Management of Phosphate Tailings
(last updated 27 Mar 2013)
> see also: Uranium in Fertilizers
> Aerial View of phosphogypsum stacks in central Florida: Google Maps · MSRMaps
> Aerial View of phosphogypsum stacks in Louisiana: Google Maps · MSRMaps
U.S. EPA study on old phosphate mining and processing sites remains incomplete
For the past several decades, the U.S. Environmental Protection Agency has kept 21 old, Central Florida phosphate mining and processing sites on a list of industrial sites that warrant evaluation to determine if they should get cleanups under the Superfund program.
However, the EPA to date has conducted an evaluation of only one of those sites, the 7,000-acre Tenoroc Mine, which was excavated between the 1960s and the late 1970s by Borden Chemical.
The company then donated the site to the state for a fish management and recreation area.
In 2001, a consultant for the EPA found "elevated levels" of both radionuclides and heavy metals in a number of soil, clay and water samples from the site.
Tetra Tech E.M., the consultant hired by the EPA to conduct the study, called for a more comprehensive site evaluation and a cleanup.
However, the EPA, which labeled the study a draft, never finalized it.
The study hasn't been finalized because the EPA is working to establish an "over-arching policy" that would set the criteria for further site evaluations and cleanups based on the relative levels of risk at all 21 of the phosphate sites, said Franklin Hill, district director of the EPA's Superfund program.
Such a policy is needed because the sites are so large, and yet few people live around them, so the risk appears to be minimal, he said.
(Sun Herald Nov. 5, 2007)
U.S. EPA seeks comment on proposed use of phosphogypsum as cover for solid waste landfill
On January 13, 2005, EPA issued a request for comment on the approval of a proposed alternative use of phosphogypsum by the Florida Institute of Phosphate Research (FIPR) .
FIPR has petitioned EPA to test the use of approximately 25 tons of phosphogypsum as a daily cover at the Brevard County Solid Waste Landfill.
On June 23, 2005, however, FIPR withdrew the petition.
> View EPA release
Revision of U.S. air emission standards for phosphate tailings
Federal Register: February 3, 1999 (Vol. 64, No. 22) p. 5573-5580 (download full rule ):
40 CFR Part 61 - National Emission Standard for Hazardous Air Pollutants; National Emission Standards for Radon Emissions From Phosphogypsum Stacks
U.S. Environmental Protection Agency: 40 CFR Part 61 National
Emission Standards for Hazardous Air Pollutants; National
Emission Standard for Radon Emissions From Phosphogypsum Stacks
- Proposed rule; Notice of Reconsideration
AGENCY: Environmental Protection Agency.
ACTION: Final rule.
"SUMMARY: The Environmental Protection Agency (EPA) is promulgating
revisions to the National Emission Standard for Hazardous Air
Pollutants (NESHAP) that sets limits on radon emissions from
phosphogypsum stacks, codified as subpart R of 40 CFR part 61. The
Agency is taking today's action in response to a petition for
reconsideration from The Fertilizer Institute (TFI), which critiqued
the risk assessment EPA performed in support of the version of subpart
R promulgated in 1992. Today's action raises the limit on the quantity
of phosphogypsum that may be used for indoor research and development
from 700 to 7,000 pounds, eliminates current sampling requirements for
phosphogypsum used in indoor research and development, and clarifies
sampling procedures for phosphogypsum removed from stacks for other
In: Federal Register: May 8, 1996 (Volume 61, Number 90),
Proposed Rules, p.20775-20779, download via GPO Access
"SUMMARY: On March 24, 1994, EPA announced its
decision concerning a petition by The Fertilizer Institute (TFI)
seeking reconsideration of a June 3, 1992 final rule revising
the National Emission Standard for Radon Emissions from
Phosphogypsum Stacks, 40 CFR Part 61, Subpart R.
EPA partially granted and partially denied the TFI petition for
reconsideration. Pursuant to that decision, EPA is convening a
rulemaking to reconsider 40 CFR 61.205, the provision of the
final rule which governs distribution and use of phosphogypsum
for research and development, and the methodology utilized under
40 CFR 61.207 to establish the average radium-226 concentration
for phosphogypsum removed from a phosphogypsum stack. This
document identifies proposed changes to be considered as part of
this reconsideration and specific underlying issues on which EPA
seeks further comment."
