sws term paper

8/2/2019 SWS Term Paper

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Pedro Palomino SWS 5551 March 20th, 2012

Florida Phosphate Mining Wastes and their Relationship to Public Health

1.0 Introduction

Discovered in 1889, phosphate mining has since become a major industry in Florida,

contributing more than $85.9 million in severance, property, sales and other taxes and fees in

2003. (Florida Industrial and Phosphate Research Institute) Phosphate has become a significant

part of the Florida economy between the mining and agricultural production, which depends on

the phosphate fertilizers. Globally, phosphate plays a vital role in meeting the demand on food

supplies of an ever growing population. For example, commercial fertilizer is estimated to be

responsible for 40 to 60% of the worlds food supply, and Florida mines play a critical role,

producing 25% of the phosphorous used in agriculture worldwide. (Table 1) (Roberts, T. L.,

2009; Florida Industrial and Phosphate Research Institute) The demand for fertilizers and animal

feed additives accounts for about 95% of the 8-10 million metric tons of phosphoric acid that is

made each year. (United States Environmental Protection Agency, 2011)


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Table 1. Wet process phosphoric acid plants. (United States Environmental Protection Agency,1992)

The extraction and refining of phosphate is composed of three steps and each of these represent a

potential to can cause damage to the local environmental and human health. Mining is the

process of removing the phosphate rock from the ground, typically 15 to 50 feet below ground.

In Florida, phosphate mining disturbs 5,000 to 6,000 acres of land annually. (Florida Department


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of Environmental Protection, 2012) Benefication is the mechanical separation of phosphate

minerals from the clay and sand that make up the phosphate rock. The waste clay is pumped into

clay settling areas (CSAs), with 100,000 gallons per minute of process water. Finally, during

chemical processing, the phosphate minerals are mixed with sulfuric acid to produce phosphoric

acid, which can be sold as a product, but more commonly is combined with other processes to

create crop fertilizer and animal feed. (Figure 1) During chemical processing, for every ton of

phosphoric acid produced, five tons of phosphogypsum are produced, a waste product that is

being stored in 25 stacks across Florida at the rate of 30 million tons every year. The phosphate

mining industry produces many more waste products that have the potential to be reclaimed or

reused, however current regulations ban their use to protect human health. (Florida Industrial and

Phosphate Research Institute) The goal of this research is to compare the health impact and

regulations of phosphogypsum with other phosphate mining wastes.

Figure 1. Phosphate chemical processing plant flow sheet


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2.0 Phosphate Mining Wastes

Similar to other mining operations, phosphate mining produces a large amount and variety of

waste products. (Table 2) The management of large waste disposal impoundments, such as dams,

ponds and stacks represent a significant disturbance to the local area and hydrology. The failure

of storage facilities can cause extensive and widespread offsite effects, such as the contamination

of surface and ground water by wastes such as fines, tailings effluents and brines. (United

Nations Environment Program; International Fertilizer Industry Association, 2001) However, the

greatest health concern is the radioactivity of the different waste materials, which is a result of

the mined mineral matrix, which naturally contains the radioactive elements uranium and

radium.


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Table 2. Wastes produced in the phosphate mining industry.

2.1 Phosphatic Clays

The mined phosphate rock contains equal parts of fluoapatite, a common phosphate mineral, clay

and sand. After benefication, the clay is collected in CSAs, which occupy 40% of phosphate

mined lands. It takes years for the clay to settle and the water to evaporate, and even after several

years these areas are still only about 25% solids, meaning that the land is not structurally sound.


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Although, researchers have shown that CSAs can be reclaimed with wetlands, improving the

local hydrology and biodiversity. (Brown, M. et al., 2010)

Phosphatic clay sediment in the CSAs has a higher level of radioactivity than sediment in natural

lakes. The average Florida soil has about 2 pCi/g of radioactivity from both uranium and

radium. A clay settling area has up to 40 pCi/g of radioactivity. When considering risks

associated with radioactivity and the clays, consider a study of typical Florida crops grown on a

CSA. The study found that if a person ate as much food as possible from the crops grown on this

CSA for a year, that person would receive a 0.03 mSv dose of radiation from the food in addition

to the 3.6 mSv dose of background radiation received naturally every year. (Florida Industrial

and Phosphate Research Institute) Studies conducted in the early 1980s by Gordon & Palm

