Editing Phosphorus (section)

===Processing===
Most phosphorus-bearing material is for agriculture fertilisers. In this case where the standards of purity are modest, phosphorus is obtained from phosphate rock by what is called the "wet process." The minerals are treated with sulfuric acid to give [[phosphoric acid]]. Phosphoric acid is then neutralised to give various phosphate salts, which comprise fertilisers. In the wet process, phosphorus does not undergo redox.{{r|Geeson2020}} About five tons of [[phosphogypsum]] waste are generated per ton of phosphoric acid production. Annually, the estimated generation of phosphogypsum worldwide is 100 to 280 Mt.{{r|Tayibi2009}}

For the use of phosphorus in drugs, detergents, and foodstuff, the standards of purity are high, which led to the development of the thermal process. In this process, phosphate minerals are converted to white phosphorus, which can be purified by distillation. The white phosphorus is then oxidised to phosphoric acid and subsequently neutralised with a base to give phosphate salts. The thermal process is conducted in a [[Submerged-arc furnace for phosphorus production|submerged-arc furnace]] which is energy intensive.{{r|Geeson2020}} Presently, about {{convert|1000000|ST|lk=on}} of elemental phosphorus is produced annually. [[Calcium phosphate]] (as [[Phosphorite|phosphate rock]]), mostly mined in Florida and North Africa, can be heated to 1,200–1,500&nbsp;°C with sand, which is mostly {{chem2|SiO2}}, and [[Coke (fuel)|coke]] to produce {{chem2|P4}}. The {{chem2|P4}} product, being volatile, is readily isolated:{{r|Shriver2010}}

:{{chem2|4 Ca5(PO4)3F + 18 SiO2 + 30 C -> 3 P4 + 30 CO + 18 CaSiO3 + 2 CaF2}}
:{{chem2|2 Ca3(PO4)2 + 6 SiO2 + 10 C -> 6 CaSiO3 + 10 CO + P4}}

Side products from the thermal process include [[ferrophosphorus]], a crude form of {{chem2|Fe2P}}, resulting from iron impurities in the mineral precursors. The silicate [[slag]] is a useful construction material. The fluoride is sometimes recovered for use in [[water fluoridation]]. More problematic is a "mud" containing significant amounts of white phosphorus. Production of white phosphorus is conducted in large facilities in part because it is energy intensive. The white phosphorus is transported in molten form. Some major accidents have occurred during transportation.{{r|ERCO}}