Page 193 - Chemical and process design handbook

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CALCIUM PHOSPHATE

Monobasic calcium phosphate [Ca(H PO ) ] is manufactured by crystal-
2 4 2
lization after evaporation and cooling of a hot solution of lime [CaO or
Ca(OH) ] and strong phosphoric acid (H PO ). The crystals are cen-
2 3 4
trifuged, and the highly acidic mother liquor returned for reuse. This acid
salt is also made by spray drying a slurry of the reaction product of lime
and phosphoric acid.
Dibasic calcium phosphate (CaHPO ) is manufactured from phosphoric
4
acid and lime:
CaO + H PO → Ca HPO + H O
3 4 2 4 2
whereas calcium metaphosphate is manufactured from phosphate rock,
phosphorus pentoxide, and phosphorous acid.
.
CaF 3Ca (PO ) + 6P O + 2HPO → 10Ca (PO ) + 2HF
2 3 4 2 2 5 3 3 3 2
In this process the phosphorus pentoxide contacts the lump rock in a
vertical shaft.
This calcium metaphosphate may be regarded as a dehydrated triple
superphosphate made directly from phosphate rock. The calcium metaphos-
phate is quite insoluble, and it must hydrolyze to become effective.
xCa(PO ) + xH O → xCa(H PO )
3 2 2 2 4 2

See Lime.

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