Mean activity coefficients, phase equilibria of ternary system KCl-KHCO3-H2O at 288.2 and 308.2 K and separation of potassium salts in pesticide imidacloprid production wastewater

Thermodynamic properties and phase equilibria of aqueous solutions containing potassium salts is of great significance for the resource recovery and utilization of pesticide production wastewater and waste residue. In order to further optimize the mixed ion interaction parameters of electrolyte solution containing HCO₃²⁻ and recover KCl and KHCO₃ from imidacloprid production wastewater, the mean activity coefficients of KCl-KHCO₃-H₂O mixed electrolyte solutions at 288.2 K and 308.2 K were investigated using the cell potential method, then the phase equilibria of the ternary system KCl-KHCO₃-H₂O at 288.2 K and 308.2 K was measured experimentally by the isothermal dissolution equilibrium method. In addition, the mixed ion interaction parameters ${\theta }_{Cl,{HCO}_3}$ and ${\Psi }_{K,Cl,HC{O}_3}$ in the Pitzer model were solved by combining the mean activity coefficients of KCl in the mixed electrolyte solutions and solubility data of ternary system, and other related thermodynamic parameters were calculated. Furthermore, the solubilities of the ternary system were calculated by using Pitzer model. The calculation results and experimental data are in good agreement. Subsequently, the precipitation amounts of various salts of imidacloprid production wastewater during isothermal evaporation were calculated based on the experimental phase diagrams at 288.2 K and 308.2 K. The process of recovering potassium salts was designed, and the theoretical basis for the separation of potassium salts in wastewater was provided.