Upcycling Anodic Sludge from Aluminum Anodizing: Leaching Efficiency and Thermal Conversion into Refractory Materials

Anodic sludges generated in the production of aluminum profiles pose both an environmental and economic problem due to their accumulation in municipal landfills. This study investigates their valorization as a raw material for industry through leaching and calcination processes. The solid residue was characterized both physically and chemically. In the leaching process, concentrations of NaOH (1–2.5 M) and solid percentages (10–30%) were evaluated, achieving a 93.7% recovery of aluminum as sodium aluminate with 2 M NaOH and 10% solids. In the calcination process, the sludges were treated at temperatures ranging from 200 to 1600 °C, and different particle sizes (−3 + 1 mm, −1000 + 400 μm, −400 + 200 μm). The best result from calcination was obtained at 1600 °C, producing a refractory material composed of corundum (α-Al2O3) and diaoyudaoite (NaAl11O17).