Producing Phosphoric Acid

Producing phosphoric acid and super phosphates

The production of phosphate fertilizers also includes a number of processes. The first is the production of sulfuric acid through the Contact process. Sulfuric acid is then used in a reaction with phosphate rock (e.g. fluorapatite (\(\text{Ca}_{5}(\text{PO}_{4})_{3}\text{F}\))) to produce phosphoric acid (\(\text{H}_{3}\text{PO}_{4}\)). For more information refer to the Chemical Industries Resource Pack.

\(\text{Ca}_{5}(\text{PO}_{4})_{3}\text{F}(\text{s}) + 5\text{H}_{2}\text{SO}_{4}(\text{l})\) \(\rightleftharpoons\) \(5\text{CaSO}_{4}(\text{s}) + \text{HF}(\text{l}) + 3\text{H}_{3}\text{PO}_{4}(\text{l})\)

Sulfuric acid can be reacted further with phosphate rock to produce single super phosphates (SSP):

\(2\text{Ca}_{5}(\text{PO}_{4})_{3}\text{F}(\text{s}) + 7\text{H}_{2}\text{SO}_{4}(\text{l})\) \(\rightleftharpoons\) \(3\text{Ca}(\text{H}_{2}\text{PO}_{4})_{2}(\text{s}) + 7\text{CaSO}_{4}(\text{s}) + 2\text{HF}(\text{l})\)

If phosphoric acid reacts with phosphate rock, triple super phosphates (TSP) are produced:

\(\text{Ca}_{5}(\text{PO}_{4})_{3}\text{F}(\text{s}) + 7\text{H}_{3}\text{PO}_{4}(\text{l})\) \(\rightleftharpoons\) \(5\text{Ca}(\text{H}_{2}\text{PO}_{4})_{2}(\text{s}) + \text{HF}(\text{l})\)