Kinetic analysis for non-isothermal solid state reduction of nickel laterite ore by carbon monoxide

Abstract

The kinetic analysis for non-isothermal solid state reduction of nickel laterite ore by carbon monoxide was investigated at four different heating rates (5, 10, 15 and 20 K min⁻¹). The mechanism function f(α) and kinetic parameters of the reduction process of nickel laterite ore were determined by the thermogravimetric curves using Coats–Redfern method, and the reduction mechanism of nickel laterite ore was analysed. The results indicated that the degree of conversion α could be considered as a function of the temperature, and heating rates had less effect. There was clear relationship between calculated values and measured values of the degree of conversion by mathematic model verification. The kinetic analysis for non-isothermal reduction of nickel laterite ore was divided into three stages for 200–600°C, 600–800°C and 800–950°C; activation energies were 32·16 kJ mol⁻¹ for 200–380°C, 33·13 kJ mol⁻¹ for 380–600°C respectively, for the initial stage, which was characterised by a very slowrate; activation energy was 60·78 kJ mol⁻¹ for the middle stage, which was characterised by a very fast rate; the reduction of nickel laterite ore remained a sluggish process at the decaying stage, and the reaction was governed by the diffusion of oxygen. The mechanism function belonged to G–B equation with differential forms f(α) = 3/2[(1−α)^−1/3−1] at the initial stage, and that belonged to Avrami–Erofeer equation (n = 4) with differential form f(α) = 1/4(1−α)[−ln(1−α)]⁻³ at the middle stage.