Nuclear regulator releases NGO report on phosphogypsum stacks in France
On April 1, 2009, French nuclear regulator Autorité de Sûreté Nucléaire (ASN) released a report it had commissioned to the NGO Robin des Bois . The report gives an inventory of coal ash and phosphogypsum deposits in France.
> View ASN release April 1, 2009 (in French)
> Download phosphogypsum report (2.3MB PDF - in French) · Annexes (1.4MB PDF - in French)
> Aerial View of phosphogypsum stacks in Huelva: Google Maps
Phosphogypsum used as fertilizer?
The Service of Protection of the Nature (Seprona) of the Civil Guard has opened an investigation into the possible spreading of phosphogypsum originating from the stacks at Huelva in an agricultural property of Gibraleón. The phosphogypsum supposedly would have been used "in an illegal way" as a means for pH correction of the soil, according to a charge formulated by the Association Mesa de la Ría . The association has at several occasions warned from the use of this phosphogypsum in agriculture for its contents in uranium and heavy metals.
(El Mundo June 29, 2011)
Supreme Court approves National Court's decision to halt phosphogypsum dumping at Huelva
The Supreme Court has upheld the sentence of the Audiencia Nacional of 27 June 2007 in which it considered Fertiberia's concession for phophogypsum disposal expired and ordered to halt the dumping in December 2010.
(El País Feb. 22, 2011)
Fertiberia to import phosphoric acid from Morocco to comply with demand to halt phosphogypsum dumping at Huelva
Fertiberia plans to avoid the shutdown of its Huelva plant by importing the phosphoric acid from Morocco. In October, Fertiberia concluded an agreement with state company OCP de Marruecos for the import of phosphoric acid. So, no phosphogypsum will arise at Huelva any longer and the plant will conform to the demand of the Audiencia Nacional to cease dumping of phosphogypsum before Dec. 31, 2010.
This means, however, that the phosphogypsum will arise in Morocco, where environmental legislation is, at least, lax, and even sea dumping of the phosphogypsum is allowed.
(El País Nov. 29, 2010)
Ombudsman deems permit for continued phosphogypsum dumping at Fertiberia plant null and void
The Defensor del Pueblo (Ombudsman) deems the authorization issed in 2008 by the regional government of Andalusia for the continued operation of the phosphogypsum dumps at the Fertiberia plant null and void. The Ombudsman urges the Environmental Council of the regional government to order an immediate halt to the dumping.
(El País Nov. 17, 2010; WWF Nov. 16, 2010)
European Commission demands end of phosphogypsum dumping at Fertiberia plant
The European Commission (EC) demanded an end to the dumping of phosphogypsum at Huelva. Brussels has given two months to the Spanish government so that it puts "order" in the production and treatment of the industrial remainders originated by the Fertiberia company.
(El País Mar. 19, 2010)
Court orders Fertiberia to cease phosphogypsum dumping by end 2010
The Audiencia Nacional central court has demanded Fertiberia to definitively cease the dumping of phosphogypsum wastes before December 31, 2010. The court decision completely ruins the global plan that the government of Andalusia and the company had agreed on in October and that established a final limit to the dumping for December 2012. The court moreover ordered Fertiberia to start reclamation work immediately and to make a deposit of EUR 21.9 million to assure the completion of the necessary reclamation works.
(El País Dec. 22, 2009)
Fertiberia plant to continue operations with imported phosphoric acid
After the planned shutdown of phosphoric acid production in 2012, the Fertiberia plant will continue operations with imported phosphoric acid. This will eliminate the need to dump phosphogypsum wastes in the area.
(El País Oct. 14, 2009)
Government accepts progressive cease of phosphogypsum dumping by Fertiberia up to 2012
The Ministry of Environment considers the plan of Fertiberia for the gradual reduction of the dumping of phosphogypsum wastes in the tailings dams of the salt marshes of Huelva "reasonable". This year, the dumping is to be cut by half. The dumping is finally to be terminated in 2012.
(El País May 6, 2009)
Andalusia establishes expert group on management of Huelva phosphogypsum dams
On Feb. 20, 2009, the president of the Junta de Andalucía, Manuel Chaves, announced the creation of a group of experts for the recovery of the phosphogypsum dams that exist in Huelva. For 20 years, the Fertiberia company has been depositing its remainders there.
