Thermodynamic and Kinetic Analysis of Cobaltite Oxidation Process

In this paper results of the thermodynamic and kinetic analysis of cobaltite oxidation process were presented. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) and energy dispersive X-ray fluorescence (ED-XRF) were used to determine the chemical composition of the examined cobaltite. The results of the chemical analysis showed that the tested sample of cobaltite mainly consists of cobalt, sulfur, calcium, arsenic, and iron, with a trace amount of some other elements. Also, some analyses were obtained by X-ray diffractometry (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS). Mineralogical analysis by X-ray diffractometry shows the existence of four phases: the minerals cobaltite, calcite, pyrite, and jaipurite. Based on the calculated phase stability diagram of the Co-S-O and As-S-O systems, a thermodynamic analysis of the cobaltite oxidation process was performed. The results of thermogravimetric analysis and differential thermal analysis (TG/DTG) were used to determine the mechanism of the oxidation process. Using the Sharpe method of reduced reaction half-time, a kinetic analysis was performed under isothermal conditions in the temperature range from 300°C to 900°C. The calculated value of the activation energy of the oxidation process is 8.3 kJ/mol–1.