Clay-free sintered bricks fabricated entirely from polyaluminum chloride residue: Process optimization, densification mechanism and chloride environmental fate

Polyaluminum chloride (PAC) residue is a chloride-rich inorganic solid waste whose large-scale disposal is limited by land use and potential environmental risks. Its aluminosilicate-rich composition, however, provides a basis for ceramic conversion. Here, PAC residue was used as the sole solid feedstock to prepare clay-free sintered bricks. Forming pressure, moisture content, heating rate, and sintering temperature were evaluated, while XRD, SEM, BET, chloride-distribution analysis, TG-MS, and leaching tests were used to resolve densification and environmental behavior. A forming pressure of 27.5 MPa and a moisture content of 17.5% produced suitable green bodies. At 1100 °C and a heating rate of 8 °C/min, the bricks reached a compressive strength of 33.5 MPa and a water absorption of 18.63%, meeting the MU30 requirements of GB/T 5101–2017. Sintering promoted densification, decreasing the specific surface area from 18.2 to 4.3 m²/g and the total pore volume from 0.027 to 0.007 cm³ /g. Leachable chloride decreased by 99.7%, while the investigated metals showed low leachability in the fired matrix. These results connect structural evolution with mechanical performance and chloride fate, supporting PAC residue as a clay-free ceramic feedstock.