Organic–Inorganic Interactions Governing Long-Term Cd Immobilization in Cement Systems Incorporating Agricultural and Metallurgical Solid Wastes: A Critical Review

Cadmium (Cd) is recognized as a toxic element with environmental hazards and is frequently concentrated in agricultural and metallurgical solid wastes (AgSW and MetSW). Incorporating these wastes into cement is a primary route for resource recovery. Although Cd immobilization in cement systems containing AgSW-MetSW has been examined, its mechanisms, assessment methods, and long-term stability have not been systematically synthesized from an organic–inorganic interaction perspective. This review details physicochemical characteristics and Cd occurrence forms of AgSW and MetSW, and critically evaluates Cd leaching, microstructural methods, and long-term stability. Furthermore, multidimensional immobilization pathways in AgSW-MetSW cement systems are elucidated, including physical sequestration, chemical bonding, and synergistic fixation, which exhibit significantly enhanced Cd leaching reduction in hybrid systems. The long-term stability of Cd immobilization is governed by the balance between organic matter properties and inorganic alkalinity, which determines the reaction pathways and final Cd speciation. Organic matter can immobilize Cd via complexation and pore refinement or mobilize it through soluble complexes and degradation, depending on its properties and chemical environment. Based on these findings, future priorities should include standardized leaching evaluation, in situ speciation monitoring, durability prediction under combined actions, and life-cycle cost assessment for harmless utilization of Cd.