Extraction of lithium from salt lake brine containing borate anion and high concentration of magnesium

Lithium recovery from salt lake brine with a high magnesium/lithium concentration ratio from Qinghai province, China, was investigated. Li+ extraction was performed using tributyl phosphate in methyl isobutyl ketone as the extractant and FeCl3 as the coextractant. An extraction mechanism, based on cation exchange of Li+ and Mg2 + with H+ and Na+, was proposed. Boron exists as B(OH)4− in salt lake brine and is extracted into organic phase as boric acid. B(OH)4− in salt lake brine can strip H+ from the regenerated organic phase; this results in extraction of larger amounts of Li+ and Mg2 + because of electroneutrality. Based on cation exchange mechanism and neutralization of B(OH)4− with H+, the extraction behaviors of Li+ and Mg2 + from salt lake brine are successfully predicted. An experiment using a five-stage mixer-settler with countercurrent flow was conducted. The results showed that B(OH)4− largely favors lithium extraction from salt lake brine.