Study On Phase Equilibria Of The Quinary System Na⁺, K⁺, Mg²⁺//Cl^-, Br^--H₂O At 313K

The subject belongs to the application foundation research of the national eleventh five-year scientifical supporting and planning projects"study on systems engineering in ecotourism exploitation of potassium and magnesium salt deposit". In order to protect environment and increase utilization as far as possible, a correct water exploitation program has been employed. However, this technology has not been applied in large-scale production at home and abroad. In order to avoid the bindness of the investment for advancing the process of industrialization of potassium and magnesium salt deposit and decrease the economic risk for the project, an exploratory research of Leaching-Experiment for K-Mg Salt-Deposit was performed in this work. Solid core of salt mine is treated with special method to be produced into leak-free and permeation-free geometrical body. Under the temperature simulated to that of the leaching, water is injected, extract brine and analyze ion change in brine. Reasonable brine extraction temperature is found for modeling in caverns in different period time in a view to learn the cavern modeling change.Further, in order to provide the necessary basic data for the industrialization of potassium and magnesium salt deposit, phase equilibrium data for related systems have been systematically measured. K-Mg Salt-Deposit is a complex chemical compound system, which is composed of many ions and molecule such as K⁺, Na⁺, Mg²⁺, Ca²⁺, Cl^-, Br^-, CO₃^2-, SO₄^2-, etc. So, the study of its phase equilibrium and the physico-chemical properties are in a dispensable elementary work for exploiting the resource of potassium salt mine.In accordance with the composition of the K-Mg Salt-Deposit, the reciprocal quinary system Na⁺, K⁺, Mg²⁺ // Cl^-, Br^--H₂O and its four quaternary sub-systems and six ternary sub-systems were studied at 313K with isothermal method at the present work. The solubilities and the physico-chemical properties of relevant equilibrium solutions, including density, refractivity index, pH value, viscosity, were determined. According to the experimental data, phase diagrams and physico-chemical property-composition diagrams of ternary systems were plotted; phase diagrams of four quaternary sub-systems and quinary system are also constructed. This work has filled the blank in this field of solubilities and the physico-chemical properties of relevant equilibrium solutions.It is founded that the system containing chloride and bromide is of solid solution type. A kind of complex salt KBr·MgBr₂·6H₂O was found in the ternary system KBr-MgBr₂-H₂O at 313K, and this complex salt also exists in the quaternary and quinary systems which contained the KBr-MgBr₂-H₂O system.Pitzer's electrolyte solution model is employed for theoretically phase relations of the high concentration multicomponent systems in this work. Using the reliable solubility data of ternary systems at 313 K, the single salt Pitzer parameters and corresponding ion-interaction mixing parameters for Pitzer's equations were fitted by multiple linear regress method. Equilibrium constant of salts for liquid-solid equilibrium at 313 K were evaluated with Pitzer's model. To study the phase equilibrium of complex ternary salt-water system containing solid solution, the equilibrium relationship between liquid composition and solid composition was established to achieve the phase diagram by simple iterative calculation. Using the Pitzer's equations, the solubilities of the simple quaternary sub-system and six ternary sub-systems were predicted. The calculated values are in agreement with experiment values on the whole.No same report to above study results has been published in literature at present.