Extraction and separation of rare earth metal ions with DODGAA in ionic liquids

In order to apply ionic liquids (ILs) to the separation of rare earth metals, liquid-liquid extraction of a series of rare earth elements into the ILs was investigated mainly using 1-octyl-3-methylimidazolium bis(trifluoromethyl sulfonyl) imide, [C8mim][Tf2N], with N,N-dioctyldiglycol amic acid (DODGAA) as the extractant. A higher selectivity was exhibited for the heavier rare earth elements as in the n-dodecane system, and the order of the extractability of Y(III) in the IL system, situated in the heavy rare earth metals, was between Tb and Dy. This position is a little different from that for the common solvent extraction system employing organophosphorus extractants such as bis (2-ethylhexyl)phosphoric acid (D2EHPA) and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC-88A). Quantitative extraction was achieved for all rare earth metals with DODGAA from sulfuric acid solutions from pH 1.5 to 4. It was confirmed that rare earth metal ions were extracted with 3 DODGAA molecules in the ILs.