Liquid-liquid extraction of lithium using lipophilic dibenzo-14-crown-4 ether carboxylic acid in hydrophobic room temperature ionic liquid

• Published in: Hydrometallurgy 2016-09, Vol.164, p.362-371
• Main Authors: Torrejos, Rey Eliseo C., Nisola, Grace M., Song, Ho Seong, Han, Jeong Woo, Lawagon, Chosel P., Seo, Jeong Gil, Koo, Sangho, Kim, Hern, Chung, Wook-Jin
• Format: Article
• Language: English
• Subjects: Carboxylic acids; Crown ether; Density functional theory; Dilution; Hydrometallurgy; Ionic liquids; Liquid-liquid extraction; Lithium; Lithium recovery; Room temperature ionic liquid; Sea water; Sodium
• ISSN: 0304-386X; 1879-1158
• DOI: 10.1016/j.hydromet.2016.05.010

A green liquid-liquid extraction (LLE) system was developed for the recovery of lithium (Li+) from sodium and potassium ions, which are typically present at high concentrations in seawater. Dibenzo-14-crown-4ether (DB14C4) was functionalized with a long lipophilic alkyl C18 chain and a pendent proton ionizable carboxylic acid group to obtain a lithium (Li+) carrier system (DB14C4-C18-COOH) with high Li+ extraction performance and good stability in the room temperature ionic liquid diluent, CYPHOSIL 109. The Li+ extraction efficiency of DB14C4-C18-COOH/CYPHOSIL 109 can be enhanced by increasing the solution pH and DB14C4-C18-COOH concentration. Further examination of extraction results reveal 1:1 coordination between DB14C4-C18-COOH and Li+ which was also supported by density functional theory calculations. At room temperature, the developed LLE system effectively extracted dilute Li+ from Na+ (selectivity αLi+/Na+=1954) and K+ (αLi+/K+=138). Kinetic and thermodynamic parameters were evaluated for optimum Li+ extraction conditions. Sequestered Li+ can be easily recovered from the LLE system using dilute hydrochloric acid. Results from recycling tests showed stable Li+ extraction performance hence it can be used for long term application. Overall results indicate the potential application of DB14C4-C18-COOH/CYPHOSIL 109 as a treatment step to recover Li+ from brine or seawater. •Crown ether in RTIL CYPHOSIL 109 LLE system was developed for Li+ recovery.•Ligand lipophilic dibenzo14C4 crown ether with ionizable COOH group was synthesized.•Highly selective LLE towards Li+ in the presence of high Na+ and K+ concentration•Ligand concentration, solution pH and temperature affected Li+ extraction.•Convenient Li+ recovery and LLE reusability via dilute acid stripping treatment