The kinetics of oxidation-reduction of Hot Briquetted Iron (HEI) has been investigated in both N2 and CO2 atmospheres over the temperature range 400 to 900 degrees Celsius. The reaction rate was measured using thermogravimetric techniques and differential thermal analysis. Reactions between wustite (FeO) and carbon, which is predominantly present as cementite (Fe3C) in HBI, were detectable in nitrogen above 500 degrees Celsius. A parabolic rate law, suggested to be governed by gas diffusion, was followed in the initial stages of reaction above 700 degrees Celsius. The highest rate of decarburisation was found at 800 degrees Celsius. In a CO2 atmosphere, the degree of the HBI oxidation increased with the temperature, though simultaneous decarburisation was detectable from 700 degrees Celsius onwards. Only external oxidation was observed, with either magnetite or wustite formation, due to the relative low porosity of the HBI samples. The decarburisation predominantly occurs by reaction of pre-existing FeO with Fe3C/C. Linear oxidation were obtained between 400 and 500 degrees Celsius, whilst parabolic oxidation was observed initially at higher temperatures. At 800 degrees Celsius, a high decarburisation rate during the first 10 minutes resulted in increased metallisation of the HBI sample.
Proceedings of the 55th Electric Furnace Conference, New Orleans, Louisiana, United States, 15-18 November 1997,