&EPA
United States
Environmental Protection
Agency
March
EPA530-F-08-009
www.epa.gov/osw
for
(FGD)
is
Gypsum is calcium sulfate dihydrate, or CaSO4»2H2O, which can come from a
number of sources. Mined gypsum is a common mineral found around the world
in sedimentary rock formations, from which it is mined or quarried. FGD gypsum
is a synthetic material of identical chemical structure produced as a byproduct from
coal-fired electric utilities. Other sources of gypsum include phosphogypsum,
citrogypsum and fluorogypsum, which are byproducts of different chemical
manufacturing processes1.
Gypsum has many beneficial uses, including agricultural applications, wallboard
products for residential and commercial buildings, as an ingredient in portland cement
manufacturing, and as a filler ingredient in some foods and toothpaste. Because of its
relatively high degree of purity, FGD gypsum can be used as a substitute for mined
gypsum in many uses, while also realizing important environmental benefits that
result from recycling this byproduct material.
in
Both mined and FGD gypsum can be used as a soil amendment in a range of soil
and hydrogeologic conditions. Gypsum can be used as a nutrient source for crops; as
a conditioner to improve soil physical properties, and water infiltration and storage; to
remediate sodic (high sodium) soils; and to reduce nutrient and sediment movement
to surface waters, among other uses. The United States Environmental Protection
Agency (USEPA) and the United States Department of Agriculture (USD A) support
the use of FGD gypsum in appropriate soil and hydrogeologic conditions as an
effective method of soil conservation and industrial material recycling. However,
before applying any fertilizer or other soil amendment, including FGD gypsum, it
is important to first assess the amendment material and soil conditions to determine
compatibility and appropriate application rates.
This brochure does not address these sources of gypsum.
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FGD
FGD gypsum is created by forced oxidation scrubbers attached to coal-fired
power plants to limit emissions of the sulfur which is released when coal is burned.
The scrubbers spray liquid lime or limestone slurry into the flue gas path, where it
reacts with sulfur in the gas to form calcium sulfite, an intermediate product with
little practical value. However, when the chemical reaction is pushed further by
the introduction of air into the FGD absorber tank, the calcium sulfite reacts to
become gypsum. The material is then dewatered and processed; the end product is a
consistent, finely divided powder. This process is known as flue gas desulfurization
(FGD), and the gypsum produced is known as FGD gypsum.
The term FGD gypsum is the name most often used by generators of the material.
Other names include recaptured gypsum, byproduct gypsum, and synthetic gypsum.
All of these terms refer to the same material produced by the forced oxidation
process. The gypsum in both FGD gypsum and mined gypsum has the same basic
chemical makeup— CaSO4«2H2O; however, the amount and types of trace materials
and unreacted sorbents found in the gypsum can vary among power plants and among
mines2. If you are considering using FGD gypsum products as a soil amendment, it is
appropriate that the chemical analysis of the material be provided by all commercial
sources to support decision-making in their use, as States may have regulations and
standards that need to be followed. To this end, it is advisable to contact your State's
department of agriculture or State extension service before FGD gypsum is used as a
soil amendment.
The of FGD
According to the American Coal Ash Association's annual Coal Combustion
Product Production and Use Survey, total production of FGD gypsum in 2006
was approximately 12 million tons. Close to 9 million tons of FGD gypsum was
put to beneficial use, while the remainder was landfilled. Of the amount used,
approximately 80 percent was used in wallboard products, and about 2 percent
(168,190 tons) was used in agriculture, with most of the rest being used in concrete
and cement applications. In the future, FGD gypsum may find more use as filler
in plastics and fiberglass, as well as in reducing mine subsidence, re-contouring
landforms, and improving soil conditions at mining sites.
2 Information about constituent concentrations in mined and FGD gypsum may
be found at http://www.epa.gov/epaoswer/osw/conserve/c2p2/ccps/fgd.htm.
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Over the next ten years, annual production of FGD gypsum may double as more
coal-fired power plants come online, and as scrubbers are added to existing power
plants to comply with the EPA's Clean Air Interstate Rule and other requirements. It
is anticipated that the majority of the new scrubbers will produce FGD gypsum,
although in some parts of the country power plants may select dry scrubbers,
resulting in materials
other than FGD gypsum.
