Ore-Max was a pioneer in the application of drip irrigation to gold and copper mines in the late 1980’s. Previously the mines had used sprinklers which had many environmental and production limitations which were solved by the application of mining solution using drip systems. Today the use of drip on mines is standard on 90% of the gold, copper and uranium mines and it is also used on nickel and extraction of lithium. It is without question “best practice” method for heap leach mining worldwide.
The Leach Mining Cycle
This drawing illustrates the concept of a typical leach mine. The leach solution is applied on the top of the mine on the highest “lift”. As it gradually percolates through the layers of ore it chemically bonds with the ore. The solution which now has the ore in it called the “pregnant” solution flows by capillary action (ideally) to the bottom of the leach pile to the geo-membrane liner. Then the solution flows by gravity to holding ponds for temporary storage. It is then pumped to the “tank house” which refines the solution and extracts the ore and then the solution is recirculated repeating the mining cycle.
How Drip is Applied in Mining
This drawing shows a typical layout of drip irrigation on a leach pad. The leaching solution is supplied to individual cells by lay flat hose. Often a pressure regulator is installed after the hose fitting to insure that the emitters operate at exactly the correct pressure, which results in the right application rate of solution. The drip lines are connected to lay flat hose at pre-determined spacing. Emitters are installed in the drip lines so that the solution is applied at a set spacing between emitters and lines. For example, a typical spacing might be 24” by 24” for a leach pad. Spacing always depends on the pre-determined ideal application rate for the particular ore.
How The Max-Emitter Works
This animation shows the operation of the Max-Emitter which is the only emitter designed to operate in the difficult mining environment. Other drip emitters are from the agriculture industry which operate with clean filtered water. It is designed to reduce plugging because mining solution always has contaminants in it. Hundreds of screens filter the solution so that it is almost impossible to plug the screens and the flow path is the largest available on the market. Further, two exit holes are standard but the emitter can be ordered with four holes to reduce plugging. All of this means that more of your emitters will be operating more of the time so you can achieve maximum ore extraction.
Max-Emitter vs. The Competition
Important Considerations in Drip Leach Mining
Emitter Spacing is Critical
The emitters must be spaced to achieve the desired application of the solution. A typical spacing is 24” as shown in the drawing but spacings vary from 18” (2 Liter) to 36” (8 liter). All of these flow rates can be used to achieve the same application rate per square meter.
Drip Solution Flows Laterally and Vertically Eliminating “Dry Spots”
When the drip solution is applied the surface area appears to be dry between drippers. What actually happens is the solution, moving by capillary action in the soil, flows both horizontally and vertically. In most soils the solution will spread up to 30-36” horizontally from the drip point. Furthermore it also moves vertically up in the soil so there are virtually no dry spot between emitters. It is very easy to test the movement of solution in your ore by taking one emitter and applying solution for an hour and then digging to find the perimeter of the moisture. However, if the solution spreads 30” remember this is the full diameter and when you have two emitters next to each other, the solution intersects at the radius so there is always plenty of solution overlap even with the widest spacing.
The Three Mistakes You Want to Avoid
Emitter plugging greatly reduces production. This is the biggest problem in achieving design production of ore because every plugged emitter means sub-optimal conditions. This is why we developed the Max Emitter.
Over-Saturation of Leach Solution
Nothing good happens when you apply too much solution and saturate the leach pad. Solution should move by capillary action through the ore not by gravity. Why? Because once the ore becomes saturated you don’t have any oxygen left and oxygen is required for the chemical and biological reactions which are necessary for extraction. No oxygen means no extraction so don’t over apply solution.
Fluctuating System Pressure
Correct pressure is vital to the proper functioning of a leach system. A drip system usually operates at 10-15 PSI so a 5 PSI pressure differential dramatically affects the flow rate of the emitters. A 5 PSI variation can result in a 33% over or under application of leach solution. Ideally every emitter (dripper) should see the same pressure to achieve uniform application of the leach solution.
Animation of Drip Wetting Pattern
This animation shows how solution spreads in the ore by capillary action. It not only moves laterally but also vertically virtually eliminating any dry spot between emitters. Emitter spacing varies but can be as wide as 36” in ore with clays to as close as 15” in very light sandy ore. The best answer on the spacing is to test your ore for wetting pattern.