magnetic separation s
"covly of saieabie iron and stee,
from municipal waste
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This report was prepared by the National Center for Resource
Recovery, Inc., as part of the work done under Contract No. 68-01-2625.
An environmental protection publication (SW-559) in the solid waste
management series. Mention of commercial products does not constitute
endorsement by the U.S. Government.
Single copies of this publication are available from Solid Waste
Information, U.S. Environmental Protection Agency, Cincinnati, Ohio
45268.
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MAGNETIC SEPARATION:
Recovery of Salable Iron and Steel
from Municipal Solid Waste
This report (SW-559) was prepared for the Office of Solid Waste
by Harvey Alter and Kenneth L. Woodruff
U.S. ENVIRONMENTAL PROTECTION AGENCY
1977
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MAGNETIC SEPARATION:
Recovery of Salable Iron and Steel
from Municipal Solid Waste
This pamphlet is an introduction to the technology,
economics and objectives of magnetic separation.
It should serve as a preliminary planning and decision
guide for a municipality considering the addition of
the magnetic separation process to its present solid
waste management system.
Magnetic separation of municipal solid waste (MSW)
is perhaps the simplest of the unit processes for
recovering materials. The process is used routinely
in other industries, such as minerals beneficiation
of iron ores. Also, the scrap industry uses magnetic
separation to produce clean iron and steel metal scrap.
Magnetic separators are used with the more than 100
automobile shredders throughout the country and more
recently have been installed at municipal solid waste
shredding installations (1). Manufacturers of magnetic
separators are listed in Appendix A.
Generally, municipal solid waste must first be shredded
to produce a salable magnetic fraction. In some process-
ing schemes, the shredded waste is air classified. If
magnetic separation follows air classification, a cleaner
and hence higher quality iron and steel can be recovered.
If shredding equipment is already installed, it is
relatively simple and inexpensive to add magnetic
separation.
What Is Magnetic Separation?
Magnetic separation utilizes the magnetic"properties of
iron and steel which allow them to be removed from the
refuse stream with a simple magnet. Proper installation
of a magnetic separator in an MSW shredding or shredding
and air classification plant permits the valuable iron and
steel fraction to be recovered as salable products. The
revenue from these materials will help offset the cost of
solid waste disposal (2,3).
The two major types of magnetic separators used for
recovering iron and steel from MSW are the drum magnet and
the overhead belt magnet. Both types of separators, the
drum and belt, are available either as"permanent type
magnets or as electromagnets.
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In a typical drum magnetic separator, Figure 1, the drum
revolves past the stationary magnet causing non-magnetic
materials to drop off and pulling the magnetic metals
from the waste stream. Another method of feeding material
to a drum separator is to suspend the drum over a conveyor
head pulley or over the end of an oscillating conveyor.
The overhead belt separator, Figure 2, is usually installed
parallel to and suspended over a conveyor carrying shredded
MSW. As shown in Figure 2, a belt moves past a stationary
magnet; the metals recovered by this method are not always
sufficiently clean to meet market specifications. This
experience led to the development of an improved type of
in-line belt separator, Figure 3, which utilizes several
magnets, arranged with alternating polarities. The
magnetic metals are pulled from the MSW and tumbled several
times while changing polarity and following the curve or
bend in configuration. The reverse magnetic fields allow
the separated metals to be tumbled causing contaminants to
drop and resulting in the recovery of cleaner metals (4) .
The magnetic separator in Figure 3 cleans the recovered
metal by using the series of magnets to pick up, drop and
pick up the material again. A similar cleaning can be
achieved using drum separators. As an example, Figure 4
shows a possible arrangement of two drum separators.
The first pulls the magnetic metals from the solid waste
while the second drum picks up the metals a second time,
allowing contaminants to drop off (5,6).
Magnetic separation devices of the capacity of 10 to 100
tons per hour of shredded MSW can be designed. The particle
size of the shredded MSW is not critical. Generally,
shredding must precede magnetic separation if clean and
salable metal is to be obtained. If air classification -
to separate the "light" paper and plastics from the
"heavy" metals, stones and wood - is used in the total
recovery system, the recovered metal is likely to be
cleaner and of higher value. (This is so only when the air
classification precedes the magnetic separation.)
Why Install a Magnetic Separator?
If a municipality has a shredder or is planning the
installation of one, a magnetic separation system properly
installed and operated can produce a salable product from
the solid waste stream and offset a portion of the disposal
cost (7). Such a system must include support structures,
conveyors and associated materials handling equipment (8).
