Kinetics and mechanism of oxidation for nickel-containing pyrrhotite tailings

Abstract: X-ray powder diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetry, differential scanning calorimetry and mass spectrometry have been used to study the products of nickel-containing pyrrhotite tailings oxidation by the oxygen in the air. The kinetic triplets of oxidation, such as activation energy (Ea), pre-exponential factor (A) and reaction model (f(α)) being a function of the conversion degree (α), were adjusted by the regression analysis. In case of a two-stage process representation, the first step proceeds under autocatalysis control and ends at α = 0.42. The kinetic triplet of the first step can be presented as Ea = 262.2 kJ/mol, lgA = 14.53 s^-1, f(α) = (1 – α)^4.11(1 + 1.51·10^–4α). For the second step, the process is controlled by the two-dimensional diffusion of the reactants in the layer of oxidation products. The kinetic triplet of the second step: Еa = 215.0 kJ/mol, lgA = 10.28 s^-1, f(α) = (–ln(1 – α))^–1. The obtained empirical formulae for the rate of pyrrhotite tailings oxidation reliably describe the macro-mechanism of the process and can be used to design automatization systems for roasting these materials.