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Pollution Prevention in the
A Manual for Pollution Prevention TechnicalAssistanceProviders;
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Pol I ution Preve ntipn
In the Primary Metals
Industry
A Manual for
Pollution Prevention
Tech nical Assistance Providers
April 1998
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Printed on Recycled Paper
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Table of Contents
Acknowledgments .............................. iii
Industry Overview ....,........?....*...*. 1
The Steel Making Industry ..» ...", 3
Background 3 ;
Steel Production from Iron Ore......... .:............ 3
References .. ................8
Annotated.Bibliography .. .........9
Case Study., ........9
Ferrous and Non-Ferrous Foundries............... 11
Foundry Processes .-. * ...;....................... 11
Pollution Prevention Methods for Foundries.......... .;. ,...16
References 19
Annotated Bibliography ...........; 19
Case Studies - " >-20
Aluminum Smelting and Refining.................... 23
Primary Aluminum Refining ..................23
Secondary Aluminum Production ...->.. ................24
Annotated Bibliography 25
Case Study . ... ...................25
Copper Processing ,....,.^....................*.... 27
Primary Production of Copper ....; .27
Secondary Copper Processing................ ......28
Annotated Bibliography ....;........................ 28
Lead Processing ......................................... 29
Pfiniary Lead Processing « - 29
Secondary Lead Processing 30
Annotated Bibliography.... ,.30
Zinc Processing.......*.........................'-->
Primary Zjnc Processing 31
Secondary Zinc Processing 31
Annotated Bibliography 32
Glossary......
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List of Tables
Table 1. Common Type of Metal Melting Furnaces./.... :.......... 13
List of Figures
Figure 1. The Steel Making Process... ^
Figure 2. The DIOS Process °
Figure 3. Metal Casting Process , -.
Figure 4. Green Sand Composition :---- '
Figure 5. Dry Sand Reclamation .. '
Figure 6. Wet Sand Reclamation ,- '
Figure 7. Thermal Sand Reclamation .- ;
ii
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Acknowledgments
We would like to than U.S. EPA Office of Pollution Prevention and Toxics and the Northeast Waste
Management Officials Association (NEWMOA) for funding to produce this information packet. Illinois
Waste Management and Research Center (WMRC) staff, past and present, who contributed to this
project include: Laura Barnes, Jerry Brown, Ester Burke, Laurie Case, Chris Harris, Tim Lindsey, Lisa
Merrifield, Gary Miller, Jackie Peden, and Li-Chen Shen. We thank them for thier contributions.
We also would like to recognize the reviewers who provided, valuable suggestions oh improving this
document. They are: Jerry Brown (WMRC), Laurie Case (WMRC), Randy Cook (Minnesota Techni-
cal Assistance Program), George Crandell, (Chrysler Indianapolis Foundry), LeRoy Euvrard (Safety and
Environmental Staff), Dieter Leidel (Tanoak, Inc.), Tim Lindsey (WMRC), Jackie Peden (WMRC),
Lisa Regenstein (NEWMOA). '
Hi
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iv
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Industry Overview
The primary metals industries include facilities
that produce metal products from metal ore
and / or scrap metal. Plants may refine metals,
cast molten metal into desired shapes, or produce
the inputs for the refining or casting process.
Primary metals industries utilize both ferrous and
.non-ferrous metals and produce pure metal
products or alloys in the form of end products or
stock for use by other industries. .
The primary metals industries included in this
manual are covered by SIC 3300: Primary Metals,
They include steel works, blast furnaces; and coke
making; ferrous and non-ferrous foundry opera-
tions; and smelting and refining of common non-
ferrous metals. Facilities may function as
independent plants which sell metal products to
other industries, or as part of a larger plant which
produces metal pieces for use within a facility or
company. Some facilities housed within larger
operations may be classified under the SIC code
of the larger operation. ,-
Pollution associated with primary metals industries
depends largely on the type of operation. The
type of facility, metal and non-metal inputs, <
processes, and equipment all factor into the
pollution sources and prevention opportunities.
As such, the primary metals industries in this
document have been divided into Steel Making
(Chapter 2), Ferrous and Non-Ferrous Foundry
Operations (Chapter 3) and Non-Ferrous Metal
. Refining, including aluminum (Chapter 4), copper
(Chapter 5), lead (Chapter 6) and zinc (Chatper
7). The processes, waste streams and pollution
prevention operations are discussed independently
for each sector. Overlapping processes and
pollution prevention opportunities are noted.
After being refined and cast, metal pieces are
usually coated to prevent corrosion or enhance
surface properties. Metal coating, electroplating,
or surface-finishing is occasionally performed at
foundries or other primary metal production
plants. However, more often, it is performed at
captive or job shops outside of primary metals.
facilities. Information about metal coating and
surface finishing can be obtained in Pollution
Prevention and the Coating Industry or Pollution
Prevention and the Metal Finishing Industry
manuals. " - ,
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The Steel Making Industry
ar
Background
Steel is an alloy of iron usually containing less
than 1% carbon. It is used most frequently in the
automotive and construction industries. Steel can
be cast into bars, strips, sheets, nails, spikes, wire,
rods-or pipes as needed by the intended user. .
