Laboratory Methods for Metal Recovery from Red Mud: Extraction Strategies and Technological Insights

Abstract

Red mud, the highly alkaline residue of the Bayer process, is generated at about 120 million t yr⁻¹ and represents both an environmental liability and a secondary resource. This study had two objectives: (i) to synthesize evidence from 162 publications on recovery routes for Fe, Al, Na, and Ti, and (ii) to demonstrate two laboratory-scale applications on a representative residue. Methods included a combined pyrometallurgical–hydrometallurgical flowsheet—carbothermic reduction smelting at 1450–1500 °C with fluxes, followed by sintering–leaching of the resulting slag—and a materials route in which red mud served as a filler in release coatings for metal molds. In smelting tests at 1450 °C, iron extraction to the metallic phase reached 88.5–91.5%, producing cast iron with 93.8 wt% Fe and 4.99 wt% C, and slags with ≤ 0.2 wt% Fe. From this Fe-depleted slag, alumina recovery by the sintering route was 69.8%, with reagent consumptions of ~309 kg Na₂CO₃, 300 kg CaO, and 282 kg NaOH per tonne of slag; sodium partitioned predominantly to sublimates and dust, indicating the need for alkali capture and recycle. In the coating application, incorporating up to 10 wt% red mud delivered densities of ~1016–1123 kg m⁻³, nominal viscosities of ~10–11 mPa·s, and ~96% sedimentation stability; higher loadings reduced stability. We conclude that integrated, site-specific flowsheets can simultaneously valorize metal values (iron to saleable metal; alumina from slag) and support direct materials uses, while scale-up success will depend on alkali management, reagent and energy intensity, and standardized performance testing. The results align with pilot-scale experience and suggest a credible pathway from laboratory data to industrial implementation.