This increased supply is
Agricultural Applications of Gypsum
an opportunity to explore 111C1C are three 8eneral uses of 8>'Psum m agricultural
the expanded use of FGD applications
A source of nutrients for plants
Improvement of soil physical and chemical
properties
Reduction in the transport of nutrients, sediment,
pesticides and other contaminants to surface waters
gypsum as a soil
amendment. Ongoing
and future research and
demonstration projects
will be able to assist
people in making
decisions about the use of
FGD gypsum.
of in
Nutrient
Gypsum is rich in calcium and sulfur, two nutrients essential to all crops. The
most common application of gypsum is to crops that have high calcium requirements,
or to areas that have calcium-poor soils. Peanuts have particularly high calcium
requirements, and gypsum often is added to peanut fields to increase yield and quality
of the crop. Many fruits, vegetables, and cereals also can benefit from increased
calcium availability; in particular, fruits such as tomatoes and cantaloupes need
calcium for skin strength, and growers may add calcium to produce fewer blemishes
and a longer shelf life.
Sulfur fertilization also is required for many crops, and gypsum can be an
effective sulfur source. There is a growing need for sulfur addition to soils, since
atmospheric deposition of sulfur has decreased, and most nitrogen and phosphorus
fertilizers no longer contain significant amounts of sulfur. Sulfur is sometimes a
constituent of nitrogen and phosphorus fertilizers, but gypsum also can be an effective
sulfur source for some crops. In addition to calcium and sulfur, gypsum, depending
on its source, may provide essential micronutrients to plants.
Improvement
Gypsum is helpful in treating sodic soils and soils suffering from crusting and
other structural problems. Gypsum is more readily soluble in water than other
calcium-rich soil amendments such as limestone, and therefore moves throughout
the soil column more easily. Calcium ions from gypsum displace excess sodium
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and other ions, which then become mobile and diffuse. The calcium ions reduce
dispersion of soil particles by promoting the aggregation of clay particles. This
improves soil structure and stability and prevents soil crusting. Reduced crusting
and better particle aggregation allow for greater water infiltration and storage in soil,
thereby reducing runoff and erosion. These soil structural improvements also ease
the emergence of seedlings and allow roots to penetrate further into the soil to take
advantage of the additional stored moisture.
Mitigation of Contaminant Transport to
In addition to water quality benefits associated with reduced runoff and erosion,
FGD gypsum application can reduce the solubility of nutrients such as phosphorus in
livestock and poultry manure and soils treated with manure. Gypsum converts readily
soluble phosphorus to less-soluble forms, which can reduce the runoff of phosphorus
into adjacent streams, lakes, or ground water. Excess phosphorus in runoff leads to
water quality problems, including algal blooms and eutrophication of water bodies.
in
Recycling coal combustion products (CCPs) and other industrial materials
can result in significant environmental benefits, including reduced greenhouse gas
emissions, less use of virgin materials, and decreased use of landfills. The USEPA's
Coal Combustion Products Partnership (C2P2) (http://www.epa.gov/epaoswer/osw/
conserve/c2p2/ ) aims to increase recycling of CCPs, including FGD gypsum. In
addition to its environmental benefits, FGD gypsum may be less expensive for users
than mined gypsum, although transportation costs can be a factor in evaluating the
practicality of using FGD gypsum as a gypsum source.
As with any fertilizer or chemical additive, there are a range of considerations
that should be kept in mind when deciding whether to apply gypsum. Gypsum is
not suitable for all soil types, soil conditions or crops. Appropriate application rates
should be determined to accomplish specific soil improvement goals, while not
exceeding state limits on the use of individual constituents. In general, application
rates of up to two tons per acre should be sufficient to accomplish most agronomic
and horticultural objectives3.
In situations where there is excess sulfur in the soil, the amount of gypsum to be
added should be balanced against copper nutrition in animals, as high levels of sulfur
in feed can interfere with copper absorption. Boron concentrations in FGD gypsum
typically are higher than in natural gypsum sources; therefore, crops sensitive to
boron uptake such as cherry, peach and kidney bean may require lower application
rates. The high calcium and sulfur content of gypsum can cause an imbalance in
other soil nutrients, such as magnesium; therefore, soil nutrient characteristics,
and potential plant and animal uptake, of these and other constituents should be
understood and considered before deciding whether to use any gypsum product.
