Application of Pitzer theory to calculation of sulfate equilibrium concentration in CaSO4-Ca(OH)2-H2O system

In order to provide some theoretical basis for the treatment and reutilization of sulfate contaminated industrial wastewater, Pitzer theory was adopted to calculate the equilibrium concentration of sulfate in CaSO4-Ca(OH)2-H2O system at different pH through C++ language programming, and the effect of Na+ on the equilibrium concentration of sulfate in this system was investigated. The results show that the equilibrium concentration of sulfate is minimal and invariant with the concentration of 0.0152 mol/L when pH is 3.0-10.0 and increases significantly when pH is higher than 12.0. The equilibrium concentration of sulfate increases with the addition of Na+ in the solution as the variation law of sulfate equilibrium concentration of the system is in agreement with that of without Na+ system.