Phosphate Ore

a natural mineral formation that contains phosphorus and phosphorus compounds in such concentrations that make it technically and economically feasible to process the ore in order to obtain phosphorus-containing products, such as mineral fertilizers, phosphate mineral supplements, and phosphate salts, for various industries. The major useful component of phosphate ore is phosphorus in the form of the phosphoric anhydride P₂O₅. The P₂O₅ content in phosphate ores varies from 2–6 to 25–34 percent, depending on the processing behavior, mining and geological conditions, and other factors.

Phosphate ores are divided into two major groups of natural formations—phosphorites and apatites. Less often, aluminum phosphates, iron phosphates, and guano serve as phosphate ores. The major components of phosphate ores are the apatite phosphate minerals, the most common of which are fluorapatite (in endogenous apatite deposits) and carbonate apatite and its modifications, francolite and kurskite (in exogenous phosphorite deposits); hydroxylapatite sometimes occurs in significant amounts.

In addition to phosphate minerals, phosphate ores also contain other minerals, which sometimes prove to be valuable by-products, for example, nepheline, sphene, titanomagnetite, magnetite, aegirine, and, as isomorphic impurities, strontium and rare-earth and rare elements. Phosphate ores may also contain harmful impurities, such as dolomite, calcite, quartz, chalcedony, glauconite, clay minerals, pyrite, and iron hydroxides.

A distinction is made between endogenous and exogenous phosphate ores on the basis of origin. Endogenous deposits include (1) magmatic (late magmatic) deposits, which occur as sheet and lenticular deposits of complex apatite ores associated with nepheline syenites (for example, at the Khibiny deposits in the USSR), and (2) carbonatite (magmatic and metasomatic) deposits related to ultrabasic alkaline masses (for example, the Kovdor and Vostochnyi Saian deposits in the USSR of complex apatite ores in the form of stocks and stockworks). Exogenous deposits include (1) chemical and biochemical sediments of ancient shelves in the form of phosphorites interbedded with carbonate-siliceous, terrigenous glauconite, and other sedimentary complexes (the Karatau, Egor’evsk, and Chilisai deposits in the USSR) and (2) residual and infiltration deposits formed as a result of the erosion of apatite- and phosphorite-bearing rocks, usually of carbonate composition, and which are regolithic (the Kovdor, Vostochnyi Saian, Belkino, and Telek deposits in the USSR).

Phosphate ores are worked by open-pit and underground-mining methods: friable phosphorites, such as those in the Baltic republics, are worked by geotechnological methods.

Various methods for concentrating phosphate ores exist, and the selection of a particular method depends on the mineral composition and the structure and texture of the ore. Apatite ores (for example, the ores of the Khibiny deposit) are concentrated by flotation, which yields a high quantity of a rich apatite concentrate (39.4 percent P₂O₅). Phosphorites (for example, the Egor’-evsk, Chilisai, and Viatka-Kama deposits in the USSR and deposits in Florida and North Carolina in the USA) are concentrated by sieving; the primary concentrate obtained is subjected to further concentration by flotation, magnetic separation, or calcination; the last method is finding increasing use. Some phosphate ores are not subjected to concentration before use, for example, those used in the electrothermal production of yellow phosphorus and thermal phosphoric acid.

The total world reserves of phosphate ores, excluding the socialist countries, are estimated (1974) at 81 billion tons (or about 18–19 billion tons of P₂O₅). Most of the reserves are located in Morocco (40 billion tons) and the United States (14.75 billion tons). Considerable reserves are found in Australia (2.5 billion tons), Tunisia (1.2 billion tons), the Western Sahara (3.0 billion tons), Peru (1.5 billion tons), and Algeria (1.0 billion tons).

The estimated reserves of phosphate ores in the USSR total (1976) 10.3 billion tons (or 1.3 billion tons of P₂O₅), including 5.4 billion tons of apatite (0.6 billion tons of P₂O₅) and 4.9 billion tons of phosphorite (0.7 billion tons of P₂O₅). Large deposits of phosphate ores have been found in the Mongolian People’s Republic (Khubsugul deposit), in Vietnam (Lao Cai deposit), and in China.

The annual world production of phosphate ores in 1974 was 110.8 million tons, of which 41.5 million tons was produced in the USA, 19.7 million tons in Morocco, 3.9 million tons in Tunisia, 2.6 million tons in Togo, 1.9 million tons in Senegal, 1.6 million tons in Jordan, and 1.5 million tons in the Republic of South Africa.