ZIMSEC O Level Combined Science Notes:  The manufacture of fertilisers

  • Some of the nitric acid produced at Sable Chemicals is used to make ammonium nitrate fertilizer
  • It is used as an input (feedstock) for the fertilizer plant at both Sable and Zimphos
  • To maintain soil fertility nitrogen containing compounds are added to the soil
  • Some of these fertilizers are known as NPK fertilizers
  • N stands for Nitrogen
  • P stands for Phosphorus
  • K stands for Nitrogen
  • These fertilizers are called by this name because they contain these elements
  • The old method of producing fertilizers used a technique where ammonia was converted into a sulphate using sulphuric acid
  • The current method is to convert ammonia into a nitrate using nitric acid
  • Nitrate fertilizers are higher in nitrogen

The manufacture of ammonium nitrate

  • Is carried out at Sable Chemical industries as this is where the required raw materials are produced
  • The raw materials are ammonia and nitric acid
  • Nitric acid isneutralised by ammonia vapour
  • Ammonium nitrate which is a salt is produced by this neutralization reaction
  • \text{nitric acid(acid)+ammonia(base)}\rightarrow\text{ammonium nitrate(salt)}
  • The solution is evaporated to produce a saturated solution
  • The saturated solution is then dried in a prill tower to give solid prills(granules)

The manufacture of phosphate fertilizers

  • Most soils in Zimbabwe are deficient in phosphorus
  • Phosphorus is required for healthy plant growth
  • It must thus be added to the soil to improve yields
  • It is usually added in the form a soluble phosphates
  • Phosphate rock from Dorowa and Zimphos is converted into a soluble form at Zimphos
  • The ground rock (calcium phosphate) treated with sulphuric acid to produce
  • Super-phosphate
  • Which is a popular fertilizer

To access more topics go to the Combined Science Notes page.

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