1693. Calcium Phosphate, Monobasic

Nomenclature

CAS number: 7758-23-8
Acid calcium phosphate; calcium biphosphate; monocalcium orthophosphate; monocalcium phosphate; primary calcium phosphate; “calcium superphosphate”.
CaH4O8P2; mol wt 234.05.
Ca 17.12%, H 1.72%, O 54.69%, P 26.47%.
Ca(H2PO4)2.

Description and references

Commercial prepn for fertilizers by treating pulverized phosphate rock with H2SO4 or H3PO4: Faith, Keyes & Clark's Industrial Chemicals, F. A. Lowenheim, M. K. Moran, Eds. (Wiley-Interscience, New York, 4th ed., 1975) pp 191-200. Laboratory prepn from CaCO3 and H3PO4: Jensen, Kathley, Inorg. Synth. 4, 18 (1953).

Properties

Monohydrate, large, shining, triclinic plates, cryst powder or granules. Non-hygroscopic when pure, but traces of impurities such as H3PO4 cause material to be deliquesc. Strong acid taste. Loses H2O at 100°, dec at 200°. d418 2.220. Moderately sol in water; sol in dil HCl or HNO3 or acetic acid.

Note

The products obtained from commercial processes are not pure monobasic calcium phosphate. The superphosphate obtained from the H2SO4 treatment is about 30% CaH4(PO4)2.H2O, 10% CaHPO4, 45% CaSO4, 10% iron oxide, silica, alumina, etc. and 5% water; it contains 18-21% available P2O5. The triple superphosphate obtained from the H3PO4 treatment contains from 43 to 50% available P2O5.

Use

Chiefly in fertilizers; as acidulant in baking powders and in wheat flours; mineral supplement for foods and feeds; in enameling.