Phase Equilibria Of Underground Brine Systems Containing Lithium,Potassium And Strontium In Sichuan Basin At 298 K

For realizing the rational exploitation and utilization of lithium potassium strontium resources in the Triassic underground brines of Sichuan Basin and revealing the mineralization process of the brine resources and the law of dissolution and crystallization of salt minerals,taking the Triassic underground brines riched in lithium,potassium,and strontium in Sichuan Basin as the research object,the stable phase equilibrium research of the quinary systems Na Cl�KCl�Mg Cl₂�Sr Cl₂�H₂O,Li Cl�Na Cl�KCl�Sr Cl₂�H₂O,Li Cl�Na Cl�Mg Cl₂�Sr Cl₂�H₂O and Li Cl�KCl�Mg Cl₂�Sr Cl₂�H₂O,as well as their subsystems under the condition of 298 K were studied in this paper.The solubility data of each system were measured and the corresponding phase diagrams were drawn.Meanwhile,the phase equilibria of partial subsystems were calculated by using the Pitzer electrolyte solution theoretical model.At 298 K,both of the ternary systems Li Cl�Na Cl�H₂O and Li Cl�KCl�H₂O belonged to the simple co-saturated type,and had no solid solution or complex salt formation,but there were corresponding solid-phase crystallization region of hydrated salts.There had no solid solution or complex salt formation in the ternary system Li Cl�Sr Cl₂�H₂O at 298 K,but it had the solubility curve of Sr Cl₂�2H₂O in phase diagrams,indicating that the phase diagrams of it belonged to hydrate type I.The ternary system Li Cl�Mg Cl₂�H₂O was a complex system at 298 K.No solid solution but the complex salt Li Cl�Mg Cl₂�7H₂O was found.In the contrast phase diagram of the above ternary systems at different temperatures,the configuration of the phase diagrams did not change significantly,and Li Cl,Mg Cl₂showed a strong salting out effect in the solution.The quaternary system Na Cl�KCl�Sr Cl₂�H₂O had no solid solution or complex salt formation at 298 K,and its phase diagram was of simple co-saturated type.In the contrast phase diagram at different temperatures,the configuration of the phase diagrams was same and the solid-phase crystalline region of Sr Cl₂�2H₂O appeared with the increase of temperature.The quaternary systems Na Cl�Mg Cl₂�Sr Cl₂�H₂O,Li Cl�Na Cl�Sr Cl₂�H₂O and Li Cl�KCl�Sr Cl₂�H₂O had no solid solution or complex salt formation at 298 K,and the solid-phase crystalline region of Sr Cl₂�2H₂O was generated under the influence of salting out effect of Mg Cl₂ and Li Cl.In the contrast phase diagram of the quaternary system Na Cl�Mg Cl₂�Sr Cl₂�H₂O at different temperatures,the configuration of the phase diagram did not change.At 373 K,the solid-phase crystalline region of Sr Cl₂�6H₂O disappeared,and that of Sr Cl₂�H₂O appeared.At 298 K,the quaternary system KCl�Mg Cl₂�Sr Cl₂�H₂O had no solid solution but complex salt carnallite?KCl�Mg Cl₂�6H₂O?formation,as well as Sr Cl₂�2H₂O,belonging to a complex system.The configuration of the phase diagram remained unchanged in the contrast phase diagram of this quaternary system at different temperatures.At 298 K,the quaternary system Li Cl�Mg Cl₂�Sr Cl₂�H₂O was a complex system.There was no solid solution but complex salt lithium carnallite?Li Cl�Mg Cl₂�7H₂O?existence.The phase equilibrium experiment results showed that the solubility of lithium salts was significantly higher than that of other salts.At 298 K,the quinary system Na Cl�KCl�Mg Cl₂�Sr Cl₂�H₂O had no solid solution but the complex salt carnallite?KCl�Mg Cl₂�6H₂O?generation,when Na Cl,KCl and Sr Cl₂ were saturated,respectively.Of all the solid-phase crystallization regions with Na Cl saturation,KCl occupied the largest proportion.Of all the solid-phase crystallization regions with Sr Cl₂ saturation,Na Cl occupied the largest proportion,and Sr Cl₂�2H₂O occupied the smallest proportion.The simplified dry-base diagram of KCl saturation was relatively simple,and the size of each solid-phase crystallization region decreased in order of Na Cl,Sr Cl₂�6H₂O and KCl�Mg Cl₂�6H₂O.At 298 K,the quinary system Li Cl�Na Cl�Mg Cl₂�Sr Cl₂�H₂O had no solid solution but the complex salt lithium carnallite?Li Cl�Mg Cl₂�7H₂O?generation,when Li Cl,Na Cl and Mg Cl₂ were saturated,respectively.The simplified dry-base diagram of Li Cl and Mg Cl₂ saturated separately was similar,and the complex salt lithium carnallite?Li Cl�Mg Cl₂�7H₂O?had the highest solubility under the above two conditions.At Na Cl saturation,the solubility of each salt increased in sequence according to Sr Cl₂�6H₂O,Sr Cl₂�2H₂O,Mg Cl₂�6H₂O,Li Cl�Mg Cl₂�7H₂O and Li Cl�H₂O.At 298 K,the quinary system Li Cl�Na Cl�KCl�Sr Cl₂�H₂O had no solid solution and the complex salt generation,when Li Cl,Na Cl,KCl and Sr Cl₂were saturated,respectively.The spatial stereogram contained twenty three isothermal solubility curves,five solid-phase crystallization regions and two invariant points.The simplified dry-base diagram of Li Cl and Sr Cl₂ saturated separately was similar,and Sr Cl₂�2H₂O occupied the smallest proportion in the solid-phase crystallization regions.When Na Cl and KCl were saturated separately,the simplified dry-base diagram was also similar.Sr Cl₂�6H₂O,Sr Cl₂�2H₂O and Li Cl�H₂O coexisted in the solid-phase crystallization regions,of which Li Cl�H₂O occupied the smallest proportion.At 298 K,the quinary system Li Cl�KCl�Mg Cl₂�Sr Cl₂�H₂O had no solid solution but the complex salt carnallite?KCl�Mg Cl₂�6H₂O?and lithium carnallite?Li Cl�Mg Cl₂�7H₂O?generation,when Li Cl,KCl and Mg Cl₂were saturated,respectively.The simplified dry-base diagram of Li Cl and KCl saturated separately had the same configuration,and the phase regions of lithium salts occupied the smallest proportion.The simplified dry-base diagram of Mg Cl₂saturation was relatively simple,and the size of each solid-phase crystallization region increased in order of KCl�Mg Cl₂�6H₂O,Sr Cl₂�2H₂O and Li Cl�Mg Cl₂�7H₂O.Based on the theoretical model of Pitzer electrolyte solution,the particle swarm optimization algorithm?PSO?was employed to conduct the theoretical calculation of phase equilibrium aiming at the quaternary systems Na Cl�Mg Cl₂�Sr Cl₂�H₂O,KCl�Mg Cl₂�Sr Cl₂�H₂O,Li Cl�Na Cl�Sr Cl₂�H₂O,Li Cl�KCl�Sr Cl₂�H₂O and Li Cl�Mg Cl₂�Sr Cl₂�H₂O at 298 K,and the results were compared with the experimental data of phase equilibria,indicating that the theoretical calculation phase diagrams were basically in agreement with the experimental phase diagrams.