Tailings dams are essential to the mining industry. With demand soaring for the metals from these mines, operators are seeking safer, more sustainable tailings storage facility construction methods (1).
One approach is to utilize specialized geomembranes that provide all the benefits of a typical geosynthetic liner while also enabling the construction of steeper slopes for more cost-effective tailings storage facilities (TSF).
Why are geomembranes important for tailings storage facilities?
Historically, the mining industry disposed of tailings via impoundments, backfilling underground mines, free-standing piles, and into open pits. Regulations led to the introduction of TSFs to address environmental concerns (1). Unfortunately, not all TSFs are made the same. There have been a consistent number of TSF failures over the last few decades and at least three significant incidents over the previous five years (2).
It is important to note that failures at tailings storage facilities also occur in regions with years of experience in mining and advanced regulatory systems, such as the United States, Canada, Australia, and Europe (3).In the United States, for example, the failure of the New Wales Plant in Mulberry resulted in 840,000 m3 of liquid contamination being released underground, reaching as far as the Florida Aquifer (2).
TSF failures are often attributed to overtopping, stope stability failures, and earthquakes. Overtopping and slope stability are controllable through more rigorous design measures and higher safety factors. In contrast, earthquake protection requires more in-depth modeling to accurately predict earthquake intensities throughout the expected service life of the facility—sometimes in perpetuity. Geomembranes offer a way to support better TSF designs.
Geomembranes are made of polymer resins combined with additives such as fillers, carbon black, lubricants, antioxidants, and plasticizers. These thermoplastic sheets are flexible, have low permeability, and are durable when installed correctly. Using geomembranes as a liner in TSFs helps support the integrity of the construction by controlling fluid migration and ensuring containment (4, 5).
Geomembranes can also be manufactured with projections, studs, or other physical characteristics to support steeper slope designs.
The top 4 benefits of geomembranes in tailings facilities
Modern TSF constructions can benefit from incorporating geomembranes into their designs.
#1 – Slope stabilization and erosion protection
The geotechnical safety of the tailings storage structure is a primary concern. The first step is understanding the mechanical and elasticity parameters to establish potential displacement, taking special note of situations where waste buildup can lead to slope failures (6).
Structured geomembranes can include physical projections that help with slope stability. Geomembranes have been researched and evaluated extensively as stabilizing mechanisms on steep slopes. One paper, for example, detailed laboratory and field tests using packed soil in boxes with a 50% slope angle. The lab samples were individually subjected to 122 mm simulated rainstorms. The tested geomembranes significantly reduced runoff and dissipated the impact of the raindrops. Field tests on 33% to 60% slopes over two years provided comparable results (7).
Using these structured geomembranes on embankments or dam walls can help minimize erosion and increase shear strength. Geomembranes have even been used to line steep rock slopes to expand TSFs (13).
#2 – Effective draining system in tailings facilities
Adequate drainage is essential for all geotechnical constructions, especially for a TSF. Geomembranes can help minimize the risk of fluid buildup and liquefaction of the saturated materials by supporting effective drainage systems. A typical TSF drainage system involves a collection ditch to collect runoff, pumps, and a collection and treatment system. The ideal system reduces the amount of stored water to zero, as most issues related to TSF often stem from liquefaction (8).
With a seepage dam wall system, a structured geomembrane with studs and a filtering geotextile can effectively drain water out of the tailings to reduce moisture buildup (9).
#3 – Long-lasting and durable
The expected service life of a TSF can change as technology develops and once useless tailings find a newfound purpose (10). For this reason, TSFs are designed to last for decades. This presents a unique engineering challenge as weather and seismic records in certain regions are limited in scope.
However, one area where engineers can confidently predict longevity is the geomembrane liner. High-density polyethylene (HDPE) geomembrane liners have more than 100 years of service life when protected and correctly installed (11). Engineers can build with high safety factors by utilizing robust components, such as an HDPE geomembrane liner, within the TSF.
#4 – Leakage protection and containment
Contaminants dangerous to human health are a concern in mining, manufacturing, and agriculture. Fortunately, advances in mining construction methods and geomembranes have offered the ability to create better barriers between a TSF and the environment. Additionally, polymer and material science advances have yielded better resins for more resistant membranes (12).
Modern geomembranes can resist degradation from UV exposure, chemical reactions, oxidation, and extreme temperatures. Furthermore, selecting a geomembrane from an authorized and trustworthy manufacturer or supplier is essential to ensure the highest quality geomembrane and technology are used. Geomembranes must be flexible and robust to withstand stress cracking for years under the load by tailings and fluid (12).
