Why flotation for copper

Copper sulphides such as chalcopyrite, bornite and chalcocite are too low-density to separate by gravity and too non-magnetic for magnetic methods, but their surfaces can be made water-repellent (hydrophobic) with a collector so they attach to air bubbles and float. Gangue minerals stay wetted and sink. Flotation is selective enough to separate copper minerals from pyrite and even, with the right reagents, to separate copper from molybdenum or lead-zinc. That selectivity is the core of the flowsheet.

The economic driver is the upgrade ratio. A typical porphyry copper ore grades only 0.5-1% Cu, far too low to smelt directly; freight and smelting of that diluted material would be ruinous. Flotation concentrates the copper roughly 20- to 50-fold into a 20-30% Cu product, so that only a small mass of high-value concentrate is shipped to the smelter while the bulk of the ore reports to tailings on site. Every percentage point of recovery lost is paid copper left in the tailing, which is why the flowsheet is engineered around recovery first and grade second, within smelter penalty limits.

The flowsheet, stage by stage

1. Crushing

Run-of-mine ore is crushed in two or three stages to a mill feed size, commonly below 10-15 mm. A jaw crusher handles primary reduction and a cone crusher takes secondary and tertiary duty. Feeders and screens, from the screening range, keep the circuit fed and closed.

2. Grinding and classification

Grinding liberates copper minerals from gangue, the single most important step for recovery. Typical flotation feed is 60-75% passing 75 micron, though finely disseminated ores need finer. A wet ball mill runs in closed circuit with a hydrocyclone cluster that returns coarse particles for regrinding and sends correctly sized pulp to flotation. Grind too coarse and copper stays locked; grind too fine and you waste power and generate slimes that hurt selectivity.

3. Flotation: rougher, scavenger, cleaner

The conditioned pulp enters the flotation circuit, the heart of the plant:

• Rougher: recovers the bulk of copper into a rough concentrate as fast as possible.
• Scavenger: treats rougher tailing to catch the last recoverable copper, improving overall recovery.
• Cleaner (often two or three stages): re-floats the rougher/scavenger concentrate to reject entrained gangue and lift grade to a saleable 20-30% Cu.

A copper flotation plant built from mechanical flotation cells provides the aeration and agitation each duty needs. Reagents, collector, frother, lime for pH control and depressants for pyrite, are dosed to the conditioning stage and tuned to the ore. See the full flotation equipment range for cell sizing.

Cell selection and arrangement matter as much as cell type. Roughers are usually larger cells run at higher pulp level to maximize froth recovery, while cleaners are smaller and run deeper to reject gangue. The reagent suite is dosed in stages: a primary collector such as a xanthate, sometimes supplemented by a dithiophosphate for selectivity, a frother to control bubble size and froth stability, lime to raise pH and depress pyrite, and where needed a specific depressant. A common error is over-dosing collector, which floats more pyrite and dilutes the concentrate; dosing to the rougher feed and staging additions through the bank gives cleaner separation at lower reagent cost. Froth depth, air rate and pulp level are the operator’s day-to-day levers for holding grade and recovery as feed changes.

4. Dewatering

The cleaner concentrate is thickened in a thickener to recover water, then filtered to a shippable cake, while flotation tailings are thickened and sent to storage with process water returned to the plant. Concentrate moisture is a real cost: every percent of water shipped is freight paid on water, so a filter that delivers a low-moisture cake earns its keep on long export hauls. On the tailings side, returning clarified water to the mill cuts freshwater make-up and the energy to pump it, which is significant given flotation circuits run at high water-to-solids ratios.

Typical performance figures

Design choices that drive results

• Grind size: set by liberation tests; the biggest lever on recovery and concentrate grade.
• Reagent scheme: collector and depressant selection determine how cleanly copper separates from pyrite.
• Circuit configuration: the number of cleaner stages trades grade against recovery; over-cleaning loses copper.
• Oxide content: oxidized copper does not float well and may need sulphidization or a leach route instead.
• By-products: gold, silver and molybdenum often report with copper and can add significant value if the flowsheet accounts for them.

Build the circuit around your ore

Two copper ores rarely respond identically, so the reagent scheme, grind and cell count must be set from testwork, not copied. Xinhai runs the ore tests, designs the flowsheet and delivers the complete copper processing plant under an EPC+M+O contract, so crushing, grinding, flotation and dewatering are balanced to your throughput and your mineralogy. For background on how flotation compares with other recovery routes, see our overview of recovery methods.