Based on statistics from The 1992 Census of
Manufacturing, 1,118 steel manufacturing facili-
ties currently exist in the United States. Steel
production is a $9.3 billion dollar industry and
employs 241,000 people.
The process of steelmaking has undergone many
changes in the 20th century based on the political,
social and technological atmosphere. In the 1950s
and 1960s, demand for high quality, steel encour-
aged the steelmaking industry to produce large
quantities. Large, integrated steel mills with high
capital costs and limited flexibility were built in the
U.S.(Chatterjee, 1995), Integrated steel plants
produce steel by refining iron ore in several steps
and produce very high quality steel with well
controlled chemical compositions to meet all
product quality requirements.
The energy crisis of the 1970s made thermal
efficiency in steel mills a priority. The furnaces
used in integrated plants were very efficient;
.hpwever, the common production practices
needed to be improved. The large integrated
plants of the 1950s and 1960s tended to produce
steel in batches where iron ore was taken from
start to finish. This causes some equipment to be
idle while other equipment was in use. Tq help
'reduce energy use, continuous casting methods
were developed. By keeping blast funfaces
continually feed with iron ore, heat is used more
efficiently.
As environmental concerns have gained impor-
tance in the 1980s and 1990s, regulations have
become more stringent, agaih changing the
steelmaking industry. In 1995, compliance with
environmental requirements was estimated to
make up 20-30% of the capital costs in new steel .
plants (Chatterjee, 1995'). Competition has also
increased during the period do to decreasing
markets and increasing foreign steel production
plants. The competition has forced steelmaking
facilities to reduce expenses and increase quality.
To meet these changing needs, just-in-time
technology has become more prominent and'
integrated steel plants are being replaced with
smaller plants, called mini-mills, that rely on steel
scrap as a base material rather than ore. Mini-
mills will never completely replace integrated steel
plants because they cannot maintain the tight
control over chemical composition, and thus
cannot consistenly produce high quality steel. :
Mini-mills have a narrower production line and
cannot produce the specialty products produced
by integrated plants. Although technology contin-
ues to improve, in the mid 1990s, mini-mills
captured less than half of the quality steel market.
Steel Production
from Iron Ore
Steelproduction at an integrated steel plant-
involves three basic steps. First, the heat source
used to melt iron ore is produced. Next the iron
ore is melted in a furnace. Finally, the molten iron.
is processed to produce steel. These three steps
can be done at one facility; however, the fuel
source is often purchased from off-site producers.
Cokemaking
Coke is a solid carbon fuel and carbon source
used to melt and reduce iron ore. Coke produc-
tion begins with pulverized, bituminous coal. The
coal is fed into a coke oven which is sealed and
heated to very high temperatures for 14 to 36
hours. Coke is produced in batch processes, with
multiple coke ovens operating simultaneously.
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ChJocer 2. The Sceel Making industry
[4eat is frequently transferee! from one oven to
another to reduce energy requirements'. After the
coke is finished, it is moved to a quenching tower .
where it is cooled with water spray. Once
cooled, tfie coke is moved directly to an iron
melting furnace or into storage for future use.
Ironmaking
During ironmaking, iron ore, coke, heated air and
limestone or other fluxes are fed into a blast
furnace. The heated air causes the coke combus-
tion, which provides the heat and carbon sources
for iron production. Limestone or other fluxes
may be added to react with and remove the acidic
impurities, called slag, from the molten iron. The
limestone-impurities mixtures float to the top of
the molten iron and are skimmed off, see Figure
1", after melting is complete.
Sintering products may also be added to the
furnace. Sintering is a process in which solid
wastes are combined into a porous mass that can
then be added,to the blast furnace. These wastes
include iron ore fines, pollution control dust, coke
breeze, water treatment plant sludge, and flux.
Sintering plants help reduce solid waste by
combusting waste products and capturing trace
iron present in the mixture. Sintering plants are
" not used at all steel production facilities.
Steelmaking with the Basic Oxide
Furnace (EOF)
Molten iron from the blast furnace is sent to a
basic oxide furnace, which is used for the final
refinement of the iron into steel (Figure 1)'. High
purity oxygen is blown into the furnace and
combusts carbon and silicon in the molten iron.
The basic oxide furnace is fed with fluxes to
remove any final impurities. Alloy materials may
be added to enhance the characteristics of the
steel. .
The resulting steel is most.often cast into slabs,
beams or billets (USEPA, 1995). Further shaping
of the metal may be done at steel foundries, which
remeltthe steel and pour it into molds, or at rolling
. facilities, depending on the desired final shape.
EOF Pollution Sources and Prevention
Opportunities
Different types of pollution result from the
different steps in steel production. Below, the
pollution sources and the possible pollution
prevention opportunities are discussed for each
process. -
Pollution Sources and Prevention for
Cokemaking
Coke production is one of the major pollution
sources from steel production. Air emissions such
as coke oven gas, naphthalene, ammonium
compounds, crude light oil, sulfur and coke dust
are released from coke ovens. Emissions control
equipment can be used to capture some of the
gases. Some of the heat can be captured for reuse
in other heating processes. Other gases may .
escape into the atmosphere. -
AIR
SCRAP
IRON PIUX
> OE5ULFURI2AT1ON
_
1NOOT CASTING CONTINUOUS CASTING
PROCESS WATER
SCALE
.
