Petrochemical refinery incinerator slag as a precursor for sustainable foam glass building insulation: Physicochemical, thermal, and processing-window assessment

Petrochemical refinery incinerator slag (PCIS) is predominantly landfilled, despite its mineral oxide composition, which is suitable for valorisation as a secondary raw material. This work presents the thermophysical and physicochemical characterisation of PCIS from the MOL Danube refinery (Hungary) as a precursor for ceramic foam glass (CFG). The characterisation combines XRF, XRD, SEM/EDS, simultaneous thermogravimetric and derivative thermogravimetric analysis (TG–DTG), heating microscopy, thermal conductivity, and ICP-OES environmental compatibility assessment. The slag is dominated by SiO₂ (45.82 wt%), Fe₂O₃ (15.30 wt%), Al₂O₃ (11.86 wt%), and CaO (10.68 wt%), with a partly crystalline silicate matrix embedded in an iron-bearing amorphous phase. Thermal analysis from room temperature to 1200 °C indicates a net oxidative mass gain of 0.85 wt%, with the main oxidation event centred in the 600-900 °C range (DTG max 0.031% min⁻¹ at 845 °C). The slag reaches the heating-microscopy foaming window (1029–1130 °C) substantially pre-oxidised, attaining a peak expansion of 106% at 1129 °C. Heating microscopy of 0–55 wt% PCIS in waste SLS glass (1.5 wt% SiC) confirms the slag oxides actively modify foaming: low-to-intermediate loadings support CFG foam formation, while ≥35 wt% compositions retain dimensional integrity (≤108%) to ~1075 °C, establishing PCIS as a compositional-tuning precursor for both CFG and refractory-additive applications. Trace elements fall within ranges routinely managed by high-temperature CFG processing. These findings establish PCIS as a thermally stable, oxidation-resistant precursor for sustainable building insulation, supporting landfill diversion in line with Sustainable Development Goals 9, 11, 12, and 13.