Selective extraction of lithium from high magnesium/lithium ratio brines with a TBP-FeCl3-P204-kerosene extraction system

The tributyl phosphate (TBP)-FeCl3-kerosene system is a common tool for lithium extraction from salt lakes. This system has two main problems. One, FeCl4 is unstable, which decreases the lithium extraction efficiency. Two, TBP readily degrades after long-term contact with high concentrations of acids and bases. Accordingly, the present authors introduce di(2-ethylhexyl) phosphate (P204) in conjunction with Fe3+ to construct a TBP-FeCl3-P204-kerosene extraction system. The optimal operating conditions were 10% P204 + 40% TBP + kerosene, an Fe3+/Li+ molar ratio of 1.6, and organic-to-acid phase ratio R(O/A) = 1. The final lithium ion single-stage extraction yield was 52.71%. The former washed 90.64% of Mg2+ when R(O/A) = 70, the latter washed 95.37% of Mg2+ when R(O/A) = 20. Using water as the stripping agent, the Li+ stripping efficiency decreased with increasing R(O/A). Ultraviolet and Raman spectroscopy indicated that TBP underwent complexation with Li+ and FeCl4, whereas P204 underwent complexation with Fe3+ only. When the Cl concentration was low, Fe3+ underwent complexation with P204 and was retained in the organic phase; whereas when the Cl concentration was high, FeCl4 formed again in a manner that facilitated co-extraction with Li+ by TBP.