Research On Solid-liquid Equilibrium And Salt-forming Dynamics For Na⁺,Mg²⁺//Cl^-,SO₄^2--H₂O System

Qinghai Salt Lake belongs to the typical salt lake brines of chloride type,sulphate type and its subtypes.Based on the salt-water system phase diagrams,the studies of the thermodynamic model of the related system has important in theory and practice.In this study,based on the symmetric eNRTL model,we use the multiphase temperature data to determine the liquid phase parameters,and the full-temperature range solid-liquid phase equilibrium data to the thermodynamic parameters of the solid phase species.An integrated thermodynamic model for physical property calculation,phase balance prediction,and phase diagram integration is obtained by phase diagram integration and comprehensive optimization of the whole temperature range.(1)First,the parameters denoted the interactive effect of electrolyte-water were regressed from experimental thermodynamic data(mean ionic activitycoefficient?osmotic coefficient?vapor pressure and heat capacity)of binary systems for NaCl-H2O?Na2SO4-H2O?MgSO4-H2O.Then,the solids thermodynamic data(Gibbs energy of formation,enthalpy of formation and heat capacity)were re-determined by regressing solid-liquid equilibrium data of the whole temperature range.Finally,the solubility curves for the three systems were obtained.(2)Based on the parameters of the binary systems,the interactive parameter of electrolyte-electrolyte and thermodynamic data of double salts were regressed by ternary solubility data on the whole temperatures region of NaCl-Na2SO4-H2O?NaCl-MgCl2-H2O?Na2SO4-MgSO4-H20?MgSO4-NaCl-H2O.And all the complete phase diagrams of the whole temperature range were obtained.(3)All the model parameters had been obtained,which were used to predict the solubility of the quaternary systems.Then we obtained water diagrams and dry base figures of the Na+,Mg2+//SO42-,Cl--H2O,Li+,Na+,Mg2+//,SO42--H2O quaternary systems,while the calculated curves and the literature data are in good agreement,reflecting that the model in the expression of physical properties and phase equilibrium of the complete thermodynamic properties is consistency.Based on the theory of dynamic salt-forming phase diagram,this paper utilizes the large amount of mother liquor produced in the sodium sulfate process,the research puts forward the innovative production methods,and makes the waste liquid to form value products of NaCl salt and MgSO4�H2O.This technology will help for the sustainable development of Yuncheng salt-lake and contribute to the improvement of the environment.