| dc.description.abstract | The production of metallurgical grade Al2O3 from bauxite ores is mainly done through the Bayer process. This process is well established and efficient, but it has environmental challenges, and the main being the formation of a solid residue, the Bauxite Residue (often called red mud) since its valorization is currently poor. The Pedersen process prevents the formation of any hazardous waste and it can valorize low grade bauxite ores. This method combines pyro- and hydrometallurgical techniques to produce pig iron that can be used further and a calcium aluminate slag for alumina recovery. Lack of literature regarding the smelting reduction of the Pedersen process motivated this research to examine the production of calcium aluminate slags and irons from pre-treated bauxite and other alumina-based materials. When this method was developed, the current environmental challenges were not that important. This study pursues possible options to lower the environmental impact by a gaseous pre-treatment of the bauxite ore in H2 gas before the smelting. Thermodynamic considerations were applied to support the design and the obtained results further. Characterization techniques as SEM, XRD, XRF, etc., were used for evaluating the characteristics of the raw materials and obtained products. A diasporic bauxite is pre-calcined (900°C) and reduced by H2 gas, and subsequently smelted at 1650°C with lime in the first part of this study. Stationary (SR) reactor and the possibility to use a fluidized-bed (FR) reactor are included for the isothermal gas reduction. The reduction rates of iron oxides from bauxite in H2 gas were found to be initially high, while the increase of temperature and H2 concentration in the gas enhanced the reduction to metallic iron. It was found that the formation of hercynite (FeAl2O4) at specific temperatures and flow rates occurs, and it will retard the complete reduction of iron oxides. In general, iron is completely reduced and separated from the slags after the smelting of both the reduced and calcined bauxite. Al2O3-containing phases that are considered leachable were obtained in the slags such as 5CaO.Al2O3, CaO.Al2O3 and 12CaO.7Al2O3 which are important phases for alumina recovery. The valorization of bauxite residue with CaO-containing materials was investigated via smelting-reduction in the last part of this study. It was observed that iron was reduced entirely and separated from the slags. The formation of Al2O3-containing leachable phases was enhanced by slow cooling and higher lime amounts. In general, there are possibilities to revise the Pedersen process, while the formation of slags with leachable Al2O3-containing phases were achieved with a control in the slag chemistry and smelting conditions. | en_US |
