Oxidation mechanism and non-isothermal kinetic studies on carbonate iron ore by thermogravimetric analysis

Abstract

Due to the uncertain and heterogeneous compositions of carbonate iron ore after magnetization roasting, an oxidation pretreatment was applied to increase the uniformity of the composition of the ore. The oxidation of carbonate iron ore was characterized using a thermogravimetric method over a temperature range of 723–948 K. It is shown that the oxidation process of carbonate iron ore is complicated and consists of multiple reactions that include the decomposition and oxidation of carbonates such as FeCO3, MnCO3, MgCO3 and CaMg(CO3)2. The main product that results from oxidation is Fe2O3. Because of the low content of other carbonates (MnCO3, MgCO3 and CaMg(CO3)2) in raw carbonate iron ore and the small change in the apparent activation energies during oxidation, the oxidation of carbonate iron ore can be treated as a single-step FeCO3 oxidation reaction. Based on the Ozawa–Flynn–Wall method, which is one of the model-free methods, the apparent activation energy for the oxidation of carbonate iron ore is 284.50 kJ mol−1. The most probable reaction model for the oxidation of carbonate iron ore is the Sestak–Berggren model as determined by the theoretical and actual master plot and eigenvalues of the Malek method. The reaction orders n and m are 1.317 and 0.0295, respectively. The pre-exponential factor is 2.628 × 1017 min−1.