Experimental synthesis of zeolites from pre-processed coal fly ash using the microwave irradiation method

Abstract

Coal power plants contribute by an excess of 40% to the generation of electricity worldwide. Coal fly ash (CFA), being a dominating by-product of coal power generation, is unique due to its physicochemical properties such as thermal stability, chemical inertness, compressive strength, and adsorption. However, reducing the inherent impurities of CFA, which is heterogeneous, has proven to enhance its ability to be valorised into different second-generation products of high value. Pre-processing has been a successful method in eliminating impurities of CFA, and washing cycles method is the preprocessing technique used in this study. Zeolites, a second-generation product from CFA, are well known for their excellent adsorption properties due to their high surface area and porosity, being an optimal solution for wastewater treatment. Also, the microwave irradiation method has proven to be useful and rapid in synthesising zeolites. This study investigates the effect of pre-processed CFA obtained through optimised utilisation of wash cycles, compared to raw CFA, and the feasible conditions of zeolite synthesis from CFA which have undergone the wash cycle preprocessing technique. NaOH concentration and microwave irradiation power were considered as key parameters. X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS) were utilised to verify the enhanced nature of CFA after pre-processing, and formation of zeolites. The results of XRD infer that Mullite (Al4+2xSi2-2xO10-x) is the major crystal match for CFA obtained from the site. Also, pre-processed CFA yields a better qualitative phase analysis with Mullite than raw CFA, with the former having a peak coverage of Mullite that is approximately three-fold than the latter. Furthermore, according to the experimental results, zeolite L and zeolite Na-Y were produced from the process, having an optimal NaOH concentration of 2.5M and microwave irradiation power of 300W. These findings have been corroborated using XRD and SEM with EDS analyses, and we recommend further extension of the frontier to check the viability of zeolite formation with other critical parameters, paving way to an effective treatment of wastewater.