SLAG EMISSION CONTROL
OUST/SLUDGE (KO81)
FORMING . .
_» =3-i > STEEL
*3> INTERMEDIATES
Figure 1: The Steel- Making Process (EPA, 1 995)
-*TO FINISHING .
PROCESSES
» FINISHED
STEEL
PRODUCTS
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Chapter 2: The Sceel Making Industry
Water pollution comes from the water used to '
cool coke after it has finished baking. Quenching
water becomes contaminated with coke breezes
and other compounds. While the volume of
contaminated water can be great, quenching water
is fairly easy to reuse. Coke breezes and other
solids can usually be removed by filtration. The
resulting water can be reused in other manufactur-
ing processes or released.
Reducing Coke Oven Emissions
Pollution associated with coke production is best
reduced by decreasing the amount of coke used in
the iron melting process. The smaller the volume
of coke produced, the smaller the volume of air
and water emissions. However, process modifica-
tions in actual coke production are not widely
available and are very expensive.
One fairly economical method of reducing coke
oven pollution is to reduce the levels of coke used
in blast furnaces. A portion of the coke can be
replaced with other fossil fuels without retrofitting
'the furnace. Pulverized coal can be substituted
for coke at nearly a 1:1 and can replace 25 - 40%
of coke traditionally used in furnaces (USEPA,
1995). Pulverized coal injection is used world-
wide to reduce coke use and, thus, coke emissions
(Chatterjee, 1995). '
Pulverized coal injection may affect the final steel
products. Pulverized coal may reduce gas perme-
ability of the metal and unburnt coal particles may
accumulate, in the furnace, decreasing efficiency.
Thus, it may not be possible to substitute pulver-
ized coal for coke in the production of high quality
steel!
Other alternative fuels such as natural gas, oil or
tar/pitch can be used to replace coke using similar
process modifications. The reduction in emissions
is proportional to the reduction in coke use.
Air and water emissions may also be reduced by
using a non-recovery coke battery. In traditional
plants, by-products are recovered from the blast
furnace. In non-recovery batteries, coke oven
slag and other by-products are sent to the battery
-where they are combusted. This technique
consumes the by-products, eliminating much of
. the air and water pollution. Non-recovery coke
batteries do require replacement or retrofitting of
traditional coke ovens. This process modification
does reduce pollution, but can be expensive.
A third method for reducing coke oven emissions
is the Davy Still Autoprocess. The process, uses
water to remove ammonia and hydrogen sulfide
from coke oven emissions prior to cleaning ofthe
oven. .''-,, ."'.,:
Cokeless Ironmaking
Cokeless ironmaking procedures are currently
being studied and, in some places, implemented..
One such procedure is the Japanese Direct Iron
bre Smelting (DIOS) process (Figured): The
DIOS process produces molten iron from coal and
previously melted ores. In this process, coal and
other ores can produce enough heat to melt ore,
replacing coke completely (USEPA, 1995).
In addition to reducing coke use, the DIOS . _
process could cut the costs of molten iron produc-
tion by about 10%, reduce emissions of carbon
dioxide by 5 - 10% and increase flexibility by
improving the starting and stopping capabilities of
the steel mill (Furukawa, 1994). However, the
DIOS process remain very expensive and requires
extensive process modification. In 1995, this
method was still being tested and economic
feasibility will be determined from those tests.
The HISmeIt process, named after the fflSmelt
Corporation of Australia, is another cokeless iron
melting process being tested. In this process, ore
fines and coal are manipulated to melt iron ore. In
1993, the process could produce eight tons of iron
ore per hour using .ore directly in the smelter.
Process modifications are expected to increase the
efficiency to 14 tons per hour. Commercial
feasibility studies were performed in 1995. ,.
Midrex is expected to be the U.S. distributor of
the process, ,
A finalcokeless iron melting process is the Corex
or Cipcor Process. This process also manipulates
coke to produce the heat required to melt iron. A
. Cprex plant is operational in South Africa. Posco
of Korea has a Corex plant operating at 70%
capacity in 1996 and is expected to continue,
progress (Ritt, 1996). India is also expected to
build aplant in 1997. The process integrates coal
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Ouonr 2: The Scee! Making Industry
Gas (carbon)
Ventun
Pressure-control
valve
Taphole opener
anctmudgun
Coal dryer
Smelting reduction
A. furnace
Molten-iron car
Nj compressor
Figure 2. The DIOS Process (Furukawa, 1994)
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Chapter 2: T,he Steel HaKJng Industry*
desulfurization, has flexible coal-type require-
ments, and generates excess electricity that can be"
sold topowergrids .(USEPA, 1995). Further
testing is being conducted to determine actual \
commercial feasibility in the U.S..
