The three methods at a glance

CIP (carbon-in-pulp) and CIL (carbon-in-leach) are both tank-leaching routes that produce a high-grade dore and suit higher-grade ore. Heap leach is a low-cost, lower-recovery route for large tonnages of low-grade oxide ore. The core difference between CIP and CIL is timing: in CIP the ore is fully leached first, then pumped to separate adsorption tanks where activated carbon captures the gold; in CIL, carbon is added directly to the leach tanks so dissolution and adsorption happen at the same time.

When CIP makes sense

CIP is the classic choice for clean, free-milling ores that leach quickly and have no carbonaceous (preg-robbing) minerals to re-adsorb dissolved gold. Because leaching is completed before adsorption, you can optimize each step independently, and the smaller number of carbon-handling tanks keeps screen wear and operating attention lower. CIP plants are well suited to deposits in the roughly 100-1,200 t/d range where the cyanide-soluble gold is fully liberated after grinding to about 70-80% passing 75 microns.

Where CIP struggles

If the ore contains organic carbon, clays or fine sulfides that slow leaching, gold can re-deposit onto those minerals before it is recovered. That is the case CIL was designed for.

When CIL is the safer route

In CIL, activated carbon sits in the leach tanks and continuously strips dissolved gold out of solution the moment it forms. This protects recovery on preg-robbing and slow-leaching ores and shortens overall residence time, since leaching and adsorption overlap. CIL has become the default for many new gold plants because it is forgiving of mineralogical surprises. The main trade-offs are slightly higher carbon inventory and more carbon attrition, so robust interstage screening and a well-sized elution and electrowinning system matter.

• Choose CIL if: the ore is carbonaceous/preg-robbing, leaches slowly, or you want a single forgiving flowsheet for variable feed.
• Choose CIP if: the ore is clean and free-milling and you want simpler, lower-attrition carbon handling.
• Choose heap leach if: you have large tonnages of low-grade oxide ore and capex/opex per tonne is the priority.

When heap leach wins on economics

Heap leach trades recovery for cost. Crushed (or sometimes run-of-mine) ore is stacked on a lined pad, irrigated with cyanide solution, and the pregnant leachate is collected and sent to carbon columns or a Merrill-Crowe circuit. Recovery is lower and leach cycles run weeks to months, but you avoid fine grinding, agitation tanks and most of the mechanical plant. For a large oxide deposit at sub-1 g/t, heap leach can be the only economic option. Coarse, well-percolating ore and a favorable climate help; clay-rich or high-fines ore that blinds the heap does not. Where fines are a problem, agglomerating the crushed ore with cement and binder before stacking can restore permeability and lift recovery.

Solution management on a heap

Heap leach is as much a hydraulic exercise as a chemical one. Irrigation rate, drip versus sprinkler emitters, lift height and pad slope all govern how evenly solution contacts the ore. Channeling leaves dead zones of unleached ore, so uniform stacking and a well-graded crush matter as much as cyanide strength. Cold climates slow kinetics further and may require covered or under-leach methods to keep the heap working through winter.

Reagent and operating cost drivers

Across all three routes, the major consumables are cyanide, lime (for pH control around 10.5-11 to keep cyanide stable) and, for carbon circuits, activated carbon and elution reagents. Cyanide consumption typically runs 0.25-1.0 kg/t depending on ore reactivity and the presence of cyanide-consuming minerals (cyanicides) such as copper and some sulfides. High cyanicide ores push operators toward CIL and tighter reagent control. Power for grinding and agitation is the other big line item in tank-leach plants, which is why ore hardness and grind size feed directly into operating cost. If your priority is trimming these costs, see our guide on cutting reagent and energy costs in cyanidation.

