Plants/Mines
Table of Contents
| Mines Source
of Phosphorus |
Plants History and Overview
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Source of Phosphorus
The phosphate rock deposits in central Florida were formed five to fifteen million years ago, a time when the state was covered by the ocean. Because phosphorus-rich sea water allowed marine organisms to thrive, large amounts of organic matter periodically accumulated on the ocean bottom. As the organic material decayed, phosphorus was released into the sediments, forming phosphate nodules and phosphatizing some marine animal remains. As the sea level fluctuated, the phosphate was concentrated by erosion, forming the deposits that are mined today.
Discovery of Phosphate Rock
While surveying the Florida wilderness in 1881, Captain J. Francis LeBaron discovered phosphate pebbles in the Peace River south of Ft. Meade. Soon after this major discovery, the speculators came. Traces of phosphate were found from near Gainesville south to Charlotte Harbor.
History of Phosphate Mining
Early methods of mining river pebble were time-consuming, due to natural obstacles. In river pebble mining, the workers had to walk into the river and pry the rock loose with crowbars, picks and oyster tongs. Rock was loaded by hand onto barges and then transported to washers.
The first pumps used to mine the pebble were installed in dredge boats in the early 1890s. The 8-inch pump, which ran on steam engines and boilers, produced an average daily yield of 35 to 45 tons of pebble. However, high production costs and increasing competition from hard rock and land pebble mines forced the decline of river pebble production in the mid-1890s.
The center of activity for hard rock mining was Dunnellon, Florida. Early methods of excavation included the use of picks and shovels, wheelbarrows, mules and wagons. The workers endured long hours; accidents caused by mining conditions and machinery were not uncommon.
Once pried loose, rock was thrown upon a mesh screen which allowed clay and finer materials to pass through. Next, at the washer, rock was placed on a screen of parallel bars measuring 2 to 2-1/2 inches apart. Streams of water washed the finer materials through the screen. After the rock left the washer, it was hand-sorted to be dried. Hard rock mining was short-lived, though, and by 1891 production began to decline.
Land pebble mining surged ahead with cheaper and more productive mining methods. Removal of the overburden was accomplished with large hydraulic and steam shovels. After rock was washed into a sump hole, the resulting slurry was removed by centrifugal pumps and carried to the washer.
After years of experimentation, hydraulic methods were introduced around 1902. In addition, electricity began to replace steam power. The mining operations were greatly improved by eliminating dredges from the pit area and pumping the matrix to washers on land.
The industry suffered a mild setback with the agricultural slump at the turn of the century. Business recovered, however, and in 1913, Florida assumed its position as industry leader, producing 82 percent of the total U.S. production. Worldwide competition began to increase, though, and by 1930, Florida land pebble phosphate held only 28 percent of total world production. Today, Florida produces about one-quarter of the world's phosphate rock.
The phosphate industry made great expansion strides after World War I. New business methods were developed along with technological advances. A breakthrough occurred in 1920 when Bill Carey introduced the dragline. Carey, president of the W. F. Carey Company, had been awarded an overburden stripping contract from the Southern Phosphate Company. This dragline had a 136-foot boom and was powered by a diesel engine. Others quickly saw the advantages it provided - savings on manpower and an increase in production. By the 1930s, draglines could remove between 600 to 700 cubic yards an hour.
Another equally important discovery was that valuable phosphate particles could be removed from former waste products. Messrs. Broadbridge and Edser of the Phosphate Recovery Corporation patented a processing method in 1928 known as the "oil flotation process." This would enable companies to recover up to 95 percent of the phosphate material previously discarded.
What started as a fledgling industry more than a century ago is now Florida’s third largest industry, behind tourism and agriculture. The phosphate companies - led by giant IMC-Agrico - directly or indirectly account for more than 50,000 jobs, and they produce 75 percent of the nation's phosphate and about one-quarter of the world's supply.
