In 2015, 27.6 million metric tons of marketable phosphate rock, orphosphorite, was mined in the United States, making the US the world's third-largest producer, afterChina andMorocco. The phosphatemining industry employed 2,200 people. The value ofphosphate rock mined was US$2.2 billion.
As of 2015, there are 10 active phosphate mines in four states:Florida,North Carolina,Idaho, andUtah. The eastern phosphate deposits are mined from open pits. The western deposits are mined from both surface and underground mines.
The exact phosphate content of the phosphate rock mined in 2015 is not available, but in the latest five-year period for which ore grades are available, 2009-2013, the grade of US phosphate rock varied from 28.5 to 29.0 percent P2O5.
As of 2016, remaining reserves of phosphate rock in the United States totaled 1.1 billion metric tons.[1]
As of 2017, there were 11 active phosphate mines in the US, operated by 5 companies. In addition, one mine in Idaho was in permitting and development status.
Phosphate mining operations in the US
| Company | Name | Location |
|---|---|---|
| Itafos Conda LLC | Rasmussen Ridge | Caribou County, Idaho |
| JR Simplot | Vernal | Vernal, Utah |
| JR Simplot | Smoky Canyon | Caribou County, Idaho |
| Bayer | South Rasmussen | Caribou County, Idaho |
| Bayer | Blackfoot Bridge | Caribou County, Idaho |
| The Mosaic Company | DeSoto (permitting) | DeSoto County, Florida |
| The Mosaic Company | Wingate Creek | Manatee County, Florida |
| The Mosaic Company | Ona | Ona, Florida |
| The Mosaic Company | South Pasture (Currently idled) | Hardee County, Florida |
| The Mosaic Company | Four Corners | Hillsborough,Manatee, andPolk counties, Florida |
| The Mosaic Company | South Fort Meade | Hardee and Polk counties, Florida |
| Nutrien Ltd | Swift Creek | Hamilton County, Florida |
| Nutrien | Aurora mine | Aurora, North Carolina |
| Fertoz Ltd. | Butte Mine | Butte, Montana |
| Itafos (previously Stonegate Agricom)[2] | Paris Hills (permitting)[3] | Paris, Idaho |
Many phosphate processing plants are located at the mines. In addition, some processing plants are located remote from the mines. Some processes import phosphate rock.
Phosphorus is an essential component offertilizer. In 2013, about 90 percent of phosphate rock was used in fertilizer manufacture. Other uses includedanimal feed anddetergents.[4]
The states mining phosphate rock as of early 2016 were, in descending order of tonnage mined: Florida, North Carolina, Idaho, and Utah. In 2016, 65 percent of US phosphate was mined in Florida.
TheBone Valley mining district, also known as the Central Florida district, or the Florida Land-Pebble district, is centered inPolk County, Florida, and extends intoHardee,Hillsborough, andManatee counties. As of 2013, phosphate was being extracted from five mines in the district, all operated by Mosaic.[5]
The Florida Hard Rock district mines phosphate from a belt up to 30 miles (48 km) wide and 150 miles (240 km) long, extending from Tallahassee on the west to Pasco County on the east. Phosphate deposits occur inBradford County,Hamilton, andUnion counties.
One mine is currently operating in the Hard Rock district: The Swift Creek mine, operated by Nutrien Ltd, inHamilton County, Florida.
The North Carolina phosphate deposit was discovered in 1955.[6] Phosphate is currently being extracted at theAurora mine, operated byNutrien Ltd.
The first large-scale phosphate mining in the US were in the vicinity ofCharleston, South Carolina, inCharleston,Colleton, andBeaufort counties. Mining started in 1868 and continued until 1938.[7]
Mining started in the centralTennessee phosphate district in 1896. Counties where mining took place includedGiles,Hickman,Maury, andWilliamson. The district has been inactive since 1991.[8] It is regarded as largely exhausted.
Parts of thePhosphoria Formation of the western United States carry economic grades of phosphorus. The Phosphoria has been mined in a wide area stretching north-south from southwestMontana, through westernWyoming and southeastIdaho, and into northeastUtah.[9]
There are currently four active mines inCaribou County, Idaho, and one being permitted inBear Lake County, Idaho.
Phosphate rock from the JR Simplot mine nearVernal, Utah, is crushed at the mine, then transferred in aslurry pipeline to the company's processing plant atRock Springs, Wyoming.[10][11]
Phosphate rock was formerly mined inBeaverhead,Granite,Powell, andSilver Bow counties in southwest Montana. The last operating phosphate mine in Montana, atGarrison, shut down in 1993. Phosphate was also formerly mined inLincoln County, Wyoming.
Although someigneous rocks have economic grades of phosphate, no igneous phosphate rock is mined in the US. Small amounts of phosphate were mined from igneousapatite deposits inVirginia,New Jersey, andNew York. But since 1948, all phosphate deposits mined in the US have beensedimentary deposits. However, a small amount of phosphate was produced in the 1970s, as a byproduct of iron mining inMissouri.[12]
Most phosphate mining is of sedimentaryphosphorite, a phosphorus-rich deposit formed under shallow marine conditions. However, a number of US phosphate deposits occur where the original marine-deposited phosphate minerals have been concentrated by weathering and redeposition, often under nonmarine conditions.
