Hydrogen Reduction of Red Mud for Extraction of Metallic Values

The current study investigates hydrogen reduction of red mud followed by acid leaching to recover the valuable elements. The key objective is to reduce the hematite to metallic iron and consequently distort the interlocked structure of red mud. Reduction at 450 & DEG;C results in formation of magnetite with similar to 10% Fe metallization in 30 min, and increment in the temperature to 900 oC results in 97% Fe metallization in 120 min. The metallic Fe particles possess characteristic spherical morphology. Gibbsite is dehydroxylated to alumina, and anatase (TiO2) is partially reduced to Ti2O3 above 750 & DEG;C. The H2SO4 leaching yielded higher dissolution of elements compared to HCl leaching of hydrogen-reduced product. Reduction at higher temperatures (750-900 ?) improves the dissolution of Fe and Ga but deteriorates for Sc, Al, and Ti. Sc is hosted by the anatase phase confirmed by the SEM mapping of feed/reduced products and a strong correlation between the dissolution values of Sc and Ti. Hydrogen reduction at 900 & DEG;C for 30 min with 0.5 L/min H-2 flowrate followed by H2SO4 leaching (2 M, 2 h, 80 ?) results in 90% Fe, 95% Ga, and 54% Sc dissolution. The final residue contains TiO2, Al2O3, and FeTiO3 phases with 42 wt% TiO2 having yield of 35%. The leach solution contains 7.1 ppm Sc, 15.9 ppm Ga, 1.74 g/L Al, and 11.4 g/L Fe, which can be used for Sc and Ga recovery after Fe removal. The hydrogen reduction is attractive compared to carbothermal reduction because of low temperature (600-900 ?), less reductant use (107 g H-2/kg red mud) and restricting fayalite and hercynite formation. [GRAPHICS]

Automated summary

This study focuses on the hydrogen reduction of red mud and subsequent acid leaching to recover valuable elements. The results show that reduction at 450°C for 30 minutes yields 10% metallization of magnetite, while increasing the temperature to 900°C results in 97% metallization of metallic iron. The hydrogen-reduced products at 900°C can be used for efficient extraction of iron, gallium, and scandium. Rating: 8/10