Iron sulphate: formula, uses and precautions

Iron sulphate is a solid green or yellow-brown crystal. In nature it is found as iron (II) sulphate (also known as ferrous sulphate, caparossa, and green vitriol), and iron (III) sulphate, (also known as ferric sulphate, and vitriol of Mars). Each one has a different level of hydration.

It is used to treat water and sewage water, and as an ingredient in fertilisers. The main problem is the threat it poses to the environment. It is necessary to take steps immediately to stop the spread of iron sulphate in the atmosphere.

Iron sulphate

Iron (II) sulphate heptahydrate (formula FeSO4 . 7H2O) crystalises into green monoclinic crystals.

When heated to 60-70ºC it releases 3 moles of water and forms the tetrahydrate iron (II) sulphate (formula FeSO4 . 4H2O).

When heated to approximately 300ºC, and in the absence of air, it forms a white powder (iron (II) sulphate monohydrate).

When heated to approximately 260ºC, and in the presence of air, the monohydrate is oxidised to iron (III) sulphate.

In its anhydrous form, iron (III) sulphate (formula Fe2(SO4)3) is a whiteish-yellow solid, which is hydrolysed when dissolved in water, producing a brownish solution.

Formulas

Iron (II) sulphate Iron (II) sulphate Iron (III) sulphate
anhydrous heptahydrate anhydrous
Formula FeSO4 FeSO4 7H2O Fe2(SO4)3

 

  • CAS: 7720-78-7 anhydrous iron (II) sulphate
  • CAS: 7782-63-0 iron (II) sulphate heptahydrate
  • CAS: 10028-22-5 anhydrous iron (III) sulphate

2D Structure

Screen Shot 2017-02-16 at 11.11.26

 Screen Shot 2017-02-16 at 11.13.43

 

Screen Shot 2017-02-16 at 11.16.58

 

3D Structure

Screen Shot 2017-02-16 at 11.21.31

Screen Shot 2017-02-16 at 11.19.33

Screen Shot 2017-02-16 at 11.25.21

 

Screen Shot 2017-02-16 at 11.23.53

Characteristics of Iron sulphate

Physical and chemical properties

  Iron (II) sulphate Iron (II) sulphate Iron (III) sulphate
  anhydrous heptahyrate anhydrous
Appearance White crystals Greenish-blue crystals Greyish-white powder crystals
Molecular mass 151.901 g/mol 278.006 g/mol 399.858 g/mol
Boiling point 90°C 90°C  
Melting point 64 °C   480 °C
Density 1898 kg/m3   1898 kg/m3
Solubility in water, g/100ml at 20°C 29.5 g/L of water   Soluble

 

Iron sulphate belongs to a group of weak reducing agents. It is a solid brownish-yellow or green crystal. Its appearance and smell vary depending on the iron salt. The most common form is heptahydrate, bluish-green in colour.

Iron (III) sulphate belongs to a group of acidic salts. It is a greyish-white powder, but can also form yellow rhombohedral crystals.

Flammability

  • Many weak reducing agents are flammable or combustible. However, they often require extreme conditions (such as high temperatures or pressure) for combustion to occur.
  • Iron (II) sulphate is not flammable, but as with other weak, inorganic reducing agents, the reaction with oxidising agents produces heat and substances that can be flammable, combustible, or reactive.
  • None of the salts are highly flammable

Reactivity

  • Reactions of weak reducing agents with oxidising agents can cause combustion and even explosions if the mixture is heated or pressurised.
  • Oxygen, a relatively strong oxidising agent that is present in the atmosphere, can react with compounds of this kind in the right condition, for example if heated, if there is a spark, if a catalyst is used or if given a mechanical shock.
  • Iron (II) sulphate is efflorescent in dry air. In humid air the crystals form a brown coating of basic iron (III) sulphate.
  • Aqueous solutions of iron (II) sulphate are slightly acidic due to the hydrolysis
  • The acidic salts acts like weak acids to neutralise bases. These reactions generate heat, although less than that generated by the neutralisation of inorganic acids, inorganic oxoacids, and carboxylic acids.
  • Iron (III) sulphate is soluble in water. It is hydrolysed slowly in aqueous solutions. It forms acidic aqueous solutions and is hygroscopic in air. It is also corrosive to copper, copper alloys, mild steel, and galvanised steel.

