Kinetic study on reduction in carbon composite magnetite pellet employing thermogravimetry and quadruple mass spectrometry

Abstract

The carbothermic reduction in magnetite was investigated from a kinetic viewpoint in the temperature range of 900–1200°C employing thermogravimetric analysis and quadruple mass spectrometry. The critical temperature for the activation of carbon gasification was found to be 1055°C by non-isothermal reduction experiments. The carbon gasification reaction was activated after all the Fe₃O₄ was reduced to wüstite, i.e. at 25% reduction, and that the Fe catalysed nature of wüstite reduction to Fe was not identified before 25% reduction. The activation energy for the reduction in Fe₃O₄ to wüstite was evaluated to be 85·5 kJ mol⁻¹, and the reduction stage is believed to be limited by mixed control of Fe₃O₄ reduction and carbon gasification. From 40·7 kJ mol⁻¹ of the activation energy for the reduction in wüstite to Fe, the second half reduction stage might be limited by mixed control of wüstite reduction by CO and the gaseous diffusion. It is believed that the wüstite reduced from Fe₃O₄ has lower reactivity for the reduction to Fe compared with that originated from Fe₂O₃. In the present study, it was considered that the changeover in reaction mechanism might be carried out from mixed control of the reduction in Fe₃O₄ to wüstite and carbon gasification to the reduction in wüstite to Fe with increasing reduction.

Keywords:

• Direct reduced iron
• Isothermal reduction
• Thermogravimetric analysis
• Quadruple mass spectrometry
• Carbon gasification
• Rate controlling step