What is tailings dam? Tailings dams are structures used in the mining industry to store byproducts of mineral extraction. These dams are designed to hold the waste material, known as tailings, in a contained area, allowing water to drain from the tailings and be recycled back into the mining process. Tailings dams can be found all over the world and are a critical part of the mining industry’s infrastructure. However, they are also a source of concern due to the potential for catastrophic failures that can have devastating environmental and human consequences. In this article, we will explore what tailings dams are, how they work, and the risks associated with them. We will also look at some of the recent high-profile tailings dam failures and the efforts being made to improve their safety and sustainability.
What is Tailings Dam ?
A tailings dam is a large man-made structure used to store the waste materials, or tailings, that are produced during the mining and processing of minerals such as copper, gold, and iron ore. These waste materials typically consist of a mixture of water, finely ground rock particles, and chemicals used in the extraction process.
Tailings dams are typically constructed by building a large earthen embankment or dam around a natural or man-made basin, which is then filled with the tailings. The embankment is usually built using materials such as rock, soil, or concrete, and may be reinforced with steel or other materials.
The purpose of a tailings dam is to contain and store the waste materials produced by mining operations, in order to protect the environment and prevent contamination of nearby water sources. However, tailings dams can be prone to failure and can pose a significant risk to human health and the environment if they are not designed, built, and maintained properly. In recent years, several major tailings dam failures have resulted in environmental disasters and loss of life.
Tailings Dam Terminology
Mine Waste Facility (MWF) is a term used to describe any location, structure or area used for the disposal or storage of waste materials generated by mining activities. It includes tailings dams, waste rock dumps, and other facilities used for the storage or disposal of mining waste.
Tailings are the waste materials produced during the processing of minerals from ore. They consist of finely ground rock particles mixed with water and chemicals used in the extraction process. Tailings are typically stored in a tailings dam or other facility designed for their containment and management.
Tailings dams are large man-made structures used to store and contain the waste materials produced during the mining and processing of minerals. They are typically constructed by building an earthen embankment or dam around a natural or man-made basin, which is then filled with the tailings.
Extractive waste refers to any waste material generated by the extraction, processing, and beneficiation of mineral resources. This includes waste rock, tailings, slag, and other materials produced during mining and mineral processing operations. Extractive waste may pose a risk to human health and the environment if not properly managed and disposed of.
Type of Tailings Dam Structures
There are several types of tailings dam structures that can be used for the storage and containment of tailings. Some of the major types are:
- Upstream construction: In this type of tailings dam, the embankment is constructed in an upstream direction, with each new layer of tailings being placed on top of the previous layer and allowed to settle before the next layer is added. This is the most common type of tailings dam construction.
- Downstream construction: In this type of tailings dam, the embankment is constructed in a downstream direction, with the tailings being placed directly against the embankment and allowed to settle before new layers are added. This type of construction is less common due to the increased risk of failure.
- Centerline construction: In this type of tailings dam, the embankment is constructed along the centerline of the basin, with tailings being placed on either side of the embankment. This type of construction is less common and is typically used for smaller tailings storage facilities.
- Rockfill construction: In this type of tailings dam, the embankment is constructed using crushed rock or other coarse materials, which are placed in layers and compacted to form a stable structure.
- Concrete construction: In some cases, tailings dams may be constructed using concrete, which provides a highly durable and stable structure. However, this type of construction is typically more expensive than other types.
- Homogeneous construction: In this type of tailings dam, the tailings are mixed with binders such as cement to form a solid mass, which is then used to construct the embankment. This type of construction is less common and is typically used for smaller tailings storage facilities.
Type of Tailings Dams Configuration
Paddock, Hillside, and Cross Valley tailings dam configurations are specific types of tailings storage facilities that are used in mining operations. Here’s an explanation of each configuration:
- Paddock Tailings Dam: In this configuration, the tailings are stored in a series of cells or paddocks bounded by earthen embankments. The paddocks are typically arranged in a grid pattern, with each paddock separated by an embankment. The tailings are pumped or gravity-fed into the paddocks, where they settle and are dewatered over time. This configuration is commonly used for smaller tailings storage facilities.
- Hillside Tailings Dam: In this configuration, the tailings are stored on a hillside, with the embankment constructed along the contour of the hill. The tailings are pumped or gravity-fed into the impoundment at the top of the hill, where they settle and are dewatered over time. The hillside configuration is commonly used in areas where there is limited space for a conventional tailings storage facility.
