Studies On The Stable Equilibria Of The Quinary System Li⁺（K⁺）,Rb⁺,Mg²⁺∥Cl^-,Borate-H₂O At 323K

The solubilities and physicochemical properties (density and refractive index) in the quinary system Li+, Rb+, Mg2+//Cl-, borate-H2O, K+, Rb+, Mg2+//Cl-, borate-H2O and the quaternary subsystem Rb+, Mg2+//Cl-, borate-H2O at 323 K belong to the Pingluo underground brine were studied using an isothermal dissolution method. Based on the experimental data, the stereo phase diagrams, the projected phase diagrams, the water-content diagrams and the physicochemical properties versus composition diagrams were constructed.Results show that the quaternary system Rb+, Mg2+//Cl-, borate-H2O at 323 K is of a complex interactive system with the formation of double salt RbCl·MgCl2·6H2O. The phase diagram consists of three invariant points, seven univariant curves, and five crystallization zones.The crystallization forms of borate in this system are penta-borate (RbB5O8·4H2O) and tetraborate (MgB4O7·9H2O), respectively. RbB5O8·4H2O has the largest crystallization field, whereas MgCl2·6H2O has the smallest crystallization field. Comparisons between the stable phase diagrams at 323K and 348 K show that the crystallization forms of the salts are not changed with the temperature, while the crystallization field of salt RbB5O8·4H2O becomes obviously larger with the increase of temperature, which means a rise in temperature is beneficial to separate RbB5O8·4H2O from the solution.The quinary system K+, Rb+, Mg2+//Cl-, borate-H2O at 323 K is of a complex type with the appearance of double salt KCl·MgCl2·6H2O, RbCl·MgCl2·6H2O and solid solution (K, Rb)Cl. The space diagram is made up of seven invariant points, twenty-one univariant curves and nine crystallization zones. The crystalloid forms of potassium borate and magnesium borate is K2B4O7·4H2O and MgB4O7·9H2O, while the crystalloid forms of rubidium borate is RbB5O8·4H2O in this system.The projected phase diagram saturated with salt KCl consists of two invariant points, five univariant curves and four crystallization areas. (K, Rb)Cl has the largest crystallization field, whereas KCl·MgCl2·6H2O has the smallest crystallization field. The projected phase diagram saturated with salt Rb2B4O7 consists of four invariant points, nine univariant curves and six crystallization areas. MgB4O7·9H2O has the largest crystallization field, whereas MgCl2·6H2O has the smallest crystallization field.The quinary system Li+, Rb+, Mg2+//Cl-, borate-H2O is of a complex type with double salts LiCl·MgCl2·7H2O and RbCl·MgCl2·6H2O formed at 323 K. The space diagram consists of seven invariant points, twenty univariant curves and eight crystallization areas. The crystalloid forms of potassium borate, magnesium borate and rubidium borate is K2B4O7·4H2O, MgB4O7·9H2O and RbB5O8·4H2O, respectively. The crystalloid forms of lithium-carnallite and rubidium-carnallite is LiCl·MgCl2·7H2O and RbCl·MgCl2·6H2O, respectively. The projected phase diagram saturated with salt Rb2B4O7 consists of three invariant points, seven univariant curves and five crystallization areas.Among the crystallization fields, the crystallization field of MgB4O7·9H2O is the largest, while the crystallization field of salt MgCl·H2O is the smallest. The projected phase diagram saturated with salt LiCl consists of three invariant points, seven univariant curves and five crystallization areas. The crystallization fields of Li2B4O7·3H2O is the largest, the crystallization fields of MgB4O7·9H2O is the second and the crystallization fields of RbCl and (?)...