How the two approaches differ

In dry magnetic separation, dry ore passes over or through a magnetic drum or roll; magnetic particles cling to the drum surface and are carried away from the non-magnetic stream. No water is used. In wet magnetic separation, ore is fed as a slurry; the magnetic fraction is captured on a rotating drum in the magnetic field and washed off as a clean magnetic concentrate while gangue exits with the water.

Particle size is the deciding factor

The single most important variable is particle size. Dry separation works well on coarse particles, roughly above 1-2 mm, where individual grains move freely and do not clump. As particles get finer, they agglomerate, trap dust and behave erratically in a dry field, so separation efficiency falls. Wet separation handles fine particles far better because the slurry keeps them dispersed and mobile, which is why finely ground magnetite is almost always processed wet. Most iron ore must be ground fine to liberate the magnetite, so the bulk of magnetite beneficiation worldwide is wet.

Side-by-side comparison

When to choose wet magnetic separation

Wet separation is the default for upgrading finely ground magnetite to a high-grade concentrate, often 60-68% Fe depending on the ore. It produces a cleaner product with higher recovery on fine feed, avoids dust entirely, and integrates naturally with a wet grinding and classification circuit. The trade-offs are water consumption and the need to dewater the concentrate afterward. A high-intensity wet drum magnetic separator is the workhorse here; explore the full magnetic separators range for field-strength options.

When to choose dry magnetic separation

Dry separation makes sense when water is scarce or expensive, when the feed is naturally dry and coarse, or as a pre-concentration step that rejects waste before grinding, saving energy on the milling stage. Dry roll and drum separators are common for coarse magnetite cobbing and for some weakly magnetic ores at high field intensity. The main challenges are dust management and generally lower concentrate grade, which may need a wet cleaning stage to finish. The dry magnetic separator suits these coarse and arid-site duties.

Field intensity: LIMS vs WHIMS

Beyond wet versus dry, the field strength must match the ore’s magnetism. Strongly magnetic magnetite is recovered on low-intensity magnetic separators (LIMS), typically permanent-magnet drums of a few thousand gauss, which are efficient and cheap to run. Weakly magnetic iron minerals such as hematite, limonite, ilmenite and martite need high-intensity or high-gradient separators (WHIMS/HGMS) operating at much higher field strengths to be captured at all. Getting this wrong is a classic failure: a LIMS drum will leave most of a hematite ore in the tailings. Magnetic susceptibility testing on the actual ore tells you which class of separator and what field strength you need before any equipment is bought.

Grind size, liberation and middlings

Magnetic separation can only sort liberated grains. If magnetite is locked to silica gangue, a coarse grind leaves composite middlings that report partly to concentrate (diluting grade) and partly to tailings (losing iron). Grinding finer improves liberation and grade but costs energy and pushes the duty toward wet separation. The economic grind size is the point where extra liberation no longer pays for the extra milling – usually found by grinding a series of samples and running each through the separator. Multiple cleaning stages then lift grade by re-treating the rougher concentrate. Browse the grinding equipment range, since mill sizing and separator choice are decided together.

Many iron ore plants use both

A common high-efficiency strategy combines the two. Dry magnetic separation runs first as a pre-concentration step on coarse, crushed ore to reject barren gangue cheaply before grinding. The pre-concentrate is then ground and processed by wet magnetic separation to reach final grade. This sequence cuts grinding energy (you only grind ore that contains iron) while still achieving a clean, high-grade concentrate. The wet concentrate then goes to dewatering before shipment.

A typical magnetite flowsheet

1. Crush ore and run coarse dry magnetic separation to reject waste.
2. Grind the pre-concentrate to liberation size.
3. Upgrade with wet drum magnetic separation, often in roughing and cleaning stages.
4. Dewater the concentrate with a thickener and filter.

Match the separator to the ore and the site

The wet vs dry choice comes down to particle size, target grade, and how much water the site can supply. Fine magnetite for a high grade goes wet; coarse pre-concentration and water-scarce sites go dry; and many plants stage both. Xinhai sizes magnetic separators from your ore’s magnetic susceptibility and liberation size, and designs the surrounding grinding and dewatering circuit under one EPC+M+O contract. Send your ore details and target Fe grade through the contact page for a recommendation.