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What is Heap Leaching or Leach Pads?
PPM Global has been involved with a vast number of Heap leach Projects around the globe.
A Leach Pad is defined as a continuously lined area which may contain one or more ‘heaps’.
Leach Heaps (Cells) are stacked on prepared pads to a height from 4m to 8m. The nominal heap height is 6m. The heaps are approximately 50-60m wide and may contain between 50,000t and 250,000t of ore each. Heap leach solution is irrigated over the ore and percolates by gravity through the ore to be collected at the base of the pad in a collection drainage system. As the solution passes through the ore various metals including copper (Cu) for the purpose of writing this piece based on copper bearing deposit, are dissolved from the ore into the passing leach solution (Leachate). The primary chemical in the leach solution is sulphuric acid (H2SO4), the copper (Cu) is solubilised according to the following simplified reaction:
The irrigated solution (raffinate) averages approximately 1-2 g/L of copper and 20 g/L free acid. The solution discharging from the heaps, Pregnant Leach Solution (PLS) will vary in copper concentration over the life of the heap, initial grades may be as high as 50 g/L Cu, at the completion of leaching the PLS grade may be only fractionally greater than the raffinate irrigated.
Air is forced into the heaps via a network of pipes located 1m above the base of each heap, the target minimum flow of air is one meter cubed of air per one meter squared of leach pad area per hour (1.0m3/m2.Hr). The air provides oxygen to both the organic and inorganic reactions occurring within the heap. Within limitations, increasing the amount of air flow into a heap will increase the temperature within the heap. Conversely increasing the flow of raffinate to the ore will reduce the temperature of the heap.
PPM Global can help clients with everything from:
- Design of new heap leaching circuits
- Test work scope development
- Columns leach Data interpretation
- Process Optimisation/ trouble shooting
- Commissioning, assistance
- Process Personnel training requirements.