Aluminium phosphate

Chembox new
Name = Aluminium phosphate
ImageFile =
ImageName = Aluminum phosphate
OtherNames = Aluminium monophosphate
Section1 = Chembox Identifiers
CASNo = 7784-30-7
Section2 = Chembox Properties
Formula = AlPO₄
MolarMass = 121.952 g/mol
Appearance = white, crystalline powder
Density = 2.566 g/cm³, solid
Solubility = insoluble
MeltingPt = decomposes
BoilingPt =
Section7 = Chembox Hazards
EUClass = Xi
NFPA-H = 2
NFPA-R = 0
NFPA-F = 0
RPhrases = R36/37/38
SPhrases = S26LD₅₀>5000mg/kg mouse oral

Aluminium phosphate (AlPO₄) is a chemical compound. It is used in cake mixes and in some baking powders as a leavening agent to help baked goods rise.

It is also used industrially as a high-temperature dehydrating agent. When strongly heated, aluminium phosphate decomposes into aluminium oxide and phosphorus pentoxide, the latter of which is very effective at absorbing water. Thus, aluminium phosphate can be used to dehydrate acetic acid through the following series of reactions:

: 4AlPO₄ → 2Al₂O₃ + P₄O₁₀: 6CH₃COOH + P₄O₁₀ → 4H₃PO₄ + 6CH₂CO: CH₂CO + CH₃COOH → (CH₃CO)₂O

Occurrence

Although it is unstable to heat, in geologically stable regions like Australia and Southern Africa, alumiunium phosphate is generally the most common form of phosphorus in soils, as it forms when phosphate in rainwater reacts with dissolved aluminium in the soil. Although it is not as insoluble as many other components of soils in those regions, aluminium phosphate can form exceedingly insoluble double salts known as taranakites with many essential elements for plant growth that are normally highly soluble in water, such as potassium and nitrogen.

In coastal areas of South Africa and Namibia, the combination of exceedingly old soils and a high input of phosphate from very fertile oceans due to the Benguela Current causes aluminium phosphate to accumulate to form a concentrated mineral, known as aluminium phosphate rock. Only in recent years has there been any interest in the mining of these considerable deposits as a source of phosphorus for agriculture, but there could be considerable economic value if low-cost treatment becomes possible.

The mineral form of aluminium phosphate, berlinite, is rarely found in the nature. It possess quartz-like structure, which makes these 2 minerals often hard to distinguish by standard laboratory methods (like Powder X-Ray Diffraction).

References