Tailings Management with Geosynthetics

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 may can be liquid, solid or a slurry of fine particles. Typically, they consist of crushed rock, water and traces of metals eg. Copper. These rejected minerals and rocks produced through the mining process also have the potential to damage the environment by releasing of toxic metals such as arsenic and mercury, causing erosion and sinkholes and contaminating soil and water supplies.

A recent United Nations (U.N.) 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 300 metres 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; and

• Use best available technology and best available practices.

Tailings dams need regular monitoring and ongoing to ensure that there is adequate drainage and 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.

In regards to containment, there are a number of elements to consider when lining the site, including: natural clay options, free ranging aggregate and additional Clay lining through to protection and leak detection. 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 is critical.

• Geosynthetic Clay Liners (GCL) – to be utilised when naturally clay is not an option yet secondary containment is a must. Additional theory is the combination of a composite covering both Geomembrane and GCL at the same time.

• High Strength Structural Woven PET and Geogrids for soil reinforcement, capping and foundation stabilisation.

For assistance in choosing the right product for your individual mining project, contact Andy Warwick- National Product Manager (andy@globalsynthetics.com.au).