FERROUS CHLORIDE (FECL2): STRUCTURE, USES, PROPERTIES - CHEMISTRY - 2025

The ferrous chloride is an inorganic solid formed by bonding a cation Fe ²⁺ and two chloride anions Cl ^-. Its chemical formula is FeCl ₂. It tends to absorb water from the environment. One of its hydrates is FeCl _{2 •} 4H ₂ O tetrahydrate, which is a greenish solid.

It should be noted that it is very soluble in water and tends to oxidize easily in the presence of air, forming ferric chloride FeCl ₃. Because it is easily oxidizable and therefore capable of acting as a reducing agent, it is widely used in chemical and biological research laboratories.

Ferrous chloride tetrahydrate FeCl _{2 •} 4H ₂ O solid. Craven. Source: Wikimedia Commons.

Ferrous chloride has several uses, the most important of which is to help other agents in the oxidation of sludge derived from sewage or sewage treatment. It is also used in the process of iron coating metals and has some uses in the pharmaceutical industry.

The use of FeCl ₂ has also been experimented with in recovering valuable metals from spent catalysts found in the exhaust pipes of gasoline or diesel powered vehicles.

It is used in the textile industry to fix the colors in some types of fabric.

Structure

Ferrous chloride is made up of a ferrous Fe ²⁺ ion and two Cl ^- chloride ions linked by ionic bonds.

Ferrous chloride FeCl ₂ where the ions that make it up are observed. Epop. Source: Wikimedia Commons.

The ferrous ion Fe ²⁺ has the following electronic structure:

1s ², 2s ² 2p ⁶, 3s ² 3p ⁶ 3d ⁶, 4s ⁰

where it can be seen that it lost two electrons from the 4s shell.

This configuration is not very stable, and for this reason it tends to oxidize, that is, to lose another electron, this time from the 3d layer, forming the Fe ³⁺ ion.

For its part, the chloride ion Cl ^- has the following electronic structure:

1s ², 2s ² 2p ⁶, 3s ² 3p ⁶

where you can see that it acquired an extra electron in the 3p shell, completing it. This configuration is very stable because all the electronic layers are complete.

Nomenclature

- Ferrous Chloride

- Iron (II) chloride

- Iron dichloride

- Ferrous chloride tetrahydrate: FeCl _{2 •} 4H ₂ O

Properties

Physical state

Colorless to pale green solid, crystals.

Molecular weight

126.75 g / mol

Melting point

674 ºC

Boiling point

1023 ºC

Specific weight

3.16 at 25 ºC / 4 ºC

Solubility

Very soluble in water: 62.5 g / 100 mL at 20 ºC. Soluble in alcohol, acetone. Slightly soluble in benzene. Practically insoluble in ether.

Other properties

Anhydrous FeCl ₂ is very hygroscopic. It easily absorbs water from the environment, forming a variety of hydrates, especially the tetrahydrate, in which for each FeCl ₂ molecule there are 4 H ₂ O molecules attached to it (FeCl _{2 •} 4H ₂ O).

In the presence of air, it slowly oxidizes to FeCl ₃. This means that the Fe ²⁺ ion is easily oxidized to the Fe ³⁺ ion.

If heated in the presence of air, it rapidly forms ferric chloride FeCl ₃ and ferric oxide Fe ₂ O ₃.

FeCl ₂ is corrosive to metals and fabrics.

Obtaining

It is obtained by treating an excess of iron metal Fe with an aqueous solution of hydrochloric acid HCl at high temperatures.

Fe ⁰ + 2 HCl → FeCl ₂ + 2 H ⁺

However, due to the presence of water by this method, ferrous chloride tetrahydrate FeCl _{2 •} 4H ₂ O is obtained.

To obtain it anhydrous (without water incorporated in the crystals) some researchers have chosen to carry out the reaction of iron powder with anhydrous HCl (without water) in the solvent tetrahydrofuran (THF) at a temperature of 5 ºC.

In this way, the compound FeCl _{2 •} 1,5THF is obtained, which when heated to 80-85 ºC under vacuum or in a nitrogen atmosphere (to avoid the presence of water) produces anhydrous FeCl ₂.

Applications

Ferrous chloride has various uses, generally based on its reducing capacity, that is, it can be easily oxidized. It is used for example in paints and coatings, as it helps to fix them to the surface.

Iron is an essential micronutrient for human and some animal health. It is involved in protein synthesis, in respiration, and in the multiplication of cells.

For this reason, FeCl ₂ is used in pharmaceutical preparations. The Fe ²⁺ ion as such is better absorbed than the Fe ³⁺ ion in the intestine.

It is used for the manufacture of FeCl ₃. It is used in metallurgy, in iron coating baths, to provide a more ductile deposit.

Here are other featured uses.

In the coloring of fabrics

FeCl ₂ is used as a mordant or dye fixative in some types of fabric. The mordant reacts chemically and binds simultaneously to the dye and the fabric, forming an insoluble compound on it.

In this way, the dye remains fixed to the fabric and its color intensifies.