(El País Feb 21, 2009)
European Commission initiates procedure of infraction against Spain concerning the phosphogypsum dams of Fertiberia in Huelva
The European Commission initiates a procedure of infraction against Spain. Europe accuses the State to allow that the facilities of Fertiberia and Foret are developing their activity "without having an Autorización Ambiental Integrada (AAI) emitted in the fixed term", explained the commissioner of environment, Stavros Dimas.
(El País Sep 27, 2008)
On March 19, 2009, the European Commission, in a subpoena, demanded the Spanish Government to supply information on the phosphogypsum dams of Fertiberia in Huelva. According to the Commission, around 120 million tons of phosphogypsum have been deposited in the salt marshes of the Río Tinto in the past 40 years.
(El País Mar 20, 2009)
European Commission demands explanation from Spain on spills at Fertiberia
The European Commission has lost the patience with the highly polluting spills of Fertiberia in the salt marshes of Huelva: on May 6, 2008, it decided to send a subpoena to the Spanish authorities in which it demands explanations on what is happening. Brussels demands measures to prevent further violations of the directive on Integrated Pollution Prevention and Control (IPPC Directive) (Council Directive 96/61/EC of 24 September 1996).
(El País May 7, 2008)
Administration deems Fertiberia's closing plan unacceptable
The Main Directorate of Coasts (Dirección General de Costas) has rejected the closing plan presented by Fertiberia in October 2007 as unacceptable. The company proposed the progressive closure of its Huelva facilities and phosphogypsum stacks over a period of 10 years. The administration rather wants a closure by 2011. The administration does not allow for the opening of new phosphogypsum stacks, but authorizes the continued use of the existing stacks.
(El País Mar. 26, 2008)
The Office of the public prosecutor investigates the spills of phosphogypsum and cesium in Huelva
The Office of the public prosecutor of Huelva will investigate the spills originating from the fertilizer factory of Fertiberia and their phosphogypsum stacks located at a distance of 500 meters from the city. The fiscal ministry also will study the releases of cesium-137 in a waste dump located next to the phosphogypsum stacks, as denounced by ecological groups such as Greenpeace or the Asociación Mesa de la Ría .
(El País Feb. 17, 2008)
CRIIRAD study confirms elevated radionuclide concentrations in Huelva phosphogypsum stacks
> View Greenpeace Spain release Dec. 4, 2007 (in Spanish)
> View CRIIRAD release Dec. 4, 2007 (in French)
> Download CRIIRAD report: Rapport CRIIRAD N°07-117, Contrôles radiologiques à Huelva (Espagne), Nov. 29, 2007 (705k PDF - in French)
Study finds high mobility of uranium and other heavy metals in Huelva phosphogypsum stacks
"Presently, about 3 million tonnes of phosphogypsum are being generated annually in Spain as by-product from phosphoric acid in a fertilizer factory located in Huelva (southwestern Iberian Peninsula). Phosphate rock from Morocco is used as raw material in this process. Phosphogypsum wastes are stored in a stack containing 100 Mt (approximately 1200 ha of surface) over salt marshes of an estuary formed by the confluence of the Tinto and Odiel rivers, less than 1 km
away from the city centre." [...]
"The main environmental concern associated to phosphoric acid production is that Uranium, a radiotoxic element, is transferred from the non-mobile fraction in the phosphate rock to the bioavailable fraction in phosphogypsum in a rate of 23%. Around 21% of Ba, 6% of Cu and Sr, 5% of Cd and Ni, and 2% of Zn are also contained in the water-soluble phase of the final waste. Considering the total mass of phosphogypsum, the amount of metals easily soluble in water is approximately 6178, 3089, 1931, 579, 232, 193 and 77 t for Sr, U, Ba, Zn, Ni, Cu and Cd, respectively. This gives an idea of the pollution potential of this waste."
Changes in mobility of toxic elements during the production of phosphoric acid in the fertilizer industry of Huelva (SW Spain) and environmental impact of phosphogypsum wastes, by Perez-Lopez R, Alvarez-Valero AM, Nieto JM, in: Journal of Hazardous Materials, 2007 Sep 30, Vol.148 (No.3), p.745-750
Legal proceedings on operation of phosphogypsum stacks in Huelva
On July 12, 2007, the Audiencia Nacional (National Court) declared the operating license for the phosphogypsum stacks null for failure to comply to the Ley de Costas (Law of Coasts). On July 23, 2007, Fertiberia challenged this decision before the Tribunal Supremo (Supreme Court). If the Supreme Court would uphold the judgement, Fertiberia would have to halt its operations immediately. The proceedings had originally been initiated by WWF/Adena in 2003.
