Abstract
Abstract It is demonstrated that Bayer–hydrogarnet technology can be developed and applied to process red mud for separating important components such as Na2O, Al2O3, Ga2О3, and V2O5 and for obtaining iron oxide pigments from hydrogarnet mud, a product of autoclave leaching of red mud. The process consists of the autoclave leaching of red mud in the presence of lime to produce hydrogarnet mud (3CaO⋅Fe2O3 (Al2O3)⋅2SiO2⋅2H2O) as a low-alkaline (0.35% Na2O) precipitate and recover important components into the solution: 98.5% Na2O, 65.3% Al2O3, 55.5% Ga2О3, and 65.8% V2O5. As a result of the treatment, almost all of the alkali and most of the aluminum that were contained in the red mud return to alumina production. Further treatment of the leach solution by step precipitation and carbonation also shows that the solution can be used to recover Ga2О3 and V2O5 into a collective concentrate containing 1.58 wt % Ga2O3 and 27.3 wt % V2O5. A fine (0.17-μm) red-brown fraction (54% of the mud) is separated from the hydrogarnet mud and it can be used as an iron oxide pigment. Mössbauer spectroscopy determined the nature of the color of the fraction, which simultaneously contains iron in several oxidation states.