Carbon handling and the gold room

In both CIP and CIL, loaded carbon is periodically pulled from the circuit, stripped of its gold in an elution column, and the gold recovered by electrowinning before the barren carbon is reactivated and returned. The gold room – elution, electrowinning and smelting – is largely the same for both routes. Sizing it correctly to the carbon movement rate avoids bottlenecks; an undersized gold room throttles the whole plant. Interstage screens that retain carbon in each tank are a common wear and maintenance point, and CIL’s in-tank carbon means slightly higher attrition than CIP.

Equipment that differs by route

Tank-leach plants (CIP/CIL) need agitated leach and adsorption tanks, interstage screens, and an elution/EW gold room. The leach reactors themselves are the heart of the circuit; see our gold leaching agitation tanks and packaged CIP gold plant. Both routes start with the same comminution and classification front end, regardless of which leach method follows. For the complete tank-leach package, explore the gold extraction equipment hub, and for a turnkey build the CIP gold processing plant bundles crushing, grinding, leaching and the gold room.

Making the decision

Start with a representative ore sample and a bottle-roll or column test. Cyanide consumption, leach kinetics, preg-robbing index and gold grade from that testwork will point clearly to one route. As a rule of thumb: low-grade oxide and large tonnage favors heap leach; higher-grade or sulfide-associated ore favors tank leaching, with CIL chosen over CIP whenever preg-robbing or slow kinetics are a risk. Xinhai runs this testwork in-house and designs the matching plant under a single EPC+M+O contract, so the flowsheet, equipment and ramp-up support all come from one source.

The first question: how does the gold occur?

Before comparing methods, characterize the ore. A few questions decide the flowsheet:

• Is the gold coarse and free-milling, or fine and disseminated?
• Is it associated with sulfides (pyrite, arsenopyrite) or free in quartz?
• Is there carbonaceous material that would re-adsorb dissolved gold?
• What is the head grade, and what recovery does the economics demand?

A gravity-recoverable gold (GRG) test and a mineralogical scan answer most of this and point to the right combination.

Gravity concentration

Gravity exploits the high density of gold (about 19 g/cm3) versus gangue (2.6-3 g/cm3). It is the cheapest method to run, uses no reagents, and recovers coarse free gold early so it does not get lost or over-ground. Centrifugal concentrators capture fine free gold down to tens of microns, while shaking tables and spiral chutes handle coarser fractions and produce a saleable concentrate. The limitation is that gravity cannot recover gold that is locked inside other minerals or too fine to settle.

Typical placement: a centrifugal concentrator in the grinding circuit to scalp free gold, with a shaking table to upgrade the gravity concentrate. See the full gravity concentration range for spirals and jigs.

Flotation

When gold is fine and associated with sulfides, flotation collects the gold-bearing sulfides into a concentrate that is a small fraction of the original mass. This is ideal for refractory or sulfide-hosted gold: instead of leaching the whole orebody, you leach (or smelt) only the concentrate, cutting reagent and energy cost dramatically. Flotation needs reagents and good liberation, and works best on sulfide minerals rather than free gold in oxide ore.

Cyanide leaching

Leaching dissolves gold chemically with dilute cyanide and recovers it onto activated carbon (CIL/CIP) or by zinc precipitation. It reaches the highest recoveries, 90-96% on amenable ores, and handles fine, disseminated gold that gravity and flotation miss. The trade-offs are reagent cost, residence time and the need for careful cyanide management. Leaching is applied either to the whole milled ore or, more economically, only to a flotation or gravity concentrate. See gold extraction equipment for leach tanks and the gold room.

Side-by-side comparison

Reagents and control in flotation

Flotation performance hinges on reagent selection and grind size. Collectors such as xanthates render the sulfide surfaces hydrophobic so they attach to air bubbles; frothers stabilize the bubble film; and modifiers (lime, copper sulfate, depressants) control pH and selectivity. Grind size must liberate the gold-bearing sulfides without overgrinding into slimes that float poorly. A typical sulfide gold flotation runs at a P80 around 75 microns, with the optimum confirmed by bench testwork. Because flotation rejects most of the gangue, the resulting concentrate is often 10-30 times higher grade than the feed, which is exactly what makes downstream leaching cheap.

