CIP vs CIL Gold Processing: Key Differences Explained

CIP and CIL are two of the most confusing names in gold processing. Both use cyanide to dissolve gold, both use activated carbon to collect it, and both run in rows of big stirred tanks that look almost identical from the outside. The difference is not what they use. It is when the carbon meets the pulp.

In carbon-in-pulp (CIP), the ore is leached first and the carbon only meets the gold-bearing slurry afterwards, in a separate set of tanks. In carbon-in-leach (CIL), the carbon goes in with the leaching slurry, so dissolving and collecting happen at the same time, in the same tanks. That one timing decision changes the tank layout, the way each stage is controlled, and which ores each method suits. This article compares the two methods step by step. For the full chain they sit inside, from crushed ore at the plant gate to doré bars, see our guide to how gold is extracted from ore.

What Is CIP (Carbon-in-Pulp)?

Leach first, adsorb second: the two-stage flow

CIP splits the job into two separate stages. In the first stage, ground ore slurry flows through a series of dedicated leach tanks where a dilute cyanide solution, with oxygen from air, dissolves the gold and holds it in solution as a soluble gold-cyanide complex. Leaching is finished before carbon enters the picture at all.

In the second stage, the now gold-bearing slurry is transferred to a separate series of adsorption tanks containing activated carbon. The dissolved gold-cyanide complex sticks to the carbon’s surface, a process called adsorption, and the carbon is later separated from the slurry and taken off for gold recovery. Because the two stages are physically separate, each can be tuned on its own terms: the leach tanks get the pH, cyanide strength and residence time that suit leaching, while the adsorption tanks get the conditions that suit carbon loading.

The counter-current tank train

The adsorption section of a CIP plant is normally arranged as a counter-current train of four to six tanks. The slurry flows one way through the train, while the carbon is moved the other way: fresh, barren carbon is added at the last tank, where it meets the most depleted pulp first, and the progressively loaded carbon advances tank by tank toward the first tank, where it meets the richest incoming slurry.

The carbon granules used are hard and much larger than the ore particles, so they can be separated from the slurry by simple screening on wire mesh, with inter-tank screens keeping the carbon in its own tank while the pulp flows through. In contact with fresh pregnant solution, fully loaded carbon in a CIP circuit can carry 4,000 to 8,000 grams of gold per tonne of carbon, while fresh carbon at the tail end can strip the outgoing solution to below 0.01 milligrams of gold per litre, leaving the slurry essentially barren.

CIP is regarded as a simple and economical method, and it is used in most industrial carbon-adsorption plants. The main exception is where competing metals make it impractical: at copper levels around 1%, for example, the copper consumes cyanide and loads onto carbon alongside the gold, and plants typically switch to methods such as froth flotation first. The method’s real strength is independence: leaching and adsorption never have to compromise with each other, so the plant tolerates changing feed conditions well.

What Is CIL (Carbon-in-Leach)?

Leach and adsorb at the same time, in the same tanks

CIL was developed from CIP with one idea: why wait? Instead of leaching first and adding carbon later, activated carbon is added directly to the leach tanks. Dissolving and adsorption happen simultaneously, in the same vessels. The moment a gold atom dissolves into the cyanide solution, carbon granules are right there to catch it.

This changes the chemistry’s balance. Because the dissolved gold is captured immediately, very little of it stays in solution at any moment. That low standing concentration matters for one particular problem, preg-robbing, which is covered below: ores containing natural carbonaceous material try to steal dissolved gold back out of solution, and CIL’s added carbon outcompetes the ore’s own carbon for it.

The trade-off is control. In CIL, the leach and adsorption conditions must suit both processes at once: the pH, cyanide level and residence time are a compromise, so the circuit is less tolerant of feed variability than CIP. Plants that run CIL need a steadier, better-understood feed to keep both jobs working together.

A typical CIL circuit, step by step

A CIL circuit follows the same preparation as any tank plant, then combines the two core steps:

1. Grinding: ore is ground to a fine slurry so the gold is liberated and exposed.
2. Thickening: the slurry is thickened to the right density for the tank circuit.
3. Conditioning with lime: lime is added to keep the slurry safely alkaline, which the cyanide chemistry requires.
4. Leach-adsorption: cyanide is added and carbon is introduced into the tank train. Dissolving and adsorption proceed together across a series of agitated tanks, with inter-tank screens keeping the carbon moving counter-current to the pulp, just as in CIP.
5. Carbon separation: loaded carbon is screened out of the first tank and sent to elution.
6. Elution and electrowinning: the gold is stripped from the carbon and recovered as a solid (see the hand-off section below).

Because leaching and adsorption share the tanks, a CIL circuit can run with fewer vessels than the equivalent two-stage CIP layout, which is one of the reasons it appeals to plant designers and to existing plants looking to convert.

CIP vs CIL Side by Side

Here is the comparison at a glance. Every row describes a tendency, not a universal law: real plants tune tank counts, carbon concentrations and residence times to their own ore, and published figures differ from plant to plant, so each is attributed rather than stated as a fixed constant.

