Smart- and Zero-Energy Utilization of Coal Ash from Thermal Power Plants in the Context of Circular Economy and Related to Soil Recovery

This study is focused on a technologically viable and zero-energy green synthesis of zeolite Na-X by aging fly ash from lignite coal (CFA) in alkaline solutions at ambient conditions resembling a quasi-natural crystallization process. The smart utilization of CFA instead of its disposal will contribute to reducing landfill areas and to the recovery of polluted soils. The obtained coal ash zeolites were characterized by X-ray diffraction, scanning electron microscopy (SEM), and N2 physisorption regarding their phase composition morphology and surface properties, respectively. The highest yield of zeolite Na-X was achieved by incubating CFA in 1.5 mol/L NaOH for 1 year. However, significant crystallization extent was established after 8 months of alkaline aging. Coal fly ash zeolites (CFAZs) obtained by atmospheric crystallization have specific surface values up to 280 m2/g CFAZ, which make them suitable amendments to uptake contaminants from polluted soils and ground waters. Examples on the retaining ability of CFAZ for methylene blue as a model dye and of Cd2+ ions were provided.