Electrochemically enhanced reduction of iron oxide from slag

Abstract

An experimental study was performed to measure the rate of reduction of iron oxide from calcia-silica-alumina slag by carbon in iron, and to determine whether the reaction rate can be increased by electrochemical means. It is shown that the reaction rate depends on both the ferric-ferrous cation ratio, and on the total amount of iron in the slag. It was observed that ferric cations are reduced at a faster rate than ferrous cations. This suggests that the overall reaction rate is limited by the rate of the ferric-to-ferrous reduction reaction when the slag contains significant quantities of ferric oxide. Results show that the rate constant decreases at low concentrations of ferrous oxide in the slag. It is concluded that mass transfer in the slag phase controls the overall reaction rate when the slag contains mainly ferrous oxide. Experiments were conducted in an attempt to increase the reaction rate by electrochemical means. The reaction rate was increased by penetrating the slag layer with a metallic rod or plate; this provided an electronic pathway from the metal bath into the bulk slag phase. A small short-circuit current was measured. In order to increase the current, a voltage was applied between the metal bath and an electrode that made electrical contact with the top of the slag layer. The reaction rate increased by 60-100%, and the increase was proportional to the current passed. A current efficiency of nearly 100% was observed for current densities on the order of 500 mA cm-2. The results of this study have been modeled with a new expression for the reaction rate: ... The rate constant k, is the chemical rate constant for the ferric-to-ferrous reduction reaction, and k2 is the mass transfer coefficient for ferrous cations in the slag; numerical values for the constants k, and k2 are offered for certain experimental conditions.