Biological methods of metal extraction - Higher

There are some alternative methods to extract metals that use living organisms. These have advantages and disadvantages compared to the usual extraction methods.

Phytoextraction

Plants absorb mineral ions through their roots. Phytoextraction makes use of this:

  1. plants are grown on an ore that contains lower amounts of metal
  2. the plants absorb metal ions through their roots and concentrate these ions in their cells
  3. the plants are harvested and burnt
  4. the ash left behind contains a higher concentration of the metal than the original ore
  5. the ash is processed to obtain the metal

Phytoextraction is slow, but it:

  • reduces the need to obtain new ore by mining
  • conserves limited supplies of more valuable ores with higher metal content

Example

Suggest reasons why phytoextraction decreases the damage done to the environment.

Mining for metal ores involves quarries, which are large holes in the ground. These create noise, dust and traffic. They also destroy natural habitats. Phytoextraction reduces the need for mining so reduces this damage.

Question

Give one disadvantage of phytoextraction.

It is a slow process.

Bioleaching

Certain bacteria can break down ores to produce an acidic solution containing copper(II) ions. The solution is called a leachate and the process is called bioleaching. Bioleaching does not need high temperatures, but it produces toxic substances, including sulfuric acid, which damage the environment.

Using scrap iron

Iron is more reactive than copper. It can displace copper from the leachate. For example:

iron + copper(II) sulfate → iron(II) sulfate + copper

Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)

Since iron is cheaper than copper, the use of scrap iron is a cost-effective way to produce copper from the leachate.

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