When you think of metal, you likely picture a shiny gold necklace, a polished chrome faucet or even rough, weathered steel. If you saw many of these materials in their natural states, however, you probably wouldn't recognize them. A few native metals look virtually the same when they're extracted from the ground as they do when they end up in homes and stores. These include the less reactive metal varieties, such as gold, silver, platinum and copper. The majority of other metals come in the form of ore, which looks like any other rock. Rocks with relatively large concentrations of a single metal are considered ores, and can be extracted from the earth for processing and refinement.
The process of locating, mining and extracting metal is incredibly resource intensive, even for native metals. For example, miners must process roughly 33 tons (nearly 30,000 kilograms) of rock and earth to produce a single ounce (28 grams) of gold [source: Herschbach]. When it comes to non-native metals like aluminum or lead, the process can be even more complex and time consuming.
Once metal ore has been extracted from the earth, it's crushed and ground in large machines to separate the rock from the metal. Mining companies then use one of three processes to transform this raw metal into a final product. The oldest and most economical option involves heating the metal in a furnace to produce a carbon-reduction process. Other metals require the use of electrolysis to separate impurities and any remaining rock from the metal ore. Finally, these companies may use chemicals to purify and decontaminate the metals. For example, sulfuric acid can be used to process copper ore, and sodium-based chemicals aid in the separation of aluminum oxides. Steel is not technically a metal, but is made with iron and some added carbon.
The resource-intensive nature of metal ore mining highlights the need for society to increase metal recycling rates. It takes a lot of extracted ore to produce a relatively small amount of metal, so metal mines often are much larger and deeper than other mining operations. Not only does this disturb the local environment and destroy habitats, but it also results in an extremely high level of energy consumption. For instance, it takes 95 percent more energy to produce aluminum from virgin resources than it does to produce the material from recycled aluminum scrap [source: The Aluminum Association]. Despite this, only 20 to 30 percent of global aluminum production comes from recycled products [source: Gitlitz]. Higher prices in the copper industry have resulted in much higher recycling rates for this metal, with about half of U.S. copper made from recycled materials [source: Copper Development Association].(Rob Belknap/iStockphoto)
It's easy to say that the modern world would not function the way it does without metal, but the same goes for the ancient world, too. The Bronze and Iron ages were crucial periods in human cultural development, thanks to the materials the people of those eras used to hunt food, make tools and fight wars. Our earliest metal-working ancestors most likely used whatever metal deposits they found at ground-level and dug into the soil if they discovered a vein. By the time of the early Egyptians, mining different metals and rock had become big business [source: Minerals, Metals, & Materials Society].
Take a look through the periodic table of elements, and you'll see that many everyday metals (iron, copper, nickel, gold, etc) occur naturally. Other metals (like steel) are classified as alloys. Alloys combine two or more metals -- or metals and nonmetals -- to enhance certain properties, such as strength, conductivity, or corrosion resistance. In the case of steel, iron is combined with carbon to add strength.
Today, most metal is mined straight out of the ground in the form of ore. Ore is any part of the Earth's crust, often a mixture of rocks, loose soil and other earthly materials, from which a valuable material can be extracted. This can be difficult, since the desirable metal is often locked in chemical compounds with other unwanted materials and filled with impurities. Ore refiners must find the best way to separate each useful element from the rest of the ore in which it lies. One common method of extraction is smelting, where refiners heat the ore to extremely high temperatures with the use of powerful furnaces. This makes it easier to get the pure metals out. In the refining of iron, for instance, the smelting process releases unwanted particles of oxygen that populate raw iron ore. To give you an idea of the energy required for this process, iron's melting point is approximately 2800 degrees Fahrenheit. Though iron is typically produced only on an industrial scale, it can also be extracted in smaller foundries [source: Make] -- though we really don't suggest you try it without the supervision of an experienced professional.
How we locate ore has come as far as our methods of mass-producing it. Thanks to metal detectors, researchers can sample the earth below them without even using a shovel. A very low frequency (VLF) metal detector uses phase shifting to distinguish between metals. A phase shift is the timing difference between the transmitter coil's frequency and that of the detected object. This phase shift can occur through inductance or resistance. Inductance creates a long phase shift because it's from an object that easily conducts electricity. Therefore it takes longer for that object's frequency to alter. An object with high electric resistance is going to have a small phase shift because even a small change in the magnetic field will register. Based on the phase shift and the averages for different types of metals, the detector can distinguish which range of metals the object is likely to be in -- a far cry from the days of hoping to literally stumble upon a good source of ore.
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