Dissolution kinetics of phosphate ore particles in excessive phosphoric acid

The reaction kinetics of phosphate ore particles reacting with excessive phosphoric acid was investigated. The effects of various operating parameters including reaction temperature (333.15-353.15 K), concentration of phosphoric acid (20-40 omega t% P2O5) and particle size (260, 190, 134, 96, 59 mu m) on the reaction performance were investigated first. The results indicated that the reaction rate increased with the increase of reaction temperature, concentration of phosphoric acid, as well as the decrease of particle size. The Drozdov model could be used to describe the reaction behaviors. The activation energy results suggested that the rate-determining step was the diffusion of H+ through the residual layer. The precipitation of insoluble phosphates would cover on the surface and lead to a decrease of dissolution extent. Controlling the product forms is crucial to the improvement of dissolution extent. The specific surface area of the phosphate ore also had a significant impact on the reaction rate and dissolution extent.