Abstract
The rate of MnO reduction from silicate slag melted in a graphite crucible as a reductant has been investigated by means of a thermo-balance. At small values of MnO activity aMnO, a large portion of the produced molten Mn was evaporated, and the rate of Mn evaporation was nearly equal to that of MnO reduction. In particular, at the value of aMnO less than 0.1, the reaction was of the first order in regard to aMnO, and the activation energy was 375 kJ/mol. It was supposed that the reaction at the slag-graphite interface proceeded by the direct reduction, (MnO)+C(s)=Mn(l)+CO(g).
At large values of aMnO, reduction was greatly accelerated by the presence of liquid Mn, because the following reactions occurred at the slag-metal interface:
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oindentThis finding was observed mainly in the MnO-SiO2 binary slags.
It was found that the reaction rate was markedly dependent on the wetting of slag on the graphite crucible wall. In general, with lower aMnO, the slag gave immersional wetting on the graphite, whereas with higher aMnO, it gave adhesional wetting. In the latter, the reduction rate was by 1 or 2 orders of magnitude lower than that in the former. These results were explained by the assumption that the wettability of the slag on a graphite crucible was intimately related to the formation of SiC at the slag-graphite interface.
It might be inferred that the reduction rate was controlled by chemical reactions.
