What is Coal Ash? 8 Things (2024) You Must Know

Today, the United States is one of the top coal producers in the world, but there’s one aspect of this production that cannot be ignored: coal ash.

When coal is burned, it leaves residual ash particles that can cause serious issues for people and the environment.

Even though the amount of coal being burned in the United States has been decreasing over the years, coal ash can’t be swept under the rug.

Luckily, there are methods that can be used to control potential dangers and ways that actually make this byproduct a beneficial resource.

But what is coal ash exactly?

Well, in this article, we’re going to break it down, including all the nitty gritty details, such as how it can be used, potential health effects, and how it can be disposed of.

So, let’s talk about some coal ash!

1. What is Coal Ash?

Coal ash refers to the residue that is created when coal is burned.

This type of ash contains leftover materials that are organic and inorganic.

The primary minerals it contains are iron, aluminum, silicon, and calcium.

However, it can also hold small amounts of heavy metals like mercury and lead.

The materials that coal ash contains depend on where the coal was sourced from and the type of combustion process.

Regardless, whenever coal is burned, such as at a power plant, coal ash is produced.

And although some of the materials could be beneficial for the environment, there are enough toxins that require careful precautions to be taken during disposal.

If the ash isn’t disposed of properly, it can contaminate nearby sources of water, cause structural failures, lead to air pollution, and pose health risks.

But before we talk more about the benefits and risks, let’s look at the different types of coal ash.

2. What Are the Different Types of Coal Ash?

Not all coal ash is the same.

When coal is burned, it creates four different types of byproducts, all of which are referred to as coal ash.

bulletFly Ash*

When coal is burned, it creates a fine, powdery material that flies out of combustion chambers.

Fly ash can potentially travel hundreds of miles from the source, depending on the size of the particles.

However, the concentration of those particles typically decreases the farther it travels.

bulletBottom Ash*

Bottom ash is heavier than fly ash and collects at the bottom of combustion chambers.

It consists of materials such as unburned coals, inorganic materials, and rocks.

Bottom ash is just like the leftovers you find when using coals to barbeque.

bulletBoiler Slag

Boiler slag refers to coal ash that melts and fuses together.

It can be found at the bottom and the walls of boilers and furnaces.

Boiler slag has a glassy appearance and is a popular resource for construction projects.

bulletFlue Gas Desulfurization Material

Coal-burning operations remove sulfur from the coal to decrease the amount of harmful sulfur dioxide that emits into the atmosphere.

The removal process leaves a wet sludge, or sometimes a dry powdered material, known as flue gas desulfurization material.

*Fly ash and bottom ash are considered to be the two primary forms of coal ash.

3. What is the Use of Coal Ash?

Coal ash is surprisingly versatile.

It’s primarily used as a construction resource that can strengthen or replace other materials; however, because of its rich nutrients, it can also be beneficial for the soil.

Reuse is an excellent strategy to prevent it from harming people and the environment, so let’s check out its main uses.

bulletRoad pavement:

Coal ash is an effective and affordable material to pave roads.

It can be used as a partial substitute for asphalt, which can harm nearby rivers, crops, and ecosystems.

However, some researchers believe coal ash should still be used with caution.

bulletCement replacement:

When coal ash is added to the concrete-making process (partially replacing a percentage of the cement being mixed in), the product is stronger, more stable, and less expensive to produce.

The process is safe as long as any excess amounts of carbon are first removed from the coal ash.

bulletBase construction materials:

In addition to concrete, coal ash can be used in a number of other construction materials, such as fillers, grouts, bricks, ceramic tiles, and much more.

It will typically improve the materials’ structural integrity and thermal insulating abilities.

bulletSoil amendment:

The minerals in coal ash, like phosphorus and calcium, help plants grow and thrive in the soil.

However, it also has a high alkaline level, and if too much is added, it can destroy plants that require more acidic soil.

4. How is Coal Ash Disposed of?

Because coal ash is toxic to humans and the environment, power plants have a few methods to dispose of it to prevent contamination.

Because of government regulations, organizations that fail to implement safe disposal strategies could be massively fined or potentially shut down.

Here are the primary methods of disposal:

bulletSurface Impoundments

Surface impoundments refer to large coal ash ponds where the material can be transferred.

These bodies of water have a barrier to prevent harmful chemicals from leaching into the nearby soil and groundwater.

If these barriers aren’t done properly, it could cause major issues, which is one of the arguments against surface impoundments.


Landfills are another common option for disposal.

Similar to surface impoundments, landfills have to be lined with a barrier to prevent harmful chemicals from leaching into the soil or groundwater and drinking water.

A layer of soil is usually placed on top of the coal ash to prevent it from spreading in the wind.

Landfills still aren’t a perfect solution and can lead to leaching if the landfill isn’t built correctly or diligently monitored.


The S&P estimates that around 64% of coal ash in the United States was recycled in 2017.

Coal ash is reused to create concrete, pave roads, and stabilize soil.

Reuse is arguably the most beneficial way to dispose of the material.

5. Why is Coal Ash Toxic to Humans?

Some of the materials in coal ash make it toxic to humans.

Heavy metals, like mercury, cadmium, lead, and arsenic, are commonly found in coal ash, and they pose serious risks to human health.

People can experience unpleasant symptoms by coming into physical contact with it, inhaling it, or ingesting it.

