Universal Kinetics of the Thermal Decomposition of Synthetic Smithsonite over Different Atmospheric Conditions
Nobuyoshi Koga, Yasuhiro Sakai, Masahiro Fukuda, Daichi Hara, Yuu Tanaka, Loïc Favergeon
Abstract
The thermal decomposition of smithsonite (ZnCO3) was studied to obtain a universal kinetic description of the process applicable to a range of reaction conditions. A synthesized ZnCO3 was subjected to thermoanalytical measurements under various heating and atmospheric conditions in a flow of dry N2 gas, or N2–CO2 or N2–H2O mixed gases. Systematic shifts of the reaction temperature to higher or lower values by the effects of CO2 or H2O, respectively, were identified as specific characteristics of the system. With reference to the physicogeometrical kinetic behavior of the reaction in a flow of dry N2 gas, the retardation effect of CO2 was demonstrated in the scheme of the physicogeometrical consecutive surface reaction (SR) and phase boundary-controlled reaction (PBR). The individual kinetics of SR and PBR were universally described over different CO2 partial pressures using an accommodation function (AF) obtained by considering the consecutive elementary steps of SR and PBR. The catalytic effect of water vapor was assumed to result from contributions of water molecules to the consecutive elementary steps of SR and to the crystal growth of the solid product of the reaction (ZnO). An alternative AF derived considering the adsorption of water molecules on solid surfaces allowed us to obtain the universal kinetic description of the thermal decomposition over different water vapor pressures.