In this lesson, you will learn about the different methods used to extract minerals from the ground and gain an understanding about how different types of mining affect the environment.
In a previous lesson, we learned about minerals, which are inorganic compounds, such as ores (like copper) and precious stones (like diamonds). The word mining sounds a lot like mineral, and that's no accident because mining is how minerals are removed from the ground. There are several different ways minerals can be extracted from the earth, but the two main methods are called surface mining and subsurface mining.
Surface mining is just what it sounds like - removing minerals that are near the earth's surface because this is where the ore deposits are located. When the ore deposits are very large, open-pit mining is utilized. A large, open pit is created as machines scrape off any earth that is not ore and set it to the side. This material is called overburden, and as the overburden is scraped off, it's piled into spoil banks.
After the overburden is cleared from the ore, explosives are used to break up the ore material that is being removed from the ground, which is then taken away to be refined. The size of the ore bed increases as mining continues, and eventually, the pit becomes a very large bowl-shaped hole in the earth's surface. When the ore is found in a wide area but it's not very deep in the ground, strip mining is used.
In strip mining, instead of creating one large pit in the ground, long narrow strips are dug out. The overburden is removed and piled up along the strip. Once the ore is removed, the overburden is dumped back into the strip. While this may sound like a good method because the holes are re-filled instead of left open, the land actually looks more like a washboard after strip mining because of all of the re-piled soil.
Some minerals are found very deep below Earth's surface - sometimes hundreds or thousands of feet deep! To remove these minerals from the ground, subsurface mining is used. In subsurface mining, a long tunnel is created either horizontally or vertically. The tunnel walls are reinforced with wood and ventilation shafts are created to provide air to the miners underground. The minerals themselves are removed a number of different ways.
One way is to blast apart the material and then send the ore pieces up to the surface in carts. Another method is longwall mining, which is when coal is sheared from the wall and collected on a conveyor belt, much like a potato peeler shears away layers of a potato. This is a very efficient way of extracting coal from an underground mine. Another method is solution mining, which is when hot water is injected into the ore to dissolve it. Once the ore is dissolved, air is pumped into it, and it's bubbled up to the surface.
The Harmful Effects of Mining
While mining provides us with the minerals we need, it is also very destructive because it disrupts the landscape both on the surface and underground. It also causes quite a bit of pollution and can harm or kill mine workers. Surface mining is destructive to landscapes because it can cause changes in the topography and drainage and strips the land of vegetation, soil and rocks. The spoil banks of surface mining erode and weather away, and rainfall leaches toxic chemicals into the earth. In some cases, entire mountaintops have been removed for surface mining!
Subsurface mining is actually less disruptive to the earth and produces less waste than surface mining, but it's also much less effective and more dangerous. Many workers die in mine collapses, which then also leaves behind a large hole from caving in of the ground above. Water may leak into the mine and dissolve toxic chemicals that may leak into aquifers and drinking water supplies. Explosions in old mining tunnels may also occur because the natural gas underground ignites very easily.
Besides erosion problems and changes to the landscape, mining also causes pollution in the air and water. Abandoned coal mines lead to acid mine drainage, which is water that is full of metals and toxins. Much like hot water dripping through coffee in a filter, rainwater picks up the harmful components in the ground and carries them off as surface and groundwater runoff. This runoff can end up in streams, rivers and lakes that are nearby.
Smelting is the process of heating ores to release the metals in them. This process separates the impurities from the metal, but also creates air pollution because gases that are created as by-products (such as sulfur dioxide) may escape and reach the air.
Mining is the removal of minerals from the ground. Once removed, minerals are then processed and refined for our everyday use. We use minerals for a variety of things, such as household products, jewelry and energy for cars and buildings. Surface mining removes ore deposits that are close to the surface, and subsurface mining removes minerals that are deep underground.
While mineral use is very important to us, there are also many environmental impacts, such as erosion, air and water pollution, land destruction and harm to mine workers. With new technologies and a conscious effort to reduce the negative effects of mining, we may be able to find a balance in how we use these important resources and reduce our impacts on the earth.
After you've finished with this lesson, you'll be able to:
- Describe the differences in surface mining and strip mining
- Summarize subsurface mining, longwall mining and solution mining
- Identify many of the harmful effects of mining