Modern mining operations may produce thousands of tons of tailings after the ore is removed and processed for valuable materials. However, this mixture of waste rock that is left behind after the desired mineral or metal is extracted is far from the only waste produced coming from a mine. All of the mine’s waste products need careful handling and containment, but they also vary in usefulness and chemical composition. Treating overburden like it is tailings is a waste of money, while doing the opposite can result in environmental damage and high remediation costs. Keeping the materials coming out of a mine separated can reduce containment costs and ensure it can all be reused as much as possible.
What is Overburden?
Overburden is the term applied to all of the material that lies above the deposit of ore or minerals that are going to be removed. It is generally low in any kind of coal, ore, or other valuable material. It can include solid rock that is blasted or drilled out of place, but it also includes a large volume of mixed rock, sand, dirt, and even the topsoil and vegetation at the very surface. If any mud or clay must be removed from the site, it will also be included in the overburden. Topsoil and soil in particular should be separated from tailings and even other types of overburden if possible. This allows for the best recovery for the site after the mine is closed because the nutrient rich material can be restored to the surface. Replacing the topsoil encourages rapid plant establishment, preventing erosion and exposure of the potentially hazardous material it is covering. Rock overburden, especially any material that contains heavy metals and other contaminants, is usually mixed in with tailings to prevent the need for a third storage space.
What is Gangue?
Gangue is another term for tailings, but it specifically refers to the rock mixed in with the ore or minerals itself. Some tailings are removed between layers of economically viable material and are specifically known as interburden. Gangue is the term for the rock material that is bound up with the desired metal or mineral, serving as its matrix to form the ore. Once the chosen processing techniques have extracted as much of the desired product as possible, gangue is what is left behind as waste rock and contaminants. The gangue portion of the tailings specifically need the best containment, with low-permeability liners, so that the heavy metals and chemicals they carry do not leach out into the environment.
What is Mill Run and Ore?
Ore is often mistaken for the material extracted from raw mine material known as mill run. However, it refers to the raw material as well because it includes both the waste rock serving as the matrix and the mineral or metal that is desired. Mill run is often sorted into waste rock and valuable ore before processing, resulting in better ratios of recovery. Waste rock sorted out at this stage must be handled as tailings since it is usually hazardous in at least one way. Ore may need additional crushing and sorting before it’s processed, or it may be heaped directly out of the mine and leached immediately to begin the process. Once the materials are extracted, everything left behind from the ore and mill run is known as tailings.
What are Raffinates?
The term raffinate refers to any liquid left over after materials are extracted in some way. In mining, raffinates are the liquids produced during heap leaching and other processing methods. Between rainwater percolating through the system and the chemicals used to actually separate metals from waste rock, there can be thousands to millions of gallons of liquid to handle after the facility shuts down. Raffinates are often mixed back in with tailings, especially finer materials that are prone to wind scouring and forming dangerous clouds of dust. These liquids also play an important role in forming any high-density pastes needed for filling voids and stabilizing excavations in the mine. However, they can’t be mixed into tailings without consideration for the seepage rate of the storage area. Any area designed to hold raffinates must be lined with a low permeability liner to control liquid loss through the soil that could cause long-term environmental damage.
No matter how these mining by-products and waste materials are stored, they must be contained with impermeable geomembrane liners. BTL Liners has all the industrial grade pit and pond lining materials you need to keep tailings, raffinates, and more right where you need them. Do not settle for remediation costs years down the road when investing in the right liners from the start can protect the environment and the profitability of the project. If you’re not sure what liner is right for your project, we’re happy to make recommendations.
