Universal Kinetics of the Thermal Decomposition of Synthetic Smithsonite over Different Atmospheric Conditions
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 N2gas, N2–CO2, or N2–H2O mixed gases. Systematic shifts of the reaction temperature to higher and lower temperatures by the effects of CO2 and H2O, respectively, were identified as specific characteristics of the system. With reference to the physico-geometrical 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 the SR and PBR were universally described over different CO2 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 the water molecules on the consecutive elementary steps of SR and on 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.
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