-4-
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FIGURE 1
MIXED MATERIAL
REVOLVING
DRUM
MAGNETIC
MATERIAL
DISCHARGE
WORKING FACE
STATIONARY
MAGNET ASSEMBLY
NONMAGNETIC
MATERIAL
Magnetic Drum Separator
-5-
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FIGURE 2
MAGNET
MIXED MATERIAL
BELT ASSEMBLY
MAGNETIC MATERIAL
DISCHARGE
NONMAGNETIC
MATERIAL
Overhead Belt Separator
FIGURE 3
MAGNETS
Dings Co. Belt Magnet Designed for Solid Waste Systems
— 6—
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Figure 4
DUAL DRUM MAGNETIC SEPARATOR
RECOVERED
METAL
CONVEYOR
-7-
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The net revenue received from magnetic metals recovery
will vary depending on local circumstances. Market value
of the recovered ferrous metals and transportation costs
are factors which can change significantly in each case.
In addition, the percentage of ferrous metals in the in-
coming waste and the recovery efficiency of the equipment
are important considerations.
Analysis of country-wide MSW samples indicated that the
average household portion of municipal solid waste contains
between 7 and 8 percent iron and steel, not including
discarded appliances and other obsolete household goods.
A recovery efficiency of almost 90 percent for magnetic
metals is hot uncommon, which means that of the waste 6 to
7 percent is recovered as ferrous metals.
The price paid for recovered magnetic metals depends on the
quality of the product, the specific buyer and the national
trends in scrap markets. Experience over xthe past few
years suggests a price range of $20 to $5Q per (long) ton.
Recent transactions indicate that magnetic metal scrap
recovered to proper specifications will bring prices in
the upper end of this range. Also, it may be possible to
obtain long term contracts for the purchase of the scrap
which reduces the vulnerability to scrap market fluctua-
tions.
Under these conditions, the gross revenues from magnetic
metals would amount to $1.07 to $3.12 per input ton of
waste. Prom this revenue, operating and transportation
costs must be subtracted. Operating costs are discussed
later in this report.
A magnetic separation system requires little operator
attention but must receive the same routine maintenance as
other industrial equipment. A separation system can be
tailored to meet the needs of the user, to match a present
or planned shredding system and to produce metal according
to the specifications. Market commitments should be
obtained before investing in detailed planning and hardware,
Specifications for recovered products are important deter-
minants of facility design.
What Is a Shredding and Magnetic Separation System?
A typical system for processing MSW includes a concrete
pad, or floor for packer trucks to dump their loads, a pit
conveyor which is filled with MSW by a front-end loader,
and an inclined conveyor to transport the MSW from the pit
conveyor to the shredder. At the discharge end of the
shredder, the pulverized MSW is usually dropped onto a
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vibrating conveyor and then onto a rubber belt conveyor
for transport to further processing. The magnetic
separator is usually installed at. the head pulley of this
belt. The non-magnetic material proceeds to further
processing, a transfer compactor, or to disposal.
A solid waste processing system, Figure 5, includes
shredding and air classification followed by magnetic
separation. The air classifier is shown for illustration
and is not absolutely needed for magnetic separation.
The heavy fraction from the air classifier which contains
metals, glass, stones, and similar heavy items, is
magnetically separated. The non-magnetic portion can be
further processed for resource recovery or disposed of in
a sanitary landfill.
The material conveyed past a magnet for separation must
be evenly fed and distributed and this is accomplished by
the installation of belt type magnetic separators above
a conveyor head pulley.
To meet customers' specifications, magnetic metals may be
reshredded, baled or just conveyed to a hopper prior to
shipment in a truck or by open rail car (9). A municipality
may purchase a magnetic separation system as part of a
"turn-key" MSW processing system'or have the system designed
by a consulting engineer, but it must be designed to meet
the particular needs of the magnetic metals market(s).
What Type of System to Install?
After determining the market specifications for the magnetic
metals (which may be for loose, baled, densified or other
form) , more detailed considerations for selecting a unit
or for preparing a request for bids should be examined.
While a full discussion of these considerations is beyond
the scope of this pamphlet, the major points to analyze are
listed below:
Magnetic Metals Markets
de-tinning
copper precipitation
steelmaking
foundry
local scrap processor
Capacity
amount to be processed, per day
and per shift
-9-
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Artist's Rendering of a Plant to Shred and Air Classify
Municipal Solid Waste and Recover Magnetic Metals.
