A Novel Reclamation Method of Chemical–Mechanical Grinding for Inorganic Binder Waste Sand in Aluminum Alloy Casting Process

The current approach to reclaiming inorganic binder waste sand discharged during the aluminum alloy casting process typically involves mechanical grinding combined with calcination treatment (650–700 °C). However, this method encounters challenges such as the accumulation of residual binder on the surface of the reclaimed sand and a subsequent decline in its refractoriness. This study proposes a novel method to reclaim inorganic binder waste sand, by integrating chemical infiltration with mechanical grinding. The effects of different types and concentrations of chemical reagents on the electrical conductivity and Na₂O content of the reclaimed sand were investigated. The microstructure and chemical composition of both waste and reclaimed sand were analyzed, and revealing the chemical-mechanical grinding reclamation mechanism. Compared to H₂C₂O₄ and MgCl₂ solution, the CaCl₂ solution demonstrates superior efficacy in enhancing the quality of reclaimed sand. The electrical conductivity and Na₂O content of the reclaimed sand exhibit a rapid decline followed by stabilization with increasing concentration of CaCl₂ solution. When the dosage of CaCl₂ solution is 5 wt% of the waste sand weight, and the concentration is 10 wt%, the electrical conductivity and Na₂O content of the obtained reclaimed sand are 776.7 μS/cm and 0.039%, respectively, meeting the utilization requirements for reclaimed sand. Microscopic analysis reveals that the CaCl₂ solution reacts with the residual binder on the surface of the waste sand, disrupting the structure and morphology of the residual binder. After drying, the reaction product crystallizes in the form of blocky inorganic salts, facilitating their removal during mechanical grinding. Finally, the clean reclaimed sand is attained, exhibiting a 24 h tensile strength exceeding 90% of that of new sand.