuse of the IL.
• Electrodeposition was found to be an unfeasible regeneration method.

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 often limited due to their high price. Therefore, regeneration and reuse of ILs is necessary. In this study the regeneration of the fatty acid based IL tetraoctylammonium oleate was investigated, because in previous study excellent metal salt extraction efficiencies were obtained with this benign IL. Two methods for regeneration were investigated, i.e. electro-deposition and chemical regeneration. Electro-deposition 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 reused with no further treatment.

From left to right: (i) Ionic liquid (IL) in contact with the metal containing aqueous phase, (ii) IL after metal extraction (E% = 99.5%), and (iii) IL after stripping with sodium oxalate (S% = 24.3%). In all cases the IL is the upper phase.Figure optionsDownload as PowerPoint slide