Solid–Liquid Equilibrium in the Aqueous System Containing the Borates of Potassium, Rubidium, and Magnesium at 348 K

Abstract

The stable phase equilibrium and phase diagram of the quaternary system K + , Rb + , Mg 2+ // borate·H 2 O at 348 K were determined by isothermal dissolution method. The densities, refractive indices, and solubility values of the equilibrated solution in the quaternary system were measured. The crystalloid forms of the solid phase of invariant point were identified by X-ray diffraction method. The stable phase diagram, water content diagram, and the diagrams of the densities/refractive indices versus composition were plotted based on the measured data. Results show that this quaternary system at 348 K without double salt or solid solution formed belongs to a simple eutectic type. The invariant point E saturated with three salts corresponding to potassium tetraborate tetrahydrate (K 2 B 4 O 5 (OH) 4 · 2H 2 O), rubidium pentaborate tetrahydrate (RbB 5 O 6 (OH) 4 ·2H 2 O), and hungchaoite (MgB 4 O 5 (OH) 4 ·7H 2 O). The crystallization field of RbB 5 O 6 (OH) 4 ·2H 2 O is the maximum, meaning that it has the smallest solubility among the coexisting salts. On the solubility curves AE (cosaturated with salts MgB 4 O 5 (OH) 4 ·7H 2 O and RbB 5 O 6 (OH) 4 ·2H 2 O) and BE (cosaturated with salts K 2 B 4 O 5 (OH) 4 ·2H 2 O and RbB 5 O 6 (OH) 4 ·2H 2 O), the water content decreases, the densities and refractive indices increase with the increase of J(K 2 B 4 O 7 ); on the curve CE (cosaturated with salts MgB 4 O 5 (OH) 4 ·7H 2 O and K 2 B 4 O 5 (OH) 4 ·2H 2 O), the water content and the densities increase, the refractive indices decrease with the increase of J(K 2 B 4 O 7 ).

Stable Phase Equilibria of Ternary Systems Li+,Rb+//SO42––H2O and Li+,Cs+//SO42––H2O at 273.2 K

“…For example, for chloride-type and borate-type salt lakes containing lithium, rubidium, and cesium in different regions, a series of phase equilibria of related systems have been studied by many scholars. Namely, Na + ,Rb + //Cl – –H 2 O at T = 288.15, 298.15, and 318.15 K; Na + ,Cs + //Cl – –H 2 O at 298.15, 308.15, and 318.15 K; Rb + ,Cs + //Cl – –H 2 O at 323 K; Li + ,K + ,Rb + //Cl – –H 2 O at 298.15 K; Rb + ,Mg 2+ //Cl – ,borate–H 2 O at 323 K; Li + ,K + ,Rb + ,Mg 2+ //borate–H 2 O at 348.15 K; and K + ,Rb + ,Mg 2+ //borate–H 2 O at 348 K . According to the main element types, the sulfate salt lake brine in Qaidam Basin can be simplified to a complex septenary system Li + ,Na + ,K + ,Rb + ,Cs + ,Mg 2+ //SO 4 2– –H 2 O .…”

Stable Phase Equilibrium and Phase Diagram of the Quinary System Li+, K+, Rb+, Mg2+//Borate-H2O at T = 348.15 K

“…The quinary system Li + , K + , Rb + , Mg 2+ //borate-H 2 O is a most important subsystem of the complex system. The quinary system contains four quaternary subsystems and the phase equilibria and phase diagram of the quaternary systems have been studied in our previous work. − The chief results were as follows: the quaternary systems Li + , K + , Rb + //borate-H 2 O, Li + , Rb + , Mg 2+ //borate-H 2 O, Li + , K + , Mg 2+ //borate-H 2 O, and K + , Rb + , Mg 2+ //borate-H 2 O at 348.15 K are all of simple type without double salt or solid solution found, and in the quaternary system mentioned above boron appears with the form of B 4 O 5 (OH) 4 2– and B 5 O 6 (OH) 4 – . The present paper is a continuation of a previously undertaken project.…”