Stable Solid–Liquid Equilibrium of the Quaternary System Na⁺//Cl^–, NO₃^–, and SO₄^2––H₂O at 333.15 K

Abstract

The stable-phase equilibrium of the quaternary system Na + //Cl − , NO 3 − , and SO 4 2− −H 2 O and its ternary subsystems at 333.15 K was measured by the isothermal dissolution method. Different from the simple phase equilibrium of the systems at 353.15 K, there is double salt generated in the Na + //NO 3 − and SO 4 2− −H 2 O system at 333.15 K. The double salt was determined to be NaNO 3 •Na 2 SO 4 •H 2 O by combining the wet residual analysis and X-ray diffraction test. Based on this characteristic, the quaternary Na + //Cl − , NO 3 − , and SO 4 2− −H 2 O system has two invariant points and five univariant curves, which generate four fields corresponding to the crystallization of Na 2 SO 4 , NaCl, NaNO 3 and the double salt. The areas of the fields indicate that the single salts have the solubilities in the sequence of Na 2 SO 4 < NaCl < NaNO 3 . Meanwhile, the crystallization region of the double salt is relatively small, which indicates that the double salt will disappear when increasing the temperature further. Related results provide the important basis for the fractional crystallization process of high-saline wastewater in the coal chemical industry.

Influence of Organic Impurities on Fractional Crystallization of NaCl and Na2SO4 from High-Salinity Coal Chemical Wastewater: Thermodynamics and Nucleation Kinetics Analysis

“…Based on classical nucleation theory and the Gibbs-Thompson equation [44], the following equation can be obtained. The interface energy can be expressed by Equation (12), where α is the slope of Equation (11). where t ind is the induction time; γ is the solid-liquid interfacial energy; V s stands for the solute molecular volume; T lim stands for the nucleation temperature; and S stands for the supersaturation.…”

“…It is known that typical coal chemical wastewater is rich in sodium sulfate (Na 2 SO 4 ) and sodium chloride (NaCl), which is considered as a classical water-salt system. To date, the crystallization processes of ternary, quaternary, and pluralistic systems containing Na 2 SO 4 or NaCl have been extensively studied, involving phase equilibrium [11][12][13], crystallization kinetics [14], and process optimization [15]. Zhang et al [16] investigated the solid-liquid equilibrium for the ternary Na 2 SO 4 -NaCl-H 2 O system at 313.15 K. Zeng et al [17] estimated the primary nucleation kinetics during Na 2 SO 4 crystallization at temperatures ranging from 313.15 to 353.15 K. Bian et al [15] conducted process parameters optimization on Na 2 SO 4 fractional crystallization in a quaternary NaCl-NaNO 3 -Na 2 SO 4 -H 2 O system.…”