Donstova et al. and other sources
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In determining the environmental suitability of FGD gypsum for a particular location,
you may find the USEPA's Industrial Waste Management Evaluation Model
(IWEM) and the chapter on land application (Chapter 7) in the associated Guide
for Industrial Waste Management (http://www.epa.gov/epaoswer/non-hw/industd/
to be useful resources. You should also consult with your State's
department of environmental protection to comply with any regulations pertaining
to the management of CCPs. You may also find it helpful to consult with your
State's department of agriculture and agricultural extension service, and with the
USD A Natural Resources Conservation Service.
FGD Gypsum Beneficial Use Considerations
Decision
1 . Is gypsum a good
choice for my needs?
2. If gypsum is a good
choice, should I use
FGD gypsum?
3 . Is the use of
FGD gypsum
envi ronmentally
protective?
Tilings to Consider
* Types of crops
* Nutrient requirements
of crops
* Soil structure
* Soil chemical profile
* Trace element
sensitivity of crops
• Purity of available FGD
gypsum
* Cost differential
* Ground water
* Direct exposure
* Ecosystem impacts
* Surface waters
Resources
* State department
of agriculture/ag.
extension agency
• USDA Natural
Resources Conservation
Service
• State department
of agriculture/ag.
extension agency
• Fertilizer supplier
• State departments
of environmental
protection
* EPA's Guide for
Industrial Waste
Management
The references and Websites below provide additional information and studies
about the uses of gypsum in agriculture.
Clark, R.B., K.D. Ritchey, and V.C. Baligar (1999) "Benefits and Constraints for
use of FGD Products on Agricultural Land." Fuel, 80:821-828.
Donstsova, K., Y.B. Lee, B.K. Slater, J. M. Bigham (no date) Gypsum for
Agricultural Use in Ohio Sources and Quality of Available Products. Ohio State
University Extension Fact Sheet. School of Natural Resources, The Ohio State
University, Columbus, OH. Available online at: http://ohioline.osu.edu/anrfact/0020.
html.
EPA (2003) Guide for Industrial Waste Management. U.S. Environmental
Protection Agency. EPA530-R-03-001. February.
Korcak, R.F. Utilization of Coal Combustion By-Products in Agriculture and
Horticulture. U.S. Department of Agriculture, Agricultural Research Service.
Beltsville, Maryland.
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OSU (2006) Gypsum for Agricultural Use in Ohio—Sources and Quality of
Available Products. Ohio State University Extension Fact Sheet, ANR-20-05.
Available online at: http://ohioline.osu.edu/anr-fact/0020.html. Accessed August,
2007.
Smith, I. (2006) Management of FGD Residues. IEA Clean Coal Centre.
London, United Kingdom. August.
Stout, W.L., J.L. Hern, R.F. Korcak, and C.W. Carlson (19SZ) Manual for
Applying Fluidized Bed. Combustion Residue to Agricultural Lands. RS-74. U. S.
Department of Agriculture, Agricultural Research Service, Washington, DC.
USGS (2005) Major- and Trace-Element Concentrations in Soils from Two
Continental-Scale Transects of the United States and Canada. Open-File Report
2005-1253, U.S. Geological Survey. Available online at: http://pubs.usgs.gov/
of/2005/1253/. Accessed September 13, 2007.
For
—USDA Natural Resources Conservation Service:
http://www.nrcs.usda.gOv/partners/for_farmers.html
—USEPA C2P2 Website: http://www.epa.gov/epaoswer/osw/conserve/c2p2
—USEPA Industrial Waste Management Website:
http://www.epa.gov/epaoswer/non-hw/industd/guide/index.htm
—FGD Products Website: http://www.fgdproducts.org/
—Information sheets on agricultural gypsum use from a leading distributor:
http://www.gypsumsales.com/gyp_whitepapers.html
—A paper on agricultural gypsum use from a distributor:
http://www.dktgypsum.com/news_content7.html
—Information sheet on FGD gypsum from the American Coal Ash
Association: http://www.acaa-usa.org/PDF/EnvFocusFinal3g2.pdf
Acknoweldgements
EPA gratefully acknowledges the following organizations for their contributions
to its preparation:
— United States Department of Agriculture
- Agricultural Research Service
-- United States Department of Energy—National Energy Technology Laboratory
- USEPA Office of Air and Radiation
— USEPA Office of Research and Development
— American Coal Ash Association
— Electric Power Research Institute
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