Cargill Fertilizer - Project Information

Frequently Asked Questions

Why is Cargill requesting an expansion of its current gypsum storage area?

So we can continue to produce fertilizer at our Tampa plant for 30 years beyond 2007. Without fertilizer, agricultural scientists estimate that only 40 percent of today's world population could be fed. Applying the appropriate fertilizer, however, can increase crops two, three or four times per acre. Cargill mines more than eight million tons of phosphate rock per year, producing over 14 percent of the total phosphate fertilizer supply in the United States. In order for us to continue producing fertilizer, we need to extend our existing gypsum storage area.

How is phosphate mined?

The mining process begins with the dragline removal of the sandy soil that covers the layer containing phosphate ore. This soil is later used for land reclamation. The ore, or "matrix", is then removed and mixed, or "slurried," with high-pressure water. The slurry is pumped to the ore processing plant where it is washed and separated by size. Through a process that washes, spins, crushes and vibrates the slurry, clay is separated from the phosphate rock. The remaining mixture of sand and fine phosphate particles is then processed further to separate out the phosphate. The resulting raw material is the basis for fertilizer products.

What products are made from phosphate rock?

Of the phosphate rock mined in Florida, 90 percent is used for fertilizer. Of the remaining 10 percent, half is used in animal feed supplements. The balance is used in a variety of products, such as vitamins, soft drinks, toothpaste, light bulbs, film, bone china, flame-resistant fabric, optical glass and other consumer goods.

What is gypsum?

Phosphogypsum is a byproduct of the production of phosphate fertilizer and is essentially identical to the natural gypsum that is mined and used in wallboard. The gypsum from phosphate manufacturing, however, contains some sand with small amounts of magnesium fluoride, radium and other elements that occur naturally in the soils from which phosphate ore is extracted.
At the Tampa facility, phosphate rock from Cargill's mine in Polk County is ground, then mixed with sulfuric acid and water to create phosphoric acid, the basic material of all phosphate fertilizers. Gypsum is the solid byproduct of that process. The gypsum is separated from the phosphoric acid and transported to a storage field in a slurry that is about 30 percent solids and 70 percent process water.

Is gypsum a hazardous material?

Gypsum is not considered a hazardous material, but it does require some special handling because of the volume that is being stored and because of the process water (or leachate, as it is sometimes called) that is transported with the gypsum. The key environmental objective is to contain the process water, which has become acidic, so that it does not reach ground or surface water areas. At Cargill, this process water is continually recycled for use in the processing of phosphate rock into fertilizer.

Does gypsum affect the air quality?

The State of Florida Department of Environmental Protection does not consider gypsum storage areas to be potential sources of significant air-emission problems, thus actual air permits are not required.

But isn't gypsum radioactive?

Gypsum has a slight, natural radioactivity. Tests conducted at our existing gypsum storage area and at other gypsum storage facilities around the state indicate that radon emissions are so low that they cannot even be measured just a few feet from the storage area. In addition, the soil and grass cover on our gypsum storage areas provides a good measure of protection against any type of air emission including dust emissions.

There is a distinct smell in the area surrounding Cargill's fertilizer plant. Is inhaling this air a health hazard?

The odor is from the water used throughout the facility that is pumped to ponds to evaporate and cool down. The cause of the odor is believed to be from sulfur compounds formed when fertilizer is made using the phosphate-rich earth that contains naturally occurring organic materials. Extensive studies have been conducted including laboratory testing of raw materials, plant operations and fertilizer products. In addition, "odor panel" studies have been conducted where community members have recorded odor descriptions in diaries. These observations have been compared to facility operations and weather conditions. These studies have concluded that the materials causing the odors are not harmful to health.
Cargill has investigated potential technologies to reduce or eliminate the odors and is planning to treat the process water ponds with hydrogen peroxide to reduce the odors. To evaluate the effectiveness of this treatment plan, a community odor panel will be recruited to conduct smell tests of the water before, during and after treatment.

Does the gypsum storage areas create a great deal of dust in the surrounding area? Is this dust a health hazard?

Both the United States Environmental Protection Agency and the State of Florida Department of Environmental Regulation have found that there are no particulate (dust) emissions from gypsum storage systems. If an emission is considered a pollutant, an industry is required to obtain an environmental permit to show how they will control it. These two agencies do not require environmental permits for dust. Numerous studies on collected particulate (dust), both before and during operation of the current gypsum storage area, have shown that the samples were not gypsum. We recognize, however, the neighborhood concern for dusts in the area, and we are ready to conduct additional studies to determine the source of the dust in the community.

How is stormwater that comes in contact with the gypsum storage areas contained?

Cargill's fertilizer plant is a zero discharge facility meaning that water that has come in contact with fertilizer is not discharged from the plant site. To prevent stormwater from coming into contact with the gypsum, the sides of the storage areas are covered with a protective layer of soil and grasses. The grass cover helps prevent erosion and filters the stormwater, slowing the rate of runoff. Stormwater that runs off the sides of the storage areas is captured in concentric swales of containment ditches at the edge of the storage area. While the stormwater collected in the outermost swale drains off the site, stormwater collected in the other two swales are transported to Cargill's water retention and recirculation system. This alternate collection and recirculation system ensures that no contaminated storm or rainwater leaves the site.

Doesn't the gypsum leach into the soil, possibly mixing with public drinking water?

The ground water supplies that lie below Cargill's gypsum storage areas are brackish, and are not likely to ever be considered as a potential source of drinking water. Even so, extreme care is taken to minimize the risk of any process water seeping into the ground water. A two-tiered clay liner serves as the foundation for the gypsum storage area. A minimum of 15 feet of undisturbed clay has been capped with an 18-inch layer of compacted clay. This combination makes a virtually impermeable liner.

Why doesn't Cargill sell its gypsum to manufacturers?

Researchers are looking into possible uses for the gypsum from phosphate mining, (e.g., road pavements, soil supplements for sulfur, rail road ties, home uses). Research combined with environmental agency approval will find appropriate uses in the long term future. .