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Location in System
after shredding
after air classification
Type of Magnetic Separator
belt or drum
permanent or electro
Redundancy
single or multiple units
contingency plan if unit is down
Maintenance
ease and schedule
Manufacturer's Warranties
term and coverage
Systems Responsibility
interfacing of shredder, buildings,
materials handling and other system
components
Manufacturers claim that the multiple drum installation
and the multi-pole belt magnet give similar performance,
but the initial cost of the drum installation may be
50 percent more than the belt separator (6). There is
also a difference in the maintenance costs of the two
separators. Belt life is guaranteed for one year by one
manufacturer while drum shell life is guaranteed for three
years by another supplier. In the long run, belt separators
may cost more to operate than drum separators.
A primary concern of any magnetic separation system
operation is the removal of organic contamination from the
magnetic metal product. This may present some difficulty
depending on the degree of shredding and treatment prior
to magnetic separation. Previous experience has shown that
blowing air perpendicular to the flow of metals can remove
much of the organic material (8).
What Does Magnetic Separation Cost?
The cost of a magnetic separator with all motors, electrical
controls and conveyors is approximately $100,000 for a
50 ton per hour (TPH) system. This includes supports and
a hopper to receive and store the magnetic metals.
The actual installed cost of a complete system is difficult
to estimate without knowledge of the specifications for the
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recovered metal and site-specific requirements. In the
fourth quarter of 1974, a conservative cost estimate,
excluding the dost of land and the air classifier, was
made of the system illustrated in Figure 5. The system,
designed to process 50 TPH of MSW, with covered storage
capacity for 500 tons of MSW, was estimated to cost
$2,412,000 using a price of $105,000 for all components
of the magnetic separation system. Table 1 details the
estimated cost.
Table 2 estimates the operating cost of the facility.
The installation was designed for 50 TPH, operating
12 hours of a two-^-shift, 16-hour work day. It was assumed
that the shredder output particle size would be four
inches, or less. If a different particle size must be
produced, maintenance and operation costs..would change.
On the basis of design criteria, the total number of
employees was placed as 22, which did not include opera-
tors for any associated landfill. Fringe benefits were
calculated at 25 percent of direct salary. Supplies
included housekeeping and office supplies, lubricants and
gasoline. Services and maintenance included major repairs
performed by outside contractors, welding rod for the
shredder hammers, replacement parts, and associated
equipment. Power cost was based on the total installed
horsepower, anticipated use factor and a cost of three
cents per kilowatt-hour. The costs of actual operation
amounted to $3.51 per ton of MSW fed to the plant on a
yearly basis.
Debt service (amortization and interest) was computed as
total debt financing (e.g., municipal bond financing).
The life of the equipment was assumed to be 10 years.
Although the buildings might have a longer life, for
simplification no breakout of this Was made, and the entire
facility was amortized over the 10 year period. The
interest is included in the calculation. The cost' of land
and its associated debt service are not included in the
capital cost estimate in Table 1. Table 2 indicates the
total anticipated plant operating costs to be $5.52 per
input ton. This figure may be compared to a cost of $4.91
per input ton for only shredding in a facility identically
designed but without magnetic separation.
Appendix B is a calculation of a reasonable revenue from
metal recovery of $2.21 per input ton. Deducting this
figure from anticipated operating costs of $5.52 per input
ton results in a net cost of $3.31 for processing each
input ton.
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TABLE 1
Sample Capital Cost Estimate of a
Shredding and Magnetic
Separation System
C4th quarter 1974 \
50 TPtt Design Capacity System
System Direct Costs
Truck. Scale $ ,.
Front End Loader (2) 120,000-
Feed Conveyor System 2(XO,(304
Shredder 350 f 000
Discharge Conveyor System 80,000
Magnetic Separation System 60,000
Magnetic Metals Discharge
Conveyor and Hopper 45,0ft&
Dual Push Pit 75,0-00
Transfer Packers (2\ 30,000
Transfer Tractors & Trailers (3\ 150, 00&
Magnetic Metals Trucks (2\ _ 50,000
Total Equipment Costs $1,225,000
Building Installation
Land $ *
Site Preparation 110,000
Receiving Building 150,000
Shredding Building 50,000
Water & Sewage Systems 25,000
Electrical Distribution System 130,000
Shop Tools & Equipment 10,000
Office Furniture & Fixtures 10
Total Building installation 485,000
Total Direct Costs $1,710,000
*Not included
Source: Reference 10
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TABLE 1—Continued
System-Indirect Costs
Contractor's Overhead $ 338,000
Contractor's Profit (5%) 85,000
Engineering (6.5%) 110,000
Contingency 169,000
Total Indirect Costs $ 702,000
Total Direct Costs $1,710,000
Total Indirect Costs $ 702,000
Grand Total $2,412,000
Table 2
Anticipated Annual Operating Costs
(4th quarter 1974)
Labor (Including Fringe Benefits) $294,000
Supplies 40,000
Services and Maintenance 120,000
Power 178,000
$632,000
Amortization or Depreciation
(10 Yr. Str. Line) 241,000
Interest (10%, 5th Year) 120,000
Total Operating Costs $993,000
Which is equivalent to $5.52 per input ton based on
processing 180,000 tons of MSW per year.
