Feasibility of ionic liquids as alternative separation media for industrial solvent extraction processes

Extraction of rare earth metals into ionic liquids (ILs) from aqueous solutions was investigated using octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (CMPO) as an extractant. Use of ILs greatly enhanced the extraction efficiency and selectivity of CMPO for metal ions compared to when n-dodecane was used as the extracting solvent. The extraction mechanism has been studied by slope analysis and extraction tests, and these confirmed that the metal extraction proceeds via a cation-exchange mechanism. Furthermore, stripping of metals from ILs into an aqueous phase by complexing agents and recycling of the extracting ILs phase was successfully accomplished.