Six IMC-Agrico mining operations are located in Polk, Hillsborough, Hardee and Manatee counties:
Fort Green - About 15 miles south of
Mulberry off S.R. 37
Four Corners - 20 miles south of Mulberry off S.R. 37
Hopewell - About 10 miles south of Plant City on S.R. 39
Kingsford - About 8 miles south of Mulberry off S.R. 37 on
Doc Durrance Road
Noralyn - About 10 miles southeast of Mulberry on S.R. 640
Payne Creek - In the rural southeast corner of Polk County
Phosphate rock (pebbles) are typically found an average of 25 feet beneath the ground's surface. The phosphate matrix is a mixture of pebbles, sand and clay. The sandy layer of soil covering this matrix is removed by electrically operated draglines. The draglines, equipped with large buckets, then dig the matrix and deposit the materials into a shallow containment area called a well. Here, high-pressure water guns, controlled by operators in a portable pit car, liquefy the material into a watery mixture called a slurry. The material is then transported through pipelines to a beneficiation plant.
For more information, see: Draglines, Water Use.
The dragline, a powerful machine that digs phosphate rock around the clock. There are 25 draglines at the six operating mines. Each has two employees - the operator and one assistant, who is called an oiler.
Draglines, which operate on electricity, can turn in a full circle and "walk" on huge feet from one mining location to the next. They also carry buckets ranging in capacity from 20 cubic yards to 83 cubic yards. The largest draglines will mine about 100 acres each year.
IMC-Agrico's smallest dragline, a Bucyrus-Erie Model 650B, weighs 840 tons and has a boom 175 feet long. The largest dragline, a Bucyrus-Erie Model 1570W, weighs 3,650 tons and has a boom 325 feet long! The oldest operating machine, a Bucyrus-Erie Model 1150B, was once nick-named the "Bigger Digger." This workhorse has been in service since 1946.
The washer is the first step in separating phosphate from the clay and sand. Here, large clay balls are mechanically disintegrated in equipment called log washers. The material then moves through a series of vibrating screens (+16 mesh) where it is cleansed of clay, and the pebble-sized phosphate is recovered as a finished product. The pebble is moved to dewatering tanks and the inventory pile by conveyors. The sand and the fine particles of phosphate (called concentrate) are retained for flotation processing.
The clay that has been separated from the matrix is pumped through pipelines to storage ponds (clay settling ponds), where the clay slowly settles to the bottom. These ponds have an abundance of wildlife and serve as important reservoirs that enable IMC-Agrico to recycle more than 97 percent of all the water required in mining and beneficiation. Eventually these ponds are reclaimed, often to agricultural uses or wildlife habitat.
At the flotation plant, reagents are mixed with sand and the concentrate. This process separates the two components. The sand is transported by pipelines to the mine for use in land reclamation. The phosphate concentrate is sent to dewatering tanks and then to the inventory pile.
History and Overview
In the early 1840s, scientists discovered that treating phosphate rock with sulfuric acid made the phosphate rock more soluble, changing the phosphorus to a form more easily used by plants. That discovery paved the way for development of the phosphate industry.
IMC-Agrico takes pride in being among the phosphate industry's most cost-efficient producers. Six manufacturing facilities (three in Florida and three in Louisiana) can produce about eight million tons of concentrated phosphate products a year for virtually every kind of crop grown in the world.
The strength of IMC-Agrico is the result of a combination of factors: the economies inherent to large-volume production; innovative application of technology; skilled in-house maintenance advantages; and a commitment to operating procedures that enhance product recovery while emphasizing worker safety and environmental protection.
IMC-Agrico has six concentrated phosphate operations:
New Wales - About 10 miles southwest of Mulberry, Fla., off S.R. 640. Produces phosphoric acid, sulfuric acid, diammonium phosphate (DAP), granular triple superphosphate (GTSP), monoammonium phosphate (MAP), and phosphate-based livestock feed supplements. Also, cogenerates electricity from the sulfuric acid steam. Built in 1975, New Wales is the world's largest concentrated phophate production facility.
Nichols - On Nichols Road several miles southwest of Mulberry, Fla. Produces phosphoric acid, sulfuric acid, diammonium phosphate (DAP) and electricity.
