Supersolubility and solubility of lithium phosphate in sodium carbonate solution.

The tail liquid generated from lithium carbonate production in salt lake brine is termed lithium-bearing mother liquor. This mother liquor exhibits a complex composition, with the Li concentration typically around 1.5 g L, representing a significant lithium resource. Preparing lithium phosphate (LiPO) from this mother liquor is critical for efficient lithium recovery. However, the lack of data on the thermodynamic behavior and LiPO crystallization in such complex solutions has hindered the high-efficiency recovery of lithium resources. In this study, the solubility of LiO in sodium carbonate solutions was determined using the dynamic dissolution equilibrium method. The effects of temperature and sodium carbonate concentration on solubility were analyzed, and experimental data were correlated using an exponential equation. Results indicated that the solubility of LiPO in pure water and sodium carbonate solutions increases with temperature and sodium carbonate concentration. The supersolubility of LiPO in LiCl-NaCO electrolyte solutions was measured turbidimetric analysis, and the metastable zone width (MSZW) was determined. The supersolubility of LiPO significantly decreased with rising temperature. In contrast, supersolubility initially increased and then decreased with higher NaCO concentrations, with reactant concentration being the decisive factor driving the crystallization reaction. Furthermore, the MSZW narrowed at elevated temperatures. Thermodynamic functions (Δ , Δ , and Δ ) for the dissolution process were calculated the van't Hoff equation, confirming that LiPO dissolution is a spontaneous and endothermic process. Based on solubility and supersolubility data, a novel process was developed to prepare battery-grade LiPO (purity: 99.80%) from salt lake mother liquor. The results of Raman, FTIR, TG and SEM suggested that the prepared lithium phosphate was pure phase. This study provides fundamental physicochemical data and theoretical insights for the efficient separation and extraction of lithium resources from lithium precipitation mother liquor.