The phosphate mineral is not soluble and is hard for the plant to access

In order to be used as crop nutrients or animal feed, apatite (the main phosphate mineral) must be converted to a water-soluble form. In general, the phosphate facilities in chemical complexes utilize a wet process in which the phosphate concentrate is mixed with sulfuric acid and filtered to make phosphoric acid which is the starting point in the production of most phosphate derivative products. So, the main reaction of phosphate with sulfuric acid produces phosphoric acid to be valorized and phosphogypsum (dihydrate or hemihydrate) to be rejected. The sulfuric acid that is needed to convert the phosphate rock into phosphoric acid is also produced at the chemical processing plant using sulfur.

The phosphoric acid produced is used to make fertilizers. It is mainly converted into three phosphate salts which are used as fertilizers. They are triple superphosphate (TSP), diamonium hydrogenphosphate (DAP) and monoammonium dihydrogenphosphate (MAP). Furthermore, purified phosphoric acid used in the food industry.

Schematic diagram of processing phosphate rock: products and associated by-products

Uses of phosphoric acid. Data from Potash Corporation, 2014