Ferrous Chloride FeCl ₂ allows colors to fix on fabrics. gina pina. Source: Wikimedia Commons.

In wastewater treatment

FeCl ₂ is used in sewage or waste water treatment plants (sewer water).

In this application, ferrous chloride participates in the oxidation of the sludge, through a process called Fenton oxidation. This oxidation causes the rupture of the mud flocs and allows the release of the water that is strongly bound to it.

Section of a sewage treatment plant where the sludge can be observed. Sometimes this is treated with ferrous chloride FeCl ₂ so that it can be more easily separated from the water. Evelyn Simak / Sewage works north of Dickleburgh. Source: Wikimedia Commons.

The sludge can then be dried and disposed of in an environmentally friendly way. The use of ferrous chloride helps to reduce the costs of the process.

It has also recently been proposed to use it to reduce the formation of hydrogen sulfide gas or hydrogen sulfide in said sewage waters.

In this way, the corrosion produced by this gas and also unpleasant odors would be reduced.

In chemical studies

Due to its reducing properties (the opposite of oxidizing), FeCl ₂ is widely used in various investigations in chemistry, physics and engineering laboratories.

Certain scientists used ferrous chloride vapors to extract valuable metals like platinum, palladium and rhodium from spent catalysts in gasoline or diesel powered vehicles.

These catalysts are used to remove gases that are harmful to humans and the environment. They are located in the exhaust pipe of cars and trucks that run on gasoline or diesel.

Exhaust pipe of a vehicle where a more voluminous section is observed which is where the catalyst is located to convert harmful gases into friendly gases with the environment. Ahanix1989 at English Wikipedia. Source: Wikimedia Commons.

After a certain time, the vehicle's catalytic converter wears out and loses effectiveness and must be replaced. The spent catalyst is discarded and efforts are being made to recover the valuable metals it contains.

Ceramic grid of the catalyst where the traces of valuable metals to be recovered with FeCl _{2 are located}. Global-Kat Recycling. Source: Wikimedia Commons.

According to the researchers, with the iron from ferrous chloride, these metals formed magnetic alloys.

The alloys could be extracted with magnets and then the valuable metals recovered by known methods.

In biochemical studies

Because it has the Fe ²⁺ cation, which is an important micronutrient in humans and some animals, FeCl ₂ is used in biochemical and medical studies.

Certain studies have shown that ferrous chloride improves the fungicidal efficacy of cold argon plasma.

Cold plasma is a technology used for the sterilization of medical surfaces and instruments. It is based on the formation of hydroxyl radicals OH · from the humidity of the environment. These radicals react with the cell wall of the microorganism and cause its death.

In this investigation, FeCl ₂ improved the effect of cold plasma and accelerated the elimination of a fungus resistant to other disinfection methods.

Some scientists found that the use of FeCl ₂ allows to increase the yield in the reactions to obtain glucose starting from sugarcane bagasse.

In this case, since Fe ^{2+ is} an essential microelement for human health, its presence in traces in the product would not affect humans.

References

1. Fukuda, S. et al. (2019). Ferrous chloride and ferrous sulfate improve the fungicidal efficacy of cold atmospheric argon plasma on melanized Aureobasidium pullulans. J Biosci Bioeng, 2019, 128 (1): 28-32. Recovered from ncbi.clm.nih.gov.
2. Ismal, OE and Yildirim, L. (2019). Metal mordants and biomordants. In The Impact and Prospects of Green Chemistry for Textile Technology. Chapter 3, pp. 57-82. Recovered from sciencedirect.com.
3. Zhang, W. et al. (2019). Co-catalysis of magnesium chloride and ferrous chloride for xylo-oligosaccharides and glucose production from sugarcane bagasse. Bioresour Technol 2019, 291: 121839. Recovered from ncbi.nlm.nih.gov.
4. Zhou, X. et al. (2015). Role of indigenous iron in improving sludge dewaterability through peroxidation. Scientific Reports 5: 7516. Recovered from ncbi.nlm.nih.gov.
5. Rathnayake, D. et al. (2019). Hydrogen sulphide control in sewers by catalyzing the reaction with oxygen. Science of the Total Environment 689 (2019) 1192-1200. Recovered from ncbi.nlm.nih.gov.
6. Taninouchi, Y. and Okabe, TH (2018). Recovery of Platinum Group Metals from Spent Catalysts Using Iron Chloride Vapor Treatment. Metall and Materi Trans B (2018) 49: 1781. Recovered from link.springer.com.
7. US National Library of Medicine. (2019). Ferrous Chloride. Recovered from: pubchem.ncbi.nlm.nih.gov.
8. Aresta, M. et al. (1977). Iron (0) Oxidation by Hydrogen Chloride in Tetrahydrofuran: a Simple Way to Anhydrous Iron (II) Chloride. Inorganic Chemistry, Vol. 16, No. 7, 1977. Recovered from pubs.acs.org.
9. Cotton, F. Albert and Wilkinson, Geoffrey. (1980). Advanced Inorganic Chemistry. Fourth Edition. John Wiley & Sons.