Phase equilibria constraints on lithium enrichment and precipitation processes in sulfate type salt lakes: a study based on the Li-Na-K-SO4-H2O system at 303.2 and 318.2 K

• Temperature plays a critical role in governing the phase diagram structure and mineral phase transformations. • The multi-ion coexistence environment significantly lowers the precipitation threshold for lithium, leading to its early and dispersed precipitation. • The enrichment behavior of lithium in sulfate type salt lakes is synergistically constrained by temperature, phase equilibria, and multi-ion interactions. The sulfate type salt lakes in the Qaidam Basin of China represent an important lithium resource base. However, lithium recovery during solar evaporation of sulfate type salt lake is generally low, and the underlying loss mechanism remains unclear. To elucidate lithium migration and precipitation from a phase equilibria perspective, this study conducted phase equilibria on the Li + , Na + , K + /SO 4 2− −H 2 O system at 303.2 K and 318.2 K, with systematic comparison to phase diagrams at 288.2 K, 298.2 K, and 373.2 K. The results reveal the presence of various lithium containing double salts with distinct thermal stability ranges, Li 2 SO 4 ·K 2 SO 4 and 2Li 2 SO 4 ·Na 2 SO 4 ·K 2 SO 4 exist within the temperature range of 288.2–373.2 K; Li 2 SO 4 ·3Na 2 SO 4 ·12H 2 O is present between 288.2 K and 318.2 K; and Li 2 SO 4 ·Na 2 SO 4 forms within the temperature range of 318.2–373.2 K. For double salts such as Li 2 SO 4 ·3Na 2 SO 4 ·12H 2 O, the minimum formation concentration depends jointly influenced on temperature and coexisting ions. At 298.2 K, the required lithium concentration decreases from 0.91% to 0.21% as more ion species coexist, promoting early lithium precipitation via double salts and limiting its further enrichment in brine. This study identifies the entry of lithium into solid phases via double salt formation as the main loss pathway, and pinpoints key stages of lithium loss during processing. The phase equilibria data and multi-temperature phase diagrams quantitatively describe lithium distribution in coexisting ion systems and clarify how temperature and coexist ions variations affect lithium enrichment efficiency by altering mineral precipitation sequences. These findings provide a theoretical basis for metallogenic analysis of sulfate type salt lakes and for optimizing evaporation processes to suppress premature lithium precipitation and improve recovery