OCT 2 1972

Braaoii-of Terfs library

The Quinary Reciprocal Salt System 

Na,K,Mg,Ca/Cl,SO4 A Review of the 

Literature With New Data

GEOLOGICAL SURVEY PROFESSIONAL PAPER 741
The Quinary Reciprocal Salt System 

Na,K,Mg,Ca/Cl,SO4 A Review of the 

Literature With New Data

By J. J. ROWE, G. W. MOREY and C. S. ZEN

GEOLOGICAL SURVEY PROFESSIONAL PAPER 741

A discussion of the melting relations and interactions of 

components of the MaCl-K2S04-MgS04-CaS04 system as 

applied to the crystallization-differentiation of the 

Gnome melt

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress catalog-card No. 72-600065

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402 - Price 50 cents (paper cover)

Stock Number 2401-2140
PREFACE

The NaCl-K2S04-MgS04-CaS04 system and its 

component subsystems were studied by the authors 

under the direction of G. W. Morey. This work, supported by the U.S. Atomic Energy Commission, was 

undertaken to develop a theory for the crystallization, during cooling, of the mass of salt melted by 

the underground nuclear explosion Gnome near 

Carlsbad, N. Mex.

With the death of G. W. Morey on October 3,1965, 

it was decided to conclude the major experimental 

work and present the data assembled in this report. 

This report is not a completed study of the extremely 

complex systems; there is considerable experimental 

work yet to be performed. Nevertheless, the comprehensive data presented herein can be of value to 

future studies of these and related systems.

CONTENTS

Preface ___________________ ________ 

Abstract ______________________________

Introduction _____________________________________

Experimental methods ___________________ 

Components ______________________________________

The system K2 SO4-MgSO4-CaSO4 ________________

Binary systems ______________________________

K2SO4-MgSO4 ____________________________

K2SO4-CaSO4 _________________________

MgS04-CaS04 ___________________________

Discussion ___________________________________

The system NaCl-K2SO4-MgSO4 ___________________

Na,K/Cl,SO4 reciprocal salt system ____________

Binary systems ___________________________

NaCl-KCl ____________________________

NaCl-Na2SO4 ________________________

KC1-K2S04 __________________________

Na2SO4-K2 SO4 ___________,_____

NaCl-K2 SO4 _________________________

KCl-Na2SO4 _________________________

Discussion _______________________________

Na,Mg/Cl,SO4 reciprocal salt system ____________

Binary systems ___________________________

NaCl-MgCl2 _________________________

MgCl2-MgSO4 ________________________

Na2 SO4-MgSO4 _______________________

NaCl-MgSO4 _________________________

MgCl2-Na2 SO4 _______________________

Discussion _______________________________

K,Mg/Cl,SO4 reciprocal salt system ____________

Binary systems __________________________

KCl-MgCk ___________________________

KCl-MgSO4 __________________________

MgCl2-K2 SO4 ________________________

Discussion _______________________________

NaCl-MgCl2-KCl ternary system ______________

Na2SO4-MgSO4-K2SO4 ternary system _________

NaCl~KCl-MgSO4 plane _______________________

Summary of NaCl-K2SO4-MgSO4 as a plane in 

the Na,K,Mg/Cl,SO4 system _________________

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The system NaCl-K2SO4-CaS04 

Na,Ca/Cl,SO4 reciprocal salt system ____________

Binary systems _________________________

NaGl-CaCh ______-____________

CaCl2-CaSO4 _____ '. 

Na2SO4-CaSO4 ____ _______________

NaCl-CaSO4 _____________ 

CaCl2-Na2SO4 _________________

Discussion ___________________________

Ca,K/Cl,SO4 reciprocal salt system ___________

Binary systems _________________________

CaCl2-KCl _________-____ __ 

CaCl2-K2SO4 _______________ 

KCl~CaSO4 ________________________

Discussion ____________________________

NaCl-KCl-CaCl2 ternary system _>________ 

Na2 SO4-K2SO4-CaSO4 ternary system __________

NaCl-KCl-CaSO4 plane _______________________

Summary of NaCl-K2SO4-CaSO4 as a plane in the 

Na,K,Ca/Cl,SO4 system _____________________

The system NaCl-MgSO4-CaSO4 ___________ 

Mg,Ca/Cl,SO4 reciprocal salt-system ________

Binary systems _________________________

CaClz-MgClz _ __ _ ___ 

CaCl2-MgSO4 ________________________

MgCl2-CaSO4 ________________________

Discussion ________ ____________

NaCl-MgCl2-CaCl2 ternary system _____________

Na2SO4-MgSO4-CaSO4 ternary system ________

Summary of NaCl-MgSO4-CaSO4 as a plane in 

the Na,Mg,Ca/Cl,SO4 system ________________

The quaternary reciprocal salt system K,Mg,Ca/Cl,SO4 

KCl-MgCk-CaCk _____________________________

Discussion _____________________________

NaCl-K2SO4-MgSO4-CaSO4 _______________________

NaCl-K2SO4 2MgSO4 (langbeinite)-K2 SO4 

2CaSO4 (calcium langbeinite) plane _________

40-percent NaCl plane in the NaCl-KaSCUMgSO4-CaSO4 system ___________________

Discussion ______________________________

Crystallization-differentiation in the Gnome melt ____

References ___________ ____________

ILLUSTRATIONS

FIGURE 1. The system NaCl-K2 SO4-MgSO4-CaSO4 with the Gnome composition projected to the base ____ _ 

2. The systems NaCl-K2SO4-MgSO4 and KCl-NaCl-MgSO4 as planes across the quaternary reciprocal salt 

system Na,K,Mg/Cl,SO4 ________________ ' 

The four quaternary reciprocal salt systems which compose the quinary reciprocal salt system Na,K,Mg, 

Ca/Cl,SO4 _______________________-_ _ _______ _-_ -

The binary system K2SO4-MgSO4 __________ 

The binary system K2 SO4-CaSO4 ______________________________________________________

Compositions studied in the ternary system K2 SO4-MgSO4-CaSO4 ______ _ __ 

The ternary system K2SO4-MgSO4-CaSO4 _____ _______________ __ 

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VI CONTENTS

Page

FIGURE 8. The binary system NaCl-KCl ______________________________________________ 9

9. The binary system NaCl-NaaSC^ ____________________________________________ 9

10. The binary system KC1-K2S04 ______________________________________________ 10

11. The binary system Na2S04-K2S04 ___________________________________________ 10

12. The pseudobinary join NaCl-K2S04 across the Na,K/Cl,S04 reciprocal salt system _____________ 11

13. The pseudobinary join KCl-Na2S04 across the Na,K/Cl,S04 reciprocal salt system _____________ 12

14. The reciprocal salt system Na,K/Cl,S04 _______________________________________ 12

15. The binary system NaCl-MgCl2 _____________________________________________ 12

16. The binary system MgCl2-MgS04 ___________________________________________. 13

17. The binary system Na2S04-MgS04 ___________________________________________ 13

18. The stable join NaCl-MgS04 in the Na,Mg/Cl,S04 reciprocal salt system __________________ 13

19. The pseudobinary join MgCl2-Na2S04 in the Na,Mg/Cl,S04 reciprocal salt system ____________ 14

20. The reciprocal salt system Na,Mg/Cl,S04 _______________________________________. 14

21. The binary system KCl-MgCh ______________________________________________ 15

22. The join KCl-MgS04 in the K,Mg/Cl,S04 reciprocal salt system ________________________ 15

23. The pseudobinary diagonal MgCl2-K2S04 in the K,Mg/Cl,S04 reciprocal salt system ___________ 16

24. The reciprocal salt system K,Mg/Cl,S04 _______________________________________ 16

25. The ternary system NaCl-MgCla-KCl _________________________________________ 16

26. The ternary system Na2S04-MgS04-K2S04 ________________-________-_________ 17

27. The ternary system Na2S04-K2S04-MgS04 ______________________________________ 17

28. The ternary plane NaCl-KCl-MgS04 across the Na,K,Mg/Cl,S04 quaternary reciprocal salt system _ 17

29. The join NaCl to KaSCk 2MgS04 on the plane NaCl-K2S04-MgS04 ____________________ 19

30. The plane NaCl-K2S04-MgS04 across the Na,K,Mg/Cl,S04 quaternary reciprocal salt system _____ 19

31. The Na,K,Mg/Cl,S04 quaternary reciprocal salt system _ _ 20

32. Stereopair for the Na,K,Mg/Cl,S04 quaternary reciprocal salt system ____________________ 20

33. The binary system NaCl-CaCh ______________________________________________ 21

34. The binary system CaCl2-CaS04 _____________________________________________ 21

35. The binary system Na2S04-CaS04 ___________________________________________ 22

36. The join NaCl-CaS04 in the Na,Ca/Cl,S04 reciprocal salt system ________________________ 22

37. The pseudobinary diagonal CaCl2-Na2S04 in the Na,Ca/Cl,S04 reciprocal salt system __________ 23

38. The reciprocal salt system Na,Ca/Cl,S04 _______________________________________ 23

39. The binary system KCl-CaCl2 ______________________________________________ 23

40. The pseudobinary diagonal CaCl2-K2S04 in the K,Ca/Cl,S04 reciprocal salt system _____________ 24

41. The binary join KCl-CaS04 in the K,Ca/Cl,S04 reciprocal salt system ____________________ 24

42. The reciprocal salt system K,Ca/Cl,S04 ________________________________________ 25

43. The ternary system NaCl-KCl-CaCl2 __________________________________________ 25

44. The ternary system Na2S04-CaS04-K2S04 ______________________________________ 26

45. The plane NaCl-KCl-CaS04 in the Na,K,Ca/Cl,S04 quaternary reciprocal salt system _________ 26

46. The quaternary reciprocal salt system Na,K,Ca/Cl,S04 _______________________ __ 27

47. The plane NaCl-K2S04-CaS04 in the Na,K,Ca/Cl,S04 quaternary reciprocal salt system _______ 28

48. The binary system CaCla-MgCh _____________________________________________ 28

49. The ternary system Na2S04-MgS04-CaS04 ______________________________________ 29

50. The Na,Mg,Ca/Cl,S04 quaternary reciprocal salt system __________________________ 29

51. The plane NaCl-MgS04-CaS04 in the Na,Mg,Ca/Cl,S04 quaternary reciprocal salt system ______ 30

52. The ternary system KCl-MgCb-CaCh _________________________________________ 31

53. The K,Mg,Ca/Cl,S04 quaternary reciprocal salt system _____________ __ ___ ____ 31

54. The join NaCl to 70-percent langbeinite: 30-percent calcium langbeinite ___________________ 33

55. The plane NaCl-K2S04 2MgS04-K2S04 2CaS04___________________________________ 33

56. The 40-percent NaCl plane in the NaCl-K2S04-MgS04-CaS04 system ____________________ 34

57. The sides and base of the tetrahedron representing the NaCl-K2S04-MgS04-CaS04 system ________ 34

58. Path of crystallization of the Gnome melt _______________________________________ 35

TABLES

Page

TABLE 1. Compilation of reported temperatures for the inversion, eutectic, decomposition, and melting of CaS(>4 __ 5

2. Compositions in the binary system MgS04-CaSC>4 ____________________________________ 7

3. Compositions on the NaCl-K2S04-MgS04 plane in the Na,K,Mg/Cl,S04 quaternary reciprocal salt system _ 18

4. Compositions on the NaCl-K2S04-CaS04 plane in the Na,K,Ca/Cl,S04 quaternary reciprocal salt system _ 27

5. Compositions on the NaCl-MgS04-CaS04 plane) injthe Na,Mg,Ca/Cl,S04 quaternary1 reciprocal salt system _ 30

6. Compositions on the NaCl-langbeinite-calcium langbeinite plane in the NaCl-KuSCk-MgSCh-CaSCk system 32

7. Compositions on the 40-percent NaCl plane in the NaCl-K2S04-MgS04-CaS04 system _____________ 33
THE QUINARY RECIPROCAL SALT SYSTEM Na,K,Mg,Ca/Cl,SOj 

A REVIEW OF THE LITERATURE WITH NEW DATA

By J. J. ROWE, G. W. MOREY, and C. S. ZEN

ABSTRACT

Data from the literature, supplemented by new experimental results, are presented for 28 binary systems, 13 

ternary systems, six ternary reciprocal salt systems, and four 

quaternary reciprocal salt systems that make up the quinary 

reciprocal salt system Na,K,Mg,Ca/Cl,S04. The data were extrapolated to the pseudoquaternary system NaCl-K.2S04- 

MgS04 CaS04 to develop a theory for the crystallizationdifferentiation of the salt melted by the Gnome underground 

nuclear explosion in the Salado Formation near Carlsbad, 

N. Mex.

INTRODUCTION

The Gnome experiment, an underground nuclear 

explosion, was one event in the Plowshare program 

to evaluate the peaceful uses of atomic energy. To 

resolve problems such as the recovery of the radioisotopes generated by the device and absorbed by the 

surrounding rocks, it was necessary to study the 

course of crystallization of the molten mass of salt 

during cooling after the explosion in the Salado 

Formation near Carlsbad, N. Mex.

To develop an understanding of the phase relations of the Na,K,Mg,Ca/Cl,S04 system, a critical 

compilation was made of the data in the literature. 

This was supplemented by additional experimental 

study to determine the stable parts of the system 

and to resolve some of the discrepancies in the 

literature.

The system consists of NaCl, K2S04 , MgS04 , and 

CaS04. The approximate mineralogical composition 

of the Gnome material according to Nathans (1965) 

is 72 percent halite, 12.5 percent polyhalite, 8 percent silt and clay, 5.5 percent anhydrite, and 2 percent water. Neglecting silt, clay, and water, the composition of the material is 80.7 percent NaCl, 4 percent K2S04 , 2.8 percent MgS04 , and 12.5 percent 

CaS04 . Projected to the base of the tetrahedron as 

shown in figure 1, the composition, in terms of sulfate, is 21 percent K2S04 , 15 percent MgS04 , and 64 

percent CaS04 . This system is of geologic interest 

insofar as the compounds and minerals represent

NaCl

K2 SO MgS04

CaS04

FIGURE 1. The system NaCl-K2 S04-MgS04-CaS04 with the 

Gnome composition projected to the base.

anhydrous end members of many naturally occurring 

hydrated mineral systems.

The four component system NaCl-K2S04-MgS04- 

CaS04 is represented by a tetranedron] (fig. 1) 

bounded by the following ternary systems: K2S04- 

MgS04-CaS04 , NaCl-K2S04-MgS04 , NaCl-K2S04- 

CaS04, and NaCl-MgS04-CaS04 . The ternary system K,Mg,Ca/S04, shown as the base of the tetrahedron, is a straightforward ternary system which 

has been studied by Mukimov, Krylova, and Bergman (1949) and restudied by Rowe, Morey, and 

Silber (1967).

