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.