Utilization of Hazardous Waste by Co-Treating Secondary Aluminum Dross and Red Mud Residue for Brickmaking

Secondary aluminum dross (SAD) and red mud residues (RMR) are hazardous wastes generated during the production of alumina and aluminum metal processing, containing unstable AlN, fluoride, chlorides, and alkalis. A novel and pragmatic approach was proposed in this study for the synergistic treatment of waste, wherein hazardous substances are modified through the incorporation of SAD, RMR, and silicate tailings (ST) derived from bauxite flotation, ultimately resulting in the production of ceramic sintered bricks. During brickmaking, AlN in SAD was transformed into Al(OH)₃ through an alkali-catalytic process, and fluorides and chlorides in SAD were efficiently modified and solidified into the silicate mineral marialite Na₄[AlSi₃O₈]₃(F,Cl). Abundant alkalis in RMR transformed into the stable mineral feldspar Na_1–xCa_xAl_1+xSi_3–xO₈, which is the main phase of the sintered brick. The optimal conditions for achieving superior performance of sintered bricks included a mass ratio of SAD, RMR, and ST at 3:3:4, sintering temperature of 1120 °C, and a sintering duration of 2 h. The water absorption rate, porosity, volume density, and compressive strength of the sintered brick in the optimum conditions were 13.69, 26.75%, and 83.04 MPa, respectively, conforming to the industry standards for brick performance.