Synergistic extraction mechanism in TBP system for recovery of lithium in low lithium concentration and high Mg/Li ratio salt lake brines

Synergistic extraction mechanism in TBP system was investigated. • Synergistic extraction system performs better at low lithium concentration. • TBP-DEC system exhibits higher β Li/Mg than other synergistic systems. • Reducing O's electric potential in C O of synergistic agents enhance lithium selectivity. This study investigates the extraction and selective separation of Li from solutions with a high Mg/Li ratio based on a synergistic extractant system involving tributyl phosphate (TBP). Different synergistic agents were investigated, including ethyl acetate (EA), butyl acetate (BA), diethyl carbonate (DEC), methyl isobutyl ketone (MIBK), N,N-Diethylacetamide and N,N-di(1-methylheptyl)acetamide (N503). The result showed that TBP-DEC synergistic extraction system achieved the highest lithium extraction rate of 71.4% and lithium magnesium separation factor of 160, when the concentration of Li = 0.50 g/L and Mg/Li ratio = 200. Fourier Transform Infrared Spectroscopy (FT-IR) analysis revealed that TBP acted as the primary extraction agent for lithium extraction, while the O atom in the C O group of the synergistic agent participates in coordination with lithium. Additionally, the lithium extraction rate of the synergistic extractant system increased with the integrated peak area of the P O stretching vibration. Mechanism analysis reveals that increase of the negative charge density on the O atom in the C O group and reduction of the intermolecular steric hindrance of the synergistic agent can enhance the lithium selectivity of TBP.