Feature	CIP (carbon-in-pulp)	CIL (carbon-in-leach)
Process flow	Two stages: dedicated leach tanks first, then separate adsorption tanks	One combined stage: leaching and adsorption happen together in the same tanks
When carbon is added	After leaching is complete, into the adsorption tank train	With the leaching slurry, into the leach tanks themselves
Tank setup	Leach circuit plus a counter-current adsorption train, usually 4 to 6 tanks (plant-specific)	Single combined tank train; can run with fewer vessels than the equivalent CIP layout
Optimisation flexibility	High: leaching and adsorption conditions (pH, cyanide, retention time) are tuned independently	Lower: one set of conditions must suit both processes at once, so it is a compromise
Feed variability tolerance	Higher: each stage is controlled on its own terms	Lower: needs a steadier, well-understood feed
Carbon inventory tendency	Plant-specific: e.g. 29 tonnes in the AusIMM Russia case study vs 61 tonnes for CIL there; design studies show the reverse can also be true	Plant-specific: e.g. 61 tonnes in the same Russia case vs 29 tonnes for CIP; the Fleming 2011 design study used 4.2 g/L carbon in CIL vs 25 g/L in CIP
Gold lockup (metal inventory) tendency	Plant-specific: 10 kg locked up in the Russia case vs 35 kg for CIL; the Fleming 2011 study showed 28 kg vs 32 kg	Plant-specific: 35 kg locked up in the Russia case vs 10 kg for CIP; the Fleming 2011 study showed 32 kg vs 28 kg
Cost tendency	No universal rule verified: vendor claims of cheaper CIL rest on marketing, not independent cost studies	Can need fewer tanks, which favours retrofits; the only hard capex evidence is the Cortez conversion case below

Which One Recovers More Gold?

The honest answer is that it depends on the ore, not on the name of the process. Vendor marketing often claims CIL recovers 1 to 3% more than CIP, with some pages quoting CIP at 85-92% and CIL at 90-96%, or even up to 99% for CIL. But real plant data tells a less tidy story.

In a published AusIMM case study of a 100 tonne-per-hour gravity and leach plant in Russia, CIP achieved 98.2% adsorption efficiency and 83.3% overall gold recovery, while CIL on comparable ore achieved 93.6% adsorption efficiency and 80.8% overall recovery. CIP won, on both measures, at that plant. A peer-reviewed design study by Fleming and colleagues (2011) likewise found the outcome depends on ore leach kinetics and how much leach time is given before carbon contact: their comparison used 6 hours of leach time before carbon in CIL versus 36 hours in CIP, with carbon concentrations of 4.2 g/L and 25 g/L respectively, and gold lockups of 32 kg and 28 kg. These are design choices matched to an ore, not constants of nature.

Where CIL genuinely shines is on preg-robbing ores: ores containing natural carbonaceous material that soaks up dissolved gold the way the plant’s own carbon does. Peer-reviewed test work on such ores (Buda et al., 2007) showed CIL beating both direct cyanide leaching and CIP, with the best results in pure CIL mode, where no leaching happens before the first carbon contact, workable for ores up to a preg-robbing index of about 1. As little as 0.1% natural carbon in the ore can preg-rob gold, according to 2018 test work at the Navachab gold mine, where typical plant residence times run 24 to 36 hours.

The takeaway: on clean, free-milling ore, either method can win depending on the circuit design, and CIP has real plant data on its side. On preg-robbing ore, CIL is the clear choice. Any source quoting one universal recovery percentage for all ores should be read with caution.

When Plants Choose CIP

CIP is the natural choice for clean, fast-leaching ores where leaching and adsorption both behave well and the plant wants to tune each independently. Its separate stages let metallurgists set aggressive leach conditions, long retention, strong cyanide, without worrying about what those conditions do to carbon loading, and vice versa.

It is also the more forgiving choice when the feed varies. Because each stage is controlled on its own, changes in ore hardness, grade or mineralogy can be answered stage by stage rather than by rebalancing the whole circuit. That independence is a large part of why CIP remains the most widely used carbon-adsorption layout in industry.

For high-grade ores, CIP has a practical edge worth noting: with leaching completed before carbon is added, the adsorption train sees a rich, well-defined pregnant solution, and loaded carbon can reach very high gold loadings before it is taken off for elution. Equipment vendors note that CIP suits high-grade feeds for exactly this reason.

When Plants Choose CIL

CIL is the method of choice for preg-robbing and carbonaceous ores. The added activated carbon outcompetes the ore’s native carbon for dissolved gold, adsorbing it before it can be preg-robbed, and the test work shows this works even when the ore’s own carbon content would otherwise ruin recovery. For an ore body with significant organic carbon, this is often the deciding factor.

