Reusing leached fly ash as a cement replacement

Industrial wastes such as fly ash often have a relatively high content of valuable metals. Many waste valorisation processes are based on hydrometallurgical methods, including leaching to dissolve and recover the desired elements, but this can change the waste’s properties. If the residual waste cannot be reused after valorisation, its management and environmental costs could make the process unprofitable or unacceptable from an environmental point of view. This paper explores the possibility of reusing germanium-rich fly ash as a cement replacement in the construction industry after hydrometallurgical valorisation to recover germanium. Several properties of the fly ash were compared before and after leaching, including chemical composition, density and particle size. Different fly ash–cement mixtures were then prepared, and the pozzolanicity, volume stability/expansion and setting time of the mixtures were compared. Next, the mechanical properties of mortars made from the mixtures were determined. The mortars containing processed fly ash were not significantly different from the control mortar, proving that the reuse of valorised fly ash in the construction industry is viable.