GCSE Chemistry revision

Alternative methods of extracting metals

Using the Earth's resources and obtaining potable water

AQA 4.10.1.4 Higher Tier only

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Plants are grown on land containing low-grade metal ores, absorbing metal ions through their roots and accumulating them within their leaves and stems.
Plants grown on soil containing low concentrations of copper absorb copper ions; once mature, the plants are harvested and burned to produce a high-grade copper ash.

The plant ash is reacted with dilute acid (such as sulfuric acid) to produce a concentrated metal salt solution, from which pure metal is extracted via displacement using scrap iron or electrolysis.
Example: Treating copper ash with sulfuric acid produces a copper sulfate solution; adding cheap scrap iron displaces the copper to yield pure metal (Fe + Cu²⁺ → Fe²⁺ + Cu).

2. Metal Extraction from Ash AQA

The plant ash is reacted with dilute acid (such as sulfuric acid) to produce a concentrated metal salt solution, from which pure metal is extracted via displacement using scrap iron or electrolysis.
Example: Treating copper ash with sulfuric acid produces a copper sulfate solution; adding cheap scrap iron displaces the copper to yield pure metal (Fe + Cu²⁺ → Fe²⁺ + Cu).

Bacteria are used to break down low-grade metal sulfide ores through metabolic processes, producing a liquid solution called a leachate containing dissolved metal ions.
Example: Bacteria breaking down low-grade copper sulfide ores release acidic leachate solutions rich in dissolved copper ions.
Metal Recovery from Leachate: The metal ions in the leachate are separated and reduced to pure metal using displacement with scrap iron or through electrolysis.
Example: Passing an electric current during electrolysis through the copper-containing leachate causes pure copper metal to deposit onto the negative cathode.

3. Leachate Production AQA

Bacteria are used to break down low-grade metal sulfide ores through metabolic processes, producing a liquid solution called a leachate containing dissolved metal ions.
Example: Bacteria breaking down low-grade copper sulfide ores release acidic leachate solutions rich in dissolved copper ions.
Metal Recovery from Leachate: The metal ions in the leachate are separated and reduced to pure metal using displacement with scrap iron or through electrolysis.
Example: Passing an electric current during electrolysis through the copper-containing leachate causes pure copper metal to deposit onto the negative cathode.

Biological extraction methods allow metals to be obtained from low-grade ores that are economically unviable for smelting, require significantly less energy, and avoid the massive landscape destruction and sulfur dioxide emissions associated with traditional open-cast mining.

4. Environmental and Economic Advantages AQA

Biological extraction methods allow metals to be obtained from low-grade ores that are economically unviable for smelting, require significantly less energy, and avoid the massive landscape destruction and sulfur dioxide emissions associated with traditional open-cast mining.

Biological methods are exceptionally slow compared to traditional smelting, yield smaller quantities of metal over time, and bioleaching carries a risk of producing acidic run-off that can contaminate nearby water supplies.