Using resources

• Corrosion


  the process by which metals are slowly broken down by reacting with substances in their environment.

  • Only the surface of the metal that corrodes, because it's exposed to substances in the environment like water & oxygen.
  • This is a problem, since it damages metals and materials
• Rusting


  An example of corrosion, where it only applies to iron and alloys of iron, like steel.

  • Both Water and oxygen has to be present, for rusting to take place
  • But with other metals, it would be corroding

  Rusting is a REDOX reaction:

  • Iron + Oxygen + Water -> Hydrated Iron (III) oxide / rust

  Iron is oxidised as it lost electrons:

  • $Fe->\:Fe^{3+}+$$3e^-$

  Oxygen is reduced as it gains electrons:

  • $O_2+$$4e^-->2O^{2-}$
• 1st nail in the tube, would not rust as it contains water but no oxygen:

  • The boiling water removes any dissolved air.
  • The layer of Oil stops new oxygen from the air, dissolving into it.

  2nd nail in the tube, would not rust as it contains oxygen but no water:

  • The Anhydrous (no water) Calcium Chlorine power removes any water vapour in the air.

  3rd nail in the tube would rust as it contains both water and oxygen

  
• When iron rusts:

  • The rust that forms at the surface gradually flakes off.
  • Revealing new metal underneath.
  • The next layer can also rust and over time, that bit will fall away as well.
  • If left long enough, the entire chunk of iron can break down until there's nothing left.

  While metals like aluminium corrode:

  • It's only the surface atoms that are affected.
  • When the top layer of aluminium atoms is oxidized to form aluminium oxide
  • It forms a protective layer around the piece of aluminium.
  • It protects the rest of the metal from the environment and further oxidation.

  
• Barrier methods:


  Coats the iron in something to prevents oxygen and water from touching the iron:

  • paint:
  • works well for really big pieces of iron.
  • Oil / Grease:
  • necessary if the object has moving parts.
  • Electroplating:
  • using electrolysis to cover the iron in a thin layer of another metal.

  
• Sacrificial methods


  Adding a more reactive metal to the iron like aluminium / zinc, so that metal reacts with oxygen instead.

  • If the object's exposed to oxygen, then a more reactive metal will be oxidised instead

  
• Galvanising:


  A method that can prevent iron from rusting that uses both barrier and sacrificial methods.

  • Coats the object in a layer of zinc.
  • The layer acts as a physical barrier to prevent water or 
  • oxygen from reaching the iron (barrier method).
  • If the zinc gets scratched though, then the zinc will still react with any nearby oxygen as it is more reactive than iron (sacrificial method).

  
• Metal ores will eventually RUN OUT and become harder to find and extract.

  • Traditional mining - digging, moving and disposing of large amounts of rock which can DAMAGE the ENVIRONMENT.
  • Alternative methods of extraction are becoming more important

  There's methods to extract LOW GRADE ORES (rocks with a small amount of metal) while minimising damage to the environment:

  • Phyto mining
  • Bioleaching
• PHYTOMINING


  Uses plants to absorb METAL COMPOUNDS from the soil.

  The steps are:

  • GROWING PLANTS:
  • Plants absorb metal compounds through their roots (when it's grown on soil that contains these compound) and it concentrate these ions in their cell.
  • HARVESTING:
  • After, they are harvested and dried.
  • PROCESSING:
  • The harvested plants are BURNED to leave behind ASH that contains the metal compounds.

  
• BIOLEACHING


  Involves using bacteria to extract metals.

  • Certain bacteria can break down low-grade ores to produce an acidic solution containing copper ions called leachate.
  • This doesn't need high temperatures or you will kill the bacteria.

  The steps are:

  • BACTERIA APPLICATION:
  • Bacteria are introduced to the ore where they produce leachate solutions that contain metal compounds.
  • COLLECTING LEACHATE:
  • The leachate is collected as it contains the desired metals.

  But this method produces toxic substances like Sulfuric acid, which damages the environment.

  
• Phyto mining is slow but it:

  • Reduces the need to obtain new ore by mining.
  • Conserves limited supplies of high-grade ores.
  • Reduces the amount of rock waste that must be disposed of after traditional mining
• Extracting the Metals


  Once you have the metal compounds from Phyto mining or bioleaching.

  • you can DISSOLVE THEM IN ACID and they can be processed to extract the pure metal.

  This can be done by:

  • DISPLACEMENT:
  • Using a more reactive metal, like scrap iron, to displace the metal from its compound.
  • ELECTROLYSIS:
  • An electrical process that separates the metal from its compound.