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:: Trunnion Magnetic Separator at Kemi Mine
An Eriez Trunnion Magnetic Separator has been utilised by Finnish ferrochromium producers, Outokumpu Tornio Works, in their efforts to improve chromite concentrate production in the company’s Kemi Mine.
The Eriez Trunnion Magnet is a powerful system for the automatic separation and removal of processing balls and ferrous chips from milled ore in ball or SAG mills. Typically the system consists of a permanent magnetic arc that partially covers a rotating blind trunnion positioned at the ball or SAG mill discharge. The milled ore is fed into the trunnion, capturing the ball chip fragments which are held by the magnetic arc. The fragments are then released at the top of the trunnion barrel where the magnetic arc terminates, and are discharged into a collection hopper on the inside.
The largest Trunnion Magnet built to date had a diameter measuring 3150 mm (124”).
The Trunnion Magnetic Separator at Kemi replaced the existing ball mill grate and costly trommel screen system which were being continually ‘blinded’ (ie blocked) by cement and steel fibres in the shotcrete used in the underground mining facility. The frequent blockages not only reduced efficiency levels in the grinding circuit but also resulted in prolonged downtime - 16 valuable production hours lost every month - while the ball mill underwent extensive cleaning to remove the impurities.
Weighing 455 kg and with an outside diameter measuring 770 mm, the 914 mm long Outokumpu Trunnion Magnetic Separator consists of a 12 mm thick stainless steel barrel complete with rubber lining. As the discharge slurry (top feed size 4 mm) passes through the magnet barrel at a volumetric rate of 60 cubed metres per hour, the chips are attracted to combined rare earth and barium ferrite magnets arranged in a 200 degree permanent magnetic arc, to be discharged into the collection hopper.
The Eriez system is credited with preventing ball chips from circulating through the sump pump and hydrocyclones, resulting in a more efficient, finer media grind whilst prolonging the lifespan of these parts. Costs and on-going maintenance have been reduced as downstream machinery is protected, and milling throughput has increased.
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