Iron Carbide Steel Production
Plants
Iron carbide production plants can be an alterna-
tive to the Basic Oxide Furnace. These plants use
: iron carbide, an iron ore that contains 6% carbon
rather than 1.5-1.8% of regular iron ore -. The
additional carbon igriite.s in the presence of oxygen
and contributes heat to the iron melting process,
'reducing energy requirements (Ritt, 1996). While
these types of plants do not reduce pollution on
site, they do reduce the electricity requirement for
steel production, reducing polution from the
power plant. .
Pollution Sources and Prevention
in Irohmaking
Slag, the limestone and iron ore impurities col-,
lected at the top of the molten iron, make up the
' largest portion of ironmaking by-products. Sulfur
dioxide and hydrogen sulfide are volatized and
captured in air emissions .control equipment and
the residual slag is sold to the construction indus-
try. While this is not a pollution prevention
technique, the solid waste does not reach landfills.
B last furnace flue gas is also .generated during
.ironmaking. This gas is cleaned to remove
particulates and other compounds, allowing it to
be reused as heat for coke furnaces or other
processes. Cleaning gas for reuse can produce
some air pollution control dust and water treat-
ment plant sludge, depending on the method used.
The dust can be reused in sintering processes or
landfilled. :
Pollution Sources and Prevention in the
BOF !
.' Slag is-amajor component of the waste produced
inBOFs. Because of its composition, this slag,
unlike that from the blast furnace, is best used as
an additive in the sintering process. As its metallic
content is lower, it does not make a good raw
material for the construction industry.
Hot gases are also produced by the BOF. Fur-
naces are, equipped with air pollution control
equipment that contains and cools the gas. The
gas is quenched and cooled using water and
cleaned of suspended solids and metals. This
process produces air pollution control dust and
water treatment plant sludge. .
Steel Production from Scrap
Metals : ;
Steelmaking from scrap metals involves melting -
scrap metal, removing impurities and casting it
into the desired shapes. Electric arc furnaces
(EAF) are often used (Figure 1). The EAFs melt
scrap metal in the presence of electric energy arid
oxygen. The process does,not require the three
step refinement as needed to produce steel from
ore. Production of steel from scrap can also be
economical on a much smaller scale. Frequently
mills producing steel with EAF technology are
called mini-mills.
Pollution Sources and Material Recovery
Gaseous emissions and metal dust are the most
prominent sources of waste from electric arc
furnaces. Gaseous emissions are collected and
cleaned, producing EAF dust or sludge. The
remaining gas contains small quantities of nitrogen
oxide and ozone and is usually released. The EAF
dust or sludge composition varies depending on
the type of steel being manufactured. Common
components include iron and iron oxides, flux,
zinc, chromium, nickel oxide and other metals
used for alloys. If the dust or sludge contains lead
or cadmium, it is listed as a hazardous waste
(RCRAK061) (USEPA, 1995).
In 1996, 500kg of EAF dust .were produced for
each tonne1 of crude steel production. In the '
United Kingdom, 70% of that dust is sold to other
companies, 20% is recycled in-plant and 10% is
landfilled. Although it is a relatively small propor-
tion of the total volume of waste, the landfilled
EAF dust amounts to 50 kg per tonne of crude
steel produced (Strohmeier, 1996).
Recycling and recovery of EAF dust can be
difficult because of the'alkalinity and heavy metal
(zinc and lead) content. The dust can be
landfilled, but, because of the fine nature, it may
-------
Chapter 2: The Steei Making Industry
leach into ground water. Several processes have
been developed to recover the zinc, lead and other
heavy metals from EAF dust. Although not
pollution prevention, metal recovery is almost
always profitable if the zinc content of the dust is
15 - 20% of the total volume. It can be margin-
ally profitable with lower levels of zinc. Other .
m.etals such as chromium and nickel can also be
reclaimed and sold.
After the heavy metals have been removed, the
dust is composed primarily of iron and iron oxides
and may be remelted. If the metal content is
Sufficient, the dust can be reused in the blast
furnaces. If it is not sufficient, the dust can be
sold to other industries for use as raw materials in
bricks, cement, sandblasting or fertilizers.
Energy Optimizing Furnaces (EOF)
EOF was developed to replace the electric arc and
other steelmaking furnaces. The EOF is an
oxygen steelmaking process. Carbon and oxygen
react to preheat scrap metal, hot metal and/or pig .
iron. These furnaces reduce capital and conver-
sion costs, energy consumption and environmental
pollution, while increasing input flexibility
(Chattergee, 1995).
Steel Forming and Finishing
After the molten metal i"s released from either the
BOF, EAF or EOV, it must be formed into its final
shape and finished to prevent corrosion. Tradi-
tionally, steel was poured into convenient shapes
called ingots and stored until further shaping was
needed. Current practices favor continuous
casting methods, where the steel is poured directly
into semi-finished shapes. Continuous casting
saves time by reducing the steps required to
produce the desired shape.
After the steel has cooled in its mold, as further
detailed in Chapter 3, continued shaping is done
with hot or cold forming. Hot forming is used to
make slabs, strips, bars or plates from the, steel.
Heated steel is passed between two. rollers until it
reaches the desired thickness.