Associates, Inc. state that clay ponds do not pose a risk to ground water. As a result of this

finding, all clay ponds at phosphate mines in Florida are exempted from State ground-water

monitoring requirements. (United States Environmental Protection Agency, 1994)

2.2 Process Waters

Water is used throughout the chemical processing to produce phosphoric acid, to operate

barometric condensers, for gas scrubbing, and to slurry the phosphogypsum produced and

transport it to stacks for storage. The process water is very acidic and is stored in ponds above

phosphogypsum stacks for cooling to be recycled. Typical process waters have a very high total

dissolved solids, total phosphorous and color, which must be treated before it is discharged into

the environment under a National Pollution Discharge Elimination System permit. Along with

the process waters, large amounts of phosphoric acid are released into these ponds. Phosphoric

acid maintains 86% of the Uranium-238 from the phosphate rock following chemical processing,


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but the concentration of U238 is at low enough levels that it is safe to use. (Florida Industrial and

Phosphate Research Institute)

However, if the storage system fails as in the case of Piney Point Phosphates, these process

waters represent a severe health hazard. Treated process water was being discharged into

Bishops Harbor to lower the amount stored in the phosphogypsum stacks and prevent structural

failure of the retaining dikes. Garret et al. (2011) found that the discharge of these high nutrient

waters caused an increased in the number of some harmful algal bloom species. In 2003, the

EPA issued an emergency permit to the Florida Department of Environmental Protection to

disperse 534.7 million gallons of treated water in the center of the Gulf of Mexico because heavy

rain risked the failure of the pond containment walls, which would have released 1.4 billion

gallons of untreated acidic process water into Tampa Bay. (Garret et al., 2011)

Figure 2. Piney Point Phosphates process water cooling ponds.

Regulations regarding phosphogypsum stacks have been improved to prevent seepage of process

waters into groundwater sources. Some of the storm water is collected and discharge is


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controlled, however in many cases the majority of the storm water runs off the site uncontrolled,

transmitting contaminants from the mining area into the surrounding environment. (Florida

Industrial and Phosphate Research Institute; United States Environmental Protection Agency,

1994)

2.3 Phosphogypsum

Phosphogypsum is primarily CaSO42H2O with small amounts of rock phosphate, sand and clay,

and is highly acidic. (Alcordo, I.S. and Rechicigl, J.E., 1995) About 1 billion tons of

phosphogypsum are currently stored in 25 stacks across Florida. (Florida Industrial and

Phosphate Research Institute) Stacks can range from a foot print between 5 and 740 acres and a

height between 10 and 200 feet. (United States Environmental Protection Agency, 2011)

Since 1990, the Environmental Protection Agency (EPA) requires that all phophogypsum is

placed in stacks or mines. Environmental contamination resulting from phosphogypsum storage

may occur from atmospheric contamination with fluoride or other toxic elements, groundwater

pollution with mobile anions, acidity or radionuclides, radon gas, inhalation of radioactive dust,

and direct exposure of gamma radiation. (Hofman, J. et al., 2000) The major health concern

related to phosphogypsum is its radioactivity. The concentrations of uranium and radium-226 in

phosphogypsum samples taken in central Florida were about 10 times the background levels in

soil for uranium and 60 times the background levels in soil for radium-226. (United States

Environmental Protection Agency, 2011) However, The EPA has determined that the risks

associated with stacking phosphogypsum are in line with acceptable risk practices. (Florida

Industrial and Phosphate Research Institute) Phosphogypsum produced in north Florida contains

roughly 510 pCi/g of radium while phosphogypsum from central Florida contains about 20


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35 pCi/g radium. (Florida Industrial and Phosphate Research Institute) As resources in north

Florida diminish, phosphate mines are moving south to mine new phosphate rock, which will

lead to more phosphogypsum containing greater radioactivity.