South Pierce - About 15 miles southeast of Mulberry, Fla., off C.R. 639. Produces phosphoric acid, sulfuric acid, granular triple superphosphate (GTSP) and electricity. This is one of the world's largest GTSP plants.
Faustina - Near Donaldsonville, La., on the west bank of the Mississippi River. Produces ammonia, urea, sulfuric acid, phosphoric acid, DAP and MAP. (Named for a plantation that once occupied the site.)
Taft - Near Hahnville, La., on the west bank of the Mississippi River. Produces diammonium phosphate.
Uncle Sam - Near Convent, La., on the east bank of the Mississippi River between New Orleans and Baton Rouge. Produces phosphoric acid for use in fertilizer production at the other two Louisiana plants, Faustina and Taft. (Named for a plantation that once occupied the site.)
Manufacturing Methods
Phosphorus is chemically combined with calcium and other elements in phosphate rock. By reacting sulfuric acid with phosphate rock, phosphorus is released in a soluble, readily available form that can be utilized by growing plants.
The process begins by grinding phosphate rock to a fine and uniform size. This finely ground material is then reacted with sulfuric acid to form phosphoric acid. The phosphoric acid is concentrated, then reacted with ammonia (a nitrogen source) and granulated to produce two key phosphate crop nutrients; diammonium phosphate (DAP) and monoammonium phosphate (MAP).
Two other fertilizer materials are produced. Granular triple superphosphate (GTSP) is a non-nitrogen nutrient produced by mixing phosphoric acid with finely ground phosphate rock. The other product, urea, is a high nitrogen fertilizer made by reacting ammonia with carbon dioxide.
In addition to the phosphate fertilizers, phosphoric acid is used to manufacture monocalcium and dicalcium phosphate products for sale to the animal feed ingredient industry by the IMC-Agrico Feed Ingredients business unit. The phosphoric acid is treated to remove fluorine, then mixed with ground limestone in a granulation process to produce the desired products. The products are used in the swine, poultry, and cattle feeding industries.
Phosphoric acid, ground phosphate rock and soda ash are used to manufacture a thermally treated product for sale as a feed ingredient for poultry.
Uses for Phosphate Rock
About 95 percent of the phosphate rock mined in Florida is used in agriculture. Of this, 90 percent goes into fertilizer and 5 percent into livestock feed supplements. The balance is used in a variety of products, including common household items such as soft drinks, toothpaste, bone china, film, light bulbs, vitamins, flame-resistant fabrics, optical glass and shaving cream.
Phosphate Terms and Definitions
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Ammoniated Phosphate - Fertilizer products made by reacting phosphoric acid with anhydrous ammonia to provide fertilizers containing both nitrogen and phosphorus. These products are called diammonium phosphate (DAP) and monoammonium phosphate (MAP).
Beneficiation - The process of separating a wanted mineral from other material that also is contained in the matrix. In the case of phosphate, this means separating clay and sand from the phosphate rock. A mechanical process called washing is used to separate the larger phosphate pebbles from the ore. A process called flotation is used to recover the finer particles of phosphate from sand.
Clays, Phosphatic Clays or Waste Clays - Materials that are removed from the phosphate matrix. Sometimes called slimes, a mining term referring to the size of the particles, clays present a disposal problem because they trap and retain large amounts of water and take long periods of time to dry. Clays are stored behind earthen dams for settling and drying.
Cooling Pond - An integral part of the chemical fertilizer processing system that conserves water by allowing used hot water to cool and continually be recycled in the manufacturing process.
Concentrate - Very tiny particles of phosphate rock that are recovered by flotation. This process uses reagents to coat the phosphate particles and float them away from the companion sands.
Cyclones - Cone-shaped devices that separate materials by centrifugal action. They are used in the phosphate industry to separate clays from the matrix and to recover dust from air streams.
Diammonium Phosphate - A high-analysis concentrated fertilizer combining two of the three primary plant nutrients, nitrogen and phosphorus. Used on almost every kind of crop grown in the United States (see Ammoniated Phosphates).
