T H E SYSTEM NICKEL SULFATE-SULFURIC ACID-WATER AT 25°C. AWD 0°C. J. A. ADDLESTONE Department of Chemistry, Virginia Polytechnic Institute, Blacksburg, Virginia Received December $0,1087
The system nickel sulfate-sulfuric acid-water has been studied by Montemartini and Losana (l),who give data for the 12.5"C. isotherm. Rohmer (2) has investigated this system at 25°C. and 50°C., and gives data for the various transition point.; of the hydrates of nickel sulfate. This study was undertaken with the purpose of obtaining the complete isotherms for this system at 25°C. and O'C. EXPERIMENTAL PROCEDURE
A series of solutions containing approximately 100 cc. of varying concentrations of sulfuric acid were saturated with nickel sulfate. For the lower acid concentrations the solutions were saturated with the hexahydrate, and in the higher acid concentrations the solutions were saturated with anhydrous nickel sulfate. For the 25°C. isotherm these solutions were placed in a constant-temperature water bath. For the 0°C. isotherm the bottles were placed in a large container packed with finely divided ice. The temperature range varied from approximately 0°C. to 0.2OC. The bottles were shaken by hand a t least three times a day and allowed to remain in the bath for four weeks. The solutions were then allowed to settle and samples of the clear liquid were taken for analysis. Solid phases were removed for analysis by means of a glass spoon, as much of the liquid phase as possible being allowed t o drain off. h'ickel was determined gravimetrically by the usual dimethylglyoxime method, and sulfate was determined by precipitation with barium chloride, The nickel was calculated to nickel sulfate, and the excess sulfate was calculated to sulfuric acid. Water was determined by difference. The composition of the solid phases in equilibrium with the various solutions was determined graphically by means of intersecting tie-lines. The analyses of the liquid and solid phases are given in weight per cent of NiSOd, HzS04, and HzO. RESULTS AND DISCUSSION
The data for the 25°C. isotherm are given in table 1 and the results are plotted in figure 1. Data for the 0°C. isotherm are given in table 2 and plotted in figure 2. 437
TABLE 1 96°C. isotherm
_LIQUID PHhSB1
I
WET RESIDUES
COMPOSITION OB SOLID P E M P
7 1
NiSOi
____
HzSO4
H10
NiSOa
HzSOI
weight per Cent
weight per cent
weieht per cent
weight per cent
weighl per cent
weighl per cent
28.13 27.34 27.16
1.79 3.86
71.87 70.87 68.98
48.07 53.32
0.63 0.23
51 30 46.45
1
26.15 23.71 22.26 16.51 15.64 11.23 IO. 56
4.92 6.85 7.93 16.52 19.34 34.48 44.68
68.93 69.44 69.81 66.97 65.02 54.29 44.76
53.62 52.60 57.02
0.85 1.27 0.47
55.95 55.63
1.96 2.14
12.80
45.12
42.08
57.84
9.55
32.61
I
9.65 4.59 2.67 0.23 0.15 0.12
48.46 58.53 63.73 72.38 84.52 91.38
41 89 36.88 33.60 27.39 15.33 8.50
68.74 73.36
12.63 11.40
18.63 15.24
43.40 26.02
44.27 64.36
0.11 0.08
93.74 96.80
6.15 3.12
24.20 21.58
71.29 76.14
//-
~
NiS04.7H20
KiSOp.6Hz0 and NiSOa.HzO
')
1
SiS04.HzO 12.33 9.62
A
FIo. 1. Plot of the data for t h e 25°C. isotherm 438
TABLE 2 0°C. isotherm WET RESIDUES
LIQUID PHASE
1-
HzO
NiSOi
HsSOl
H10
NiSOi
weight per cent
weight per cent
weight per cent
weight pet cent
weioht per cent
weight per cent
21.17 19.22 13.86 9.41 9.22
2.63 10 .06 18.36 22.64
78.83 78,15 76.08 72.23 68.14
47.67 51.08 49.08
1.74 1.81 2.96
47.11 47.96
8.58 5.06 2.62 4.68
25.05 30.10 42.88 50.72
66.37 64.84 51.50 44.60
53.04 54.74 49.25 51.36
2.45 1.92 7.27 6.28
5.42
52.88
42.30
51.10
15.83
4.15 3.71 0.24
58.12 60.11 75.19
37.73 36.18 24.57
39.63
33.30
0.18 0.11
79.83 86.67
19.99 13.22
Trace 26.24 Trace
82.12 59.44 84.96
0.09 0.07 0.06
90.82 94.25 97.19
9.09 5.68 2.75
32.33 41.85 24.58
57.96 49.95 69.13
j
COMPOBITION OF SOLID PHASE
/j
33.07
NiS01.6H20 and
I’
15.04
H2S04.HzO and ?iiSOa,HZO
FIG.2. Plot of the d a t a for the 0°C. isotherm 439
440
J. A. ADDLESTONE
At 25°C. the solubility of the various hydrates decreases with increasing sulfuric acid concentration. The solubility decreases rapidly at about 60 per cent sulfuric acid. The stable solid phases at 25°C. are the heptahydrate, the hexahydrate, the monohydrate] and anhydrous nickel sulfate. Evidence of ci metastable tetrahydrate of nickel sulfate was found between approximately 45 per cent and 50 per cent sulfuric acid. These solid phases agree with those reported by Rohmer (2). The solubility curves at 0°C. exhibit the same general shape as those a t 25°C. The stable solid phases at 0°C. are the heptahydrate, the hexahydrate, and the monohydrate of nickel sulfate. The monohydrate of sulfuric acid also exists as a stable solid phase at this temperature. Anhydrous nickel sulfate, which was found a t 25°C. and reported by Montemartini and Losana (1) to be present a t 12.5"C., was not found a t 0°C. The dihydrate of nickel sulfate was not present at O"C., although Montemartini and Losana (1) found this hydrate to be stable a t 12.5"C. SUMMARY
The 25°C. and 0°C. isotherms for the system nickel sulfate-sulfuric acid-water have been determined. The stable solid phases at 25°C. are NiSO4.7H20, NiS04.6Hz0, NiS04.H201and NiS04. NiS04.4H20 exists as a metastable phase. The stable solid phases a t 0°C. are NiS04.7H20, NiS04.6Hz0, NiS04.Hz0, and HzS04.H20. The author is grateful to Dr. H. D. Crockford for suggestions concerning this work. REFERENCES
(1) MONTEMARTINI AND LOSANA: L'Industria chimioa 4, 199 (1929). (2) ROHMER: Compt. rend. 201,672 (1935).