The other three ternary systems are made complex by the formation of reciprocal salts. NaCl reacts with each of the sulfates to form the following 

three ternary reciprocal salt systems, each consisting 

of two anions and two cations:

2NaCl + K,S04 = 2KC1 + Na? S04 

2NaCl + MgS04 = MgCl2 +Na2S04 

2NaCl + CaS04 = CaCl2 + Na2S04

(Na,K/Cl,S04 ) 

(Na,Mg/Cl,S.04 ) 

(Na,Ca/Cl,S04 )
QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

The secondary reactions of MgCl2 , CaCl2 , and KC1 

with the sulfates provide three more systems:

2KC1 + MgS04 = MgCl2 +K2S04 

2KC1 + CaS04 = CaCl2 + K2S04 

MgCl2 + CaS04 =MgS04 + CaCl2

(K,Mg/Cl,S04 )

(K,Ca/Cl,S04 )

(Mg,Ca/Cl,S04 )

Each of the three ternary sides of the tetrahedron 

(fig. 1) can be considered as a plane across a prism 

representing a quaternary reciprocal salt system. A 

quaternary reciprocal salt system is bounded by 

three ternary reciprocal salt systems. For example, 

we can show the NaCl-K2S04-MgS04 system as a 

plane across the Na,K,Mg-/Cl,S04 quaternary reciprocal salt system, as in figure 2. Another plane across 

the prism from two chlorides to one sulfate will 

further subdivide the prism into three quaternary 

systems. If the planes represent true ternary sysMgCI 2

Na2S04

K,S04

FIGURE 2. The systems NaCl-K2SO4-MgSO4 (shaded) 

and KCl-NaCl-MgSO4 (ruled) as planes across the 

quaternary reciprocal salt system Na,K,Mg/Cl,SO4.

terns, then each quaternary system formed can be 

treated as an individual system.

The complexity of the system under study is apparent. The quaternary system of figure 1 can be 

considered to be part of the quinary reciprocal salt 

system Na,K,Mg,Ca/Cl,S04 . Ricci (1964) discussed 

some of the problems of representing phase diagrams of the molten salts in reciprocal salt systems. 

The entire problem is further complicated by the 

high temperature decomposition of MgS04 and 

CaS04 to MgO and CaO, respectively; the volatilization of NaCl; and the extensive occurrence of complex solid solutions.

We summarize data from the literature supplemented by some experimental study of the eight 

possible components (five of which are independent), 

28 binary systems, 13 of the 56 ternary systems, six 

ternary reciprocal salt systems, and four quaternary 

reciprocal salt systems shown in figure 3. Our presentation of this extremely complex problem will be 

to develop information for the K2S04-MgS04-CaS04 

system which is the base of the tetrahedron of figure 

1 and then to describe each ternary side as a plane 

across the quaternary reciprocal salt system. Finally, 

we will discuss the tetrahedron and its component 

sections as related to the crystallization of the 

Gnome material.

EXPERIMENTAL METHODS

Charges to be studied were prepared from purified 

reagents that were checked by X-ray diffraction and 

by spectrographic analysis. These mixtures were repeatedly melted, ground, mixed, and remelted.

Compositions rich in MgS04 or CaS04 could not 

be prepared by melting because of the decomposition 

of MgS04 to MgO and CaS04 to CaO at high temperatures. We found that we could achieve reactions 

in the solid state without decomposition by heating 

the charges at 700°-800°C over a period of several 

weeks. The heating was interrupted periodically for 

mixing and grinding. X-ray diffraction patterns 

were run during this process to check on the progress of the reactions. We found that compositions 

could also be prepared hydrothermally. The mixed 

and ground components were placed in a 10-ml 

(milliliter) platinum crucible which was inserted 

into a Morey bomb (Morey and Ingerson, 1937). 

The crucible was loosely covered with a platinum 

cover and the bomb was closed. After heating to 

600°C in a furnace, water was pumped into the 

bomb to generate 7,500 psi (pounds per square inch) 

of steam pressure- The pressure and temperature
EXPERIMENTAL METHODS

K,SO,

A. Na,K,Mg/CI,S04

K2S04

CaCI

B. Na,K,Ca/CI,S04

CaCI CaCI,

K2S04

CaCI;

CaCI, MgCI2 CaCI,

CaS04

C. Na,Mg,Ca/CI,S04

CaS04 MgSO, K,S04 CaS04

CaS04

D. K,Mg,Ca/CI,S04

CaS04

FIGURE 3. The four quaternary reciprocal salt systems (A, B, C, and D) and their constituent binary, ternary, and 

ternary reciprocal salt systems which compose the quinary reciprocal salt system Na,K,Mg,Ca/Cl,S04.

were maintained for 1 to 2 days. Pressure was then 

reduced to atmospheric and heating continued for 

about 15 minutes to eliminate water. The bomb was 

permitted to cool slowly before opening. The crucible 

with the powders was weighed to determine whether 

any loss occurred and also to assure that water 

which might form hydrates was not absorbed.

Thermocouples used for quenching and heatingcooling studies were standardized against a thermocouple calibrated by the Bureau of Standards. 

Thermocouples were also checked using the known 

melting temperatures of NaCl (800.4°C), Na2SO4 

(884°C), Na3Si2 05 (874°C), and the alpha-beta 

quartz inversion (573°C).

Quenching studies were made by the usual method 

(Morey, 1923) of placing a small amount of the 

powdered material in a platinum foil envelope and 

dropping the envelope into mercury after the material had been subjected to a definite temperature 

for a suitable time to assure equilibrium. The 

quenched material was then examined using the 

petrographic microscope and X-ray diffractometer 

to identify crystalline phases and to determine 

whether melting had occurred. If the equilibrium 

temperature was below the liquidus temperature, 

crystalline material represents the primary phase, 

whereas glass or quenched crystals represent liquid 

in equilibrium with the crystals.

For quenching study of compositions which decompose before melting, such as MgS04 above 900°C, 

the powder was sealed in a platinum tube. The decomposition of some MgS04 to S03 plus MgO produced the pressure necessary to prevent further decomposition of the balance of the MgS04 .

Heating-cooling curves were made for many of 

the compositions to determine subsolidus, eutectic,

465-683 O - 72 - 2
QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

and liquidus thermal effects. A small platinum crucible containing the sample was suspended in an 

electric furnace. A thermocouple of platinum versus 

platinum with 10-percent rhodium measured the 

temperature of the samples, and a thermocouple of 

"platinel" (Donne, 1964) with one junction in the 

sample and the other junction in refractory tubing 

just above the sample measured the difference in 

temperature between the sample and its environment. These measurements were simultaneously 

plotted by a multichannel strip chart recorder. A 

furnace temperature controller was programmed to 

automatically cycle at a uniform rate between set 

limits. Usually the rate was 5° to 10° per minute 

but was varied to achieve the best results for the 

particular composition under study.

Thermal analysis utilizing heating-cooling curves 

or a modified DTA (differential thermal analysis) is 

a classical method which provides data regarding 

structure inversions, unmixing, solidus reactions, 

and eutectics, as well as liquidus temperatures. 

Thermal analysis methods, however, are nonequilibrium procedures. Sluggish reactions may not give 

detectable thermal effects. When metastable phases 

persist during cooling (undercooling), erroneous results may be obtained.

Hot-stage microscopy was also used to determine 

liquidus temperatures. The sample was placed directly on the loop of a thermocouple and inserted 

into a small furnace on the microscope stage. The 

behavior of the sample was observed during heating 

and cooling under low magnification with transmitted light.

The large number of systems to be examined for 

this study required that we refer to results of many 

other investigators. Most of the German work was 

done using thermal analysis. The Russian studies 

were made using the so-called visual polythermal 

method of Kurnakov as modified by Kumanin and 

described by Bergman (1955). This method is based 

on the observation of the surface of the liquid in a 

platinum crucible. The liquidus temperature is the 

temperature at which the last crystals will disappear 

during heating or the first crystals will appear on 

cooling. Little or no information regarding primary 

phases or subsolidus effects can be derived from this 

method.

For some systems, there are differences in the 

data reported by various investigators. These differences are to be expected considering that each study 

is based on an individual interpretation of observations using a variety of methods. When inconsistencies were found, we generally made laboratory

studies to resolve discrepancies; when this was not 

possible, we show the results of the various studies. 

Some workers have reported their results in terms 

of mole percent, others have used weight percent. 

Unless otherwise indicated results given here will be 

in weight percent.

COMPONENTS

The system NaCl-K2S04-MgS04-CaS04 is not 

limited to four components. Reciprocal salt reactions 

generate four more compounds KCI, MgCl2 , CaCl2 , 

and Na2S04 resulting in a total of eight components 

as follows:

NaCl: Sodium chloride melts at 800.4°C and boils at 

1,445°C according to Kracek (1942).

.K2SO4 : Potassium sulfate has a reported melting 

temperature of 1,069.1 °C and a transition from 

orthorhombic to hexagonal at 583°C (Roberts, 

1924). The latter has been verified by many studies including an X-ray diffractometer study by 

Bernard and Hocart (1961). We confirmed these 

results.

KCI: Potassium chloride has a reported melting temperature of 770.3°C and boils at 1,465°C (Roberts, 

1924).

MgCl2 : Magnesium chloride melts at 712°C as reported by Klemm, Beyersdorfer, and Oryschkewitsch (1948).

CaCl2 : The melting temperature for CaCl2 is 777°C 

(Scholich, 1920).

Na2SO4 : Sodium sulfate melts at 884.7°C (Roberts, 

1924). It occurs in five enantiotropic modifications 

with a complicated pattern of inversion which has 

been described by Kracek (1929). The existence 

of a new high temperature form above 548°C was 

reported by Simanov and Kirkina (1957).

CaSO4 : Calcium sulfate decomposes to CaO and SO3 

on heating above 1200°C in open crucibles. Numerous temperatures have been reported for the 

melting, decomposition, and inversion of CaS04 as 

shown in table 1.

We made our studies of the melting temperature for CaS04 in sealed platinum tubes by the 

quenching technique and found it to be 1,462°C 

(Rowe and others, 1965). This temperature represents a minimum, because of the formation of 

CaO, which would reduce the liquidus temperature 

as the system becomes binary (CaO-CaSO4 ). Decomposition starts at about 1,200°C, making the 

system binary, with a eutectic at 1,365°C, 20 percent CaO according to Newman (1941).
COMPONENTS

TABLE 1. Compilation of reported temperatures in degrees 

Celsius, for the inversion, eutectic, decomposition, and melting of CaSO4

Reference

a-0 CaSO4-CaO Decominversion eutectic position Melting

Bellanca (1942) __. 

Briner, Pamm, and

Paillard (1948) _. 

Bye and Kiehl (1948) 

Florke (1952) ____. 

Gay (1965) _____- 

Golubeva and

Bergman (1956) __. 

Grahmann (1913) __. 

Gruver (1951) ____- 

Janecke and

Muhlhausser (1936) 

Kracek (1942) ____. 

Masuda (1932) ___. 

Miiller (1910) ____. 

Newman (1941) _____ 

Ostroff and

Sanderson (1959) __ 

Rowe, Morey and

Silber (1967) ____

1,195

> 1,HO

1,196 ____

1,196 __

1,230 1,350

__ 1,380

1,000 ____

> 1,000 1,297

__ 1,450

1,150 __

__ 1,450

none 1,450

__ 1,450 

1,230 1,450

1,350

1,232 __

1,214 1,365 > 1,200 __

__ __ 1,149 ____

1,195 1,360 > 1,200 1,462

The inversion to a high temperature form has 

been questioned by Gay (1965). We observed a reversible thermal effect at 1,195°C in our heatingcooling studies but were unable to obtain crystals 

of the high-temperature form from our quenching 

experiments. We presume, as did Florke (1952), 

that the high-temperature form reverts to the 

low-temperature form very rapidly on cooling.

MgSO4 : The determination of the temperature at 

which MgS04 melts is complicated by the decomposition to MgO and S03 . Rowe, Morey, and Silber 

(1967) found by thermogravimetric analysis that 

MgS04 starts to decompose at 895°C. It was therefore necessary to use the sealed tube method to 

determine its approximate melting temperature.

Various temperatures have been reported for 

the melting of MgS04 . Some of these are 1,185°C 

(Janecke, 1912), 1,125°C (Grahmann, 1913), 

1,124°C (Nacken, 1907), 1,120°C (Ginsberg, 

1909), 1,187°C (Mukimov, Krylova, and Bergman, 1949), and 1,185°C (Kracek, 1942). From 

quenching experiments in sealed tubes, Rowe, 

Morey, and Silber (1967) found that MgS04 melts 

at 1,136°±4°C. Because of the formation of a 

small amount of MgO, this represents a minimum 

melting temperature.

We found that MgS04 exists in two enantiotropic forms. The beta form described by CoingBoyat (1926) was easily prepared by dehydration 

of MgS04 -H2 0 at 700°C. The high temperature 

form was found after heating the ,/3-MgS04 which 

was sealed in platinum tubes. The temperature of

the reversible transition of one form to the other 

is uncertain. Our results suggest that the inversion 

is between 997° and 1,095°C, probably close to 

1,090°. The X-ray diffraction patterns for this 

new form are given in Rowe, Morey, and Silber 

(1967). Dewing and Richardson (1959) performed experiments in which N_, S02 , and 02 

were passed over MgS04 during heating while 

thermal effects were measured with a differential thermocouple. They report a transition at 

1,010° ±10°C.

THE SYSTEM K2SO4-MgSO4-CaSO4

The ternary system K2S04-MgS04-CaS04 is the 

base of the tetrahedron for the quaternary system 

shown in figure 1. It consists of three binary systems: K2S04-MgS04 , K2S04-CaS04 , and MgS04- 

CaS04 .

BINARY SYSTEMS 

K2SO4-MgSO4

The K2S04-MgS04 system was studied by Nacken 

(1907), Grahmann (1913), Mukimov, Krylova, and 

Bergman (1949), and Rowe, Morey, and Silber 

(1967). Some of these results are shown in figure 4. Only one binary compound, langbeinite 

(K2S04 -2MgS04 ), is found in this system. Grahmann 

(1913) and also Mukimov, Krylova, and Bergman 

(1949) reported its melting temperature to be 

930°C. By quenching techniques and heating-cooling 

studies, Morey, Rowe, and Fournier (19.64) found 

that langbeinite melted at 943°C. The eutectic between langbeinite and K2 S04 occurs at 750°C and 

27.5 percent MgS04 . Nacken (1907) and Grahmann 

(1913) reported this eutectic at 750°C and 29.6 percent MgS04 . The eutectic between langbeinite and 

MgS04 was given by Nacken (1907) as 884°C and 

70.9 percent MgS04 . We verified this value. Mixtures 

containing more than 80 percent MgS04 could not be 

melted in air without decomposition.

