Producing Compound Fertilizers

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Producing compound fertilizers: The nitrophosphate process

The nitrophosphate process is one of the processes used to make complex fertilizers. It involves acidifying calcium phosphate (\(\text{Ca}_{3}(\text{PO}_{4})_{2}\)) with nitric acid to produce a mixture of phosphoric acid and calcium nitrate (\(\text{Ca}(\text{NO}_{3})_{2}\)):

\(\text{Ca}_{3}(\text{PO}_{4})_{2}(\text{s}) + 6\text{HNO}_{3}(\text{l}) + 12\text{H}_{2}\text{O}(\text{l})\) \(\to\) \(2\text{H}_{3}\text{PO}_{4}(\text{aq}) + 3\text{Ca}(\text{NO}_{3})_{2}(\text{aq}) + 12\text{H}_{2}\text{O}(\text{l})\)

When calcium nitrate and phosphoric acid react with ammonia, a compound fertilizer is produced.

\(\text{Ca}(\text{NO}_{3})_{2}(\text{s}) + 4\text{H}_{3}\text{PO}_{4}(\text{l}) + 8\text{NH}_{3}(\text{l})\) \(\to\) \(\text{CaHPO}_{4}(\text{s}) + 2\text{NH}_{4}\text{NO}_{3}(\text{s}) + 8(\text{NH}_{4})_{2}\text{HPO}_{4}(\text{s})\)

If potassium chloride or potassium sulfate is added, the result will be a NPK fertilizer.

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