Phytomining and bacterial extraction are two methods used to obtain copper from low-grade ores. Explain how bacterial extraction is used to obtain copper from a low-grade ore, and suggest why mining companies might prefer bacterial extraction over traditional mining for low-grade ores.

OCR GCSE Chemistry A: Gateway Science (J248) — C6.1 Improving processes and products · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Copper is a widely used metal, but high-grade copper ores are becoming increasingly scarce. Mining companies must now process low-grade ores that contain very small amounts of copper. Two biological methods have been developed to extract copper from these low-grade ores.

Model answer (4 marks)

Bacteria such as *Acidithiobacillus ferrooxidans* oxidise the sulphide minerals in the low‑grade ore, breaking down the ore matrix and releasing copper ions into solution. The oxidation produces an acidic solution that contains Cu²⁺ ions. The copper can then be recovered by adding a more reactive metal (for example scrap iron) which displaces copper from the solution, or by other precipitation methods. Mining companies prefer bacterial extraction because it is cheaper and less environmentally damaging than conventional mining of low‑grade ores, which would be uneconomic and would cause excessive waste for the small amount of copper obtained.

Examiner tips

  • Use the exact terms ‘bacteria oxidise the ore’, ‘acidic solution containing Cu²⁺’, ‘displace copper with a more reactive metal’, and explain the economic and environmental advantages.
  • Show the sequence of steps clearly: oxidation → acidification → copper recovery.
  • Mention the key point that low‑grade ores are not profitable by traditional methods.

Common mistakes

  • Confusing bacterial extraction with phytomining or omitting the step of copper displacement.
  • Using vague phrases like ‘bacteria break down ore’ without specifying acid production or copper recovery.
  • Failing to state why bacterial extraction is preferred (e.g., not mentioning cost or environmental impact).

Mark scheme (4 marks)

  1. Bacteria break down / decompose the low-grade ore
  2. An acidic solution containing copper ions is produced
  3. Copper can then be obtained / displaced from the solution (e.g. by adding a more reactive metal / scrap iron)
  4. Bacterial extraction is preferable for low-grade ores because traditional mining of low-grade ores is not economically viable / is too expensive / causes too much environmental damage for a small yield of copper

Key terms in this question

bacterial extraction · low-grade ore

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