AEEP | Mineral

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Phosphate rock is obtained from geological deposits. Its primary constituent is apatite, a calcium phosphate mineral. There are different sources of phosphate rock. The most common one is sedimentary marine deposits while the other is igneous deposits. Phosphate rock is the basis material for almost all phosphate fertilizers, either as such or transformed into phosphoric acid. Phosphate rock from sedimentary origin contains lower phosphate than phosphate rock from igneous origin (29% vs. 36%). However, it has a soft structure which confers a high reactivity to the contrary of phosphate rock from igneous origin whose structure is much harder. When added to the soil, phosphate rock slowly dissolves and gradually releases its nutrients. This happens only in slightly acidic soils and if the rock is soft enough. This product is usually used to recharge the pool of phosphorus in soils.

Single superphosphate (SSP) used to be the most common mineral fertilizer. It is produced by addition of sulfuric acid to natural phosphate rock. SSP contains both monocalcium phosphate and gypsum for a P2O5 content between 16 to 20%. By the addition of sulfuric acid in the manufacturing process, the phosphate is solubilized, which makes it readily available to plants. SSP is advantageous on an agronomic point of view as it also provides sulfur and calcium, which are secondary nutrients.

Triple superphosphate (TSP) is produced by addition of liquid phosphoric acid to natural phosphate rock. It has a very high level of P2O5 (45%) and also contains a significant level of calcium (15%). TSP is the fertilizer material that has the highest content of phosphorus without nitrogen and over 90% of its phosphate content is soluble. When dissolving in the soil, TSP generates an acidic environment. TSP is interesting for fertilization of leguminous crops that don’t necessarily need nitrogen on top of biological nitrogen fixation.

Monoammonium phosphate (MAP) (chemical formula NH4HPO4) is a water soluble ammonium salt produced by reaction of phosphoric acid with ammonia (ratio 1:1). It contains two of the three primary nutrients for plants: nitrogen and phosphate. Typical composition is 11% N, 52% P2O5. In a granular form MAP dissolves rapidly in soil when there is sufficient moisture. It generates a moderate acidity in the solution surrounding the granule, which makes it very suitable for soils with a neutral or high pH.

Diammonium phosphate (DAP) (chemical formula (NH4)2HPO4) is a water soluble ammonium salt produced by reaction of phosphoric acid with ammonia. It contains two of the three primary nutrients for plants: nitrogen and phosphate. Typical composition is 18% N, 46% P2O5. The nutrient content in DAP is relatively high compared to other materials which makes it one of the most common fertilizer component and is widely used in Europe. When dissolving, DAP creates an alkaline pH around the granule. This is a temporary situation as the ammonium will be converted to nitrate by soil bacteria and the pH of the soil will subsequently reduce.

Nitrophosphates are produced by reaction of nitric acid with phosphate rock. The reaction generates phosphoric acid, calcium nitrate and hydrofluoric acid. The phosphoric acid is then mixed with other nutrients to form compound fertilizers. The chemical composition will vary depending on the compounds used to make the final product. From this process either NP fertilizers or NPK fertilizers are produced.