Toxicity

  • Most weak reducing agents are toxic to ingest. They can cause chemical burns if they are inhaled or if they come into contact with skin.
  • If they are ingested, iron (II) sulphate can cause gastrointestinal tract issues. If large quantities are ingested by children, it may result in vomiting, hematemesis (vomiting blood), liver damage, and peripheral circulatory collapse
  • With regards to the salts, toxicity varies. The solutions of these substances are usually corrosive to skin and irritating to mucous membranes.
  • The inhalation of iron (III) sulphate powder irritates the nose and throat and ingestion causes mouth and stomach irritation. The powder irritates the eyes and can also irritate the skin if contact is prolonged.

Uses

  • Iron (II) sulphate is used in the preparation of other iron compounds.
  • It is used to make ink and iron pigments. It is also used in printmaking and lithography, in the preservation of wood, and in animal fodder, among other things.
  • These processes generate by-products which affect the environment. This has encouraged research into suitable alternatives.
  • Large quantities of iron (II) sulphate are used to filter effluents. The remaining sludge can be used as fertilizer.
  • The treatment of iron(II) sulphate with calcium chloride has been proposed, to produce plaster and iron (III) chloride.
  • As a cement additive, iron (II) sulphate can reduce the content of water-soluble chromates.
  • Iron (II) sulphate can be used against chlorosis, a disease in vines and plants. It can also be used to treat alkaline ground, and to get rid of moss.
  • Iron (III) sulphate can be used to prepare alumina and iron oxide pigments. It is also used as a coagulant for the treatment of effluent liquids.
  • Ammonium iron (III) sulphate is used for tanning. Solutions containing iron (III) are used to reduce the volume of sludge from sewage treatment plants.

Clinical effects

Iron has historically been one of the main causes of poisoning of children. Exposure has been reduced in recent years due to better packaging, but it still has a significant morbidity and mortality rate.

Iron is necessary for proteins and enzymes, including haemoglobin, myoglobin, and cytochromes, to function normally, but it is toxic to cells and corrosive to gastrointesintal mucous.

It can be found as a nutritional supplement in vitamins (usually iron sulphate (II) or ferrous sulphate). It is used to treat and prevent iron-deficiency anaemia.

Among the main adverse effects of its use, are gastrointestinal illnesses and constipation.

The symptoms of iron poisoning are severe vomiting, diarrhoea, lethargy, metabolic acidosis, shock, gastrointestinal bleeding, a coma, seizures, hepatotoxicity (chemically-induced liver damage), and intestinal stenosis.

Excessive long-term ingestion of iron compounds can lead to a build up of iron in the body, particularly in the liver, the spleen, the lymphatic system, pancreatic fibrosis, diabetes mellitus, and liver cirrhosis. The signs and symptoms include irritability, nausea, vomiting, and normocytic anaemia.

Safety and risks

The Globally Harmonised System of Classification and Labelling of Chemicals (GHS) is an internationally agreed system, created by the United Nations, and designed to replace the different rules of classification and labelling used in different countries, through the use of a consistent approach.

The hazard classes (and their corresponding chapter in the GHS), the rules of classification and labelling, and the recommendations for iron (II) sulphate are the following (European Chemicals Agency, 2017; United Nations, 2015):

Screen Shot 2017-02-16 at 11.31.31

(United Nations, 2015, p. 368)

Screen Shot 2017-02-16 at 11.33.45

(United Nations, 2015, p. 371)

Screen Shot 2017-02-16 at 11.35.40

(United Nations, 2015, p. 382)

Screen Shot 2017-02-16 at 11.41.43

(United Nations, 2015, p. 385)

