Phase Equilibria of the Reciprocal Quaternary System (Na⁺, Ca²⁺//Cl^–, Borate–H₂O) at 288.15 K and 0.1 MPa

Abstract

To exploit the valuable features of brine resources with high concentrations of borate ions, the solubility data and corresponding physicochemical properties (refractive index, density, viscosity, and pH) for the reciprocal quaternary system (Na + , Ca 2+ //Cl − , borate−H 2 O) at 288.15 K were determined experimentally using the method of isothermal dissolution equilibrium. The dry-salt and water-phase diagrams and the diagrams of physicochemical properties (refractive index, density, viscosity, and pH) against J(B 4 O 7 2− ) in the solution were established. In the dry-salt phase diagram of the quaternary system at 288.15 K, two invariant points, five univariant curves, and four crystallization regions corresponding to gowerite (CaB 6 O 10, and sodium chloride (NaCl) were found. The area of crystallization region of CaB 6 O 10 •5H 2 O is larger than that of other coexisting salts, which indicates that the solubility of gowerite in this system is the lowest and that it is more easily separated by crystallization; the areas of crystallization regions of Na 2 B 4 O 7 • 10H 2 O, NaCl, and CaCl 2 •6H 2 O are decreased in turn. In this system, there are no double salts or solid solutions experimentally found. The water-phase diagram of the system indicates regular variation of J(H 2 O) on J(B 4 O 7 2− ), and the physicochemical properties of the quaternary system varied regularly with increasing Janecke index values of J(B 4 O 7 2− ).

Solid–Liquid Equilibrium of Quinary Aqueous Solution Composed of Lithium, Potassium, Rubidium, Magnesium, and Borate at 323.15 K

“…Commonly, the dissolution and crystallization behavior of salts in solution can be obtained through the phase equilibria study of the complex salt–water system at multiple temperatures. Therefore, to understand the thermodynamic behaviors of the borates in aqueous solution, several phase diagrams of the system containing borates have been reported, for example, Na + //BO 2 – , OH – –H 2 O at (263.15–323.15) K; − Li + //Cl – (SO 4 2– ), BO 2 – –H 2 O at 288.15 and 298.15 K; , Na + , Ca 2+ //Cl – , borate–H 2 O and Li + , Na + , Ca 2+ //Cl – , borate–H 2 O at 288.15 K; , Li + , K + //SO 4 2– , B 4 O 7 2– –H 2 O at 288.15 K; Li + , Na + , Mg 2+ //B 4 O 7 2– –H 2 O at 273.15 K; Li + , Na + , K + //CO 3 2– , B 4 O 7 2– –H 2 O and Na + , K + //Cl – , SO 4 2– , B 4 O 7 2– –H 2 O at 298.15 K; , and the phase equilibria of quinary, quaternary, and ternary subsystems of system Li + , K + , Rb + , Mg 2+ //Cl – , borate–H 2 O. − After comprehension of the above research, three forms of boron ions such as BO 2 – , B 4 O 7 2– , and B 5 O 8 – appeared in the solution, and the coexisting ions in the solution and temperature have a direct effect on the structure of boron ion.…”

Solid–Liquid Phase Equilibria of the Quinary System Containing Lithium, Sodium, Calcium, Chloride, and Borate Ions at T = 288.15 K and p = 101.325 kPa

“…However, it should be pointed out that there are several species of borates in aqueous solution, including BO 2 – , B 4 O 7 2– , B 5 O 8 2– , B 6 O 10 2– , and so on, and this depends on the concentration of the total boron and counter ion in the solution. , However, the certain concentration of each kind of borate is impossibly difficult to determine by present analytical techniques. Therefore, the concentration of the total borates was obtained and often expressed by different forms on the basis of the statistical principle of group contribution …”

“…Moreover, it is academically known that phase equilibria and phase separation are the fundamental techniques and the basis and guidance of the utilization and separation for liquid resources. Although several phase diagrams and physicochemical properties of relevant systems, such as (Li + , Ca 2+ //BO 2 – –H 2 O) at 288.15 and 298.15 K, (Ca 2+ //Cl – , B 6 O 10 2– –H 2 O) at 308.15 and 323.15 K, (Li + , Na + , Ca 2+ //Cl – –H 2 O), (Na + , K + , Ca 2+ //Cl – –H 2 O), and (Na + , Ca 2+ //Cl – , B 4 O 7 2– –H 2 O) at 288.15 K, have been reported, there are still little reports concerning equilibrium solubility data of more components systems, which is more effective to reflect the physicochemical changes in natural brines. Considering that the statistical temperature in the Qaidam Basin from spring to summer in a year is between (283 and 313) K from 1981 to 2015, the phase equilibrium study at 288.15 K could better describe the actual system state and provide detailed information about the solar pond process in the Qaidam Basin.…”

Experimental Data and Thermodynamic Model in the Salt–Water Ternary System (NaBO2 + Na2B4O7 + H2O) at T = 298.15 K and p = 0.1 MPa

“…Borates can exist in many different forms in aqueous solution, such as metaborate (BO 2 – ), triborate (B 3 O 5 – ), and polytetraborate (B 4 O 7 2– , B 6 O 10 2– ), and the dissolution behavior of boron is very intricate. − In order to make full use of brine resources, some subsystems containing borate have been studied in various temperatures, such as the Li 2 B 4 O 7 –Li 2 SO 4 –LiCl–H 2 O system at 298.15 K, the LiCl–LiBO 2 –H 2 O system at 288.15, 298.15, 308.15, and 323.15 K, − the NaCl–NaBO 2 –H 2 O system at 288.15, 298.15, and 308.15 K, , and the (Li 2 B 4 O 7 + MgB 4 O 7 + H 2 O) and (Na 2 B 4 O 7 + MgB 4 O 7 + H 2 O) systems at 298.15 K . However, few systems containing two borates, except some systems containing magnesium borate or calcium borate, , were reported in the literature.…”

“…3−5 In order to make full use of brine resources, some subsystems containing borate have been studied in various temperatures, such as the Li 2 B 4 O 7 −Li 2 SO 4 −LiCl−H 2 O system at 298.15 K, 6 the LiCl− LiBO 2 −H 2 O system at 288. 15, 298.15, 308.15, and 323.15 K, 7−9 the NaCl−NaBO 2 −H 2 O system at 288.15, 298.15, and 308.15 K, 10,11 12 However, few systems containing two borates, except some systems containing magnesium borate or calcium borate, 13,14 were reported in the literature.…”