Studies On The Stable Phase Equilibrium Of The Quinary System Li⁺,K⁺,Mg²⁺//Cl^-,borate-H₂O At 348 K

In order to comprehensive develop and utilize the underground brine resources in sichuan basin,based on the components of the underground brine,the stable phase equilibria of the quinary system Li⁺,K⁺,Mg²⁺//Cl^-,borate-H₂O,two reciprocal quaternary and two ternary sub-systems were investigated at 348 K using an isothermal dissolution saturation method.Equilibrium solubilities and physico-chemical properties such as the density,refractive index and p H value of the solution were determined at 348 K.On the basis of experimental data,the equilibrium phase diagrams and the physico-chemical properties vs composition in two ternary systems at 348 K were constructed;the equilibrium phase diagrams,the water-content diagrams,the density-composition diagrams,the refractive index-composition and the p H-composition diagrams of the both of the quaternary systems were also constructed;The stereo phase diagram,the projected phase diagram(saturated with Mg B₄O₇ and KCl),water content diagrams,potassium content diagram and magnesium content diagram and physico-chemical properties vs composition diagrams in the quinary system were plotted.The experimental consequent show that the ternary system K⁺,Mg²⁺//borate-H₂O at 348 K is of a sample eutectic type,no double salt or solid solution is formed.The phase diagram of the system consists of one invariant point,two univariant curves,and two crystallization fields.The two crystallization fields correspond to single salts potassium tetraborate tetrahydrate(K₂B₄O₇·4H₂O)and hungtsaoite(Mg B₄O₇·9H₂O).Salt potassium borate(K₂B₄O₇)and magnesium borate(Mg B₄O₇)has a strong salting-in effect on each other.The ternary system Li⁺,Mg²⁺//borate-H₂O at 348 K was of a sample eutectic type,no double salt or solid solution is formed.The phase diagram of the system consists of one invariant point,two univariant curves,and two crystallization fields.The two crystallization fields correspond to single salts lithium tetraborate trihydrate(Li₂B₄O₇·3H₂O)and hungtsaoite(Mg B₄O₇·9H₂O),respectively.The quaternary system K⁺,Mg²⁺//Cl^-,borate-H₂O at 348 K is of a complex type,with a double salt of potassium and magnesium chloride named carnallite(KCl·Mg Cl₂·6H₂O)formed,no solid solution formed.There are three invariant points,seven univariant curves,and five crystallization fields in the stable phase diagram of the K⁺,Mg²⁺//Cl^-,borate-H₂O at 348 K.Five crystallization fields correspond to single salt potassium tetraborate tetrahydrate(K₂B₄O₇·4H₂O),potassium chloride(KCl),magnesium chloride hexahydrate(Mg Cl₂·6H₂O),hungtsaoite(Mg B₄O₇·9H₂O),and a double salt carnallite(KCl·Mg Cl₂·6H₂O),respectively.The salt Mg B₄O₇·9H₂O has the largest crystallization field,while the salt Mg Cl₂·6H₂O has the smallest crystallization field.Mg B₄O₇·9H₂O and Mg Cl₂·6H₂O has a strong salt-out effect on the other salts existing in this system.In the reciprocal quaternary system Li⁺,Mg²⁺//Cl^-,borate-H₂O,the double salt of lithium and magnesium chloride(Li Cl·Mg Cl₂·7H₂O)was formed at 348 K,no solid solution was found.The stable phase diagram has three invariant points,seven univariant curves,five crystallization fields.Five crystallization fields correspond to lithium chloride monohydrate(Li Cl·H₂O),hungtsaoite(Mg B₄O₇·9H₂O),lithium tetraborate trihydrate(Li₂B₄O₇·3H₂O),magnesium chloride hexahydrate(Mg Cl₂·6H₂O),double salt lithium and magnesium chloride(Li Cl·Mg Cl₂·7H₂O),respectively.Comparisons between the phase diagram at 348 K and 288 K show that there is no change in the crystallization forms and distribution of the crystallization field at these two temperatures,while the size of crystallization field of salt has changed obviously.The crystallization area of salt Li₂B₄O₇·3H₂O becomes smaller,whereas the crystallization area of salt Mg Cl₂·6H₂O,Li Cl·H₂O and double salt Li Cl·Mg Cl₂·7H₂O becomes bigger at 348 K.The results show that there are two double salts potassium and magnesium chloride(KCl·Mg Cl₂·6H₂O),lithium and magnesium chloride(Li Cl·Mg Cl₂·7H₂O)formed in the quinary system Li⁺,K⁺,Mg²⁺//Cl^-,borate-H₂O at 348 K.Three-dimensional phase diagram of this system consists of five invariant points,sixteen univariant curves and eight crystallization fields.The eight crystallization fields correspond to salt potassium chloride(KCl),lithium chloride monohydrate(Li Cl·H₂O),magnesium chloride hexahydrate(Mg Cl₂·6H₂O),potassium tetraborate tetrahydrate(K₂B₄O₇·4H₂O),hungtsaoite(Mg B₄O₇·9H₂O),lithium tetraborate trihydrate(Li₂B₄O₇·3H₂O),potassium and magnesium chloride(KCl·Mg Cl₂·6H₂O),lithium and magnesium chloride(Li Cl·Mg Cl₂·7H₂O),respectively.The projected diagram saturated with Mg B₄O₇ of this system consists of five invariant points,eleven univariant curves and seven crystallization fields.Seven crystallization fields correspond to salt potassium chloride(KCl),lithium chloride monohydrate(Li Cl·H₂O),magnesium chloride hexahydrate(Mg Cl₂·6H₂O),potassium tetraborate tetrahydrate(K₂B₄O₇·4H₂O),lithium tetraborate trihydrate(Li₂B₄O₇·3H₂O),potassium and magnesium chloride(KCl·Mg Cl₂·6H₂O),lithium and magnesium chloride(Li Cl·Mg Cl₂·7H₂O),respectively.Among them,Li Cl·H₂O has the smallest crystallization field,whereas Li₂B₄O₇·3H₂O has the largest crystallization field.The projected diagram saturated with KCl of this system consists of five invariant points,eleven univariant curves and seven crystallization fields.The seven crystallization fields correspond to salt hungtsaoite(Mg B₄O₇·9H₂O),lithium chloride monohydrate(Li Cl·H₂O),magnesium chloride hexahydrate(Mg Cl₂·6H₂O),potassium tetraborate tetrahydrate(K₂B₄O₇·4H₂O),lithium tetraborate trihydrate(Li₂B₄O₇·3H₂O),potassium and magnesium chloride(KCl·Mg Cl₂·6H₂O),lithium and magnesium chloride(Li Cl·Mg Cl₂·7H₂O),respectively.Among them,Li Cl·H₂O has the smallest crystallization field,whereas Mg B₄O₇·9H₂O has the largest crystallization field.