Extraction of Rare Earth Ions from Hydrochloric Acid Solution with TBP-[Cnmim][Tf2N] and Their Back Extraction

Abstract

Mutual separation of rare earth ions is very difficult because of their similar chemical properties. In this study, extraction of Nd (III), Dy (III), and Pr (III) from hydrochloric acid solution and their back extraction have been investigated using the mixture of tributyl phosphate, TBP, and 1-alkyl-3-methylimidazoliumbis[ (trifluoromethyl) sulfonyl]imide, [Cnmim][Tf2N] (n, the alkyl chain length, was 2, 4, and 6), in order to clarify the possibility of mutual separation and recovery of these elements. Synergistic effect between TBP and [Cnmim][Tf2N] was found because the extraction was highly enhanced using their mixture, while the extraction by the individual reagent was very low. Although the extraction was increased with a decrease in the n value, mutual separation was difficult because the extraction behavior was similar to one another. Ammonium formate was found to be effective as a back extraction reagent because Pr (III) and Nd (III) were precipitated out as formates while Dy (III) was quantitatively back extracted without precipitation. Precipitation formation was faster in Pr (III) than Nd (III). Based on these results, a possibility of the mutual separation among these three ions was shown.

Keywords

• rare earth
• ionic liquid
• solvent extraction
• extraction
• back extraction