Arfosfaatit

Arfosfaatit, also known as alkali‑earth phosphates, are inorganic compounds composed of divalent alkali‑earth metals (such as calcium, magnesium, barium, strontium, or radium) bonded to the phosphate ion (PO₄³⁻). These salts form by a precipitation reaction between a soluble phosphate (e.g., ammonium phosphates or phosphoric acid) and a soluble carbonate or hydroxide of the alkali‑earth metal. The general formula is M₃(PO₄)₂ where M represents the alkaline earth cation.

Physical properties of arfosfaatit vary with the metal. Calcium phosphate, for instance, is a pale white solid with a density of about 3.15 g cm⁻³, while barium phosphate is bright yellow and less soluble in water. Most alkali‑earth phosphates have relatively low solubility in water, increasing the tendency to form solid precipitates. They crystallize in either cubic or orthorhombic lattice structures, depending on the specific metal.

In industrial contexts, calcium phosphate (Dicalcium phosphate) is widely used as a feed additive and as a component of phosphoric fertilizers. Magnesium phosphate serves as a source of magnesium in nutritional supplements and in some specialty glass compositions. Certain arfosfaatit are also used in the production of phosphate glasses and ceramics, where their crystalline structure imparts desirable optical or mechanical properties.

In biology, calcium and magnesium phosphates are key constituents of bone and teeth, forming hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) in vivo. Although arfosfaatit in bulk form are not present in living organisms, the inorganic chemistry of phosphate salts underlies many biological processes involving energy transfer and enzyme function.

Environmental aspects include the potential for phosphate runoff to cause eutrophication in aquatic ecosystems. Therefore, the handling, disposal, and regulation of arfosfaatit production and use are governed by environmental protection standards in many jurisdictions.

The study of arfosfaatit spans materials science, chemistry, and environmental science, offering insight into crystal chemistry, industrial processing, and ecological impacts.