Solvent extraction of rare earth metals with crown ethers

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. (author)