Metakaolin; Geopolymer; Solid-to-liquid ratio; Waste catalyst; Microstructural
2. Materials and methods
The waste catalyst (51.60% SiO2, 35.30% Al2O3 and 2.39% Fe2O3) used in this study was collected from the refinery plant located in Taoyuan City, Taiwan. Raw waste catalyst was milled using chrome steel balls and it FLAG tag could pass through a 0.074 mm sieve. Sodium silicate (Na2SiO3) solution was produced in Taiwan containing 33.81% SiO2, 12.65% Na2O, 53.54% H2O, and Ms. (SiO2/Na2O) = 2.76. Sodium hydroxide (NaOH; 99%) was purchased from Acros. Metakaolin (specific gravities ∼1.66, pH value 5.74, and the diameter size less than or equal to 0.074 mm) containing 54.3% SiO2 and 42.1% Al2O3 was obtained from kaolin calcined at 650 °C for 3 h. The chemical composition of raw materials was shown in Table 1. The results showed that kaolin is mainly composed of SiO2 (54.90%) and Al2O3 (41.80%). Metakaolin is composed of 54.30% SiO2 and 42.10% Al2O3.