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 metal ions through their roots. Phytoextraction is not yet used to extract metals for commercial purposes but it does help remove toxic metals from contaminated soil (for example around old mines).

In the future, when supplies of higher grade ores have run out, metals could be extracted by burning the plants to produce ash. The ash would contain a higher concentration of the metal than the soil.

How copper metal forms
Question

Explain why phytoextraction is not currently used by mining companies for extracting metals.

Phytoextraction only produces a small quantity of metal and is very slow. Mining companies can make more money from other methods of extraction.

Bioleaching

Certain bacteria found in the spoil heaps of old mines, can oxidise metal sulfide ores. These bacteria work best in acidic conditions so the spoil heaps are sprayed with acid.

Copper(II) sulfate solution is produced and is carefully collected.

This solution is called a leachate and the process is called bioleaching.

Copper may be extracted from the copper(II) sulfate by a displacement reaction with iron or electrolysis.

A disadvantage of bioleaching is that it introduces toxic substances, including sulfuric acid, into the environment

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