A KINETIC-STUDY OF THE REACTION OF ZINC-OXIDE WITH IRON-POWDER

Electric are furnace (EAF) dusts contain significant quantities of zin c, 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 b e developed to treat this waste, One possible alternative process woul d involve reacting the zinc oxide in the dust with either solid or liq uid iron. In addition, in the carbothermic reduction processes, which have been designed to treat the dust, metallic iron is formed, and thi s iron can participate in the reduction of zinc oxide. In the present research, the reduction of zinc oxide by iron according to the reactio n ZnO(s) + Fe-(s) = Zn-(g) + FeO(s) was studied using a thermogravimet ric technique. Briquettes of zinc oxide powder and electrolytic iron w ere reacted in the temperature range of 1073 to 1423 K in an argon atm osphere. First, a thermodynamic analysis was performed using the Facil ity for the Analysis of Chemical Thermodynamics (FA*C*T) computationa l system, and then the effect of experimental variables on the reactio n kinetics was determined. These variables included argon gas flow rat e, reaction temperature, reagent particle size, iron to zinc oxide rat io, aspect ratio of the briquette, briquetting pressure, and alkali an d alkaline earth additions. It was found that, initially, the reaction was chemically controlled with an activation energy of 230 kJ/mol. Ad ditions, such as sodium chloride and calcium fluoride, promoted the re action, and the activation energies were 172.5 and 188.7 kJ/mol, respe ctively. Once a product layer had formed, the reaction was limited by the diffusion of zinc gas away from the reaction interface. The experi mental data were fitted to a parabolic rate law, and the parabolic rat e constant was found to be k(p) = -2.47 + 0.0021 T (K)