Conversion and Surface Alteration of Na-P1 Zeolite Synthesized from Coal Fly Aash by Treatment with Sub-Critical Water

Abstract

Physicochemical function of Na-P1 zeolite formed in an artificial zeolite material synthesized from coal fly ash was further modified by sub-critical water treatment. In the sub-critical water treatment, 15g of the Na-saturated artificial zeolite was mixed with 60mL of water or dilute alkali (LiOH, NaOH or KOH) solution, and heated at 200 to 300℃ for 3h. The treatment with water at 300℃ caused the conversion of Na-P1 to analcime, while the treatment with the dilute alkali solutions lowered the above conversion temperature. The degree of decrease in the conversion temperature increased in the order, KOH<LiOH<NaOH. Treatment with KOH at 200℃ did not cause the conversion of Na-P1 into analcime, but caused increase in its CEC value measured at pH=10 with index cation of 0.1 M K^+. After the treatment, FT-IR spectra of the sample showed the increase of the OH groups IR band near 3600cm^<-1>. These suggest the breaking of Si-O-Si (Al) bonds followed by the formation of Si-OH (Al-OH) groups at the surface of Na-P1 crystal.