Chlorination Kinetics of ZnFe₂O₄ with Ar-Cl₂-O₂ Gas

Abstract

Chlorination rate of ZnFe₂O₄ with Ar-Cl₂-O₂ gas was measured at 1023 to 1123 K by gravimetry. The effects of temperature, partial pressures of chlorine and oxygen on the rate were investigated. Zinc oxide contained in ZnFe₂O₄ specimen was selectively chlorinated and evaporated in gas, while iron oxide remained as oxide in a chlorinated residue. Chlorination rate increased with increasing partial pressure of chlorine. On the other hand, chlorination rate slightly decreased with increasing partial pressure of oxygen and chlorination of iron oxide was prevented. Since the order of chlorination rate with respect to partial pressure of chlorine was approximately 0.5, the rate-determining step of chlorination is considered to be the dissociative adsorption of chlorine gas on the surface of solid ZnFe₂O₄. Decrease of chlorination rate with the increase of partial pressure of oxygen could be explained by the occupation of adsorption sites of chlorine atoms by oxygen and the chlorination rate was expressed as functions of partial pressures of chlorine and oxygen as r=k·(P_Cl₂^1/2/1+K_OP_O₂^1/2) The activation energy of chlorination was 35.1±2.2 kJ/mol which is relatively small compared to that of ZnO chlorination reaction (58.2 kJ/mol). It is considered that this low activation energy is due to the weak adsorption of chlorine atom on the adsorption site.