A Kinetic Study of the Carbothermic Reduction of Zinc Oxide with Various Additives

Abstract

Most processes for recovering zinc from electric arc furnace (EAF) dust employ carbon as a reducing agent for zinc oxide in the dust. In the present work, the reduction reaction of zinc oxide with carbon in the presence of various additives was kinetically studied. The effects of temperature and the additives of Fe2O3, mill scale, and CaCO3 on the kinetics of the reduction reaction were measured in the temperature range of 1173–1373 K under nitrogen atmosphere. The mill scale is one of byproducts generated from the steel rolling process. It was found from the experimental results that all three additives enhance the reaction rate of zinc oxide with carbon, but the effect of CaCO3 addition is the highest. The increase in the reaction rate is because Fe2O3, mill scale, and CaCO3 in the reduction reaction promote the carbon gasification reaction. The spherical shrinking core model for a surface chemical reaction control was also found to be useful in describing the kinetics of the reaction, which had an activation energy of 224 kJ/mol (53 kcal/mol) for ZnO-C reaction system, 175 kJ/mol (42 kcal/mol) for ZnO-Fe2O3-C reaction system, 184 kJ/mol (44 kcal/mol) for ZnO-mill scale-C reaction system, and 161 kJ/mol (39 kcal/mol) for ZnO-CaCO3-C reaction system.