- Cross Valley Tailings Dam: In this configuration, the tailings are stored in a large impoundment that spans a valley or other natural depression. The embankment is constructed across the valley, typically using a combination of earthfill and rockfill materials. The tailings are pumped or gravity-fed into the impoundment, where they settle and are dewatered over time. The cross valley configuration is commonly used in areas where a conventional tailings storage facility would require significant excavation and earthwork.
Reasons for Dams Failures
There are several reasons why tailings dams can fail, including:
- Foundation failure: Tailings dams must be built on a stable foundation to ensure their stability. If the foundation is not properly prepared or the underlying soil is not strong enough to support the dam, it can lead to foundation failure and subsequent dam failure.
- Overloading: Excessive loading of the tailings dam can cause it to fail. This can occur if the dam is filled beyond its design capacity, or if additional weight is added to the dam, such as heavy equipment or buildings.
- Seepage: Seepage of water through the dam can cause internal erosion and weaken the embankment, leading to dam failure. This can occur if the dam is not properly designed or constructed, or if the materials used in the construction of the dam are not impervious to water.
- Slope instability: The embankment of the tailings dam can fail due to slope instability, which can be caused by a variety of factors such as erosion, foundation failure, or seismic activity.
- Human error: Human error can also contribute to tailings dam failures. This can include errors in design, construction, operation, or maintenance of the dam. Failure to properly monitor and maintain the dam can also lead to its failure.
- Extreme weather events: Natural disasters such as heavy rainfall, floods, or earthquakes can also cause tailings dam failures. Extreme weather events can cause the embankment to become unstable, or increase the loading on the dam beyond its design capacity. Please refer to this article for more information about natural disasters in each country: Natural Disaster Risks in Asia: A Country-by-Country Overview
- Liquefaction: Liquefaction can occur when the tailings within the dam become saturated with water, causing them to lose their strength and behave like a liquid. This can occur during seismic activity or other events that cause the tailings to vibrate, such as blasting or heavy equipment operation. Liquefaction can cause the embankment to lose its stability and lead to dam failure.
- Erosion: Erosion can occur when water flows over or through the tailings dam, causing the particles within the dam to be eroded and carried away. This can occur during heavy rainfall, flooding, or when the tailings are not properly compacted or stabilized. Erosion can weaken the embankment and lead to dam failure.
Examples of Tailings Dam Failures in the World
Here are some examples of major tailings dam failures that have occurred around the world:
- Mount Polley mine disaster, Canada (2014): The Mount Polley tailings dam failure in British Columbia, Canada, is one of the most significant tailings dam failures in recent history. The failure released 25 million cubic meters of waste into nearby waterways and caused extensive environmental damage.
- Brumadinho dam disaster, Brazil (2019): The Brumadinho tailings dam failure in Minas Gerais, Brazil, released 12 million cubic meters of tailings, killing over 250 people and causing extensive environmental damage.
- Samarco dam disaster, Brazil (2015): The Samarco tailings dam failure in Minas Gerais, Brazil, released 50 million cubic meters of tailings, killing 19 people and causing extensive environmental damage.
- Ajka alumina plant accident, Hungary (2010): The Ajka tailings dam failure released 1 million cubic meters of red mud tailings, killing 10 people and causing extensive environmental damage.
- Omai mine disaster, Guyana (1995): The Omai tailings damfailure released 3.5 million cubic meters of tailings, causing extensive environmental damage and contaminating the local water supply.
- Merriespruit tailings dam disaster, South Africa (1994): The Merriespruit tailings dam failure released 600,000 cubic meters of tailings, killing 17 people and causing extensive damage to the surrounding area.
- Stava Valley disaster, Italy (1985): The Stava Valley tailings dam failure released 180,000 cubic meters of tailings, killing 268 people and causing extensive damage to the surrounding area.
- Los Frailes mine disaster, Spain (1998): The Los Frailes tailings dam failure released 4 million cubic meters of tailings, causing extensive environmental damage and contaminating the local water supply.
These and other tailings dam failures have highlighted the importance of proper design, construction, and maintenance of tailings storage facilities, as well as the need for effective monitoring and emergency response plans to mitigate the risk of dam failure and minimize the impact of any incidents that do occur.
For more information about tailings dams, please refer to a reading published by Scor Re (www.scor.com/sites/default/files/2021-10/202110_Handbook_Tailing_Management_Facilities.pdf)
Want to know how to transfer your project risks of tailings dams failure and protect your company cashflow? Please contact us by email: leo.c@projectriskinsights.com
