BACKGROUND Alkaline amorphization of fly ash (FA) and crystallization of the potassium W zeolite from the resultant amorphous materials was carried out at different scales by a straightforward hydrothermal method. The experimental factors and levels were evaluated during the FA amorphization study by variation of the metallic hydroxide, concentration, temperature and time for the hydrothermal reaction. RESULTS The alkaline FA hydrothermal activation study quantified a set of optimal conditions to obtain amorphous materials easy to be recrystallized into W zeolite. The activation process at laboratory scale involved the hydrothermal treatment of 3.6 g FA with 74.43 mEq KOH dissolved in 21 mL water at 125 degrees C for 4 h. A product with <= 94.7% of the amorphous phase was obtained. The direct zeolitization of FA was performed at 175 degrees C for 16 h with a KOH:FA weight ratio of 0.33 and molar ratios of 1.64, 17.08 and 3.90 for SiO2:KOH, H2O:SiO2 and SiO2:Al2O3, respectively. An amount of dried zeolitic material c.25% higher than the weight of FA used was obtained. CONCLUSION Adsorbents formulated with the W zeolite showed higher water adsorption capacity than the commercial molecular sieves used by industry for drying wet natural gas. (c) 2019 Society of Chemical Industry