Effects of CaO/CaCO₃ on the Carbothermic Reduction of Titanomagnetite Ores

Effects of CaO/CaCO₃ on the carbothermic reduction of titanomagnetite (TTM) ores were investigated from a kinetic viewpoint in the temperature range of 1273 K to 1423 K (1000 °C to 1150 °C) by employing thermogravimetric analysis (TGA) and quadruple mass spectrometry (QMS). The method of evaluating the reduction progress of TTM and char by TGA was compared with that calculated using the oxygen amount combined with Fe in the reduced TTM. Improved reducibility of TTM by adding CaO was explained by the variation of rates of reduction and gasification which was evaluated using QMS data. The activation energy for the carbothermic reduction of TTM was greatly decreased by adding CaO, which is ascribed to the formation of CaO·SiO₂ improving the reducibility of TTM. The activation energy for the carbothermic reduction of TTM containing CaCO₃ was further decreased, which is due to the activation of char gasification by CO₂ supplied from CaCO₃ in addition to the contribution of CaO to the increase of TTM reducibility. It is believed that the admixing of CaO/CaCO₃ to TTM would play a predominant role in controlling the reduction rate and the final metallization degree of TTM in direct reduction processes.