Solvent extraction of rare earth metals with crown ethers

Abstract

Crown ethers, such as 15-crown-5, 12-crown-4 and dibenzo-18-crown-6, were used to extract individual rare earth ions from aqueous solutions containing picrate into nitrobenzene solution. The rare earth metal ion europium(III) is extracted as a 2:1 crown - ion sandwich complex with 12-crown-4, but as a 1:1 complex with both 15-crown-5 and dibenzo-18-crown-6. From studies of picric acid concentration effects on complexation, the extracted species of Eu(NO₃)₃ with 15-crown-5 and dibenzo-18-crown-6 are Eu[(15-crown-5)-(picrate)₂(NO₃)] and Eu[(dibenzo-18-crown-6)(picrate)₂(NO₃)], respectively, but Eu[(12-crown-4)₂(picrate)₃] is formed with 12-crown-4. The extraction of rare earth ions showed that Tb³⁺, Eu³⁺, Gd³⁺, Nd³⁺ and Yb³⁺ can be easily extracted using 15-crown-5; however, the extraction of Ce⁴⁺, Sm³⁺, Dy³⁺ and Lu³⁺ is more difficult.