PHOSPHATES

Export of these compounds is vital to the economies of Israel, Jordan, and Morocco.

Natural calcium phosphate deposits occur worldwide in the crust of Earth. Although the global phosphorous content is only 0.1 percent, in economically viable deposits it ranges between 26 percent and 38 percent, measured in phosphorous pentoxide, or P2O5. Many Arab countries produce phosphate rock for transformation into phosphoric acid and other complex fertilizers. These include Morocco, Algeria, Tunisia, Egypt, and Jordan, as well as Syria, and Iraq. Some other countries in the region are minor players in phosphate production and export. In 2000, the economic reserves of the main five producers were estimated at 7 billion tons, 1.6 billion tons, 267 million tons, 600 million tons, and 1.27 billion tons, respectively. These five countries provide close to half the world's production, which is mostly processed for use as agricultural fertilizers. Morocco produces the richest phosphate (32% P2O5 at Khouribga). Important Moroccan sites are Khouribga, Benguerir, Youssoufia, and Bougraa-Layoune in the Western Sahara. Algeria's phosphate reserves are located in the Constantine region, in the east of the country. At 15 percent P2O5, they are not as rich as Moroccan deposits. They were mined early by the colonial French, during the nineteenth century. A number of Algerian sites were abandoned or exhausted, including Djebel Dekna, Djebel Dyr. Four sites are still in production: M'zaita, Tocqueville, Bordj R'dir, and Kouif. Tunisia's phosphates contain 30 percent P2O5. Major production in Tunisia is in various sites in the Gafsa province, in the southwest, including Mdilla, Metlaoui, and Moulares. The quality of Egypt's phosphate is similar to Tunisia's. Abu Tartur, located 31 miles (50 kilometers) west of the Kharga Oasis in the Western Desert, is its major phosphate site. Jordan's phosphate is mined at Eshidyia, al-Hassa, al-Abyad, and al-Rusayfa. In these five countries, phosphate production, processing, and export represent an important component of economic output, and at the same time a serious source of industrial pollution. In 1998, fertilizer production accounted for $8.5 billion of the $13 billion chemical industry output in the Arab region.

Bibliography

Hamdi, Ali, and Ashkar, Shafik. "The Growing Capability of AFA Member Companies to meet Global Ferltilizer Demand." Arab Fertilizer Association, Egypt. Available from <www.fertilizer.org/ifa/publicat/PDF/1999_biblio_84.pdf>.

karim hamdy

Phosphates

Pure phosphorus is rare in nature. It usually combines with oxygen to form phosphate ions or groups (PO 3- 4 ). Phosphates are considered organic when phosphate groups attach to carbon atoms or inorganic when phosphate ions associate with minerals such as calcium. Organic phosphates provide the energy for most chemical reactions in living cells.

The weathering of rocks releases inorganic phosphorus into the soil, and plants take this up and convert it to organic phosphate in their tissue. Humans and animals eat the plants, and when they die, phosphorus is returned to the soil by the action of bacteria and then again taken up by plants. This is the so-called phosphorus cycle.

Phosphates are normally a limiting factor for aquatic plant growth. When large amounts of phosphorus enter water, for instance, from farm runoff containing fertilizer, plants can grow out of control. Concentrations as low as 0.01 milligrams per liter (mg/L) can greatly impact a stream. This overfeeding is called eutrophication and may cause an algae bloom. The algae eventually die and sink to the bottom. Bacteria feeding on the algae remove oxygen from the water for respiration. As oxygen levels become lower, animals that need high oxygen levels such as fish will die. This is especially a problem at night when no photosynthesis occurs to replenish the oxygen.

If organic oxygen levels drop sufficiently, aerobic organisms can no longer survive and anaerobic bacteria take over. The end products of anaerobic respiration may smell like rotten eggs, fishy, or wormy.

see also Agriculture; Fish Kills; Health, Environmental; Wastewater Treatment; Water Pollution.

internet resource

University of Maryland. "Impact of Phosphorus on Aquatic Life." Available from http://www.agnr.umd.edu/users.

Diana Strnisa

phosphates Phosphate is present in many sedimentary rocks as grains of apatite minerals (calcium phosphate). Rocks that are largely composed of phosphate (phosphorites) are less common but of economic importance as a resource for fertilizers. These phosphorites are formed either directly from a marine source or indirectly through biological uptake.

Marine deposits such as the Upper Cretaceous rocks of North Africa and the Middle East (a leading world resource) form in specific environments. Phosphate in the shallow photic zones is used up by marine organisms, but it will accumulate below this zone if oxygen is sufficiently depleted. This phosphate will form deposits if there is a low influx of sediments, particularly where there are upwelling currents of cold phosphate-rich waters. The phosphate replaces the carbonate in skeletons and lime mud; and phosphate in decaying organic matter can be liberated by bacterial decay. Together this phosphate accumulates as small nodules or crusts and can be seen forming on the ocean shelves today.

Biogenic phosphorites may form where phosphate-rich matter, such as bones, teeth, or excrement, is concentrated and cemented together or dissolved and later precipitated. Guano is made from seabird and bat droppings; it may be up to 30 m thick and is an economic resource in the eastern Pacific. These biogenic deposits may be cemented together into rocks or may be dissolved and re-precipitated within limestones as cements or as nodules.

N. Mann

Bibliography

Shelley, R. C. (1988) Applied sedimentology. Academic Press, London.
Tucker, M. E. (1981) Sedimentary petrology: an introduction. Blackwell Scientific Publications, Oxford

monazite , yellow to reddish-brown natural phosphate of the rare earths , mainly the cerium and lanthanum metals, usually with some thorium . Yttrium, calcium, iron, and silica are frequently present. Monazite sand is the crude natural material and is usually purified from other minerals before entering commerce. Monazite occurs in North Carolina, South Carolina, Idaho, Colorado, Montana, and Florida in the United States, and in Brazil, India, Australia, and South Africa. It is an important source of cerium, thorium, and other rare-earth metals and compounds.

monazite Mineral (Ce,La,Y,Th)PO₄; sp. gr. 4.9–5.4; hardness 5.0–5.5; monoclinic; clove-brown to reddish-brown to orange and green; off-white streak; resinous to waxy lustre; crystals small, short, prismatic to tabular grains, with larger crystals showing striated faces; cleavage imperfect basal monoclinic; found extensively as an accessory mineral in granites and pegmatites, in gneisses and carbonatites, and concentrated in alluvial sands and placers. It is used as a source of cerium, thorium, and other rare-earth metals and compounds.

phosphates Rock or deposit made up largely of inorganic phosphate, commonly calcium phosphate (e.g. the minerals apatite, autunite, monazite, pyromorphite, torbernite, turquoise, vivianite, and wavellite).

phosphates Salts of phosphoric acid; the form in which the element phosphorus is normally present in foods and body tissues. See also polyphosphates.