Thermodynamic modeling and phase diagram prediction of salt lake brine systems.Ⅰ. Aqueous Mg^2+–Ca^2+–Cl^- binary and ternary systems

Salt lake brine is a complex salt-water system under natural environment.Although many models can express the thermodynamic properties and phase equilibrium of electrolyte aqueous solution,the multi-temperature characteristics and predictability are still the goals of model development.In this study,a comprehensive thermodynamic model system is re-established based on the eNRTL model and some improvements:(1) new expression of long-range electrostatic term with symmetrical reference state is proposed to handle the electrolyte solution covering entire concentration range;(2) the temperature dependence of the binary interaction parameters is formulated with a Gibbs Helmholtz expression containing three temperature coefficients,the liquid parameters,which associated with Gibbs energy,enthalpy,and heat capacity contribution;and(3) liquid parameters and solid species data are regressed from properties and solubility data at full temperature range.Together the activity coefficient model,property models and parameters of liquid and solid offer a comprehensive thermodynamic model system for the typical bittern of MgCl2-CaCl2-H2 O binary and ternary systems,and it shows excellent agreement with the literature data for the ternary and binary systems.The successful prediction of complete phase diagram of ternary system shows that the model has the ability to deal with high concentration and high non-idealitv system,and the ability to extrapolate the temperature.

Integrated system of comprehensive utilizing the concentrated brine of Yuncheng salt-lake basing on salt-forming diagram

The comprehensive utilization and environment-friendliness of processes for recovering fresh water or valuable salt from seawater, salt-lakes, or mineral deposits are of utmost importance for sustainable development.One primitive sustainable process for recovering salt from sodium-sulfate-type brine in Yuncheng salt lake had been considered one of the greatest inventions of ancient China, however, the replaced process of mass extraction of single Na_2SO_4 in recent years, has reduced a large amount of residual brine.In this research, relying on the salt-forming diagram in the non-equilibrium state, the technical secrets of ancient salt processes were uncovered, and a new comprehensive utilization system was proposed and tested experimentally.The new system includes a vacuum salt-making process and a normal pressure kieserite process, which can gradually eliminate the existed waste liquid and aid in the sustainable development of the Yuncheng salt-lake.The continuous experiment of salt-making process running stably in the double salt region without double salt formation, which proves the feasibility of salt-forming diagram applied in industrial process.Thus salt-forming diagram would be extremely valuable to industry process design and control, especially, the treatment of concentrated brine.