K2SO4-CaSO4

The system K2S04-CaS04 had been previously 

studied by Miiller (1910), Grahmann (1913), Bellanca (1942), Mukimov, Krylova, and Bergman 

(1949), and Golubeva and Bergman (1956). The 

study by Rowe, Morey, and Hansen (1965) to resolve the differences between the results reported by 

previous investigators confirmed the results of Bellanca with only slight differences.

Calcium langbeinite (K2S04 -2CaS04 ) is the only 

compound in this binary system. It melts incongruently at 1,011 °C to CaS04 plus a liquid of com-
QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

1200

O Rowe, Morey, and Silber (1967)

A Nacken (1907)

D Mukimov, Krylova, and Bergman (1949)

D K2S04 -2MgS04

A +

LIQUID

MgS04 + K2S04 -2MgS04

+ K2S04 -2MgS04

+ K2S0 4 -2MgS04

500 

K2SQ 40 50 60 

WEIGHT PERCENT

90 MgS04

FIGURE 4. The binary system K.2S04-MgS04 (from Rowe and others, 1967).

position 57.5 percent CaS04 . X-ray diffraction 

studies provided no evidence of the 1:1, 2:3, 1:3, or 

1:4 ratios for K2S04 CaS04 compounds reported by 

Mukimov, Krylova, and Bergman (1949) and by 

Golubeva and Bergman (1956). There is limited 

solid solution of CaS04 in K2S04 . The eutectic between calcium langbeinite and K2S04 is, at 875°C, 

34 percent CaS04 . Figure 5, from Rowe, Morey, and 

Hansen (1965) shows our data plotted with that of 

Bellanca (1942).

MgSO4-CaSO4

The binary system MgS04-CaS04 has not been 

previously studied. Ramsdell (1935) and Mukimov, 

Krylova, and Bergman (1949) presumed that this 

was a simple binary eutectic system, containing no 

compounds. Bodaleva and Lepeshkov (1956) reported no compound formation in the system 

MgS04-CaS04-H2 0.

Investigation of this system was hampered by the 

decomposition of MgS04 above 890°C and CaS04

above 1,200°C. We carried out a limited study of the 

system by investigating (1) subsolidus reactions by 

long-time heating at temperatures below decomposition temperatures, (2) liquidus relationships by 

quenching studies of charges sealed in platinum capsules to limit the amount of decomposition of the 

sulfate mixtures, and (3) subsolidus reactions during hydrothermal heating at 600°C and 7,500 psi of 

steam pressure.

A new compound, CaS04 -3MgS04 , containing 28.3 

percent CaS04 was discovered, and the X-ray diffraction pattern was reported by Rowe, Morey, and 

Silber (1967). Compositions containing less than 

28.3 percent CaS04 gave patterns for MgS04 plus 

CaS04 -3MgS04 ; those containing more than 28.3 

percent CaS04 gave patterns for CaS04 plus 

CaS04-3MgS04 . In studies on the NaCl-CaSQ4- 

MgS04 system, compositions on the join NaClCaS04-3MgS04 showed the presence of NaCl plus 

CaS04-3MgS04 (fig. 51).
THE SYSTEM K2S04-MgS04-CaS04

1500

1400-

1300-

1200-

EXPLANATION

o Rowe, Morey, and Hansen (1965) 

A Bellanca (1942)

(9K2 S04 S.S. + |3K2S04 -2CaS04

1462

^1195

1011

940

500 

K,S04 10 30 40 50 60 

WEIGHT PERCENT

70 80 90 CaS04

FIGURE. 5. The binary system K2S04-CaS04 (from Rowe and others, 1965). S.S. indicates solid solution.

Liquidus temperatures, determined by the sealed 

tube quenching technique are given in table 2. These 

results are subject to uncertainties which are inTABLE 2. Compositions in the binary system MgS04-CaS04

CaSO« Liquidus 

(wt. percent) Phases present temperature (°C) Primary phase

0 MgS04 1,136

5 MgS04 + CaS04 3MgS04 __

10 MgS04 +CaS04»3MgS04 __

13.91 MgSO4 + CaS04»3MgS04 __

15 MgSO4 + CaS04 »3MgS04 - _

20 CaSO4 »3MgS04 + MgS04 __

28.3 CaSO4 »3MgSO4 1,201 ±4

30 CaS04 3MgS04 + CaS04* __

40 CaSO4 »3MgS04 + CaS04 1,165

50 CaSO4 »3MgS04 + CaSO4 1,130

53 CaSO4 »3MgSO4 + CaSO4 1,116

60 CaSO4 + CaS04»3MgS04 1,140

70 CaSO4 + CaS04»3MgS04 1,210

80 CaSO4 + CaS04»3MgS04 1,275

90 CaSO4 + CaS04»3MgS04 1,385

100 CaS04 1,462

o-MgS04

MgS04

MgS04

____

CaSO4 3MgS04

CaS04 3MgS04

_ _ _

CaSO4 3MgS04

CaSO4 3MgS04

CaSO4

CaS04

CaSO4

CaSO4

 

* Trace CaSO4.

herent in the experimental procedures. As the sulfates in the sealed tubes start to decompose, the 

partial pressure of S03 increases to prevent further 

sulfate decomposition. Depending on the amount of 

sulfate that decomposed, the final compositions may 

have changed slightly from those listed in table 2.

Quenching experiments using sealed platinum 

tubes gave erratic results in regard to phase identification. In some charges which were quenched from 

high temperatures, there were shifts in the X-ray 

lines for the CaS04 -3MgS04 compound, suggesting a 

possible partial solid solution with other compounds. 

Another compound may possibly be formed at high 

temperature in compositions containing 50 percent 

CaS04 . Still another X-ray pattern was obtained 

from some charges of starting composition between 

MgS04 and CaS04 -3MgS04 . However, these results 

do not permit positive conclusions, since some of the
8 QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

observed effects may be due to decomposition reactions.

To completely describe this binary system, additional work should be performed using controlled 

partial pressures of S03 . For the scope of this study, 

we are assuming the binary to be a simple eutectic 

system with a congruently melting compound 

(CaS04-3MgS04 ). The eutectics may be near 15 percent and 55 percent CaS04.

DISCUSSION

The ternary system K2S04-MgS04-CaS04 had been 

studied by Mukimov, Krylova, and Bergman (1949) 

and parts had been investigated by Ramsdell (1935). 

A complete restudy was made by Rowe, Morey, and 

Silber (1967) of compositions shown in figure 6.

The ternary system as determined by Rowe, 

Morey, and Silber (1967) is shown in figure 7. There 

are five fields of primary crystallization. Three of 

these are the pure components K2S04, CaS04, and 

MgS04 . A solid solution field has a minimum between congruently melting langbeinite and incongruently melting calcium langbeinite. The compound CaS04-3MgS04 has a field extending into the 

ternary system. A ternary eutectic occurs at 67.5 

percent MgS04, 27.5 percent K2S04 , 5 percent CaS04 , 

where liquid plus MgS04 plus CaS04-3MgS04 plus 

langbeinite solid solution coexist at 882 °C. Another

MgS04 EXPLANATION 

+ MgS04

ACaS04 -3MgS04 

O CaS04 

x Solid solution 

LJ K2S04

:CaS04 «3MgS04

K2S04 -2MgSO,

K2 S04

FIGURE 6. Compositions in weight percent, studied in the 

ternary system K2S04-MgS04-CaS04. Primary phases are 

shown. Compositions on the join langbeinite-calcium langbeinite are numbered 1 through 12 (from Rowe and others, 

1967).

MgSO* 

1136°C

884

CaS04 -3MgS04 

' 1201

K 2S04 -2MgS04 

943

740,

750

K2S04 

1069 °C

875 K2 S04-2CaS04 

1058

CaS04 

1462 °C

FIGURE 7. The ternary system K2 S04-MgS04-CaS04 plotted 

in weight percent. Contours show liquidus temperatures; 

contour interval is 25°C (from Rowe and others, 1967).

eutectic at 880 °C occurs at 49 percent MgS04, 32 

percent K2S04, and 19 percent CaS04 , where liquid 

plus CaS04 plus CaS04-3MgS04 plus langbeinite 

solid solution coexist. A minimum in the system 

occurs at 740°C at 25 percent MgS04, 69 percent 

K2S04, and 6 percent CaS04, where liquid plus K->S04 

plus langbeinite solid solution coexist. This minimum is at the intersection of the trough of the solid 

solution field and the boundary between K2S04 and 

the langbeinite solid solution field.

The Gnome composition, projected to the base of 

the tetrahedron of figure 1, in terms of sulfate, is in 

the field where anhydrite (CaS04 ) is the primary 

phase.

THE SYSTEM NaCl-K2SO4-MgSO4

The system NaCl-K2S04-MgS04 can be considered 

as a plane across the prism representing compositions in the quaternary reciprocal salt system Na,K, 

Mg/Cl,S04 (fig. 2). The phase relations on this plane 

provide one ternary side of the tetrahedron (fig. 1) 

representing the quasi-quaternary system NaClMgS04-K2S04-CaS04. The prism representing the 

Na,K,Mg/Cl,S04 system consists of the reciprocal 

salt systems Na,K/Cl,S04 ; Na,Mg/Cl,S04 ; K,Mg/ 

C1,S04 ; and ternary systems Na,K,Mg/Cl and 

Na,K,Mg/S04 (fig. 3A).
THE SYSTEM NaCl-K2S04-MgS04

Na,K/Cl,SO4 RECIPROCAL SALT SYSTEM

The Na,K/Cl,S04 reciprocal salt system consists 

of the NaCl-KCl, NaCl-Na2S04 , KCl-Na.SCX, and 

K2S04-Na2S04 systems as edges and the NaCl-K2S04 

and KCl-Na2S04 systems as diagonals.

BINARY SYSTEMS

NaCl-KCl

Kurnakov and Zemczuznyj (1907) found that 

NaCl and KC1 form a complete series of solid solutions which unmix at lower temperatures. The 

liquidus temperatures have been studied by Treis 

(1914), Janecke (1908), Gemsky (1913), and Akopov and Bergman (1954). A minimum in the solid 

solution series is at 664°C and 50 mole percent 

(43.6 wt percent) KC1. The unmixing was studied, 

using X-ray diffraction methods, by Bunk and Tichelaar (1953) and also by Nguyen-Ba-Chanh (1964) 

who found the upper consolute temperature to be 

500°±5°C at 69.5 mole percent KC1 (fig. 8).

800

700-

600-

500-

uj 400-

300-

200

100

NaCl

I I I I I II

776

MOLE PERCENT

FIGURE 8. The binary system NaCl-KCl (from NguyenBa-Chanh, 1964).

NaCl-Na2S04

The NaCl-Na2S04 system studied by Janecke 

(1908) is a simple system with the eutectic at 628° C, 

and 65 mole percent (69.3 wt percent) Na2S04 (fig. 

9). Akopov and Bergman (1954) confirmed Janecke's 

results.

KC1-K2SO4

The KC1-K2S04 system studied by Janecke 

(1908) is a simple system with a eutectic at 690°C, 

58 mole percent (55.2 wt percent) KC1 (fig. 10). 

There was no solid solution as evidenced by the 

inversion temperature of K2S04 , 587°C, remaining 

unchanged with addition of KC1. Akopov and Bergman (1954) and Golubeva and Bergman (1956) 

agreed with the results of Janecke.

Na2SO4-K2SO4

Janecke (1908), Perrier and Bellanca (1940), 

Bellanca (1942), and Mukimov, Krylova, and Fillipova (1949) all found a solid solution series between 

Na2S04 and K2S04 with the following temperatures 

reported for the minimum: 823°C (Bellanca) 

845°C (Janecke), and 830°C (Mukimov, Krylova, 

and Fillipova). They agreed that the minimum is at 

20 mole percent K2S04 . The complicated solid phase 

transitions were studied by Hilmy (1953). X-ray

900

884

800

£700 

cc

600

500

628

800

Na2S04 NaCl

MOLE PERCENT

FIGURE 9. The binary system NaCl-Na2S04 (from Janecke, 

1908).
10 QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

776

MOLE PERCENT

FIGURE 10. The binary system KCl-K2SO4 (from Janecke,

1908).

measurements of the thermal expansion of K3Na 

(S04 ) 2 were made by Fischmeister and Ronnquist 

(1960). Figure 11 is from Perrier and Bellanca 

(1940).

NaCl-K2SO4

We found the join NaCl-K2S04 in the reciprocal 

salt system Na,K/Cl,S04 to be a pseudobinary 

diagonal crossing the fields of NaCl; (Na,K)Cl 

solid solution; KC1; (Na,K)S04 solid solution; and 

K2S04 . KC1 was the primary phase from 66.4 percent K2S04 to 54 percent K2S04.

Janecke (1908) treated this diagonal as a binary 

system with a eutectic at 540°C and 65 mole percent (60 wt percent) K2S04. Akopov and Bergman 

(1954, 1959) found that it was not a binary but a 

pseudobinary diagonal. Our results and those of 

Janecke and Akopov and Bergman are plotted in 

figure 12.

Many of the subsolidus thermal effects observed 

in heating-cooling studies represent the complex

1071

595

884

Solid solution

428

191 /

235

K2S04 Na2 S04

MOLE PERCENT

FIGURE 11. The binary system Na2SO4-K2SO4 (from Perrier 

and Bellanca, 1940).

unmixing of the (Na,K)Cl solid solution and reactions of the (Na,K)S04 solid solution series. We 

and Janecke did not attempt to resolve these thermal 

effects.

This join is one side of the plane NaCl-K2S04- 

MgS04 and the plane NaCl-K2S04~CaS04 .

KCl-Na2SO4

Janecke (1908) studied the system KCl-Na2S04 

by means of heating-cooling curves and reported a 

complete solid solution series with complicated inversions and unmixing at lower temperatures which 

he did not attempt to clarify. Akopov and Bergman 

(1954) reported that this join crossed the field of a 

compound, probably 2Na2S04-K2S04, that formed 

by the decomposition of the solid solution. The later 

work done by Akopov and Bergman (1959) on this 

pseudobinary diagonal indicated that it goes from 

Na2S04 through a field of (Na,K)S04 solid solution, 

across fields of two of the three compounds formed 

from the breakdown of the (Na,K) S04 solid solution 

with a minimum at 525°C, and finally through the 

(Na,K)Cl solid solution field to KC1. Janecke used 

heating-cooling curves, whereas Akopov and Bergman relied on the visual polythermal method. Both 

results are shown in figure 13. Neither of the pre-
THE SYSTEM NaCl-K2 SO4-MgS04 11

1100

1000 -

900 -

800 -

700 -

600-

500

400 

NaCI

EXPLANATION 

n This report 

A Jahecke(1908) 

O Akopov and Bergman (1954)

10 40 50 60 

WEIGHT PERCENT

80 90 K2S04

FIGURE 12. The pseudobinary join NaCl-K2S04 across the Na,K/Cl,S04 reciprocal salt system. Symbols represent thermal effects observed in heating-cooling study.

vious investigators used X-ray or optics to identify 

primary phases.

