CIL vs CIP: which suits tailings retreatment?

This page puts carbon-in-leach and carbon-in-pulp directly side by side, since a technical reader who has read both separately usually lands here next to actually make the call. Both processes recover gold from cyanide solution using activated carbon; the only real question this page settles is which arrangement of tanks gets there more efficiently for a specific tailings feed.

What does the decision actually come down to?

The decision comes down to two practical factors: whether the specific tailings feed leaches fast enough that simultaneous adsorption doesn't cost recovery, and whether the project is building fresh infrastructure or inheriting an existing tank train. Fast-enough leach kinetics favor CIL's simpler, lower-footprint design. Slow kinetics or inherited sequential infrastructure can make CIP the more sensible choice, even though it isn't the default most fresh designs start from.

These two factors don't always point the same direction, which is exactly why the decision needs a genuine technical evaluation rather than a rule of thumb. A project might find its tailings leach quickly enough to favor CIL on kinetics grounds, yet also inherit a structurally sound CIP-configured tank train that would be expensive to convert, in which case the capital-preservation argument for keeping CIP can outweigh the marginal kinetics advantage CIL would otherwise offer.

Attribute comparison

The table below summarizes the practical differences a technical team weighs when choosing between the two configurations, each of which is explained in full context on its own dedicated page elsewhere in this recovery methods set.

Who actually makes this call, and at what project stage?

The CIL-versus-CIP decision sits with the metallurgical and process engineering team during flowsheet design, informed directly by the diagnostic testwork results rather than by a project manager's preference or a contractor's standard offering. It is finalized during feasibility study work, since it drives detailed tank sizing, civil works design, and a meaningful share of total processing capital cost, all of which need to be locked down before construction financing is arranged.

Investors and technical due diligence reviewers typically expect this decision to appear explicitly in a project's feasibility study, supported by the specific bottle-roll or pilot data behind it, rather than stated as a bare conclusion. A feasibility study that simply asserts "the project will use CIL" without showing the leach kinetics data behind that choice leaves a real technical question unanswered, one a careful investor should be comfortable pressing on before committing capital.

When does CIP still win?

CIP still wins on slow-leaching or heavily preg-robbing material, where carbon competing for gold too early in the leach genuinely reduces overall recovery, and on projects reusing an inherited tank train built around a sequential design, covered in more depth on carbon-in-pulp explained. Neither case is unusual on a Ghanaian tailings project, particularly the second, given how many legacy plants used sequential circuits.

A less obvious case worth naming is a project processing tailings from more than one historic source or era on the same site, where blending different vintages of material into a single feed stream can produce a blended leach kinetics profile that behaves less predictably than either source material alone. Where that blended behavior is uncertain, the added process control CIP's separated stages provide can be worth its extra cost until enough operating experience with the blend accumulates to justify simplifying to CIL.

Can an existing CIP circuit be converted to CIL, or vice versa?

Converting an existing CIP tank train to run as CIL is possible in principle, since it mainly means adding carbon to what were previously carbon-free leach tanks, but it is rarely as simple as flipping a switch. Tank agitation, aeration capacity, and screening infrastructure at each stage were originally designed around each tank's specific function, and retrofitting carbon handling into tanks not built for it can require real engineering work rather than a purely operational change. The reverse conversion, running a CIL train as though it were CIP by holding carbon out of the early tanks, is operationally simpler to trial but sacrifices the very efficiency advantage CIL's simultaneous design was built to capture, so it is rarely done as a permanent configuration rather than a short-term operational test.

How does each configuration change a project's risk profile?

CIL's lower capital cost and smaller footprint reduce upfront project risk, which matters disproportionately on a first-phase retreatment operation still proving out a dump's economics before committing to full-scale infrastructure. Its single risk, relative to CIP, is that a project misjudges leach kinetics at the design stage and ends up under-recovering gold that separated leaching would have captured, a risk that proper diagnostic testwork is specifically designed to eliminate before it ever becomes a real production problem.

CIP's risk profile runs the other way: its higher capital cost and larger footprint are locked in regardless of whether the extra separation the design provides turns out to be needed, which is a real cost if testwork later confirms the feed would have leached just as well under CIL. Where CIP is chosen because of inherited infrastructure rather than kinetics, that specific risk doesn't apply since the capital was mostly already spent by an earlier owner, which is part of why the inherited-infrastructure case is treated as a meaningfully different decision from a genuinely fresh design choice.

How does testwork actually settle this for a specific dump?

Diagnostic leach testing settles the CIL-versus-CIP question for a specific dump by directly measuring leach kinetics rather than assuming an answer from grade or composition alone, the same testwork-first principle already established on gold tailings composition and fire assay: how gold grade is measured. A project that skips this step and defaults to CIL because it's the more common modern choice risks under-recovering on feed that actually needed the sequential approach.

A typical diagnostic program runs parallel bottle-roll tests, one simulating CIL's simultaneous carbon addition and one simulating CIP's delayed addition, on the same representative sample, then compares final extraction and the extraction-versus-time curve between the two. Where the two curves converge to essentially the same final recovery, CIL's lower cost makes it the straightforward choice. Where CIP's delayed-addition test shows a meaningfully better final recovery, that gap needs to be weighed in dollar terms, additional recovered ounces against additional tankage and operating cost, rather than decided on kinetics alone.

Sample representativeness matters enormously here, following the same Gy's sampling theory principles referenced elsewhere on this site. A diagnostic leach test run on an unrepresentative sample can point a project toward the wrong configuration entirely, since the whole comparison depends on the sample's leach behavior genuinely reflecting the bulk dump rather than one unusually fast- or slow-leaching pocket within it.