Recovery of valuable metals from red mud with hydrometallurgical processes

The Bayer process is the most common way in global alumina production. During the process, the bauxite ore is dissolved with caustic soda. A considerable part of aluminium in the ore is leached out then separated from the red mud which is considered as waste by filtration. The red mud, which constitutes at least 35% of the ore body, contains mainly iron, valuable metals such as aluminium, titanium and rare earth elements. Red mud is at the focal point of most of the works because some of the elements in residue are radioactive, the pH value is high and they require large storage areas. Recovery of metals by suitable methods can provide an alternative source of raw materials for different industrial applications, thus reducing the environmental concerns. The purpose of this study is to investigate the behaviour of metals in red mud for the recovery with hydrometallurgical processes. The composition of red mud samples taken from Seydişehir Alumina Plant has been determined by physical and chemical characterization methods. For the removal of the existing metals, hydrochloric acid and citric acid were used with different concentration, temperature and process time. For both acids, it has been determined that the leaching time does not have a significant effect on dissolution, but xiv concentration is an important parameter. While the effect of temperature is high for mineral acid leaching, it exhibits different behavior for organic acid leaching. All of the iron, 84% of titanium and 69% of aluminium in the red mud have been dissolved in 8M HCl solution at 100°C. In addition, leaching efficiencies of some rare earth elements (Sc, La, Ce, Nd, Y) have been found to maximum 8%. Leaching efficiencies of metals in citric acid have decreased as acid concentration increased. The efficiencies of aluminium and calcium at the end of 5 hours have been obtained as 59% and 53% respectively in dissolved 10 g citric acid in 50 mL distilled water. However, rare earth elements and iron leaching yields have been found to be lower than 1%. As a result of the study, the dissolution behavior of the minerals in red mud in hydrochloric acid and citric acid has been revealed. Aluminium and calcium were selectively dissolved in citric acid solution.