Abstract
Recently, an alkylhistidine extractant His-EH (histidine-2-ethylhexylamide) was found to be efficient for the extraction of intermediate transition metal ions. In the present study, the extraction mechanism of Co(II) using His-EH in an ionic liquid extraction system using 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF6]) as the diluent was investigated. The stoichiometries of the complex between His-EH and Co(II) in the ionic liquid and in chloroform were found to be different. The results of slope analysis confirmed that Co(II) was extracted using His-EH by a cation-exchange reaction according to the following equation: Co2+(aq) + 3His-EH(IL) + 2(hmim+PF6-)(IL) = Co2+(His-EH)3(PF6-)2(IL) + 2hmim+(aq).