(El País July 29, 2007; WWF/Adena July 12, 2007)
Greenpeace demands to declare phosphogypsum stacks at Huelva, Spain, radioactive installations
On March 19, 2007, Greenpeace protested against the situation of the phosphogypsum stacks at Huelva. Greenpeace found radiation levels up to 111 times above permissible levels. The stacks cover an area of 1,200 hectares and contain an estimated amount of 50 million tonnes of phosphogypsum, mostly generated from the Fertiberia fertilizer plant, and in part by the Foret enterprise.
(El País March 26, 2007)
Phosphogypsum tailings dam failure in Huelva, Spain
50,000 cubic meters of acidic (pH 1.5) and toxic liquid spilled from a phosphogypsum stack at Huelva in Southern Spain at 3 p.m. on December 31, 1998. The 75-hectares tailings dam, operated by the companies Fertiberia and FMC Foret, is located in the salt marshes of Rincón in the outskirts of Huelva, and it contained 1 million cubic meters of liquid. It failed during a storm, when waves of four meters height damaged the embankment. The liquid spilled into Ría de Huelva, a tributary to Río Tinto.
The director of the Fertiberia plant in Huelva indicated that the dam was constructed "following the guideline of a North American company of great experience and prestige", and that Ría de Huelva will not suffer damages since those remainders were spilled there directly until 1997.
Ecologists claim that 400,000 cubic meters spilled, instead of 50,000.
(El Mundo / El País / La Vanguardia Jan. 2 & 3, 1999)
> see also: Safety of Tailings Dams
> For more phosphogypsum dam failures, see: Chronology of major tailings dam failures (watch for ore "phosphate")
> see also: here
On Aug. 18, 2011, Gecko Namibia released the Comparative Marine Environmental Risk Assessment reports for the proposed chemical production plants ("Vision Industrial Park"):
> Download EIA Reports (Gecko Namibia)
For a plant producing 200,000 tonnes per year (tpa) of phosphoric acid 1,000,000 tpa of phosphogypsum by-product will be produced. The expected doubling of production after a few years implies the production of 2,000,000 tpa of phosphogypsum.
The phosphogypsum is to be "discharged to the marine environment".
Potential impurities associated with the phosphogypsum are related to fluorides, radionuclides, and trace metals such as arsenic, cadmium, copper, lead, nickel, zinc and mercury. These compounds are naturally occurring in the phosphate rock and are concentrated in the phosphogypsum by-product during the phosphoric acid production process. (see p.28-30 of the Comparative Marine Environmental Risk Assessment)
The concentration of heavy metals can be high and consequently are of potential concern, particularly in terms of their long-term accumulation in sediments. (p. 109)
There are many impurities in phosphogypsum, the amounts and proportions of which depends on the chemical composition of the phosphate rock. Typically, the impurities contained in the phosphogypsum that are considered to be potentially harmful are:
According to European Best Available Techniques, phosphogypsum disposal into water is generally not regarded as the best environmental option.
In fact, today all phosphoric acid plants in the EU practice land disposal since disposal to the sea is no longer accepted.
- Residual acidity (P2O5);
- Fluorine compounds;
- Undesirable trace elements such as arsenic, cadmium, copper, lead, nickel, zinc and
- Radioactive compounds.
IAEA: Radiation Protection and Management of NORM Residues in the Phosphate Industry
Radiation Protection and Management of NORM Residues in the Phosphate Industry , Safety Reports Series 78, STI/PUB/1582, International Atomic Energy Agency (IAEA), 288 pp., March 2013 (6.8MB PDF)
Soil cover enhances chemical processes in phosphogypsum pile that may endanger stability of the pile
"The present study aims to assess the effect of redox conditions existing within the tailings dump on the stability of phosphogypsum (e.g. sulphate reduction) and uranium(VI). Phosphogypsum sampling and in-situ measurements were carried out at a coastal tailings dump in Vasiliko Cyprus, pH, E(H) and solubility experiments were performed in simulated laboratory systems and thermodynamic calculations using MINTEQA2.
Generally, in the open tailings dump oxidizing conditions
predominate stabilizing sulphur and uranium in their hexavalent oxidation states.