. Cold forming is used to produce wires, tubes,
sheets and strips. In.this process the steel is
passed between two rollers', without being heated,
. to reduce the thickness. The steel is then heated
in an annealing furnace to improve the ductile
properties. Cold rolling is more time consuming,
but is used because the products have better
mechanical properties, better machinability, and
can more easily be manipulated into special sizes
and thinner gauges.
After rolling is completed, the steel pieces are
finished to prevent corrosion and improve proper-
ties of the metal. The finishing process is detailed"
in the Pollution Prevention and the Metal Finish-
ing Industry manual.
Pollution Sources and Prevention
from Steel Forming
The primary wastes produced in the metal form-
ing process include contact water, oil, grease, and
mill scale. All are collected in holding tanks. The
scale settles out and is removed. It can be reused
hi sintering plants or, if the metal content is
sufficient, may be sold as a raw material else-
where. The remaining liquid leaves the.process as
waste treatment plant sludge. As the waste results
in a small portion of pollution produced by
steelmaking, pollution prevention and process
modification opportunities are not a priority.
References
Chatterjee, Amit. "Recent Developments in
Ironmaking and Steelmaking." Iron and Steel-
making. 22:2 (1995), pp. 100-104.
Frukawa, Tsukasa. "5000 Daily Tons of Direct
Iron-Ore Smelting by 2000." NewSteel. 10:11
(November, 1994), pp. 36-38.
McManus, George, ed. "Replacing Coke With
Pulverized Coal." New Steel. 10:6 (June, 1994),
pp. 40-42.
Ritt,~Adam. "DRI comes to the Gulf Coast,"
New Steel. January, 1996, pp. 54-58.
Strohmeier, Gerolf, and John Bonestell. "Steel-
works Residues and the Waelz Kiln Treatment of
Electric Arc Furnace Dust." Iron and Steel
Engineering. April, 1996, pp. 87-90.
U.S. Department of Commerce. 7992 Census of
Manufacturers Blast Furnaces, Steel Works
8
-------
and Rolling-and FinishingMills. 1992.
USEPA. "Profile of the Iron and Steel Industry.".
EPA/310-R-95-010, U.S. Environmental Protec-"'.
tioh Agency. Washington, D.C., September 1995.,
Annotated
Bibliography
Andres, A. and J.A. Irabien. "The Influence of
Binder / Waste Ratio on Leaching Characteristics
of Solidified / Stabilized Steel Foundry Dust.','
Environmental Technology.- 15 (1994), pp. 343-
. 3'51. This article discusses effective methods for
steel dust stabilization.
Andres, A.,-et al. "Long-term Behavior of Toxic
Metals in Stabilized Steel Foundry Dust." Journal
of Hazardous Waste Materials. 40 (1995): pp.
31-42. This study describes the leaching proper-
ties of heavy metals in steel dust.
Chapter 2: The Steel Making Industry
Berry, Brian. "Hoogovens Means Blast Furhaqes
And Clean Air." New Steel. December, 1994.
pp. 26-30. Pulverized coal injection, particularly
in Holland, are discussed. '...'.
McManus, G.J. "The Direct Approach to Making
Iron." Iron Age.' July, 1993. pp. 20-23. Direct
ironmaking; Corex plants and other alternatives to
the BOF are discussed.
Mohla, Prem. "New Ductile Iron Process Meets
the Challenge of the 1990's Head Oh." Foundry
Management and Technology: 121:4(April,
1993), pp. 52-56. Discusses alternative produc-
tion processes to help reduce pollution.
Schriefer, John. "Hot Iron Without Coke - Ands
Blast Furnaces." New Steel. August, 1995, pp.
50-52. Cdrex, direct iron-ore smelting and
HISmelt processes are all alternatives to the coke
oven and blast furnace: Examples are discussed
in this article.
'UK weight measurements
Case Study
Metal Recovery from Electric Arc Furnace Dust
Case Study: CS616
North Carolina Department of .Natural Resources and Community Development,
July, 1989
The Florida Steel Company of Charlotte, North Carolina produces significant amounts of ;
baghouse dust with a high zincfrbm their steel smelting .operations. The air pollution control
system on their electric arc furnaces capture the zinc-rich dust. Rather than disposal, the furnace
dust is sent directly to a zinc smelter for metal recovery.
At this writing, 2700 tons per year were sent to the zinc smelter for recovery at a cost of $61 per
ton. By allowing the zinc to be reused, Florida Steel saves $130,000 per year over the cost of
landfilling. > ._.'-
9
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10
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Ferrous and Non-Ferrous
Foundries ^^=_=^=^_=
Ferrous and non-ferrous foundries specialize in
melting and casting metal into desired shapes.
Foundry products are most often used in automo-
biles, plumbing fixtures, train locomotives, air-
planes and as metal pieces in other kinds of
equipment. Independent foundries are classified
under SIC code 3300; however, many specialty or
smaller production foundries often operate .within
larger plants classified under other'SIC codes.
