Synthesis of zeolite from waste fly ash for adsorption of CO2

Zeolitic sorbents for CO2 adsorption were prepared from waste coal fly ash (FA) through hydrothermal treatment at various ratios of NaOH/FA and NaAlO2/FA, including an initial alkali fusion step. The fusion step decomposed the fly ash into very small amorphous particulate zeolite forms. The fly ash was converted to Na-P1 type with a NaOH/FA ratio of 0.5 and Na-A type with a NaAlO2/FA ratio of 0.53. The product properties were affected by the reaction temperature: Na-P1 and Na-A types were formed at 100°C. Temperatures above 140°C led to the formation of more sodalite because of the redissolving and recrystallization of zeolite crystals. Alkali metal and alkaline earth metal cations were impregnated in the synthesized Na-P1 and Na-A zeolite through an ion-exchange method. The completed zeolitic sorbents were applied to the adsorption of low-level CO2. As a result of the experiments, calcium ions were found to be the best for CO2 adsorption owing to their electrostatic behavior and acid-base interaction.