Introduction to Phosphoric Acid

Phosphoric acid (H3PO4) is an important inorganic acid and an important intermediate product in the production of fertilizer industry. It is used to produce high concentration phosphate fertilizers and compound fertilizers. Phosphoric acid is also a raw material for various phosphates and phosphate esters used in soap, detergents, metal surface treatment agents, food additives, feed additives, and water treatment agents. As a raw material for phosphate fertilizer production, it is an aqueous solution of orthophosphate or polyphosphate.

The concentration of commercial orthophosphate is generally 52% to 54% P2O5, and polyphosphate is a mixed aqueous solution of orthophosphate and polyphosphate with different degrees of polymerization. Polyphosphate includes pyrophosphate (H4P2O7), triphosphate (H5P3O10), and long-chain polyphosphate. The general formula for polyphosphate can be written as Hn+2PnO3n+1 (an integer with n ≥ 2).

It has acidic properties, and its acidity is weaker than sulfuric acid, hydrochloric acid, nitric acid, but stronger than acetic acid, boric acid, etc. Soluble in water and ethanol, when heated to 213 ℃, it loses some water and transforms into pyrophosphate; When heated to 300 ℃, it loses one molecule of water and further transforms into metaphosphate (HPO3). Has hygroscopicity and can absorb moisture from the air. Corrosive to the skin, with a high allowable concentration of 1mg/m3 in the air.

The main raw materials for phosphoric acid are phosphate rock and inorganic acids (sulfuric acid, hydrochloric acid or nitric acid, mainly sulfuric acid). Natural phosphate ore can be divided into two categories: apatite and phosphate rock, both of which are mainly composed of calcium fluorophosphate [Ca10F2 (PO4) 6].

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