DISCUSSION

The representation of reciprocal salt systems developed by Janecke (1908) is made by plotting 

compositions on a square, with the four salts as 

corners, one axis giving the fraction of the cations 

(in equivalents) and the other, the fraction of the 

anions. With temperature as the vertical axis, the 

diagram is a square prism, and the orthogonal projection of the liquid-solid relations on the composition square is the usual phase diagram.

Janecke (1308, 1950) (fig. 14) described the 

Na,K/Cl,SO4 reciprocal salt system as consisting 

of two complete series of solid solutions (Na,K)Cl 

and (Na,K) 2SO4 which meet in a boundary curve. 

He reported a minimum liquidus on the boundary 

curve at 515° C at a composition of 43 percent

Na2 , 57 percent K2 , 46 percent C12 , and 54 percent 

S04 (in mole percent). In terms of weight percent 

the composition of this point is 20.6 percent 

NaCI, 19.8 percent KCI, 16.0 percent Na2S04, and 

43.6 percent K2S04.

Akopov and Bergman (1954, 1959) and Akopov 

(1960) reported the existence of three Na2S04- 

K2S04 double compounds of unknown composition. 

These result from the breakdown of the continuous solid solutions of sodium and potassium sulfates below 736°C. They reported that the double 

compounds form limited solid solutions with one 

another and the other components of the system. 

In the binary system Na2SO4-K2S04, the solid 

solutions break down at a much lower temperature forming the 1:1 compound at 476°C. There 

has been no X-ray confirmation of the double compounds in this system.

We did not attempt to resolve the differences between Janecke and Akopov and Bergman regarding

465-683 O - 72 - 3
12 QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

1000

900

800

700

600

500

EXPLANATION 

A Janecke (1908) 

x Akopov and Bergman (1959)

Na,SQ

A

A A

(Na,KJ2S04 

solid solution

A A 

A 

A

A A A

400Q 

Na2S04

A A A A

20 40 60 80 100 

KCI

WEIGHT PERCENT

FIGURE 13. The pseudobinary join KCl-NaaS04 across the 

Na,K/Cl,S04 reciprocal salt system. Symbols represent 

thermal effects observed in heating-cooling study.

the complex subsolidus reactions in the system. Additional study should be performed to clarify the 

Na,K/Cl,S04 reciprocal salt system.

1074 °C 

K2S04

889 °C 

Na 2S04

691

629

(KCI)2 

778 °C

665 

MOLE PERCENT

(NaCI) 2 

801 °C

FIGURE 14. The reciprocal salt system Na,K/Cl,S04 

(from Janecke, 1950).

Na,Mg/Cl,SO4 RECIPROCAL SALT SYSTEM

The reciprocal salt system Na,Mg/Cl,S04 forms 

the second side of the prism representing the quaternary reciprocal salt system Na,K,Mg/Cl,S04 (fig. 

2A). The diagonal NaCl-MgS04 is one side of the 

ternary plane NaCl-MgS04-K2S04 (fig. 1). This 

reciprocal salt system is bounded by NaCl-MgCl2 , 

MgCl2-MgS04, Na2S04 -MgS04 , and NaCl-Na2S04.

BINARY SYSTEMS

NaCl-MgCl2

Klemm and Weiss (1940) (fig. 15) and Klemm, 

Beyersdorfer, and Oryschkewitsch (1948) studied the 

binary system NaCl-MgCl2 using X-ray techniques 

to identify phases. They reported two incongruently 

melting compounds 2NaCl MgCl2 (melting point 

485°C) and NaCl MgCl2 (mp 465°C). Bondarenko 

(1962) agreed with these results. The eutectic is 

at 450°C and 62 mole percent NaCl.

Menge (1911) reported only one compound 

(NaCl MgCl2 ) in this system. Scholich (1920) and 

Speranskaya (1938) reported two compounds, 

2NaCl-MgCl2 (mp 476°C) and NaCl 2MgCl2 

(mp 462°C), and the eutectic at 444°C and 53 mole 

percent NaCl. The latter compound was found to be 

a mixture of NaCl MgCl2 and MgCl2 by Klemm 

and Weiss (1940).

MgCl2-MgSO4

Janecke (1912) found MgCl2-MgS04 to be a 

simple system with the eutectic .at 667°C and 20 

mole percent MgS04 . Speranskaya (1938) found 

the eutectic at 656° C and 22.5 mole percent MgS04 

(fig. 16).

800

700-

600-

500 -

400 

MgCI2 40 60 

MOLE PERCENT

NaCl

FIGURE 15. The binary system NaCl-MgCl2 (from Klemm 

and Weiss, 1940).
s 712

cc

THE SYSTEM NaCl-K2S04-MgS04

1187

1200

13

i [

656

MgCI2 MgS04 

MOLE PERCENT

FIGURE 16. The binary system MgCl2-MgS04 (from Speranskaya, 1938).

Na2SO4-MgSO4

The system Na2S04-MgS04 was studied by Nacken 

(1907), who reported that Na2S04 -MgS04 melts congruently. Ginsberg (1909) (fig. 17) found three 

compounds in the system: Na2S04 -3MgS04 (antivanthoffite) which melts incongruently at 814°C to 

MgS04 plus liquid of composition 70 mole percent 

MgS04 ; Na2S04 -MgS04 which decomposes at 604°C 

to solid solution plus Na2S04 -3MgS04 ; and vanthoffite, 3Na2S04 MgS04 which forms solid solution plus 

Na2S04 -MgS04 above 506°C. The eutectic for the 

system is at 670°C and 43 mole percent MgS04. The 

NasSCX-rich solid solution series contains 36 mole 

percent MgS04 at the eutectic and becomes poorer 

in MgS04 as the temperature is lowered. Speranskaya (1938) and Mukimov, Krylova, and Fillipova 

(1949) accepted Ginsberg's results.

NaCl-MgSO4

Speranskaya (1938) (fig. 18) found the system 

NaCl-MgS04 to be of the simple eutectic type with 

no binary compounds. The eutectic is at 642 °C and 

48.5 mole percent MgS04 (49.2 wt percent). This 

system is assumed to be a stable diagonal in the 

reciprocal salt system. We obtained liquidus results 

agreeing with Speranskaya but our MgS04-rich

0 10 20 30 40 50 60 70 80 90 100 

Na2S04 MgS04 

MOLE PERCENT

FIGURE 17. The binary system Na2S04-MgS04 (from Ginsburg, 1909).

800

642

1185

Na,Cl s

MOLE PERCENT

MgS04

FIGURE 18. The stable join NaCl-MgS04 in the Na,Mg/ 

C1,S04 reciprocal salt system (from Speranskaya, 1938).
14 QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

melts were milky indicating some decomposition of 

MgS04. We also experienced considerable difficulty 

with creeping of the melt and volatilization of NaCl. 

From our heating-cooling curves, we confirmed the 

eutectic at 642°C.

MgCl2-Na2SO4

Speranskaya (1938) (fig. 19) studied the pseudobinary diagonal MgCl2-Na2S04 in the reciprocal 

salt system Na,Mg/Cl,S04 . -On addition of MgCl2 

to Na2S04 , the liquidus falls rapidly from 884°C to 

about 575°C where the field of NaCl is met at about 

19 mole percent MgCl2 . The temperature of the 

liquidus then rises to a maximum at 662 °C (40 mole 

percent MgCl2 ) while crossing the NaCl primary 

field. It then descends to the MgS04-NaCl boundary 

at 642°C (49 mole percent MgCL) where MgS04 

becomes the primary phase until the MgCl2-MgS04 

boundary is met at 588 °C (86 mole percent MgCl2 ) 

after which the liquidus rises to the melting point 

of MgCl2 , 712°C.

DISCUSSION

The reciprocal salt system Na,Mg/Cl,S04 as 

studied by Speranskaya (1938) (fig. 20) shows the 

following seven fields of primary crystallization: 

Na2S04 , Na2S04-3MgS04, NaCl, MgS04, MgCl2 , 

NaCl-2MgCl2 , and 2NaCl-MgCl2 . The differences 

between the results of Speranskaya (1938) and 

those of Klemm and Weiss (1940) and Klemm, 

Beyersdorfer, and Oryschkewitsch (1948) regarding 

the compound NaCl-2MgCl2 were discussed on page 

12.

Orlova and Yanat'eva (1963) in a study of the 

Na,Mg/Cl,S04,H2 0 system at 100°C reported the

712

'588

575

MgCI2

884

Na 2S04

MOLE PERCENT

FIGURE 19. The pseudobinary join MgCl2-Na2S04 in the 

Na,Mg/Cl,S04 reciprocal salt system (modified from Speranskaya, 1938).

SOOT 

Na 2CI 2 618

884 °C 

Na2S04

670

NaCl' 

2MgCI 814

MgCI2 

712°C

655

MOLE PERCENT

MgS04 

1185°C

FIGURE 20. The reciprocal salt system Na,Mg/Cl,S04 (from 

Speranskaya, 1938).

existence of a compound of composition MgS04- 

3NaCl-9Na2S04 , which gave DTA effects at 525 °C, 

620°C, and 720°C. At 525°C, the compound decomposes to NaCl + Na2S04-MgS04 +(Na,Mg)S04 solid 

solution.

The join from MgCl2 to Na2S04 represents a 

pseudobinary diagonal which crosses the field of 

MgS04. NaCl-MgS04 is a stable diagonal which 

divides the system into two stable ternary systems.

K,Mg/Cl,SO4 RECIPROCAL SALT SYSTEM

The reciprocal salt system K,Mg/Cl,S04 consists 

of KCl-MgCl2 , MgCL-MgS04 (fig.16), K2S04- 

MgS04 (fig. 4), and KC1-K2S04 (fig. 10) as edges 

and KCl-MgS04 and MgCl2-K2S04 as diagonals.

BINARY SYSTEMS

KCl-MgCl2

Klemm, Beyersdorfer, and Oryschkewitsch (1948) 

studied the system KCl-MgCl2 using X-ray methods 

to identify phases. They reported the two compounds: anhydrocarnallite, KCl-MgCl2 (mp 488°C), 

and 2KCl-MgCl2 (mp 433°C), both melting congruently as shown in figure 21.

This is in agreement with Menge (1911) and 

Ivanov (1952). Janecke (1912) and Scholich (1920) 

reported only KCl-MgCl2 in the binary system but 

did not use X-ray methods in their work.
THE SYSTEM NaCl-K2 S04-MgS04 15

800

700

600 -

500 -

400 60 80 100 

MgCI2

20 / 40 I 

KCI 2KCI-MgCI2 KCI-MgCU

MOLE PERCENT

FIGURE 21. The binary system KCl-MgCh (from Klemm 

and others, 1948).

KCl-MgS04

The KCl-MgS04 system is a stable diagonal according to Janecke (1912) (fig. 22). The compound 

KCl-MgS04 (anhydrokainite) is isotropic, probably 

tetrahedral, and melts congruently about 920 °C.

1000

900

800

700

600

870 V

665

MgS04

50 

MOLE PERCENT K2CI 2

FIGURE 22. Stable diagonal KCl-MgS04 in the reciprocal salt system K,Mg/Cl,S04 (from Janecke, 1912)

The melting point could not be determined precisely 

by Janecke because the decomposition of MgSO.t 

prevented synthesis of the pure compound. The 

eutectic between KCI and KCl-MgS04 is at 665° C 

and 33.3 mole percent (30 wt percent) MgSO t. 

Janecke (1912), from results slightly off of this 

diagonal, assumed the eutectic between KCl-MgS04 

and MgS04 to be at 870°C. Bergman and Selivanova 

(1938) accepted Janecke's results in their study of 

the plane NaCl-KCl-MgS04 .

There has been some question regarding the existence of KCl-MgS04. We prepared a melt of composition KCl-MgS04 (38.2 percent KCI+ 61.8 percent 

MgS04 ) which gave an X-ray diffraction pattern of 

langbeinite plus KCI plus a trace of MgCl2 or KCIMgCl2 , whereas we should have observed anhydrokainite. Heating-cooling curves of the composition 

KCl-MgS04 indicate thermal effects at 418°, 490°, 

610°, and 885°C. Linstedt (1952) made heavy liquid 

separation of a melt of KCl-MgS04 composition and 

found langbeinite. He also questioned the existence 

of a KCl-MgS04 compound. Additional study is 

therefore indicated to resolve the discrepancies and 

to revise Janecke's (1912) diagram of the K,Mg/ 

C1,S04 system.

MgCl2-K2S04

The join MgCl2-K2S04 was studied by Janecke 

(1912, 1950) as part of the system K,Mg/Cl,S04. 

On the addition of MgCl2 to K2 S04 , the liquidus is 

lowered from 1,069°C to about 650 °C at 33 mole 

percent (9 wt percent) MgCl2 where KCl-MgS04 

becomes the primary phase. The liquidus then rises 

to about 790°C as the anhydrokainite field is crossed. 

At 650°C and 76 mole percent (63 wt percent) 

MgCl2 , MgS04 becomes the primary phase. At 580°C 

and 87 mole percent (76 wt percent) MgCl2 , the 

field of MgCl2 is entered. The liquidus temperature 

then rises to the melting point of MgCl2 , 712°C. 

Figure 23 is from data of Janecke (1912).

DISCUSSION

This reciprocal salt system, studied by Janecke 

(1912), is shown in figure 24. The binary K2S04- 

MgSO4 system has eutectics at 725°C and 875°C, 

according to Janecke. We found eutectics at 750°C 

and 884°C (fig. 4). There are seven fields of primary crystallization: the four pure compounds and 

the binary compounds K2S04 -2MgSO4 (langbeinite), 

KCl-MgCl2 (anhydrocarnallite) (fig. 21), and possibly KCl-MgSO4 (anhydrokainite) (fig. 22). Additional study, using modern methods, should be performed to verify the phase diagram for this system.
16

1100

1000

900

800

700

600

500

K2S04

K2 S04

QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

the end of the prism formed from the three reciprocal salt systems: K,Mg/Cl,SO4 ; Na,K/Cl,S04 ; and 

Na,Mg/Cl,S04. The NaCl-MgCl2-KCl system was 

studied by Scholich (1920) (fig. 25). He reported 

no ternary compounds. Fields are shown for the incongruently melting binary compounds NaCl-2MgCl2 , 

2NaOMgCl2 and the congruently melting KCl-MgCl2 

(anhydrocarnallite). Below about 480°C, the solid 

solution (Na,K)CT unmixes.

The results shown by Scholich (1920) are different from those later reported by Klemm, Beyersdorfer, and Oryschkewitsch (1948) for the binary 

systems NaCl-MgCl2 (fig. 15) and KCl-MgCl2 (fig. 

