THESYSTEM CaC12-hTgClz-KCl-H20
April, 1949 [COSTRIBUTION FROM
THE
1233
DEPARTMEKT O F CHEMISTRY AND CHEMICAL ENGINEERIXG O F CASE INSTITUTE TECHNOLOGY ]
OF
Equilibria in Saturated Salt Solutions. IV. The Quaternary System CaC1,-MgC1,KCl-H,O at 75" BY
WILLIAM J. LIGHTFOOT AND CARLF. PRUTTON
In previous paper^',^,^ the isotherms for the tei-nary systems a t 33 and 73" and for the quaternary system a t 3.5" were reported for the system CaC12MgClz-KCl-H20. Experimental Method The experimental methods used were identical with those employed in the earlier papers. Temperature a t which solutions and soljd phases were brought into equilibrium was 75 * 0.02 . The three methods of identification for the solid phases employed in the earlier work3 were used.
The Quaternary System.-The data for the quaternary system a t 73" are given in Table I. In Fig. 1 the upper portion of the quaternary tetrahedral figure is shown schematically. The relative proportions of the saturation surfaces are indicated. The same characteristic of magnesium chloride solutions that was noted in the ternaries and quaternary a t 35" is found here: carnallite remains almost insoluble in solutions saturated for MgClZ. 6HzO. Tachydrite solutions dissolve considerably more carnallite, particularly as the saturated solution becomes richer in calcium chloride. This ability of tachydrite solutions to dissolve more carnallite is more pronounced than a t 35'. The presence of the field of a new compound, 2KC1. CaC12.2H20, decreases the range of existence of carnallite appreciably.
The saturation surface of MgC12. 6H20has been reduced so that i t now covers a very small part of the diagram. The area of saturation of CaClz. 2H20 is the second smallest with tachydrite and 2KCl.CaC12.2H20 coming next in size, each with about the same area. Again KC1 and carnallite occupy the largest areas in the diagram. However, the field of carnallite no longer extends from one side almost to the other. With the introduction of a new solid phase, 2KC1. CaC12.2Hz0, the relationships in the quaternary diagram have been altered considerably. LYhere a t lower temperatures, CaClz 4Hz0 and carnallite were in equilibrium along a portion of the isotherm, the presence of the new phase completely separates CaC12.2H20 from carnallite. X o formation of a quaternary compound was found a t 75". In Fig. 2 the quaternary isotherm has been projected on the MgC12-KCl-H20 plane. Points F, G, MI N, T, and U are the respective invariant points of the associated ternary systems. Area IFQU, is the saturation surface of KCl; FGORQ, that of carnallite, KC1. MgCl2. GH20; KOGB, that of ,IlgC12.6HzO; AIKORS, that of tachydrite, CaClz.2MgC12.12H20; AMST, that of CaCl2. 2H20 ; and RSTUQ, that of 2KC1. CaClz 2Hz0. 2
A
10
20
30
N
B 40
MgCL, %. Fig. 2.-Equilibria in the quaternary system CaC12MgC12-KCI-Hs0 at 75 ', projection on the MgC12-KClHsO plane. CoCI,
Fig. 1.-The
system CaC12-MgC12-KCI-H20 upper portion of tetrahedron.
at 75 ',
(1) Lightfoot and Prutton, THISJOURNAL, 68, 1001 (1946). (2) Lightfoot and Prutton, ibid., 69, 2098 (1947).
(3) Lightfoot and Prutton, ibid., 71, 1236 (1949).
The curve FQ is the intersection of the KCl surface with the carnallite surface, and all points on it represent equilibrium between the two solid phases, KC1 and carnallite, and saturated solution. GO represents solutions saturated with carnallite
WILLIAMJ. LIGHTFOOT AND CARLF. PRUTTON
1234
Point or line
F FQ FQ FQ FQ FQ FQ
Q Q Q Qmean
G GO 0 0 0 Omean OR OR
OR R R R Rmean RQ T TS M MS S
TABLE I THEQUATERNARY SYSTEM MgCl2-CaC12-KCI-H20
-
-
Saturated solution Wet residue Weight per cent. MgClz CaClz KC1 MgClx CaClz KCl
29.26 23.14 16.71 10.89 6.39 4.48 3.85 3.49 3.44 3.49 3.47 38.86 36.20 33.64 33.69 33.66 33.68 26.95 16.12 7.92 6.76 6.73 6.79 6.76 5.58
... 1.85 5.28 4.66 4.56
... 8.56 18.07 27.57 36.76 41.95 44.63 46.28 46.34 46.32 46.31
... 4.26 8.38 8.40 8.42 8.40 16.96 32.00 44.90 46.44 46.46 46.40 46.43 46.69 57.66 55.23 52.58 52.47 52.45
5.57 5.56 5.61 5.85 6.73 7.81 8.80 9.70 9.70 9.70 9.70 0.32 0.38 0.40 0.38 0.39 0.39 0.67 1.58 3.68 5.11 5.12 5.11 5.11 6.25 3.59 3.35
S
4.54 52.54
3.06
S
4.54 52.55
3.06
Smean
4.55 52.51
3.07
SR SR SR
4.51 4.97 5.44 6.68
SR U UQ N
84.01 62.10 41.37 24.5$ 12.99 21.46 25.80 12.81 8.26 6.72
52.29 3.19 51.21 3.44 50.06 3.81 46.63 5.02 . . . 51.20 10.33 2.71 47.32 9.84 33.91 8.31 ...
.. .
