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Florida's Wealth: Phosphate Roberta Matousek, George Jenkins High School, Polk County Florida, Florida Industrial and Phosphate Research Institute (FIPR) 366364531750Florida's production of phosphate accounts for more than 70 percent of the nation’s rock supply and about 20 percent of the world’s fertilizer supply of this important nutrient. Florida's phosphate is used to produce fertilizer and animal-feed supplements. Phosphate is also used in other household products that we use every day, such as detergents, insecticides, iron alloys, water softeners, and toothpaste. Phosphate has been the most profitable mineral resource in Florida's history. Within 10 years of its discovery near Dunnellon in the 1880s, phosphate was being exported to foreign countries. In 2008, the industry employs more than 4,500 people. For every one job in a phosphate company, there are five more jobs in supporting industries. The phosphate industry also pays the state millions of' dollars in severance taxes. This money is used by the state to buy conservation land, restore old phosphate mining sites, and conduct research. View of the world’s largest walking dragline at work mining phosphate-Phosphate rock was formed approximately 15 million years ago Noralyn, Florida, 1952, State Archives during the late Miocene Epoch. The mineral phosphorus was of Florida present in the ocean water that covered the Floridian Plateau. In the most widely accepted theory of how it was formed, cold water bearing phosphorus-rich material flowed toward the surface as a result of upwelling ocean currents. Tiny marine animals, such as plankton, thrived on this new food source. When these animals died out, their remains further enriched the layer of organic material on the ocean floor by releasing a PO4 (phosphate) ion. As a result of low oxygen conditions, this organic material underwent a chemical reaction and the PO4 (phosphate) ion precipitated out to form francolite, a phosphate mineral. When the ocean receded, the phosphorus settled and mixed with sand and clay. Today this mixture varies in thickness from 12 to 15 feet and is covered by overburden, or a layer of sand. Animal fossils are often found where phosphate is mined. Bone Valley is the name commonly given to the area in central Florida where the largest deposits of fossils are found. In Florida phosphate deposits, the sandy overburden is 15 to 30 feet deep. This overlying material must be removed before the matrix of phosphate, clay, and sand can be removed. The phosphate occurs as pebbles and small, sand-sized particles that are bound to the sand by very fine clays. Beneath the phosphate is limestone that is sometimes covered by a thin layer of clay. Mining phosphate is a complex operation. Once the mineral deposits have been found, the quality of the ore must be established. A sample of the ore is analyzed and the amount of phosphate that can be recovered is determined. If the deposit is a valuable one, soil scientists and engineers prepare site plans. Site plans include provisions for water, drainage, road and rail transportation, electric power, waste disposal, and land restoration. These plans are reviewed by government officials before mining permits are granted. After the plans are approved, huge machines called draglines remove the overburden and set it aside to be used later for reclamation. The dragline operators then dig out the matrix and dump it into a pit where highpressure water guns are used to create a slurry that is 35-40% solids. The slurry is then pumped through pipes to a beneficiation plant. This is where the phosphate rock is separated from the sand and clay. The first step is to separate the pebble sized phosphate from the finer particles. Generally, the slurry that comes from the mine site is fed into a flume, which uses water and gravity to break-up large clumps of matrix. Next, the trommel screen captures the largest-sized phosphate and filters the smaller rock through the screen. Phosphate pebbles recovered from the washers are sent to bins where they are stored according to grade (quality) and sent to the chemical processing plant to be converted into the soluble form needed to make fertilizer. Smaller particles, which are called feed, are sent to hydrocyclones to remove the slime (phosphatic clay). After screening and washing, the feed goes to a storage bin and the clay is sent to a clay settling pond. When the feed leaves the storage bin, it heads into the flotation plant where it is fed through a hydrocyclone that takes away most of the water. Fatty acid, fuel oil and a pH adjuster are then added to the feed, enabling the sand-sized phosphate to be floated to the top on bubbles while the sand sinks. This is known as rougher flotation. Because some residual sand floats up with the phosphate this concentrate is sent to a scrubber where sulfuric acid is added to remove the fatty acid and fuel oil from the phosphate particles. The resulting acid-scrubbed rougher concentrate goes to the cleaner flotation step where amines are added. In the cleaner flotation step, the process is reversed and the remaining sand is floated away from the phosphate. Sand tailings separated in both the rougher and cleaner flotation steps are sent to the mine site to be used in reclamation. Phosphate that has been recovered in the beneficiation process is loaded onto trains and sent to a chemical processing plant. At the chemical processing plant, phosphate rock is ground to a uniform size and reacted with sulfuric acid to produce phosphoric acid used to make fertilizer and a co-product, calcium sulfate. This co-product of phosphate chemical processing, also known as phosphogypsum, is stacked in huge piles because it is slightly radioactive and its uses are regulated by the EPA. The phosphoric acid is combined with ammonia to make small pellets or granules known as diammonium phosphate (DAP) or monoammonium phosphate (MAP). Later the granules may be blended with other nutrients such as potassium and magnesium and sold to commercial retailers. Farmers will then spread it where it is needed on fields to help crops grow. The phosphate industry recycles over 90% of the water it uses in all of its processes. Mined land must be reclaimed and reclamation begins immediately after the dragline is finished in an area. The phosphate industry continues the job of converting mined-out areas into a variety of land uses such as agricultural, wildlife and residential communities. Geologists and industry experts predict that Florida has enough phosphate reserves to continue the current rate of mining for more than 30 years. With improvements in technology, mining can perhaps continue even longer. Source: Matousek, R. (2012). Phosphate Mining and Reclamation: A High School Grade Level Unit. Retrieved from Schematic Diagram of Phosphate Mining in Florida to accompany paragraphs 7-10 The phosphate matrix, at depths of 6–10 m below the ground surface, is open-pit mined where the soils on top of the matrix (overburden) are piled to the side in spoil piles. The phosphate matrix, high in clay content, is slurred and pumped to the beneficiation plant. The by-products from beneficiation are: clays, which are pumped into elevated clay settling ponds, and sand-tailings used to back-fill mined areas (not shown in the illustration). Granular calcium phosphate is converted to super phosphate fertilizer in chemical plants producing a gypsum by-product that is stacked high near the plant. The final land uses after mining are reclaimed land (about 50–60% of the landscape), clay settling areas (40% of landscape) as well as chemical plants, transportation and gypsum stacks (about 10%) which most frequently are constructed on unmined land. Mark T. Brown, Landscape restoration following phosphate mining: 30 years of co-evolution of science, industry, and regulation, Ecological Engineering, Volume 24, Issue 4, p. 310, 5 April 2005 ................
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