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

This work analyzed the extraction of Zn 2+, Cd 2+, and Fe 3+ 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 Zn 2+, Cd 2+, and Fe 3+ from the aqueous solutions. Furthermore, efficient selective separation of Zn 2+ /Fe 3+ and Cd 2+ /Fe 3+ was achieved using 1-methyl-3-octylimidazolium tetrafluoroborate, [omim + ][BF 4 − ], since high extraction percentages were reached for Zn 2+ and Cd 2+ (extraction percentage > 90) while this parameter was very low for Fe 3+ . 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.