Acid Leaching Extraction Mechanism of Aluminum and Iron Ions from Coal Gangue Based on CaF 2 Assistance and Process Optimization.

To reveal how CaF 2 improves the dissolution ratios of aluminum and iron ions in coal gangue, CaF 2 and hydrochloric acid are used to extract Al 3+ and Fe 3+ from the coal gangue calcined powder. The leaching ratios of Al 3+ and Fe 3+ are measured, and the filter residues are analyzed by BET, XRD, and SEM. The results show that adding 3% CaF 2 could increase the extraction ratio of Al 3+ from 62.96% to 92.10% under optimized conditions, and that of Fe 3+ is increased from 85.12% to 95.73%. The mechanism of CaF 2 as an auxiliary to improve the leaching ratio of Fe 3+ is that HF reacts with the thin layers of gangue calcined powder containing silica to form soluble SiF 4 , thus forming pores that promote the diffusion of H + and inner ions, improving the leaching ratios of Al 3+ and Fe 3+ . Finally, the CaF 2- assisted acid leaching process is optimized. The results showed that it is efficient and feasible to extract Al 3+ and Fe 3+ with the assistance of CaF 2 and that HF has a catalytic effect in the reaction system. This work provides a reference for the next step of actual production.