Solvent Extraction Process and Extraction Mechanism for Lithium Recovery from High Mg/Li-Ratio Brine

A co-extraction system of tributyl phosphate (TBP) and KPF6 was used for lithium ion extraction from brine containing a high ratio of magnesium and lithium. The effects of the phase ratio R(organic/aqueous), aqueous phase pH, and PF6−/Li+ molar ratio on the extraction of lithium were studied. The single-stage extraction efficiency of lithium was 82.29% under optimal conditions, and the back-extraction efficiency was 93.99% when using 1 mol/L HCl +3 mol/L NaCl as the stripping agents at R(O/A)=1. The stoichiometry of the extraction complex was investigated by nuclear magnetic resonance spectroscopy and slope analysis.