Study On The Phase Equilibrium Of The Quinary System Li⁺,K⁺,Rb⁺//Cr,Borate-H₂O At 348K

Although the west of Sichuan basin contains precious underground brine resources,which abounded with lithium,potassium,rubidium and boron,and with high quality for exploiting,it is still at the priminary stage of development.Aimed at making the most of the brine,the stable phase equilibria of the reciprocal quinary system Li~+,K+,Rb+//Cl-,borate-H2O,its two boron systems quaternary subsystems and two ternary systems were investigated at 348 K using an isothermal dissolution equilibrium method.Till to now,the stable phase equilibria of the systems mentioned above have not been reported in the literature.The solubilities,densities and pH value of the equilibrated solutions were determined.According to the experimental data,the stable phase diagrams and physicochemical properties-composition diagrams of the relevant system were plotted.The equilibrium phase diagrams,the water-content diagrams,the density vs composition diagrams,and the pH values vs composition diagrams of the quaternary system were plotted.The projected phase diagrams(saturated with Li2B4O7or LiCl),corresponding water content diagrams and ion content diagrams of the quinary systems were constructed.The ternary system K+//Cl-,borate-H2O at 348 K is of a simple eutectic type,no double salt or solid solution was formed.Two crystallization areas of the system correspond to the single salts K2B4O7�4H2O and KCl.The comparisons between the phase diagrams of the ternary system at 348 K,323 K and 298 K show that the crystallization forms of salt K2B4O7�4H2O and KCl are the same,whereas the crystallization field of salt KCl enlarges along with the increases of temperature,while the crystallization field of salt K2B4O7�4H2O decreases along with the increases of temperature,and also the salting out effect of salt potassium chloride to potassium borate is enhanced at 348 K.The termary system K+,Rb+//borate-H2O at 348 K was of a simple eutectic type and no double salt or solid solution was found.In the phase diagram,the ternary system has one incariant point,two univarinat curves and two fields of cryatallization corresponding to salts K2B4O�4H2O and RbB5O8�4H2O.The experimental results show that there is no salting-out or salting-in effect between the two salts.There is no double salt or solid solution formed in the quaternary system Li~+,K+//Cl-,borate-H2O.The phase diagram of the system consists of two invariant point,five univariant curves and four crystallization fields corresponding to salt LiCl�H2O,Li2B4O7�3H2O,K2B4O7�4H2O,KCl,respectively.The solid solution[(K,Rb)Cl]was found in the quaternary system K+,Rb+//Cl-,borate-H2O at 348 K.In the phase diagram,the quaternary system has three invariant point,seven univariant curve and five fields of crystallization.The solid solution[(K,Rb)Cl]was also formed in the quinary system Li~+,K+,Rb+//Cl-,borate-H2O at 348 K.The projected diagram of this system,saturated with Li2B4O7,consists of five crystallization fields,six univariant curves and three invariant points.The projected diagram of this system which saturated with LiCl,consists of four crystallization fields,five univariant curves and two invariant points.