When compared to other widely used mining and processing methods, heap leaching is one of the least environmentally impactful options for producing precious metals. However, it still involves using leachate that is highly concentrated in compounds that can be potentially hazardous. Proper handling of leachate is essential to keep these risks to a minimum. Leaks and seepage are preventable with proper leach pad design, but first it’s important to understand what the risks really are if a pad design fails.
Groundwater Contamination
The greatest, long-term risk, of improperly designed heap leaching pads, is groundwater contamination. Most of the seepage and leaks that occur in a heap will go straight down rather than radiating far from either side. As the leachate travels through the layers of soil and rock, it can settle into the water table and spread much farther than expected from this pattern. This can lead to groundwater contamination that affects human health, livestock, or crops irrigated with the water. Chemicals like cyanide and sulfuric acid are just part of the problem. Other compounds are extracted along with the ore like heavy metals and toxins. While leachate from a heap mining pad is not the most concentrated or hazardous liquid waste product, it is still risky enough to be worth containing securely.
Surface Water Damage
The damage to water supplies isn’t limited to groundwater. While seepage doesn’t usually spread horizontally through the soil from a damaged pad, surface runoff that makes it past a berm at the edge of the pad can be a problem. This often leads to contamination of nearby creeks, ponds, and rivers. Mining facilities are often set up near bodies of water to take advantage of the easy access to a steady water supply. This means they have a responsibility to control leachate loss and runoff issues so that nearby waterways aren’t negatively impacted. The chemicals found in mining leachate tend to have long-term effects on surface water, so it’s better to control leaks and runoff from the start than to try and deal with remediation efforts later.
Long-Term Soil Issues
Leachate, from mining, tends to add both heavy metals and salts to the soil around the pad unless it’s properly lined. Clay liners can’t prevent soil contamination, but an intact geomembrane will. The leachate ingredients that are most hazardous to plant and animal life, including cyanide residues, are also the ones that tend to stay in the soil for years. Since many mines are located in areas also used for agriculture, it’s important to protect nearby farms and fields with appropriate liner selection.
Lost Profits
Don’t underestimate the amount of profit that can be lost to a leaking or badly designed heap leaching pad. As the base of the entire process, the pad is the key to keeping the leachate flowing steadily and extracting as much ore as possible. Allowing leachate to escape into the soil or water only translates into wasting valuable ore that could’ve been recovered. It’s unfeasible to try to treat the contaminated soil or water to extract the ore in most cases, meaning that it’s lost forever to the recovery cycle. Keep ore where it’s needed instead, to collect every last ounce of gold, silver, or uranium from the waste water before it’s disposed of.
Flooding Risks
As with all wastewater holding facilities, there’s always a risk that a clogged pipe or other issues could lead to a dangerous back up of fluid. A leachate flood is far more dangerous and expensive to clean up after than a release of fresh water, due to the extra contaminants and compounds. It’s also a waste and represents a large loss of the valuable ore being extracted by the process. Make sure that any ponds, collection pipes, sumps, and other parts of the system designed to hold liquid have plenty of outlets for safe drainage. Consider the path of any potential flooding and try to align the site so the leachate wouldn’t come in contact with residential or commercial areas. While most mines are located far from any buildings that might be occupied or damaged, others are located closer than expected to sensitive areas.
Take charge of the risks of leachate loss by addressing it head on with an impermeable geomembrane liner. Don’t gamble with unreliable clay liners when BTL Liners has everything you need for a secure and seepage proof leaching pad. Ensure that every drop of leachate is captured for ore removal rather than lost to the environment where it will only cause damage rather than produce a profit. Protecting the environment can be profitable when it also maximizes your ore recovery rate from a heap leach pad.
