Kinetic modeling of thermal decomposition of zinc ferrite from neutral leach residues based on stochastic geometric model

Abstract

The stochastic geometric model was applied to kinetic modeling the complex process of thermal decomposition of zinc ferrite from neutral leach residues, at different operating temperatures (600°C, 750°C, 950°C and 1150°C). Based on functional dependence of Avrami׳s constant (n) in a function of the effective activation energy (Ea), it was found that at T>950°C, the crystallization process takes place in autocatalytic stage, under the conditions where the rate of nucleation rapidly increases. It was established that the high nucleation rate can be attributed to formation of both Zn and Fe rich regions which provide a high number of heterogeneous nucleation sites. Based on the obtained final shape of the particles, it was found a strong presence of zinc, iron (present only in the form of Fe3O4 (magnetite)), magnesium (in the form of Mg2Si2O6), and also lead oxides. Thermodynamic analysis showed that the decomposition depends on the introduction of heat, and exerts a positive value of the Gibbs free energy of activation. Such a feature was expected since the ferrite system has been submitted to a forced decomposition and volatilization reactions.