The process of leaching ore to breakdown and extract metals has been around for many centuries. However, only in the last 40 years has the process been refined into what we now refer to as modern day “heap leaching,” also known as “leach mining” and “run of mine dump leaching.” Today, mining companies around the world utilize the process of heap leaching to process oxidized low grade Copper, Gold, Silver, Nickel and Uranium ores because of the economic feasibility of much lower capital investment and operating costs involved over more conventional extraction methods. Heap leach mining has revolutionized the mining industry. It delivers viability to the processing of low grade ores, which up to this point would have otherwise been regarded as waste rock.
The seemingly simple yet complex process involves the stacking of mined ore onto an impermeable layer in a heap, then distributing a lixiviant solution through an irrigation system onto the top of the heap. The solution percolates under gravity and capillary action through the heap. Over time a chemical dissolution reaction takes place, thereby releasing the target mineral from the host rock and dissolving it in solution. At this stage the solution is termed pregnant solution. This pregnant solution then drains down to the bottom of the heap where it is collected by drainage pipes at the base of the heap and conveyed to a processing plant for mineral recovery. After the target mineral has been removed from pregnant solution, the stripped barren raffinate solution is pumped back to the top of the heap for continual closed loop leaching.
Impact Sprinklers vs. Drip-Irrigation
Up until the 1990’s, the preferred method of irrigating the heaps was with impact/rotating sprinklers. They provided a large area of solution dispersion coverage per unit at a fairly uniform application rate. However, sprinkler irrigation requires the solution to be thrown at an upwards angle over great distance. This causes excessive solution evaporation and reduction of heap surface permeability as well as environmental and safety hazards. Over time the need to resolve these issues opened the door to the implementation of agricultural drip-irrigation systems in leach mining.
Mineral recovery rates are dependent on many variables. However one that can be categorized as of utmost importance is the even solution distribution onto and within the heap, which leads to complete heap saturation and thus target metal recovery. Today, drip-irrigation is the preferred method of irrigation specifically for that reason. It renders a precise application rate and uniform solution distribution onto the heap, while maintaining the integrity of the heap surface permeability and greatly reducing solution evaporation. Drip-irrigation’s slow solution application allows greater time for solution to percolate and saturate the heap evenly, reducing the potential for over-saturation and solution channeling which is often seen with sprinkler irrigation systems.
Challenges and Solutions in Drip-Irrigation
Any irrigation system has its drawbacks especially in the leach mining setting where the solution is in a closed cycle continuously being circulated through the heaps picking up contaminants, and drip-emitters are of no exception to this. Drip-irrigation systems have the potential to clog due to suspended and dissolved solids in solution, and many mines experience emitter clogging on a daily basis. As much as drip-irrigation is an ideal method of delivering solution to the heaps due to the low solution flow rate per unit area, the typical low flow agricultural emitters often times clog/plug too easily by suspended and dissolved solids and require replacement several times throughout the leach cycle, thus increasing operating expense over the life of mine.
To solve these problems DRTS is proud to offer a new mining grade product, the Minoro™ drip-emitter specifically designed for drip-irrigation in heap leach mining. The Minoro™ dripper has our revolutionary Omni-Flow Labyrinth design which eliminates labyrinth dead zones to maintain consistent turbulence, reducing the settling of suspended solids which prevents clogging. The long 360° labyrinth wraps around the dripper making this dripper extraordinarily consistent with a very low CV. Additionally, the elevated filter draws from water/solution that is flowing closer to the center of the pipe where water/solution travels at highest velocity. The higher velocity helps keep the filter surface clean while the elevated filter entrance inhibits solids from settling on it between flow cycles, regardless of dripper orientation in the pipe. The Minoro™ Dripper has gone through rigorous lab and field-testing and has out-performed many of the well-known mining dripper brands. Additionally Minoro™ is the lowest flow mining emitter on the market today. DRTS has leach-mining specialists ready to assist with system designs and recommendations for your desired leach pad.