Recycling Steel

  • Around 25% of “new” steel is formed from recycled scrap metal added during the BOS process. It makes up 100% of the steel made from the electric arc process.
  • Miscasts, waste from previous batches etc. from the steelworks themselves make up much of the scrap used in steelmaking. This is better because the steelmakers know the composition of their own wasted steel, whereas scrap from discarded products must be carefully graded and selected.
  • Steelmakers must know the content of the scrap steel, so that they don’t add any unwanted elements to the metal.

Recycling tin cans

  • Before the cans are “detinned”, they first have to be cleaned and shredded. Usually the can is first burned to remove any paper/food.
  • However, during burning, the tin diffuses into the steel making it less useful.
  • The “detinning” process takes advantage of the fact that tin, unlike iron, is not a transition metal, and therefore is able to dissolve in alkaline solutions.
  • The clean, shredded tin cans are treated with a hot solution of sodium hydroxide, in the presence of an oxidising agent (tin will dissolve in strongly alkaline solutions, iron will not):

    Sn(s)+ 6OH-(aq) [Sn(OH)6]2-(aq) + 4e-

  • The steel left behind is rinsed and pressed into bales for transport to a steel plant.
  • The tin can be recovered by electrolysis.

Useful books for revision

Revise A2 Chemistry for Salters (OCR A Level Chemistry B)
Salters (OCR) Revise A2 Chemistry