Natural Phosphates

Phosphates, Natural

 

a class of minerals of the salts of orthophosphoric acid, H3PO4, with highly variable composition. There are about 180 phosphate minerals; middle salts, for example, xenotime, Y[PO4], and monazite, are rare. Natural phosphates are primarily complex compounds with two or more cations [for example, Ca2+, Fe2+, Fe3+, Al3+, (UO2)2+, Cu2+, Mn2+, Pb2+, and Zn2+] and additional anions (OH, Cl, F, O2–, CO32 –) or molecular water. Their composition rarely includes acid radicals, such as [SO4]2–, [SiO4]2–, and [BO3]3–. Certain natural phosphates are acid salts of the type resembling monetite, CaHPO4.

The basic crystal structure of natural phosphates consists of insular [PO4]3– tetrahedral units attached to one another by salt-forming cations. According to the nature of the spatial distribution of the attached [PO4]3– tetrahedrons and cation polyhedra, natural phosphates are classified as insular (predominant type), chain, layered, or skeletal.

Natural phosphates occur in the form of massive granular aggregates, earthy masses, oolites, concretions, and incrustations; they sometimes occur in the form of faceted crystals. The coloration is varied. Natural phosphates have a Mohs’ hardness ranging from 2 (for many aqueous natural phosphates) to 5–6 and a density ranging from 1,700 to 7,100 kg/m3.

Natural phosphates are generally disseminated in rocks. The most widely distributed minerals of practical value are apatite (also a constituent of phosphorites), torbernite, autunite, vivianite (Fe2+, Fe3+)[PO4]8H2O, monazite, xenotime, amblygonite LiAl[PO4](F,OH), and turquoise.

Natural phosphates are primarily formed in the upper part of the earth’s crust—on ocean and lake bottoms, in swamps, in soils, and in weathering crusts—as well as in the oxidation zone of many ore deposits. Some natural phosphates are of magmatic origin, for example, apatite associated with alkaline igneous rocks and monazite and xenotime associated with pegmatites and granites. A number of natural phosphates occur as accessory minerals in hydrothermal veins.

Natural phosphates are used as phosphate ores (apatite and phosphorite). Some natural phosphates have a more limited application; for example, vivianite is used as an inexpensive blue pigment and local phosphorus fertilizer, monazite as a source of rare earths and thorium, amblygonite as a lithium ore, and turquoise as an ornamental stone.

REFERENCES

Godovikov, A. A. Mineralogiia. Moscow, 1975.

G. P. BARSANOV and A. I. PEREL’MAN

References in periodicals archive ?
(2009), in which the increase in the efficiency of reactive natural phosphates associates to the reduction in the pH of the soil.
In this manner, the reactive natural phosphate (phosphate rock) might be an alternative in the fertilization of forage grasses, reducing the phosphorus fixation through its slow solubilization, besides reducing the cost of the phosphate fertilization.
A possible manner of utilizing the reactive natural phosphate after liming is through associating this fertilizer with the nitrogen fertilization.
Thus, phosphate fertilization management along with liming and the combination of soluble and natural phosphates favor absorption efficiency and increase production in agricultural crops (Oliveira et al., 2007; Too et al., 2014; Costa et al., 2016).
To isolate the effect of the application of natural phosphates on crop dry matter production, the Agronomic Efficiency Index (AEI) of the natural phosphate (NP) was calculated based on the dry matter content obtained in the control (zero dose), using the following equation (Eq.
Natural phosphates are equivalent to soluble phosphates regarding the accumulated production over various cycles.
They demonstrated that the degradation of SPP by natural phosphates in freshly ground pork contributes to its ineffectiveness against L.
Other gardeners, knowing the ignorance of using artificial fertilizers, spread bags of crushed rock powders, natural phosphates and other soil amendments, relying on the natural minerals, while many older gardeners just add mulch each year and state that any tillage of their garden is unnecessary.
Natural phosphates and thermophosphates have great potential for agricultural use, becoming more efficient in acidic environments with [H.sup.+] supply and long cycle cultures (Souza et al., 2007).
By precomposting, the fermentation was eliminated, allowing the colonization of the earthworms aiming the solubilization of the natural phosphates. The chemical characteristics of the manure are described in Table 1.
However, these studies do not mention the use of natural phosphates. Most studies on phosphate fertilization have been conducted using seedlings (Prates et al., 2012) or in combination with salinity and in pot conditions (Souza et al., 2012).
The viability of these sources is related to the existence of large deposits of natural phosphate, with low cost (Silva et al., 2012), associated with its compensatory residual effect, compared with soluble phosphates (Resende et al., 2006).