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.