Coal is the most widely used fossil fuel in the world, but it doesn't get nearly as much attention as its cousin, oil. Oil is a part of our daily routines as we drive cars that rely on gasoline, a byproduct of oil refining. But coal is perhaps just as important, if not more important, because the majority of our power plants burn it to create electricity. The power company I buy my electricity from uses a coal-fired plant. Coal is abundant and, most of the time, cheap. But it will never be clean...no matter how much the industry and politicians want it to be.
Coal takes a long time to make. That's why it's called a nonrenewable resource. The coal being mined here in the United States started forming about 300 million years ago in swamps and humid forests. This was a unique time in Earth's history as well as life's history because plants had outraced the decomposers in the evolution arms race. Nothing existed at the time that could break down the proteins in the new forms of plants. So, when the plants died, they just sat on the ground without really rotting. Eventually, the plants were buried in mud and a lot of carbon was locked away in the ground. 300 million years later, we are unlocking this carbon reserve and releasing it into our atmosphere as we burn coal to satisfy our ever-increasing appetite for energy.
Plants don't simply turn into coal underground, even after 300 million years. The carbon undergoes several changes or phases before we reach coal. Phase 1 is peat. Peat is best known in the British Isles where it is still harvested from the ground and dried into bricks which are then burned for heat or fuel. It is a gooey, dark brown mess that resembles a congealed swamp...which is basically what it is. Peat bogs are swamps where oxygen does not exist and plant material cannot be broken down (nothing can, for that matter). The acids in the water and anoxic conditions make a peat bog an ideal preservation material. Humans thrown into peat bogs thousands of years ago are found so well preserved that we can discern what their last meal was. As a fuel, though, peat is horrible. Sure, it burns, but it burns with a dirty, sooty ash and smoke. Obviously, peat is not an ideal energy source, but when it's all you have due to the lack of trees, you make it work.
Phase 2 of coal formation is lignite. Lignite is often called "brown coal" because it is, indeed, brown. It is woodier than peat and is used in areas where peat or coal is not available. Similar to peat, lignite is typically used by people harvesting it from the ground for their own needs in their homes. Also similar to peat, it is a dirty material to burn. A great deal of ash and smoke is produced by burning lignite compared to the heat produced.
Phase 3 is actual coal. Well, one variety of coal, anyway. Bituminous coal is called "soft coal" because it is soft and will break apart in your hands. Handling bituminous coal will leave your hands covered in black soot. This is the most common coal found on Earth (or rather, in Earth). It burns easily and produces less ash and soot compared to lignite or peat. But it is still dirty and does produce those byproducts. Mining bituminous coal leads to black lung as the dust is inhaled.
Phase 4 is anthracite coal. Anthracite is hard coal. As bituminous coal is exposed to immense heat and stress from the Earth, it hardens to anthracite. Anthracite is a shiny, black material that, once ignited, burns for a long time. It is the most sought after type, but exists in small patches. In terms of comparing the types of coal, anthracite is the cleanest...but it is still dirty. Coal just cannot be clean.
A particular mineral family often found associated with coal is the sulfide family. Members of the sulfide family include pyrite (iron sulfide), galena (lead sulfide), and cinnabar (mercury sulfide). When coal is burned, some of these minerals are also burned which sends particulates of iron, lead, and mercury into the atmosphere. They will then fall back to Earth in rain and acid rain to pollute streams and groundwater. Sulfur and oxygen molecules also move into the atmosphere and mix with water to form acids of sulfur...like sulfuric acid (aka battery acid). It is just not possible to remove all of the sulfur compounds from coal before burning it. Therefore, there will always be some sort of acid rain or heavy metal pollution associated with burning coal. By the way, heavy metals like lead and mercury cannot be removed from your body and slowly build up over time.
Another nasty little byproduct of burning coal is coal ash. In 2014, Duke Energy was responsible for a massive coal ash spill into the Dan River in Eden, NC. They had collecting ponds for coal ash, but decided not to line the interior of the ponds as it was not required and cost a lot of money. A pipe carrying runoff from a parking lot ran underneath one of these ponds. In February 2014, a leak formed from the pond to the pipe and emptied thousands of gallons of coal ash water into the Dan River. Coal ash contains high concentrations of lead and other toxic metals that didn't burn off into the atmosphere. That ash is currently sitting at the bottom of the river in Danville and other areas downstream. It settles to the bottom but gets stirred up again during heavy storms or from boat traffic. All coal plants produce this ash which can be used in making certain types of cement called fly ash cement. But, otherwise, it sits waiting for someone to do something with it. Also, we are importing coal ash from other countries. All of this coal ash has the potential to cause environmental harm.
So, can coal ever get clean? Industries will tell you how they put scrubbers in their exhaust towers to remove large amounts of pollutants from entering the atmosphere. But that doesn't stop carbon dioxide. Some plants are using carbon capturing technology to sequester the carbon dioxide underground, but that can lead to earthquakes. And, then there is the coal ash. What to do with all of the ash produced? Some can be used as fly ash, but not all of it. And the levels of toxic materials are high in coal ash. We can clean coal all we want, but it will never be truly clean...only cleaner than the very dirty peat or lignite. It will never be as clean as the alternatives solar, wind, hydroelectricity, or geothermal.
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