Sustainable Production of Ceramic Tiles Using Gypsum Sludge as a Partial Replacement Material

The present study aims to apply the principles of the circular economy by utilizing special inorganic waste, specifically gypsum sludge from a Zn refinery to produce ceramic tiles. Samples containing up to 50% of gypsum sludge were prepared as partial replacements of traditional materials such as clay, feldspar, quartz, and kaolin. The properties of the mixtures were analysed in accordance with ABNT NBR ISO 10545 standards, including tests for water absorption, flexural strength, stain and chemical resistances and deep abrasion resistance (ASTM G65-16). The results indicated that the addition of up to 15% of gypsum sludge maintains acceptable mechanical and physical properties, while higher contents significantly increase porosity and water absorption, compromising structural strength. Thermogravimetric analysis revealed that the thermal decomposition of calcium sulphate promotes the release of SO2 at temperatures above 1120°C, requiring emission controls to meet environmental regulations. To conclude, the incorporation of gypsum sludge in ceramic formulations proved to be technically viable, supporting circular economy principles by lowering production costs, reducing the use of virgin raw materials, and finding a destination to industrial waste. The resulting ceramic bodies exhibited properties compatible with the requirements of ABNT NBR ISO 10545 for wall and low-traffic floor tiles, particularly in terms of water absorption and flexural strength, confirming their suitability for non-structural applications.