Abstract:High-purity AlF₃ was prepared by the combined process of leaching the raw material of waste aluminum electrolytes with aluminum chloride, electrolyzing the leaching solution, and then mixing with ammonium hydrogen fluoride for roasting. Under the optimal leaching conditions of a fluorine to aluminum molar ratio of 2.0, a liquid-to-solid ratio of 12, a temperature of 90 °C, and time of 4 h, the fluorine leaching rate can reach 99.15%. Under the action of electrolysis, the H⁺ is reduced to H₂ in the cathode, while the remaining OH^- combines with AlF²⁺ and AlF₂⁺ to precipitate aluminium hydroxyfluoride hydrate. The results show that electrolysis is beneficial to reduce the impurity content of aluminium hydroxyfluoride hydrate. When the current density is 0.2 A/cm², the temperature is 90 °C, the stirring speed is 200 r/min, and the electrolysis endpoint pH is 3.0, the total content of Na, K and Ca impurities in the precipitation is only 0.64 wt.%. Moreover, the hydrolysis can be inhibited effectively by adding ammonium hydrogen fluoride in the mixed-roasting process. When the mass ratio of aluminium hydroxyfluoride hydrate to ammonium hydrogen fluoride is 2？1, the purity of the AlF₃ product is even 99.51 wt.%. Conducively, the high-purity AlF₃ can be returned to the aluminum electrolysis industry or used as a reagent.

Key words: waste aluminum electrolyte; aluminum chloride solution; electrolysis; aluminium hydroxyfluoride hydrate; ammonium hydrogen fluoride; anhydrous aluminum fluoride