The science behind sulfur contamination in coal mining regions

Sulfur contamination remains a persistent challenge in mining regions. When burned, coal with high sulfur levels releases sulfur dioxide (SO2), a major contributor to acid rain and air pollution. Even before combustion, its presence already complicates extraction and lowers coal quality. It is a risk that is as operational as it is environmental.

Understanding the geochemical, geological, and technological aspects of sulfur in coal is imperative, especially as demand for cleaner energy production grows along with tightening regulatory scrutiny.

Why sulfur is present in coal

Coal naturally contains sulfur in three main forms – organic, inorganic, and sulfate. The amount and distribution vary depending on the peat's depositional environment. In freshwater settings, coal contains less than 1% sulfur and is classified as low-sulfur coal.

In contrast, coal with a sulfur content ranging from 3 – 6% is considered high-sulfur and is associated with marine-influenced environments. Sulfate-rich seawater interacts with peat swamps, enabling anaerobic bacteria to biologically reduce sulfates into hydrogen sulfide. This reacts with iron to form pyrite, greigite, and other sulfur-bearing minerals.

As coal undergoes diagenesis and epigenesis, sulfur compounds transform. Organic forms such as thiophenes, sulphides, and thiols become more prominent as coal matures. These compounds embed into the coal matrix or precipitate in fractures and cleats due to circulating fluids.

Environmental and health impacts

Sulfur contamination is not confined to coal seams. It can also affect nearby communities. When sulfates leach into groundwater, they may convert into hydrogen sulfide, which produces a rotten egg odour, even at concentrations as low as 1 part per million. Ingesting this contaminated water can lead to severe dehydration and gastrointestinal symptoms, especially in individuals with sensitive stomachs.

At the operational level, burning sulfur-rich coal releases both pyritic and organic sulfur as sulfur dioxide, a major contributor to acid rain. The high acidity is strong enough to erode stone structures, harm forests, and acidify lakes and rivers. Since sulfur dioxide can travel long distances via wind, its effects extend beyond mining areas.

Workers and residents exposed to polluted air have a 21% higher risk of developing multiple health issues, particularly respiratory and cardiovascular diseases. Although initiatives like the US’s Acid Rain Program have helped reduce SO2 emissions by up to 95% annually in regulated regions, countries with weak enforcement, such as parts of Asia, continue to face elevated emissions and serious public health consequences.

What to do with high-sulfur coal

High-sulfur coal can be burned in power plants equipped with sulfur-reduction technology (scrubbers) to minimise harmful emissions like sulfur dioxide. Alternatively, it can be blended with lower-sulfur coal or purchased emission allowances on the open market to offset the environmental impact. Chemical and biological methods can also be used to reduce the sulfur content before or during combustion.

Bridging science and strategy for cleaner coal

Understanding sulfur in coal is key to cleaner mining. Instead of viewing contamination as a fixed problem, the industry must adopt solutions like coal beneficiation, emission controls and AI-driven mapping. These steps cut environmental impact and costs and support safer communities and a future where coal remains viable through continuous improvement.

Author bio

Jane Marsh is a seasoned environmental journalist and the Editor-in-Chief of Environment.co, specialising in in-depth coverage of environmental trends, sustainability, and the evolving energy landscape. With her work featured on leading platforms like Renewable Energy Magazine, Manufacturing.net, and Nation of Change, Jane brings a keen perspective on the intersection of energy innovation and industry practices.

Read the article online at: https://www.worldcoal.com/power/17072025/the-science-behind-sulfur-contamination-in-coal-mining-regions/