Thermal decomposition behaviour and kinetics of Xinjiang siderite ore

Abstract

In order to provide a better theoretical foundation for utilisation of Xinjiang siderite resources in China, its thermal decomposition behaviour was studied in neutral and oxidising atmospheres by employing thermodynamics analysis, chemical titration, thermogravimetric, and X-ray diffraction means. Isothermal experiments were conducted to investigate the thermal decomposition kinetics of siderite lump in a weakly oxidising atmosphere at 500–850°C. The results reveal that siderite has self-magnetisation characteristics under controlled conditions, and the phase evolution process and final products of decomposition depend temperature and atmosphere. The phase transformation process in weak oxidising atmosphere follows the steps as: FeCO₃ → Fe₃O₄ → γ-Fe₂O₃ at 550°C, and FeCO₃ → FeO + Fe₃O₄ → Fe₃O₄ → γ-Fe₂O₃ → α-Fe₂O₃ at 800°C. In inert atmosphere, the decomposition pathway is FeCO₃ → Fe₃O₄ below 733°C and FeCO₃ → FeO + Fe₃O₄ above 733°C. The molar ratio of FeO/Fe₃O₄ increases with temperature. The decomposition kinetics of siderite lump in oxygen-deficient atmosphere is consistent with chemical reaction control in the temperature range 500–700°C and nucleation and growth mechanism in the 750–850°C. The corresponding activation energies are 53·73 and 38·15 KJ mol⁻¹, respectively.