Reduction of ferrous oxide from smelting slags by solid carbon

The reduction of CaO-SiO;The effect of the form of the carbon was studied by using graphite, coke and coal char as the reductant. No significant difference in the reaction rate, at similar FeO contents was found in spite of the considerable difference in the surface structure and interfacial reaction area. This indicated that the gas-carbon reaction was not a limiting step to the overall reduction reaction.;The reaction was observed continuously using the X-ray fluoroscopy technique. After the reaction was initiated, the slag was observed to foam and a gas film separated the solid carbon from the slag. Bubbles of two different size ranges were observed. The smaller bubbles, a few mm in diameter, stabilised the foamed slag. Larger bubbles, 1-2 cm in diameter, grew from the gas film, detached and travelled through the slag without disturbing the foam.;The rates of the slag-gas reaction and the gas-carbon reaction were estimated using rate constants taken from published literature. A comparison between the measured rates indicated that mass transfer of FeO in the slag and the slag-gas reaction together were limiting the reduction reaction. A mixed control model considering the above two steps was used to analyse the experimental results. It was possible to characterise the mass transfer coefficient in terms of the contribution from rotation and gas evolution. The measured reaction rates were in agreement with the published results for experiments done under similar conditions.;The reaction rate was measured under conditions where the mass transfer conditions in the slag phase were defined. This was done by using a rotating carbon rod in slag contained in an alumina crucible. Rotation of the carbon rod was found to increase the reaction rate. This implies that mass transfer of FeO in the slag is one of the rate limiting steps to the reduction reaction. The reaction rate was also found to increase with the FeO content of the slag and the variation did not take place in a linear manner. This was due to the effect of the gas evolution rate, which is a consequence of the reaction, on mass transfer.