Dragline - A large machine used in excavation. In the Florida phosphate industry, draglines with bucket capacities of up to 83 cubic yards are used to remove the overburden and excavate the phosphate matrix.
Filters - Mechanical devices employing a vacuum used to recover wet process phosphoric acid from the gypsum slurry.
Flotation - The process of separating the finer particles of phosphate from the sand (see Beneficiation).
Gypsum - A naturally-occurring, finely-grained solid consisting primarily of calcium sulfate (CaSO4). It also is chemically produced when making phosphate fertilizer and is known as phosphogypsum.
Gypsum Stack - Phosphogypsum and process water are pumped through pipelines to a storage area where the gypsum settles out and the water is recycled to the manufacturing plant. The stored pile of gypsum is called a stack.
Matrix - The strata of phosphate, sand and clays in which phosphate is found. The ore-bearing stratum is found about 25 feet below the earth's surface.
N-P-K - The chemical symbols for nitrogen, phosphorus and potassium. These three elements are required by all forms of plant life. On a bag of fertilizer, the N-P-K content is indicated by three numbers, such as 10-10-10. This indicates the fertilizer contains 10 percent nitrogen (N), 10 percent phosphate (P2O5) and 10 percent potash (K2O).
Overburden - The earth that lies above the phosphate matrix and must be removed before the matrix is mined. It is later used for land reclamation.
Pebble or Pebble Phosphate - Large-sized pebbles recovered at the beneficiation plant in a series of washing and screening steps.
Phosphate Rock - A mineral containing the element phosphorus, a basic plant nutrient, which is essential to all forms of life.
Phosphoric Acid - The basic ingredient used in making phosphate fertilizers and phosphate-based animal feed ingredients. It is produced by reacting ground phosphate rock with sulfuric acid.
Pit Car - A small, portable structure that houses controls for the high-pressure water jets (called guns) which are used to mix the phosphate matrix with water, so it can be pumped through pipelines to the beneficiation plant. The pit cars are located near the draglines.
(P2O5) Phosphorus Pentoxide - The chemical expression P2O5 has been defined as "phosphate" and is used in the agronomic discipline and the fertilizer industry to express the phosphorous (P) content in soils and fertilizers even though the P2O5 form does not exist in either soils or fertilizers as such. To convert the P2O5 value mathematically to the elemental (P) form, multiply the P2O5 value by 0.44. To convert (P) to the P2O5 form, multiply the P2O5 value by 2.29.
Reagents - Substances used to recover the tiny particles of phosphate rock during the flotation process. Phosphate reagents include fuel oil, soap skimmings and fatty acids. When coated with these substances, the phosphate particles repel water and are attached to air bubbles which float them to the surface of the vessel, while the sand sinks.
Reclamation - Returning land to a beneficial use after mining.
Scrubbers - Air pollution control devices which generally use water sprays to trap gases and dust.
Slimes - A mining term referring to the size of phosphate clay particles (see Clays).
Slurry - A mixture of water and solid material.
Sulfuric Acid (H2SO4)- Made by burning molten sulfur with air. Sulfuric acid is used to "digest" or dissolve phosphate rock containing the nutrient phosphorus to make phosphoric acid.
Uranium - A naturally-occurring element found in some 160 minerals, including phosphate rock.
Urea {CO(NH2)2} - A fertilizer made by combining nitrogen and carbon dioxide, and granulating the solution to form a product with 46-percent nitrogen (N) content.
Washer - A facility where clay is separated from the phosphate matrix using water and vibrating screens. Here the phosphate pebbles, one millimeter wide and larger, are recovered and sent to a stockpile for sale to customers.
Well - A small, shallow depression at the mining site where phosphate matrix is mixed with water for transportation through pipelines to the beneficiation plant.
Wet Process Acid - Phosphoric acid produced by reacting or "digesting" phosphate rock with an acid, usually sulfuric acid. It is called "wet process" to distinguish it from furnace acid.