Synthesis of Zeolites by Alkaline Activation of Fly Ash

In terms of mineral transformation, and chemical composition of acid-soluble component as a function of reaction time, the effect of alkaline solution on zeolite-like fly ash was studied by employing fly ash and NaOH solution as starting materials. When fly ash and 1-10 mol/L NaOH solution were processed at 100 ℃ for 24 h with 1:10 W/S ratio in a relatively closed system, powder XRD patterns of resulting products indicated the formation of various zeolites. Zeolite P crystallized early at low alkaline concentration, which was replaced then by zeolites X and A. At high concentration, hydroxy sodalite was the only new phase. Quartz, in fly ash and NaOH solution system, gradually dissolved, and mullite, however, remained stable. It was concluded that, with Al/Si and Na/Si finally reaching equilibrium in molar ratio, composition of starting mixtures affects the crystallization of zeolite from fly ash.