On the other hand, after the application of a soil/vegetative cover and in the
presence of natural organic matter, anoxic conditions prevail (E(H)<-70mV)
resulting in S(VI) and U(VI) reduction to S(-II) and U(IV), respectively.
Although, the sulphide anion can form very insoluble compounds with heavy metal
ions (e.g. Cd(II), Pb(II) etc.) and U(IV) oxide has very low solubility, partial
reduction of sulphate to sulphide within gypsum may affect the stability of
phosphogypsum resulting in enhanced erosion of the material by rain- and seawater
and washing out of contaminants in particulate/colloidal form." [emphasis added]
Redox chemistry of sulphate and uranium in a phosphogypsum tailings dump, by Papanicolaou F, Antoniou S, Pashalidis I, in: Journal of Environmental Radioactivity, ahead of print March 30, 2010
Feasability Analysis: A Comparison of Phosphogysum and Uranium Mill Tailing Waste Unit Designs
by U.S. Environmental Protection Agency, Office of Solid Waste,
January 1997, 33p.
Download (238k, PDF format)
Summarized Comparison between 1993 Florida
Phosphogypsum Management Regulations, New/Proposed Gypsum Stacks
in Florida, and Uranium Mill Tailings Management
"There are some trends and differences that can be
highlighted from Table 5-1, as follows:
- The 1993 Florida Phosphogypsum Management regulations are
less stringent than the uranium mill tailings standards defined
in 40 CFR 192 Subpart D in several important respects.
- First, the uranium tailings standards require a double
composite liner with two geomembranes and an underlying
layer of 3 feet of compacted soil with minimum hydraulic
conductivity of 1x10-7 cm/sec. The gypsum standards
require only one geomembrane and 2 feet of compacted gypsum with
minimum hydraulic conductivity of 1x10-4 cm/sec (or
an underlying 18-inch layer of compacted soil with maximum
hydraulic conductivity of 1x10-7 cm/sec, which has
not been used in any of the four cases analyzed in Section 4).
- Second, the uranium tailings standards require a
leachate collection system that is also used as
detection system. If the measured volume of liquids recovered
exceeds a pre-determined action leakage rate, a response action
plan is set in motion to mitigate or stop any leaks. In the
gypsum case, leakage through the liner is expected and it is
actually calculated in the technical reports presented in the
- All three gypsum stacks constructed or proposed since the
enactment of the 1993 Florida Phosphogypsum Management
regulations have followed or exceeded the Florida standards but
none of the designs approach the protectiveness of the uranium
mill tailings standards.
- The Plant City gypsum stack proposal goes beyond the Florida
standards due to the environmental sensitivity of the area
(i.e., proximity of a potential future wellhead area) and, quite
likely, because of increased public concern in Florida after
recent environmental incidents in the phosphoric acid industry.
- A trend that is clearly noticeable in the technical reports
presented to support the Florida permit applications is an
increasing level of detail and analysis. For example, a new
topic that is receiving more attention (both in field work
efforts and proposed preventive measures) is sinkhole potential.
- The approach at the Nichols plant of a modified gypsum stack
is interesting, as it allows usage of an old stack for the
remaining years of its useful life, fulfilling at the same time
the 1993 Florida regulation's closure requirements. Furthermore,
it is a potential solution for those situations with land
availability restrictions; it does not have to go through the
DRI process as it does not change the footprint of the original
gypsum stack; and the ZOD is not reduced, but remains within a
horizontal range to the property boundary."
Handling of radium and uranium contaminated waste piles and
other wastes from phosphate ore processing
by G.Schmidt, C.Küppers; annex by P.Robinson
Nuclear Science and Technology, Report EUR 15448 EN. 121 p. ISBN
92-827-4076-5, published by the European Commission, Luxembourg
"Natural phosphate ores contain radionuclides
of the uranium series. In this report, calculations and
evaluations of radiation doses for the public and for workers
from the phosphate industry are performed. From these findings,
it is evaluated whether established radiation protection
procedures should also apply to certain facilities, occupations
and waste management practices in the phosphate industry.
Measures for improvement and remediation are discussed and
evaluated, and recommendations given."
