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
and processing use up enormous amounts of energy.
contribute to greenhouse gas emissions and other forms of pollution (such as
acid rain and the production of unwanted minerals).
sometimes involve the use of poisonous chemicals.
use up precious supplies of ores – some metals are very rare.
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:
sustainable economic activity
that the environment is not irreversibly damaged or contaminated
that the are of land required to support a community is not increased
efficient use of materials and energy and, in the case of metals, consider
(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.