magnetic separators (magnetic separators)

Magnetic separators are stationary or rotating devices that use a strong permanent magnet or electromagnet to attract and remove ferrous metals — iron, steel, and nickel-based alloys — from a moving material stream. They are the first metal-recovery step in virtually every Indian recycling and waste-processing line, sitting above conveyor belts, at the discharge of shredders, or at the inlet of sensitive downstream equipment like pulverisers, pyrolysis reactors and digesters.

Three configurations dominate practice. Overband magnets are suspended above a conveyor at 200-400 mm air gap; ferrous fragments leap upward against gravity onto the magnet's belt and are conveyed off-line into a recovery bin. They handle high-volume, mixed-stream applications like MSW and ELV shredder discharge. Drum magnets are rotating magnetic cylinders integrated into the head pulley of a conveyor; non-ferrous material falls in a parabolic trajectory while ferrous wraps around the drum and is released into a separate chute. Magnetic pulleys embed the magnet inside the conveyor's head roller for inline separation on smaller streams.

Field strength is specified in gauss or tesla; common Indian installations use neodymium-iron-boron permanent magnets at 4,000-12,000 gauss at the working face for general scrap, and high-intensity electromagnets at 15,000+ gauss for fine ferrous capture in shredded e-waste and battery recycling. Capture efficiency typically reaches 95-98% of ferrous fraction when feed depth on the belt is uniform; thicker beds reduce efficiency by burying small fragments below the magnet's effective reach.

The sector-specific reasons for magnetic separation differ. In CBG plants it protects pumps, shredders and digester pipes from impact damage and clogs caused by nails, wires and tin scrap mixed with food waste. In tyre pyrolysis it recovers steel wire from the reactor output at 10-15% of input tyre mass, sold separately at ₹25-32 per kg. In e-waste it recovers ferrous shells and frames before metallurgical processing. In Li-ion battery recycling it removes ferrous cell casings before chemical leaching, where iron contamination would foul cathode-material recovery. The trade-off is straightforward: capex of ₹3-15 lakh per unit recovers material value plus downstream equipment protection that pays back typically within 8-18 months.