การสังเคราะห์จีโอพอลิเมอร์/ซีโอไลต์จากเถ้าถ่านหินและดินเกาลินเผาสำหรับการดูดซับสีย้อม

Abstract

This research paper investigated the synthesis of geopolymer/zeolite composites using lignite fly ash and calcined kaolinitic clay as main starting materials with combined reactions of geopolymerization and zeolitization under hydrothermal treatment. The initial molar ratios of SiO2/Al2O3 were designed in the range of 3.0-8.0 using different hydrothermal alkalinities, hydrothermal temperature and time, and specimen preparation type in hydrothermal system. With low SiO2/Al2O3 molar ratios (3.0-4.0) at 70C for 24 and 48 hours under hydrothermal treatment using DI water, SiO2/Al2O3 molar ratio at 3.0 using fly ash, provided sodalite and hydrogarnet as main phases incorporating with carbonate compounds such as pirssonite, calcite and thermonatrite (Na2CO3H2O) as minor phases that can lower compressive strength of the hardened material. Sodalite was disappeared when SiO2/Al2O3 molar ratio of 4.0 and reacting temperature and time at 70C and 48 hours, respectively were used in the synthesis. Sodalite was also promoted with uses of 1.0 M NaOH solution and 100C hydrothermal temperature together with a development of geopolymeric matrix resulting in a strong structure. Zeolite P was formed at SiO2/Al2O3 molar ratios of 5.0-8.0. Sample preparation in a powdery form provided the larger content of zeolite P than bulk sample. SiO2/Al2O3 molar ratio of 8.0 possessed analcime incorporating with zeolite P and geopolymeric gel. With an increase in curing time to 144 hours (6 days) at the constant SiO2/Al2O3 molar ratio of 6.0, the highest of porosity and high specific surface area (SBET100.22 g/cm3) could be obtained with a combination of isotherms as Type-I and Type-IV shapes. When compared to sample cured at 48 hours, Type-II isotherm, so called “non-porous characteristic” due to the abundant geopolymeric gel over the zeolitic material. Moreover, substitution of calcined clay in the range of 5-100 wt%, various kinds of zeolites such as zeolite Y, Na-X and P could be obtained at 25 wt% substitution. On the other hand, an increase in calcined clay in the range of 50-100 wt% provided zeolite P and analcime due to higher content of alumina that favored the formation of analcime. In addition, the prepared geopolymer/zeolite composite with SiO2/Al2O3 molar ratio of 6.0 in both powdery and bulk forms could adsorb MO dye that the fitted with Freundlich sorption isotherm as multilayer physical adsorption considered from E value of D-R (1.05 kJ/mol).