Heavy metal migration, conversion and control technology in the preparation of coal gasification slag-based carbon-silicon composites

As the main solid waste in the coal conversion process, coal gasification slag is the key challenge for the sustainable development of our country’s modern coal chemical industry under the background of "double carbon". This study focuses on the technical route of high value-added carbon-silicon composites in the preparation of coal gasification slag, and systematically reviews the migration and transformation behaviors of heavy metals and their environmental risk control strategies in the process of preparing carbon-silicon composites from coal gasification slag, aiming to realize the resource utilization of coal gasification slag with “pollution reduction, carbon reduction and synergy”. Firstly, the mineral composition, pore structure and occurrence characteristics of heavy metals (such as Cd, Pb, Zn, etc.) of coal gasification slag are clarified, and it is pointed out that the mineral composition of coal gasification slag is complex, the pore structure is developed, and the highly active heavy metals enriched in fine slag are mainly in the non-residual state, which are easy to be released in acid leaching, calcination and other processes. Secondly, this paper deeply analyzes the various methods and approaches of coal gasification slag to prepare carbon-silicon composites, compares the three resource paths of landfill, building material utilization and composite material preparation, and emphasizes the application advantages of near-zero pollution and high-value component (high specific surface area and functional characteristics) of carbon-silicon composites in the fields of adsorption and catalysis. Finally, the migration mechanism of heavy metals in the preparation of carbon-silicon composites is revealed, including high-temperature volatilization (Hg and Cd enriched in fly ash), pickling to destroy mineral lattices (as acid solubility ratio increases), alkali activation releases encapsulated heavy metals (Zn, Pb redistribution), etc., in order to assess and control the potential leaching exposure risk of these heavy metals, a dynamic risk assessment framework based on continuous extraction morphology analysis (BCR) and environmental risk index method (RAC) evaluation is proposed. To track the morphological evolution and risk level changes of heavy metals, it is clear that Cd and other elements belong to medium and high risk (RAC > 30%). In the future, the analysis of multi-scale interfacial reaction mechanisms, green process innovation, full life cycle evaluation and intelligent material development should be strengthened to promote the technology from laboratory to industrial application. This innovative study systematically reveals the migration mechanism of heavy metals in specific processes, proposes dynamic evaluation and collaborative control strategies, and provides important theoretical support and technical paths for the high-value utilization and environmental safety of coal-based solid waste.