Beneficial Uses of Phosphogypsum

There are two major proposed uses for phosphogypsum. They include use as a soil amendment to

improve the quality of agricultural soils, and a road base or construction material. Only about 5%

of the phosphogypsum produced in United States is utilized for beneficial use. In the United

States, phosphogypsum can be used as a conditioner for clayey or and sodic soils because of its

moisture retaining and salt leaching properties. Its critical for maintaining soil productivity in

the southeastern United States where highly weathered soils have poor physical properties and

high erodability. Phosphogypsum has successfully been used in as a base in roads, parking lots

and storage facilities in Florida, and in other states. This does, however, pose a potential health

risk of direct radiation exposure from gamma-rays and radon-222. Research has shown that the

radiation emitted from the phosphogypsum in the road base is near background levels, and thus

does not harm human health. The phosphogypsum used in these practices all meet the regulatory

radiation limit set by the EPA. (United States Environmental Protection Agency, 1992)

Phosphogypsum Regulations

Phosphogypsum with an average radionuclide greater than 5 pCi 226-Radium per gram of solid

waste or greater than 10 Ci for any single discrete source is considered a hazardous waste,

according to the EPA. (Alcordo, I.S. and Rechicigl, J.E, 1995) The majority of phosphate

production in Florida is in the Bone Valley area of central Florida, so much of the

phosphogypsum cannot be beneficially used. On the contrary, most European countries apply the


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recommendation that the population should not be exposed to more than 0.7 mSv of radiation

from building materials; therefore the total gamma radiation dose should not exceed the limit of

1 mSv per year. Converting this limit in terms of 226Ra, the phosphogypsum used in building

material cannot exceed 18 pCi/g, according to the European Commission Recommendation.

(Tayibi et al., 2009)

Phosphogypsum Risk Assessment

The EPA evaluated the health risks to set the level of the regulation limiting the use of

agricultural use of phosphogypsum. There are three main exposure pathways, direct exposure as

in the case of gamma rays, inhalation in the case of 222-Radon gas and radionuclide-

contaminated particles, and ingestion in the case of drinking water or eating food with various

radionuclides. (Alcordo, I.S. and Rechicigl, J.E., 1995) The EPA assumed seven different

scenarios to model possible exposure routes. Each of these varied in the type of soil,

concentration of 226Ra in the phosphogypsum amendment, populations exposed, distance from

the phosphogypsum application site, application rate over 100 years and tillage depth. The

results showed that highest health risk was associated with the on-site agricultural worker, who

received external gamma radiation from the phosphogypsum amendment and indoor Rn

inhalation from the soil. Since this population exposed to the greatest risk, the EPA chose this

scenario for its rule making. Under this scenario, the EPA assumed that the highly exposed

individual lived in a house for 70 years on property that was previously an agricultural site,

where was 1225 kg/ha of phosphogpysum was applied biennially for 100 years. The EPA also

assumed that a lifetime (70 years) 1x10-4 risk of fatal cancer was a safe limit. From these

assumptions, the regulation for the maximum individual risk of fatal cancer over 70 years of

continuous exposure does not exceed 3x10-4. From this maximum individual risk, the limit on


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226Ra in phosphogypsum was set at 10 pCi/g for agricultural use. (Alcordo, I.S. and Rechicigl,

J.E., 1995)

From the perspective of the fertilizer industry, this concentration is too low and was improperly

determined. The phosphate industry argues that the 226Ra concentration was based only on the

scenario of greatest exposure, giving a very low limit. Under this scenario, phosphogypsum

would account for 30% of the soil by weight at a 15 cm tillage depth, meaning the assumed

application rate may be too high. Also, the homeowner's risk of radon-related health concerns

only slightly exceeded the EPA's acceptable limits. That risk is equivalent to a radiation dose of

1 mSv per year beyond the natural background radiation dose of 3.6 mSv that the average person

in the United States receives per year. For comparison, the average two-pack-a-day smoker

subjects himself or herself to about 8,000 dose units per year from the inhaled radioactivity in the

tobacco leaves. (Florida Industrial and Phosphate Research Institute) The Fertilizer Institute

believes that the parameters selection and dose-risk model overestimate risk by 2.5, so they have

proposed that the EPA increase this limit to 26 pCi/g 226Ra in phosphogypsum. This would allow

the dose-risk model used by the EPA to be tested in the real world environment and set a more

accurate, safe limit. (Alcordo, I.S. and Rechicigl, J.E., 1995)

Conclusion

The Florida phosphate industry is responsible for a relatively large portion of the phosphate

fertilizer used to meet the worldwide demands on food supplies. This industry produces many

waste products, but phosphogypsum has the potential to be used as a soil amendment or road

base material. However, current EPA regulations limit the amount of radiation in

phosphogypsum that is beneficially used. Much of the phosphogypsum produced in Florida


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exceeds the limit, and the fertilizer industry has proposed to increase the limit to 26 pCi/g 226Ra.

