Review on coal gasification slag (CGS) for green cemented backfill in mines: activation method, performance influencing mechanism and environmental benefit

The large amount of CGS stored on the ground poses unknown environmental risks, underground green cemented backfill provides a potential way for the large-scale harmless disposal of CGS. This article reviews CGS as a cemented backfill material from activation methods, performance influencing mechanisms, and environmental benefits, demonstrating its considerable application potential for green backfilling in mines. The activation methods of CGS include physical activation, chemical activation, thermal activation, and synergistic activation, and their activation mechanisms, influencing factors, process equipment, etc. are introduced. Various activation methods have an "impossible triangle" effect in terms of activation effectiveness, cost, and environmental impact. The influence of CGS on the performance of backfill materials is mainly attributed to its own properties and composition, including particle size effect, microstructure, and potential activity. The leaching concentration of most heavy metals in CGS-based backfill materials is lower than that of the original CGS, which is attributed to the solidification/stabilization mechanisms of heavy metals, including chemical precipitation, ion exchange, physical adsorption, and encapsulation. The other component materials, additives, external water environment and curing time also have a significant effect on the performance and leachability of CGS-based backfill materials. Activated CGS substitution for cementitious materials in backfill materials can significantly reduce carbon emissions and costs. CGS-based backfill materials have good carbon sequestration capacity, and CO2 sequestration can also affect the performance of backfill materials. This review provides guidance for the engineering application of green cemented backfill with CGS in underground mines.