6.1.2Global Challenges
Biological Extraction Methods — OCR Gateway GCSE Combined Science A J250 - Chemistry Revision Notes & Topical Questions
5 min read 6 parts Lesson 3 of 12
Section 1 of 6Why new methods are needed (HT only)
High-grade ores are running out
- High-grade ores are running out (HT only) Mining is only worthwhile when an ore contains a high proportion of the metal.
- Iron and aluminium ores are examples.
- Ores of metals such as copper and nickel are becoming scarcer, so low-grade ores must be used to meet demand.
Damage from traditional mining
- Damage from traditional mining Conventional mining involves digging up, moving and disposing of huge quantities of rock,
- which damages habitats and landscapes.
Biological alternatives
- Biological alternatives Phytomining and bioleaching use living organisms, avoid much of this damage,
- and can also be used to clean up mining waste that contains small amounts of metal.
Section 2 of 6Phytomining: stages
1
Plants that absorb metal compounds through their roots are grown on soil or waste that contains the metal, such as copper.
2
As the plants grow, the metal ions are taken up and concentrated in the shoots and leaves.
3
The plants are harvested and dried.
4
The dried plants are burned. The ash left contains the metal compounds in a concentrated form.
5
The metal is extracted from the ash by displacement with a more reactive metal such as scrap iron, or by electrolysis.
Section 3 of 6Bioleaching
1Bacteria added
- Bacteria added Special bacteria are put on low-grade ore, for example copper sulfide.
2Ore broken down
- Ore broken down The bacteria obtain energy from the ore and break it down, producing an acidic solution.
3Leachate forms
- Leachate forms The solution, called a leachate, contains metal ions such as copper(II).
4Metal recovered
- Metal recovered The metal is obtained from the leachate by displacement with scrap iron or by electrolysis.
Section 4 of 6Comparing the methods
| Aspect | Traditional mining | Phytomining / bioleaching |
|---|---|---|
| Ore needed | High-grade ore | Low-grade ore and waste can be used |
| Speed | Fast | Very slow, taking months or years |
| Environmental impact | Large-scale digging, waste rock, habitat loss | Less disturbance and no high temperatures, but bioleaching makes toxic substances that need treating |
| Further steps | Reduction or electrolysis | Displacement or electrolysis is still needed to get the pure metal |
| Waste clean-up | Not normally involved | Can extract metal from mining waste, helping to clean it |
Section 5 of 6Key terms
| Term | Meaning |
|---|---|
| Low-grade ore | An ore containing only a small proportion of the useful metal. |
| Phytomining | Using plants to absorb metal compounds from the soil, then burning them to obtain the metal. |
| Bioleaching | Using bacteria to break down ore and produce a solution containing metal ions. |
| Leachate | The metal-rich solution produced during bioleaching. |
| Displacement | A reaction in which a more reactive metal takes the place of a less reactive metal in a compound. |
Section 6 of 6Exam technique
1
Saying that biological methods give the pure metal directly. A displacement or electrolysis step is still needed.
2
Writing that phytomining and bioleaching are fast. Their slow speed is a main disadvantage.
3
Claiming bioleaching has no environmental problems. It produces toxic substances that must be treated.
4
Forgetting to mention that the plants are burned and the metal is extracted from the ash.
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