Crystallization Thermodynamics And Kinetics Of KCl In The KCl-MgCl₂-H₂O System

The crystallization thermodynamics and kinetics of potassium chloride in the electrolyte solutions have played an important role in many fields, such as mineralogy of Earth, exploiting and utilizing KCl resource in salt lake and other aspects. In this work, the crystallization thermodynamics and kinetics of potassium chloride in the KCl-MgCl2-H2O ternary system have been investigated in respect of the exploiting and utilizing KCl resource of salt lake. Researches are mainly about the following three aspects:(1) Determination of the solubility data of KCl and MgCl2.During the production of chloride potassium which was prepared from Carnallite,the decomposition of liquid contains large amounts of magnesium ions,so hanve seriously affect the yield and quality of the potassium chloride. We can know that the solubility data of KCl and MgCl2is very important. The solid-liquid equilibrium data of KCl and MgCl2in the KCl-MgCl2-H2O ternary system have been measured by isothermal dissolution method (static method) respectively:a series of the solubility and liquid composition of potassium chloride and magnesium chloride in the KCl-MgCl2-H2O ternary system have been measured and drawed phase diagrams in the temperature range of278.15～323.15K and the concentration of magnesian ion range of0～saturation state.Results show that the KCl-MgCl2-H2O ternary system has five crystal regions at every temperature:KCl crystal region,KCl+Car crystal region,Car crystal region,Car+Bis crystal region,Bis crystal region.When the temperature is constant, the solubility of KCl decreases with the increase of MgCl2concentration;when the concentration of MgCl2is constant, the solubility of KCl increases with increasing temperature.Controlling the crystallization of regional in the KCl+Car crystal region can improve the yield of KCl crystallization.(2) The paper has studied the effects of supersaturation and temperature for the crystallization of KCl in KCI-MgCl2-H2O ternary system. Through the saturation and temperature control, the optimization of crystal quality, such as morphology, particle size, etc.can be realized. The results show that lower supersaturation proves successful in producing well developed nubby KCI crystals with large particle size, smooth surface and high sedimentation rate. The higher supersaturation can prove the yield of KCI crystallization with constant temperature.(3)The paper has severely calculated the crystal growth rate of potassium chloride in KCl-MgCI~2-H~2O ternary system.In this calculation, the OLI software has been used to estimate the activity coefficient and thermodynamic equilibrium constant of potassium chloride in the magnesium chloride solution at25℃. The results show that higher supersaturation proves the greater growth rate of KCl at a constant temperature; and the higher temperature also proves the greater growth rate of KCl at a constant supersaturation.The effect of temperature for the growth rate of KCl is greater at high supersaturation.In this work, the crystallization thermodynamics and kinetics of potassium chloride in salt lake system have laid the foundation of exploiting and utilizing KCl resource in salt lake.