Kinetic analysis of the carbonation of lithium orthosilicate using the shrinking core model

With the aim of investigating the reaction mechanism of the carbonation of Li4SiO4, a kinetic analysis was performed using the shrinking core model. Isothermal experiments were conducted with Li4SiO4 samples at ten different target temperatures between 500 and 730 degrees C under 100 kPa and 100vol% of CO2. The measurement results were analyzed in accordance with the shrinking core model. The results indicated that the rate controlling process at low temperatures is the shell diffusion during the entire reaction. However, at high reaction temperatures, the rate controlling process varied from the chemical reaction process to the shell diffusion process as the reaction progressed. Based on Arrhenius plots, the activation energy of diffusion Ed was calculated to be 22.3 kj mol(-1) in the temperature range 500-600 degrees C. On the other hand, the Ed becomes negative at temperatures between 700 and 730 degrees C. This result implies the presence of an exothermic pre-equilibrium reaction, attributed to the dissolution of CO2 in liquid Li2CO3. This reaction offers a path for CO2 transportation, resulting in an enhanced carbonation of Li4SiO4 at high temperatures.