The first stage in making metals is to mine the ore-bearing rock. Sometimes huge amounts of ore are needed to make a small amount of metal – most copper, for example, exists in sulphide ores that contain as little as 0.25% copper. The metal then has to be extracted from the rock using furnaces and electrolytic processes. Finally, before the metal can be used, it often has to undergo further processing. For example, 98% pure ‘blister copper’, created by smelting and reduction, then has to be ‘electrorefined’ to produce copper of 99.99% purity.

Making metals in this way is not very sustainable.

• Mining and processing use up enormous amounts of energy.

• They contribute to greenhouse gas emissions and other forms of pollution (such as acid rain and the production of unwanted minerals).

• They sometimes involve the use of poisonous chemicals.

• They use up precious supplies of ores – some metals are very rare.

Sustainable mining

Mining is not sustainable in the sense that the minerals removed from the ground will never be replaced. To be described as sustainable, a mining project must:

• Generate sustainable economic activity

• Ensure that the environment is not irreversibly damaged or contaminated

• Ensure that the are of land required to support a community is not increased

• Make efficient use of materials and energy and, in the case of metals, consider their recyclability

• (based on the draft guidelines for environmental regulation of mining, UNEP and the UN DESA)

A new breakthrough – bio-extraction

A new method has recently been developed to extract copper and other metals using microbes. Known as ‘bio-extraction’, it is not only economically viable, but also environmentally friendly.

Bio-extraction involves the use of lithotrophs – a primitive life form that can survive in extreme environments such as high temperature and high acidity. Lithotrophs tap the chemical energy stored in rocks as the form of minerals using just a bit of water and some sulphide minerals. They chemosynthesise (like photosynthesise), using the chemical energy in the rocks instead of sunlight. As soon as a bit of ore is exposed, they get to work. They are found everywhere, especially in rainfall, and so are easily able to land on rocks and have the necessary conditions to react. The microbes then take the metal into solution, from which it can be removed by displacement or solvent extraction, in a relatively simple and environmentally friendly way.