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Water solubility

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Description of key information

Water Solubility (as reported in the EU Risk Assessment for nickel sulphate, 2008-2009): 		
anhydrous: 293 g/l at 20°C
873 g/l at 100°C
hexahydrate: 625 g/l at 0°C
655 g/l at 0°C
3407 g/l at 100°C
heptahydrate: 756 g/l at 20°C
Please note that the two different values at 0°C for hexahydrate are from different sources (as reported in the EU Risk Assessment for nickel sulphate, 2008-2009).

Key value for chemical safety assessment

Additional information

(Cited from the EU Risk Assessment for nickel sulphate, 2008-2009.)

The available literature on the aqueous solubility of inorganic nickel compounds has been reviewed (Carlsen, 2001).

 

NiSO4 is found with varying amount of water attached to the salt, the number of water molecules ranging from 1 to 7. The actual number of water molecules attached to solid NiSO4 in equilibrium with a saturated NiSO4-solution is dependent of the solution temperature. Thus, in the temperature range up to ca. 30°C NiSO4•7H2O prevails, whereas at temperatures up to 90 - 100°C NiSO4•6H2O is dominant (Linke, 1965) (see also Table 1.1.B [of the EU Risk Assessment for nickel sulphate]).

 

A priori, it could have been expected that the presence of different amounts of crystal water might dramatically affect the solubility. However, in the case of nickel sulphate it appears that independently of the number of water molecules attached as crystal water, the compound is readily soluble in water (Carlsen, 2001).

 

The solubility of NiSO4 at 25°C is given as 29 g/100 g solution (CRC, 2000) corresponding to a concentration of 2.64 mol/L (40.8 g/100 g water; Gmelin, 1966). A smooth increase in the water solubility of nickel sulphate with increasing temperature can be noted. (Table 1.3.B).

Table 1.3.B. Solubility of nickel sulphate as function of temperature (Gmelin, 1966)

Temperature (°C)

Solubility
(g/100 g water)

Solubility
 (mol/L)

Solid phase NiSO4•xH2O;
x

0

27.6

1.78

7

5

30.1

1.95

7

10

32.7

2.11

7

15

35.4

2.29

7

20

38.0

2.46

7

25

40.8

2.64

7

30

43.7

2.82

7

35

45.8

2.96

6

40

47.9

3.10

6

45

50.2

3.24

6

50

52.4

3.39

6

 

It should be noted that these figures are somewhat lower than the solubility of 120 g/L solution as nickel (equal 316 g NiSO4) at 20°C mentioned by Maximilien (1989). The corresponding figure based on the above table is 275.4 g/L solution. The solubility of NiSO4 significantly decreases with increasing amount of sulphuric acid in the solution (Gmelin, 1966). The same effect, which must be ascribed to the presence of excess sulphate ions, has been observed if potassium sulphate is present (Carlsen, 2001).

 

The dissolution process appears to be significantly more rapid for the hydrated form of the salt, which apparently is rapidly dissolved and the anhydrous form that is dissolved only in 1 to 2 days at 37°C (Maximilien, 1989).

References:

Carlsen L (2001): Aqueous Solubilities and Complex Stabilities of Ni(II) Species. Part 1: Inorganic Ligands. Draft report to the Danish EPA.

CRC (2000): Handbook of Chemistry and Physics, 81th Edn., CRC Press Inc. Boca Raton, Florida.

Gmelin (1966): Gmelins Handbuch der Anorganischen Chemie, 8te Aufl. Nickel (System-Nummer 57), Teil B – Lieferung 2, Verlag Chemie, Weinheim

Linke WF. (1965): Solubilities. Inorganic and metal-organic compounds. A compilation of solubility data from the periodical literature, Vol II, 4th edition, American Chemical Society, Washington, D.C.

Maximilien, R (1989): Critical review of animal carcinogenesis by nickel and its inorganic compounds, Part 2, Appendices, EUR 12456 EN/2, Commission of the European Communities, Luxembourg.

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