Calcium (Fluoro, Chloro, Hydroxyl) Phosphate
Ca5(PO4)3(OH,F,Cl)
The color in apatite is often due to the presence of rare earth elements or by natural irradiation.
The History Says
The name apatite is from the Greek word to deceive because the gem varieties were often confused with other minerals. Previously apatite was used as a source of phosphate for fertilizer, but today mainly phosphorites are used.
The Present Scenario
Apatite is said to enhance one's insight, learning abilities and creativity, and to give increased self-confidence. It also is said to help achieve deeper states of meditation. Using apatite is said to facilitate the desired results when working with other minerals. Apatite is said to be usefull to help improve one's coordination and to strengthen muscles, and to help suppress hunger and ease hypertension.
APATITE AND ROCK PHOSPHATE are the two important minerals of phosphorous. Apatite is of two types:
| Chlorapatite | 3Ca3(PO4)2CaCl2 | - |
| Flour apatite | 3Ca3(PO4)2CaF2 | containing a small percentage of fluorine (3.8% max.) |
Theoretically, their percentage composition is as follows:
| Chlor-apatite | P2O5 41.0, CaO 53.8, Cl 6.8 = 101.6 |
| Fluor-apatite | P2O5 42.3, CaO 55.5, F 3.8 = 101.6 |
Apatite is of igneous origin and is found in veins. Rock phosphate cannot be strictly called a mineral, as it has no definite chemical composition. It is a secondary deposit formed due to the accumulation of organic remains, like bones and by replacement of limestone, calcite, etc., by phosphoric solutions to form a mixture of calcium phosphate. The rock phosphate is commonly termed as 'phosphate nodules' as it is found in nodular form. It is customary in the trade to give or indicium Phosphate of Lime (TPL). It is also termed as Bone Phosphate of Lime (BPL).
Apatite and rock phosphate are valued mainly for their phosphorous content. These minerals, are mostly utilized for the manufacture of fertilizers.
Phosphorous obtained from apatite and rock phosphate is utilized mainly for the manufacture of phosphoric acid (H3PO4) which in turn is utilized for the production of pure chemicals like sodium phosphate, monocalcium phosphate, fluorine-free dicalcium phosphate as animal food supplement.
Phosphate products are also used in pharmaceuticals, ceramics, silk, textiles, insecticides, sugar refining and in the manufacture of explosives.
Pure phosphorus has limited uses. It is of two types viz., white phosphorus and red phosphorus. White phosphorus, nearly insoluble in water, is slightly soluble in alcohol and certain organic liquids; it dissolves readily in carbon disulphide and in ammonia. At 34ºC, white phosphorous ignites spontaneously in air, evolving white fumes of phosphorus pentoxide (P2O5) which in turn combine with water to form orthophosphric acid (H3PO4). The melting point of white phosphorus is 44.1ºC, boiling point is 280ºC and sp. gr. 1.82.
Red phosphorous is a dark amorphous solid obtained by heating white phosphorus to 250ºC out of contact with air. It is used in match industry.
| Hardness | Associated Minerals | Chemical/Typical composition | Colour | characteristics | Luster | Field Indicators |
| 5 | hornblende micas nepheline calcite | CaO 55.07 % P2O5 41.82 % H2O 0.59 % Cl 2.32 % O 38.76 % F1 0.24 % | typically green but also yellow, blue, reddish brown and purple | An unusual "partially dissolved" look similar to the look of previously sucked on hard candy | vitreous to greasy and gumdrop | crystal habit, color, hardness and look. |
Manufacturing process
Superphosphate is manufactured by acidulating powder rock phosphate or apatite with dilute sulphuric acid (approximately of 70% strength) in fixed proportions and the resulting slurry is allowed to cure for about two weeks to reduce the free acid and finally bagged. The main idea behind the acidulation is to convert the insoluble tricalcium phosphate content of the mineral into water soluble mono calcium phosphate.
On an average, the consumption of raw materials for the manufacture of one tonne of superphosphate is as under:
- Rock Phosphate (P2O5; 27 to 34%) about 0.6 tonne.
- Sulphuric acid (100% purity) about 0.38 tonne equivalent to 0.132 tonne of sulphur.
Specifications
For the manufacture of superphosphate, industries generally prefer rock phosphate containing a minimum of 70% BPL, though upto 63-65% BPL is also being consumed. Presence of iron and alumina should be as low as possible as they unnecessarily consume too much of sulphuric acid and also cause reversion of water soluble phosphoric acid in superphosphate. Sulica should also be as low as possible.
For the manufacture of phosphoric acid by wet process, usually rock phosphate containing 30-32% P2O5 is required.
World Resources
The USA, North Africa, the USSR and the Pacific islands are the principal phosphate rock producing countries. Most of the countries in Europe and Asia depend upon imports of phosphatic minerals from these countries. The total world reserves of rock phosphate and apatite are estimated at 47,000 million tonnes.
USA
Florida, Tennessee and the discovered island, 64 km. off the California coast 182 metres deep midway between San Diego and San Clemente islands, are the important producing states. Florida is the largest producer in the world and produces nearly half the quantity of the total world production.
There are a series of phosphate deposits running from south of Salt Lake City in Utah, traversing Nevada, Idaho, Wyoming and Montana. They occur in two horizones, one of Mississippian age and the other of Permian age.
South America
Brazil - Rock Phosphate reserves are estimated at 250 million tonnes. Chile - Estimated apatite reserves are 4 million tonnes. Both guano and apatite are worked. The deposits are worked in Atacama and Coquimbo provinces. The average grade worked is 25% P2O5. The production of guano comes from Antofagasta and Tarapaca provinces worked by Sociedad Chilena de Fertilizantes.
North Africa
Morocco - Phosphate bed is found in sediments of the Eocene age for a distance of 320 km. between the Atlas Mountains to the east and the Atlantic coast in the west. The sediments are composed of shale, limestone and sandstone of marine origin. Phosphate occurs in limestone. The largest producing mine is the Khouribga (Kourigha). The phosphate rock from this mine is known as 'Morocco Phosphate' in trade, guaranteed to contain a minimum of 73% BPL. The thickness of the phosphate bed is 3 metres.
There is another mine at Louis-Gentil; the output from this mine is known as 'Safi Phosphate' with about 70% BPL guaranteed. The output of the Khouribga mine is sent to Casablanca port ant that of Louis Gentil to Safi port for export.
Algeria & Tunisia
Phosphate deposits of Eocene age occur on both sides of the border for a distance of 320 km. Mining is underground. The mineral worked is transported over cableways and narrow gauge railway owned by the mining company to Tebessa and transferred to the State railway for haulage to the port of Bone on the Mediterranean sea.
In Tunisia, the largest producing mines are at Moulares and Redeyef of the western extension of the deposits worked at Djebel Onk in Algeria. The bed varies in thickness from approximately 2 to 3 metres.
The phosphate deposits of Tunisia and Algeria are of a comparatively low grade which ranges from 58 to 66% BPL.