In 1990, iron and steel accounted for 84% of
metals cast (McKinley, 1994). The remaining
15% of foundry operations come from aluminum,
copper, zinc and lead production. The foundry
industry currently produces 11 million tons of
metal product per year, with a shipment value of
$ 19 billion. Almost 200,000 people are employed
in over 3,000 foundries in the United States.
Although the large iron and steel foundries pro-
duce billions of dollars in metal each year and
provide many jobs, most foundries have far
smaller budgets and employ less than 100 people.
Foundry Processes
Cast Making
The first step in metal casting (Figure 3) involves
. the creation of a mold into which the molten metal
will be poured and cooled. The materials used to
make the trio Ids depend on the type of metal being
cast and the desired shape of the final product.
Sand is the most common molding material;
however, metals, investment materials, and other
compounds may also be used.
-Green sand mold are used in 85% of foundries. .
Green sand is a mixture of sand, clay, carbon-
aceous material and water (Figure 4). The sand
provides the structure for the mold, the clay binds
the- sand together and the carbonaceous materials
prevent rust. Water is used to activate the clay.
The green sand mixture is packed around a .
Clay
5%
Figure 4..Green Sand Composition
pattern of the metal piece and allowed to harden.
The mold is carefully removed from the pattern
and prepared for the molten metal.
Sand molds are used only once. Molten metal is
poured into the mold and allowed to cool. After
cooling, the mold is broken away from the metal
piece in a process called shakeout. Most of the
sand from green sand molds is reused to make
future molds.
Sand mixtures are also often used to create cores.
Cores are pieces that fit into the mold to create
detailed internal passages in the metal piece.
Cores must be strong and hard to withstand the
molten metal, and collapsible so they can be
removed from the metal piece after it has cooled.
To obtain these properties, resins or chemical
binders are usually added to sand mixtures.
Depending on the binder used, molds may be
either air or thermally set.
Other molding materials include chemically
v bonded sand, metal or refractories. These
materials are used in the remaining 15% of .
foundry applications. Shell molds use chemically
bonded sand to make the molds. Permanent
metal molds may be used in foundries that
11
-------
Chapter 3r Ferrous and Non-Ferrous Foundries
Figure 3. Metal Casting Process (USEPA/ 1981)
12
-------
Chapter 3: Ferrous and Non-Ferrous Foundries
produce large quantities of the same piece.
Investment molds are made from ceramic sub-
stances called refractories. They are used in high
precision metal castings. ,
Metal Melting
Foundries melt metals in one of several types of
furnaces depending on the type of metal being
used (Table 1). Furnaces types include cupolas,
electric arc, induction, hearth or reverberatory and
crucible. Because of the different nature of .
metals, different inputs are required and different
pollution is released from each type.
Cupola Furnaces
Cupola furnaces are the oldest type of furnaces
used in foundries. They are tall and roughly ;
cylindrical and are most often used for melting
iron and ferro alloys.. Alternating layers of metal
and ferro alloys, coke, and limestone are fed into
the furnace from the top. Coke makes up 8 -
16% of the total charge to provide the heat that
melts the metal (USEPA, 1992). Limestone is
added to react with impurities in the metal and
floats to the top of the metal as it melts. As in
steel melting, this limestone/impurities combina-
tion is called slag. By floating on top of the metal
while it melts, the slag protects the metal from
oxidation.
Cupola furnaces are lined with refractories, or
hard, heat resistant substances such as'fire clay,
bricks or blocks. The refractory protects the
furnace shell from abrasion, heat and oxidation.
Over time the refractory breaks down and eventu-
ally becomes part of the slag.
Cupola furnaces are usually attached to emissions
control systems to capture air emissions. Usually,
the air emission systems use either high energy
wet scrubbers that use water to remove air
pollution from the gas stream or dry baghouse
systems that use fabric filters to capture the
emissions.
Furnace Type
Cupola Furnace
Electric Arc
Furnace
Induction Furnace
Reverberator/, Hearth,
orCrucible Furnace
Raw Materials
Iron ore, scrap iron,
lime, coke
Scrap iron, flux
Scrap iron or non-
ferrous metals
Non-ferrous metals,
flax
Outputs
Molten iron
Molten iron
. and steel
Molten iron or
non-ferrous
metals
,. Molten non-
ferrous metals
Process
Alternative layers of metal and coke
are fed into the top of the furnace.
The metal is melted by the hot
gasses from the.coke combustion.
Impurities react with the lime and
a re separated.
Electric arcs from carbon electrodes
meltthe scrap metal. The flux
reacts with impurities. .
Induction furnaces are the most
common type used by both ferrous ,
and non-ferrous foundries. Copper
coils heat the metal using alternating
currents. The flux reacts with '
impurities. - '
Reverberatory furnaces melt metals in
batches usirig a pot-shaped crucible
that holds the m'etal over an electric
heater or fuelrfree burner. The flux
reacts with impurities
Table T. Common Type.s.of Metal Melting Furnaces
13
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Chapter 3; Ferrous jnd Non-Ferrous Foundries
Electric Arc Furnaces
Electric arc furnaces are often used in large steel
foundries and steel mills. The metal is charged
into the furnace, with additives to make recovery
of slag easier, and heat to melt the metal is
produced with an electric arc from three carbon or
granite electrodes. The electric arc furnace is
lined with refractories which slowly decompose
and are removed with slag. Electric arc furnaces
also usually employ air emissions equipment to
capture most air pollution.
