Geopolymer/zeolite-P materials prepared from high-CaO fly ash, biomass ash, and metakaolin using geopolymerization with a hydrothermal process for environmental clean-up

Abstract

This study aims to synthesize geopolymer/zeolite-P (GP-ZP) materials as a building material for environmental clean-up. High-CaO fly ash (FA), biomass ash (BMA), and metakaolin (MK) are designed as starting materials to generate geopolymeric and zeolitic materials simultaneously through geopolymerization and zeolitization using hydrothermal treatment at only 100 °C. This study explores that CaO can be quarantined in the geopolymeric structure using SiO₂/Al₂O₃ molar ratios of 6.0 and 8.0 while at lower SiO₂/Al₂O₃ molar ratios, CaO tends to precipitate various calcium compounds. Various SiO₂/Al₂O₃, Na₂O/Al₂O₃, CaO/Al₂O₃, and CaO/SiO₂ molar ratios are investigated using different ratios of FA and BMA mixes to explore the geopolymeric binding characteristics and evaluate the types of zeolites formed. Unmilled and milled MK are also used to partly replace FA to improve the development of porous zeolite-P materials in geopolymeric matrix. Furthermore, the differences in the material characteristics obtained from the powdered and bulk materials are compared in terms of the mineralogical composition, surface morphology, specific surface area, and cation exchange capacity. The mechanical properties of the materials are also investigated to understand the relationship between the phase development and binding properties. Hydrothermal treatment improves the mechanical properties when the FA and BMA system is used with an SiO₂/Al₂O₃ ratio of 8.0, or when the FA, BMA, and MK system is used with an SiO₂/Al₂O₃ ratio of 6.0, showing the better development of geopolymeric gel composited with zeolite-P. The environmental clean-up capability is determined using powdered and bulk material dosages of 1.0 g and 10.0 g, respectively, to remove nearly 100 % of 20 mg/L methyl orange dye.