Effect of particle size on precipitation-dissolution equilibrium of CaF_2

The thermodynamic properties were studied by dissolution experiment.The effects of pH and particle size of CaF2 on the precipitation dissolution equilibrium of Ca2+-F--H+-H2O system were investigated,and then the factors influencing the precipitation effect were determined combined with the thermodynamic analysis.The results show that the particle size of CaF2 is a critical factor that influences the equilibrium concentration of F.The solubility of CaF2 and equilibrium concentration of F decreases with increasing the particle size of CaF2.The equilibrium concentration of F is less than 8 mg/L with coarse particles larger than 16.97 μm,while it is more than 25 mg/L with fine particles.In order to decrease the solubility of CaF2 and improve the F removal efficiency in the precipitation process,the terminal pH value of the reaction should be controlled between 4.0 and 10.0,while the particle size of the precipitate should be increased as much as possible.