Mineralogy-guided two-stage sustainable dealkalization separation from red mud via staged classification and recyclable acetic-acid leaching

Herein, we develop a mineralogy-guided, two-stage dealkalization of red mud that integrates low-temperature fractionation with recyclable acetic-acid leaching. Automated mineral mapping shows most Na is hosted by sodalite/zeolite-type aluminosilicates that preferentially accumulate in <30 μm fines. Thermal classification at 90 °C selectively concentrates Na in the ultrafine stream to 8.1 wt% Na₂O (∼1.5× over the feed), enabling fraction-specific treatment. Mild acetic-acid leaching removes 69.23 %, 88.31 %, and 63.22 % of alkali from coarse, medium, and fine fractions, respectively, delivering >65 % overall Na elimination while using a weak, recyclable acid. Synthetic analogs clarify phase-specific mechanisms: kaolinite evolves along zeolite → sodalite → cancrinite at 240 °C (up to 26.5 wt% Na₂O), anatase forms amorphous sodium titanate (>22 wt% Na₂O), and Fe-oxides carry predominantly surface Na that is water-washable. Dealkalization remains <50 % for Si[sbnd]Ti phases, and cancrinite is notably acid-resistant but amenable to carbothermal conversion. By aligning mineral hosts with process levers under mild conditions, this work advances a practical, closed-loop route for red-mud upcycling and more circular alumina production. The flowsheet thus couples source partitioning (fractionation) with reactive separation (weak-acid leaching) to deliver separations-grade Na removal and solid-product upgrading suitable for downstream purification.