Synthesis of zeolites from Brazilian coal ash and its application in SO2 adsorption

Coal ash is a waste generated in large quantities in the power plants. Interestingly, ashes can be used for the synthesis of zeolites. In this work, the synthesis of zeolites from fly ash and its application for gas desulfurization was studied. The synthesis was performed by the hydrothermal method using an alkaline solution of KOH. The variables temperature (373 and 423 K), alkaline solution concentration (3 and 5 mol L−1) and reaction time (8, 24, 48 and 72 h) were studied. The materials were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), specific surface area (BET) and cation exchange capacity (CEC). It was possible to identify the formation of the merlinoite and perlialite zeolites for some of the investigated conditions. The highest BET surface area (102.4 m2 g−1) was obtained under the synthesis conditions of 423 K, 5 mol L−1 and 72 h. The CEC values varied between 0.7 and 2.0 meq NH4+ g−1. Desulfurization tests were carried out for the samples that showed the most interesting properties. For comparison, adsorption tests on the precursor ash, activated carbon and commercial zeolite were also conducted. The zeolites synthesized from ash showed higher values of maximum adsorption.