Modelling of lithium extraction with TBP/P507–FeCl3 system from salt-lake brine

Abstract Recovery of lithium from Mg-rich salt-lake brines by solvent extraction has been widely studied for high Li+/Mg2+ selectivity and Li+ extraction efficiency. In a previous study, a ternary synergistic solvent extraction system consisting of tributyl phosphate (TBP), 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (P507, denoted as HL) and FeCl3 was developed, in which high Li+ selectivity and efficient Li+ stripping simply with water were realized. In this study, to further elucidate the extraction mechanism of the TBP/P507/FeCl3 system and minimize the efforts on the process optimization for Li extraction from Mg-rich salt-lake brines with different component concentrations from different sources, a thermodynamic empirical model based on mass balances and equilibrium equations has been developed. The model parameters were optimized by fitting the calculated data to experimental results. By calculating the distribution of species in the organic phase with the model, it was found that Li+ primarily existed in the form of [Li(TBP)2][FeCl4], followed by [Li(TBP)][FeCl4]. When Li+ was stripped with water, Fe3+ mainly existed in the form of FeCl2L·HL·2TBP in the organic phase at low O/A ratios but converted to [H(TBP)2][FeCl4] at high O/A ratios. This thermodynamic model provides a guide for the design of practical process flow.