Integrated separation of precipitation and three-liquid-phase extraction for boron, lithium and magnesium from salt lake brine with high magnesium-lithium ratio

A novel integrated separation process for boron (B), lithium (Li), and magnesium (Mg) is developed using precipitation and three-liquid-phase extraction (TLPE) methods from salt lake brine with high Mg-Li ratio. Simulated brine is precipitated using (NH4)2SO4 and subsequently extracted through the three-liquid-phase system which comprises 2-ethyl-1,3-hexanediol (BEPD) dissolved in butyl acetate (BA), polyethylene glycol with average molecular weight of 2000 (PEG2000), and brine. After optimizing the experimental conditions, the process achieves a precipitation of 95.6 % for Mg2+ and extraction rates of 87.2 for B3+, 73.5 % for Li+, and 91.9 % for Mg2+. The separation performance for actual brine demonstrates the extraction rates of B3+, Li+, and Mg2+ was 84.9, 74.8, and 91.5 %, respectively, which is similar to the results obtained from simulated brine. Moreover, TLPE mechanism is analyzed that B is combined with polyhydroxy compounds in the top phase as H3BO3, while Li+ is extracted by the electrostatic interaction of oxygen atom active groups in the middle phase, and Mg2+ is remained in the bottom phase due to hydration. Our precipitation and TLPE methods show apparent advantages in achieving integrated separation with high efficiency for B, Li, and Mg in the brine.