Synthesis of functional ionic liquids with high extraction rate and electroconductivity for lithium-magnesium separation and metallic magnesium production from salt lake brine

The effective separation between Li + and Mg 2+ in high Mg/Li ratio brine and the high-efficiency dehydration of MgCl 2 ·6H 2 O during metallic Mg production are two major challenges of salt lake chemical industry. Herein, a functional ionic liquid with high electroconductivity and extraction rate on Mg 2+ was successfully synthesized with methyltrioctylammonium ([A336] + ) as the cation and saponified di-(2-ethylhexyl) phosphoric ([P204] − ) as the anion. When methyl isobutyl ketone (MIBK) was used as the diluent, the single extraction rate for Mg 2+ with a concentration up to 50.42 g·L −1 reached 83.99% at the phase ratio R (O/A) = 10:1, and the electroconductivity of the organic phase after extraction was more than 550 μS·cm −1 . The Mg 2+ was confirmed to be extracted by coordination interaction to form MgCl 2 ·2[A336][P204], and meanwhile the low intermiscibility of the extraction system with brine was also illustrated by the extraction phase equilibrium . Based on these excellent performances, the extraction system was successfully applied for Mg 2+ and Ca 2+ purification from lithium-rich brine. In particular, because of the high extraction rate and electroconductivity of the developed system, a novel “extraction-electrodeposition” technology was proposed for metallic Mg production from salt lake brine, by which it successfully avoids the dehydration process of MgCl 2 ·6H 2 O and the high temperature molting of anhydrous MgCl 2 during the traditional production of metallic Mg by electrolysis. The simplicity and low energy consumption properties of the proposed technology provides a new strategy for the effective exploitation of Li and Mg resources in salt lake brine.