Alternative Methods of Metal Extraction (Phytomining and Bioleaching) — AQA GCSE Chemistry

As high-grade ores run out, new biological methods extract metals from low-grade ores with less environmental impact.

The problem

Traditional mining of metal ores is damaging to the environment and uses a lot of energy. High-grade copper ores are running out, so we increasingly need to extract copper from low-grade ores — which would be uneconomic by traditional methods.

Phytomining

Phytomining uses plants to extract metals:

1. Plants are grown on soil containing low concentrations of metal compounds.
2. The plants absorb the metal compounds as they grow.
3. The plants are harvested and burned, producing ash that contains the metal compounds in a higher concentration.
4. The metal can then be extracted from the ash.

Bioleaching

Bioleaching uses bacteria:

1. Bacteria are grown on a low-grade ore.
2. The bacteria produce leachate solutions that contain dissolved metal compounds.
3. The metal is extracted from the leachate, e.g. by displacement with scrap iron or by electrolysis.

Advantages and disadvantages

• Advantages: lower environmental impact than traditional mining; allow use of low-grade ores; reduce the need to dig up and process large amounts of rock.
• Disadvantages: both methods are slow.

Exam tips

• These methods extract metals from low-grade ores with less damage than mining.
• Phytomining: plants absorb metals, are burned, and the metal is extracted from the ash.
• Bioleaching: bacteria produce a leachate solution containing the metal.
• The metal is obtained from solution by displacement (scrap iron) or electrolysis.