Efficient selective separation of yttrium from holmium and erbium using carboxyl functionalized ionic liquids

The efficient extraction separation of yttrium (Y) from holmium (Ho) and erbium (Er) is always difficult because of their similar physical and chemical properties. In this work, three pyridine carboxylic acid ionic liquids were synthesized and used to extraction of Y. The effects of aqueous phase acidity, extraction time, extractant concentration, temperature and alkyl chain length of ionic liquids on extraction of Y were investigated systematically. The extraction efficiency of [(CH 2 ) 7 COOHpyr][NTf 2 ] for Y increased with an increase in pH, and could reach 99.3% at a pH of 2.5. Meanwhile, the extraction process could achieve equilibrium completely within 5 min. In addition, both the separation coefficients of Ho/Y and Er/Y were greater than 2, which were higher than other ionic liquid extractants. At last, 98.5% of Y could be stripped from the loaded ionic liquid phase with a single step using 0.04 mol/L HCl, and the extraction efficiency of the [(CH 2 ) 7 COOHpyr][NTf 2 ] for Y still maintained about 98% after 8 cycles. A possible cation exchange extraction mechanism was proposed by slope analysis and FTIR spectroscopy.