Kinetic Analysis of Isothermal Decomposition Process of Zinc Leach Residue in an Inert Atmosphere. The Estimation of the Apparent Activation Energy Distribution

Abstract

Thermal decomposition of zinc leach residue has been studied in a tubular furnace under a constant nitrogen gas flowing, at four different operating temperatures (600°C, 750°C, 950°C, and 1150°C). Using a detailed kinetic analysis, it was shown that the investigated process can be described by a two-parameter autocatalytic Šesták–Berggren reaction model. It was noted that the apparent activation energy values E_a increase progressively with a degree of conversion, accompanied by the appearance of a convex Arrhenius dependence. This behavior is a characteristic of a system of parallel competing reactions. It was concluded that the investigated isothermal decomposition process is characterized by unusually very low preexponential factor and low values of the apparent activation energy. Based on the derived density distribution function of E_a values, it was concluded that the isothermal decomposition process probably occurs through four reaction steps, where each step is characterized by one parallel reaction.

Keywords:

• agglomeration
• furnaces
• hydrothermal processing
• mathematical modeling
• reduction
• zinc

ACKNOWLEDGMENTS

The authors would like to thank Deutsche Forschungsgemeinschaft DFG in Bonn for financial support of the project FR 1713/13-1: Zn-recovery from steel making dusts—Kinetics and mechanism of thermal zinc–ferrite phase decomposition (Srećko Stopić, Aybars Güven, and Bernd Friedrich).

The authors would also like to thank the Ministry of Science and Environmental Protection of Serbia under the Project 172015 (Bojan Janković).

Notes

^a The global reaction order.

^b Adj. R-square.

^c Residual sum of squares (RSS).