Source: Reference 10
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How Does the Cost of Shredding and Magnetic Separation
Compare With Current Costs?
Capital and operating costs of adding shredding and magnetic
separation, or magnetic separation only, to a solid waste
management system may be determined and compared to current
or projected costs if all costs are calculated on the same
basis. The.installed cost of the new system should be
estimated using the entries in Table 1. Then, the costs
of an existing soljLd waste disposal system and the projected
costs of shredding and magnetic separation must be
calculated and compared item by item. The anticipated
annual operating costs estimate in Table 2 may be used as
a guide. Appendix C is a worksheet for making this item by
item calculation. In all likelihood, present or projected
costs have not been calculated or estimated for all of the
entries in Appendix C. If this has not been done, current
costs cannot be used as a planning guide and must be
recalculated using tne worksheets provided. The worksheets
allow direct comparison of shredding and magnetic separation
to current (or projected) costs on a per ton basis.
Credits to the new system include savings from possibly
using less landfill space, cover dirt, landfill equipment
and revenue from the sale of the recovered magnetic metals.
What Is the Next Step?
The municipal manager is urged to use the discussion
presented here and the sample calculations made on. the
worksheets in Appendix C to determine if shredding and.
magnetic separation should be considered further. Potential
purchasers of the magnetic metals in the local area
should be contacted. These may include steel companies,
foundries, de-tinnersr and scrap processors. If discussions
and projections for sale and use of the recoverable magnetic
metals are encouraging, the next step is to contact shredder
and magnetic separation suppliers or a reputable consulting
firm with solid waste processing experience for detailed
planning of the recovery and disposal system.
The municipal manager is also urged to obtain market
commitments for the recovered metal in advance of investing
in detailed planning or hardware. Part of the commitment
will be a specification for the recovered metal (.9). This
specification will help determine the design of the recovery
facility. If these steps are not followed, it is possible
that the shape, form and cleanliness of the recovered
metal will not be suitable for any application within a
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reasonable shipping distance. In addition, a municipality
should attempt to obtain from potential purchasers a floor
or base price for the scrap, when possible. This is
discussed in more detail in a separate publication (11).
Information concerning specifications for the recovered
magnetic metals may be obtained from the American Society
for Testing and Materials. Free professional advice on
obtaining specifications and purchase commitments in
advance is available to municipal planners from the
Institute of Scrap Iron and Steel and from the American Iron
and Steel Institute. The addresses of these organizations
are listed in Appendix D.
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APPENDIX A
Magnetic Separator Manufacturers
Dings Company
4740 Electric Avenue
Milwaukee, Wisconsin 53246
Eriez Magnetics
Asbury Road at Airport
Erie, Pennsylvania 16512
Stearns Magnetics, Inc.
6001 South General Avenue
Cudahy, Wisconsin 53110
Indiana General
407 Elm
Valparaiso, Indiana 46383
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APPENDIX B
Revenue Potential
Magnetic Metals
Assume 180,000 TPY Refuse Processed
7% Magnetic Metals
90% Recovery of Magnetic Metals
6.3% x 180,000 TPY = 11,340 TPY Magnetic Metals
Assume Selling Price of $35.00 per short ton, net
of shipping costs
11,340 TPY x $35.00 » $.396,900 per year.
Revenue = $2.21 per input ton
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APPENDIX C
Operating Cost Comparison
Annual Cost
Current (or Projected) Solid
Waste Management System
Tonnage Handled
Tons Per Day
Days Per Week
Tons Per Year
Annual Cost
Shredding & Magnetic Separation
Waste Management System
Tonnage Handled
Tons Per Day
Tons Per Week
Tons Per Year
Direct Operating Costs
Personnel
Title, Salary, Benefits, Total
Direct Operating Costs
Personnel
Title,Salary,Benefits, Total
Total $
Total $
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APPENDIX C
Operating Cost Comparison
(continued)
Annual Cost Annual Cost
Current (or Projected) Solid Shredding & Magnetic Separation
Waste Management System Waste Management System
Materials & Supplies
Unit
Item, Quantity, Price, Cost
Materials & Supplies
Unit
Item, Quantity, Price, Cost
Total $
Total $
Power, Utilities & Services* Power, Utilities, & Services
Unit
Item, Quantity, Price, Cost
Unit
Item, Quantity, Price, Cost
Total $
Total $
*Outside services and maintenance can be calculated as 5%
of capital investment.
