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EVERWHINGouMAGNETICSEPARA

NEVERKNEW ABOUT.......................................................

Recoveryof ferrous metals from refusemeans money.Here's a look at bow it can be done.

evenue from municipal solid waste (MSW2processing plants is derived from sale ofoutput products. Salable products include re-m\-rrrd ferrous and non-ferrous metals, glass.am1 otl~rr aterials u s r d for fuel, animal-feed

constituents, and more.As in all processing systems, percentage recoven,

grade of recovered product, per-ton recoven cost, andmarket demand govern the output product's marketability.

Figure OneBasic System for Recoveryetall ics from -.unic ipal Sol id Waste- . . IU' ..~

Tlus article deals with the recovery of ferrous metalsfrom refuse through the use of magnetic separationteclulolog?:Processing schemes and mag netsFerrous metals generally represent 7% to 8% of arefuse processing plant's input feed. Most existingplants shred refuse to reduce size and liberaterwoverat)le materials.By D.G. MORGANMorgan 1s presldent of Applled Magnetlc Systems, Mllwaukee. Wls

Figure Tw oA FullScale RecoveSystem for aMunic ipa lWaste Reclamat ionP7 nt .Figure One represents a basic system in whic

the shredder's output passes directly under two mnetic drums. Note that these are designed to remapproxllnatel~~5% of the ferrous metal-and, insystem fflustratrd, no sizing de ~ icrs in h e ollothe shredder.

Figure "w o displays a system that uses both s

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trommel) and gravity (an ir classifier) on shredderas well as the same magnet configuration

, ~ v n reviously..;lso shown is another magnet configuration (amag-head pulley), farther downstream. This

of the non-ferrousfinal eparation.

Perma nent Magnet ic Head Pul ly Arrangem eri t -

d beoMagnets used are usually either permanent magnetic

or electromagnetic units.Permanent magnetsno power, keeping maintenance and operationalsts quite low.

Electromagnetics provide an advantage: one can varytic field intensity. Generally, there are three con-drums, and suspended magnets.

through Five show typical respectiveSix illustrates a variation of the

in m e ive.Each of the three magnet configurations is discussed

ulleyto be separated are conveyed on a belt overThree) o that thefalls freely onto the next-convey-

device.Ferrous metals are attracted to themagnetic headlley. These are then carried on the conveyor belt,r the magnetic head pulley, past he free-fall zone of

are then deposited ontointo a bin or hopper.

S i ce non-ferrous materials (paper, textiles, or plas-objects andbelt traversing the head pulley, these can be

T h u s , sometimes ancleaning step is required before the ferrous

can be soldThe conveyor belt should be cleated to assure posi-

scharge of the ferrous product.drum

magnetic drum usually consists of a stationary

Figure FourA Mu l t ip l e T an d em Mag n et i c Dru m Arran g emen t

Lmagnet assembly mounted insideof a rotating outecylinder. The drumcan be arranged for either overor underfeed. As before, cleated drums provide posdischarge of the product.In the ove7feed method, material is fed onto thedrum's top centerline from a relatively uniformly ditributed waste bed. Magnetic material either holds the drum hrough the magnetic arc's length or deflsufficiently from the normal path to be taken onto next processing step. A splitter device assures cleanseparation.

In the underfed armngement.,material is donvinto position near the drum's base. Metals are attracto the face of the drum, conveyed up and over the(or deflected horizontally), and discharged ontoa c

'veyor. Non-magnetics fall onto another conveyor.Generally, the overfeed anangement nets higher

ferrous recovery and more entrapment of non-magnetic material, e& plastics, a p e r s , textiles, etc.wfiile the underfeed method providesa cleaner ferproduct at the xpense of asomewhat lower recovA t y p i c a l concurrent,doubledrum anangement,shown in F'gure Four, generally results in an even

'. cleaner ferrous productSuspended m agne tThesegenerally are supplied with a cleated belt,anmounted either in-line with or perpendicular o thematerial flow. h he latter case, they& referred tocross-belt units.

Figure FiveAn Inline MaanetieS ep ar at or A s n g e m e n t

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Figure SixA Triplex Magnet with Armored Belt

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JSuspended magnets are usually positioned shghtlyabove and ahead of the pulley delivenng the product.Large piecesof material may occasionally cause jamson cross-belt versions; in-line arrangements are not assusceptible to lh s problem.

Attracted metals are lifted from the material flow,carried along the bottom of the cleated belt, and d wcharged onto a second conveyor. Non-magnetic matterfalls onto another conveyor. A common in-line, sus-pended arrangement is illustrated in Fgure Five.

A triplex magnet, a proprietary belt-driven,pended separator, is itlustrated in Figure Six. Tharrangement uses multiple magnets arrangedsometals are agitated both laterally and transversmoving through the magnetic field; the -tationreduces the amount of material trapped with thmetals. Stainless steel platesmay be installed alcenter line of the cleated belt to minimize belt wBest return on investmentMagnetic separation of ferrous metals fromMSWhere today, proven technology. Ithas a long-shistory of generatlng profits, a resultof experienfrom applications in ore beneficiation, slag reclaautomobile shreddmg, and scrap processmg ind

Magnetic separation equipment is generally thcostly of all the equipment needed in a waste pmg facility. The return on investment for magnseparators may well be among the m e s t n thplant.I

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