The manufacture of fertilizers

• 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.