Tailings are by-products, the materials that remain after the process of separating the target mineral from the uneconomic fraction of an ore. They are different from the waste rock or other material that overlies an ore or mineral body, which are displaced during mining without being processed. Tailings can be liquid, solid or a slurry of fine particles. Typically, they consist of crushed rock, water and traces of metals. These rejected minerals and rocks produced through the mining process also have the potential to damage the environment by releasing toxic metals such as arsenic and mercury, causing erosion and sinkholes and contaminating soil and water supplies.
A recent United Nations Environment report called for international action to make the storage of mine waste more secure. In the past, tailings were disposed of in the most convenient manner, such as in downstream running water or down drains. However, due to the concerns about these sediments in the water and other places, tailings dams came into existence. Tailings dams can be as large as lakes and reach 1,000-feet (300-m) high. As the slurry of waste is piped into the dam, the waste solids migrate to the bottom, and the water is recycled to be used in the separation process again. Rather than reinforced concrete, tailings dams use earth or rock to create a bank (barrage). However, it is more common for tailings dams to use the cheaper but more hazardous upstream method of construction, only using the tailings themselves to create the barrier layer. The dam is then raised to accommodate more waste, making them more unstable and prone to failure.
When designing tailings storage facilities, such as dams it is imperative for them to:
- Never fail—including during the most extreme weather events imaginable in their geographic location accounting for climate change
- Ensure safety takes precedence over cost
- Use best available technology and best available practices
Tailings dams need regular monitoring and ongoing maintanence to ensure that there is adequate drainage and that the dam is strong enough to withhold the mining waste. With the increase in the size of mining sites and the depth of tailing dams, geosynthetics are increasingly playing a vital role in the containment and erosion control of the basal lining of these facilities. The geomembrane-lined tailings play a vital role in reducing the environmental footprint of the mining industry. Therefore, the geosynthetics used must be functional, sturdy and proven in aggressive environments over the long term.
When selecting the geomembrane type, key properties that need to be considered are chemical resistance of the geomembrane, tensile strength, temperature resistance, installation conditions, cost, and previous experiences of its application and overall performance.
Global Synthetics containment solutions include:
- Geomembrane solutions: Ensuring that the site in question is fully lined to contain the liquids while preventing any leakage; flexibility, durability and chemical resistance are critical.
- Geosynthetic clay liners (GCL): GCLs are to be utilized when natural clay is not an option yet secondary containment is a must. Some geotechnical engineers combine a geocomposite covering both the geomembrane and the GCL.
- High-strength structural woven polyethylene (PET) geotextiles and geogrids: PET geotextiles and geogrids are effective for soil reinforcement, capping and foundation stabilization.
This article originally appeared on the Global Synthetics blog, https://globalsynthetics.com.au/blog/.