Chlorination kinetics of ZnO with Ar-Cl2-O2 gas and the effect of oxychloride formation

Abstract

The chlorination rate of ZnO with Ar-Cl 2 -O 2 gas was measured from 1023 K to 1273 K and the effects of temperature and partial pressures of chlorine and oxygen were investigated. The ratedetermining step of chlorination was considered to be the dissociation of intermediate between ZnO and Cl 2 from linear relationship between reciprocal values of reaction rate and partial pressure of chlorine. The activation energy of chlorination was 58.2 6 2.5 kJ/mol. This comparatively low activation energy as a chemically controlled reaction was consistent with estimated rate-determining step of the dissociation of unstable compound. Increasing the partial pressure of oxygen slightly increased the chlorination rate, and this effect is considered to be caused by the increase in the formation rate of zinc oxychloride. To clarify the formation of zinc oxychloride, the equilibrium between Ar-Cl 2 -O 2 gas and ZnO was investigated by the transpiration method at 1073 K. Calculated partial pressures of ZnOCl from experimental results were in the same order with or one order of magnitude larger than those estimated from reported Gibbs energy of formation of ZnOCl. Zinc oxychloride formation in ZnO chlorination must be taken into consideration as well as ZnCl 2 and Zn 2 Cl 4 formation.

Chlorination and Evaporation Behaviors of PbO-PbCl2 System in Ar-Cl2-O2 Atmosphere

“…8. Chlorination rate of ZnO measured in the same condition 28) was also shown in this figure. PbO chlorination rate was somewhat larger than ZnO chlorination rate.…”

“…The demonstrated relationships between logarithmic values of apparent chlorination and evaporation rates, and reciprocal temperature were linear, which indicate that activities of PbO and PbCl 2 for the PbO-PbCl 2 melts in the steady state are almost the same from 1 023 to 1 123 K. The apparent activation energies of chlorination and evaporation rates were obtained to be 35 kJ/mol and 156 kJ/mol, respectively. Present authors reported the activation energy of ZnO chlorination as 58 kJ/mol 28) and that of evaporation rate of ZnCl 2 from FeCl 2 -ZnCl 2 and PbCl 2 -ZnCl 2 as 180 kJ/mol 29) and 200 kJ/mol, 30) respectively. The rate determining step of present chlorination-evaporation process for PbO-PbCl 2 system is not clear yet and the present system is not chloride but oxychloride melt.…”

Chlorination Kinetics of ZnFe<SUB>2</SUB>O<SUB>4</SUB> with Ar-Cl<SUB>2</SUB>-O<SUB>2</SUB> Gas

“…In this figure, chlorination rate of ZnO measured in the same experimental condition 21) was shown. The chlorination rate of ZnO slightly increased with increasing oxygen partial pressure which is different from the case of ZnFe 2 O 4 chlorination.…”

“…A slight increase of chlorination rate of ZnO is caused by the production of gaseous zinc oxychloride together with ZnCl 2 in oxidizing atmosphere. 21,24,25) On the contrary, chlorination rate of ZnFe 2 O 4 decreases due to the occupation of reaction sites by oxygen atom and the interference of the adsorption of chlorine atom as well as production of ZnCl 2 . Figure 16 shows the temperature dependence of chlorination rate constant obtained by eq.…”

Kinetics of Zn Removal from ZnO–Fe2O3–CaCl2 System

“…Various new selective chlorination and evaporation processes have been proposed. [8][9][10][11][12][13][14][15][16][17][18][19] The Cl 2 gas was used as the chlorination resource in these investigations. However, CaCl 2 is a more selective chlorinating agent for volatilizing Zn, Pb and so on.…”