Reduction of FeO in molten slag by solid carbonaceous materials for HIsarna alternative ironmaking process

To investigate the use of biomass in the novel HIsarna technology, the reduction of FeO in the slag by chars produced from thermal coal (TC), charcoal (CC), and Bana grass char (BGC) was studied. A drop tube furnace coupled with a quadrupole mass spectrometer (DTF-QMS) was employed to study the injection of chars into pre-melted slag in the temperature range between 1450 °C and 1525 °C. The reduction rate was calculated from evolved gases and the extent of FeO reduction was confirmed by wavelength-dispersive X-ray fluorescence (WDXRF). The FeO reduction proceeds through two stages, starting with a rapid reduction, which is dependent on the carbon type, and followed by gradual leveling off. The reduction rate with the charcoal char (CC) was the highest, over 60 pct reduction was achieved in the first 500 seconds at 1500 °C, while ~ 50 and 40 pct achieved with TC and BGC chars, respectively, for the same reaction time. The kinetic analysis suggests that the first and second stages of the reaction can be described by the second-order (F2) and three-dimensional diffusion (D3) models, respectively. The apparent activation energy values for the first stage were 290, 229 and 267 kJ/mol for reactions with TC, CC and BGC chars, while 265, 369, and 282 kJ/mol were obtained for the second stage. Based on the experimental data and kinetic results, it can be concluded that the first stage is controlled by chemical reactions on the carbon surface, and the second stage is influenced by a mixed-controlling mechanism.