Stephanie BOUDESOCQUE1, Viau LYDIE1
1 Reims Molecular Institut of Chemistry UMR CNRS 7312 - Université de Reims Champagne-Ardenne, Reims, France
In this study, we have explored a strategy to develop new ionogels as materials for metal extraction. The methodology applied here consists first in confining a commercial salt [THN][Br] in silica-based ionogels in order to determine their extracting properties. Anionic metathesis was then carried out in-situ on the [THN][Br] ionogels with anions of other salts (NaDca or LiTFSI) to enhance their extracting efficiency or to bring selectivity in the extraction process. The treatment of the [THN][Br] ionogels with those salts ensures a quasi-quantitative replacement of bromide ions by Dca and TFSI. The replacement of bromides anions was confirmed by thermogravimetric analyses (TGA) and Infra-red spectroscopy. Nitrogen adsorption-desorption isotherms measured before and after metathesis allows us to confirm that no structural modification has been induced by the anionic exchange.
[THN][Br] ionogels were used for the extraction of Au(III), Pt(IV), Co(II) and Cr(IV). Au(III), Pt(IV) and Cr(VI) were fully extracted while the extraction of Co(II) did not exceed a few percent. The treatment of [THN][Br] with NaDca improved the extraction capabilities of the material with respect to Co(II) which was fully extracted in a saline environment. The treatment with LiTFSI allowed the separation of Au(III) from Pt(IV), with separation factors higher than 500. It also increased the separation of Au(III) from Cu(II) compared to the brominated ionogel. The extraction performances of each ionogel were compared to those of the pure similar ionic liquid or ionogel made directly with task-specific ionic liquids. This work has shown that the confinement of ionic liquids in a silica matrix ionogel is an interesting way to facilitate the implementation of the extraction process and the phases separation. Starting from the same ionogel, the extracting properties can be modulated as desired by simple anion exchange.