Rate of Reduction of Chromium Oxide in Aluminate Slag by Solid Carbon

In the relation to the reduction of molten chromite ores with carbon, the rate of CrO reduction from aluminate slag melted in a graphite crucible has been studied by means of thermogravimetry under Ar atmosphere.The reduction of CrO occurs at an interface between the slag and the carbon contained chromium melt which is formed on the crucible wall after contact of the molten slag with the graphite. The rate of CrO reduction is represented by the first-order-type rate equation. The reduction of CrO by solid carbon is a slow reaction, and the rate constant ranges from 10−4 to 10−3 kg/m2s at 1893 K. The constant increases with increasing cao/Al2O3 ratio. In some slags, the temperature dependence of the rate constant at lower temperatures is larger than that at higher temperatures. The reduction rate of CrO is affected by the geometry of the graphite crucible as a reductant. It is considered that the area of the slag in contact with the graphite depends strongly on the foaming of the slag in the early stage of the reduction. At low concentrations of CrO, the reduction is controlled by chemical processes.