Separation of precious metals by using undiluted ionic liquids

The ionic liquid (IL), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][Tf₂N]), was evaluated as an extractant without dilution for the separation and recovery of precious metals. Au(III) was efficiently extracted from the aqueous phase to the IL phase, and a concentrated Au(III) solution almost 8 times higher than the initial feed solutions could be produced. In contrast, Pd(II) was rarely extracted and Pt(IV) was partly extracted under the present experimental conditions. Furthermore, the effect of the IL anions on the extraction ability for the metal ions was examined, and it was found that an IL having an anion component slightly more hydrophilic compared to [Tf₂N], such as 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim][PF₆], showed a higher extraction ability than [Bmim][Tf₂N]. It was suggested that the extraction proceeded via an anion exchange mechanism and it was shown that ILs could be effective extractants for the separation of precious metals.