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.