Superphosphate is a fertilizer produced by the action of concentrated sulfuric acid on powdered phosphate rock.
- Ca3(PO4)2 + 2H2SO4 → Ca(H2PO4)2 + 2CaSO4
++++++++++++++++++++++++++++++++++++ Phosphate rock is mostly apatite Ca5(PO4)3(OH,Cl,F), not Ca3(PO4)2. The balanced equation for dissolution of hydroxyapatite is 2Ca5(PO4)3OH + 7H2SO4 --> 3Ca(H2PO4)2 + 7CaSO4 + 2H2O ++++++++++++++++++++++++++++++++++++
History and development
In the 1840s, scientists found that coprolites could be dissolved in sulphuric acid to produce what became known as superphosphate. In 1840, Justus Von Liebig wrote, "The crops on the field diminish or increase in exact proportion to the diminution or increase of the mineral substances conveyed to it in manure." Von Liebig was the first to discover that phosphate of lime in bone meal could be rendered more readily available to plants by treatment with sulphuric acid. Sir John Bennett Lawes about the same time discovered that phosphate rock underwent the same reaction and could be used as a source ingredient. Bennett Lawes was the first to manufacture superphosphate at his factory in Deptford, England in 1842.
A large market for superphosphate was created in the second half of the 20th century by the development of aerial topdressing in New Zealand which allowed superphosphate to be spread economically over large areas.
Superphosphate can be created naturally in large quantities by the action of guano, or bird feces, resulting in deposits around sea bird colonies which can be mined. The most famous mining site is the island of Nauru in the South Pacific much of the "soil" from which was mined, creating temporary wealth for the inhabitants, but destroying their environment.
References
- Yara corporate History Accessed May 2007
