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Description

Iron phosphate (iron(II) orthophosphate, Fe3(PO4)2) is a salt of divalent iron and orthophosphoric acid, a mineralogical analogue of vivanite.

Basic Attributes

• CAS No: 14940-41-1
• Chemical formula: Fe,2/3H3O4P
• Molecular weight: 222.88; exact mass 222.93100
• EU number: 239-018-0
• UNII: D07L04MRWI
• DSSTox ID: DTXSID20872569
• PSA specifications: 132.98000; XLogP3: 0.12630

Physico-chemical characteristics

• Density: 2.580
• Solubility in water: insoluble; soluble in mineral acids

Safety Information

WGK Germany: 3.

Scope of application

Iron(II) phosphate is used as a component of inorganic pigments (including the historical vivanite-based blue pigment), as a precursor in the production of cathode materials for lithium iron phosphate (LiFePO4) batteries - oxidation to iron(III) phosphate followed by lithiation, and as a source of iron and phosphorus in specialized fertilizers and feed additives. In the chemical industry it is used as an intermediate in the synthesis of other iron compounds.

Mineralogical features

A natural analogue of the compound, the mineral vivanite, is characterized by the fact that freshly mined crystals are almost colorless or pale greenish, but quickly darken in air, acquiring a rich blue or blue-violet hue due to the partial oxidation of iron(II) to iron(III) under the influence of oxygen. The same phenomenon is observed in synthetic iron(II) phosphate: when stored in the open air or in a humid environment, the material gradually turns blue, which serves as a visual indicator of oxidation and at the same time limits the shelf life of the commercial form without a protective atmosphere.

Role in the production of cathode materials

In the synthesis of LiFePO4 cathodes, iron(II) phosphate is oxidized in a controlled manner to iron(III) phosphate (FePO4), which is then lithiated by introducing lithium ion into the crystal lattice. The purity of the initial iron(II) phosphate, the uniformity of the particles and the absence of foreign cations directly affect the electrochemical characteristics of the finished cathode material - capacity, charge-discharge rate and battery life.

Storage and transportation conditions

Store in a closed container, in a dry place, away from strong acids and oxidizing agents - the substance, being a salt of ferrous iron, is prone to oxidation to iron(III) compounds in air.

Difference from iron(III) phosphate

Unlike iron(III) phosphate (FePO4), an insoluble white or peach-colored powder used primarily as a molluscicide, iron(II) phosphate is a parent, more reduced compound that has yet to be oxidized to obtain the target form for cathode materials or pigments. The valence of iron in these two salts determines their completely different areas of application, although they have the same elemental composition (iron and phosphate).