There are many methods for extracting ore from the raw rock and minerals they’re often mixed in with. If the ore is pure enough, mining is enough to extract chunks and pieces of material ready to go straight to the smelter. Low-grade ores are wasteful to immediately smelt because the amount of energy required to separate the materials is unfeasible for the value of the ore. Yet, most mines generate a large volume of mid to low-grade run-of-mine material that is a waste to just dispose of in a pit. Techniques like heap leaching help mine operators generate an additional stream of profitable ore without a major investment in new technology or equipment. Relying on some chemical leaching agents and the power of time and gravity, leaching dissolves ore from minerals and sends it to secure ponds for further processing.
A Long History of Heaping
Despite being used today as a modern method, heap leaching is actually one of the oldest forms of metallurgy. It’s a dissolution technique that relies on the solvent nature of water to separate ore from rocks and minerals that aren’t as useful or needed. The earliest written description of heap leaching for mining dates back to the middle of the 16th century. Those methods relied on water alone or rudimentary solutions based on salt. Today’s heap leaching is accomplished with a wide range of chemicals known as lixiviants, but the goal to separate ore from rock remains the same.
Modern Leaching Processes
In addition to changes in the chemicals used to dissolve the ore, modern heap leaching also relies on a durable and impermeable liner. This liner system actually has multiple layers to collect the leachate that contains the valuable ore. Without permeable layers across the top of this system, it’s impossible for the impermeable geomembrane at the base to collect the pregnant solution. Multi-layer collection systems direct the solution to the series of processing ponds that will settle and condense out the various materials. In contrast to historical heap leaching processes, modern leaching can either go quickly, in a matter of days, or stretch out over the course of months to slowly achieve a high rate of recovery.
Making the Most of Lower Grade Ores
Heap leaching first gained popularity in the late 1960s as an alternative to the costly and environmentally impactful furnace operations. It simply wasn’t feasible to use expensive fuels to directly smelt low-grade ores that produce relatively little useful metal by volume. Hundreds of tons of raw, low-grade ore might only turn into a few hundred pounds of usable metal or even less for valuable materials like gold. Heap leaching is a slow and gradual process, but it uses little energy and can be highly efficient with the use of the right chemicals. It’s possible to achieve ore extraction rates of up to 90% or more with the right match of chemical dissolution agents to the minerals and ores being processed.
Pros and Cons of Heap Leaching
Heap leaching is a low-cost method that requires little energy and has a relatively low impact on the environment. With the careful use of geomembrane liners with minimal permeability, it’s possible to enjoy high rates of ore recovery at a low cost. However, a large volume of liquid is needed to accomplish the task. This can be offset by directing wastewater from some other source to serve as the leaching solution for the pad. Also, poorly designed leach pads and processing ponds can damage the environment. Using a durable liner from BTL Liners goes a long way in preventing this problem in particular.
Why Liners are Needed for All Stages of Leaching
Every part of the heap leaching system needs an impermeable geomembrane liner at the base. It’s not enough to simply rely on clay-heavy soils or compaction methods to keep liquids from being lost through the ground. Allowing seepage to occur at the heap pad or in the processing ponds is likely to result in high environmental remediation costs. It also leads to losses of valuable ore and minerals that could be sold for a profit. Putting in durable liners may cost a little more than using an unlined pond design, but it’s also the only permitted design in most states for environmental reasons.
Designing a new heap leaching system, or overhauling an old one, shouldn’t require second guessing or months of research. Narrowing down the liner selection, in particular, is easy with the help of our team here at BTL Liners. Put our 40 years of industry experience to work for you. We’ll help you choose which of our liner products is right for your heap leaching project.
