Oxidation kinetics of ilmenite concentrate by non-isothermal thermogravimetric analysis

Abstract

The non-isothermal oxidation experiments of ilmenite concentrate were carried out at various heating rates under air atmosphere by thermogravimetry. The oxidation kinetic model function and kinetic parameters of apparent activation energy (E_a) were evaluated by Málek and Starink methods. The results show that under air atmosphere, the oxidation process of ilmenite concentrate is composed of three stages, and the chemical reaction (G(α) = 1−(1−α)², where a is the conversion degree) plays an important role in the whole oxidation process. At the first stage (α = 0.05−0.30), the oxidation process is controlled gradually by secondary chemical reaction with increasing conversion degree. At the second stage (α = 0.30−0.50), the oxidation process is completely controlled by the secondary chemical reaction (G(α) = 1−(1−α)²). At the third stage (α = 0.50−0.95), the secondary chemical reaction weakens gradually with increasing conversion degree, and the oxidation process is controlled gradually by a variety of functions; the kinetic equations are G(α)= (1−α)⁻¹ (β=10 K · min⁻¹, where β is heating rate), G(α) = (1−α)⁻¹/² (β=15−20 K · min⁻¹), and G(α) = (1−α)⁻²(β=25 K · min⁻¹), respectively. For the whole oxidation process, the activation energies follow a parabolic law with increasing conversion degree, and the average activation energy is 160.56 kJ · mol⁻¹.