Pyrolysis behavior of bastnaesite in an air environment: Thermodynamics, phase transition and kinetics

Abstract

BackgroundOxidation roasting is an eco-friendly pre-treatment process that is utilized before leaching bastnaesite concentrate, and it is currently the main process for pretreating bastnaesite concentrate in China. Despite this, there is still a lack of systematic and detailed studies on the pyrolysis behavior of bastnaesite concentrate in an air environment. MethodsThe reaction thermodynamics, pyrolysis characteristics, phase transition and kinetics of bastnaesite pyrolysis in air were studied in detail by thermogravimetric and mass spectrometric, in-situ X-ray diffraction, and advanced kinetic parameter analysis method recommended by ICTAC. Significant findingsCe7O12, CeF3, and CO2 were the primary pyrolysis products of bastnaesite in the air. Spontaneous reactions dominated during the process, and the oxidation of pyrolysis products released heat. Bastnaesite pyrolysis initially occurred within the temperature range of 400°C to 500°C, with higher temperatures facilitating easier pyrolysis. The non-isothermal pyrolysis kinetic triplets for bastnaesite concentrate in the air were determined, which included activation energy (Eα) of 161.52 kJ/mol, pre-exponential factor (lnA) of 26.70 s−1, and appropriate kinetic mechanism of random nucleation and growth model (n=3/2–2).