21).

Na2SO4-MgSO4-K2SO4 TERNARY SYSTEM

Janecke (1950), in compiling the data on the 

ternary reciprocal salt system K,Mg,Na/Cl,S04 , 

found that the system Na2S04-MgS04-K2S04 had 

not been previously studied. He deduced the phase 

diagram shown in figure 26 from the phase diagrams 

of the component binary systems. Janecke's diagram will be used for our compilation of the 

Na,K,Mg/Cl,S04 quaternary reciprocal salt system.

Mukimov, Krylova, and Fillipova (1949), using 

the visual polythermal method, reported that the 

field of MgS04 extended between the fields for langbeinite and Na2S04 -3MgS04 (fig. 27). They agreed 

with Janecke regarding the extension of the (Na,K) 

S04 solid solution into the ternary system.

Additional study should be done on this ternary

20 40 60 80 100

MgCI2

0 

K2S04

MOLE PERCENT

FIGURE 23. Pseudobinary diagonal MgCl2-K2S04 in the reciprocal salt system K,Mg/Cl,S04 (data from Janecke, 1912).

NaCl-MgCl2-KCl TERNARY SYSTEM

The ternary system NaCl-MgCl2-KCl represents 

the three chlorides in the quaternary reciprocal system Na,Mg,K/Cl,S04 . It can be considered to be

725 MgS04

690

K,CI

667

42£> | 495 470 " MgCI2

KCI-MgCI2 

(ANHYDROCARNALITE)

FIGURE 24. The reciprocal salt system K,Mg/Cl,S04 (from 

Janecke, 1912).

MgCI

NaCI-2MgCI2

488 

KCI-MgCI2

443

2NaCI-MgCI 2

MOLE PERCENT

NaCI

FIGURE 25. The ternary system NaCl-MgCb-KCl (from 

Scholich, 1920).
THE SYSTEM NaCl-K2S04-MgS04 17

MgSO.

884 Na 2S04 -3MgS04

K2S04 -2MgS04

K,SO. 823

MOLE PERCENT

Na2 S04

FIGURE 26. The ternary system Na2S04-MgS04-K2S04 

(modified from Janeeke, 1950).

system using X-ray diffraction to identify the primary phases.

NaCl-KCl-MgSO4 PLANE

The NaCl-KCl-MgS04 plane across the prism 

representing the quaternary reciprocal salt system 

Na,K,Mg/Cl,S04 was studied by Bergman and Selivanova (1938) as shown in figure 28. There are no 

ternary compounds. Ternary eutectics are at 

616° and 624°C. The field for anhydrokainite 

(KCl-MgS04 ) extends into the ternary system. The 

study of Bergman and Selivanova was done entirely

MgS04

884,

K 2 S04 -2MgS04 

930

Na2S04 -3MgS04 

814

£70

750

K 2S04 

1076°C

823

MOLE PERCENT

Na 2S04 

884 °C

FIGURE 27. The ternary system Na2 S04-K2S04-MgS04 

(from Mukimov, Krylova, and Fillipova, 1949).

1185°C 

MgS04

870

KCI-MgSO. 

920

642

665

Na2CI 2 

SOOT

MOLE PERCENT

FIGURE 28. The ternary plane NaCl-KCl-MgS04 across 

the Na,K,Mg/Cl,S04 quaternary reciprocal salt system 

(modified from Bergman and Selivanova, 1938).

by the visual polythermal method. There was no 

phase identification by X-ray or optical methods, 

hence, the existence of the field shown for anhydrokainite should be reexamined.

For this compilation and for preparation of the 

phase diagrams of the quaternary reciprocal salt 

system, we will show this ternary system as a stable 

plane in the system.

SUMMARY OF NaCl-K2SO4-MgSO4 AS A PLANE 

IN THE Na,K,Mg/Cl,SO4 SYSTEM

The system NaCl-K2S04-MgS04 is a plane across 

the prism representing the quaternary reciprocal 

salt system Na,K,Mg/Cl,S04 as shown in figures 2 

and 3A. The phase relations will be discussed in relation to the phase volumes intersected.

The prism may be further subdivided into subsystems by various joins between the components 

and the compounds KCl-MgCl2 , NaCl-2MgCl2 , 

Na2S04 -3MgS04, K2S04-2MgS04 , and KCl-MgS04 . We 

did not attempt to determine which of these joins 

would form stable binary, ternary, and quaternary
18 QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

subsystems. Within each of the quaternary subsystems are invariant points or "stars" of liquid plus 

four solid phases.

Janecke (1950) derived the phase relations in the 

quaternary reciprocal salt system Na,K,Mg/Cl,S04 , 

which he called double-ternary. The following internal phase volumes were deduced from the bounding ternary reciprocal salt systems: Na,K/Cl,S04 

(fig. 14), Na,Mg/Cl,S04 (fig. 20), and K, Mg/Cl,SOt 

(fig. 24). Internal information was from the study 

by Bergman and Selivanova (1938) of the plane 

NaCl-KCl-MgS04 (fig. 28), which intersects phase 

volumes of NaCl, KC1, MgS04 , and KCl-MgS04 and 

also forms one ternary side of the quaternary system NaCl-KCl-MgCl2-MgS04 (fig. 2).

To determine the phases that occur on the plane 

NaCl-K2S04-MgS04 and to learn whether the plane 

will further subdivide the prism into two more 

stable quaternary systems, we prepared compositions shown in table 3. The data for compositions on 

the join NaCl-K2S04 -2MgS04 are shown in figure 29. 

From the coexistence of langbeinite and NaCl for 

all compositions on this join, we can assume that it 

is a true binary system. A minimum at 632°C was 

found at 47.5 percent NaCl. Other compositions on 

this plane, between the NaCl-langbeinite join and 

the NaCl-K2S04 join, show NaCl; KC1; (Na,K)S04 

solid solution (aphthitalite); and K2SO4 -2MgS04 

(langbeinite). The NaCl-K2S04 join is a pseudoternary join. The system is not ternary but is 

quinary in this part of the plane, hence it does not 

divide the prism into two more stable quaternary 

systems.

The join NaCl-MgS04 is a stable diagonal of the

Na,Mg/Cl,S04 system. Hence we can assume that 

the plane is stable between the NaCl-langbeinite 

join and the NaCl-MgS04 binary system. NaCl, 

MgS04 , and K2S04-2MgS04 are the three phases 

found in this part, as shown in figure 30. Additional 

study is necessary to completely delineate this plane.

To aid in visualizing the complex quaternary 

reciprocal salt system Na,K,Mg/Cl,S04 , we prepared 

figure 31, which shows the prism opened. A stereopair, representing the prism and the internal planes, 

is shown in figure 32. The graphic representation of 

the system is complicated by the solid solution series 

(Na,K)Cl, (Na,K)S04 , and (Na,Mg)S04 .

It can be seen from figures 30-32 that the plane 

NaCl-K2S04-MgS04 intersects phase volumes of 

K2S04 -2MgS04 (langbeinite), NaCl, MgS04 , K2S04 , 

KC1, and (Na,K)S04 solid solution. The phase volume of langbeinite extends a greater distance into 

the prism than was thought by Janecke (1950). 

Anhydrokainite (KCl-MgS04 ) (figs. 22-24) is reported to have a field in the NaCl-KCl-MgS04 plane 

(fig. 28).

To determine completely this complex system and 

the numerous invariant points requires considerable 

additional experimental study of the many sections 

across the various subsystems.

THE SYSTEM NaCl-K2SO4-CaSO4

The system NaCl-K2S04-CaS04 can be considered 

as a plane across the prism representing compositions in the quaternary reciprocal salt system Na,K, 

Ca/Cl,S04 . The phase relations on this plane will 

provide us with another ternary side of the tetraTABLE 3. Compositions on the NaCl-K2SO4-MgSO4 plane in the Na,K,Mg/Cl,SO4 quaternary reciprocal salt system

NaCl 

(wt 

percent)

100

90

80

70

60

50

40

30

20

10

0

40

40

K2SO4

(wt 

percent)

0

4.2

8.4

12.59

16.79

20.99

25.19

29.39

33.59

37.78

41.8

50

40

MgSO* 

(wt 

percent)

0

5.8

11.6

17.41

23.21

29.01

34.81

40.61

46.41

52.22

58.2

10

20

Phases present

Compositions on the join NaCl-langbeinite (KzSCh '

NaCl

NaCl + langbeinite

do

do

do

do

do

do

do

do

Other compositions

[ss indicates solid solution]

+ KCl+(Na,K)SO4ss 

do

Liquidus 

temperature

 2MgSO4 )

800.4

775

740

715

675

645

688

745

805

877

943

640

560

Temperature of 

other thermal 

effects

540

630, 540

632, 540

632, 540

632, 510

635, 510

635, 510

635, 510

510

540, 510

510

Primary phase

NaCl.

NaCl.

NaCl.

NaCl.

NaCl.

NaCl.

Langbeinite.

Do.

Do.

Do.

Do.

KC1.

Langbeinite.
THE SYSTEM NaCl-K2S04-CaS04 19

1000

900

800,

EXPLANATION 

A Heating-cooling data 

O Quenching data

700

600

500

400

300

NaCI 80 70 60 50 40 

WEIGHT PERCENT

30 20 10 K2Mg2(S04)3

554 642

558

K 2 S04 

1076°C

FIGURE 29. The join NaCI to K2SO4 2MgSO4 (langbeinite) on the plane NaCl-K2 SO4-MgS04.

hedron for the quasi-quaternary system NaClMgS04-K2S04-CaS04 (fig. 1).

The prism representing the Na,K,Ca/Cl,S04 system 

consists of the reciprocal salt systems Na,K/Cl,S04 ; 

Na,Ca/Cl,S04 ; and Ca,K/Cl,S04 and the ternary systems NaCl-KCl-CaCl2 and Na^SO.-K.SCVCaSO, 

(fig. 35).

Na,Ca/Cl,SO4 RECIPROCAL SALT SYSTEM

This reciprocal salt system consists of the NaClCaCl2 , NaCl-Na2S04, CaCl2-CaS04, and Na2S04- 

CaS04 systems as edges and NaCl-CaS04 and 

CaCl2-Na2S04 as diagonals.

BINARY SYSTEMS

NaCl-CaCl2

'Scholich (1920) found the NaCl-CaCl2 system to 

be a simple binary system with a eutectic at 506°C 

and 53 mole percent (68.2 wt percent) CaCl2 , as 

shown in figure 33.

Menge (1911) had reported an incongruently 

melting compound 4NaCl-CaCl2 . Examination of

(Na,K)S04 / K2S04-2MgS04 

solid solution

750 884

K 2 S04 -2MgS04

MgS04 

1136°C

FIGURE 30. The plane NaCl-K2SO4-MgSO4 across the 

Na,K,Mg/Cl,SO4 quaternary reciprocal salt system.
20 QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

K2CI 2

K2CI 2 KCI.MgCI 2 MgCI 2 K,CI,

MgS04

K2S04 -2MgS04 

(Langbeinite)

MgCI Na ?CI2

K 2S04 K? S04

K2S04

Na,K, Mg/CI,S04

K2S04 

FIGURE 31. The Na,K,Mg/Cl,S04 quaternary reciprocal salt system.

Menge's data shows a thermal effect for the eutectic 

in compositions containing more than 80 mole percent NaCl, which would preclude the existence of the 

4NaCl-CaCl2 compound.

CaCl2-CaSO4

fjanecke and Miihlhausser (1936), in a study of the 

reciprocal salt system K,Ca/Cl,S04 indicated that 

this was a simple system with a eutectic at 730°C 

and about 10 percent (8.7 mole percent) CaS04 .

However, they did not specifically study this binary 

system. Golubeva and Bergman (1956) (fig. 34), repeated this system and reported a eutectic at 706°C 

and 12.5 mole percent CaS04 . Palkin (1949) and 

Zimina, Bergman, and Nagornyi (1965) report this 

eutectic to be at 712°C.

NaCl-CaSO4

The system Na2 S04-CaS04 (fig. 35) has been 

studied by many, starting with Le Chatelier (1887),

MgS°4

FIGURE 32. Stereopair for the Na,K,Mg/Cl,SO4 quaternary reciprocal salt system.
THE SYSTEM NaCl-K2S04- CaS04 21

800

10 20 30 40 50 60 70 80 90 100

MOLE PERCENT

FIGURE 33. The binary system NaCl-CaCh (from Scholich,

1920).

with many contradictions and different interpretations of the experimental data. There is general 

agreement on the liquidus exhibiting solid solution 

with a maximum between 20 and 25 mole percent 

CaS04 , and a temperature between 944° and 950°C. 

The greatest differences are in the nature and composition of phases formed. Miiller (1910) reported a 

4Na2S04 -CaS04 compound. La Chatelier (1887) 

found a 2Na2S04-CaS04 compound, which was confirmed by Speranskaya and Barskaya (1961) by an 

X-ray study. Komissarova, Plyushchev, and Stepina 

(1955) in a study using thermal, optical; and X-ray 

methods reported finding glauberite (Na2S04 -CaS04 ) 

in the solidus as did Plyushchev (1962). Bellanca 

(1942), also using X-ray methods, reported no compounds but found that solid solution was formed of 

approximately 3Na2S04-CaS04 . Kracek (1942) gave 

the melting temperature of naturally occurring 

glauberite as 905 °C with decomposition below the 

liquidus to CaS04 and solid solution, and he stated 

that glauberite cannot be prepared from the melt. 

This was confirmed by Speranskaya and Barskaya 

(1961).

There are also some differences in the reported 

temperature and composition of the eutectic. Miiller 

(1910) found the eutectic at 913°C (40 mole percent CaS04 ); Komissarova, Plyushchev, and Stepina 

(1955), at 890°C (40 mole percent CaS04 ); Speranskaya and Barskaya (1961) and also Mukimov 

and Fillipova (1949), at 918°C (49 mole percent 

CaS04 ); Zimina, Bergman, and Nagornyi (1965), at 

910°C (49 mole percent CaS04 ); Plyushchev (1962,

775

All96 

706

CaCU CaS04

MOLE PERCENT

FIGURE 34. The binary system CaCljj-CaSO* (from Golubeva and Bergman, 1956).

at 890°C (40 mole percent CaS04 ); and Bellanca 

(1942), at 912°C (50 mole percent CaS04 ).

The eutectoid in the solidus was reported by 

Komissarova, Plyushchev, and Stepina (1955) and 

Plyushchev (1962) as 185°C (6 mole percent 

CaS04 ) which confirmed the interpretation of 

Miiller (1910). Bellanca (1942) found it to be 225°C 

(5 mole percent CaS04 ).

