Mechanisms and Kinetics of Solid State Reduction of Titano Magnetite Ore with Methane

Abstract

Sustainable development aims to reduce energy demand and carbon footprint in all fields of industry. In this study, a new approach to decrease these has been performed. Methane, a hydrocarbon gas, has been employed as a reductant with better reducing properties than solid carbon and hydrogen separately. Reduction of a titano magnetite ore has been executed at temperature ranging from 800 to 1200 °C using methane contents between 10 and 30 vol% in the hydrogen–methane gas mixture. Due to the high carbon activity reaching up to approximately aC = 200, higher reduction degrees has been achieved at lower temperatures compared to ordinary carbothermic reductions. Kinetically, the reduction of titano magnetite ore was most likely mix controlled regardless of the methane contents used. The reduction process especially at the early stages displayed shrinking core behaviour. The calculated activation energies, based on the obtained experimental metallisation data, varied when assuming the reaction is controlled by diffusion (iron 25–28 kJ/mol, titanium: 335–355 kJ/mol) or chemical reaction rate (iron 21–25 kJ/mol, titanium 178–184 kJ/mol) indicating a likely mixed control process. Iron was fully reduced at 1000 °C after 1 h and at 1200 °C in half an hour. The calculated rate constants for metallisation of titanium, vanadium and iron varied too, i.e. Fe from 0.00454 to 0.01150. The possible reduction mechanism is presented and discussed based on the kinetics results achieved and SEM–EDS observations.