Liquid–liquid extraction of Li⁺ using mixed ion carrier system at room temperature ionic liquid

Abstract

An environmentally benign technique for the separation and recovery of lithium (Li⁺) from aqueous streams, containing mixed metal ions was developed via liquid–liquid extraction (LLE). Hydrophobic room temperature ionic liquids (RTIL) were tested as the main extracting solvents. To increase the metal extraction, a proton-ionizable agent bis(2-ethylhexyl) phosphoric acid (DEHPA) was added into the RTIL. To enhance the metal uptake selectivity, three Li⁺-selective neutral ion carriers such as 6-hydroxy-dibenzo-14-crown-4, dibenzo-14-crown-4, and tri-n-octyl-phosphine (TOPO) were also used and tested as extractant additives. Among the tested RTILs, phosphonium-based CYPHOS IL 109 was the most stable extractant as it exhibited the lowest loss when contacted with water. Addition of proton-ionizable agent DEHPA in CYPHOS IL 109 afforded a high extraction of multivalent cations with negligible recovery of monovalent metals. On the other hand, the addition of neutral ion carrier TOPO in DEHPA/CYPHOS IL 109 extractant resulted in a selective Li⁺ uptake which was maximized when the pH of the aqueous solution was maintained at 13, with TOPO/DEHPA molar ratio = 8. The overall process could be a two-stage LLE system wherein the unwanted multivalent cations are initially removed using DEHPA/CYPHOS IL 109 followed by the selective extraction of Li⁺, using TOPO/DEHPA/CYPHOS IL 109 system.

Keywords:

• Ion carrier
• Ionic liquid
• Liquid–liquid extraction
• Lithium ions
• Crown ether
• Facilitated transport

Acknowledgement

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean Government (MEST) [grant number 2012R1A2A1A01009683] and 2013 Research Fund of Myongji University.

Notes

Presented at 2013 International Environmental Engineering Conference and Annual Meeting of the Korean Society of Environmental Engineers (IEEC 2013), Seoul, Korea, June 11–13, 2013