Despite the risks that come with using chemicals to separate ore from rock, heap leaching is one of the safest and least damaging methods to use. Yet, there are plenty of measures needed to protect from the risks of environmental damage that can still occur. Without appropriate lining and leak detection, like monitoring wells or sensors, it’s all too easy for processing ponds to cause damage. Since these ponds can hold chemical solutions for months or even years as the leaching process proceeds, they must be built to withstand the wear and tear of the harsh environment. Here’s why it’s important to secure every part of an ore recovery system to prevent environmental damage.
Risks of Processing Pond Spills
It’s the chemicals used for the leaching process, also known as lixiviants, that create the majority of the environmental risk from a leak or spill. For example, sulfuric acid can harm humans that come in contact with it and acidifies soil to interrupt plant growth. Cyanide is dangerous to animals, people, fish, plants, and more. However, the ore itself often poses a hazard as well if it’s considered a heavy metal. Uranium is the most impactful on the environment if it escapes the processing pond environment, but even nickel and iron can create problems when deposited in large amounts.
EPA and State Regulations
It’s not just the actual risks of the spill that makes it worth preventing. The Environmental Protection Agency (EPA) and numerous state agencies are involved with each new mining or ore processing project. Not only do they have approval over these facilities, but they also have the ability to fine them heavily when there is a proven leak. The more environmental damage that could possibly occur, the worse the penalties. Even if the damage turns out to be less severe than expected, the fines can easily make a profitable mining operation go under. Conforming with the bare essentials of various regulations may not be enough, making it a smart idea to overbuild the system to avoid failures in the future.
What Causes Leaks and Spills?
There are many pathways to chemical loss and environmental issues in each ore recovery system. The risks begin at the heap leaching pad, which will seep chemicals slowly into the soil if built without a liner. Yet, even if the liner is put in correctly, it can still rip or tear from the wear of the mounded material pressing down on it. The same is true for liners installed in processing ponds containing millions of gallons of slurry. All of the weight of the liquid quickly adds up between the water and what’s suspended in it. Wear and tear on the liner from dredging and ore removal can also lead to leaks eventually. Using a reinforced material like RPE is the best way to prevent those issues. Finally, failing to size the system for record-breaking rainfall could lead to flooding at some point. While many EPA and state regulations only call for using 25-year flood records to determine the highest possible risk, moving to a 50 or 100-year record could give you more protection from overflowing.
Multi-Pond Systems and Compounding Risk
Few heap leaching facilities rely on a single pond to hold the leachate and process it. Most systems call for a pregnant solution pond to collect the raw leachate as it first flows out of the heap pad. This pond experiences the highest amount of chemical exposure, so it’ll need a compatible liner material. Some systems also use this pond as the primary processing area for separating ore from waste materials. In other systems, one or more intermediate ponds are used specifically for processing. If they’re aerated or include other mixing equipment to assist with ore recovery, these ponds will need liners that can handle the wear. Finally, barren ponds hold the wastewater left behind after processing is completed. If they are built as deep enough pits, they may also double as storage solutions for permanent disposal. These ponds definitely need long-lasting liners since they’ll contain water and tailings for decades to come.
Double Liner Systems for Leak Detection
One of the most secure ways to monitor and prevent leaks, and the resulting environmental impact at a metal processing facility, is a double liner system. This is installed in processing ponds where a single layer of geomembrane is usually used. They can also be installed under heap leaching pads, but they’re usually replaced with sump wells installed in the existing multi-layered leachate collection system. Double liners are used on their own for the holding ponds at a mine to ensure that leaks are caught long before they ever reach the soil. Since even a relatively small leak can shut down the processing facility and lead to fines, it’s worth the cost to contain and catch them with constant detection rather than occasional inspection.
Monitoring Wells and Pumps
If a full double liner leak control system is overkill for a specific leaching pad or processing pond, monitoring wells should still be used around the edges of the installation. These wells are semi-permeable so that water traveling through the soil can flow into them. If there is liquid escaping from the surrounding edges of the processing pond, some of it will become trapped in the wells. Regular inspection or automatic pumping alerts the facility owner so they can track down the leak and repair it. However, these monitoring methods do allow some amount of leachate to escape into the soil before the problem is detected.
Tailings Risks After Processing
The risks to the environment from mining byproducts don’t end as soon as processing wraps up. After as much water is removed from the raw material as possible, the resulting solid fines are known as tailings. Tailings are usually high in chemical contamination and may even be radioactive if they’re the result of uranium mining. These materials must be either productively reused or buried for safety, so some processing ponds are designed to serve as the final storage area for tailings in particular. This reduces excavation, handling, and transportation costs for a potentially hazardous waste.
While heap leaching typically reduces the impact of ore recovery on the environment, it still comes with its own set of risks to go with the rewards. These facilities can be built with minimal to nearly no impact on the surrounding environment with a little extra care and the right materials. Since secure containment begins with impermeable geomembranes to use as liners under ponds and pads, you’ll need our help here at BTL Liners. We’re happy to help with expert advice and some of the most durable RPE liners on the market.