The hazard classes (and their corresponding chapter in the GHS), the rules of classification and labelling, and the recommendations for the heptahydrate iron (II) sulphate are the following (European Chemicals Agency, 2017; United Nations, 2015):

Screen Shot 2017-02-16 at 11.33.45

(United Nations, 2015, p. 371)

corrosion cutanea

(United Nations, 2015, p. 382)

eye damage

(United Nations, 2015, p. 385)

The hazard classes (and their corresponding chapter in the GHS), the rules of classification and labelling, and the recommendations for iron (III) sulphate are the following (European Chemicals Agency, 2017; United Nations, 2015):

corrosivemetals

(United Nations, 2015, p. 368)

oral371

(United Nations, 2015, p. 371)

skin381

(United Nations, 2015, p. 381)

skin382

(United Nations, 2015, p. 382)

388.sensibilizacion

(United Nations, 2015, p. 388)

eye384

(United Nations, 2015, p. 384)

2ndeye385

(United Nations, 2015, p. 385)

final395

(United Nations, 2015, p. 395)

References

  1. European Chemicals Agency (ECHA). (2017). Summary of Classification and Labelling.
  2. Harmonised classification – Annex VI of Regulation (EC) No 1272/2008 (CLP Regulation. Diiron tris(sulphate). Retrieved from echa.europea.eu.
  3. European Chemicals Agency (ECHA). (2017). Summary of Classification and Labelling.
  4. Harmonised classification – Annex VI of Regulation (EC) No 1272/2008 (CLP Regulation). Iron (II) sulfate. Retrieved from echa.europea.eu.
  5. European Chemicals Agency (ECHA). (2017). Summary of Classification and Labelling.
  6. Harmonised classification – Annex VI of Regulation (EC) No 1272/2008 (CLP Regulation. Iron (II) sulfate (1:1) heptahydrate, sulfuric acid, iron(II) salt (1:1), heptahydrate.
  7. ferrous sulfate heptahydrate. Retrieved from echa.europea.eu.
  8. Hazardous Substances Data Bank (HSDB). TOXNET. (2017). Ferrous sulfate. Bethesda, MD, EU: National Library of Medicine.
  9. National Center for Biotechnology Information. PubChem Compound Database. (2017). Iron(II) sulfate. Bethesda, MD, EU: National Library of Medicine. Retrieved from nhi.gov.
  10. National Center for Biotechnology Information. PubChem Compound Database. (2017). Iron(II) sulfate heptahydrate. Bethesda, MD, EU: National Library of Medicine. Retrieved from nhi.gov.
  11. National Center for Biotechnology Information. PubChem Compound Database. (2017). Ferric sulfate. Bethesda, MD, EU: National Library of Medicine. Retrieved from nhi.gov.
  12. National Oceanic and Atmospheric Administration (NOAA). CAMEO Chemicals. (2017). Chemical Datasheet. Ferrous sulfate. Silver Spring, MD. EU.
  13. National Oceanic and Atmospheric Administration (NOAA). CAMEO Chemicals. (2017). Chemical Datasheet. Ferric sulfate. Silver Spring, MD. EU.
  14. National Oceanic and Atmospheric Administration (NOAA). CAMEO Chemicals. (2017). Reactive Group Datasheet. Reducing Agents, Weak. Silver Spring, MD. EU.
  15. National Oceanic and Atmospheric Administration (NOAA). CAMEO Chemicals. (2017). Reactive Group Datasheet. Salts, Acidic. Silver Spring, MD. EU.
  16. Smokefoot, (2016). Structure of iron(II) sulfate heptahydrate [imagen]. Retrieved from wikipedia.org.
  17. Wildermuth, E., Stark, H., Friedrich, G., Ebenhöch, F. L., Kühborth, B., Silver, J., & Rituper, R. (2000). Iron Compounds. En Ullmann’s Encyclopedia of Industrial Chemistry. Wiley-VCH Verlag GmbH & Co. KGaA.

LEAVE A REPLY

Please enter your comment!
Please enter your name here