Abstract:Coal constitutes the cornerstone for safeguarding China energy security, with the coal industry providing critical support and stability for national economic operations. In recent years, the rapid development of the coal industry has resulted in substantial generation of coal-based solid wastes such as coal fly ash and gasification slag from combustion and gasification processes in coal-fired boilers and gasifiers, causing extensive wastage of land resources and severe ecological pollution. Despite massive output volumes, China resource utilization rate of coal-based solid wastes remains low. Comprehensively enhancing solid waste recycling efficiency is pivotal for cultivating new-quality productive forces in the energy sector, wherein developing economically viable and efficient carbon-ash separation technologies serves as the fundamental prerequisite. This paper systematically examines the physicochemical characteristics of two representative coal-based solid wastes coal fly ash and gasification fine slag and synthesizes current research advances in their decarbonization via flotation. Both materials exhibit fine particle sizes, averaging below 74 μm, with gasification fine slag typically finer predominantly under 45 μm. Morphologically, they comprise porous flocculent unburned carbon and spherical inorganic glass beads, coexisting in discrete, adherent, or fused forms, while hydrophilic functional groups extensively cover unburned carbon surfaces. Currently, flotation stands as one of the most cost-effective methods for carbon removal from these wastes; however, severe surface oxidation of unburned carbon, highly developed pore structures, carbon-ash fusion, and ultrafine particle size collectively constrain separation efficiency. Consequently, research predominantly focuses on developing high-efficiency compound reagents, enhancing pre-flotation pretreatment, and optimizing flotation circuits. Compared to gasification fine slag, coal fly ash achieves superior flotation efficiency with lower reagent demand. Although synergistic integration of flotation reagents, pretreatment, and process optimization has moderately improved gasification slag decarbonization, fundamental challenges persist including excessive reagent consumption, operational complexity, and suboptimal separation outcomes. Despite similar properties between coal fly ash and gasification slag, critical distinctions exist: although both feature porous carbon structures, internal pore characteristics may differ significantly; their analogous mineral compositions contrast with potentially divergent ionic environments in flotation solutions. Future research should thus investigate pore microstructure properties and solution chemistry impacts on flotation mechanisms. This review consolidates existing challenges, current research status, and future trajectories in flotation decarbonization of coal-based solid wastes, aiming to provide strategic insights for sustainable resource utilization and green development of coal-derived or other bulk industrial solid wastes.