Lithium Extraction from Acidic Salt Lake Brine Using Solvent Extraction to Prepare Lithium Carbonate: Process Optimization and Mechanism Analysis

This study proposed a simplified process in which FeCl3 was directly dissolved in actual acidic salt-lake brine, in contrast to the conventional tributyl phosphate (TBP)/FeCl3 extraction system that requires predissolving FeCl3 in an acidic, saturated MgCl2 solution prior to mixing with TBP to prepare the Fe3+-loaded organic phase. This modification streamlined the operational procedure and significantly reduced the rate of reagent consumption. Under optimized conditions (organic-to-aqueous phase ratio = 2, 70 vol % TBP, Fe/Li molar ratio = 1.5), the process achieved a lithium-extraction efficiency of 93.34%. The extraction mechanism of Li+, which involves cation exchange and coordination between TBP and Li+, was elucidated by Fourier-transform infrared spectroscopy and nuclear magnetic-resonance analysis. Furthermore, lithium carbonate with a purity of 97.48% was obtained from the stripping solution. Overall, this work provides a practical basis for the design and optimization of lithium extraction from salt-lake brine with high Mg/Li ratios.