Geology Home Page physical geology historical geology planetary gems
Roger Weller, geology instructor
by Melanie Strate
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.
Where are phosphates found?
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.
largest rock phosphate deposits in the United States are in what is called the
region of central
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.
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,
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:
3. Melanie Strate
4. http://online.wsj.com/articles/SB10001424052748703945904575645142173001212 6. Melanie Strate