Controlled Leaching Systems for Reliable ResultsBy Andrea Villar | Mon, 09/28/2020 - 09:39
Q: How do your irrigation systems for leaching systems work?
A: Our systems spray acid-based water instead of pure water. The acid is chosen depending on the type of mine. For example, if it is a gold mine, it is irrigated with cyanide. If it is copper, it is irrigated with sulfuric acid.
Depending on the size of the mine operation, we can make water flow with a capacity of 3 to 12 liters per square meter. This is calculated according to the needs of the leaching yard. For example, if the yard has a great deal of clay, we lower the water flow capacity so that there is no excess moisture. The water flow capacity is regulated with leaks at different distances and pressures.
Once the material is irrigated and completely soaked, the percolation process begins. This occurs when fluids slowly pass through porous materials that degrade the mineral until it becomes gold ions. Gold ions come out in liquid form known as PLS (Pregnant Leach Solution). The PLS that comes out goes to the processing plant and the mineral becomes doré bars with a mix of other minerals. Once the bar leaves the mine, it is sent to the refining process.
Q: What factors do you consider when putting your irrigation system in place?
A: Generally, we take into account the type of material. A granulometry analysis is made that can determine the infiltration rate to know what type of dripper we need to use to avoid saturating the soil. This is due to the fact that we cannot over-wet or fall short of a solution because the minerals in the leaching yard are difficult to handle, moisture cones can develop, and areas may remain unleached. That is why it is important that all processes in a leaching yard are uniform. Our customers constantly ask us for bigger drippers so that the pipes do not get clogged. What is important, however, is reducing the water flow to have more emitters within a given area. That increases uniformity. If the uniformity increases, the infiltration rate increases and, therefore, the proper percolation to recover the PLS is achieved.
Q: Why is it a problem for pipes to be clogged in leaching yards?
A: The pipes are arranged depending on the solution used for irrigation. For example, it is common for mines to add cyanide and lime to the ore to control pH and prevent gases. They can also add sodium hydroxide. This causes temperature to rise. The calcium precipitates and clogs the dropper. Thus, it is necessary to add antifouling agents in the irrigation solution. Miners believe that uniformity is obtained when there is an emitter every 90 centimeters or every meter. On the contrary, attaching several emitters on hoses so that funnels are avoided is better.
Once the irrigation grid is determined, the first issue to solve is the pressure controls. Pressure controls are important because they ensure that the system always run properly. We usually keep the irrigation systems at 15 pounds. To solve this, the mines regulate the pressures with butterfly valves. The problem is that when they close a hole, others begin to gradually clog.
Profumisa’s valves are intelligent because they work by pressure differential, which means our valves indicate if there is overpressure. If there is overpressure in the pilot, a stroke goes up and down depending on the pressure and has a spring that handles the backpressure of the valve. The valves must be at low pressure to avoid the pumping system becoming overloaded. Low pressure is also economical, because it makes it unnecessary to spend on pipes or hoses.
Q: What is the difference between drip and spray systems and why do you promote the former?
A: We offer both types of systems and the mine determines which one to use depending on the material it has. However, with spray systems the soil compaction percentage is very high due to the constant dripping. Also, in very hot areas such as Sonora, spray systems are harmful when depositing the moisture in a certain place. This is because the water can be controlled until it reaches the tip of the sprinkler nozzle, but once it leaves, if there is wind or evaporation it does not allow it to reach the target. This is a problem because it is desirable to maintain a high cyanide retention rate. That is why we always recommend the drip system, not only for ecological reasons but also for economic reasons, because the irrigation system is well controlled and the area of influence of each dropper is adequately determined.
Profumisa is a Mexican company that designs irrigation projects for leaching yards, either drip or sprinkler, according to the necessities of each mine.