Metal Extraction

Metals have been used for a variety of things throughout history- tools, weapons, cooking appliances, the list goes on. However metals are all extracted in very different ways, and these extraction methods have changed over time.

Most metals are extracted from the ground, but not all metals can be extracted in their pure state. Metals are generally quite reactive, so often combine with other elements such as oxygen to form ores. However some metals are very un-reactive, most notably gold and silver and these do not easily combine with other elements, so are often found in their pure or native states. However this does not mean that extracting gold or silver is particularly easy, as both are generally found in very low concentrations in the ground. For example, a ton of gold rich rock might contain around 10 grams of actual gold.  One method used to extract the gold from the rest of the material is to use a solution of potassium cyanide, which dissolves the gold. The liquid can then be filtered out and the gold becomes separated. However there are other methods of gold extraction that are also quite interesting, in particular some methods make use of plants to extract trace amounts of gold from the soil. For example, wheat can be planted around old gold mines that are no longer worth mining with conventional methods. The wheat plants then absorb small particles of gold, so at harvest time, the entire crop is burnt and the precious metals inside can be extracted.

Historically gold was much harder to extract- in ancient times a sheep’s fleece used to be used to separate the tiny particles of gold that lay in stream beds. The wool fibres would catch the gold particles, which could then later be rinsed out of the fleece with water. A more famous method is gold panning, which was made famous by the Gold Rushes in California. Panning takes advantage of the fact that gold is denser than other materials, so by swirling a pan of sediment, the gold will naturally separate.

However extracting metals from their ores is a little more difficult, as the metals are chemically combined with other elements, most commonly oxygen. Iron ore is heated with carbon (usually coke) in a blast furnace, and the oxygen combines with the carbon to form carbon dioxide, leaving the iron in its impure form as pig iron. This pig iron is then either formed into cast iron in a process called blending, or steel is created by removing some of the carbon.

What is particularly interesting about metal extraction is the effects that in can have upon the price of metal. Before the discovery of electrolysis (the process used to extract aluminium from its ore), aluminium used to be very very expensive, as it needed a massive amount of heat to produce.  Of course new extraction methods may be thought of which could dramatically change the commodities markets- for example the price of gold per ounce today might drop if someone found a really efficient way of extracting it from the ground.