How can you design an effective heap leaching system?

Heap leaching is a process of extracting valuable metals from low-grade ores by applying a leaching solution to a pile of crushed ore. The solution percolates through the ore and dissolves the target metals, which are then recovered from the solution. Heap leaching is widely used for gold, copper, uranium, and other minerals, but it also poses several challenges, such as environmental risks, operational costs, and metallurgical efficiency. How can you design an effective heap leaching system that maximizes metal recovery and minimizes negative impacts? Here are some key factors to consider.

1 Ore characteristics

The first step in designing a heap leaching system is to understand the characteristics of the ore, such as its mineralogy, grade, particle size, permeability, and acid consumption. These factors affect the leaching kinetics, the amount and type of solution required, and the heap stability. For example, fine-grained ores may have higher metal content, but they also tend to form impermeable layers that reduce solution flow and oxygen diffusion. Therefore, you need to optimize the ore size distribution, blending, and agglomeration to ensure adequate heap porosity and irrigation.

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Michael McClintock, P.Eng.

Founder & Principal @ McClintock Group | Enhancing Mineral Projects, Advocating for Shareholders
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Have to do the leach test to determine the ammenability. Bottle roll tests are a relatively cheap and quick way to determine if leaching will be possible and the consumption levels. If the material is ammenable the doing column testing at various configurations may be warranted. As with any metallurgical testing it is good to have some sense of the economics and what the objectives are when developing the test work. Last note, don't necessarly assume because a bottle roll came back as a poor test that the material does not leach. I have seen many times where process methods were crossed out early because of one test from which an irregularity caused an issue with the test.

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2 Solution chemistry

The second step is to select the appropriate leaching solution and adjust its chemistry to enhance metal dissolution and extraction. The solution may consist of water, acid, base, salt, or other reagents, depending on the ore type and the metal of interest. For example, cyanide is commonly used for gold leaching, while sulfuric acid is used for copper and uranium leaching. You also need to monitor and control the solution pH, temperature, concentration, and redox potential to optimize the leaching performance and prevent unwanted reactions, such as precipitation, hydrolysis, or passivation.

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3 Heap configuration

The third step is to design the heap configuration, which includes the shape, size, height, slope, and drainage of the ore pile. The heap configuration affects the solution distribution, the metal recovery, and the stability of the heap. For example, a higher heap may increase the ore capacity and the metal yield, but it also increases the solution pressure and the risk of slope failure. Therefore, you need to balance the economic and technical aspects of the heap geometry and ensure proper geotechnical analysis and testing.

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Elhadi Mohammed

Owner of Golden Ideas Mining Consultancy & Training Experts
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A persistent cause of failure of heap leach operations is the presence of excess fines in the materials placed on the pad. Excess fines results in a low permeability material and thus the seepage rate of the lixiviant is too slow for economic pad operations.

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4 Irrigation system

The fourth step is to design the irrigation system, which includes the layout, type, and operation of the solution delivery and collection devices. The irrigation system affects the solution flow rate, uniformity, and efficiency, as well as the metal recovery and leaching kinetics. For example, a drip irrigation system may provide better solution control and coverage than a sprinkler system, but it also requires more maintenance and protection from clogging and freezing. Therefore, you need to select the irrigation system that suits your ore characteristics, climate conditions, and operational requirements.

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5 Bioleaching option

The fifth step is to consider the option of bioleaching, which is a form of heap leaching that uses microorganisms to enhance metal dissolution and extraction. Bioleaching can offer several advantages, such as lower energy and reagent consumption, higher metal recovery, and lower environmental impact. However, bioleaching also has some limitations, such as slower leaching rates, higher sensitivity to temperature and pH, and potential biohazard issues. Therefore, you need to evaluate the feasibility and profitability of bioleaching for your ore type and leaching objectives.

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6 Monitoring and control

The sixth and final step is to implement a monitoring and control system that allows you to measure and adjust the key parameters of the heap leaching process, such as the solution flow, composition, and metal content, the heap temperature and moisture, and the heap stability and deformation. The monitoring and control system can help you improve the leaching efficiency, detect and prevent problems, and optimize the metal recovery and quality. You can use various sensors, instruments, and software tools to collect and analyze the data and make informed decisions.

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7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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Mining Engineering

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How can you design an effective heap leaching system?

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4

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1 Ore characteristics

2 Solution chemistry

3 Heap configuration

4 Irrigation system

5 Bioleaching option

6 Monitoring and control

7 Here’s what else to consider

Mining Engineering

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How can you design an effective heap leaching system?

1

2

3

4

5

6

7

1 Ore characteristics

2 Solution chemistry

3 Heap configuration

4 Irrigation system

5 Bioleaching option

6 Monitoring and control

7 Here’s what else to consider

Mining Engineering

Rate this article

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