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APPENDIX C
Operating Cost Comparison
(Continued)
Annual Cost
Current (or Projected) Solid
Waste Management System
Current System
Indirect Operating Costs
Depreciation or Amortization
S
Building & Structures
Annual Cost
Shredding & Magnetic Separation
Waste Management System
Shredding & Magnetic Separation
System
Indirect Operating Costs
Depreciation or Amortization
Building & Structures
Equipment
Equipment
Land Purchased for Facility Land Purchased for Facility
.Annualized Cost Annualized Cost
Interest 0:1 Capital
Total $
Interest on Capital
Total $
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APPENDIX C
Operating Cost Comparison
(continued)
Annual Cost
Current (or Projected) Solid
Waste Management System
Annual Cost
Shredding & Magnetic Separation
Waste MAnagement System
Current System
Annual Cost
Shredding & Magnetic Separation
System
Annual Cost
Personnel
Materials &
Supplies
Power & Services
Administration
Insurance
Depreciation or
Amortization
Interest
Total
Annual Cost
Tons Per Year
Personnel
Materials &
Supplies
Power & Services
Administration
Insurance
Depreciation or
Amortization
Interest
Total
Annual Cost
Tons Per Year
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APPENDIX C
Operating Cost Comparison
(continued)
Annual Cost
Current (or Projected) Solid
Waste Management System
Annual Cost
Shredding & Magnetic Separation
Waste Management System
Current System
Shredding & Magnetic Separation
Annual Cost
Annual Cost
Cost Per Ton =
Cost Per Ton =
Annual Cost
Tons Per Year
Annual Cost
Tons Per Year
per ton
per ton
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APPENDIX D
For free advice on specifications and markets for
recovered iron and steel, contact:
American Society for Testing and Materials
(specifications only)
Attn: Committee E-38.02
1916 Race Street
Philadelphia, Pennsylvania 19103
Institute of Scrap Iron and Steel
1729 H Street, N.W.
Washington, B.C. 20006
American Iron and Steel Institute
1000 16th Street, N.W.
Washington, D.C. 20006
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REFERENCES
(1) Committee of Tin Mill Products Producers. Solid Waste
Processing Facilities. (American Iron and Steel
Institute, Washington, D.C.) 1973 and revisions.
(2) Steel Can Recovery - What's the Attraction. Resource
Recovery. April, May, June 1974: 10-11.
(3) Magnetic Separation...A Basic Process. National Center
for Resource Recovery, Inc. Bulletin. Vol. 4,
No. 4 (Fall) 1974.
(4) U.S. Patent No. 3,809,239. May 7, 1974.
(5) Twichell, E.S. Eriez New Model SF Super Scrap Drum.
Secondary Raw Materials. August 1972: 118-119.
(6) Twichell, E.S. Magnetic Separation Equipment for
Municipal Refuse. (Presented at 104th Annual
American Institute of Mechanical Engineers Meeting.
New York City. February 17-20, 1975).
(7) Drobny, N.L., H.E. Hull and R.F. Testin. Recovery and
Utilization of Municipal Solid Waste. U.S.
Environmental Protection Agency. Report SW-10.
1971.
(8) Materials Recovery System - Engineering Feasibility
Study. National Center for Resource Recovery, Inc.
Washington, D.C. December 1972. 365 pp. Supplement
1974, 100 pp.
(9) Alter, H. and W.R. Reeves. Specifications for Materials
Recovered from Municipal Refuse. U.S. Environmental
Protection Agency- Report EPA-670/2-75-034. 1975.
(10) NCRR estimates based on engineering design and telephone
quotes from vendors. Installation and operation
costs are based on vendor quotes, standard reference
sources and NCRR estimates. See reference 8.
(11) Garbe, Y. and S. Levy. Resource Recovery Plant Implemen-
tation:' Guides for Municipal Officials - Markets.
Environmental Protection Publication SW-157.3
(Washington, D.C.), U.S. Environmental Protection
Agency, 1976.
H01246
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