Phosphogypsum
Encyclopedia
Phosphogypsum refers to the gypsum
formed as a by-product
of processing phosphate
ore into fertilizer
with sulfuric acid
.
Phosphogypsum is produced from the fabrication of phosphoric acid
by reacting phosphate ore (apatite
) with sulfuric acid
according to the following reaction:
Phosphogypsum is radioactive due to the presence of naturally occurring uranium
and radium
in the phosphate ore.
Marine-deposited phosphate typically has a higher level of radioactivity than igneous phosphate deposits, because uranium is present in seawater.
The United States Environmental Protection Agency
has banned most applications of phosphogypsum with a radium-226 concentration of greater than 10 picocurie
/gram (0.4 Bq
/g). As a result, phosphogypsum which exceeds this limit is stored in large stacks.
Florida
has a large quantity of phosphate deposits, particularly in Bone Valley
region. However, the marine-deposited phosphate ore from central Florida is highly radioactive, and as such, the phosphogypsum by-product is too radioactive to be used for most applications. As a result, there are about 1 billion tons of phosphogypsum stacked in 25 stacks in Florida (22 are in central Florida) and about 30 million new tons are generated each year.
Various applications have been proposed for using phosphogypsum, including using it as material for:
Gypsum
Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...
formed as a by-product
By-product
A by-product is a secondary product derived from a manufacturing process or chemical reaction. It is not the primary product or service being produced.A by-product can be useful and marketable or it can be considered waste....
of processing phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
ore into fertilizer
Fertilizer
Fertilizer is any organic or inorganic material of natural or synthetic origin that is added to a soil to supply one or more plant nutrients essential to the growth of plants. A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use...
with sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
.
Phosphogypsum is produced from the fabrication of phosphoric acid
Phosphoric acid
Phosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral acid having the chemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more general way...
by reacting phosphate ore (apatite
Apatite
Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, chlorapatite and bromapatite, named for high concentrations of OH−, F−, Cl− or Br− ions, respectively, in the crystal...
) with sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
according to the following reaction:
- Ca5(PO4)3X + 5 H2SO4 + 10 H2O → 3 H3PO4 + 5 CaSO4 · 2 H2O + HX
- where X may include OH, F, Cl, or Br
Phosphogypsum is radioactive due to the presence of naturally occurring uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
and radium
Radium
Radium is a chemical element with atomic number 88, represented by the symbol Ra. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226,...
in the phosphate ore.
Marine-deposited phosphate typically has a higher level of radioactivity than igneous phosphate deposits, because uranium is present in seawater.
In the United States
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
has banned most applications of phosphogypsum with a radium-226 concentration of greater than 10 picocurie
Curie
The curie is a unit of radioactivity, defined asThis is roughly the activity of 1 gram of the radium isotope 226Ra, a substance studied by the pioneers of radiology, Marie and Pierre Curie, for whom the unit was named. In addition to the curie, activity can be measured using an SI derived unit,...
/gram (0.4 Bq
Becquerel
The becquerel is the SI-derived unit of radioactivity. One Bq is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. The Bq unit is therefore equivalent to an inverse second, s−1...
/g). As a result, phosphogypsum which exceeds this limit is stored in large stacks.
Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
has a large quantity of phosphate deposits, particularly in Bone Valley
Bone Valley
The Bone Valley is a region of central Florida, encompassing portions of present-day Hardee, Hillsborough, Manatee, and Polk counties, in which phosphate is mined for use in the production of agricultural fertilizer...
region. However, the marine-deposited phosphate ore from central Florida is highly radioactive, and as such, the phosphogypsum by-product is too radioactive to be used for most applications. As a result, there are about 1 billion tons of phosphogypsum stacked in 25 stacks in Florida (22 are in central Florida) and about 30 million new tons are generated each year.
Various applications have been proposed for using phosphogypsum, including using it as material for:
- Road pavementPavement (material)Road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past cobblestones and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete. Such...
- Soil conditionerSoil conditionerA soil conditioner, also called a soil amendment, is a material added to soil to improve plant growth and health. A conditioner or a combination of conditioners corrects the soil's deficiencies in structure and-or nutrients.-Purpose:...
- Cover for landfillLandfillA landfill site , is a site for the disposal of waste materials by burial and is the oldest form of waste treatment...
s - Roof tiles
- Artificial reefArtificial reefAn artificial reef is a human-made underwater structure, typically built to promote marine life in areas with a generally featureless bottom, control erosion, block ship passage, or improve surfing....
s & oysterOysterThe word oyster is used as a common name for a number of distinct groups of bivalve molluscs which live in marine or brackish habitats. The valves are highly calcified....
beds
See also
- AlabasterAlabasterAlabaster is a name applied to varieties of two distinct minerals, when used as a material: gypsum and calcite . The former is the alabaster of the present day; generally, the latter is the alabaster of the ancients...
- AnhydriteAnhydriteAnhydrite is a mineral – anhydrous calcium sulfate, CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium and strontium sulfates, as might be expected from the...
- Calcium sulfateCalcium sulfateCalcium sulfate is a common laboratory and industrial chemical. In the form of γ-anhydrite , it is used as a desiccant. It is also used as a coagulant in products like tofu. In the natural state, unrefined calcium sulfate is a translucent, crystalline white rock...
- Calcium sulfate (data page)Calcium sulfate (data page)- Material Safety Data Sheet : The handling of this chemical may incur notable safety precautions. It is highly recommend that you seek the Material Safety Datasheet for this chemical from a reliable source and follow its directions....
- GypsumGypsumGypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...
- Gypsum plaster
- Selenite (mineral)