Iron(III) phosphate

Iron(III) phosphate, also ferric phosphate,[3][4] is the inorganic compound with the formula FePO4. Several related materials are known, including four polymorphs of FePO4 and two polymorphs of the dihydrate FePO4·(H2O)2. These materials find several technical applications as well as occurring in the mineral kingdom.[5][6]

Iron(III) phosphate
IUPAC name
Iron(III) phosphate
Other names
Ferric orthophosphate, Ferric phosphate
3D model (JSmol)
ECHA InfoCard 100.030.123
Molar mass 150.815 g/mol (anhydrous)
Appearance yellow-brown solid
Density 3.056 g/cm3 (anhydrous)
2.87 g/cm3 (20 °C, dihydrate)
Melting point 250 °C (482 °F; 523 K)
(dihydrate) decomposes[1]
0.642 g/100 mL (100 °C)[1]
+11,500.0·10−6 cm3/mol
180.5 J/mol·K (dihydrate)[1]
171.3 J/mol·K (dihydrate)[1]
-1888 kJ/mol (dihydrate)[1]
GHS pictograms [2]
GHS Signal word Warning
H315, H319, H335[2]
P261, P305+351+338[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references


The most common form of FePO4 adopts the structure of α-quartz. As such the P and Fe have tetrahedral molecular geometry. At high pressures, a phase change occurs to a more dense structure with octahedral Fe centres. Two orthorhombic structures and a monoclinic phase are also known. In the two polymorphs of the dihydrate, the Fe center is octahedral with two mutually cis water ligands.[7]


Iron(III) phosphate can be used in steel and metal manufacturing processes. When bonded to a metal surface, iron phosphate prevents further oxidation of the metal. Its presence is partially responsible for the corrosion resistance of the Iron pillar of Delhi.

Iron phosphate coatings are also primarily used as base coatings for paint in order to increase adhesion to the iron or steel substrate. It is often used in rustproofing. It can also be used for bonding fabrics, wood, and other materials to these surfaces. Iron phosphate coatings are usually applied as part of a painting or powder coating process.

Anhydrous iron phosphate has been investigated as an intercalation electrode in a lithium-ion battery despite having low electronic conductivity.


Iron phosphate is one of the few molluscicides approved for use in the practice of organic farming.[8]

Pesticide pellets containing iron phosphate plus a chelating agent, such as EDTA, leach heavy metals from soil into groundwater.[9] The Research Institute of Organic Agriculture (FiBL) reported the EDTA content and stated products were likely to be no safer than metaldehyde baits.[10] Ferric phosphate slug and snail baits marketed in the U.S. contain EDTA.[11]


Iron(III) phosphate is not allowed as food additive in the European Union. It was withdrawn from the list of allowed substances in the directive 2002/46/EC in 2007.

See also


  1. "iron(III) phosphate dihydrate". Retrieved 3 July 2014.
  2. Sigma-Aldrich Co., Iron(III) phosphate dihydrate. Retrieved on 2014-05-03.
  3. "Iron(III) Phosphate". NIH, U.S. National Library of Medicine. Retrieved 22 January 2016.
  4. "FERRIC PHOSPHATE". Retrieved 22 January 2016.
  5. Roncal-Herrero, T., Rodriguez-Blanco, J.D., Benning, L.G., Oelkers, E.H. (2009) Precipitation of Iron and Aluminium Phosphates Directly from Aqueous Solution as a Function of Temperature from 50 to 200°C. Crystal Growth & Design, 9, 5197-5205. doi: 10.1021/cg900654m.
  6. Song, Y.; Zavalij, P. Y.; Suzuki, M.; Whittingham, M. S. (2002). "New Iron(III) Phosphate Phases: Crystal Structure and Electrochemical and Magnetic Properties" (PDF). Inorganic Chemistry. 41 (22): 5778–5786. doi:10.1021/ic025688q. PMID 12401083. Archived from the original (PDF) on 14 July 2014. Retrieved 3 July 2014.
  7. Zaghib, K.; Julien, C. M. (January 2005). "Structure and electrochemistry of FePO4·2H2O hydrate". Journal of Power Sources. 142: 279–284. doi:10.1016/j.jpowsour.2004.09.042. Retrieved 3 July 2014.
  8. "COMMISSION REGULATION (EC) No 889/2008". European Union law. Retrieved 3 July 2014.
  9. "The Regional Institute - Slugs, Snails and Iron based Baits: An Increasing Problem and a Low Toxic Specific Action Solution 1". 11 September 2018.
  10. "Archived copy" (PDF). Archived from the original (PDF) on 2007-07-10. Retrieved 2016-03-05.CS1 maint: archived copy as title (link)
  11. "National Organic Standards Board Crops Subcommittee Petitioned Material Proposal Ferric Phosphate (to Remove)" (PDF). August 15, 2012.
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