Kinetics and mechanism of oxidation for nickel-containing pyrrhotite tailings

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 oxygen in the air. The kinetic triplets of oxidation, namely, activation energy (E_a), pre-exponential factor (A), and reaction model (f(α)) being a function of the conversion degree (α), were adjusted by 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 in the first step is E_a = 262.2 kJ/mol, lg A = 14.53 s⁻¹, and 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 in the second step is Е_a = 215.0 kJ/mol, lg A = 10.28 s⁻¹, and 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.