Abstract: The recovery of valuable elements from spent LiFePO4 (LFP) black powder has become a significant research focus. A key challenge in the high-value recovery of this spent powder is the deep removal of aluminum (Al3+) from acidic solutions containing iron (Fe), aluminum (Al), and phosphorus (P) to produce battery-grade iron phosphate materials. In this study, the chemical composition of acidic leachates from sulfuric acid leaching of spent LFP powder was used as a reference, and Na2SO4-Li2SO4-Al2(SO4)3 solutions were designed to optimize Al3+ removal via cryolite precipitation. Based on the optimization of the cryolite precipitation process for aluminum removal, the formation rules of various types of cryolite, including Na1.5Li1.5AlF6, Na2LiAlF6, and Na3AlF6, were clarified, with a particular focus on how the initial Na/Li molar ratio and Al3+ concentration in the solution affected the formation of cryolites. The conditions for generating pure phases of each cryolite were established, which provided practical guidance for Al3+ removal through cryolite precipitation. This method was applied to the deep removal of Al3+ from acidic leachates following the leaching of spent LFP powder. It was found that the optimal conditions for cryolite precipitation to remove aluminum were a F/Al molar ratio of 6.6, an initial pH of 2.5, a reaction temperature of 50℃, and a reaction time of 2 h. Under these conditions, when the initial Na/Li molar ratio was set at 1.50 or 2.00, the precipitated Al-bearing solid was Na1.5Li1.5AlF6 cryolite, while at a ratio of 3.00, Na3AlF6 formed. The presence of iron and phosphorus in the solution hindered the formation of Na2LiAlF6. Using cryolite precipitation, the concentration of Al3+ could be reduced from 0.50 g/L to less than 20 mg/L, with minimal lithium loss by forming Na3AlF6. This research offers a viable solution for deep Al3+ removal from acidic leachates, ensuring minimal lithium loss during the hydrometallurgical recycling of spent LFP powder.

Key words: lithium iron phosphate waste powder, synthesis of cryolite, cryolite method for aluminum removal, acid leachate of waste powder

摘要： 从LiFePO4 (简称LFP)废粉中回收有价元素已成为当下重要的研究方向之一。在此过程中，高效回收该废粉中的有价元素面临一个关键挑战，即如何在含铁、铝、磷的酸性溶液中深度去除Al3+，以便于后续制备电池级磷酸铁。本研究参考LFP废粉硫酸全浸液的成分，配置了Na2SO4-Li2SO4-Al2(SO4)3溶液，并利用冰晶石沉淀法脱除Al3+。在对冰晶石沉淀除铝条件进行优化的基础上，深入阐明了多种类型冰晶石(如Na1.5Li1.5AlF6, Na2LiAlF6和Na3AlF6)的形成规律，尤其明确了溶液初始Na/Li摩尔比和初始Al3+浓度对冰晶石形成的影响机制，进而确定了各类冰晶石纯相的生成条件，为冰晶石沉淀法除铝提供了理论依据。将该方法应用于LFP废粉酸浸液中的Al3+深度脱除研究，结果表明，冰晶石沉淀除铝的最佳条件为：F/Al摩尔比为6.6、初始pH值为2.5、反应温度为50℃、反应时间为2 h。在上述条件下，当初始Na/Li摩尔比为1.50或2.00时，沉铝产物为Na1.5Li1.5AlF6冰晶石；当Na/Li摩尔比为3.00时，则形成Na3AlF6冰晶石。同时发现溶液中铁和磷的存在会抑制Na2LiAlF6的生成。利用冰晶石沉淀法，Al3+质量浓度可从0.50 g/L降至20 mg/L以下，并能在低锂损的同时生成Na3AlF6冰晶石。本研究为LFP废粉湿法回收过程中Al3+的低锂损深度选择性脱除提供了有效方法。

关键词: 磷酸铁锂废粉, 冰晶石合成, 冰晶石法除铝, 废粉酸性浸出液