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

Abstract

The effective separation between Li+ and Mg2+ in high Mg/Li ratio brine and the high-efficiency dehydration of MgCl2·6H2O 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 Mg2+ 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 Mg2+ 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 Mg2+ was confirmed to be extracted by coordination interaction to form MgCl2·2[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 Mg2+ and Ca2+ 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 MgCl2·6H2O and the high temperature molting of anhydrous MgCl2 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.