Characteristics of Brazilian coal fly ashes and their synthesized zeolites

Abstract

Five different Brazilian fly ashes were used to synthesize zeolites by hydrothermal treatment. Raw fly ash materials and zeolitic products were characterized in terms of pH, conductivity, real density (Helium Pycnometry), specific surface area (BET method), morphological analysis (SEM), chemical composition (XRF), mineralogical composition (XRD) and cation exchange capacity (CEC). Humidity and loss of ignition (LOI) of the fly ashes were also evaluated. Results indicated that the fly ash sample from Figueira power plant (FG) has a high content of Pb. The fly ash from São Jerônimo power plant (SJ) presents a higher content of unburned carbon. Chemical composition analyses indicate that the content of SiO2 and Al2O3 is above 70 wt.% in all fly ashes. After hydrothermal treatment, various zeolites such as hydroxy-sodalite, NaP1 and X zeolites were formed depending on sourced fly ash. Hydroxy-sodalite zeolite was formed in all samples. NaP1 zeolite was formed in fly ashes with high content of Ca while X zeolite was formed from the fly ashes with high content of Al. CEC values of the zeolitic materials are 40 times higher than fly ash samples, potential for use as ion exchangers.