Additional study of this system is needed, using 

differential thermal analysis, longtime subsolidus 

heating, quenching techniques, and the heating stage 

X-ray diffractometer to clarify the differences and 

to determine if, and at what temperature, glauberite 

melts incongruently or decomposes.

NaCl CaSO4

Bye and Kiehl (1948) studied this binary diagonal 

of the reciprocal salt system Na,Ca/Cl,S04. The
22 QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

1200

1100

1000

900

800

700

600

500

400

300

200

100

0 

Na 2S04

EXPLANATION

_ O Speranskaya and Barskaya (1961) 

A Bellanca (1942)

Liquid

20 40 60 

MOLE PERCENT

80 100 

CaSO<

FIGURE 35. The binary system Na,,SO4-CaS04 (from Speranskaya and Barskaya, 1961, and Bellanca, 1942).

eutectic is at 725° C and 37 percent CaSO4. The 

study was not carried beyond 70 percent CaS04 because of the decomposition of CaS04 . Palkin (1949) 

and also Rubleva and Bergman (1956) repeated this 

system and found the eutectic at 726° and 33 weight 

percent (30 mole percent) CaSO4 . We experienced 

difficulty in trying to verify their results because of

gravitative differentiation in the melts. Calcium sulfate settled out in the thin liquid. We prepared 

several compositions in the system and verified the 

eutectic thermal effect at 725°C. Figure 36 shows 

the results of Bye and Kiehl (1948) and of Rubleva 

and Bergman (1956).

CaCl2-Na2SO4

This is a pseudobinary diagonal in the reciprocal 

salt system Na,Ca/Cl,S04. Palkin (1949), without 

giving any experimental data or actual temperatures, reported that upon the addition of CaCl2 to 

Na2S04, the liquidus was lowered from 884°C until 

the composition reaches the boundary where CaS04 

becomes the primary phase. The CaS04 field is 

crossed to where CaCl2 becomes the primary phase; 

the liquidus then rises to the melting point of CaCl2 , 

775°C. (See fig. 37.)

1300

1200

1100

1000

700

600

500

EXPLANATION

O Rubleva and Bergman (1956) 

A Bye and Kiehl (1948)

o

NaCI

20 40 60 

WEIGHT PERCENT

80 100 

CaS04

FIGURE 36. The join NaCl-CaSO4 in the Na,Ca/Cl,SO4 reciprocal salt system (from Bye and Kiehl, 1948, and 

Rubleva and Bergman, 1956).
THE SYSTEM NaCl-K2S04-CaS04 23

884

900

800

700

600

0 10

Na ?S04

1 I I I I

CaS04

775

20 30 40 50 60 

MOLE PERCENT

70 80 90 100 

CaCI,

FIGURE 37. The pseudobinary diagonal CaCl2-Na2S04 in the 

Na,Ca/Cl,S04 reciprocal salt system (from Palkin, 1949).

DISCUSSION

This system was reported by Palkin (1949) and 

by Zimina, Bergman, and Nagornyi (1965) (fig. 

38). The liquidus minimum at 628°C in the NaClNa2SO4 system rose to a maximum at 640 °C because of the Na2 SO4 solid solution, and then descended to a eutectic at 634°C (Zimina and others, 

1965). There are primary fields for CaS04 , (Na,Ca) 

S04 solid solution, NaCl, and CaCl2 with no ternary 

compounds shown. The stable join NaCl-CaSO4 

divides the system into two stable ternary systems,

800 °C 

Na 2 CI 2 495

628

772 °C 

CaCI2

712

Na 2S04 

884 °C

944 CaS04 

1464°C

FIGURE 38. The reciprocal salt system Na,Ca/Cl,S04 

(from Zimina and other, 1965).

NaCl-CaS04-Na2S04 and NaCl-CaS04-CaCl2 . Eutectics are at 634 °C and 485°C, but there is no indication of a field for glauberite or the extent of the 

solid solution field of (Na,Ca)S04.

Ca,K/Cl,SO4 RECIPROCAL SALT SYSTEM

The third reciprocal salt system in the quaternary 

reciprocal salt system Na,K,Ca/Cl,S04 is the Ca,K/ 

C1,S04 system (fig. 35). This system consists of 

CaCVKCl, CaCl2-CaSO4 , KC1-K2SO4 , and CaSO4- 

K2S04 as edges and CaCl2-K2S04 and KCl-CaSO4 as 

diagonals.

BINARY SYSTEMS

CaCl2-KCl

The system CaCl 2-KCl was studied by Menge 

(1911) (fig. 39) who found only one compound, 

KC1 QaCl2 , which melts congruently at 754°C. Eutectics are found with KC1 at 597 °C and 65 percent 

KC1 and with CaCl2 at 641°C and 19 percent KC1. 

Menge's results were essentially confirmed by 

Golubeva and Bergman (1956), Janecke and Miihlhausser (1936), and Scholich (1920).

CaCl2-K2SO4

The pseudobinary join CaCl2 -K2S04 in the system 

Ca,K/Cl,SO4 was studied by Janecke and Muhlhauser 

(1936). They found that the addition of CaCL to 

K2SO4 lowered the liquidus from 1,069°C to about 

770° near 26 mole percent CaCl2 where calcium 

langbeinite becomes the primary phase (fig. 40).

= 597

30 40 50 60 70 

WEIGHT PERCENT

I I I I I I

40 60

MOLE PERCENT

FIGURE 39. The binary system KCl-CaCb (from Menge,

1911).
24

HOOr

1000 -

900 -

EXPLANATION

O Golubeva and Bergman (1956) 

X Janecke and Muhlhauser (1936)

800 -

700 -

600 -

500

K,SO

QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

eutectic at 685°C and 31 mole percent (29 wt percent) CaS04 . Golubeva and Bergman (1956) found 

the eutectic to be 688°C and 32 mole percent CaS04 

and reported an incongruently melting compound, 

2KCl-CaS04 , with a peritectoid at 790°C and 44.5 

mole percent CaS04 . Rubleva and Bergman (1965) 

also studied this binary and reported the eutectic to 

be 687°C and 30.5 mole percent CaS04 and the 

peritectoid to be 827°C and 47.5 mole percent CaS04. 

The data of Golubeva and Bergman (1956), 

Rubleva and Bergman (1956), and Janecke and 

Miihlhausser (1936) are plotted in figure 41.|Liquidus 

determinations provide slight evidence of an incongruently melting compound of possible composition 

2KCl-CaS04 . Janecke and | Miihlhausser, however, detected a thermal effect at 688°C for a composition 

containing 60 mole percent CaS04 which would indicate that such a compound does not exist. We prepared, by melting and annealing, a composition containing 52 mole percent (50 wt percent) CaS04 . 

X-ray examination showed only KC1 and CaS04 . 

Heating-cooling study of this composition showed a

50 

MOLE PERCENT CaCI 2

FIGURE 40. The pseudobinary diagonal CaCl-K2SO4 in the 

K,Ca/Cl,SO4 reciprocal salt system (from Golubeva and 

Bergman, 1956, and Janecke and Miihlhausser, 1936).

The liquidus rises as it crosses the calcium langbeinite primary phase to 790°C and 43.5 mole percent CaCl2 where CaS04 becomes the primary phase. 

It then rises and falls again as it crosses the CaS04 

field to meet the boundary of the CaCl? field, whence 

it rises to the melting point of CaCl2 , 779°C. The 

part of the system high in CaCl2 was not investigated but was extrapolated from the internal sections and binary data.

According to Golubeva and Bergman (1956) the 

diagonal passes through five fields: CaCl2, CaS04, 

K2S04 -2CaS04 (calcium langbeinite), 2K2S04 -3CaS04 , 

and K2S04 , intersecting the boundaries at 720°C and 

26.5 mole percent CaCl2 , 785°C and 42.5 mole percent CaCl2 , and 645°C and 90 mole percent CaCl2 . 

The study of the K2S04-CaS04 system by Rowe, 

Morey and Hansen (1965) failed to find any evidence of the 2K2S04 -3CaS04 compound reported by 

Golubeva and Bergman (1956). Figure 40 is from 

data of Golubeva and Bergman (1956) and Janecke 

and Muhlhauser (1936); the plot of Golubeva's data 

seems to confirm the interpretation of Janecke.

KCl-CaSO4

Janecke and Miihlhausser (1936) reported that the 

KCl-CaS04 join was a stable binary system with a

1200

1100

1000

900

800

700

600

500

EXPLANATION

o Golubeva and Bergman (1956) 

X Janecke and Miihlhauser (1936) 

A Rubleva and Bergman (1956) 

n This report

XO X0 

K2 CI 2

20 40 60 

MOLE PERCENT

80 100 

CaS04

FIGURE 41. The binary join KCl-CaSO4 in the K,Ca/Cl,SO4 

reciprocal salt system.
THE SYSTEM NaCl-K2 SO4-CaSO4 25

thermal effect at 685°C, which corresponds to a 

eutectic on this join. We must therefore accept the 

results of Janecke and Muhlhausser as being more 

correct. Additional study should be made of this join 

to further resolve the differences between investigators.

DISCUSSION

Janecke and Muhlhausser (1936) studied the 

Ca,K/Cl,S04 system and found ternary eutectics at 

646°C (KCl + K2S04-2CaS04 + K2S04 = liquid) ; 680°C 

(KCl + K2S04-2CaS04 + CaS04 = liquid); 582°C (KC1 

+ CaS04 +KCl-CaCl2 = liquid) and another which 

was not determined (CaCl2 + KCl-CaCl2 + CaS04 = 

liquid).

Golubeva and Bergman (1956) also studied this 

system, using the visual poly thermal method. They 

reported that, in addition to calcium langbeinite, 

there was a 2K2S04 -3CaS04 binary compound with 

a field extending into the reciprocal salt system and 

also an incongruently melting compound, believed 

to be KCl-CaS04 or possibly 2KCl-CaS04. Finkel' 

shtein, Bergman, and Nagornyi (1965), in a study 

of the K,Ca,Ba/Cl,S04 system, accepted the results 

of Golubeva and Bergman (1956).

Rubleva and Bergman (1956) in their study of 

the KCl-NaCl-CaS04 plane in the Na,K,Ca/Cl,S04 

system reported the internal compound to be 2KC1- 

CaS04 . The questionable existence of this compound 

was discussed in the section on KCl-CaS04.

The join KCl-CaS04 is a binary join, dividing 

the ternary reciprocal salt system into two stable 

ternary systems: KCl-CaS04-K2S04 and KC1- 

CaS04-CaCl2 .

Figure 42 is from Janecke and Muhlhausser (1936) 

We did not include the fields for 2K2S04 -3CaS04 and 

2KCl-CaS04 reported by Golubeva and Bergman 

(1956).

NaCl-KCl-CaCl2 TERNARY SYSTEM

The ternary system NaCl-KCl-CaCl2 formed by 

the three chlorides of the quaternary reciprocal salt 

system Na,K,Ca/Cl,S04 was studied by Scholich 

(1920). There are no ternary compounds. The field 

of the binary compound KCl-CaCl2 extends into the 

ternary system. Plyushchev and Kovalev (1960) 

(see fig. 43) restudied the system and confirmed 

most of the results of Scholich but obtained different temperatures for the invariant points. They reported the eutectic to be 465°C and the minimum on 

the boundary between solid solution (Na,K)Cl and 

KCl-CaCL to be 515°C.

698

(KCI)2 

776 °C

600 KCaCI,

MOLE PERCENT

-r r-7-S" 73°

640 CaCI2 

777 °C

FIGURE 42. The reciprocal salt system K,Ca/Cl,S04 

(from Janecke and Miihlhauser, 1936).

Na2SO4-K2SO4-CaSO4 TERNARY SYSTEM

This ternary system, formed by the three sulfates 

of the quaternary reciprocal salt system, was studied by Bellanca (1942). The phase diagram (fig. 44) 

shows three fields: CaS04 , K2S04-2CaS04 , and (K,Na, 

Ca) S04 solid solution.

NaCI 

800 °C

660 

MOLE PERCENT

KCI 

776 °C

FIGURE 43. The ternary system NaCl-KCl-CaCl2 (from 

Plyushchev and Kovalev, 1960).
26 QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

917

K2S04 

1076 °C

MOLE PERCENT

884 °C

FIGURE 44. The ternary system Na2S04-CaS04-K2S04 

(modified from Bellanca, 1942).

NaCl-KCl-CaSO4 PLANE

The NaCl-KCl-CaS04 plane across the quaternary reciprocal salt system Na,K,Ca/Cl,S04 was 

studied by Rubleva and Bergman (1956). They reported that the compound 2KCl-CaS04 had a field 

which extended from the side face of the ternary 

reciprocal salt system K,Ca/Cl,S04 into the ternary 

system. They found a minimum in the system at 

605°C, 38.5 mole percent 2KC1, 19.0 mole percent 

CaS04 , and 42.5 mole percent 2NaCl. Decomposition 

of the (Na,K)Cl solid solution was found at temperatures below about 515°C.

We did not find evidence for the 2KCl-CaS04 compound in the KCl-CaS04 binary system. Examination of the liquidus curves of Rubleva and Bergman 

(1956) and those of Golubeva and Bergman (1956) 

provide only meager evidence for the existence of 

this compound, considering that they used only the 

visual polythermal method. We are therefore discounting the field for the 2KCl-CaS04 compound. 

Figure 45 is modified from Rubleva and Bergman 

(1956).

SUMMARY OF NaCl-K2SO4-CaSO4 AS A PLANE 

IN THE Na,K,Ca/Cl,SO4 SYSTEM

The NaCl-K2S04-CaS04 side of the quaternary 

system NaCl-K2S04-MgS04-CaS04 (fig 1) is a 

plane across the prism representing the quaternary 

reciprocal salt system Na,K,Ca/Cl,S04 (figs. 3£ and

726 687

Na 2CI2 

800 °C

658 

MOLE PERCENT

K2 CI 2 

770 °C

FIGURE 45. The plane NaCl-KCl-CaS04 in the Na,K,Ca/ 

C1,S04 quaternary reciprocal salt system (modified from 

Rubleva and Bergman, 1956).

46). We will discuss the phase relations on this 

plane with respect to the phase volumes of the 

quaternary reciprocal salt system which it intersects.

In the manner used for discussion of the Na,K, 

Mg/Cl,S04 system (p. 17), we will consider whether 

or not two planes, as in figure 2, will divide the 

system into three stable quaternary systems. The 

NaCl-KCl-CaS04 system, which is a stable ternary 

system according to Rubleva and Bergman (1956), 

can be shown as a plane across the prism. It subdivides the prism to give a stable quaternary system, 

NaCl-KCl-CaS04-CaCl2 , in which phase volumes can 

be represented in the usual manner.

The NaCl-K2S04-CaS04 plane represents a pseudoternary system which does not subdivide the prism 

into two more stable quaternary systems (fig. 46). 

