Abstract:The recovery of valuable metals from spent lithium iron phosphate black mass is currently a significant research focus, with hydrometallurgy as the dominant recycling strategy. A solution containing valuable metals obtained through hydrometallurgical leaching often contains impurity ions such as copper, aluminum, and fluoride, necessitating solution purification prior to the conversion of valuable metal products. In particular, the efficient removal of aluminum ions while minimizing the physical adsorption and chemical co-precipitation losses of lithium remains a key challenge. Neutralization precipitation is a commonly used method for aluminum removal, but the resulting aluminum precipitate exhibits non-negligible lithium adsorption. The cryolite precipitation method can be employed in more acidic environments, producing highly crystalline aluminum-bearing precipitates with low lithium adsorption. However, when applied to lithium-containing solutions, it tends to form lithium-containing cryolite, resulting in significant lithium co-precipitation losses. This study focuses on the hydrometallurgical recovery of lithium from sodium-lithium cryolite (Na1.5Li1.5AlF6), addressing the limitations of the cryolite-based aluminum removal method. This study proposes a novel approach to convert Na1.5Li1.5AlF6 into a mixture of Na3AlF6 and LiF solids in a NaF solution. Furthermore, for the phase separation of this solid mixture, this study develops a method to selectively dissolve LiF in a sulfuric acid medium containing sodium sulfate, utilizing the common ion effect of sodium ions. The sodium-containing acid medium was found to inhibit the dissolution of Na3AlF6. Experimental results showed that complete conversion of Na1.5Li1.5AlF6 into Na3AlF6 and LiF was achieved under the following conditions: NaF concentration of 45 g/L, temperature of 70 ℃, liquid-to-solid ratio of 15 mL/g, and reaction time of 3 h. After solid-liquid separation, the filtrate can be reused for the cryolite conversion process after replenishing the consumed NaF. Moreover, under conditions of an initial sulfuric acid concentration of 90 g/L, a Na+ concentration ≥ 8 g/L, a dissolution temperature of 20–30 ℃, a liquid-to-solid ratio of 15 mL/g, and a dissolution time of 1 h, Na3AlF6 remained undissolved while LiF was completely dissolved. A second solid-liquid separation was then conducted. The Li-bearing acid solution was subsequently routed to the recovery process for spent lithium iron phosphate black mass. Through this two-step conversion and separation process, effective separation of aluminum and lithium from Na1.5Li1.5AlF6 was achieved, with aluminum enriched in the Na3AlF6 solid phase and lithium transferred to the liquid phase. This study provides a viable strategy for the efficient extraction of Li from lithium-containing cryolite. Close-