Phosphorus feeds every living thing, and nothing can replace it — but it arrives locked in rock that plants can't take up. Unlocking it with acid is the easy part; the waste, and the geography, are not.
Nine parts in ten grow the world's food. The rest turns up around the house — in the kitchen, the bathroom, even the extinguisher on the wall.
The whole journey
Making phosphate fertiliser is really one trick repeated: take a rock a plant can't use, and change its chemistry until it can. Sulphuric acid dissolves the rock into phosphoric acid; ammonia turns that acid into a dry, storable salt. Tap any step to see what happens.
Three raw materials. The rock holds the phosphorus, sulphuric acid frees it, and ammonia turns it into something a plant can take up — the phosphoric acid in between isn't bought in, the plant makes it from the first two.
A bag of phosphate fertiliser looks like a mineral, but most of it was built in a chemical plant. The starting point is genuine rock; almost everything after that is there to change the rock's chemistry so a root can absorb it.
The phosphorus. Sedimentary apatite, roughly 30–35% P₂O₅, and almost insoluble in water. It also carries fluorine and traces of cadmium and uranium (USGS, 2026).
The unlocker — the single biggest thing a phosphate plant consumes. It dissolves the rock so the phosphorus can be pulled out. See how sulphuric acid is made →
The nitrogen. It turns runny phosphoric acid into a solid salt and doubles the fertiliser as a nitrogen source — though as a Haber–Bosch product, it is itself one of the pricier inputs. See how ammonia is made →
Almost everything starts by dissolving rock in acid. What you add next decides whether you get fertiliser, a food additive or weedkiller.
Over nine-tenths of mined rock takes this path. Sulphuric acid digests the rock to phosphoric acid; ammonia then converts that acid into a solid, high-grade salt such as MAP or DAP. It is cheap, continuous and forgiving of impurities — which is why it dominates. The five interactive steps above walk through it end to end.
A small share of rock skips the acid entirely. Smelted with coke and sand near 1,500 °C, it gives off pure phosphorus vapour; burned to phosphorus pentoxide and hydrated, that yields a very pure phosphoric acid — clean enough for colas, food, electronics and the weedkiller glyphosate. The catch is electricity: the furnace is among the most power-hungry processes in heavy chemistry.
There is also an older shortcut still in use. React rock with sulphuric acid and simply stop — don't separate anything — and you get single superphosphate (0-20-0), the first manufactured fertiliser, patented in 1842. Swap the sulphuric acid for phosphoric acid and you get the stronger triple superphosphate (0-46-0).
The code on a fertiliser bag — 18-46-0 — is just the recipe: how much nitrogen, phosphorus and potassium it carries.
Phosphate "salts" are simply what you get when phosphoric acid is neutralised by different bases — ammonia, lime, soda. Which base you use sets the grade and the job. By long convention the phosphorus is measured as "P₂O₅": the number on the bag is phosphorus reported as if it were the oxide, even though the salt contains none.
The three numbers are always percentages of N, P₂O₅ and K₂O, in that order — here, DAP.
| Salt | Grade (N-P₂O₅-K₂O) | What it is / where it goes |
|---|---|---|
| DAP | 18-46-0 | Diammonium phosphate — the world's most-used P fertiliser, and the price benchmark |
| MAP | 11-52-0 | Monoammonium phosphate — the highest-phosphate granule; a common starter fertiliser |
| TSP | 0-46-0 | Triple superphosphate — a calcium phosphate carrying no nitrogen |
| SSP | 0-20-0 | Single superphosphate — the 1842 original; lower grade, but carries sulphur |
| MCP / DCP | — | Mono- and di-calcium phosphate — animal feed and baking powder |
| Sodium phosphates | — | Detergents, processed-food emulsifiers, water treatment |
| Food-grade acid | — | Purified phosphoric acid — soft drinks, food, electronics |
Once you know how phosphate fertiliser is made, the next surprise is where the raw phosphorus actually comes from.
One country holds two-thirds of the rock the world will ever mine — and the biggest maker of the finished salts is a different country again.
China alone mines nearly half the world's rock; Morocco mines far less, but holds most of the reserves.
Marketable phosphate rock, gross weight. USGS Mineral Commodity Summaries 2026.
China, Morocco, the US and Russia lead the mining of the rock itself.
China is the largest producer of phosphoric acid and fertilisers; Morocco's OCP is the largest exporter. Only about a tenth of phosphoric acid is ever traded — most is used where it's made.
Demand growth is led by Asia and South America, close to where new mining capacity is being built.
50 of 73 billion tonnes of world reserves (USGS 2026, derived); the rest is shared between China, Egypt, Tunisia, Russia and others. Reserves are not scarce in total — the fragility is geographic.
The USGS reports the world's phosphate reserves under "Morocco", with no separate line for Western Sahara, so this page does the same. One of Morocco's mines — Bou Craa — lies in Western Sahara, a disputed territory administered by Morocco. By the USGS's own country reporting that deposit holds around 800 million tonnes, roughly 2% of the combined reserve base, so the great majority of the 68% sits in Morocco proper. Different organisations describe the territory differently; this page follows the USGS figures.
Both the United States and the EU now treat this concentration as a strategic risk. Phosphate rock was added to the US critical-minerals list in November 2025, and the EU lists both phosphate rock and phosphorus as Critical Raw Materials.
The same element that grows our food chokes our lakes when it escapes — and we mostly throw it away after a single pass through a plant.
The waste mountain. Every tonne of P₂O₅ from the wet route comes with roughly five tonnes of phosphogypsum — the exact figure shifts with the rock and the process. Because the parent rock is faintly radioactive, with traces of uranium and radium riding along, most of it can't be sold or reused. Billions of tonnes now sit in stacks worldwide, growing by well over a hundred million tonnes a year.
The runoff. Phosphorus that misses the crop runs off into rivers and seas, where it feeds algal blooms and the low-oxygen "dead zones" that follow. Phosphorus is one of the planetary limits scientists judge humanity to have already crossed.
The impurities. The same rock carries cadmium into soils — enough that the EU has argued over legal limits in fertiliser.
The concentration. There is no substitute for phosphorus, and the reserves sit largely in one place. That is why both the EU and the US now class it as critical.
Stacked per tonne of P₂O₅, and mostly unused — a waste stream still looking for a market.
Struvite recovered from wastewater is about as rich in phosphate as triple superphosphate; Switzerland and Austria now require recovery.
Cleaner rock or de-cadmiation against a fixed limit — a sourcing choice, not a settled one.
The obvious answer is to stop treating phosphorus as disposable — to recover it rather than mine it fresh. But recovered phosphorus still meets only a fraction of demand, and mined rock stays cheaper. For now the world keeps digging, and keeps stacking the gypsum.