Influence of Processing Variables on the Hydrothermal Synthesis of Zeolite–Geopolymer Aggregates from Kaolin

ABSTRACT This study addresses the influence of key processing variables on the hydrothermal alkaline treatment of low‐temperature fired kaolin‐aggregates for the development of zeopolymers (zeolite–geopolymer composites). Parameters such as hydrothermal treatment temperature (90 and 150°C), reactor volume (250 and 500 mL), liquid‐to‐solid (L/S) ratio (2, 4, 8, and 12 mL/g), posttreatment washing, and drying temperature (60, 90, 105, and 120°C) were systematically varied to assess their impact on the mineralogical and technological properties of the resulting lightweight aggregates. The results demonstrate that all hydrothermal treatments led to zeolite formation (between 17.4% and 58.4%), with zeolite type and content strongly dependent on treatment temperature (being the dominant phases zeolite A at 90°C and cancrinite at 150°C). Unwashed samples exhibited higher mechanical strength, with values exceeding 6 MPa, and zeolitization efficiencies were maximized at 150°C. The L/S ratio has an important influence on the final results, while the drying temperature and reactor size have much less impact. The produced materials have densities with values between 1.67 and 1.77 g/cm 3 and showed favorable porosity and water absorption characteristics. These results provide a solid foundation for future research aimed at developing advanced zeopolymer materials through hydrothermal treatments with optimized processing variables.