Extraction relationship of Li⁺ and H⁺ using tributyl phosphate in the presence of Fe(III)

During the extraction of lithium from high Mg-containing salt lake brines by tributyl phosphate (TBP) in the presence of Fe(III), H+ is used to stabilize Fe(III). However, the distribution ratio of H+ (DH) is 4–6 times higher than that of Li+ (DLi), which affects the extraction of Li+ significantly. In this study, the competition mechanism between H+ and Li+ was investigated by spectral analysis and thermodynamic equilibrium. The extracted species are determined as HFeCl4 · 2TBP and LiFeCl4 · 2TBP for H+ and Li+, respectively. The apparent equilibrium constants are KH = 799.8 and KLi = 120.6, respectively. Both equilibrium constants and the distribution ratios for H+ and Li+ extraction show that extraction of H+ is stronger than Li+.