Iron sulphate

Water solubility

Description of key information

Initially very soluble (>>10 g/L), rapid transformation/speciation in environmental waters and body fluids
Initial solubilities are
FeSO4: Anhydrous 228 g/L; Monohydrate 295 g/L

Additional information

Testing for this endpoint has been waived in accordance with column 2 restrictions. All soluble iron salts dissociate in aqueous media to the respective anions and kations, and are then subject to further change of oxidation and speciated state according to the conditions. Thus the salts are not stable and undergo fast hydrolysis (DT50 < 12 h) in water, particularly if oxygen is present and the pH is in the common environmental ranges. Nonetheless a number of generally high initial water solubilities are published, which are reported in the following paragraphs. Comparably aqueous solutions are initially (i.e. before transformation/speciation) unlimitedly miscible with water and water solubility is not a relevant endpoint for them, as they are unlimitedly miscible with water.

Ferrous sulphate (FeSO4)

The most reliable value of 228 g/L at 25 ºC has been reported in the CRC handbook (Lide 2003, in agreement with Seidell et al 1940) for the anhydrous salt and 295 g/L for the monohydrate (Lide 2002), for which solubilities at elevated temperatures are available (Washburn 1926). One less reliable source states a higher value of 328 g/L (Anon 1987). The anhydrous salt and hydrated forms have thus high solubility in water.

Table: Initial water solubilities [g/L] of the registered category member salt forms

Salt	Anhydrous form	Solid hydrate form	Aqueous solution
Ferrous sulphate, FeSO4	228 at 25 °C	Monohydrate (CAS 17375-41-6): 295	Unlimited miscibility

Ferric and ferrous kations

The following Table below shows the maximum dissolved concentration of the iron kations in pure water as it depends upon pH (see section on Hydrolysis).

Table: Calculated maximum solubility of iron in solution at 20 °C depending on pH (OECD 2007, table 13, p 33)

pH	Ferrous iron (II)		Ferric iron (III)
	[mg Fe/L]	[mmol/L]	[mg Fe/L]	[mmol/L]
4	>1E+06	>1.8E+04	6.16E-02	1.1E-03
5	>1E+06	>1.8E+04	6.16E-05	1.1E-06
6	>1E+06	>1.8E+04	6.16E-08	1.1E-09
7	89600	1600	6.16E-11	1.1E-12
8	896	16	6.16E-14	1.1E-15

In conclusion the limit of the ferric iron kation solubility is even at significantly acidified conditions is of the order of ng Fe(III)/L.

• Anon (1987). Ferrous sulphate. Dang Prop Ind Mat Rep 7:55-60.
• Lide DR ed (2002). CRC Handbook of Chemistry and Physics. 83rd edn. ISBN 0-8493-0483-0. Boca Raton, FL, U.S.A. CRC Press. 2664 p.
• Lide DR ed (2003). CRC Handbook of Chemistry and Physics. 84th edn. ISBN 0-8493-0484-9. Boca Raton, Florida, U.S.A. CRC Press. 2616 p.
• Seidell A, Link W F eds (1940). Solubilities of Inorganic and Metal Organic Compounds. 3rd edn. New York, NY, U.S.A. D Van Nostrand.
• OECD Organisation for Economic Co-operation and Development (2007). SIDS Initial Assessment Report for SIAM 24. Chemical Category: Iron Salts. Self-published, Paris, France, 17-20 April. 138 p.
• Washburn EW ed (1926). International Critical Tables of Numerical Data, Physics, Chemistry, and Technology, 1st Edition (1926-1933). Published for the National Research Council by McGraw-Hill Book Company. New York. U.S.A.