A carbon-in-leach circuit is a train of agitated tanks, each one handed a caustic, abrasive slurry and asked to keep moving it forward around the clock. The tanks that make up that train are some of the hardest-worked steel vessels on a mine site, and they are almost never taken fully offline for maintenance the way a standalone storage tank would be.
Cyanide leach liquor, suspended ore particles and activated carbon moving through an agitated tank produce a combination of chemical attack and mechanical abrasion that standard water storage coatings and steel specifications are not built to handle. Refurbishment on a CIL tank has to account for both failure modes at once, and it has to be planned around a circuit that the rest of the plant is depending on.
Abrasion at the agitator zone and tank floor
The area directly under the agitator and across the tank floor sees the highest particle velocity in the vessel, and it is almost always where coating and, eventually, base metal loss shows up first. A visual inspection from the top of a CIL tank routinely misses early-stage floor wear entirely, because the damage is happening below a slurry level that never gets checked without draining or diving the tank.
Cyanide and caustic attack on welds and coating breaks
Leach liquor is caustic by design, and any coating breach becomes a concentrated attack point rather than a slow, even loss of material. Weld heat-affected zones are frequently where this shows up first, since the coating over a weld is typically thinner and more prone to early breakdown than the coating over flat plate.
Staged, single-tank shutdowns rather than a full circuit stop
Most CIL refurbishment work is planned as a rotating single-tank outage, with the circuit rebalanced to run on the remaining tanks at reduced residence time for the duration. This keeps the plant producing, but it means the refurbishment scope, access and program have to be locked in tightly before the tank comes offline, because every extra day is a day the rest of the circuit is running outside its normal design point.
Bypass and inter-tank piping considerations
Isolating one tank in a leach train usually means temporary bypass piping or valving changes to route slurry around the tank under repair, and this needs to be planned as carefully as the tank work itself. A refurbishment that is structurally excellent but poorly coordinated with the bypass arrangement can still cost the site more in lost throughput than the repair was worth.
A CIL tank refurbishment is judged as much on how little it disrupts the circuit around it as on the quality of the repair itself.
| Check point | Why it matters on a leach circuit |
|---|---|
| Floor and agitator-zone plate thickness | Highest-abrasion area, usually the first to need attention |
| Weld heat-affected zone coating condition | Coating breaks concentrate caustic and cyanide attack |
| Bypass and isolation piping plan | Determines whether the rest of the circuit can keep running |
| Coating system chemical resistance rating | Standard potable-water coatings are not rated for leach liquor |
Can a CIL tank be refurbished without stopping the whole circuit?
In most cases, yes. The typical approach is a rotating single-tank outage with the circuit rebalanced across the remaining tanks, though this depends on circuit design and available residence time margin.
Why do standard tank coatings fail faster in a CIL circuit?
Leach liquor combines caustic chemical attack with continuous mechanical abrasion from agitated slurry - a combination most coating systems specified for water storage are not rated to handle.
How is agitator-zone wear typically detected?
Because the highest-wear area is usually below slurry level, it is generally found through a draining or diving inspection rather than a visual check from the top of the tank.
Planning a CIL or leach tank refurbishment that needs to work around a live circuit? PC Water Infrastructure delivers mine-site tank repairs coordinated with your process schedule.
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