They view the current regulation of 10 pCi/g 226Ra as and deriving from a flawed method. As a

comparison, the European Commission has recommended that the maximum concentration in

phosphogypsum should be 18 pCi/g 226Ra, which splits the difference between the regulators and

private industry. The EPA regulation for radiation in phosphogypsum is too conservative and

leads to phosphogypsum stacking, which has a multitude of environmental consequences. The

limit should be increased to avoid some of the issues associated with the phosphogypsum wastes.

This will also give researchers an opportunity to prove or disprove the accuracy of the previous

EPA limit in real world situations.


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References

Alcordo, I.S. and Rechicigl, J.E. (1995) Phosphogypsum and Other By-ProductGypsums. (pp. 366412). In J.E. Rechcigl, Soil Amendments and Environmental

Quality. Boca Raton, FL, USA: CRC Press, Inc.

Brown, M., Boyd, M., Ingwersen, W., King, S., McLaughlin, D. (2010) Wetlands on claySettling Areas. Bartow, FL, USA: Florida Institute of Phosphate Research

Esmeray, E. and Aydin, M. E. (2011) An investigation on natural radioactivity frommining industry.African Journal of Biotechnology. 10(20) 43134317.

Florida Department of Environmental Protection. Chapter 62-671 Phosphate MiningWaste Treatment Requirements

Florida Department of Environmental Protection (2012) Mandatory Phosphate Programhttp://www.dep.state.fl.us/water/mines/manpho.htm

Florida Industrial and Phosphate Research Institute.http://www1.fipr.state.fl.us/PhosphatePrimer

Garret, M., Wolny, J., Truby, E., Heil, C., Kovach, C. (2011) Harmful algal bloomspecies and phosphate-processing effluent: Field and laboratory studies.Marine Pollution

Bulletin. (62) 596601.

Hofman, J., Leicht, R., Wingender, H. J., Worner, J. (2000) Natural RadionuclideConcentrations and in Materials Processed in the Chemical Industry and Related

Radiological Impact. European Commission: Nuclear Safety and the Environment.

Roberts, T. L. (2009) The Role of Fertilizer in Growing the Worlds Food.Better Crops.93 (2)
http://www.dep.state.fl.us/water/mines/manpho.htmhttp://www.dep.state.fl.us/water/mines/manpho.htmhttp://www1.fipr.state.fl.us/PhosphatePrimerhttp://www1.fipr.state.fl.us/PhosphatePrimerhttp://www1.fipr.state.fl.us/PhosphatePrimerhttp://www.dep.state.fl.us/water/mines/manpho.htm


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Tayibi, H., Gasco, C., Navarro, N., Lopez-Delgado, A., Alguacil, F. J., Lopez, F. A.(2009) The Radiological Impact and Restrictions on Phosphogypsum Waste.

Applications. 1st Spanish National Conference on Advances in Materials Recycling and

EcoEnergy. 7174.

United Nations Environment Program and International Fertilizer Industry Association.(2001) Environmental Aspects of Phosphate and Potash Mining. Paris, FR: United

Nations Publication.

United States Department of the Interior: Bureau of Mines. (1983) Use of FloridaPhosphogypsum in Synthetic Construction Aggregate. Bartow, FL, USA: Florida

Institute of Phosphate Research.

United States Environmental Protection Agency (1992) Potential Uses ofPhosphogypsum and Associated Risks. Washington, DC, USA: 40 CFR 61 Subpart R:

National Emissions Standards for Radon Emissions from Phosphogypsum Stacks

United States Environmental Protection Agency. (1994) Mine Site Visit: IMC FourCorners Mine.Extraction and Benefication of Ores and Minerals, Volume 7: Phosphate

and Molybdenum. Washington, DC, USA: United States Environmental Protection

Agency.

United States Environmental Protection Agency (2011) About Phosphogypsum.http://www.epa.gov/radiation/neshaps/index.html
http://www.epa.gov/radiation/neshaps/index.htmlhttp://www.epa.gov/radiation/neshaps/index.htmlhttp://www.epa.gov/radiation/neshaps/index.html

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