History of Phosphate Fertilizer Production
Until the 1950s, fertilizer manufacturing facilities were relatively small and produced fertilizers tailored to the soil needs of area farmers, commonly within a 100-mile radius. In these days, only about 4 million tons of primary nutrients – nitrogen (N), phosphate (P) and potassium (K) – were produced yearly. But this began to change when domestic agriculture and industry, as well as European and Western Pacific markets devastated in World War II, increasingly requested these nutrients.
In the 1960s, the Tennessee Valley Authority (TVA) and the land grant colleges changed the way fertilizers were produced and began to promote higher analysis fertilizers so that more phosphate could be delivered to farmers at lower costs. More concentrated phosphates began replacing normal superphosphate as the primary fertilizer commodity, turning what had been strictly a mining business into chemical production. This was especially true in Florida, which produces approximately 75% of the phosphate rock mined in the U.S. Phosphate rock is no longer sold for direct fertilizer manufacture. It is exclusively used to make phosphoric acid, almost all of which is used in the production of phosphate fertilizers.
Today the ammoniated phosphate fertilizer products produced in Florida allow farmers to apply more fertilizer in one pass, which cuts back significantly on labor costs. The higher-analysis fertilizers also save on freight costs.
Florida phosphate products today include:
- DAP (Diammonium Phosphate): The fertilizer that quickly became the item of commerce because it had the highest concentration of phosphate and nitrogen at 18N – 46P2O5 – 0K2O.
- MAP (Monoammonium Phosphate): This fertilizer is essentially the same as DAP, but it has a lower concentration of nitrogen at 11N – 52P2O5 – 0K2O.
- GTSP (Granulated Triple Superphosphate): This fertilizer is very similar to the superphosphate fertilizer that was the fertilizer that traditionally provided the most nutrients to the plant at 46% P<2O5. Since GTSP is made by reacting phosphate rock with phosphoric acid, it also provides some calcium and sulfur to the plant.
- Superphosphoric Acid: A product that is used to make a higher-analysis, or a more concentrated, fluid fertilizer. Liquid fertilization was said to be the future for fertilizer in the 1970s. It did not, however, prove to be much better than traditional DAP or MAP, which both can be slurried if necessary. Today the demand for the product is not high and only a few companies produce superphosphoric acid. The only Florida company producing the acid is PCS in north Florida.
- Phosphoric Acid: In the past, phosphoric acid was shipped to granulation plants that flourished in farming areas. There it was mixed with ammonia to make phosphate fertilizer. Today only a few independent granulation plants exist because the phosphate companies add the ammonia themselves to produce the ammoniated phosphate fertilizer products they sell. Purified technical- and food-grade phosphoric acid are also sold for use in items such as soft drinks. This product, however, mostly comes from North Carolina and Louisiana phosphate operations.
- Animal Feed Supplements: Defluorinated phosphate rock or phosphoric acid are used to make animal feed supplements. PCS, in north Florida, and Mosaic in central Florida produce animal feed supplements. One way to produce the feed is to combine phosphate rock with a small amount of phosphoric acid, sodium carbonate and then calcine. The most common method, however, is to defluorinate phosphoric acid and react it with lime to get dicalcium phosphate.
- Sulfuric Acid: This acid is produced at phosphate plants for use in reacting with phosphate rock to produce phosphoric acid. The heat generated off sulfuric acid production is used to power phosphate manufacturing plants and extra energy is often sold back to the area electric grid. Some sulfuric acid may be sold separately as a product.