There are two ways in which phosphoric acid can be produced. The first is the wet process, where a phosphate-containing mineral such as calcium hydroxyapatite is treated with sulfuric acid. This produces phosphoric acid along with calcium sulphate precipitate.
The second approach is called thermal process. Pure phosphorus reacts with air to give phosphorus pentoxide. This on reaction with water , produces phosphoric acid. This method allows heat to be recycled and reused.
Salts of phosphoric acid:
One or more of hydrogen atoms from phosphoric acid gets replaced by a positive ion and forms salts. These are ammonium, calcium and sodium salts of phosphoric acids. These salts are widely used in several industries.
Ammonium phosphates- Monoammonium dihydrogenphosphate and diammonium hydrogenphosphate are much used as fertilizers and are made by mixing the correct proportions of phosphoric acid with anhydrous ammonia in a rotating drum.
Calcium phosphates – The calcium phosphates are used extensively as fertilizers. Superphosphate and triple superphosphate are the two salts of phosphoric acid that are widely used in fertiliser industry.
Sodium phosphates- Monosodium dihydrogenphosphate, Disodium hydrogenphosphate, Trisodium phosphate and Disodium pyrophosphate are some of sodium salts of phosphoric acids.
Health and Safety:
Products such as soft drinks that contain phosphoric acid pose no threat to human health in general. At moderate concentrations phosphoric acid solutions are irritating to the skin. Contact with concentrated solutions can cause severe skin burns and permanent eye damage.