Iron(II) chloride
Iron(II) chloride (FeCl2), also called ferrous chloride, is an inorganic salt of iron in the +2 oxidation state. It is supplied as the anhydrous solid, as hydrates (most commonly the pale green tetrahydrate) or as aqueous solutions. It is used in wastewater treatment, as a reducing agent and as a precursor for other iron compounds. It is hygroscopic and gradually oxidises in air to iron(III) species.
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Ferrous chloride 23%
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What is iron(II) chloride and how is it supplied?
Iron(II) chloride, FeCl2, is the chloride salt of divalent iron. The anhydrous form (CAS 7758-94-3, molar mass approx. 126.75 g/mol) is a hygroscopic, off-white to tan solid. The tetrahydrate (CAS 13478-10-9) forms pale green crystals. Industrial grades are often sold as aqueous solutions, frequently derived from spent pickle liquor produced when steel is pickled with hydrochloric acid. Reagent grades are used for laboratory synthesis.
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What is it used for?
In municipal and industrial wastewater treatment, FeCl2 serves as a coagulant, for phosphate precipitation and for sulfide (odour) control. In the laboratory it is a mild reducing agent and a starting material for other iron(II) and iron(III) compounds and coordination complexes. It is also a precursor in the preparation of iron oxide nanoparticles.
What should buyers and laboratories check?
Iron(II) is readily oxidised to iron(III) by air and moisture, so the iron(III) content is a key quality parameter. Material should be stored tightly sealed, ideally under inert gas for anhydrous grades. Check the CoA for:
- assay
- the hydrate form supplied
- Fe(III) content
- trace metal impurities
Also confirm the CAS number, because the anhydrous and hydrated forms have different numbers. Iron(II) chloride carries GHS hazard classifications, including acute oral toxicity and skin and eye effects. Consult the supplier's SDS for the exact classification of the specific grade and concentration, and check its REACH registration status where relevant.
Related concepts
Iron(III) chloride (FeCl3) is the oxidised counterpart and is widely used as a coagulant and etchant. Iron(II) sulfate is an alternative ferrous salt for water treatment. Further relevant topics include oxidation states of transition metals, hygroscopic materials and handling under inert atmosphere.
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