Lithium recovery from salt lake brine by counter-current extraction using tributyl phosphate/FeCl3 in methyl isobutyl ketone

Salt lakes in northwest China have rich lithium reserves. However, because of their high Mg/Li ratios, lithium recovery is very difficult. In this work, lithium was recovered from Qarhan salt lake using counter-current extraction. The Li+ ions were extracted using tributyl phosphate (TBP) in methyl isobutyl ketone (MIBK) as the extractant and FeCl3 as the coextractant. The process involved four sections: extraction, washing, stripping and regeneration. The optimal conditions for each section were first determined based on equilibrium data. Then the process was conducted in a 10-stage mixer-settler with LiCl/NaCl as the washing agent, HCl/NaCl as the stripping agent, and NaOH/NaCl as the regenerating agent. The operation was stable over 14 cycles. The overall recovery of lithium was higher than 98% and the Mg/Li molar ratio changed from 94.8 in salt lake brine to 0.03 in the stripping solution. The results show that solvent extraction is a highly effective method for lithium recovery from salt lake brines with high Mg/Li ratios.