Why most plants combine all three

A well-designed gold plant rarely relies on one method. A common high-recovery flowsheet runs gravity inside the grinding circuit to pull out coarse free gold first (which is hard to leach and easy to lose), then sends the rest to flotation or directly to leaching depending on mineralogy. For sulfide ores, gravity plus flotation concentrates the gold into a small mass that is then leached. This staged approach maximizes overall recovery while keeping reagent consumption proportional to the gold-bearing mass, not the whole orebody.

A typical free-milling flowsheet

1. Crush and grind to liberation size (often 75-106 microns).
2. Gravity scalp coarse free gold with a centrifugal concentrator.
3. Leach the gravity tailings by CIL/CIP.
4. Recover gold from loaded carbon by elution and electrowinning.

A typical refractory/sulfide flowsheet

1. Crush, grind and run gravity for any free gold.
2. Float the gold-bearing sulfides into a concentrate.
3. Treat the concentrate (leach, or oxidize then leach).

Reading recovery numbers correctly

Be careful comparing the recovery figures for each method, because they measure different things. Gravity recovery is quoted as a share of total contained gold and is inherently limited to the coarse free fraction, so 20-60% is normal and not a weakness – it simply reflects how much of the gold is recoverable by density. Flotation recovery is quoted to concentrate, where 85-95% is typical, but that concentrate still has to be treated to produce metal. Leaching recovery is the closest to a true overall figure. The number that ultimately matters is plant recovery across the whole flowsheet, which a well-staged combination maximizes by sending each gold form to the method best suited to it.

Cyanide management is part of the design

Any cyanidation circuit must address safety and environment from the outset: pH is held around 10.5-11 with lime to keep cyanide stable and avoid hydrogen cyanide release, and tailings are detoxified before discharge. These requirements influence reagent cost and permitting, and are a reason flotation pre-concentration is attractive – leaching a small high-grade concentrate uses far less cyanide than treating the whole orebody.

Matching method to ore is the whole game

Choosing gold recovery methods is really about reading the ore correctly. Coarse free gold to gravity, sulfide-locked gold to flotation, fine and disseminated gold to leaching, and almost always a combination. Xinhai runs the gravity, flotation and leach testwork in-house, then designs the integrated flowsheet and supplies the equipment under one EPC+M+O contract. For the CIL vs CIP vs heap leach decision specifically, see our gold processing plant comparison.

How gravity separation works

Every gravity device exploits the same principle: in a moving film of water, dense particles settle, lag or report differently than light particles. The usable density contrast is commonly expressed by the concentration criterion, (SG heavy – 1) / (SG light – 1). A value above about 2.5 means easy separation at almost any size; between 1.75 and 2.5 separation is feasible above roughly 0.15 mm; below 1.25 gravity alone struggles. Gold (SG 19), cassiterite (SG 7) and chromite (SG 4.5) separate readily from silica (SG 2.65); fine coal and some oxidized ores do not.

The two variables that decide everything

• Particle size: fine feed needs gentle, film-flow devices; coarse feed needs pulsing or tumbling action.
• Throughput vs. grade: high-tonnage roughing favors spirals and jigs; final cleaning to a sellable concentrate favors tables and centrifugal bowls.

The four main gravity devices compared

Shaking tables

A gold shaker table uses a riffled deck with asymmetric horizontal motion and a thin cross-flow of water. Dense particles migrate along the riffles to the concentrate end while light gangue washes over the edge. Tables give the sharpest separation of any gravity device and produce a clean, high-grade concentrate, which is why they are almost always the final cleaning stage in a small gold plant. The trade-off is low unit capacity, so tables are usually fed from a pre-concentrating device rather than raw ore. Browse the full range of gravity concentration equipment to see how tables pair with upstream units.

