Phase equilibria for the pseudo-ternary system (NaCl + Na 2 SO 4 + H 2 O) of coal gasification wastewater at T = (268.15 to 373.15) K

The equilibrium solubility and physical properties (n D, η, and ρ) of NaCl and Na2SO4 in cyclohexanol and cyclohexanone aqueous solutions at 323.15 K were determined by an isothermal solution saturation method. According to the experimental data, the phase diagrams and diagrams of physical properties vs composition were plotted. The system of NaCl and Na2SO4 in cyclohexanol aqueous solution at 323.15 K can be divided into one invariant point, two univariant curves, and three crystallization regions. The physical properties of this system changed regularly with the change of the solubility of Na2SO4. The solubility of Na2SO4 and NaCl significantly reduced due to the presence of cyclohexanol in water. With the increase of the cyclohexanol content in aqueous solution in the system, the crystallization region of Na2SO4 increased obviously. The system of NaCl and Na2SO4 in cyclohexanone aqueous solution consisted of one invariant point, two univariant curves, and two crystallization regions corresponding to NaCl and Na2SO4. When Na2SO4 and NaCl were analyzed as 5.22 and 23.91 wt %, respectively, the solution reached saturation at 323.15 K. The presence of cyclohexanone in water has little effect on the solubility of Na2SO4 and NaCl. The equilibrium solids were verified by X-ray diffraction. It can be seen from the experimental results that the influence of the presence of organic impurity in water on the solubility of Na2SO4 and NaCl cannot be generalized. The measured data, especially the crystalline regions, could provide the fundamental basis, which would be of great value in designing and optimizing the crystallization process of NaCl and Na2SO4 in coal chemical high-salinity wastewater.

Section: Introductionmentioning

confidence: 99%

Determination of NaCl and Na₂SO₄ Equilibrium Solubility in Cyclohexanol and Cyclohexanone Aqueous Solutions at 323.15 K

Zhu

et al. 2020

“…Until now, there are several publications which report the equilibrium data for the related multicomponent systems. Because Na 2 SO 4 and NaCl are conventional inorganic salts existing in the classical systems such as salt lake brine and concentrated seawater, and the phase equilibrium investigations for the ternary system Na + //Cl – , and SO 4 2– –H 2 O are adequate, which cover the temperature range from 258.15 to 373.15 K under atmospheric pressure. − There are even equilibrium data reported at the conditions of higher temperatures and pressures up to 793.15 K and 130 MPa. − By contrast, the phase equilibrium investigations are relatively lacking for the systems containing NaNO 3 . To the best of our knowledge, Zhang and Huang measured the stable phase equilibrium data for the quaternary system Na + //Cl – , NO 3 – , and SO 4 2– –H 2 O at low temperature conditions of 258.15, 268.15, 273.15, and 278.15 K, while Bian et al and Yang et al reported its stable phase equilibrium data at high temperature conditions of 353.15 and 373.15 K, respectively.…”

Section: Introductionmentioning

confidence: 99%

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

Chen¹,

Bian

et al. 2019

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.

“…At present, the treatment is usually to evaporate them to dryness and transport to stack somewhere. As a result, these large numbers of mixed salts with impurities not only occupy large area lands but also lead to secondary pollution with rainfall infiltration because of their high water solubility and thus are identified as hazardous wastes . Hence, separating and recovering of these salts from such industrial wastewaters become an urgent task for the enterprise.…”

Section: Introductionmentioning

confidence: 99%

Phase Equilibria in the Aqueous Ternary System (NH₄)₂SO₄ + Na₂SO₄ + H₂O at T = (303.15 and 313.15) K and p = 0.1 MPa

Fan

Guo

et al. 2018

The solubility for the aqueous ternary system (NH4)2SO4 + Na2SO4 + H2O at T = (303.15 and 313.15) K and p = 0.1 MPa was investigated experimentally with the method of isothermal dissolution equilibrium. In the phase diagram of the ternary system at 303.15 K, there are eight crystallization regions, four univariant curves, and three invariant points corresponding to (Na2SO4·10H2O + Na2SO4), (Na2SO4 + Na2SO4·(NH4)2SO4·4H2O), and (Na2SO4·(NH4)2SO4·4H2O + (NH4)2SO4). However, in the phase diagram of the same ternary system at 313.15 K, the crystallization region of Na2SO4·10H2O is disappeared, and there are three single salt crystallization regions corresponding to Na2SO4, Na2SO4·(NH4)2SO4·4H2O, and (NH4)2SO4. A comparison of the phase diagrams for this ternary system at (273.15, 288.15, 298.15, 303.15, 313.15, and 333.15) K shows that the area of Na2SO4·(NH4)2SO4·4H2O and (NH4)2SO4 is increased obviously, whereas the area of Na2SO4 (or Na2SO4·10H2O) is decreased significantly and no solid solution was found. The experimental phase equilibria and phase diagrams can provide a fundamental basis for salt recovery in industrial wastewaters.