Book Description

Solid state reduction of an Australian chromite was thermogravimetrically studies at temperatures between 1000-14000C with coals under an argon atmosphere. Temperature had the greatest influence on the reduction followed by chromite particle size and silica addition. The affect of silica on the reduction process was from a temperature of around 13000C, with the formation of a silicate slag. The initial reduction involved the nucleation of metallic iron at lattice defect sites of the chromite. This led to the formation of an iron carbide layer around the chromite. Further reduction of the iron was possible by diffusion of the ionic iron to the surface of the chromite where it was reduced through the carbide phase. A counterdiffusion of chromium and magnesium ions also occurred within the partially reduced zone of the chromite. In the presence of added silica and a temperature of 13000C, subsequent reduction of the chromium and the remaining iron were through the dissolution of these species into the slag. This mechanism resulted in a two stage reduction kinetics which was experimentally observed. The first stage was controlled by the solid state diffusion of the cations. The activation energy was 111 kJmol-1. The second stage was controlled by the dissolution process. The slag contained some chromium and trace amounts of carbon and iron. Some silicon was also reduced at 14000C. The concentrations of carbon and silicon in the alloys were inversely proportional to each other. The reductions of Cr2O3, Fe2O3, and chromite by activated carbon were through the gas phase based on the in situ measurement of the partial pressure of oxygen. The reduction of the Fe2O3 was stepwise which did not show for the Cr2O3 and the chromite systems. The product gas in the reduction of chromite was determined to be mostly of carbon monoxide.ls were.