Spiral chutes

The spiral chute separator has no moving parts: pulp flows down a helical trough and centrifugal plus gravitational forces band the minerals across the channel, where splitters cut concentrate, middling and tailing. Spirals shine on fine, high-tonnage duties such as iron ore, chromite, ilmenite and zircon sands. They are cheap to run, easy to operate and scale simply by adding starts, making them a favorite roughing device ahead of magnetic or table cleaning.

Jigs

Jigs pulse water up through a bed of particles so dense grains stratify to the bottom and report through the screen. Because they handle coarse feed, jigs are ideal for alluvial deposits, coarse gold, tin and tungsten, and for pre-concentrating run-of-mine before grinding, which cuts downstream mill load. They tolerate variable feed and require little water relative to tonnage.

Centrifugal concentrators

A centrifugal concentrator applies many times the force of gravity in a fluidized, rotating bowl, capturing fine free gold that tables and spirals lose. Installed in or after the grinding circuit, it recovers gold as soon as it is liberated, often lifting overall plant recovery by several points and reducing the gold tied up in circulating load. It is the standard answer to the question, where does my fine gold go.

Centrifugal bowls run in two modes. Batch units periodically stop to rinse a high-grade concentrate and are common in small plants and for cleaning duty, while continuous units discharge concentrate on a timed cycle without stopping the feed, suiting larger throughputs. The captured concentrate is small in mass but high in grade, so it is almost always cleaned on a shaking table before smelting. Because the bowl applies tens of g, it recovers gold down to roughly 10-25 micron that a table would lose, which is exactly the fraction that otherwise reports slowly, or not at all, to a downstream leach.

Where gravity sits in the flowsheet

In most plants gravity is not the only step. It is a fast, cheap pre-concentration stage that pulls coarse and free values early, leaving a smaller, upgraded stream for flotation or leaching. A typical gold flowsheet runs the milled pulp through a centrifugal concentrator and table to recover free gold, then sends the gravity tail to a flotation circuit or a CIL/CIP leaching plant. This hybrid approach maximizes recovery while shrinking cyanide and reagent demand. For the full picture of how recovery routes combine, see our guide to gold recovery methods compared.

Wear, water and operating cost

Part of gravity’s appeal is low operating cost, but each device has its own wear and consumable profile worth budgeting. Spirals have no moving parts, so wear is limited to the polyurethane or rubber lining of the trough and the splitters, replaced periodically. Tables wear the deck surface and riffles and depend on a reliable head-motion drive. Jigs wear screens, diaphragms and the drive mechanism, and consume ragging where used. Centrifugal bowls wear the fluidization fittings and the bowl liner. None of these approaches the reagent and energy bill of flotation or leaching, which is precisely why gravity is placed first wherever the ore allows it.

Selection checklist

• Run a particle-size and SG analysis first; size dictates the device.
• Coarse and free values: jig or centrifugal up front.
• Fine, high tonnage: spirals for roughing, tables for cleaning.
• Always confirm the concentration criterion before committing to gravity alone.
• Test on a representative sample; Xinhai’s lab can recommend a flowsheet sized to your ore.

Know where the money goes

Before optimizing, understand the typical split. Grinding usually consumes the largest share of plant energy, often 40% or more. Cyanide and lime are the biggest reagent costs, with carbon, flocculant and grinding media adding up. The table below shows the main cost drivers and the most effective lever for each.

Lever 1: recover free gold by gravity first

The cheapest gold to recover is the gold you never leach. Installing a centrifugal concentrator in the grinding circuit captures coarse free gold as soon as it is liberated, before it has to be dissolved. A shaking table cleans that gravity concentrate to a smeltable product. Removing free gold ahead of the leach cuts cyanide consumption, shortens leach time and reduces the gold inventory tied up in carbon. For many free-milling ores this single change is the biggest cost reducer available. See the gravity concentration range for sizing.

