**7.3.1. Cycle of phosphorus**

is believed that rainwater can carry soluble phosphate from guano and trickle over rocks, where phosphate interacts to form phosphatic layers, e.g. phosphatized coral rock. Bird guano, mainly from Peru, achieved the greatest importance in about the middle of the 19th century, shortly before the phosphate rock industry began to

furnaces operating on iron ores with significant content of phosphorus. Basic slag contains tetracalcium phosphate (Ca3(PO4)2·CaO) and silicocarnotite (Ca3(PO4)2·Ca2SiO4), which are applied directly as fertilizers. Recorded world

contains not only substantial amounts of phosphorus in soluble organic form but also calcium and microelements. Ground (bone meal) or calcined and ground (bone ash)

**ii. Basic slag** [25]: is a minor source of phosphorus. This waste is the product from blast

**iii. Meat and bone meal (MBM) or bone ash** [25],[68]: as an animal byproduct, MBM

Other important commercial sources of phosphorus are casein and lecithin. Casein is ob‐

Weathering (**Section 7.3.2**) leads to the formation of enriched residual and replacing depos‐ its from phosphatic deposits not otherwise minable. The Tennessee "brown rock" phosphate deposits consist of nowadays residuum developed through the decomposition of phosphatic limestones of Ordovician age. The "river pebble" deposits prominent in early history of phosphate mining in Florida and South Carolina are mostly placers formed by alluvial concentration of phosphatic pebbles eroded from the phosphatic formations of adjacent

The Tennessee "white rock" and Florida "hard rock" deposits were formed by the redeposi‐ tion of phosphate derived from the decomposition of apatite under more advanced weather‐ ing. The same decomposition-phosphatization process accounts for the formation of calcium aluminum phosphate and aluminum phosphate in the "leached zone" of the Bone Valley field

As was described above, the number of different elements can substitute into the structure of

anion and cation sites. This means that apatite can be used as an indicator of planetary halogen compositions. The quantitative ion microprobe measurements of apatite from lunar basalts showed that portions of the lunar mantle and/or crust are richer in volatile species than

and this mineral can contain a number of trace elements by the substitution in both

production is mainly from France, Germany and Luxembourg.

bones were recognized as a source of phosphorus at an early date.

tained from bovine milk. Lecithin was extracted from soy bean oil [25].

356 Apatites and their Synthetic Analogues - Synthesis, Structure, Properties and Applications

and deeply weathered Cretaceous and Eocene deposits of west Africa [27].

25 The tools based on the isotope composition of apatite were already described in **Section 6.5**.

establish itself.

**7.2.3. Phosphorite weathering derivates**

**7.3. Geological role of apatite**

terrain [27].

apatite,25

previously thought [4].

In the Earth's crust, phosphorus takes the second place after carbon, and in comparison with all known elements, it takes about 12th place in natural abundance [25]. The phosphorus cycle is quite different from the nitrogen and sulfur cycles in which phosphorus is present in only one oxidation state and it forms no gases stable in biosphere or atmosphere. Also, in contrast to nitrogen and sulfur, substantial proportions of phosphorus in soil appear in inorganic form [76],[77].

About 10 Mt of phosphorus are released by weathering of apatite annually. In soil, monoba‐ sic (H2PO4 <sup>−</sup> ) and dibasic (HPO4 2−) phosphates are generally available to plants. Phosphates are precipitated by calcium in alkaline soils and most of phosphate is adsorbed on alumi‐ num and iron oxides in acidic soils. Phosphates are most readily available in slightly acidic to neutral soil. Much of such phosphorus in surface soils appears in organic matter. This phosphorus is used repeatedly by recycling in plants and organisms that decompose the plant detritus. Little amount of phosphorus is lost by leaching through soils, but the erosion losses of soil particles and the plant detritus carried off to aquatic systems may be substantial [76].

**Fig. 11.** Major natural cycle of phosphorus (a) and the contribution of the man to the cycle (b) [78].

The availability of phosphorus is a major factor limiting the biomass production in both terrestrial and aquatic ecosystems. Mycorrhizas are efficient scavengers of phosphorus for plants growing in soils with limited availability of this element. The phosphorus fertilization in agricultural lands can have detrimental effect, as it increases phosphate amounts in the runoff soil resulting in the accumulation of phosphate in aquatic plants and algal growth. If the decomposers of plants and algae use practically all oxygen from water, the habitat becomes unsuitable for fish and other aquatic animals. The process of abundant nutrient-induced biomass production in lakes and rivers and its decay to deplete the water oxygen is called the eutrophication [25],[76],[78].

