**3.2.2 The measurements of the physicochemical properties**

For the physicochemical properties determinations, a PHS-3C precision pH meter supplied by the Shanghai Precision & Scientific Instrument Co. Ltd was used to measure the pH of the equilibrium aqueous solutions (uncertainty of ± 0.01). The pH meter was calibrated with standard buffer solutions of a mixed phosphate of potassium dihydrogen phosphate and sodium dihydrogen phosphate (pH 6.84) as well as borax (pH 9.18); the densities (*ρ*) were measured with a density bottle method with an uncertainty of ± 0.2 mg.cm-3. The viscosities (*η*) were determined using an Ubbelohde capillary viscometer, which was placed in a thermostat at (308.15 ± 0.1) K. No fewer than five flow times for each equilibrium liquid phase were measured with a stopwatch with an uncertainty of 0.1 s to record the flowing time, and the results calculated were the average. An Abbe refractometer (model WZS-1) was used for measuring the refractive index (*n*D) with an uncertainty of ± 0.0001. The physicochemical parameters of density, refractive index and pH were also all placed in a thermostat that electronically controlled the set temperature at (308.15 ± 0.1) K.

## **3.3 Experimental methods of phase equilibria**