Lever 2: grind to liberation, not finer

Over-grinding burns power and generates slimes that slow settling and raise reagent demand, while under-grinding leaves gold locked and uextractable. The optimum, often 70-80% passing 75 micron for free-milling ore, comes from liberation testwork. Running a closed grinding circuit with a well-tuned hydrocyclone keeps the product size consistent and avoids both over- and under-grinding. A few micron of unnecessary fineness can add measurable cost per tonne across the life of a plant.

Lever 3: dose cyanide and oxygen to demand

Cyanide is consumed not only by gold but by cyanicides such as copper and reactive sulphides. Measuring free cyanide and titrating to a target, rather than running a fixed high addition, prevents the costly habit of over-dosing for safety margin. Likewise, gold dissolution needs dissolved oxygen; matching aeration or oxygen injection to the actual leach kinetics in the early tanks, where demand is highest, speeds leaching and lets you hold cyanide lower. Modern leaching agitation tanks with efficient aeration help here.

The two reagents interact, which is where real savings hide. Gold dissolution depends on both free cyanide and dissolved oxygen, and if oxygen is the limiting factor, adding more cyanide does nothing but raise cost and feed cyanicides. Many circuits are oxygen-starved in the first one or two tanks where leaching is fastest; supplying oxygen there, by sparging pure oxygen or by improving impeller aeration, lets the same recovery be reached at a lower cyanide concentration. A simple program of measuring dissolved oxygen and free cyanide profiles down the tank train usually reveals where reagent is being wasted, and the fix is operational rather than capital.

Lever 4: manage pH efficiently

Lime is added to hold pH around 10-10.5, which prevents cyanide from escaping as toxic HCN gas and protects against acid loss. Over-liming wastes reagent and can passivate gold surfaces; under-liming loses cyanide and creates a safety hazard. Efficient lime slaking and pH control instrumentation pay back quickly by keeping addition to what the circuit actually needs.

Lever 5: recycle water and carbon

• Water: a thickener returns most process water and, in a CIL/CIP plant, residual cyanide with it, lowering both make-up water and reagent make-up. This is decisive in arid regions.
• Carbon: efficient elution and regeneration in a well-run elution and electrowinning system keeps carbon activity high so less make-up carbon is needed.
• Tailings detox and reuse: recycling cyanide-bearing solution reduces fresh cyanide demand where regulations allow.

Lever 6: control grinding media and liner wear

Grinding is not only the largest energy consumer; steel media and mill liners are a steady consumable cost that often goes unmanaged. Matching ball size and charge to the feed, keeping the mill at its optimal filling and choosing liner profiles suited to the ore all reduce steel consumption per tonne and stabilize the grind, which in turn stabilizes downstream leach performance. Erratic grind size forces operators to over-dose reagents as a buffer, so tightening grinding control quietly lowers reagent cost as well as media cost. It is a good example of how energy and reagent savings are linked rather than independent.

CIL vs CIP and the cost picture

Circuit choice affects cost too. CIL combines leaching and adsorption in the same tanks, suiting ores with preg-robbing carbon, while CIP separates them and can be cheaper to operate on clean ores. The right choice depends on ore behavior; our guide to CIL vs CIP vs heap leach covers the trade-offs in detail. Either way, a properly sized gold extraction circuit with the right tank count avoids the cost penalty of carbon attrition and incomplete leaching.

Put it together

None of these levers requires exotic technology; they require a flowsheet designed for the ore and instrumentation to dose to demand. Combined, gravity pre-recovery, optimized grind, demand-based cyanide and oxygen, efficient pH control and water and carbon recycling commonly trim 10-30% off reagent and energy cost per ounce. Because Xinhai designs and builds the full circuit under an EPC+M+O contract, these efficiencies are built into the plant from the testwork stage rather than retrofitted later.

Match the plant to the ore first

Before any equipment is bought, two questions decide the whole design: is the gold free-milling or refractory, and is it coarse or fine. Free-milling, coarse gold can be recovered largely by gravity alone, which is the cheapest plant to build and run. Finely disseminated or sulphide-locked gold needs leaching, which adds tanks, reagents and an elution circuit but lifts recovery from perhaps 40-60% (gravity only) to 88-95% (gravity plus CIP). A 1-2 tonne metallurgical test on a representative sample is the single best investment you can make before ordering steel.

