Iron dichloride

Water solubility

Description of key information

Initially very soluble (>>10 g/L), rapid transformation/speciation in environmental waters and body fluids
Initial solubility of the anhydrous form 650 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 chloride (FeCl2)

The anhydrous salt and hydrated forms have high initial solubility in water of 650 g/L (Lide 2002), which is characterized as “freely soluble in water” in another source (O’Neil et al 2006, The Merck Index).

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

Salt	Anhydrous form	Solid hydrate form	Aqueous solution
Ferrous chloride, FeCl2	650 at 25°C		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.

• 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.
• O'Neil MJ, Heckelman PE, Koch CB, Roman KJ eds (2006). The Merck Index. An encyclopedia of Chemicals, Drugs, and Biologicals. 14th edn. ISBN: 978-0-911910-00-1. Whitehouse Station, NJ, U.S.A. Merck and Co. 1740 p.
• 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.