Induction Furnaces
I nduction furnaces are the most widely used type
of furnace for melting iron and are increasingly
popular for melting non-ferrous metals (USEPA,
1992). They are popular because they provide
excellent metallurgical control and are relatively
pollution free. Coreless induction furnaces are
used for smaller (5-10 ton) operations. In coreless
induction furnaces, refractory lined crucibles are
surrounded by water-cooled, copper coils.
For larger quantities, channel induction furnaces
are used. In these furnaces the copper coils are
surrounded by inductors to promote metal melt-
ing. Channel furnaces are commonly used to hold
the molten metal prior to casting.
Induction furnaces use alternating currents to
create heat and melt the metal. The refractories
are usually made of silica, alumina or magnesia.
They break down over time and become part of
the slag.
Reverberator/ or Hearth Furnaces
Hearth furnaces are used in batch melting of non-
ferrous metals. The hearth can be heated by
either electric or natural gas methods. Hearth
furnaces are used to produce small quantities of
metal, usually for art and similar industries.
Metal Casting
After metal has been melted, it is poured into a
mold and allowed to cool. To remove the mold,
sand castings enter a process called shakeout
where the sand mold is shaken from the metal
piece. During the process dust and smoke are
collected by dust control'equipment. Permanent
molds are pried from the metal pieces without
being destroyed. Investment molds and shell
molds are destroyed during removal, creating solid
waste.
Any additional parts used.to hold the piece during
casting are removed. The metal piece is cleaned
using steel shot, grit or other mechanical cleaners
to remove any remaining casting sand, metal flash
or oxide.
A surface coating may be applied to the metal
piece at the foundry; however, such coating is
usually done at metal finishing plants. Further
discussion of metal .finishing can be found in The
Pollution Prevention for the Metal Finishing
Industry. .
Foundry Waste Streams
The waste products produced by foundries
directly relate to the metal type, the furnace type .
and the molding technology used. For example,
foundries that use sand molds generate the most
waste from sand. Nonferrous foundries and steel
foundries may produce hazardous waste because
of the lead, zinc, cadmium and other metal
present in the waste. Cupola furnaces produce
more air pollution than induction furnaces due to
coke use and sand castings produce more solid
waste than permanent molds because of the sand
fines that cannot be reused.
By volume, gaseous waste is the largest waste ..
source from foundries (Dieter, 1995). Air emis-
sions come from the binder systems used in mold
making, the vapors from metal melting and
airborne sand used in the pouring and shakeout
steps. Air'emissions have not been well quanti-
fied; however, they generally contain metals,
semi-volatile and volatile organic compounds.
They mainly come from the melting procedures.
Pouring and cooling steps contribute about 16% of
the total organic and semi-volatile wastes front
foundries (Shah, 1995).
Most of the gaseous metal emissions are captured
in the emissions control systems attached to
furnaces, shakeout and cleaning areas of the
foundry. Cupola furnaces contributed more
metallic air emissions than other furnace types.
Metal emissions from induction furnaces are very
small. The core and mold making processes
14
-------
.Chapter 3: Ferrous and Noii-Ferrous Foundries
.produce almost insignificant levels of metal
emissions. Emissions from the pouring process
depend on the metal temperature. The hotter the
metals, the more metal emissions (Shah, 1995).
Organic air emissions come largely from unreacted
components of resins, solvents and catalysts:
They come primarily from the core and mold
making steps and are not well quantified (Shah,
1995). OSHA standards have been the primary
reason for monitoring air emissions in the past.
However, with the Clean Air Act and its amend-
ments as well as increasing regulations from the
EPA, more air emissions studies are being done.
Liquid Emissions,
Liquid pollution makes up a small portion of the '
total waste stream from foundries (Dieter, 1995).
Liquid waste conies from non-contact cooling
water used to cool metal and other work pieces or
from wet scrubber air emission systems. Water
runoff from floor cleaning and other maintenance
procedures may also produce liquid waste.
' However, volumes of liquid waste are relatively
small and do not pose a large pollution problem
for foundries. Some plants have water treatment
facilities to remove contaminants for water reuse.
Solid Waste
s
Solid waste makes up a large portion of the
pollution from foundries. One-quarter to one ton
of solid waste per one ton of castings is expected
(Shah, 1995). The waste comes from sand, slag,
emissions control dust and spent refractories.
Sand waste from foundries using sand molds has
been identified as the most pressing waste prob-
lem in foundries (Twarog, 1992). Molding and
core sand make up 66-88% of the total waste.
from ferrous foundries (USEPA, 1992).
Sand Waste .
Green foundry sand is routinely reused. After the
sand is removed from the metal piece, it can easily
be remolded. However, sand fines develop with
reuse. These particles are too small to be effec-
tlve in molds and have to be removed and often
landfilled. ,
. Sand that is chemically bound to make cores or
shell molds is more difficult to reuse effectively
and may be landfilled after a single use. Sand
recovery methods, as discussed later, have been
investigated with mixed results.
