In order to obtain the crystalline forms of the salts of the potassium

ammonium

calcium coexisting chloride system

the phase equilibria relationship of quaternary system K

+

NH

4

+

Ca

2+

//Cl

-

-H

2

O at 298.2

323.2

and 348.2 K was studied by isothermal dissolution equilibrium method. The solubility and density of equilibrium liquid phases of the system were experimentally determined; X-ray powder diffractometer was used to determine the compositions of the equilibrium solid phase at the quaternary invariant point. It is found that the quaternary system is a complex system at these three temperatures. The phase diagram at 298.2 K consists of three invariant points

seven univariate curves and five crystalline phase regions

forming the solid solutions (NH

4

Cl)

x

(KCl)

1-

x

and (KCl)

x

(NH

4

Cl)

1-

x

; while at 323.2 and 348.2 K the phase diagram consists of five invariant points

eleven univariate curves and seven crystalline phase regions

the double salts (KCl·CaCl

2

) and (2NH

4

Cl·CaCl

2

·3H

2

O)

solid solutions (KCl)

x

(NH

4

Cl)

1-

x

and (NH

4

Cl)

x

(KCl)

1-

x

were formed. Among them

the crystalline phase region of solid solution (KCl)

x

(NH

4

Cl)

1-

x

is the largest at three temperatures

indicating that it is the easiest to crystallize in this system. Comparing the phase diagrams of the quaternary system at 298.2

323.2

and 348.2 K

it can be seen that the crystalline form of CaCl

2

changes with the increase of temperature: CaCl

2

·6H

2

O at 298.2 K

CaCl

2

·2H

2

O at 323.2 and 348.2 K. From 323.2 to 348.2 K

the crystalline phase regions of (KCl·CaCl

2

) and (2NH

4

Cl·CaCl

2

·3H

2

O) increased gradually.