Most geomembranes today are created from polymer resin combined with additives (stabilizers, carbon black, lubricants, and antioxidants) to ensure long-term performance and protection against degradation for as long as possible. Geomembranes are commonly made of five types of materials, including HDPE, which most often have low-compression strength, are non-transparent, and have a higher chemical resistance than the other types (5, 10).
For best results, geomembranes should be installed using proper techniques and quality control procedures. Companies like AGRU America offer technical support and training to maximize geomembrane performance through effective installation techniques. See our video on welding techniques.
Geomembranes by AGRU
ARGU offers a variety of geosynthetic solutions for tailings storage facilities. AGRU supports projects with exceptional technical expertise, superior customer support, and an evolving inventory of innovative products to solve any challenge. AGRU uses the flat-die extrusion method for more consistent thickness control and improved tensile properties in its geomembranes than those created with the blown film process.
Two recent AGRU innovations include FrictionSpike and CleanSeam.
FrictionSpike is a first-in-class, patented multi-tiered geomembrane solution that enables engineers to increase slope angles, maximize containment air space, and increase Factor of Safety. Owners can use FrictionSpike for landfills, mines, and regions with unique interface shear strength requirements to meet project slope stability conditions and unlock new capabilities and designs.
CleanSeam is a protective strip on high-density polyethylene (HDPE) liners that installers can peel away to dramatically reduce the time required to prepare the liner’s welding zones.
1. “TECHNICAL REPORT: Design and Evaluation of Tailings Dams.” EPA. (1994) Accessed online 28 May 2022. https://archive.epa.gov/epawaste/nonhaz/industrial/special/web/pdf/tailings.pdf.
2. “Chronology of Major Tailings Dam Failures (From 1960).” Wise Uranium. (2022). Accessed online 29 May 2022. https://www.wise-uranium.org/mdap.html#USCOLD.
3. D. M. Chambers. “The Increasing Number of Tailings Facility Failures: Navigating The Decade 2020-2029” Center for Science in Public Participation. (2019). Accessed online 28 May 2022. http://www.csp2.org/files/reports/Increasing%20Number%20of%20Tailings%20Facility%20Failures%20-%20Chambers%20Oct19.pdf.
4. I. V. Muralikrishna and V. Manickam. “Environmental Management.” Science Direct. (2017). Accessed online 3 June 2022. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/geomembranes.
5. W. W. Müller and F. Saathoff. “Geosynthetics in geoenvironmental engineering.” Science and Technology of Advanced Materials. 16 (3): 034605. (2015). Accessed online 16 June 2022. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5099829/.
6. K. Koda et al., “Landfill Slope Stability Improvements Incorporating Reinforcements in Reclamation Process Applying Observation Method.” Applied Sciences – MDPI. 2020.
7. M. Agassi. “Stabilizing Steep Slopes with Geomembrane.” Soil Technology. (1997). Accessed online 3 June 2022.
8. “Water Management Considerations for Conventional Storage.” Tailings. Accessed online 15 July 2022. https://www.tailings.info/technical/water.htm.
9. S. Hedin et al. “Passive Treatment of Toe Drain Discharges from a Tailings Storage Facility using an Oxic Granite Bed.” https://www.hedinenv.com/pdf/IMWA%202015_toe_drain_discharges_full%20paper.pdf.
10. Ruiz et al. “Planning the Dewatering of a Tailings Storage Facility.” Mine Water Enviro. (2021). Accessed 3 June 2022. https://link.springer.com/content/pdf/10.1007/s10230-020-00745-z.pdf.
11. M. Koerner et al. “Geomembrane Lifetime Prediction: Unexposed and Exposed Conditions.” Geosynthetic Institute. (2011). Accessed 3 June 2022. https://geosynthetic-institute.org/papers/paper6.pdf.
12. K. Rowe and K. C. Berger. “Research Update on Geomembranes at Tailings Storage Facilities.” (2017). Accessed 3 June 2022. https://www.klohn.com/blog/kcblog-research-update-geomembranes-tailings-storage-facilities/.
13. J. Purdy et al. “Lining Steep Rock Slopes with a Geomembrane Liner to Facilitate Tailings Facility Expansion.” Tierra Group International, LTD., (Private Publication). (2013). Accessed online 28 May 2022. https://www.tierragroupinternational.com/assets/documents/Lining-Steep-Rock-Slopes.pdf.