Reaction Mechanism Process Analysis with Phosphogypsum Decomposition in Multiatmosphere Control

This paper proposes a two-step method for phosphogypsum (PG) decomposition by circulating various atmospheres instead of a single atmosphere. To achieve a high concentration of CaO in the final product, the PG was decomposed in reducing atmosphere with CO (99.99%) at rising temperature until the mass loss changes stably in the first step reaction. For the second-step reaction, the atmosphere was changed from a reducing atmosphere to an oxidizing one of air at a constant temperature. With different final constant temperatures, the analysis of thermogravimetric analyzer (TGA) and Factsage6.1 Reaction and Phase diagram module indicated that the purity of CaO improved in repeating atmosphere after 1000 degrees C, which was proved by the XRD analysis. Especially, the final product is almost entirely CaO in 1100 degrees C when compared with other temperatures. The kinetic mechanism model of CaS oxidization was established using the Kissinger, FlynnWallOzawa, and CoatsRedfern methods.