phosphate rock

phosphorite

[fos-fuh-rahyt]
or phosphate rock

Rock with a high concentration of phosphates in nodular or compact masses. The phosphates may be derived from a variety of sources, including marine invertebrates that secrete shells of calcium phosphate and the bones and excrement of vertebrates. Typical phosphorite beds contain about 30percnt phosphorus pentoxide (P2O5) and constitute the primary source of raw materials for phosphate fertilizers. Significant deposits in the U.S. include the Phosphoria Formation in Idaho and the Monterey Formation in California. Major deposits also occur in the Sechura Desert in Peru.

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Phosphate rock or phosphorite is a general description applied to several kinds of rock which contain significant concentrations of phosphate minerals, which are minerals that contain the phosphate ion in their chemical structure.

Many kinds of rock contain mineral components containing phosphate or other phosphorus compounds in small amounts. However, rocks which contain phosphate in quantity and concentration which are economic to mine as ore for their phosphate content are not particularly common. The two main sources for phosphate are guano, formed from bird droppings, and rocks containing concentrations of the calcium phosphate mineral, apatite.

The United States is the world's leading producer and consumer of phosphate rock, which is used to manufacture phosphate fertilizer and industrial products.

China, the United States and Morocco are the world's largest miners of phosphate rock, each producing about a quarter of the total world production. Other countries with significant production include Brazil, Russia, Jordan and Tunisia. Historically, large amounts of phosphates were obtained from guano deposits on small islands such as Nauru, Banaba and Christmas Island, but these sources are now largely depleted.

Phosphate rock is mined, beneficiated, and either solubilized to produce wet-process phosphoric acid, or smelted to produce elemental phosphoric acid or smelted to produce elemental phosphorus. Phosphoric acid is reacted with phosphate rock to produce the fertilizer triple superphosphate or with anhydrous ammonia to produce the ammonium phosphate fertilizers. Elemental phosphorus is the base for furnace-grade phosphoric acid, phosphorus pentasulfide, phosphorus pentoxide, and phosphorus trichloride. Approximately 90% of phosphate rock production is used for fertilizer and animal feed supplements and the balance for industrial chemicals.

For general use in the fertilizer industry, phosphate rock or its concentrates preferably have levels of 30% phosphorus pentoxide (P2O5), reasonable amounts of calcium carbonate (5%), and <4% combined iron and aluminium oxides. Worldwide, the resources of high-grade ore are declining, and the beneficiation of lower grade ores by washing, flotation and calcining is becoming more widespread.

References

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