Advancing waste-derived feedstocks valorization and cleaner coal utilization: A critical review of co-gasification synergistic mechanisms, process optimization, multiscale modeling, and prospects

Coal and waste-derived feedstocks co-gasification is a promising strategy for waste valorization and cleaner coal utilization by integrating the high energy density and process stability of coal with the high volatile content, reactivity, and inherent mineral catalytic components of waste-derived feedstocks. This review critically summarizes recent progress in coal and waste-derived feedstocks co-gasification, focusing on feedstock complementarity, synergistic mechanisms, key operating parameters, alkali and alkaline earth metals (AAEM) behavior, reactor type, and multiscale modeling approaches. The analysis shows that co-gasification performance is not a simple linear combination of individual feedstocks. Both synergistic and inhibitory effects have been reported, indicating that synergy is a conditional phenomenon governed by feedstock composition, AAEM availability, K–Si–Al interactions, Ca competitive reactions, temperature, gasifying agent, blending ratio, and reactor type. In particular, total AAEM content alone is insufficient to predict gasification behavior. The speciation, mobility, and accessibility of K, Na, and Ca, as well as their interactions with Si and Al, determine whether AAEM promote char gasification or become deactivated through stable silicate and aluminosilicate formation. Therefore, K/Si, K/Al, and Ca/(Si + Al) ratios can serve as useful indicators for interpreting the transition from catalytic promotion to mineral-induced inhibition, but they should not be regarded as universal thresholds. This review also discusses the applicability of thermodynamic, kinetic, machine learning, and numerical simulation to different research objectives. Future research should emphasize standardized and dynamic synergy evaluation, controlled validation of mineral threshold hypotheses, direct characterization of AAEM migration and deactivation, mechanism-informed catalyst/additive design, and integrated mechanism–model–system frameworks to support scale-up and industrial application.