Towards Sustainable Utilization: A Review on Red Mud-Based Cementitious Systems from the “Earth’s Macro-Cycle” Perspective

Driven by the urgent need for large-scale disposal and resource valorization of bauxite residue (red mud), this review adopts a narrative review perspective, grounded in the Earth’s Macro-Cycle concept, and employs a structured yet non-systematic literature survey across multiple databases (Web of Science, ScienceDirect, etc.) to compare the physicochemical property differences of red mud derived from different production processes and to establish a classification–evaluation system integrating calcium content gradient with reaction type. Building upon this framework, three distinct cementitious systems are elucidated: three-dimensional network formation via low-calcium geopolymerization, the symbiotic coexistence of C-(A)-S-H and N-A-S-H dual gels in medium- and high-calcium systems, and the integration of clinker hydration with alkali activation in high-calcium systems. Furthermore, by evaluating alkalization, heavy metal stabilization, and fluoride immobilization behaviors, we propose optimal, scenario-specific application pathways: Low-calcium geopolymer systems are ideal for the ecological or structural remediation of acid-contaminated sites, medium-to-high-calcium systems for backfilling large-scale mining voids, and high-calcium systems for the structural repair of expressways. This work bridges the gap between fundamental solid waste mineralogy and practical engineering applications, offering robust strategies for the high-value, environmentally safe, and large-scale recycling of industrial solid wastes.