High-quality AlSi alloy fabrication via efficient green synergistic recovery of aluminum and silicon from coal fly ash

The large-scale resource utilization of coal fly ash (CFA) poses a significant technological challenge in industrial solid waste management and the sustainable development of coal-based industries. This study addresses critical issues in producing Al Si alloys from CFA via molten salt electrolysis, such as high impurity content in the final alloy and unclear reaction mechanisms during electrolysis, by developing an integrated “hydrometallurgical purification-aluminum-silicon oxide preparation-molten salt electrolysis” process. Through systematic experimental research and theoretical calculations, we comprehensively investigated the dissolution characteristics and electrochemical behavior of aluminum-silicon oxide (ASO) in cryolite-based electrolyte systems. The results indicate that Al 2 O 3 promotes the stable existence of silicon in the form of NaAlSi 3 O 8 , effectively suppressing SiF 4 gas generation and reducing silicon loss from 25.84 % to 0.70 %. The formation of aluminosilicate enhances the dissolution rate of ASO by 2.4 times compared to Al 2 O 3 . Electrochemical analysis confirms that the reduction of Si(IV) follows a unique electrochemical-aluminothermic synergistic mechanism. Compared with melting-casting method, the molten salt electrolysis process effectively reduces the grain size of the alloy by approximately 43.3 %, leading to improved overall mechanical properties. The process achieves high utilization rates of 98.31 % for silicon and 94.55 % for aluminum from CFA, offering an innovative technical solution for high-value-added resource utilization of this industrial solid waste.