The largest source of US phosphate is theBone Valley, or Central Florida mining district, which produces from thePliocene-ageBone Valley Formation.[13]
The Florida Hard Rock district mines phosphate from theAlachua Formation of Pliocene age. The Alachua Formation is nonmarine and consists of sediments rich in phosphate that was weathered from the Hawthorne Formation ofMiocene age.[13]
The North Carolina phosphate deposit occurs in thePungo River Formation ofMiocene age.[14] The phosphate was deposited under shallow marine conditions.[15]
The South Carolina river-pebble deposits formed along modern rivers which reworked and concentrated lower-grade phosphate deposits.
Three classes of phosphate deposits have been mined in central Tennessee; in order of decreasing importance: brown phosphate rock, blue phosphate rock, and white phosphate rock.[16]
The most important phosphate deposits were the so-called brown phosphate rock, mined fromOrdovicianlimestones, some parts of which are rich in phosphate. The highest-grade deposits were found where weathering or shallow groundwater had preferentially dissolved away thecalcium carbonate. The last mine in Tennessee, which produced phosphate rock from the Bigby-Cannon formation, closed in 1991.
The blue phosphate rock was found in theDevonian-ageChattanooga Shale.
Minor phosphate production was mined from white phosphate rock, which formed inkarstedSilurian limestones.
The western deposits, in Utah, Wyoming, Idaho, and Montana, are in thePhosphoria Formation ofPermian age. The phosphate deposits occur in two members of the Phosphoria: the Retort phosphatic shale member in the upper part of the formation, and the Meade Peak phosphatic shale member in the lower part of the formation.
Although not presently mined, phosphate deposits occur in theBrazer limestone ofMississippian age in Utah.
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Large-scale phosphate mining in the US began in 1868 in coastal South Carolina. Access to river transport and proximity to the port ofCharleston encouraged exports, and by 1885 South Carolina was producing half the world's phosphate. Phosphate mining in South Carolina declined rapidly in the 1890s, when mining of the higher-grade deposits in central Florida began. The central Florida district has provided the majority of US phosphate ever since.
US production of phosphate rock peaked in 1980 at 54.4 million metric tons. The United States was the world's largest producer of phosphate rock from at least 1900, up until 2006, when US production was exceeded by that ofChina. In 2015, the US produced 12 percent of the world's phosphate rock.
For each ton of phosphoric acid produced by the processing of phosphate rock, five tons of waste are generated. This waste takes the form of impure, useless, radioactive solid calledphosphogypsum. Somewhere between 100,000,000 and 280,000,000 tons of phosphogypsum waste is estimated to be produced annually worldwide.[17]
Thesetailings piles andrelated ponds and dams can be sources of toxic chemicals, and are vulnerable to breach. For example, the 2021Piney Point phosphate plant dam breach is predicted to have significant negative impacts onTampa Bay.[18]
Phosphorite typically contains more than 3%fluoride, in the mineralfluorapatite. Only a small amount is recovered.
In 2015,fluorosilicic acid equivalent to 114,000 tons offluorite (fluorspar) was produced as a byproduct of phosphate rock processing. This material represented nearly all the US production of fluoride, which is subsequently converted to fluorine. The produced fluorine is used to prepare polymers, pharmaceuticals, etc.
The phosphorite deposits of Florida and of the western states contain from 0.005 to 0.02 percenturanium. Phosphorite deposits contain sufficient uranium to be an economic source when theprice of uranium is high.
Uranium was extracted at two phosphate plants in the central Florida district from 1952 to 1961, and at seven plants during the period 1976-1998. The average uranium recovery was about 0.9 pounds (0.41 kg)triuranium octoxide (U3O8) per metric ton ofP2O5.[19] However, uranium recovery is feasible only from the process that produces double superphosphate;[why?] most phosphate is processed into normalsuperphosphate, a process not amenable to uranium recovery.[20]
Although no uranium has been recovered from US phosphate plants since 1998, the Central Florida phosphate deposits remain North America's largest uranium resource, containing an estimated one million tons of uranium.[21]
Some parts of thePhosphoria Formation, which is mined for phosphate in the western US, contain potentially economic concentrations ofvanadium. In 2008, Rocky Mountain Resources announced that they had defined 6.7 million tons of ore containing 0.88 percent V2O5, at its Paris Hills prospect. The vanadium occurred in an 11-foot-thick (3.4 m) bed in theMeade Peak shale member of the Phosphoria, immediately below a 15-foot (4.6 m) bed of ore-grade phosphate rock.[22] The property has since been sold to Stonegate Agricom, and as of mid-2016 was still in permitting and development status.[23]
As of 2015, no vanadium was being recovered from US phosphate operations.[24]
The US was a long-time exporter of phosphate rock, and from the 1960s into the 1990s a major exporter. The US became a net importer of phosphate rock for the first time in 1996. Since then the US has been a net importer each year. In 2015, the US imported about 12 percent of the phosphate it used.