MINERAL PROCESSING KNOWLEDGE · GOLD ORE PROCESSING
CIL and CIP both load dissolved gold onto activated carbon, but the order of leaching and adsorption decides which ores each circuit can handle.
Technical overview. Actual process selection depends on representative ore samples, mineralogy, testwork and site conditions.
CIL and CIP are often described as two versions of the same idea. The difference is structural: one circuit leaches first and adsorbs afterwards, the other performs both duties at once. That change of arrangement decides how much tank volume a plant needs, how precisely the leach can be controlled, and whether a carbonaceous ore will give up its gold or take it back.
Technical note: The following is a principle-level explanation of how CIL and CIP differ. It is not an engineering design, a tank sizing calculation or a guarantee of metallurgical performance, and it is not an operating procedure for cyanide handling, carbon elution or tailings detoxification. Any leaching circuit must be designed, permitted and operated by qualified professionals.
1. The structural difference between CIL and CIP
In a carbon-in-pulp (CIP) circuit the slurry follows a defined order. It is first pre-deslimed or thickened, then passes through a train of leach tanks in which cyanide dissolves gold into the aurocyanide complex (Au(CN)2-). Only after leaching does the pulp reach adsorption tanks, where activated carbon moves counter-current to the slurry, loading gold out of solution as it goes. Leaching and adsorption are separate unit operations, and each can be given its own residence time.
In a carbon-in-leach (CIL) circuit the two duties are merged. Cyanide and activated carbon sit in the same leach-adsorption tanks, so dissolution and adsorption proceed simultaneously. Gold does not build up in solution; it is captured by carbon as soon as it dissolves. Fewer tanks are needed, because there is no separate adsorption train behind the leach.
2. Where CIP is the stronger choice
CIP separates the two variables that most often conflict in a gold plant: the time gold needs to dissolve, and the way carbon is moved, screened and returned. Decoupling them gives high control precision, because the leach is held at one set of conditions while adsorption is managed independently.
The arrangement suits three conditions together. The ore should be relatively high grade, the leaching kinetics should be slow enough that a dedicated leach stage is worth building, and the pulp should carry little slime, which is why the circuit opens with a pre-desliming or thickening step. A continuous leach of 24-48 hours is the working range before the pulp reaches carbon.
3. Where preg-robbing points to CIL
Some ores contain material that competes with activated carbon for dissolved gold. The usual offenders are:
- natural organic carbon in the ore;
- graphite;
- clays with a high adsorption capacity.
In a conventional leach these substances pull gold out of solution and hold it, so the gold leaves with the tailings attached to the ore instead of being recovered on carbon. This is preg-robbing, and it is the most common reason to leach and adsorb in the same vessel.
The mechanism that makes CIL work is competitive adsorption. Activated carbon is a far stronger adsorbent than the organic carbon in the ore, so when carbon is present in the leaching tank gold is taken onto it almost as soon as it dissolves, and the preg-robbing surfaces never get the chance to load it first. On an ore with a significant preg-robbing component, a CIP circuit can underperform no matter how well the leach is run, because the interval between dissolution and adsorption is where the gold is lost.
4. Side-by-side comparison
The table sets out the points that usually decide a flowsheet.
| Aspect | CIP | CIL |
|---|---|---|
| Process order | Leach in dedicated tanks, then adsorb in a separate train | Leach and adsorption in the same tanks |
| Leach residence | Continuous leach of 24-48 hours before adsorption | No separate leach stage |
| Preferred ore | Higher grade, slower kinetics, low slime content | Ores with preg-robbing carbon, graphite or adsorptive clay |
| Control | Tuned separately, with high precision | One vessel condition for both duties |
| Tank volume | Larger total tank volume | Fewer leach tanks |
| Footprint and capital | Larger footprint, higher capital investment | Smaller footprint, 15%-25% lower capital investment |
5. Tank volume, footprint and capital
Capital cost is where the CIL arrangement usually wins. Because leaching and adsorption share tanks, total tank volume falls, the building footprint shrinks and installed capital cost is 15%-25% lower than an equivalent CIP arrangement. Where the ore is preg-robbing, those savings come on top of the metallurgical benefit rather than instead of it.
For a high-grade ore with slow kinetics and little carbonaceous matter the arithmetic reverses. The larger tank volume of CIP is the price of a leach stage that can be run to completion before carbon ever enters the circuit.
6. What to confirm before choosing
- Measure preg-robbing on representative samples rather than inferring it from the presence of carbonaceous material.
- Establish leach kinetics to fix the residence time the dissolution actually needs.
- Assess slime and clay content, since it affects pulp handling and the value of a pre-desliming step.
- Compare total tank volume, footprint and capital for both arrangements on the same duty.
- Confirm carbon handling, elution and tailings detoxification requirements early, because they constrain the layout.
Conclusion
Neither circuit is more modern than the other. CIP buys control and a fully completed leach at the cost of tank volume and capital. CIL buys a compact circuit and protection against preg-robbing at the cost of closer coupling between two duties. Ore mineralogy, leach kinetics and adsorptive carbon should settle the question, and testwork on representative samples makes the answer defensible. The upstream route is described under gold ore processing.
How LiCheng Tech can help
LiCheng Tech matches equipment to your material, feed size and target capacity from our product catalogue, and connects you with suitable Chinese suppliers where a specification falls outside our standard range. For a gold project that means a ball mill, a classifier to close the grind, mixing tanks for slurry conditioning and a filter press for the dewatered product. Adsorption, elution and electrowinning equipment sit outside our standard range and need separate supplier confirmation.
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