Fly Ash Derived FAU Zeolite Synthesis and Characterization

Abstract

Zeolites are expensive materials which find broad applicability as adsorbents and catalyst for a variety of industrial processes attributed to their structure with specific surface, well defined pore dimension, and chemical properties. The synthesis of zeolites from coal fly ash is widely reported and offers an opportunity to valorize wastes in such a way that creates great environmental and economic impacts. In this study the alkaline hydrothermal synthesis method was used to identify the key synthesis parameters of zeolites from fly ash and their effects on the crystallinity. The raw fly ash, obtained from Sasol Coal mining, South Africa, was used as source of alumina and silica that gave the zeolite formation. Prior to the synthesis, the ash was calcined at 850ᵒC, followed by fusion with sodium hydroxide at 550ºC, and the mixture was then dissolved with appropriate volume of deionized water and exposed to an aging step with stirring for several hours. The synthesis was optimized by varying the reaction conditions, such as the composition of starting materials, the synthesis temperature, and time which achieved a faujasite (FAU)-type zeolite with good crystallinity yield. The treated fly ash reveals good properties of Si/Al ratio, surface area, thermal stability, improved morphology, N2-adsorption, and good cationic exchange capacity characteristic of FAU zeolites. Thus, the coal fly ash-to-zeolite conversion can gain notice amongst investors due to its potential market value while assisting with solid waste management as practical way to relieve the environmental pressures of coal ash dumps which is one goal of sustainable development.