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.