For hundreds of years, heap leach pads were simple constructions of graded and berm soil with ore piled directly on top of the ground. In the 1960s to 1980s, mine operators finally began to put the various geomembrane products available to good use in lining these pads. Yet, there’s no reason why a heap leaching mound should only feature a single layer of liner at the very bottom. In fact, some of the latest designs in this technique call for lining every lift instead of just the pad. This creates a series of mini-pad layers that can offer a number of benefits over the single liner system.
First, interlift liners help reduce the compression effect caused by the accumulated weight of the fines. As the fines press down with each new lift added, it’s easy for compacted areas to develop that crush just some of the pipes or tear through a section of the bottom liner. By adding a liner as every level or every few levels of ore are added, the weight of each lift is better distributed across the entire surface area of the pad. This can prevent both leaks and a lack of leachate flow over time.
Controlling Horizontal Losses
Horizontal losses of leachate aren’t common with most heap leaching mounds, but they can be an issue in valley designs. If the valley isn’t completely bermed and lined, contact between the heaped ore and the surrounding soil can lead to leachate traveling out of the containment area. Interlift liners stop the risk of that kind of loss by ensuring there is no contact between the mound and the soil around the edges of the pad. Each new layer of liner overlaps to create a completely enclosed system. This is important if high levels of lixiviant are used for the extraction process.
Spreading out the weight of each lift as widely as possible does more than just control compression from the force pressing downward on the collection system. It also reduces the chances of sliding and slumping occurring between the layers of material. Isolating each lift that is added with a geomembrane stops vertical cracks and rifts from traveling upward through a heap. This can be a real issue with irrigation since water can always move unevenly through the material and cause it to wash out below the surface. Interlift systems allow for better stabilization at every level, ensuring there’s as little risk of a sudden collapse or shift as possible.
The lifts used today in modern heap leaching are far thinner than the layers once used for the traditional form of this procedure. However, they’re still quite thick on many projects, with average lift height ranging anywhere from just 2 feet to 20 feet or more. The thicker the lift layer, the more likely it needs an interlift liner system to support it. Thicker lifts produce more leachate, and the compaction that occurs between layers can make it hard for large amount of liquid to cross the barrier. Liners help direct that volume to a drainage and storage system rather than allowing it to trickle straight down, reducing the chances of destabilization and other issues.
Greater Total Height
With both greater stability and less compression occurring with an interlift system of liners, it’s possible to build a heap with a far greater total height than with a single layer of liner at the bottom. With demand for heap height growing as leachate techniques improve, it’s not surprising that many operators have pushed the limits to stack ore as high as 300 to 500 feet above the pad. With that much ore in one place, it’s essential to reduce the risks of a collapse or slide as much as possible.
BTL Liners has the products you need for a complete interliner system. Our flexible RPE liners can stabilize each lift of a system for better capture and leachate control. Let our reinforced geomembranes add stability so you can stack the ore fines as high as you like.