Study on Precipitation Dissolution Equilibrium of Lithium Sodium Cryolite

This article uses aluminum sulfate, lithium sulfate, sodium sulfate, and ammonium fluoride as raw materials to synthesize lithium sodium cryolite (Na3Li3Al2F12) by regulating the coordination of fluorine and aluminum. The precipitation dissolution equilibrium behavior of Na3Li3Al2F12 is studied, providing a basis for the fluorination coordination and removal of Al from waste LiFePO4 powder acid leaching solution. The system investigated the effects of F-/Al3+ molar ratio, Na+/Al3+ molar ratio, Li+/Al3+ molar ratio, initial reaction pH, reaction temperature, and reaction time on the coordination precipitation process. Obtain optimized precipitation conditions: F-/Al3+ molar ratio of 7, Na+/Al3+ molar ratio of 1.5, Li+/Al3+ molar ratio of 2, reaction temperature of 70 ℃, reaction pH of 4.5, and reaction time of 3 hours. Under the optimal process conditions, after the fluorinating agent coordinates and precipitates Al, the concentrations of various ions in the filtrate tend to stabilize, with an Al3+ concentration of 75.43 mg/L. When the temperature is 30 ℃ and the pH is less than 3, the higher the acidity, the greater the solubility of Na3Li3Al2F12. When the pH is greater than 3, the pH value has little effect on the solubility of Na3Li3Al2F12. To verify its guiding significance, in practical applications, the precipitation rate of Al3+ reached 99.4% after NaF coordination precipitation of waste LiFePO4 cathode material acid leaching solution, achieving deep removal of Al.