Thermodynamic-environmental optimization of refinery oily sludge-derived ceramics: balancing stabilization performance, mechanical integrity and energy burden

The sustainable incorporation of refinery oily sludge (ROS) into clay-based ceramics requires simultaneous evaluation of contaminant stabilization, material performance, and thermal processing demand. In the present study, ceramic specimens containing 0%, 5%, and 10% ROS were fired at 950°C and 1050°C in order to investigate the coupled thermo-environmental behavior of waste-derived ceramic systems. Physical, thermo-physical, mechanical, and environmental properties were evaluated through measurements of water absorption, apparent porosity, thermal conductivity, flexural strength, and heavy-metal immobilization efficiency. In parallel, a semi-quantitative thermodynamic framework was developed to estimate thermal energy demand and specific energy consumption during firing. The results indicated that intensified firing generally promoted partial matrix consolidation, reduced pore-related properties, and improved thermal conductivity and contaminant immobilization behavior for several elements. However, the higher firing regime was also associated with substantially increased thermal energy demand, revealing a non-linear relationship between thermal processing intensity and overall ceramic performance. A thermo-environmental index (TEI) integrating stabilization efficiency and thermodynamic burden demonstrated that the additional thermal energy demand at 1050°C did not always produce proportional environmental or structural benefits. Multivariate PCA and HCA analyses further supported the existence of coupled thermo-environmental trade-offs among densification behavior, contaminant stabilization, and thermal energy consumption. The study demonstrates that optimization of ROS-derived ceramics should not rely solely on intensified firing conditions, but rather on balanced thermo-environmental performance criteria. The proposed framework contributes to the development of energy-aware waste valorization strategies for sustainable ceramic manufacturing within the circular economy context.