Effects of Preheating and Alkaline Roasting on Gangue Removal During the Alkaline Hydrothermal Treatment of Low-Grade Iron Ores

This study investigated the effects of preheating and alkaline roasting on gangue removal during the alkaline hydrothermal treatment of low-grade iron ores. Such processes are a crucial aspect of addressing the challenges faced by the steelmaking industry due to the declining quality of iron ore resources. Three types of low-grade iron ores having different chemical compositions were subjected to preheating at temperatures in the range of 350 °C to 900 °C and alkaline roasting at temperatures in the range of 200 °C to 900 °C. The primary objective was to enhance the removal of impurities such as silicon (Si), aluminum (Al) and phosphorus (P) that are typically present in low-grade iron ores and can negatively impact steel properties. Preheating up to 400 °C was found to significantly improve gangue removal by increasing the porosity of the ores. This effect was particularly pronounced for lower treatment temperatures, at which the increased porosity enhanced interactions between the gangue components and the alkaline solution during hydrothermal treatment. Alkaline roasting and water washing further improved the gangue removal efficiency by converting these impurities into more soluble forms, particularly in the case of phosphorus (P). Hydrothermal treatment or water washing and alkaline hydrothermal treatment of alkaline roasted ore effectively increased the Si and Al removal efficiencies. Assessments using X-ray diffraction established that α-FeOOH in the as-received iron ores was converted to Fe₂O₃ through hydrothermal treatment or water washing combined with the alkaline hydrothermal treatment. The results of this study demonstrate that preheating and alkaline roasting not only increase the Si, Al, and P extraction efficiencies but also increase the iron content and ore density. These findings suggest that the present optimized treatment process could significantly enhance iron extraction efficiency while reducing energy consumption, lowering CO₂ emissions and decreasing production costs during steelmaking. This research should contribute to the development of innovative, energy-efficient technologies in the steel industry, ensuring resource security and environmental sustainability.