Phosphate
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What is phosphate? Phosphates are a variety of chemical compounds containing phosphorous combine with existing rocks. In Tennessee the commonest are Phosphorous pentoxide (P2O5) and Bone phosphate of lime (Ca3(PO4)2) |
 found by Pat Hollyday in the hermitage Formation, Franklin, TN |
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| Where is it found geographically? Tennessee's phosphate is found to the south and west of the Nashville Basin
When was it deposited? It was deposited during the Paleozoic Era when Central Tennessee was an uplifted structural (Nashville is now within a topographic basin) that was sometimes submerged below the shallow Ordovician sea that covered most of interior of North America. Phosphate was deposited on the boundary between the shallow water over the dome and deeper water to the west. Being that the phosphate (in the form of nodules) is less soluble than the limestone in which it was deposited, it is concentrated in the overlying residual soil when limestone erodes. |
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| Uses of Phosphate: The major use of phosphate is as an agricultural fertilizer. Until its damage to the environment became know, it was an ingredient in detergent. It is also used as a flavoring in soft drinks and an ingredient in toothpaste.
The products shown, from an exhibit at the Phosphate Museum in Mt. Pleasant (Maury County), all contain phosphate. |
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History of phosphate use in Tennessee: Phosphate was discovered by a prospector in Maury County in 1888. Chemical fertilizers had been introduced into American agriculture in the 1840's and by 1890, production of fertilizer had become big business. Many local mining companies were formed to exploit the new opportunities. By the 1930's local mines had been bough up by a few national companies and production became mechanized. Beginning in the 1970's phosphate mines started closing in Maury County. The opening of new quarries in Florida, where the cost of extraction was lower, made mining in Tennessee unprofitable. the industry closed down entirely in 1990. |
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| How is it mined and processed? Phosphate is mined from open pits. In the early 20th century much of the mining was done by hand, especially where the phosphate and settled into cracks in the limestone. In later years, the mining was mechanized.
Phosphate ores are usually contaminated with lime, silica, sand and iron, and must be milled and washed before processing. Filtration plays an important role in the process. |
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from Tennessee Rock and Mineral Resources by Robert J. Floyd, Tennessee Division of Geology Bulletin 66 |
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| Environmental impact of phosphate: The leaching of phosphates into waterways, whether from mine tailings, or from phosphates in fertilizer or detergents has proved to be a major pollutant. Phosphate, since it is a fertilizer, encourages the growth of algae which poisons the water. As a result, phosphate has been removed from detergents. Phosphate recycling has now become a topic of discussion both as an environmental action and as a source of phosphate |
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