Despite the advantage for which phosphorus is used, it is doubtful that man has significant contribution to the Earth's cycle of phosphorus (**Fig. 11**). The 2·109 tons of mined phosphate rock is less than 0.15% of known reserves of phosphorus ore and less than 1·10−5% of the Earth's cycle of phosphorus [78].

At least 100 millions years before humankind exerted any influence on the cycles of phospho‐ rus, the pattern had already been established (**Fig. 12**). Phosphorus was continuously leached from igneous rocks as the rocks were weathered to sedimentary deposits and this released phosphorus flowed to the seas, which had long since become saturated with phosphorus. Each new addition causes a similar quantity of phosphorus to precipitate as sediment. If the

**Fig. 12.** The establishment of the Earth's cycle pattern of phosphorus [78].

are precipitated by calcium in alkaline soils and most of phosphate is adsorbed on alumi‐ num and iron oxides in acidic soils. Phosphates are most readily available in slightly acidic to neutral soil. Much of such phosphorus in surface soils appears in organic matter. This phosphorus is used repeatedly by recycling in plants and organisms that decompose the plant detritus. Little amount of phosphorus is lost by leaching through soils, but the erosion losses of soil particles and the plant detritus carried off to aquatic systems may be substantial [76].

358 Apatites and their Synthetic Analogues - Synthesis, Structure, Properties and Applications

**Fig. 11.** Major natural cycle of phosphorus (a) and the contribution of the man to the cycle (b) [78].

contribution to the Earth's cycle of phosphorus (**Fig. 11**). The 2·109

eutrophication [25],[76],[78].

cycle of phosphorus [78].

The availability of phosphorus is a major factor limiting the biomass production in both terrestrial and aquatic ecosystems. Mycorrhizas are efficient scavengers of phosphorus for plants growing in soils with limited availability of this element. The phosphorus fertilization in agricultural lands can have detrimental effect, as it increases phosphate amounts in the runoff soil resulting in the accumulation of phosphate in aquatic plants and algal growth. If the decomposers of plants and algae use practically all oxygen from water, the habitat becomes unsuitable for fish and other aquatic animals. The process of abundant nutrient-induced biomass production in lakes and rivers and its decay to deplete the water oxygen is called the

Despite the advantage for which phosphorus is used, it is doubtful that man has significant

rock is less than 0.15% of known reserves of phosphorus ore and less than 1·10−5% of the Earth's

At least 100 millions years before humankind exerted any influence on the cycles of phospho‐ rus, the pattern had already been established (**Fig. 12**). Phosphorus was continuously leached from igneous rocks as the rocks were weathered to sedimentary deposits and this released phosphorus flowed to the seas, which had long since become saturated with phosphorus. Each new addition causes a similar quantity of phosphorus to precipitate as sediment. If the

tons of mined phosphate

precipitate formed when an island sea had invaded a land area, the new sediment became landlocked. The new landlocked sedimentary deposits are more easily leached than igneous rocks from which they are derived. When the seas recede sufficiently to expose the new sediments to the greater solvent action of fresh water, the sediments begin to weather and the cycle is complete. Best estimates of the cycle time of phosphorus in the oceans today are in the range of 50,000 years. This is a short period compared to 3·109 years, which were required for the saturation of oceans for the first time [78].

**Fig. 13.** Natural and artificial cycles of phosphorus [25].

Recently, man has only a slightly stronger influence on the total amount of the Earth's phosphorus than his prehistoric ancestors. If man made a significant alteration in the cycles of phosphorus, it had an impact on the cycles of fresh surface waters. The detergent phos‐ phates have been blamed for degrading freshwater lakes and there is no doubt that several lakes have been overabundant with phosphates and sewage. Sewage treatment will alleviate most of the problems associated with point-source loading of lakes [78].

The overall natural and artificial cycles involving phosphorus are introduced in **Fig. 13**.
