Smelting reduction mechanism of Fe-O-S melts using solid carbon

Abstract

The reduction of iron oxide in Fe-O-S melts by solid carbon was investigated to determine the reduction rate of iron oxide and to elucidate the reduction mechanism. The solid iron product deposits at the carbon surface, and grows towards the melt. On immersion of a graphite rod into the melt, the reduction rate reaches a maximum value and continues to stay at the value for some length of time, and then exhibits a gradual fall, followed by a constant residual rate. The temperature dependence of the rate is well represented by the Arrhenius equation, and the activation energy is 190 kJ mol-1 for 53.4 wt% FeO. The maximum rate shows a first order dependence on the FeO concentration, and is directly proportional to the geometric interfacial area between the graphite and the melt. Agitation of the melt hardly affects the rate of reduction. Solid iron produced at the graphite surface is very low in carbon, showing a ferritic structure. It is concluded that the reduction is controlled by the chemical reaction at the interface. The electrochemical reactions Fe2+ + 2e- = Fe(s) and O2- + C(s) = CO(g) + 2e- take place and are responsible for the major portion of the reduction reaction until the carbon surface has been fully covered by the product iron. The dissolution rate of carbon from the graphite rod into the product iron is much slower than either the diffusion rate of carbon in the iron or the reaction rate of iron oxide by carbon diffused in the iron. This results in the product iron being very low in carbon and ferritic in structure.