CIL and CIP are the two standard processes for extracting gold from ore using cyanide and activated carbon. They sound similar, they are often quoted interchangeably by suppliers, and choosing the wrong one for your ore will cost you recovery for the entire life of the plant.
This article explains the real difference between them, when each one wins, and what you should test before you commit.
The one difference that matters
Both processes do the same two things: dissolve gold into cyanide solution (leaching), and then pull that gold out of solution onto activated carbon (adsorption). The difference is where adsorption happens.
- CIL — Carbon In Leach. Activated carbon is added directly into the leach tanks. Leaching and adsorption happen simultaneously in the same vessels. Gold is dissolved and captured on carbon almost immediately.
- CIP — Carbon In Pulp. Leaching happens first in a separate train of tanks. Only after leaching is complete does the slurry move to a separate adsorption train where carbon is added.
That is the whole architectural difference. Everything else — tank sizes, carbon transfer systems, desorption, electrowinning, regeneration — follows from it.
Why the difference changes your recovery
Because CIL adsorbs gold as soon as it dissolves, the gold concentration in solution stays very low throughout the leach. This matters enormously for a certain class of ores.
Preg-robbing ores — ores containing carbonaceous material, graphite, or certain clay/shale components — actively adsorb dissolved gold onto themselves instead of letting it stay in solution. In a CIP circuit, the gold that gets robbed onto the ore is simply lost with the tailings. In a CIL circuit, the activated carbon competes for the gold and usually wins, because it is present from the first tank at high concentration.
If your ore is preg-robbing, CIL is not a preference — it is the difference between a viable project and one that loses a large share of its gold.
Where CIP still wins
CIP is not obsolete. It has real advantages on the right ore:
- Cleaner control. Because adsorption has its own dedicated train, the carbon advance rate, carbon concentration and elution schedule can be optimised independently of the leach conditions. On a clean oxide ore, this often produces a slightly higher overall recovery and a more consistent carbon loading.
- Simpler chemistry. Reagents are added to a leach circuit that contains no carbon, so less cyanide is adsorbed and consumed by the carbon itself.
- Better for high-silver ores in some cases. Silver behaviour on carbon differs from gold, and a separate adsorption train can give more flexibility in managing it.
- Lower carbon attrition in some configurations — carbon spends less time in high-shear, high-solids leach tanks.
In practice, most modern gold plants that handle a mix of ore types are built as CIL, because it is more forgiving. CIP is typically chosen when test work shows the ore is clean and requires no preg-robbing protection.
Side-by-side comparison
| Factor | CIL | CIP |
|---|---|---|
| Where adsorption happens | In the leach tanks | In a separate adsorption train |
| Gold in solution during leach | Kept very low | Builds up to a normal leach profile |
| Preg-robbing ore | Handles it | Loses gold to the ore |
| Tank count for the same throughput | Fewer, because leach and adsorption are combined | More, because both stages need their own tanks |
| Process control flexibility | Lower, but more forgiving | Higher |
| Typical application | Mixed and difficult ores, most new projects | Clean oxide ores with completed test work |
What you must test before choosing
The choice should never be made on ore type description alone. Before committing to CIL or CIP, you need:
- Bottle roll or leach tests at your target grind size, to establish the achievable gold extraction and the reagent consumption.
- A preg-robbing test — a carbonaceous matter assay plus a comparative leach with and without carbon present. This is the single most important test, and the one most often skipped.
- Grind size optimisation — finer grinding liberates more gold but consumes more power and can create more preg-robbing fines. The optimum is ore-specific.
- Carbon activity and attrition testing — to size the carbon inventory and predict make-up consumption.
- Settling and viscosity tests — clay-rich ores can make slurry handling and carbon screening difficult regardless of which process you choose.
These tests need very little material and can be run before you commit capital. Doing them in the wrong order is how projects end up rebuilding their leach circuit two years after commissioning.
What comes after the leach circuit
Whichever process you choose, the back end of the plant is essentially the same, and it is where projects are most often under-sized:
- Desorption (elution) — stripping the gold off the loaded carbon, usually by the Zadra or AARL route depending on scale.
- Electrowinning — recovering the gold from the pregnant eluate onto steel wool or plates.
- Carbon regeneration — thermal regeneration in a kiln to restore carbon activity. Under-sizing this kiln is a common and expensive mistake, because it forces you to keep buying fresh carbon.
- Smelting — producing the final doré bar.
Get the regeneration kiln capacity right at the design stage. It is far cheaper than adding capacity later.
How plant scale changes the answer
Small plants and large plants do not make the same choice. At the smaller end of the range — tens of tonnes per day — CIL with a small number of combined leach-adsorption tanks is usually the practical option, because it needs the fewest vessels and the least instrumentation. As throughput grows into the hundreds of tonnes per day and beyond, the extra tanks of a CIP train become an affordable way to buy process control, provided the ore permits it.
If you want to see how the equipment is arranged at each of these scales, our CIP / CIL production line page lists standard configurations by daily capacity, from 50 t/d up to 1,000 t/d.
The three mistakes that cost the most
- Choosing CIP without a preg-robbing test. The mistake that destroys projects. If the ore robs carbon, no amount of operational skill will recover the lost gold.
- Under-sizing the desorption and regeneration circuit. The leach tanks get all the attention; the back end gets skimped. The result is a plant that cannot keep up with its own loaded carbon.
- Designing for a grind size you cannot achieve. Test work at 75 microns is meaningless if your mill circuit cannot consistently deliver it. Match the flowsheet to your grinding circuit, not the other way around.
Next step
If you are at the design stage, send us your ore test results — extraction percentage, reagent consumption, grind size, and whether any preg-robbing behaviour was observed. We will tell you which process fits and give you a tank arrangement and equipment list for your target capacity.
If you have not run the tests yet, we can supply the laboratory equipment to do the work at site scale before you commit to a full line.
Get in touch with our process engineers here and we will come back with a configuration and a budget figure.