Experimental investigation and performance optimisation of washing cycles for pre-processing of coal fly ash

Abstract

Coal Fly Ash (CFA), a by-product of thermal power plant combustion, has a profound focus among researchers due to its pozzolanic properties, porosity, wide chemical composition, and thermal stability. While being suitable for many applications (e.g., pozzolanic material, soil stabiliser, and structural fill), CFA is also a potential precursor for synthesising zeolites, broadly used in wastewater treatment. However, pre-processing is crucial due to the heterogeneous nature of CFA. This work focused on pre-processing CFA prior to wastewater treatment through continuous washing cycles at various operating temperatures. To this end, we studied the pH and conductivity of the solution after washing over multiple cycles, Sauter mean diameter, and the mineralogy of the settled CFA. The gathered results were analysed and optimised through response surface methodology. This was done to find the best combination of the number of washing cycles and temperature to remove soluble ions and increase the surface area of CFA particles. The analytical outcome revealed that five washing cycles at 70°C were adequate, with minimal soluble ions and maximum surface area. Evidently, these findings demonstrated significant improvements in the physical and chemical properties of CFA as a precursor for zeolite synthesis. Therefore, we recommend further studies on this front to extend the effective usage of CFA for the synthesis of commercial zeolites to be used for wastewater treatment.