Reductive roasting of red mud with carbon and sulfuric acid dissolution of iron and aluminum: Transformation phases and leaching characteristics

A novel approach is proposed, combining pyrometallurgical and hydrometallurgical processes, to enhance the recovery of Fe and Al while effectively breaking down the mineral composition of red mud. The study delves into the roasting reduction behavior and conversion mechanism of red mud, utilizing thermodynamic analysis and conducting roasting experiments. Extensive investigations were conducted to analyze the impact of roasting temperature and time on the carbothermal reduction of red mud. The results indicate that the most favorable leaching effect of iron and aluminum from red mud was achieved after roasting at 1000 °C for 45 min. The behavior of roasted red mud during acid leaching was meticulously explored. During the roasting process, the majority of hematite in the red mud underwent reduction to wustite (FeO) and zero-valent iron, while the aluminum-bearing minerals melted and decomposed to form NaAlSiO4 and Ca2Al2SiO7, along with other substances. The formation of low-valent and independently present iron products played a role in achieving high Fe leaching efficiency. The presence of Ca and Al-containing compounds such as Ca2Al2SiO7 in the product of roasting proved difficult to leach, leading to poor Al leaching efficiency. The acid leaching process exhibited promising results, with maximum leaching efficiency of iron and aluminum reaching 95.7% and 72.5%, respectively. This success can be attributed to the control over experimental conditions, which allowed for the generation of desired iron oxides with various valence states.