Using geosynthetics in mining heap leach pads

Industry News
Photograph courtesy of NAUE GmbH & Co. KG

Industrial mining is essential in our tech-driven world. The need to create more efficient and cost-effective solutions has led to the rising popularity of a large-scale mining technique called heap leaching. Heap leaching utilizes chemical reactions to separate desired minerals from raw ore. The technique can produce desired concentrations of the target mineral at a lower cost compared with other processing methods.

To further enhance heap-leaching operations, engineers have turned to geosynthetics as a lightweight, durable and cost-effective long-term solution for building modern heap leach pads. These geosynthetic products include low-permeability liners for containment, geotextiles for protection and filtration, and structured liners for slope stability and drainage. This article will discuss heap leach pads along with the related geosynthetic products.

Creating heap leach pads with geosynthetics

Creating a heap leach on a flat pad, on-off pad or valley pad typically requires only a single composite liner. A composite liner incorporates multiple layers—such as a geosynthetic liner and geotextile—to provide several benefits in a single product. Most heap leach pads will start with the foundation, or subgrade, with a low-permeability layer directly above. The low-permeability and absorption layer will comprise compacted clay (if it can be locally sourced) or a geosynthetic clay liner (GCL) made with bentonite. Directly above the clay/GCL is the geomembrane liner with low permeability for containment. A protection layer is placed above the geomembrane and is made with a geotextile, padding and separating the geomembrane from the heap. Above the geotextile is the mineral drainage layer, which includes the piping system to collect the solution.

Heap leach pads are designed to reduce cost by utilizing passive techniques, such as chemical reactions to separate desired minerals and gravity to move the solution through various basins for further processing. Heap leach pads are typically built on a slight slope so that the solution naturally flows into a collection basin. To support sloped pads, the composite liner may also benefit from using a structured liner with asperities that offer improved slope stability through enhanced interface shear strength.

The benefits of geosynthetics over competing solutions

The primary benefit of using geosynthetics over other products is the myriad of ways that geosynthetics can be manufactured to serve different purposes. Additionally, most geosynthetic products will share similar properties including high chemical resistance, flexibility and durability. For example, the high-density polyethylene (HDPE) resin used to create some geomembranes can resist the harsh chemicals required in heap leaching. HDPE’s durability is also useful for withstanding the point loads that are typical in heap leaching. And if necessary, the resin can be substituted for an alternative like linear low-density polyethylene (LLDPE), which offers improved flexibility and elongation.

There are also benefits for using a GCL instead of importing clay. Because a GCL is made by sandwiching a layer of water-absorbing bentonite between two nonwoven geotextiles, even a 394-mil (10 mm) thick liner can perform equal to or better than 11.8 inches (30 cm) of compacted clay. Therefore, using a GCL can significantly reduce material transportation costs and improve installation times.

This article originally appeared on the AGRU America blog, https://agruamerica.com/blog.