1 - Phosphate in Agriculture
Introduction to Phosphate as a Fertilizer
History of Phosphate Fertilizer Production
Phosphate and Organic Fertilization
2 - Phosphate in Florida
Florida's Phosphate Deposits
Phosphate and How Florida Was Formed
Fossils: What They Tell Us About Florida’s Natural History
Discovery of Phosphate in Florida
Florida Phosphate Mining History
Timeline of Phosphate Communities
The Phosphate Industry and Florida's Economy
How Long Will Florida Phosphate Mining Go On?
3 - Phosphate Throughout the World
Other Phosphate Deposits
4 - Phosphate Processes
Phosphate Mining Today
Clay Settling Ponds
Chemical Processing of Phosphate
Phosphogypsum and the EPA Ban
Potential Phosphogypsum Uses
Reclamation: Strategies and Stages
5 - Environmental Quality, Safety, and Public Health
Introduction to Radioactivity
Radon and Homes
Radiation and Phosphogypsum
Radiation and Phosphoric Acid
Radioactivity and Phosphatic Clay Ponds
Phosphate Companies and EPA's Toxic Release Inventory
6 - Environment and Health
Spill from a truck, train or pipeline:
Radon and gamma radiation:
Materials of concern are transported through the phosphate mining region. They include molten sulfur, sulfuric acid, phosphoric acid, ammonia and phosphatic clay.
At the mining areas slurry is moved several miles by pipeline to the beneficiation plants and settling areas. If a pipe breaks and the slurry makes its way into a stream or a river, the suspended clay in the water can cause environmental problems. Pipes are patrolled regularly to watch for breaks. For the most part leaks are found quickly because the flow at the end is diminished. When a leak is detected, the pipeline is shut down.
Molten sulfur is transported by truck and train to the chemical processing plants where sulfuric acid is made. It takes one ton of molten sulfur to produce three tons of sulfuric acid. The sulfuric acid is mostly transported within company property.
Ammonia is trucked and piped between the Port of Tampa and the mining region. The pipeline is equipped with an automatic shut-off valve in case of a pipe leak. The port has an intricate safety system to handle the ammonia. Fumes from an ammonia spill can be fatal at a high enough concentration.
The trucks, trains and pipes that are used to transport these materials are all specially designed with safety systems. There is, however, always the possibility of an accident as with trucks carrying gasoline, propane, liquid hydrogen and pure oxygen used at many different industrial sites and medical facilities all over the country.
The main issue related to increased radiation in a mined area is what it means to people who live in a home on reclaimed land. The buildup of radon in a closed house is the subject of much scientific debate. The debate is where to draw the line between the level of radon that is no more harmful than the outside air and where there is a real increase in the risk of lung cancer.
The U.S. EPA has a guideline of 4 picocuries per liter of indoor air (pCi/L), but studies of people living in homes with much higher levels (tens of pCi/L) show no increase in lung cancer. Studies of homes built in the phosphate mining region indicates an increase of up to a few pCi/L in homes built directly on mined lands. Most often the 4 pCi/L guideline is not exceeded, and depends mainly on the type of home construction.
There are various methods to prevent radon entry into homes or reduce radon concentrations after entry. These modifications are not required by law and contractors don’t usually include them in a house design. The EPA has a Radon Contractor Proficiency (RCP) Program to certify contractors in these methods. Most often house modifications are made when residents of an existing home have the house radon tested and find the radon level is too high for their comfort. Radon mitigation can cost $500 to $2500, depending on the modification needed.
A good mitigation system for slab-on-grade home construction is called sub-slab ventilation. With that system a pressure differential is used to draw air from under the house and vent it out before the radon gas can enter through cracks in the floor. Radon gas can be easily reduced to outdoor levels by opening a window(s) to let the outside air mix in and the radon level reach equilibrium with the atmosphere. Doing this about every other day would solve the problem for most houses. Any air handling system that exchanges air with the outside environment also helps. Ventilation is more of a problem in colder climates where people close their homes tightly through many cold months.
Radiation connected to phosphogyspum
Gamma radiation is emitted by many natural radioactive materials and is very similar to X-radiation. It is measured in terms of microRoentgens per hour (μR/hr). This is an extremely small unit of measurement because the natural levels are so low.
The background level chosen as an average for all of Florida by the Department of Health (DOH) is 6 μR/hr. Levels over unmined mineralized lands average about 8 μR/hr and over mined and reclaimed lands average about 12 μR/hr. Land averaging under 20 μR/hr is considered safe, and lands naturally exceed that amount in some areas and are still considered safe because variation in exposure to all sources of environmental radiation is so great.
- Both natural gypsum and phosphogypsum contain radioactivity, but phosphogypsum contains more.
- In the manufacture of phosphoric acid, the acid is filtered through cloth to remove solids. The radium is filtered out with the solids. The solid portion is known as phosphogypsum.
- Phosphogypsum produced in North Florida contains roughly 5 – 10 picocuries per gram (pCi/g) of radium while phosphogypsum from Central Florida contains about 20 – 35 pCi/g radium.
- The U.S. EPA prohibits the use of phosphogypsum. An exception is made for phosphogypsum with an average concentration less than 10 pCi/g radium which can be used as an agricultural amendment.
- Phosphogypsum is primarily calcium sulfate, and plants need the sulfur it contains. Since much of the North Florida phosphogypsum is below the EPA restriction level, it could be as a crop amendment.
- The Central Florida phosphogypsum is restricted to storage on land in large piles called “stacks.”
- The overall radioactivity in the stacked phosphogypsum is actually less than what was in the original phosphate ore that was taken out of the ground.
Clay dam breaks:
Long-term fate of chemicals the industry uses:
When a clay settling area dam breaks, millions of gallons of water with suspended clay particles can be loosed into the environment and cause damage to the land and any waterway it makes its way over and into.
In December 1971 water from a dam burst near Fort Meade made its way into the Peace River and killed river fish as far south as the Gulf of Mexico. The next year the state mandated that all new dams be built to tough engineering standards. In 1994 one of the dams built according to the new standards failed and sent water into the Alafia River. No fish appeared to have died from this spill, but it did impact the water in some area wells for a short time, during which the phosphate company supplied residents with drinking water.
The Florida Department of Environmental Protection put together a technical advisory team that looked at the situation and came up with recommendations that resulted in new regulations for earthen dams used in phosphate mining. There have been no breaks in dams built to the latest standards.
Until recently, no one was sure about how the reagents (chemicals) the phosphate industry uses in its beneficiation process impacted the environment.
To find out, FIPR funded a study in 1995 to examine the environmental impact of the reagents. The study found that chemicals used in the phosphate industry to separate the sand from the phosphate are all broken down in nature, but to different extents. These chemicals are fatty acids, amines and fuel oils. The sandy soils at the mines are good for reducing the fatty acids and fuel oil. Amines were not detected at all in ground water. Fuel oil could be detected in groundwater on site, but decreased with time.
The amount of fuel oil found in the surficial aquifer was within EPA’s acceptable limits. While there is no significant risk from the fuel oil, FIPR is doing research on ways to cut down on the amount of fuel oil used in flotation and launching further study into the fate of fuel oil in the environment.