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Impact of mechanical activation of graphite as reductant on the reduction of the iron ore containing niobium in terms of lowering the reaction temperature

For the purpose of lowering the reaction temperature, the impact of mechanical activation of graphite as reductant by ball milling on the reduction of iron ore containing niobium in terms of reaction temperature was studied by means of non-isothermal gravimetry (TG), and differential scanning calorimetry (DSC), the reduction mechanism was studied by kinetic simulation, and the thermodynamics and kinetics concerned were theoretically analyzed. Through milling, the intrinsic stratiform structure of the graphite was gradually destroyed, the resultant particles became finer, and specific surface area was increased remarkably. After a certain time for milling, the stratiform structure of the graphite was completely destroyed, the fine particles were agglomerated considerably, which hindered the further increase of the specific surface area. The impact of mechanical activation of graphite as reductant on reduction thermodynamics is the lowering of the threshold temperature for indirect reduction, while on kineics is the decrease of the apparent activation energy and increase of the rate constant, both the direct and indirect reduction were controlled by interfacial chemical reaction, which given by TG, DSC, and kinetic simulation. However, the decrease of the apparent activation energy for direct and indirect reduction ascribed to different reasons: for the former, it is the energy storage for the graphite as reactant caused by milling, for the latter, it is the improved contact of the reactants for gas-solid reaction. However, the impact on indirect reduction is more remarkable compared to that on direct reduction. The results obtained from TG, DSC and kinetic simulation conformed well to the theoretical analysis.