Study on Influence Factors of Co-Crystallized P2O5 in Phosphogypsum Formation and its Mechanism

Abstract

Influence factors of co-crystallized (lattice) P2O5were investigated from the dihydrate process conditions and aimed to optimize the process conditions and reduce the co-crystallized (lattice) P2O5content in phosphogypsum. It is found that: 1) reaction temperature, P2O5concentration in liquid phase and SO3concentration in liquid phase are main factors influencing the content of co-crystallized (lattice) P2O5; 2) increasing the reaction temperature, can reduce the supersaturation ratio of the crystallization, decrease the solution viscosity, which help ions diffusion and reduce the content of co-crystallized (lattice) P2O5; 3) improvement of SO3concentration in liquid phase can increase the collision probability between calcium sulfate lattice and SO42-, reduce the Ca2+concentration and prevent the dissociation of phosphoric acid, so HPO42-concentration does not increase, thereby reducing content of co-crystallized (lattice) P2O5; 4) increasing the P2O5concentration in liquid phase will lead to a corresponding increase of the HPO42-concentration, solution viscosity increasing, diffusion problems, and deterioration of crystallization conditions, which increased the content of co-crystallized (lattice) P2O5; 5) the formation mechanism of co-crystallized (lattice) P2O5is: any changes in the reaction system whatever can make the local concentration or average concentration of Ca2+and HPO42-in the solution increased, will increase the probability of the formation of co-crystallized (lattice) P2O5.