22.97 44.74 62.22 73.70 77.34 77.92
6.83 33.82 26.93
37.18
3.03
5.83 77.86 99.18 . 4.37 88.64 10.43
36.16
6.29
4.11
..
19.73 28.15
79.30 60.45 3.75 32.43 14.02
19.78 38.04 64.39 79.47
16.19 31.25 14.98
9.21 53.02
11.60 79.64 9.54 79.78 . . 94.14 6.83 3.06 91.40 9.13 90.87 1.54 7.80 87.77
9.63 46.60
6.65
11.51 31.19 25.95 1.08 59.95
... 2.65 3.08
Jdnecke projection weight, % MgClt CaCh
.
7.57 87.33 87.16 85.89 84.40 79.94 . . 83.21 1.49 39.94 32.06 4.53 79.04 80.32 19.68
6.55 45.18
15.19
7.52 8.34 9.17 11.45
and llIgC12 6H20; RQ, carnallite and 2KC1. CaClz. 2H20 ; UQ, KC1 and 2KC1. CaClz 2H20 ; TS, CaClz 2Hz0 and 2KC1. CaClz 2H20 ; SR, tachydrite and 2KC1-CaCl2.2H20; MS, CaClz * 2Hz0 and tachydrite; and NO, h/IgC12.6Hz0and tachydrite. There are four isothermal invariant points in the system, R, S, Q, and 0. The three solid phases in equilibrium with saturated solution a t each point are: a t Q, KC1, carnallite and 2KC1CaClz.2Hz0; a t S, CaClz.2Hz0, tachydrite, and
.
AT
Vol. 71
75'
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
Solid phase
Carnallite KCl Carnallite KCI Carnallite KCl Carnallite KCl Carnallite KC1 Carnallite KC1 Carnallite KC1 Carnallite KCI 2KCl.CaClz.2HpO Carnallite KC1 2KCl.CaC12.2HzO Carnallite KCI 2KCI.CaC12.2H20 KCl 2KCl.CaC12.2H20 Carnallite Carnallite MgCI2.6Hz0 Carnallite MgC12.6H20 Carnallite MgCI2.6Hz0 Tachydrite Carnallite MgC12.6H20 Tachydrite Carnallite MgC12.62HO Tachydrite MgC12.6H20 Tachydrite Carnallite Carnallite Tachydrite Carnallite Tachydrite Carnallite Tachydrite Carnallite Tachydrite 2KCI.CaC12.2H20 Carnallite Tachydrite 2KCI.CaC12.2H20 Carnallite Tachydrite 2KCI.CaC12.2H20 Carnallite Tachydrite 2KCI.CaC12.2H20 2KCl.CaC12.2H20 Carnallite CaC12.2H~0 2KCl.CaC12.2HzO CaClz.2Hz0 2KCl.CaC12.2H20 CaCl2.2H~0 Tachydrite CaC12.2H~0 Tachydrite CaC11.2H20 Tachydrite 2KCI.CaC12. 2H20 CaC12.2Hz0 Tachydrite 2KCl.CaC12. 2H20 CaCl2.2H~0 Tachydrite 2KCI.CaCl:. 2H20 2KClCaC12. CaC12.2H20 Tachydrite 2H20 Tachydrite ~KCI.C~CIZ.~HZO Tachydrite 2KCI.CaC12.2H20 Tachydrite 2KCl.CaCl2.2H~0 2KCI.CaC12.2HzO Tachydrite KCI 2KClCaCl2.2H~0 2KCl.CaC12.2HzO KCI Tachydrite MgC12.6H~0
+ +
+ + + +
+ + + +
+ + + +
+ + +
+
+
2KC1. CaCl . 2 H ~ ;0 and a t 0, MgClz. GH20, tachydrite, and carnallite. In Figs. 3 and 4, the quaternary relationships have been projected on the CaC12-KCl-H20 and the CaC12-MgC12-H20 planes respectively. In the projection on the CaC12-KCl-H20 face there appears to be an overlapping of the KC1 and carnallite surfaces. This is due only to the method of projection. The saturation curves can be readily distinguished from one another. The projection on the CaClZ-MgC12-H20 plane is perhaps the
THESYSTEM CaC12-MgC12-KCl-H20
April, 1949
clearest in that there is no overlapping or superimposing of the different curves.
60A
50
40
30
20
10 N
1235
The data on the quaternary system a t 75' are given in Table I on a water free basis, and have been plotted in Figure 5, which gives the Janecke projection. The coexistent solid phases are connected by straight lines, the triangles formed represent the three solid phases which are in equilibrium a t the invariant points. The notations are consistent with those used in the other projections. Comparison with the similar type of diagram a t 35' shows that all areas in general have increased except MgClz. 6HzO. The main difference is that saturated solutions dissolve more KC1.
B
yo CaC12. Fig. 3.-Equilibria in the system CaClr-MgCl2-KC1-H?O a t 75' projected on the CaCli-KCl-H20 plane.
A M D Tach. N B CaC12 MgC12.6HzO MgC12 Fig. 5.-Quaternary system CaC12-MgC12-KCl-HSO at. 75", Janecke projection. 20
30
40
50
CaC12, %. Fig. 4.-Equilibria in the quaternary system CaC12MgCln-KCl-H20 a t 75 ', projection on the CaC12-MgC12H20, plane.
Summary 1. The isotherm for the quaternary system CaC12-MgC12-KCl-H20 a t 75' has been determined. CLEVELAND HEIGHTS,OHIO RECEIVED AUGUST25, 1948
