Preparation of porous geopolymer carriers derived from coal fly ash and municipal solid waste incineration bottom ash for shape-stable phase change paraffin and its formation mechanism

The accumulation of coal fly ash (CFA) and municipal solid waste incineration bottom ash (MSWI-BA) not only poses environmental hazards but also leads to resource wastage. Meanwhile, porous geopolymers have emerged as an ideal matrix for phase change materials (PCMs) owing to their exceptional structural stability, high mechanical strength, and superior PCM loading and encapsulation performance. In this study, CFA and MSWI-BA were utilized to prepare porous geopolymers through the geopolymerization process. The orthogonal experiment of porous geopolymer preparation was conducted and analyzed by multi-index matrix. The optimal formula of porous geopolymer was water glass modulus 1.5, oleic acid content 6 %, hydrogen peroxide content 4 % and CFA to MSWI-BA ratio 5:5. The prepared porous geopolymer carrier exhibits an open porosity of 78.1 ± 0.35 %, a thermal conductivity of 0.156 ± 0.005 W/(m·K), and a compressive strength of 1.34 ± 0.05 MPa. The amphiphilic nature of oleic acid molecules and the soap molecules generated from their saponification reaction with OH⁻ reduce interfacial tension and stabilize pore templates, which are critical factors in promoting the formation of open-pore structures in porous geopolymer. Through heavy metal leaching experiments, it was learned that the prepared porous geopolymer has excellent heavy metal fixation properties and meets the optimal grade standards required by GB8978-1996.The mass loss and enthalpy loss of CFA-MSWI-BA geopolymer shape-stable paraffin (CGSP) after 100 thermal cycles were 2.8 % and 5 % respectively. The thermal conductivity and enthalpy value of CFA-MSWI-BA geopolymer shape-stable paraffin were 0.2537 ± 0.012 W/(m·K) and 57.94 J/g. This study combines multiple advantages such as resource recovery, cost-effectiveness, physical and chemical stability, and excellent thermal properties, making it a functional material with great potential.