Cochise College           Student Papers in Geology

Geology Home Page                   physical geology  historical geology  planetary  gems           

Roger Weller, geology instructor

by Melanie Strate
Physical Geology
Fall 2014


What are phosphates?

In geology, phosphate refers to a rock or ore that contains phosphate ions. A phosphate is a compound that contains phosphorus, oxygen, and at least one more element, such as sodium, calcium, potassium, or aluminum. Phosphate rock is primarily calcium phosphate. Phosphates are the natural form in which the element phosphorus is found in living organisms, ecosystems and rocks. The three main allotropes (forms of phosphorus that are physically and chemically different) are named for their colors: white (or yellow) phosphorus, red phosphorus, and black (or violet) phosphorus. White phosphorus is highly reactive and can catch fire spontaneously because of the ease with which it combines with oxygen. For this reason, white phosphorus is stored in water. White phosphorus is also phosphorescent (gives off light). Because of its high reactivity, white phosphorus is not found on its own in nature, but usually occurs as a phosphate. The abundance of phosphorus in the Earth's crust is estimated to be 0.12 percent, making it the 11th most common element. However, the only important commercial source of phosphorus is phosphate rock. Below is an example of pebble phosphate found in Florida.

Description: Pebble phosphate.jpg

Where are phosphates found?

Phosphate rock can be found in the oceans in the form of calcium phosphate, or phosphorite. It is deposited in layers over thousands of square miles. It is believed that the phosphate layers were formed from precipitation (a process in which the dissolved phosphorus in the seawater solidified) from sea water combined with skeletons and waste products of creatures living in the ocean. Although these oceanic deposits are large, mining them is far too expensive so they are left where they are. Phosphate rock is also found on land and some of the largest land deposits are found in China, Israel, Jordan, Morocco, Russia, Tunisia, and the United States. China is the world’s largest producer of phosphate, followed by Morocco, then the United States.


Description: World Phosphate Rock Production and Demand

The largest rock phosphate deposits in the United States are in what is called the Bone Valley region of central Florida and the coast of North Carolina. About 86 percent of phosphate rock in the United States comes from these two areas. The phosphate rock deposits in Florida and North Carolina are unique because they are the only deposits that are rich in fossils. This is why the central Florida mining region is named Bone Valley. In this area, the deposits that contain phosphate rock are 12-15 feet thick and lay 15-30 feet beneath the surface.

Fossils from a phosphate mine in Polk County, Florida:


How is phosphate mined and processed?

The phosphate mining process in Florida is fairly simple. First, the mining company is required to obtain permits and have a reclamation plan. Years ago, mining pits were just left as they were and, over time, vegetation grew back and wildlife was able to return. Today, however, mining companies are required to actively rehabilitate the land. They must re-vegetate and make the land suitable for human use or wildlife habitat. Wetlands, however, must be completely restored to their original state. After permits are obtained and reclamation plans are approved, the land is cleared.

The next step of the mining process is to dig away the top 15-30 feet of soil. This layer is known as overburden. Early miners used wheelbarrows, picks, and shovels to do the mining. As technology progressed, mining processes transitioned from picks and shovels to mule drawn scrapers, then to steam dredges and barges, and finally to draglines. A dragline is a giant surface excavator with a large bucket that is pulled by a wire cable. The bucket on an average dragline holds between 40 and 80 cubic yards of material. In the early mining days it took an entire year to mine 15 acres, a job that can now be done with a dragline in one month.

Description: cat

Phosphate comes out of the ground in a mixture with equal parts sand and clay. This is known as the matrix. This matrix is dumped into a pit where high pressure water guns spray it to create slurry (slurry is just a mixture of water and particles…in this case phosphate matrix) that can be pumped to a processing plant where the phosphate is separated from the sand and clay.


Once the phosphate is separated from the sand and clay it is transported to another facility to be further processed. At this facility, sulfuric acid is used to convert the phosphate into phosphoric acid. The sulfuric acid that is needed to convert the phosphate rock into phosphoric acid is produced at the chemical processing plant using liquid (molten) sulfur. This process creates a significant amount of heat which most Florida phosphate companies capture and use to produce steam. The steam is used to produce the heat required to concentrate the phosphoric acid and also to produce electricity to run the plant. This allows the plants to be fairly self-sustaining and usually enables them to sell a significant amount of energy back to the power companies.

What are phosphates used for?

Phosphates are central to the structure of bones and teeth, to DNA (genetic material), photosynthesis in plants, many proteins, and for the transfer of energy within cells. Essentially, phosphates are central to all body functions, particularly nerve and brain cells and muscles. Because phosphorus is essential for all living organisms, phosphates are mined in order to obtain it for use in both agriculture and industry. Phosphates are naturally present in food and the minimum intake requirement for adults is approximately one gram per day. Although they are naturally present in food, phosphates are often added to many foods including, baked goods, cereals, cola drinks, pasta, meats and seafood. Phosphates are also added both to animal feeds and to certain baby foods to improve their nutritional value. In addition to being added to foods, phosphates can be found in IV fluids, vitamins, medicines, skin care products, cosmetics, and toothpaste.

A collection of products containing phosphates:


Agriculturally, phosphates are used as fertilizer. The main commercial use of phosphorus compounds for production of fertilizers is due to the need to replace the phosphorus that plants remove from the soil. As a result, approximately 90 percent of phosphates that are mined are used in the production of fertilizers.

The table below gives a good visual of the path phosphate takes from mining to consumption:

Description: Phosphate — A Simplified Flow Diagram


Image Sources:

3. Melanie Strate

6. Melanie Strate