Editorial for special issue "Coal fly ash as a resource : advances in characterization, utilization and sustainable solutions"

Abstract

Coal fly ash (CFA), the fine particulate by-product of coal combustion in thermal power plants, has traditionally been regarded as an environmental liability. Its large volumes, heterogeneous composition, and potential for trace metal release have posed persistent challenges related to disposal, land use, and long-term environmental management. Increasingly, however, this perception is shifting. Rather than being viewed solely as waste, CFA is now recognized as a secondary resource rich in reactive mineral phases and valuable elements suitable for industrial and environmental applications. This evolving perspective aligns closely with the principle of the circular economy, in which materials once destined for disposal are redirected into productive value chains, thereby reducing environmental burdens while conserving primary raw materials. Within this context, the present Special Issue was conceived to consolidate recent advances that deepen our understanding of CFA properties while showcasing innovative strategies for its beneficiation, functionalization, and utilization across diverse sectors. Emphasis has been placed on rigorous characterization, novel processing routes, and practical demonstrations of application pathways capable of transforming CFA into high-value products. Between 2024 and 2026, five contributions were assembled that collectively fulfill these objectives. Although differing in technical focus and application domain, all studies share a common theme: the systematic integration of detailed physicochemical and mineralogical characterization with targeted performance outcomes. Together, they demonstrate how fundamental understanding enables the rational and sustainable design of value-added uses for CFA.