Four compositions on the plane NaCl-K2S04-CaS04 

were prepared as shown in table 4 and figure 47 to 

determine the phase volumes intersected. We found 

the presence of KC1 and (Na,K,Ca)S04 solid solution in addition to NaCl and K2S04-2CaS04 (calcium 

langbeinite). Hence this plane is one of greater than 

ternary complexity, probably of five components, 

crossing through the two subquaternary systems 

within the prism, KCl-Na2S04-K2S04-CaS04 and 

NaCl-KCl-Na2S04-CaS04.
THE SYSTEM NaCl-K2 S04-CaS04 27

K2 CI2

K2 S04

CaCI Na2CI 2

K,S(X

Na 2S04

Na,K,Ca/CI,S04 K2S04

K2S04

FIGURE 46. The quaternary reciprocal salt system Na,K,Ca/Cl,S04.

Although the KCl-CaS04-Na2S04 plane had never 

been studied, it must also be a pseudoternary system 

because the KCl-Na2SQ4 join is a pseudobinary system. (See fig. 13.) It will also fail to subdivide the 

prism into the aforementioned subquaternary systems.

Nevertheless, from the limited data available, we 

can conclude that the phase volume for CaS04 occupies a considerable part of the prism, intersecting 

the planes NaCl-K2S04-CaS04 and NaCl-KClCaS04 . The calcium langbeinite (K2S04 -2CaS04 ) 

phase volume extends from the ternary Na2S04- 

K2S04-CaS04 system to intersect the NaCl-K2S04-

CaS04 plane; it does not occur in the NaCl-KClCaS04 plane. The phase volumes of (Na,K,Ca)S04 

and (Na,K)Cl solid solutions intersect the NaClK2S04-CaS04 plane. Other arrangements of the 

boundary curves are possible, although all the fields 

shown are required by their presence in the bounding systems.

Additional study is needed to resolve the differences between previous investigators regarding KC1- 

CaS04 and the Na,K/Cl,S04 system. Study should 

also be made of the KCl-CaS04-Na2S04 plane and 

the further subdivision of the prism by joins to calcium langbeinite and to KCl-CaCl2 .

TABLE 4. Compositions on the NaCl-KsSC^-CaSCU plane in the Na,K,Ca/Cl,S04 quaternary reciprocal salt system

NaCl 

(wt percent)

10.0

20.0

50.0

35

K2SO4 

(wt percent)

35.1

31.2

19.5

30

CaSO4 

(wt percent)

54.9

48.8

30.5

35

Liquidus 

temperature 

Phases present (°C)

K2S04 2CaS04 +NaCl+ (Na,K,Ca)S04 +

KCl + CaSO4

K2SO4 2CaS04 +NaCl + KCl +

(Na,K,Ca)S04 + CaS04

CaS04 + NaCl + KCl+ (Na,K,Ca) S04

CaS04 + NaCl + KCl+ (Na,K,Ca)S04

946

825

660

 

Temperature of 

other thermal 

effects (°C)

800, 515

630, 515

630, 515

560, 515

Primary 

phase

CaS04

CaS04

(Na,K)Cl

CaS04
28 QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

K2S04 

1076 °C

884 1011 1057 

WEIGHT PERCENT

CaS04 

1464 °C

FIGURE 47. The plane NaCl-K2 S04-CaS04 in the 

Na,K,Ca/Cl,S04 quaternary reciprocal salt system.

THE SYSTEM NaCl-MgSCX-CaSCK

The system NaCl-MgS04-CaS04 is a plane across 

the prism representing the quaternary reciprocal salt 

system Na,Mg,Ca/Cl,S04, which consists of the reciprocal salt systems Na,Ca/Cl,S04 ; Na,Mg/Cl,S04 ; 

and Mg,Ca/Cl,S04 and the ternary systems of NaClMgCl2-CaCl2 and Na2S04-MgS04-CaS04 (fig. 3C).

Mg,Ca/Cl,SO4 RECIPROCAL SALT SYSTEM

The Mg,Ca/Cl,S04 reciprocal salt system consists 

of CaCl2-MgCl2 , CaCl2-CaS04, MgCl 2-MgS04, and 

CaS04-MgS04 as edges and CaCl2-MgS04 and 

MgCl2-CaS04 as diagonals.

BINARY SYSTEMS

CaCl2-MgCl2

Menge (1911) found CaCl2-MgCl2 to be a simple 

eutectic system with the eutectic at 621 °C and 39.1 

mole percent (42.8 wt. percent) CaCl;2 (fig. 48). 

Ivanov (1952) reported the eutectic to be 611°C.

CaCl2-MgSO4

We found no information in the literature regarding the CaCl2-MgS04 diagonal of the reciprocal salt 

system Mg,Ca/Cl,S04 nor did we study it.

MgCl2-CaSO4

No information is available for this binary diagonal.

DISCUSSION

We have no reference to any previous study of the 

Mg,Ca/Cl,S04 reciprocal salt system. There is information regarding each of the binary side systems 

including an incomplete study we made of the

800 -

777

10 20

MgCI 2

WEIGHT PERCENT

CaCI2

FIGURE 48. The binary system CaCb-MgCb (from Menge,

1911).

MgS04-CaS04 system. No binary compounds are 

reported for three of the four side systems. In the 

CaS02-MgS04 system we found at least one compound, CaS04-3MgS04. It is not known how far 

into the reciprocal salt system its field will extend. 

The internal sections of this reciprocal salt system 

should be studied to determine the extent of the 

CaS04-3MgS04 field and the boundaries of the fields 

of MgS04, CaS04 , MgCl2 , and CaCl2 , and to learn if 

any heteroionic compounds formed. If any such 

compounds are found, it would be necessary to determine the phase volumes in the quaternary reciprocal salt system Na,Ca,Mg/Cl,S04 .

NaCl-MgCl2-CaCl2 TERNARY SYSTEM

This ternary chloride system formed from the 

three reciprocal salt systems Na,Mg/Cl,S04, Na,Ca/ 

C1,S04, and Ca,Mg/Cl,S04 has not been previously 

studied. In the CaCl2-MgCl2 system there are no binary compounds. In the NaCl-MgCl2 system, Klemm 

and Weiss (1940) found two incongruently melting 

compounds, 2NaCl-MgCl2 and NaCl-MgCl2 . Scholich 

(1920) reported that the NaCl-CaCl2 system was a 

simple eutectic system with no binary compounds. 

Because of the limited data, the ternary system 

NaCl-MgCl2-CaCl2 is shown in figure 50 as an incomplete system.

Na2SO4-MgSO4-CaSO4 TERNARY SYSTEM

This ternary sulfate system had been studied by 

Mukimov and Fillipova (1949) (fig. 49), using the
THE SYSTEM NaCl-MgS04-CaS04 29

1450 °C 

CaS04

MgS04 

1187°C

/ 670 

Na 2S04-3MgS04

MOLE PERCENT

Na 2S04 

884 °C

FIGURE 49. The ternary system Na2S04-MgS04-CaS04 

(from Mukimov and Fillipova, 1949).

visual polythermal method. They reported that they 

were unable to study the MgS04-CaS04 binary system and the part of the ternary system adjacent to

it. They presumed the CaS04-MgS04 system to be a 

simple binary system with no compounds. The problems associated with study of this system were discused on page 6, where the results of our studies 

are presented.

Mukimov and Fillipova (1949) reported a ternary 

eutectic at 650°C, 7 mole percent CaS04, 40 mole 

percent MgS04, and 53 mole percent Na2S04 and a 

transition point at 695°C, 13 mole percent CaS04 , 44 

mole percent MgS04 , and 43 mole percent Na2S04 . 

There is a ternary field for the incongruently melting Na2S04-3MgS04 (antivanthoffite).

This system should be restudied to determine the 

field of CaS04 -3MgS04 and the extent of the (Na,Ca) 

S04 and (Na,Mg)S04 solid solutions.

SUMMARY OF NaCl-MgSO4-CaSO4 AS A PLANE 

IN THE Na,Mg,Ca/Cl,SO4 SYSTEM

The system NaCl-MgS04-CaS04 is one side of 

the tetrahedron representing the quaternary system 

NaCl-K2S04-MgS04 , shown in figure 1. It can be 

considered to be a plane across the prism for the 

quaternary reciprocal salt system Na,Mg,Ca/Cl,S04, 

as shown in figure 50.

Compositions on this plane, as shown in table 5 

and figure 51, were prepared and studied using heating-cooling, quenching, and hot-stage microscopy.

MgCI 2 MgCI2

CaCI Na 2CI 2

MgSO, MgS04

CaSO,

CaS04 -3MgS04

Na 2S04 -3MgS04

Na,Mg,Ca/CI,S04

Na2 S04

MgS04

FIGURE 50. The Na,Mg,Ca/Cl,S04 quaternary reciprocal salt system.
30 QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

TABLE 5. Compositions on the NaCl-MgSO4-CaSO4 plane in the iNa,MgyCa/Cl,S04 quaternary reciprocal salt system

NaCl 

(wt 

percent)

(wt 

percent)

CaSO4 

(wt 

percent) Phases present

Liquidus 

temperature

Temperature of 

other thermal 

effects

Primary phase

Compositions of the join NaCl to CaSCh 3MgSO4

0 

20 

30 

40

50 

60 

70 

80

40 

50 

50 

40

72.5 

57 

50 

43 

36 

28.5 

21.5 

13.5

50 

30 

20 

30

28.5 

23 

20 

17 

14 

11.5 

8.5 

5.5

10 

20 

30 

30

CaSO4 3MgS04 

NaCl+CaS04 »3MgS04 

NaCl+CaS04 »3MgS04 

NaCl+CaS04 »3MgS04 

NaCl+CaSO4 »3MgS04 

NaCl+CaSO4 3MgS04 

NaCl+CaSO4 '3MgSO4 

NaCl + CaSO4 »3MgS04

NaCl + MgSO4 

NaCl+CaSO4 

NaCl+CaSO4 

NaCl+CaS04

Other

"{"C3.SO-4- * 

+ CaSO4 « 

+ CaSO4 « 

+CaS04 «

compositions

3MgSO4 

3MgSO4 

3MgSO4 

3MgS04

1201 

880

660

660

 

640 

680 

700 

710

645, 575

645, 630, 575

645,

640, 

675, 

640,

630, 580

585 

645, 580 

580

CaS04 

CaSO4 

CaSO4 

CaSO4 

CaSO4 

NaCl 

NaCl

MgSO4 

CaS04 

CaS04 

CaSO4

3MgSO4 

3MgSO4 

3MgSO4 

3MgSO4 

3MgSO4

Coexisting phases in the cooled melt and in quenches 

were identified by X-ray and optical properties. Because extensive experimental study was not completed, only limited data are available. Nevertheless, 

we can conclude that it is a ternary plane across the 

prism, intersecting phase volumes of MgS04, CaS04 , 

NaCl, and CaS04 3MgS04 as shown in figures 50 

and 51.

The join from NaCl to CaS04 -3MgS04 is a stable 

join. We found NaCl plus CaS04 -3MgS04 in the 

cooled melt for all compositions on this join. ComMgS04 

1135°C

CaS04 -3MgS04 

1201°C

WEIGHT PERCENT

FIGURE 51. The plane NaCl-MgS04-CaS04 in the Na,Mg, 

Ca/Cl,S04 quaternary reciprocal salt system.

positions richer in CaS04 showed CaS04 plus CaS04 - 

3MgS04 and NaCl, while compositions richer in 

MgS04 showed MgS04 plus CaS04 -3MgS04 and 

NaCl.

Additional study should be made to determine the 

subdivision of the quaternary reciprocal salt system 

Na,Mg,Ca/Cl,S04 into stable subsystems by additional planes and joins. These studies should include 

the plane NaCl-MgCl2-CaS04 and the various joins 

to Na2S04-3MgS04 , NaCl-MgCl2 , and 2NaCl-MgCL. 

The systems for which data are lacking should also 

be included in future studies.

THE QUATERNARY RECIPROCAL SALT 

SYSTEM K,Mg,Ca/Cl,S04

The K,Mg,Ca/Cl,S04 quaternary reciprocal salt 

system consists of the reciprocal salt systems K, 

Ca/Cl,S04 ; K,Mg/Cl,S04 ; and Mg,Ca/Cl,S04 and the 

ternary systems KCl-MgCl2-CaCl2 and K2S04- 

MgS04-CaS04 (fig. 3D). All of these systems have 

been considered earlier except for the KCl-MgCl2- 

CaCl2 ternary system.

KCl-MgCl2-CaCl2

This ternary system was studied by Ivanov (1952) 

(fig. 52), who found no ternary compounds in the 

system. There are fields in the ternary system for 

the binary compounds KCl-MgCl2, 2KCl-MgCl2 , and 

KCl-CaCl2 .

DISCUSSION

No study has been made of the internal planes 

of the prism representing compositions in the quaternary reciprocal salt system K,Mg,Ca/Cl,S04 . Figure 53 shows the three ternary reciprocal salt sys-
THE QUATERNARY RECIPROCAL SALT SYSTEM K,Mg,Ca/Cl,SO4 31

467

KCI-MgCI2

CaCI

611 440 

437Viw2KCI-MgCI2

434

641°C KOCaCI2 597 °C 

WEIGHT PERCENT

KCI

FIGURE 52. The ternary system KCl-MgCk-CaCh (from 

Ivanov, 1952).

terns and the two ternary systems comprising this 

quaternary reciprocal salt system. The 2KCl-MgCl2 

compound reported by Ivanov (1952) and Klemm, 

Beyersdorfer, and Oryschkewitsch (1948) was not

MgCI 2

shown by Janecke (1912) in the K,Mg/Cl,S04 system which was used for this compilation; however 

it will be included ,in the following discussion. It is 

not known how far into the composition prism the 

phase volumes of CaS04 -3MgS04 , K2S04 -2MgS04 

(langbeinite), K2S04 -2CaS04 (calcium langbeinite), 

solid solution of langbeinite-calcium langbeinite, 

KCl-CaCl 2 , KCl-MgCl2 , 2KCl-MgCl2 , CaS04 , MgS04, 

K2S04, CaCl2 , MgCl2 , and KCI will extend. Since 

KCI is found in the system NaCl-K2S04-MgS04- 

CaS04, the effects and interactions of KCI with 

K2S04-MgS04-CaS04 should be considered in the 

overall evaluation of the entire so-called quaternary 

system. It is not possible to predict the behavioi^of 

this quaternary reciprocal salt system without considerable experimental data, which is not available 

at present. Nevertheless, the quaternary reciprocal 

salt system is shown with the Ca,Mg/Cl,S04 system 

and the internal plane KCl-MgS04-CaS04 left incomplete.

