Sustainable Alkali‐Activated Geopolymers From Red Mud and Ferroalloy Residues: Structure and Properties

Abstract

The growing accumulation of industrial by‐products necessitates the development of sustainable routes for their utilization in construction materials. In this study, geopolymer composites based on red mud (a Bayer process by‐product rich in alumina and iron oxides) and ferrosludge (a silica‐rich ferroalloy residue) were synthesized enabling precise control of the Si/Al ratio. Red mud exhibited high crystallinity (∼32% calcite and ∼22% magnetite) and heterogeneous micrometer‐sized particles, while ferrosludge showed amorphous silica dominance (∼85 wt% SiO2) with submicron agglomerates, confirming their chemical complementarity. XRD revealed optimal amorphous geopolymer matrix development at 80:20 ratio, with preserved crystalline fillers (e.g., magnetite) acting inertly; further ferrosludge increased Si/Al, limiting polycondensation. SEM displayed composite microstructures of spherical particles embedded in binding gel, evolving to denser matrices at higher ferrosludge. FTIR confirmed aluminosilicate gel formation via intensified Si‒O‒T bands (∼1150 cm‒1, peaking at 70:30 ratio), alongside carbonate vibrations.