While selecting the right liner is key to longevity and good performance under a leaching heap, it’s not the only factor to consider. Even the toughest RPE liners from will eventually fail before their expected lifespan is up if they’re installed incorrectly or used in a way incompatible with their design. Understanding the limitations of geomembrane liners and what affects them is essential to using them successfully as part of a leach pad. Careful site preparation and extra materials. like underlayment, go a long way in preventing all of these threats from shortening the lifespan of the liners in a leach pad system.
Concentrated Weight
The amount of weight pressing down on any individual square foot of liner greatly determines how long it will last and the likelihood of a tear. Widespread pads may be harder to evenly irrigate, but they spread the total weight of a few million tons of rock out over a much larger piece of liner. This means that the weight pressing down on any specific square foot is much lighter, reducing wear and tear and extending the lifespan of the pad. Tall and narrow pads may save ground space, but they’re harder to keep properly lined to the concentration of the total weight of the load. Valley pads in particular are prone to concentrating weight on the liner, so it may be necessary to upgrade to a thicker material when planning one of these designs.
Punctures
All geomembrane liner material, even reinforced polyethylene, is prone to puncturing. This is due to both poor site preparation and the use of angular and sharp materials on top for a drainage collection layer. Laying down a thick layer of compacted clay or a synthetic geotextile underlayment over the dirt can prevent punctures from below. Only a durable and reinforced material can compensate for the puncture risks from the material heaped above the pad. Reinforced materials are a must since this manufacturing method greatly increases the resistance to puncturing and tearing alike.
Heavy Wear and Tear
Aside from wear and tear caused by the addition of ore fines to the pad, the surrounding area around the heap sees plenty of traffic from heavy machinery. Trucks may need to travel over the pad hundreds of times to spread out the various layers of material. Even after a base layer is established and the equipment isn’t contacting the liner material directly, the weight and movement of the equipment still transmit stress down to the liner through the various layers. This is another reason a reinforced liner material is essential for heap pads, especially On/Off pads that are both loaded and unloaded after every use.
Aggressive Lixiviant Agents
The same chemicals and compounds needed to break the bonds between the ore and rock for extraction tend to break down the liner material as well. While geomembranes vary in their ability to withstand chemicals, most are susceptible to at least one lixiviant agent commonly used for heap leaching today. Some can’t withstand the erosive effects of bioleaching in particular, while others react badly to acids or alkali solutions only. Matching the chemical resistance of the liner material to the specific process and lixiviant agents is essential for long-term success, especially for pads that will be used for multiple cycles. RPE has the best general chemical resistance, but you should still check individual compatibility with any chemicals you plan to use for leaching.
Sliding or Slumping
When a lift is improperly loaded, doesn’t get compacted correctly, or the heap simply goes too high, the entire pile is prone to shifting sideways. This can cause sliding or slumping that unexpectedly changes the stress and weight on the liner and pad as a whole. It’s not uncommon for a large-scale slide to rip the liner and crack the entire pad open as well, resulting in extensive contamination and environmental exposure. Only careful planning and limitations on lift height and total heap height can protect the liner from this kind of damage. It’s not worth risking the cost of clean-up and remediation after a major spill just to try and add a few more feet of material to an already strained pad.
UV Exposure
Most heap leach pad designs call for covering the impermeable liner material with a base layer of permeable rock or compacted soil. This not only protects the base liner from UV damage, but it also creates a collection zone for the leachate to accumulate before draining out into the storage ponds. Yet, the liner in the trenches, storage ponds, and containment areas around the heap pad is often left exposed after installation. This material must be rated for constant UV exposure, so it doesn’t threaten to shorten the lifespan of the entire system. Using highly UV resistant liners in general is a good idea to keep accidental exposure from shortening the lifespan of a pad when it’s being built or repaired.
With care taken to minimize risks and threats to the liner, heap leach pads can last for decades. Since many conventional heap leach pads are capped with the fines in place rather than cleaned off, the liners must last as long as possible to protect the environment for years to come. Make sure you’re choosing geomembranes that are up to the task by working with our experienced team here at BTL Liners.
