**3.2 Analytical methods**

## **3.2.1 The chemical analysis of the components in the liquids**

For phase equilibrium study in this phase equilibrium system (NaCl - KCl – Na2B4O7 - K2B4O7 - H2O), the composition of the potassium ion in liquids and their corresponding wet

control the temperature was installed. When the solution temperature in the container was under (308.15 ± 0.2) K, the apparatus for controlling the temperature formed a circuit and the heating lamp began to heat. Conversely, the circuit was broken and the heating lamp stopped working when the temperature exceeded 308.15 K. Therefore, the temperature in the box could always be kept to (308.15 ± 0.2) K. An electric fan installed on the box always

Fig. 2. The schematic diagram of the isothermal evaporation chamber. 1, electrical contact thermograph; 2, precise thermometer; 3, electric relay; 4, electric fan; 5, heating lamp; 6,

Of course, the experimental conditions of an air flow velocity, a relative humidity, and an evaporation rate were controlled as similar as to those of the climate of reaching area in a

For phase equilibrium study, reagents used should be high-purity grade otherwise the recrystallized step was needed. For the stable and metastable phase equilibria in the salt-water system (NaCl - KCl – Na2B4O7 - K2B4O7 - H2O), the chemicals used were of analytical grade, except borax which was a guaranteed reagent (GR), and were obtained from either the Tianjin Kermel Chemical Reagent Ltd. or the Shanghai Guoyao Chemical Reagent Co. Ltd: sodium chloride (NaCl, ≥0.995 in mass fraction), potassium chloride (KCl, ≥ 0.995 in mass fraction), borax (Na2B4O7·10H2O, ≥ 0.995 in mass fraction), potassium borate tetrahydrate (K2B4O7·4H2O, ≥ 0.995 in mass fraction), and were re-crystallized before use. Doubly deionized water (DDW) with conductivity less than 1.2×10-4 S·m-1 and pH 6.60 at 298.15 K was used to prepare the series of the artificial synthesized brines and chemical analysis.

For phase equilibrium study in this phase equilibrium system (NaCl - KCl – Na2B4O7 - K2B4O7 - H2O), the composition of the potassium ion in liquids and their corresponding wet

**3.2.1 The chemical analysis of the components in the liquids** 

worked to accelerate the evaporation of water from the solutions.

evaporating container; 7, isothermal container.

simulative device.

**3.1 Reagents** 

**3. Experimental methods** 

**3.2 Analytical methods** 

solid phases was analyzed by gravimetric methods of sodium tetraphenyl borate with an uncertainty of ≤ ±0.0005 in mass fraction; Both with an uncertainty of ≤ ± 0.003 in mass fraction, the concentrations of chloride and borate were determined by titration with mercury nitrate standard solution in the presence of mixed indicator of diphenylcarbazone and bromphenol blue, and by basic titration in the presence of mannitol, respectively (Analytical Laboratory of Institute of Salt Lakes at CAS, 1982). The concentration of sodium ion was calculated by subtraction via charge balance.
