A Kinetic study of the reaction of zinc oxide with iron powder

Electric arc furnace (EAF) dusts contain significant quantities of zinc, mostly in the form of zinc oxide. This dust has been classified as a hazardous waste due to the presence of lead, cadmium, and hexavalent chromium. It is important that environmentally acceptable processes be developed to treat this waste. One possible alternative process would involve reacting the zinc oxide in the dust with either solid or liquid iron. In addition, in the carbothermic reduction processes, which have been designed to treat the dust, metallic iron is formed, and this iron can participate in the reduction of zinc oxide. In the present research, the reduction of zinc oxide by iron according to the reaction $ZnO_{(s)} + Fe_{(s)} = Zn_{(g)} + FeO_{(s)} $ was studied using a thermogravimetric technique. Briquettes of zinc oxide powder and electrolytic iron were reacted in the temperature range of 1073 to 1423 K in an argon atmosphere. First, a thermodynamic analysis was performed using the Facility for the Analysis of Chemical Thermodynamics (F*A*C*T) computational system, and then the effect of experimental variables on the reaction kinetics was determined. These variables included argon gas flow rate, reaction temperature, reagent particle size, iron to zinc oxide ratio, aspect ratio of the briquette, briquetting pressure, and alkali and alkaline earth additions. It was found that, initially, the reaction was chemically controlled with an activation energy of 230 kJ/mol. Additions, such as sodium chloride and calcium fluoride, promoted the reaction, and the activation energies were 172.5 and 188.7 kJ/mol, respectively. Once a product layer had formed, the reaction was limited by the diffusion of zinc gas away from the reaction interface. The experimental data were fitted to a parabolic rate law, and the parabolic rate constant was found to be $k_p = - 2.47 + 0.0021 T(K)$