Removal of Metal Ions from Aqueous Solutions by Extraction with Ionic Liquids

This work analyzed the extraction of Zn2+, Cd2+, and Fe3+ from aqueous hydrochloride solutions using ionic liquids in the absence of chelating agents. For this purpose, ionic liquids based on 1-(n-alkyl)-3-methylimidazolium and tetraalkylammonium cations and several anions (hexafluorophosphate, bis[(trifluoromethyl)sulfonyl]imide, tetrafluoroborate, and chloride) were tested. It was found that the ionic liquid methyltrioctylammonium chloride, [MTOA+][Cl−], allowed almost complete removal (extraction percentage > 94) of Zn2+, Cd2+, and Fe3+ from the aqueous solutions. Furthermore, efficient selective separation of Zn2+/Fe3+and Cd2+/Fe3+ was achieved using 1-methyl-3-octylimidazolium tetrafluoroborate, [omim+][BF4 −], since high extraction percentages were reached for Zn2+ and Cd2+ (extraction percentage > 90) while this parameter was very low for Fe3+. These results indicate that the use of ionic liquids as an alternative to traditional extraction agents in liquid/liquid extraction of heavy metal ions is very promising.