Chemistry Reference
In-Depth Information
PHOSPHORIC ACID (H
PO
)
3
4
Also “orthophosphoric acid”
Properties
Pure phosphoric acid is a colorless solid melting at
42
C. Soluble in all proportions in water.
Commercial 85% phosphoric acid in water is a
colorless, odorless, heavy liquid.
°
Commercial grades
75%, 89%, 85%, 105-117% in technical, food, and
electronic grades.
Uses
The highest value inorganic acid marketed in the U.S.
and second in value to sulfuric acid. Used primarily
for the preparation of salts used as fertilizers
(ammonium and calcium salts), water softeners and
detergents, animal feeds, and baking powder. Food-
grade phosphoric acid is used to acidify soft drinks,
e.g., Coca Cola. Organic phosphates are used in
flame retardants.
Manufacture
Mined phosphate rock is reacted with sulfuric acid.
The product phosphoric acid is isolated as a 28-35%
solution by filtering off the insoluble calcium sulfate
co-product.
Ca
3
PO( )
phosphate
rock
+
3H
2
SO
4
sulfuric
acid
2H
3
PO
4
+
3CaSO
4
gypsum
2
Suppliers
Albright and Wilson, Coyne Chemical, FMC Corp.,
General Chemical, Hoechst, Monsanto, Rhone
Poulenc, Texas Gulf, others.
The element phosphorus, like nitrogen, is essential to plant and animal life.
Although phosphorus was not identified and isolated until 1669, phospho-
rus-containing materials have been used as fertilizers since ancient times,
usually from bird droppings, fish, and bone. The first phosphoric acid was
made by treating bone ashes with sulfuric acid. This marked the beginning
of the commercial fertilizer industry. Eventually, mined phosphate rock, a
poor fertilizer by itself, was substituted for bones as a raw material for
phosphoric acid in the mid-1880s.
