Thermal decomposition of a Brazilian laterite nickel ore: non-isothermal kinetic methods and quantitative mineralogical analysis
摘要
A Brazilian laterite nickel ore sample was characterized through the following techniques such as scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and X-ray diffractometry (XRD) with Rietveld Method (RM) analysis. Thermogravimetric analysis (TG) was performed to investigate the thermal decomposition behaviour of the sample. This analysis revealed five distinct thermal events, which were then quantified. The Vyazovkin method and a non-isothermal multilayer perceptron neural network (MLP) were employed to analyse the kinetic parameters of three primary thermal decomposition events of laterite nickel ore: i) the two-stage decomposition of goethite and ii) the decomposition of hematite. The activation energy (Ea) for the first goethite decomposition event increased with the conversion degree, ranging from a minimum value of 63.8 kJ mol−1 to a maximum of approximately 144.7 kJ mol−1, with a rate constant of 0.2967 min−1. For the second step, the activation energy ranges from a minimum of 27.9 kJ mol−1 to a maximum of 380.2 kJ mol−1 and the rate constant is 0.2115 min−1. The third process, i.e. magnetite’s formation, exhibited a minimum of 882.4 kJ mol−1 and maximum of 1323.7 kJ mol−1. This step presented the most significant rate constant, value of 0.3808 min−1, explaining the high rate of reaction observed. All events proceed through a combination of Avrami–Erofeev equations, with Am2 model (Avrami–Erofeev order n = 2) being the main mechanism. This suggests that both nucleation and growth process are rate-limiting steps for all the reactions involved in laterite nickel ore thermal decomposition.