Determination of the kinetic triplet by an isoconversional and a regression method applied to the decomposition of mineral iron carbonate in nitrogen

Abstract

The determination of a suitable combination of reaction model f(α), activation energy Ea, and pre-exponential factor A – the kinetic triplet – is a key issue in the modeling of solid state decomposition reactions. Two complementary methods for determination of the kinetic triplet were applied and compared: (1) an isoconversional method and (2) the multi-variate nonlinear regression method proposed by Opfermann (J. Therm. Anal. Calorim. 2000). The isoconversional method was based on the evaluation of master plots y(α) and z(α) and the activation energy according to the Friedman and Kissinger-Akahira-Sunose approach. The kinetic computations were performed for the determination of the kinetic triplet of the decomposition of mineral iron carbonate in nitrogen atmosphere. The industrial practice for mineral iron carbonate beneficiation is sintering in air to convert it into Fe2O3. Thermal decomposition of mineral iron carbonate in inert nitrogen atmosphere produces FeO and Fe3O4. Consequently, the specific iron content of the solid product is increased. This is economically and environmentally advantageous, as less reducing agent is needed for iron production from FeO and Fe3O4 compared to production from Fe2O3.