Here are the potential symptoms that short-term exposure can cause:


bulletNose and throat irritation

bulletShortness of breath



Here are the potential symptoms that long-term exposure can cause:

bulletVarious cancers

bulletKidney damage

bulletLiver damage

bulletCardiac arrhythmia

Heavy metals can interfere with normal biological processes by attaching to enzymes and proteins, resulting in serious medical issues.

People living close to power plants that burn coal are at a direct risk of developing both short-term and long-term health problems.

Additionally, workers at these plants are extremely vulnerable to both short and long-term symptoms.

So, the side effects are serious business.

If you are deciding about buying a property near a coal-fired power plant, you should weigh the risks and thoroughly investigate the plant’s reputation.

6. What are the Environmental Impacts?

So, what is coal ash’s environmental impact?

When coal is improperly disposed of, it gets into the air, water, and soil and ultimately wreaks havoc on the local ecosystems.

Coal is a type of fossil fuel, and is considered to be one of the dirtiest forms of energy as well as a major cause of climate change.

So, let’s take a closer look at how coal ash impacts air, water, and soil and its repercussions on wildlife.

bulletHow Coal Ash Affects Air Quality

Because coal ash contains chemicals like nitrogen oxides, sulfur dioxide, and mercury, it’s a big contributor to smog.

As these toxins float through the air, they can result in acid rain, which is a highly acidic rain that can disrupt natural bodies of water and ecosystems, and it can also cause the corrosion of buildings.

Additionally, smog and poor air quality can shorten lifespans and cause various respiratory diseases.

bulletHow Coal Ash Affects Water Sources

The heavy metals in coal ash can cause severe issues for lakes, ponds, and groundwater.

If enough of these substances are introduced to a water source, it can poison fish, cause health problems like cancer and neurological disorders in humans, and make the water unusable for agricultural uses.

bulletHow Coal Ash Affects Soil

Soil is very fragile, and when its chemical levels get thrown off, it can be detrimental.

The alkalinity of coal ash has the ability to change pH levels in soil.

Most plants prefer neutral or slightly acidic soil, and if it suddenly becomes more alkaline, it could stunt crop growth or prevent plants from growing at all.

Other problems include changes in soil structure, nutrient deficiencies, and the introduction of heavy metals.

bulletHow Coal Ash Affects Wildlife

As the environment becomes more contaminated by coal ash, wildlife begins to suffer.

Animals’ water sources become toxic, food sources disappear, and the polluted air causes health problems.

If this contamination is severe enough, it can cause alarming declines in animal populations and threaten the entire ecosystem.

7. Is Coal Ash Considered Hazardous Waste?

Despite the severe impact coal ash has on humans and the environment, the Environmental Protection Agency (EPA) does not consider it a hazardous waste–strange, right?

Instead, it is categorized as solid waste, which is what household garbage is also categorized as.

If it were to be labeled as hazardous waste, coal companies would be subject to far more stringent federal regulations.

So, why is something that’s such a major threat to the health of people and the environment not being classified appropriately?

Well, for years, coal companies have been successfully lobbying against categorizing coal ash as hazardous waste at a federal level.

Luckily, a handful of states, such as California, Florida, New York, Illinois, and Oregon, have taken matters into their own hands and implemented strict regulations.

Although there are no direct signs that the EPA will classify coal ash as hazardous waste anytime soon, as climate change becomes more of a pressing issue, the department may have no choice but to reevaluate its decision.

8. How Can We Reduce the Amount of Material Generated?

So, what can we do about coal ash?

There are a number of strategies that can be implemented to reduce the amount generated.

Many of these tactics are already being used today; however, there’s plenty of room to expand and improve upon them.

Here are ways we can reduce the amount of coal ash generated:

bulletStricter Regulations

If the Federal Government implemented stricter regulations, it would result in fewer toxins spreading into the environment.

A great first step would be classifying coal ash as hazardous waste.

That categorization would force coal companies to operate under close scrutiny and receive harsh punishments in the case of improper practices.

bulletCleaner Burning Technologies

Not all coal-burning processes are the same, and some produce less harmful emissions than others.

For example, Fluidized Bed Combustion and the Integrated Gasification Combined Cycle are both far less problematic than the traditional coal-burning process of using a furnace or boiler.

Cleaner burning technologies are, however, more expensive and difficult to build.

bulletAlternative Energy Sources

Switching over to alternative energy sources that don’t introduce harmful toxins into the environment is arguably the most effective method to reduce the amount of coal ash being generated.

In the last ten years, the United States has already seen a decrease in the amount of this material due to solar power, wind turbines, and hydroelectric power.

bulletProper Disposal

Proper disposal minimizes the amount of harmful chemicals that spread into the world.

Upgrading and monitoring storage facilities is a foolproof way to keep the surrounding people and environment safe from contamination.

Final Thoughts

As more research verifies that coal ash is responsible for a number of health and environmental problems, the more important it is to know the answer to the question of what is coal ash.

Although there are several wonderful uses for the byproduct, such as improving structural materials, its downsides can’t be ignored.

So, as the United States and the world progress away from fossil fuels, coal ash may become part of the distant past.

But for now, it is still a pressing issue that’s yet to be solved.

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Erika Gokce Capital

Disclaimer: we are not lawyers, accountants or financial advisors and the information in this article is for informational purposes only. This article is based on our own research and experience and we do our best to keep it accurate and up-to-date, but it may contain errors. Please be sure to consult a legal or financial professional before making any investment decisions.


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