CIL also appeals where tank count and footprint matter. The Cortez mill case is the concrete example: when converting a CCD circuit, the engineers found that a CIP option would have needed the same screens and air plus an extra building of at least four agitated CIP tanks, making CIP the highest-capital-cost option there. The CCD-to-CIL conversion instead delivered about 7% better gold recovery than the old CCD circuit on the London Extension ore. No greenfield cost study has been independently verified, so cost should be treated as a plant-by-plant tendency, not a rule, but the retrofit logic at Cortez is sound engineering.

After the Carbon Is Loaded: Elution to Doré

Whichever method loads the carbon, what follows is the same. The loaded carbon is screened out and the gold is stripped from it in elution, where a hot caustic cyanide solution washes the gold back off into a small volume of rich liquid. That liquid passes through electrowinning cells, where an electric current plates the dissolved gold (and silver) onto cathodes as a metal-rich sludge. The sludge is dried, mixed with fluxes and smelted into doré bars, as described in our guide to the gold smelting process, and the doré is then shipped to a refinery for final purification in the gold refining process.

Key Takeaways

• CIP and CIL both use cyanide leaching and activated carbon; the difference is when the carbon meets the pulp: after leaching in CIP, during leaching in CIL.
• CIP’s separate stages allow independent tuning of leaching and adsorption, and tolerate feed variability better.
• CIL’s simultaneous contact suits preg-robbing ores, where added carbon outcompetes the ore’s native carbon, and can need fewer tanks.
• Neither method universally recovers more gold: real plant data shows CIP winning on some ores (83.3% vs 80.8% in the AusIMM Russia case) and CIL winning on preg-robbing ores.
• Carbon concentrations, inventories and lockup figures are plant-specific design choices, not fixed constants; recovery depends on the ore and the circuit design.
• After carbon loading, both routes converge: elution, electrowinning, smelting into doré, and refining.

FAQs

What is the fundamental difference between CIL and CIP processes?

Timing of carbon contact. In CIP (carbon-in-pulp), leaching is completed first and activated carbon is added afterwards in separate adsorption tanks. In CIL (carbon-in-leach), carbon is added to the leach tanks so leaching and adsorption happen simultaneously.

Which gives higher gold recovery, CIP or CIL?

It depends on the ore. A published AusIMM plant case study found CIP recovering 83.3% versus 80.8% for CIL, while peer-reviewed test work on preg-robbing ores found CIL clearly better than CIP. No honest source picks one universal winner.

Is a CIL plant cheaper to build than a CIP plant?

There is no verified universal rule. CIL tends to need fewer tanks, which favours retrofits: at the Cortez mill, a CIP option would have needed an extra building of at least four agitated tanks, making it the highest-cost option there. But no independent greenfield cost study has verified a general CIL cost advantage, and vendor cost claims should be treated as marketing until independently checked.

When should a plant choose CIP over CIL?

For clean, fast-leaching ores, and whenever the plant needs independent control of leaching and adsorption, for example when feed conditions vary. CIP is also the more common industrial layout and suits high-grade feeds, where the adsorption train sees a rich pregnant solution.

Which process is better for high-grade ores?

CIP is often favoured for high-grade ores, because leaching finishes before carbon is added, so the carbon train contacts a rich solution and can load to very high gold levels before elution.

Which process suits ores with high organic carbon content?

CIL. Ores with natural carbonaceous material preg-rob dissolved gold, and even 0.1% carbon in the ore can cause the problem. CIL’s added activated carbon outcompetes the ore’s native carbon and captures the gold first.

Sources and Further Reading

• Prominer (Shanghai) Mining Technology: What are the key differences between CIP and CIL processes? (CIP two-stage flow; independent optimisation vs CIL compromise)
• Xinhai Mining: What are the Differences Between CIP Process and CIL Process? (CIL developed from CIP; simultaneous leach-adsorption)
• Wikipedia: Carbon in pulp (counter-current 4-6 tank train; carbon loading 4,000-8,000 g/t; strip to below 0.01 mg/L Au; CIP simplicity and the copper caveat)
• 911Metallurgist: Why Convert a CCD Gold Circuit to CIL (Cortez mill case: tank counts, capex comparison, ~7% recovery gain over CCD)
• Buda et al. (2007), AusIMM via OneTunnel: Assessment of Options for Economic Processing of Preg-Robbing Gold Ores (CIL advantage on preg-robbing ores; pure CIL mode; preg-robbing index up to ~1)
• Journal of the Southern African Institute of Mining and Metallurgy (2018): Test work to examine the potential for improving gold leaching performance at Navachab Gold Mine (0.1% carbon preg-robs; 24-36 h residence time)
• AusIMM Kalgoorlie branch: Case Study #1 – CIP vs CIL (Russia 100 t/h plant: CIP 83.3% vs CIL 80.8% recovery; carbon inventory 29 t vs 61 t; lockup 10 kg vs 35 kg)
• Fleming et al. (2011), Minerals Engineering 24: Factors influencing the rate of gold cyanide leaching and adsorption on activated carbon (design comparison: leach time 6 h vs 36 h; carbon 4.2 g/L vs 25 g/L; lockup 32 kg vs 28 kg)