"The findings in this report are summarized
with the following statemens:
- Processing and waste handling in the phosphate industry is
associated with radiation levels of concern for
workers and the public. The level of protection for these groups
should be more similar to the level of protection that is state
of the art in other industries, particularly the nuclear
- Radiation protection measures for workers
are necessary, especially for certain areas of the facility and
for repair jobs, because potential radiation doses reach a
relatively high level of concern compared to protection levels
in other industrial branches.
- Some waste management practices still found in the phosphate
industry of today deliver relatively high individual and/or
collective doses to the public, that can be
substantially reduced by shifting to alternative management
- Environmental risks from phosphogypsum piles can be reduced
using relatively simple and cheap measures such
as covers, liners or a more sophisticated wastewater treatment.
These are in place and working well at other facilities in and
- The unrestricted reuse of materials from
phosphate processing facilities and of waste materials creates
potential hazards to man that exceed established limits for
Office for Official Publications of the European Communities
2, rue Mercier, L-2985 Luxembourg, Luxembourg
Tel. +352-2929-1, Fax: +352-488573 / 486817
(or from national distributor of EU publications)
Natural Radionuclide Concentrations in Materials Processed in the Chemical Industry and the Related Radiological Impact
by J. Hofmann, R. Leicht, H.J. Wingender, J. Wörner, August 2000, 115 p.
Nuclear Safety and the Environment, Report EUR 19264, European Commission, Directorate-General Environment
> Download full report (325k PDF)
"Subject of this study is the potential radiation risk that can result from the presence of naturally occurring radioactive materials in raw materials usually considered as not radioactive and used in the manufacturing of chemical products.
In a review concerning such raw materials (phosphate ores, Zirconium, various metal ores) basic information on major companies involved, quantities produced, range of radionuclide concentration, chemical processes, products and by-products has been compiled for EU member states.
Typical radiation exposure scenarios such as radiation exposure of staff due to direct radiation, dust inhalation and dumping of various materials as well as the exposure of the public due to dumping and use of products have been investigated. The results show that the inhalation of dust is the major source of dose uptake which may require limiting dust concentrations.
In a survey concerning the current legislation in the European Union and its member states the problems radon at workplaces, testing and remedying existing workplaces, controlled and supervised areas and protection against exposure from natural sources are discussed. Regarding the regulation and classification schemes identified and taking into consideration the exposure estimates derived, it can be concluded that the dust inhalation situation of staff should be carefully and specifically re-considered before any additional regulatory measures are taken."
Phosphate and Molybdenite - Extraction and Beneficiation of
Ores and Minerals
Technical Resource Document: Other Mining Sectors, Volume 7.
U.S. Environmental Protection Agency, Office of Solid Waste,
EPA/530-R-94-034, NTIS/PB94-201001, November 1994, 135
[Report summarizes EPA site visits to phosphate and
molybdenite mines. Includes reports of EPA site visit to IMC
Fertilizer's Four Corners (phosphate) Mine near Duette, Florida
and Cyprus Minerals Corporation's Thompson Creek (molybdenite)
Mine near Challis, Idaho. Discusses the extraction and
beneficiation activities at each site. The report includes a
description of mine operations, mine waste generation and
management practices, and regulatory status on a site-specific
basis; The information was gathered from State and Federal
agency files, as well as observations made during the site
Available from: National
Technical Information Service , 5285 Port Royal Road,
Springfield, VA 22161, USA, Tel. +1-703-487-4650, Fax: +1-703-
Also available by
Download (1366k PDF)
by C.L.Lindeken, U.S. DOE, UCRL-84927, 1980, 22 p.
by C.B. Chernoff and G.J. Orris, USGS Open-File Report 02-156A&B, 2002
Radon Flux Measurements on Gardinier and Royster Phosphogypsum Piles Near Tampa And Mulberry, Florida
by J.N. Hartley and H.D. Freeman,
U.S. Environmental Protection Agency, EPA 520/5-85-029, January 1986
> Download full report (7.2MB PDF)
U.S. EPA: 40 CFR Part 61 - National Emission
Standards for Hazardous Air Pollutants: Select for Download (PDF format)
Subparts of interest:
- Subpart K - National Emission Standards for Radionuclide Emissions From Elemental Phosphorous Plants
- Subpart R - National Emission Standards for Radon Emissions From Phosphopgypsum Stacks
The Phosphate Fertilizer Industry: An Environmental Overview (Fluoride Action Network)
About Phosphogypsum (U.S. EPA)