Acid Mine Drainage: An Overview and Sustainability

Summary

This lesson, prepared by Andy Long and Sam Der, explores the history, origin, and treatment of acid mine drainage (AMD) in Southeastern Ohio. It explains how mining activities, particularly underground and surface mining, have caused environmental problems such as acid mine drainage, which is the single largest surface water impairment in the region. The script covers the chemical processes behind AMD, its environmental effects, and how treatments like alkalinity reagents and passive/active systems help neutralize acidity and remove metals. It also highlights sustainable remediation methods that repurpose neutralized materials for products like pigments and bricks.

Takeaways

• 😀 Southeast Ohio was heavily mined in the late 1800s and early 1900s, primarily through underground mining, leading to significant environmental impacts.
• 😀 Acid mine drainage (AMD) is one of the largest environmental problems in Southeast Ohio, caused by abandoned mines generating sulfuric acid from pyrite exposure to oxygen and water.
• 😀 Acid mine drainage results in the formation of iron complexes, which precipitate out of the water, creating yellow boy or orange rust on the stream bottom.
• 😀 AMD is highly acidic and contains suspended metals like iron, which pollutes streams and affects aquatic life and water quality.
• 😀 Remediation of acid mine drainage focuses on neutralizing acidity and removing metals through chemical processes and physical treatment systems.
• 😀 The primary goal of AMD remediation is to raise the pH of the mine water by adding alkaline materials such as calcium hydroxide.
• 😀 Metals are removed from acid mine drainage by creating settling ponds or sacrifice zones where metals precipitate out of the water.
• 😀 Alkaline reagents such as sodium hydroxide and calcium hydroxide are used in AMD remediation to neutralize acidity and reduce metal concentrations.
• 😀 Passive treatment systems, like ponds lined with limestone, increase pH and precipitate metals from AMD without requiring ongoing energy or chemical inputs.
• 😀 Active treatment systems add alkaline material directly to the AMD, but they are less sustainable due to higher costs and the need for constant maintenance.
• 😀 Sustainable AMD remediation efforts include capturing and selling the products of neutralization reactions, such as iron hydroxide, which can be used in paint, plastics, or bricks.

Q & A

What is acid mine drainage (AMD) and how does it impact the environment?

Acid mine drainage (AMD) occurs when sulfuric acid is generated by the oxidation of pyrite in coal during and after the mining process. This results in highly acidic water that contains suspended metals, which can harm aquatic ecosystems and degrade water quality. AMD is one of the biggest environmental problems associated with mining, especially in Southeast Ohio.

What are the primary causes of acid mine drainage in Southeast Ohio?

The primary cause of AMD in Southeast Ohio is the exposure of pyrite (iron sulfide) to oxygen and water during mining, which generates sulfuric acid. This acid lowers the pH of water, causing it to suspend harmful metals like iron in solution, which eventually enters streams, contaminating the water.

Why is iron a significant concern in AMD?

Iron is a significant concern in AMD because it precipitates from the water as iron hydroxide, which settles on the streambed and forms a yellowish-orange layer known as 'yellow boy' or rust. This process can smother aquatic habitats and reduce the oxygen levels in the water, harming aquatic life.

What methods are used to treat acid mine drainage?

There are two main methods for treating AMD: passive treatment and active treatment. Passive treatment involves using ponds lined with limestone where the water's pH is increased and metals are precipitated out. Active treatment adds alkaline materials directly to the acidic water to neutralize it and remove metals.

What is the goal of acid mine drainage remediation?

The goal of AMD remediation is to eliminate the source of acidity or raise the pH of the contaminated water. Additionally, it aims to remove harmful metals from the water, preventing them from harming ecosystems. This can be achieved through various treatment methods like neutralization and precipitation.

How does neutralization work in AMD remediation?

Neutralization in AMD remediation involves adding alkaline materials, such as calcium hydroxide, to the acidic mine water. This increases the pH of the water, causing metals like iron to precipitate out of the solution and settle on the streambed, improving water quality.

What is passive treatment and how does it help AMD?

Passive treatment involves the use of ponds lined with limestone where acid mine drainage flows through. As the water enters these ponds, the pH increases, and metals are precipitated out. This process can reduce acidity and remove harmful metals from the water without active intervention.

What are the challenges associated with active treatment systems for AMD?

Active treatment systems require the addition of alkaline materials directly to the AMD water at treatment facilities. While effective, these systems are not sustainable in the long term due to high costs and the ongoing need for intervention to maintain water quality.

How is sustainability incorporated into AMD treatment?

Sustainability is a key concern in AMD treatment. Scientists and engineers are developing methods to make remediation more sustainable by capturing and selling byproducts, such as iron hydroxide, which can be turned into pigments for paints or bricks. This reduces the overall cost and makes the treatment process more economically viable.

What practical activity is involved in this lesson to understand AMD remediation?

In this lesson, students will participate in a hands-on activity where they extract iron from AMD water using a neutralization reaction. The resulting iron hydroxide will be used to create pigments for painting, helping students understand both the scientific and practical aspects of AMD remediation.