Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

The quaternary water salt system Rb+, Mg2+//Cl , borate H2O is an important subsystem of the composition of Pingluo underground brine, Sichuan province. An isothermal dissolution equilibrium method was used to study the phase equilibrium of the system, and the solubilities, densities, and refractive indices of the equilibrated solution of the system were determined. On the basis of the solubility data, the isothermal dissolution phase diagram, the water figure, the diagrams for the density-composition and refractive index-composition were obtained. Results suggest that the quaternary system is of a complex reciprocal system with the formation of double salt RbCl*MgCl2*6H2O. Three invariant points and seven univariant curves divide the phase diagram into five crystalline zones. The five crystalline regions correspond to four single salts, rubidium chloride (RbCl), bischofite (MgCl2*6H2O), rubidium pentaborate tetrahydrate (RbB5O6(OH)4*2H2O), and hungchaoite (MgB4O5(OH)4*7H2O), and one double salt rubidium-carnallite (RbCl*MgCl2*6H2O). The size of the RbB5O6(OH)4*2H2O crystallization field is the largest, whereas that of MgCl2*6H2O is the smallest. Comparisons between the stable phase diagrams at 323 K and 348 K show that there is no change with the crystallization forms of the salts, while the crystallization field of salt RbB5O6(OH)4*2H2O becomes obviously larger with the increase of temperature; a rise in temperature is beneficial to separate RbB5O6(OH)4*2H2O from the solution.