Kinetic analysis on carbothermal reduction process of phosphorite based on the isoconversional methods

Phosphorus is a very important element in both chemical and biological fields. The primary industrial production method of yellow phosphorus is mixing phosphorus ore, silica, and coke, which then undergo carbothermal reduction reactions at high temperature. Most of the current studies regard the kinetics as a single-step kinetics and ignore the complexity of its process. This study uses isoconversional methods to prove that the process has complex kinetics and can be divided into two stages according to the conversion rate(α), controlled by chemical reaction (0.1＜α＜0.65) and diffusion (0.65＜α＜0.85). The master plot method indicates that the first stage aligned with the F_n model, whereas the second stage does not correspond to any of the models. The activation energies of these two stages are found to be 247.246 kJ/mol and 326.593 kJ/mol, respectively, by nonlinear fitting. In addition, albite is added to the system as a flux. It significantly enhances the reaction at 1623.15 K. In only 30 min, α reaches 94.421 %, reducing the time needed by approximately 40 %. The analysis indicates that this system should also be divided into two stages, 0.1＜α＜0.7 and 0.7＜α＜0.85, and has the same model matching situation as the system without albite. At this point, the activation energies of the two stages are 278.039 kJ/mol and 299.451 kJ/mol, respectively. Furthermore, combined with the mechanism analysis, this study provides a theoretical basis for the optimization of industrial phosphorus production.