Carbon-in-pulp (CIP) explained

CIP is the direct sibling process to carbon-in-leach, and understanding it mainly means understanding what changes when leaching and adsorption are split into two stages instead of combined into one. CIP predates CIL historically, and many of the fundamentals that made carbon-based gold recovery practical at industrial scale in the first place were worked out on sequential circuits before the simultaneous CIL design was widely adopted.

How does the two-stage leach-then-adsorb sequence work?

CIP runs slurry through dedicated leach tanks first, with no carbon present, giving cyanide time to dissolve gold into solution without any competition for it. Only once that leach stage is substantially complete does the slurry move into separate adsorption tanks, where activated carbon is added to strip the now-dissolved gold out of solution. That is the direct contrast with CIL, which adds carbon into the same tanks the leaching happens in, adsorbing gold as it dissolves rather than afterward.

The leach tanks in a CIP train are typically agitated and aerated in much the same way CIL's tanks are, since the dissolution chemistry itself, described in full on cyanidation basics: chemistry of gold leaching, is identical between the two processes. What differs is purely the absence of carbon during this first stage, which means dissolved gold concentration in solution is allowed to build up rather than being continuously stripped out as it forms. Once the slurry crosses into the adsorption train, the carbon there is working against a solution already carrying its full dissolved gold load rather than a gradually increasing one.

Why does keeping leaching and adsorption separate matter for kinetics?

Separating the two stages matters because adsorption and leaching can, in some feed types, compete for the same underlying driving forces rather than reinforcing each other the way CIL's design assumes. Where a specific ore or tailings stream leaches slowly, introducing carbon too early can, in principle, adsorb any gold that has dissolved before the bulk of the remaining gold has had a chance to dissolve too, without meaningfully speeding up the leach reaction itself. Running leaching to substantial completion first, then adsorbing in a dedicated stage, avoids that interaction entirely, at the cost of the extra tankage a two-stage design requires.

Why would a project choose CIP over CIL?

CIP tends to make sense when leach kinetics are slow enough that carbon competing for gold too early would actually reduce overall leach efficiency, since dissolved gold needs to build up in solution before adsorption becomes worthwhile in some feed types. It also fits naturally where a project already has separate tank trains in place, whether from an existing plant being reused for retreatment or a design inherited from an earlier project phase, rather than building a fresh CIL train from scratch.

Preg-robbing feed is a further scenario worth naming specifically. Where tailings carry a high proportion of carbonaceous material that competes with activated carbon for dissolved gold, some flowsheets deliberately delay carbon addition until the leach reaction has progressed further, essentially borrowing CIP's separation logic even within a broadly CIL-style circuit, or in some cases favoring blanking-off carbon addition in the earliest leach tanks specifically to reduce the preg-robbing material's chance to compete before the carbon does.

Does CIP's elution and electrowinning stage differ from CIL's?

The elution and electrowinning stages that follow CIP's adsorption tanks are functionally identical to those following a CIL circuit, since by that point the process is handling loaded carbon regardless of which route produced it. A Zadra or AARL elution strips gold from the loaded carbon back into a concentrated solution, and electrowinning then plates that dissolved gold onto steel wool cathodes as metallic gold sludge ready for smelting. This shared downstream equipment is one reason a project weighing CIL against CIP is really only deciding between two ways of getting gold onto carbon, not redesigning the whole recovery circuit from that point onward.

What does CIP cost and complexity look like relative to CIL?

CIP generally needs more total tanks and a larger footprint than CIL for the same throughput, because the leach and adsorption functions each need their own dedicated vessels rather than sharing tanks. That is a real tradeoff, not simply a worse option: the extra footprint buys cleaner separation of the two chemical processes, which can matter for certain feed types even though it costs more in steel and plant area.

Beyond the extra tankage itself, CIP's two-stage design also duplicates some of the ancillary equipment a single-stage CIL circuit shares across its whole train: additional agitator drives, additional instrumentation for monitoring each stage separately, and in some designs an interstage screening step to keep the leach and adsorption populations properly separated. All of this adds capital cost and, to a lesser extent, ongoing maintenance burden relative to CIL, which is the main reason CIL has become the default choice for greenfield tailings retreatment flowsheets today.

None of this makes CIP obsolete or inferior in every case, though. On feed where separated leaching genuinely improves recovery, the additional capital cost can be justified by the extra ounces recovered, in the same way centrifugal gravity equipment's higher cost is justified by the fine gold it captures that conventional equipment cannot. The decision, as with most equipment and flowsheet choices covered across this site, is a testwork-driven economic comparison rather than a fixed preference for either configuration.

Where has CIP historically been more common?

CIP was more common in older plant designs than in modern greenfield builds, in part because sequential leach-then-adsorb circuits were the established approach before CIL's simultaneous design became standard practice. That history matters directly for tailings retreatment: many of the legacy Ghanaian plants that created today's retreatable tailings, described on why old tailings still contain gold, used exactly this kind of sequential circuit rather than the CIL design a fresh flowsheet would default to today.

This history is directly relevant to how a retreatment project sizes its own new leach circuit, since the original plant's tank train, if it still exists physically on site, represents a known, inspectable asset rather than an assumption. Where that infrastructure is structurally sound and its tankage volume genuinely fits the new project's residence time requirements, reusing it rather than demolishing and rebuilding can be a meaningful capital saving, one more reason CIP retains real relevance on brownfield Ghanaian retreatment sites even though CIL is the default choice for a fresh design.

Ghana's mining history spans multiple eras of plant construction, and a retreatment project surveying a site for existing infrastructure should expect to find a range of vintages depending on when the original operation was built and how many times it changed hands or was expanded. Treating each inherited asset on its own technical merits, rather than assuming either that old infrastructure is automatically reusable or automatically worthless, is the discipline that actually protects a project's capital budget.