Aqueous Salt Solutions

Equilibrium calculations based on the Extended UNIQUAC model can be
performed by calls from visual basic programs such as Microsoft Excel®.
Dynamic Link Libraries (DLL-files) containing simulation tools for
solid-liquid equilibrium and vapor-liquid equilibrium calculations are
available. A sample program can be downloaded for free. The program includes
the ions Na^{+}, H^{+}, Cl^{-}, HSO_{4}^{-},
SO_{4}^{2-}, and OH^{-}. Based on the users input of
temperature and composition, the program performs:

- Solid-liquid equilibrium calculations.
- Bubble point calculations determining the vapor pressure of the solution at a given temperature and composition.
- Calculation of saturation index (Degree of saturation/supersaturation).
- Calculation of enthalpy of formation and heat capacity.
- Calculation of water activity and mean molal activity coefficient
- Calculation of freezing point depression.
- Calculation of phase diagrams for salt systems

The calculation accuracy achieved with this sample program is typical for the performance of the extended versions of the program too. The license will expire after approximately one year. After the license has expired, you can come back and download a new version. The sample program comes with a short manual, that explains about installation and use of the program.

Extended versions of the program containing additional ions and solvents are generated according to the needs of customers. More advanced versions of the program with multi phase flash (vapor-liquid-solid and vapor-liquid-liquid-solid equilibrium calculations) can also be provided.

One extended version of the program includes the pressure dependency of
solubility. This program contains the ions Na^{+}, H^{+}, Mg^{2+},
Ca^{2+}, Ba^{2+}, Sr^{2+}, Cl^{-}, OH^{-},
SO_{4}^{2-}, HSO_{4}^{-}, CO_{3}^{2-},
HCO_{3} and is meant for calculations of oil field scale or
prediction of precipitation in geothermal energy production.
More details about the oil field scaling
calculation program here.

The program is called via the Microsoft Excel® file included in the download. In the excel file you can perform your own calculations with the model. You will also see a number of calculation examples which have been calculated already. These include:

A phase diagram for the binary NaCl - H_{2}O system:

A phase diagram for the binary Na_{2}SO_{4} - H_{2}O
system:

A phase diagram for the binary NaOH - H_{2}O system:

A triangular phase diagram for the ternary NaOH - Na_{2}SO_{4}
- H_{2}O system at 30°C

A Phase diagram for the Na_{2}SO_{4} - H_{2}SO_{4} - H_{2}O system at 82.5°C:

Osmotic coefficients for Na_{2}SO_{4} in dilute and in supersaturated solutions
at 25°C. The precipitation of glauber's salt, Na_{2}SO_{4}·10H_{2}O starts
at 1.9 molal Na_{2}SO_{4}:

Mean molal activity coefficients of NaCl solutions at 50°C. The data plotted together with the calculated line are correlated data from Clarke E.C.W. and Glew, D.N., Evaluation of the thermodynamic functions for aqueous sodium chloride from equilibrium and calorimetric measurements below 154 C., J. Phys. Chem. Ref. Data, 14(1985)489-610 (2):