Geopolymer Synthesis from Coal Fly Ash and Slag for Immobilization of Toxic Metals in Waste Materials

Abstract

The increasing generation of industrial waste materials containing toxic metals has created significant environmental concerns related to soil contamination, groundwater pollution, and hazardous waste disposal. The present study investigates the synthesis of geopolymer materials from coal fly ash and blast furnace slag for the immobilization of toxic metals in contaminated waste matrices. The research focuses on evaluating the influence of precursor composition, alkaline activator concentration, curing conditions, and slag-to-fly ash ratio on geopolymerization behavior, mechanical strength, and metal immobilization efficiency. Experimental analysis demonstrates that the aluminosilicate-rich structure of coal fly ash combined with the calcium content of slag promotes the formation of dense geopolymeric networks capable of encapsulating and chemically binding toxic metal ions. Results indicate that optimized synthesis conditions significantly improve compressive strength, reduce porosity, and minimize heavy metal leaching from treated waste materials. The study further reveals that alkaline activation enhances dissolution and polymerization reactions, leading to stable three-dimensional geopolymer structures with improved environmental durability. Comparative assessment with conventional cement-based stabilization methods confirms that geopolymer systems provide superior immobilization performance, lower carbon emissions, and enhanced resistance to chemical degradation. In addition, the utilization of industrial byproducts such as fly ash and slag contributes to waste valorization and sustainable resource management. Long-term leaching evaluations demonstrate substantial reductions in the mobility of hazardous metals, supporting the suitability of geopolymer technology for hazardous waste containment applications.