Channeling (heap leach)
- Also known as
- channeling, preferential flow
Channeling in a heap leach is uneven flow of leach solution through the ore pile, in which solution follows a limited number of preferred paths and bypasses other parts of the heap. Ore that the solution does not reach is not leached, which lowers metal recovery.
What is channeling?
In heap leaching, ore is stacked on a lined pad and irrigated with a leach solution that percolates down, dissolving the target metal. The metal-bearing pregnant leach solution collects at the base. For the process to work, solution must contact as much of the ore as possible.
Channeling, a form of preferential flow, occurs when solution concentrates in certain paths, such as zones of coarse, open rock, and moves quickly through them, while fine-grained or compacted zones stay relatively dry. The bypassed ore is effectively unleached.
Causes
- Fines and clay, which migrate and block pore spaces, diverting flow.
- Segregation during stacking, when coarse and fine particles separate into layers or zones.
- Compaction from equipment traffic or the weight of overlying lifts.
- Poor agglomeration, which leaves fines unbound.
- Poor wetting of some ore surfaces.
- Uneven irrigation, such as poorly distributed drippers or sprinklers.
Effects
- Lower and slower metal recovery.
- Ponding on the heap surface where solution cannot infiltrate.
- Slope stability risks in severe cases.
How channeling is reduced
- Agglomeration, binding fines to coarser particles with cement, lime or binders before stacking.
- Stacking practices that limit segregation and compaction.
- Irrigation design and rates matched to the heap’s permeability.
- Wetting agents and surfactants in the leach solution, used to help solution spread into ore that resists wetting.
Frequently asked questions
Signs include low recovery compared with column tests, ponding, and solution breaking through faster than expected. Tracer tests and moisture monitoring can confirm it.
No. It can occur in any heap leach, including copper and gold operations.
Sources
- SME Mineral Processing and Extractive Metallurgy Handbook, Society for Mining, Metallurgy and Exploration (SME), 2019