Quaternary salt systems

The sodium chloride – potassium chloride – calcium chloride – water system

In the quaternary (Na+,K+, Ca2+) – Cl-H2O system at 50°C, the following solid phases appear:

  • NaCl (halite)
  • KCl (sylvite)
  • CaCl2·2H2O (sinjarite)
  • KCl·CaCl2 (chlorocalcite, baeumlerite)

In the triangular diagram shown in the figure to the right, compositions are shown on a dry basis. At any point in the diagram, the mass percents of the three salts NaCl, KCl, and CaCl2 add up to 100%. A saturated solution contains the amount of water given in mass percent in the diagram and an amount of salt with a composition corresponding to the location in the diagram.

Solubility diagram for the sodium chloride - potassium chloride - calcium chloride - water system at 50 °C. The composition of salts are given in mass percent on a dry basis
Solubility diagram for the sodium chloride – potassium chloride – calcium chloride – water system at 50 °C. The composition of salts are given in mass percent on a dry basis

The experimental points and the calculated phase diagram lines represent compositions at which two solid phases are in equilibrium with the same saturated liquid. Each field in the diagram represents solution compositions that can only be in equilibrium with a single solid phase. The two fields representing CaCl2·2H2O and KCl·CaCl2 are very small. This is indicative of a high solubility relative to the other salts in the diagram.

The aqueous sodium chloride – potassium sulfate reciprocal salt system

In the quaternary (Na+,K+)-(Cl,SO42-)-H2O system at 100°C, the following solid phases appear:

  • NaCl, Sodium chloride
  • Na2SO4, Sodium sulfate
  • KCl, Potassium chloride
  • K2SO4, Potassium sulfate
  • NaK3(SO4)2, Glaserite

The phase diagram to the right shows the concentration ranges in which the various solid phases appear. The concentration unit is charge fraction, which corresponds to equivalent fraction. The water contents of the saturated solutions are indicated by the numbers given at the grid intersections as mass percent water.

Each corner of the phase diagram represents a binary solution, and each of the four sides a ternary solution. The lower left corner of the figure to the right represents a KCl solution, the lower right corner a K2SO4 solution. Correspondingly, the upper corners represent a NaCl and a Na2SO4 solution.

 

Phase diagram for the aqueous sodium chloride - potassium sulfate reciprocal salt system at 100 °C
Phase diagram for the aqueous sodium chloride – potassium sulfate reciprocal salt system at 100 °C

A contour chart of the same system is shown below to the right. This diagram does not show the phase diagram lines, but only the water content in each part of the diagram. The water content is indicated by colors as shown in the legend, where the numbers are mass% water. The brown color indicates a high water content and the dark blue a low water content.

Below to the left is a 3-D plot of the same diagram. It uses the same color scheme as the contour plot to indicate the water level. The phase diagram lines can be seen in the 3-D plot as the lines corresponds to the “valleys” in the 3-D plot. The low water content at the phase diagram lines is indicative of the common tendency of salting in.

Jänecke diagram for the aqueous sodium chloride - potassium sulfate reciprocal salt system at 100 °C. The water content is shown as the height of the surface
Jänecke diagram for the aqueous sodium chloride – potassium sulfate reciprocal salt system at 100 °C. The water content is shown as the height of the surface
Jänecke diagram for the aqueous sodium chloride - potassium sulfate reciprocal salt system at 100 °C. The water content is shown as contour lines
Jänecke diagram for the aqueous sodium chloride – potassium sulfate reciprocal salt system at 100 °C. The water content is shown as contour lines

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