Eddy Current vs Magnetic Separation: When to Use Each Technology

Eddy current separators (ECS) and magnetic separators look similar from the outside — both are belt-and-rotor machines that auto-sort metals — but they exploit different physics and target different metal classes. Picking the wrong one wastes capex and leaves money in the tail. This guide compares the two technologies head-to-head and shows how they sequence in real plants.

Different physics, different metals

• Magnetic separation uses static or low-frequency magnetic fields. Particles respond based on magnetic susceptibility: strongly attracted (ferromagnetic — iron, magnetite), weakly attracted (paramagnetic — hematite, chromite), or unaffected (diamagnetic — quartz, copper, aluminum).
• Eddy current separation uses a fast-rotating high-frequency magnetic field. Particles respond based on electrical conductivity: high-conductivity non-ferrous metals are repelled and launched; insulators and inerts drop near-vertically.
• Bottom line — magnetic separators recover ferromagnetic and paramagnetic metals/minerals. Eddy current separators recover conductive non-ferrous metals. They do not overlap on aluminum/copper/brass nor on iron/magnetite.

Side-by-side comparison

• Force mechanism — magnetic: direct attraction. ECS: induced repulsion via Faraday/Lenz.
• Target metals — magnetic: iron, steel, magnetite, hematite, ilmenite. ECS: aluminum, copper, brass, zinc.
• Sensitivity to ferrous — magnetic: by design. ECS: rotor heats and belt sticks if ferrous reaches the head; ferrous must be removed upstream.
• Sensitivity to stainless steel — magnetic separators capture some ferritic stainless. ECS produces a small launch but typically insufficient; dedicated stainless separators handle this gap.
• Particle size envelope — magnetic: 0.05–100 mm depending on type. ECS: 1–80 mm typical, fine ECS down to 0.5 mm with high-pole rotors.
• Moisture tolerance — magnetic: drums handle slurries; dry units tolerate <3%. ECS: dry feed required (<5% surface moisture).
• Maintenance driver — magnetic: pole face wear, belt alignment. ECS: belt life (eccentric rotors much better), splitter wear.

Typical magnetic separation jobs

• Iron ore concentration — recovering magnetite at 65%+ Fe with dry drum LIMS and wet drum LIMS.
• Tramp removal — protecting crushers and shredders with overband magnetic separators or permanent overband magnets.
• Industrial mineral purification — silica, kaolin, feldspar deironing with high-intensity wet electromagnetic separators.
• Slag beneficiation — iron-and-steel slag and ferronickel slag recovery; see slag beneficiation plants.
• Tramp ferrous extraction from shredded scrap — first stage in any aluminum or copper recovery line.

Typical eddy current jobs

• Aluminum recovery — UBC, ASR, IBA, electronic scrap; classical ECS duty.
• Copper and brass recovery — turning shavings, mixed wire, e-waste shredder fines.
• Glass cullet cleaning — closure removal before re-melt.
• PET flake polishing — aluminum foil residual removal.
• MRF non-ferrous polishing — final product quality control before bale.

Hybrid plant flow that works

A typical metal recycling line — say a shredded automotive scrap plant — runs a sequence rather than a one-shot machine. Numbers below are illustrative for an EU mid-size operation processing 30 t/h.

1. Shredder discharge → ferrous recovery: overband magnet captures 60–75% of the mass as ferrous bundle.
1. Heavy media or air classification removes inerts (rubber, foam, plastics light fraction).
1. Magnetic drum + secondary overband cleans residual ferrous to <0.5%.
1. Eccentric-rotor eddy current separator recovers Zorba (mixed non-ferrous) at 90–98% of the available aluminum/copper.
1. Sensor sorting (XRT, induction) splits Zorba into Twitch (Al-rich) and Zurik (Cu-rich) traded products.
1. Stainless steel separator at the tails recovers austenitic stainless that ECS could not launch.

Skipping the magnetic stage damages the ECS rotor; skipping the ECS stage leaves >$1,000/t aluminum in the residue.

Misapplication signals — wrong-tool diagnostics

• ECS recovery falls every shift, belt heats unevenly: ferrous is reaching the rotor; add or upsize magnetic stage.
• Magnetic concentrate carries non-magnetic gangue: liberation is poor; revisit grinding, not the magnet.
• WHIMS produces clean concentrate but tonnage drops sharply on dry days: feed slurry density is too high; add water, not field.
• Aluminum is wrapped in steel cans/composites: ECS yield drops; shred finer or pre-sort.
• Stainless steel reports to ECS reject as "lost": specify a stainless-steel separator downstream.

Where BAS fits

BAS supplies the full chain — magnetic drums and overbands, WHIMS-style high-intensity wet units, eccentric-rotor ECS, stainless separators, and integrated scrap separation plants. Use the separator selection wizard to map a feed to the right train, and contact BAS engineering for a flowsheet review.

Frequently Asked Questions

Can an eddy current separator replace a magnetic separator?

No. ECS only sorts conductive non-ferrous metals (aluminum, copper, brass). It does nothing for iron and steel, and ferrous reaching the ECS damages the belt and rotor. Magnetic separators must come first.

In what order should I install magnetic and eddy current separators?

Always magnetic first, ECS second. The magnetic stage strips ferrous so the ECS belt life is preserved and so the non-ferrous product purity is maximised. In some lines, a second magnetic polish runs after ECS to catch residual ferrous that survived shredding.

Can a magnetic separator recover aluminum?

No. Aluminum is non-magnetic in the dia/paramagnetic sense — it has very low magnetic susceptibility. Aluminum recovery requires an eddy current separator that exploits its high electrical conductivity instead.

What is Zorba and how do I produce it?

Zorba is the mixed non-ferrous metal product from shredded scrap, dominated by aluminum with copper, brass, zinc, and some stainless. It is produced by feeding shredded scrap to an eddy current separator after ferrous removal. Sensor sorting then splits Zorba into Twitch (Al-rich) and Zurik (Cu-rich) traded fractions.

Are there single machines that do both magnetic and eddy current separation?

No standalone machine performs both functions reliably. Some lines combine a head-pulley magnet directly upstream of an ECS in a single chassis, which saves footprint, but the magnetic and eddy stages are still separate magnets.