Valorization of porcelain tile polishing residue in the production of cellular ceramics

Porcelain tiles polishing residues are the leftovers of the tiles after the polishing step, formed by a mixture of a glassy phase, from the porcelain tiles, water, organic substances, and abrasive particles, mainly SiC, resulting in a sludge. When the sludge is dried and fired at high temperature, the SiC particles of the abrasive are oxidized and form SiO2 and CO2, producing gases that can expand the glassy phase of the sludge forming cellular ceramics. In this context, this work aimed to study the feasibility of producing cellular ceramics from porcelain tiles polishing residues and to evaluate their physical, mechanical, and microstructural characteristics. A 2³ factorial design was used, where the study variables were the compaction pressure (20 and 40 MPa), the firing temperature (1170 and 1200 °C) and the firing time (30 and 60 min). The mechanical strength, apparent density and linear expansion after firing were determined for the cellular ceramics, being the response variables of the DoE. SEM analysis was performed to evaluate the porous microstructure of the ceramics. By image analysis, the average pore size was determined. Based on the experimental results and statistical analysis, cellular ceramics can be produced using the porcelain tile polishing residue. The ceramics subjected to the highest firing temperature (1200 °C) and firing time (60 min) have resulted in the highest linear expansion, lowest apparent density, largest pores, and lowest tensile strength due to the increase in porosity caused by the presence of SiC, since at these temperatures the pore formation kinetics is higher.

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