A composition on a join from KCI to 22.5 percent 

CaS04, 36.5 percent MgS04 , and 41.0 percent K2S04 

(in the ternary base), containing 50 percent KCI, 

was prepared and studied. The cooled melt showed 

KCI and langbeinite solid solution as the only 

phases. We can assume that the phase volume for

MgCI

MgSO

CaCI MgCI 2

MgS04 CaSO,

MgS04

FIGURE 53. The K,Mg,Ca/Cl,SO4 quaternary reciprocal salt system.
32 QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

langbeinite-calcium langbeinite solid solution occupies a considerable portion of the prism.

X-ray examination of a melt of composition 50 

percent KCI on a join from KCI to CaS04 -3MgS04 

showed the presence of KCI, MgCl2 , and langbeinite 

solid solution. It must be concluded that the phase 

volume of langbeinite solid solution extends up into 

the composition prism to intersect the plane KC1- 

MgS04-CaS04 . Therefore, the plane KCl-MgS04- 

CaS04 is pseudoternary.

Additional study should be done on the Ca,Mg/Cl, 

S04 ternary reciprocal salt system and on planes in 

the K,Mg,Ca/Cl, S04 quaternary reciprocal salt system to properly define this system.

NaCl-K2SO4-MgSO4-CaSO4

The system NaCl-K2S04-MgS04-CaS04 is the 

part of the quinary system Na,K,Mg,Ca/Cl,S04 

which has direct application to the crystallization of 

the Gnome melt. It is a pseudoquaternary system in 

that fields are found for KCI and Na2S04 . Hence its 

complete graphical representation is not quantitatively possible. To study parts of the system, we investigated the plane NaCl-langbeinite-calcium langbeinite and a section containing 40 percent NaCl.

NaCl-K2SO4 2MgSO4 (LANGBEINITE) 

K2SO4 2CaSO4 (CALCIUM LANGBEINITE)

PLANE

This is the plane from NaCl through langbeinite 

and calcium langbeinite across the tetrahedron (fig. 

1) representing compositions in the system NaClK2S04-MgS04-CaS04. The liquidus on the join NaCl 

to K2S04 -2MgS04 (langbeinite) exhibits a minimum 

at 632°C and 47 percent NaCl (table 3, fig. 29). The 

liquidus on the join NaCl to K2S04-2CaS04 (calcium

langbeinite) shows a minimum at 630°C and 42 percent NaCl (table 4, fig. 47).

We prepared several compositions on the join 

NaCl to 70 percent langbeinite : 30 percent calcium 

langbeinite. Heating-cooling, quenching, and hotstage microscope studies were made to determine 

thermal effects, liquidus, and primary phases. Results are shown in table 6 and figure 54. The liquidus 

minimum on this join is at 615°C and 37 percent 

NaCl. Langbeinite is the primary phase to this 

point; NaCl or (Na,K)Cl solid solution is the primary phase for compositions richer in NaCl than 

37 percent.

Three compositions were prepared on the join 

from NaCl to 50 percent langbeinite on the langbeinite-calcium langbeinite join in the K2S04- 

MgS04-CaS04 system. These were studied to determine the extent of the primary phase volume of 

CaS04 (see table 6 and fig. 55). From quenching 

experiments, CaS04 was found to be the primary 

phase for the compositions containing 30 percent 

NaCl. It can be assumed that the langbeinite solid 

solution, on this join, decomposes to CaS04 plus 

liquid as was found in the ternary system K2S04- 

MgS04-CaS04 . The phase volume for CaS04 intersects the plane of this section and the NaCl becomes 

(Na,K)Cl within the system; hence, it is a pseudoternary system.

40-PERCENT NaCl PLANE IN THE 

NaCl-K,SO4-MgSO4-CaSO4 SYSTEM

The compositions we prepared on this plane are 

shown in table 7 and figure 56. The final cooled melts 

of compositions on this section show the presence 

of NaCl, KCI, Na2S04 , MgS04 , CaS04 , langbeinite 

solid solution, and CaS04 -3MgS04 .

TABLE 6. Compositions in the NaCl-langbeinite-calcium langbeinite plane in the NaCl-K2SO4-MgSO4-CaSO4 system

[Lgss = langbeinite solid solution; ss = solid solution]

NaCl 

(wt 

percent)

KaSO4

(wt 

percent)

MgSO4 

(wt 

percent)

CaSO4

(wt 

percent)

Compositions on the join NaCl

0 

10 

20 

30

40 

50

41.95 

37.75 

33.6 

29.36 

25.2 

20.98

40.60 

36.55 

32.5 

28.42 

24.4 

20.3

17.45 

15.7 

13.9 

12.22 

10.4 

8.72

Compositions on the join NaCl

30 

50 

70

28.4 

20.3 

12.2

20.6 

14.7 

8.8

21 

15 

9

Phases present

to 70 percent langbeinite : 30

Lgss 

Lgss+(Na,K)Clss 

Lgss+(Na,K)Clss 

Lgss+ (Na,K)Clss 

Lgss+ (Na,K)Clss 

Lgss+(Na,K)Clss

to 50 percent langbeinite : 50

(Na,K)Clss+Lgss 

(Na,K)Clss + Lgss 

(Na,K)Clss + Lgss

Liquidus 

temperature (°C)

Temperature of 

other thermal 

effects 

(°C) Primary phase

percent calcium langbeinite

900 

820 

729 

640 

630 

705

610, 515 

610, 515 

610, 515 

610, 565, 515 

615, 515

Lgss 

Lgss 

Lgss 

Lgss 

(Na,K)Clss 

(Na,K)Clss

percent calcium langbeinite

>620 

650

610 

610, 515

CaSO4 

(Na,K)Clss 

(Na,K)Clss
NaCl-K2S04-MgS04-CaS04 33

1000

9006-

800 -

700

600

500

400

Langbemite

solid solution

+ liquid

(Na,K)CI solid solution 

+ liquid

10 30

70 percent K2Mg2(S04) 3 

30 percent K2Ca2(S04 )3

50

WEIGHT PERCENT

70 90

NaCI

FIGURE 54. The join NaCI to 70 percent langbeinite : 30 percent calcium langbeinite.

On the 40-percent NaCI plane, we have what appears to be a stable quaternary system in the area 

bounded by the langbeinite-calcium langbeinite join 

and the CaS04-MgS04 binary system. For compositions richer in K2S04 than those on the langbeinitecalcium langbeinite join, the system is made complex 

by the formation of NaaS04 (below the liquidus)

630

943 °C

K2S04 -2MgS04 

(Langbeinite)

890 °C 

WEIGHT PERCENT

1057°C

SO^Ca

(Ca langbeinite)

FIGURE 55. The plane NaCl-langbeinite (K2S04 2MgS04>- 

calcium langbeinite (K2S04 2CaS04>.

and KC1 and is no longer quaternary but of higher 

order, containing five components; hence, all the 

phase composition cannot be graphically represented.

DISCUSSION

The four ternary systems which make up this 

so-called quaternary system are shown in figure 57. 

The phase relations were derived from the data of 

our incomplete study and the data from previous 

studies supplemented by limited experimental checking. The difficulty in representing a system of this 

complexity has been discussed earlier in this report.

TABLE 7. Compositions on the 40-percent NaCI plane in the NaCl-K2S04-MgS04-CaS04

[Lg = langbeinite, fcSCU 2MgSO4; Lgss = langbeinite solid solution, (K.Mg.CaJSCU]

(wt

percent)

10

15

15

16.6

20

25

33.3

35

35.5

38.3

41.6

50

50

59

66.6

MgSO* 

(wt

percent)

80

58.3

43.4

50

20

60

33.3

20

38.7

41.7

41.6

35

25

20

16.7

CaSO4 

(wt 

percent)

10

26.7

41.6

33.4

60

15

33.3

45

25.8

20

16.8

15

25

21

16.7

Phases present

NaCl + CaS04 3MgS04 +MgS04 +Lg

NaCl+CaS04 3MgS04+CaS04 +Lg

NaCl+CaS04 3MgS04 +CaS04 +Lg

NaCl + CaS04 3MgS04+CaS04 +Lg

NaCI + CaS04 + Lgss

NaCI + CaS04 + Lgss +CaS04 3MgS04

NaCI +CaS04 + Lgss

NaCI + CaS04 + Lgss

NaCI +CaS04 + Lgss

NaCI + CaS04 + Lgss

NaCI + Lgss +KCl+Na2S04

NaCl+Lgss+KCl + Na2S04

NaCI + Lgss + KC1 + Na2S04

NaCI + Lgss + KC1 + Na2S04

NaCI + Lgss +KCl + Na2S04

Liquidus 

temperature

885

890

773

660

1020

625

620

745

654

630

625

600

700

572

578

Temperature of 

other thermal 

effects 

CO

620

548

616

_

555

490

610

_

608

510

510

590, 540, 485

_

562

Primary phase

MgS04

CaS04 

CaS04

CaS04

CaS04

Lgss

CaS04

CaS04

Lg

NaCI

NaCI

NaCI

NaCI

NaCI

NaCI

3MgS04
34 QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

40 percent NaCI 

60 percent MgS04

Langbeinite 

solid solution

40 percent NaCI 

60 percent K2S04

40 percent NaCI 

60 percent CaS04

FIGURE 56. The 40-percent NaCI plane in the NaCl-K2S04- 

MgSO4-CaSO4 system. O, compositions studied; A, intersection of the Gnome composition with this plane.

The tetrahedron representing the NaCl-K2S04- 

MgS04-CaS04 system can be subdivided by planes 

joining the compounds in the system. The Gnome 

composition, shown as a triangle in figures 56 and 

57, lies in a subtetrahedron bounded by NaClCaS04-K2S04 -2MgS04-K2 S04 -2CaS04 . Compositions 

on the 40-percent NaCI plane adjacent to the Gnome 

composition showed NaCI plus CaS04 plus langbeinNaCI

MgS04

(Na,K,Ca)SO,

NaCI CaSO, NaCI

FIGURE 57. The sides and base of the tetrahedron representing the NaCl-K2 SO4-MgS04-CaSO4 system. A, Gnome 

composition.

ite solid solution as the final phases in the cooled 

melt. Compositions in the tetrahedron bounded by 

NaCl-K2S04-2MgS04-CaS04-CaS04-3MgS04 showed 

NaCI plus CaS04 plus langbeinite plus CaS04- 

3MgS04. The composition in the tetrahedron NaClCaS04 -3MgS04-K2S04-2MgS04-MgS04 gave NaCI 

plus MgS04 plus CaS04 -3MgS04 plus langbeinite as 

the final phases.

The following quaternary isobaric invariant points 

will be considered in the discussion of the crystallization of the Gnome melt:

NaCI + CaS04-3MgS04 + CaS04 + langbeinite=liquid

(1)

NaCI + CaS04-3MgS04 + MgS04 + langbeinite = liquid

(2)

The NaCI in both 1 and 2 probably contains some 

KC1 in solid solution, but the system will be nearly 

quaternary. Thus, these points may actually be isobarically univariant with the assemblages stable 

over a small temperature range. In other parts of 

the system, it has not been possible to determine 

invariant points because of the complexity.

CRYSTALLIZATION-DIFFERENTIATION 

IN THE GNOME MELT

From the limited work done in the various complex systems composing the NaCl-K2S04-MgS0.4- 

CaS04 system, we can develop a theory for the probable course of crystallization of the melt after the 

Gnome event. We will assume that the melt consists 

of 5,000 tons of material with a composition of 80.7 

percent NaCI, 4 percent K2S04, 2.8 percent MgS04, 

and 12.5 percent CaS04 excluding silt, clay, and water. The impurities of silt, clay, and water occur as 

separate beds interlayered in the halite and account 

for less than 10 percent of the original material.

The first phase to crystallize will be NaCI (fig. 58) 

at about 760°C. It will crystallize along the tieline 

from NaCI through the original composition, until 

the liquid composition reaches the surface of the 

phase volume of CaS04 . The composition of the melt 

will have passed through the phase volume of NaCI, 

and about 2,900 tons of NaCI will have crystallized. 

The composition of the remaining 2,100 tons of liquid will then be 55 percent NaCI (1,135 tons), 9.5 

percent K2S04 (200 tons), 7.0 percent MgS04 (140 

tons), and 28.5 percent CaS04 (650 tons).

After the liquid composition meets the surface of 

the CaS04 phase volume, NaCI and CaS04 will simultaneously crystallize and the composition of the liquid will trace a path on the CaS04 phase volume
CRYSTALLIZATION-DIFFERENTIATION IN THE GNOME MELT 35

NaCI

MgSO*

Langbeinite\7 

olid solution/

CaSCU

K,S04

FIGURE 58. Path of crystallization of the Gnome melt.

surface determined by a plane through the NaClCaS04 edge of the tetrahedron and the composition 

of the aforementioned liquid. The liquid will reach 

the phase volume of the langbeinite-calcium langbeinite solid solution at about 640°C. Then langbeinite solid solution will start to crystallize along with 

CaS04 and NaCI. The liquid composition will proceed 

along the boundary of the phase volumes as determined by the formation of solid solution. For the 

composition with which we are concerned the final 

crystallization should be langbeinite solid solution 

(figs. 6, 7). Hence the crystallization will end, not 

at a eutectic, but at a point determined by the properties of the solid solution. At this point, estimated 

to be 610°C, the composition of the liquid will be 

about 22.5 percent K2S04 , 30 percent MgS04, 17.5 

percent CaS04, and 30 percent NaCI. Langbeinite 

solid solution, NaCI, and CaS04 will all continue to 

crystallize to completion.

In the preceding discussion, it was assumed that 

the system contained only the salts NaCI, K2S04 , 

MgS04, and CaS04. If other constituents are present 

in minor amounts, they will remain in solution until 

after the quadruple point is reached, provided that 

they are soluble in the melt. These impurities would 

include bomb materials and silicates which may further depress the final freezing point. The process of 

crystallization-differentiation should result in the

accumulation of all minor components soluble in the 

melt and complete solidification at a temperature 

below the quadruple point.

Kahn and Smith (1966) in a study of the actual 

Gnome melt, found that the radioactivity was concentrated in the portions which were not water soluble. The water soluble portion did not exhibit any 

radioactivity. Of the radioactive insoluble material, 

they found considerable CaS04 as gypsum and anhydrite, in addition to minor amounts of olivine 

(Fe,Mg) 2Si04 and kirschsteinite (CaFeSi04 ). Although they assumed that the gypsum and anhydrite 

crystallized early in the cooling process, we feel that 

they were among the last to crystallize from the residual liquid after most of the NaCI had crystallized.

We had planned to study the effects of Si02 as 

another component, with the possible formation of 

feldspars and olivines during cooling of the melt, but 

this would have enormously increased the complexity of our study. Hence the work was limited to the 

quinary reciprocal salt system Na,K,Mg,Ca/Cl,S04 

to develop a theory for the crystallization of the salt 

mass.

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36 QUINARY RECIPROCAL SALT SYSTEM REVIEW OF LITERATURE WITH NEW DATA

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