Two diagnostic tests are worth commissioning early. A gravity-recoverable-gold (GRG) test tells you how much of the gold can be won by gravity alone, which sets the size of the gravity stage and the cyanide you can avoid. A bottle-roll cyanidation test on the gravity tailing tells you the leach recovery and reagent consumption to expect. Together they convert the vague question of which plant into hard numbers: recovery, reagent cost per tonne and the split between gravity and leach. Skipping this step is the most expensive shortcut in small-scale gold, because it tends to surface only after the plant is built and underperforming.

The equipment list, stage by stage

1. Crushing and feeding

Run-of-mine ore is reduced to a millable size, usually below 15-25 mm. A small plant typically uses a single-stage or two-stage crusher with a feeder ahead of it.

• PE jaw crusher for primary reduction; a PE-400×600 handles roughly 15-60 t/h.
• Vibrating grizzly feeder to meter ore and scalp fines.
• A spring cone crusher as a second stage if a finer, tighter product is needed.

2. Grinding and classification

Grinding liberates the gold, typically to 60-80% passing 75 micron for leaching. A closed circuit of mill plus classifier keeps the product size consistent.

• Wet ball mill sized to your tonnage and target grind.
• Spiral classifier or a hydrocyclone to close the grinding circuit.

3. Gravity recovery

Free gold should be captured as soon as it is liberated, before it dissolves slowly or is lost. A gravity stage is cheap insurance and often recovers a third or more of the gold.

• Centrifugal concentrator in the grinding circuit to catch fine free gold.
• Shaking table to clean the gravity concentrate to a smeltable grade.

4. Leaching and recovery (for refractory or fine gold)

The gravity tail goes to a cyanide leach. A CIP plant adsorbs dissolved gold onto activated carbon in a train of agitated tanks, then an elution and electrowinning system strips the carbon and recovers gold for smelting. For the choice between CIP, CIL and heap leach, see our guide to CIL vs CIP vs heap leach.

A small leach circuit is usually a string of six to eight agitated tanks giving a total residence time of 18-30 hours, sized so the gold is fully dissolved and adsorbed before the pulp leaves the last tank. Lime is added to hold pH around 10-10.5, air or oxygen is sparged to supply the dissolved oxygen leaching needs, and carbon is advanced counter-current to the pulp so the loaded carbon is drawn from the first tank. Getting the tank count and residence time right is what separates a plant that hits its recovery target from one that chronically leaves gold in the tailing.

Indicative budget by plant size

The ranges below are equipment-only and indicative; they exclude civil works, freight, duties and installation. Frame them as starting points to scope your project, not quotes.

Hidden costs to budget for

• Civil and installation: often 20-40% on top of equipment cost.
• Power and water: grinding dominates power draw; secure supply or a genset early.
• Reagents: cyanide, lime and carbon are ongoing operating costs in a leach plant.
• Tailings and water return: a thickener pays back in recovered water and is increasingly required for permitting.
• Spares and wear parts: mill liners, balls, crusher jaws and pump parts.

Phasing a project on a tight budget

Cash-constrained projects often build in phases. A common approach is to commission a gravity-only plant first to generate early cash flow from the free gold, then add the leach circuit once the deposit and the cash position are proven. This works only if the layout is planned for the leach from the start, with tank pads, power and water sized for the final configuration; retrofitting a leach into a plant laid out for gravity alone wastes money. Plan the full flowsheet on paper even if you build it in stages.

Build it as one system

The most common small-plant mistake is buying machines piecemeal that do not balance, leaving a bottleneck that caps throughput. Because Xinhai supplies turnkey mineral processing plants under an EPC+M+O model, the crusher, mill, gravity and leach stages are sized against one another and against your ore test, and the package includes installation, commissioning and operator training so the plant reaches nameplate faster.