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

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