Selective extraction of heavy metals (Fe, Co, Ni) from their aqueous mixtures by Task-Specific salicylate functionalized imidazolium based ionic liquid

Abstract

Iron (Fe), cobalt (Co) and nickel (Ni) together are known as the iron triad exhibiting similar chemical and physical affinities in the periodic table. We have developed a green, efficient, highly selective, environmentally benign, water-IL biphasic solvent extraction system for the selective extraction of iron triad elements from their aqueous mixtures at room temperature using a new salicylate functionalized imidazolium based task specific ionic liquid (TSIL) i.e. 1,3-dioctylimidazolium 2-hydroxybenzoate [DOIM][OHB]. Co2+ was extracted within 5 min as a blue complex while the residual mixture was allowed to stand overnight. In the meantime, Fe2+ was oxidized to Fe3+ without using any additional oxidants and was extracted as a red coloured complex. Ni2+ was not observed visibly, however atomic absorption spectroscopy (AAS) indicated the presence of less than 1% Ni2+. The extraction of heavy metal ions follows neutral extraction mechanism elucidated through UV visible spectroscopy.