Rate of FeO Reduction from a CaO-SiO₂-Al₂O₃ Slag by Carbon-Saturated Iron

Abstract

Reaction rates have been measured for the reduction of FeO from a lime-silica-alumina slag over carbon-saturated iron in graphite crucibles. The initial FeO concentrations were under 5 pet in a base slag composition of 46 to 47 pet CaO, 38 to 39 pet SiO₂, 15 to 16 pet A1₂O₈.

The reaction rate was found to be proportional to about the second power of the analyzed iron content of the slag. Two rate constants were obtained for simultaneous reactions at the slag-metal and slag-graphite interfaces. Values for these constants at 1430°C (2606°F) were k₁ = 0.00058 g FeO per (min) (sq cm) (pet FeO)² at the metal and k₂ = 0.00012 (same dimensions) at the graphite. The temperature coefficient was not measured independently for the two reactions, but the net effect of a 140°C rise in temperature was small.

Iron droplets rose to the surface of the slag with gas bubbles and collected in a ring adjacent to the crucible wall in amount equal to or greater than the weight of iron calculated from FeO reduction, in those runs with both slag and metal. When only slag was present in the crucible, the iron beads were more evenly distributed over the entire crucible wall and were smaller in size and total amount.

It is not possible to deduce a reaction mechanism to interpret the observations on the basis of these experiments alone, but several alternatives have been discussed in terms of intermediate reaction products, dissociation of FeO in the slag, diffusion, nucleation of gas or metal, and surface phenomena leading to reaction through iron films on rising bubbles of CO in the slag.

The rate of reduction of FeO in the absence of sulphur is qualitatively consistent with the part that this reaction is believed to play in the desulphurization of iron by slags under similar experimental conditions.