Kinetics of Oxidation of Beneficiated Indian Graphite

Graphite is naturally found in association with various minerals and impurities, typically exhibiting a low percentage of fixed carbon. To enhance its purity, the material undergoes a sequence of crushing, grinding, and beneficiation processes. With repeated beneficiation, the fixed carbon content increases significantly, leading to the production of high-purity graphite. In India, the primary sources of graphite include Palamau in Jharkhand, Bolangir in Odisha, and Shivaganga in Tamil Nadu.

Following physico-chemical evaluation of these graphite samples, their oxidation behavior was analyzed using Differential Thermal Analysis (DTA) and Thermogravimetric Analysis (TGA). The experiments were conducted under controlled atmospheres to investigate the reaction kinetics and determine the activation energy under specific conditions. Three oxidation temperatures were selected based on the oxidation peaks observed in the DTA/TGA curves.

Kinetic modeling revealed that up to certain temperatures, the oxidation rate was primarily governed by the chemical reaction between carbon and oxidizing gas at the interface. At higher temperatures, a shift from chemical control to diffusion through a decarburized pore zone was observed. The oxidation process corresponded to models such as the phase boundary-controlled reaction, contracting disc, and two-dimensional diffusion.

The formation of a decarburized zone alters the activation energy, reflecting a transition in mechanism. Additionally, particle size variations influence activation energy values, showing multiple slopes across temperature ranges.