A novel method for selective recovery of indium from end-of-life liquid crystal displays by 15-crown-5 ether and its derivatives

The present study has proposed a promising liquid-liquid extraction system using novel extractants of 15-crown-5 (15C5), benzo-15-crown-5 (B15C5), and thia-benzo-15-crown-5 (TB15C5) for selective indium recovery from end-of-life liquid crystal displays (LCDs) leaching solution. The focus was placed on the selectivity of the crown ethers toward In3+ over the most competing ion of Sn2+. The molecular design of the crown ethers and their complexations with In3+ were theoretically evaluated through density functional theory (DFT) modeling from the perspectives of geometrical structure, electrostatic potential, independent gradient model, molecular orbital and thermodynamic analysis. The results show that the complexation affinity of the crown ethers toward In3+ is in the order of 15C5 > B15C5 > TB15C5. On the basis of the theoretical analysis, the target crown ethers of 15C5, B15C5, and TB15C5 were synthesized and the corresponding solvent extraction experiments were carried out. The experimental results are in excellent agreement with the theoretical evaluations that 15C5 has the best selectivity to In3+ over Sn2+ among the three crown ethers with the separation coefficient being 5.5, which is followed by 4.1 for B15C5 and 1.6 for TB15C5.