Sand wastes from brass and bronze foundries
pose further waste problems as they are often
hazardous. Lead, copper, nickel, and zinc may be
found in the sand in sufficient levels to require
further treatment before disposal. If metal levels
are sufficent, recovery methods may be em-
ployed. -,-.
Investment Casting Waste
Although investment castings are not as widely
used as sand castings, they'also produce-solid.
waste/as they are usually destroyed when re-
moved from a work piece. Spent molds are non-
hazardous unless heavy metal alloy constituents .
are present. Spent wax, used as patterns for the
molds, also contribute to solid waste. The
patterns are removed by melting the wax and can'
usually be reused.
Cleaning Room Waste :
-Finished metal pieces are often cleaned in abrasion
cleaning systems. The abrasive cleaners and the
sand they remove from the metal pieces contrib-
ute to solid waste. Grinding wheels and floor .
sweepings also add solid waste. These wastes
are collected and usually landfilled.
Air Emissions Control Systems
Baghouse air emission control systems are one of
the most frequently used technology for'cohtroling
air emissions in foundries.. Air is pumped into the
baghouse where particulates accumulate on a
fabric filter. The system is efficient for removing
particles above or below 0.1-0.3 micrometers
, (Shah, 1995). Othertypes of air emissions
, control systems may also be used including wet
scrubbers, absorption and adsorption systems,
combustion and electrostatic precipitation. All
systems produce a.'solid waste from the air ,
emissions and release the cleaned air.
The emissions control dust is collected at almost
all stages of foundry production. If it does not
contain hazardous wastes, it is usually landfilled.
However, steel foundries frequently produce
emissions control dust that contains zinc, lead,
nickel, cadmium, and chromium, depending on
15
-------
Chapter 3: Ferrous and Non-Ferrous Foundries
the metal content. Nonferrous emissions control
dust may also be classified as hazardous due to
copper, aluminum, lead, tin and zinc. Depending
on the metals content in the emissions control dust
it may be permitted for land fill, or it may require
further treatment before disposal. Nonferrous
foundry dust often contains sufficient levels of
metals to make metal recovery economically
favorable.
Slag Wastes
Slag waste is often very complex chemically and
contains a variety of contaminants from the scrap
rnetals. Common components include metal
oxides, melted refractories, sand, and coke ash (if
coke is used). Fluxes may also be added to help
remove the slag from the furnace. Slag may be
hazardous if it contains lead, cadmium, or chro-
mium from steel or nonferrous metals melting.
Iron foundry slag may be highly reactive if
calcium carbide is used to desulfurize the iron.
Special handling is required for highly reactive
. waste.
Pollution Prevention
Methods for
Foundries
Sand Reclamation
Green sand can be reused multiple times without
significant refinement. The sand is filtered to
remove fines that develop from the process.
Additional sand is added to account for sand that
is lost. Then the sand is remolded for a different
metal piece.
Chemically bound sand used for core making and
other types of molds is not so easily reused.
However, many methods have been developed to
recover foundry sand, with mixed success. The
object of sand reclamation is to remove residual
binders and contaminants from the sand grains so
the sand can be reused without affecting the
quality of the mold. The sand reclamation
process is defined by the American Foundrymen's
Society Sand Reclamation and Recovery Commit-
tee as "the physical, chemical or thermal treatment
of a refractory aggregate to allow its reuse without
significantly lowering its original useful properties
as required for the application involved."
Four methods for.recovering sand have been
developed. The method that will be useful,
depends largely on the type of metal cast, the
binders used, and the desired reuse.
Attrition Sand Reclamation
Attrition sand reclamation technology spins two
streams of sand in opposite directions in the
presence of heat. The combination of sand
abrasion and binder combustion free the sand
particles from some binders. Attrition cannot
remove all residual binders, but works well with
no-bake binders. The yield from this process is a
high strength recycled sand.
Because all binders cannot be removed through
attrition, the sand characteristics may be changed-.
For some casting operations the characteristics
may be changed significantly enough that the sand
may be be ineffective for furture castings.
Attrition methods of sand reclamation may also
produce large quantities of dust. The dust can be
captured in air emission control equipment, hence
contributing to the total volume of solid waste.
Dry Sand Reclamation
Dry sand reclamation relies on mechanical and
pneumatic scrubbers to remove lumps and binders
from sand (Figure 5). Mechanical scrubbing
moves each sand grain through a sand-to-metal or
sand-to-sand interface to remove impurities.
Pneumatic scrubbers use air to propel sand
between baffles. These scrubbers are particularly
good for removing clay from molding sands and
binders in systems that are not baked.
Dry reclamation can produce large quantities of
dust. These air emissions have to be monitored
and captured by control equipment. Dry sand
reclamation may also not be capable of removing
binders to the extent necessary for reuse in some
foundry operations.
Water (Wet) Reclamation
Wet reclamation uses water to remove sand
binders (Figure 6). The process uses on the
.16
-------
Chapter 3: Ferrous and Non-Ferrous Foundries
//////// / // / / W.
/// ;77 ?/s
Figure 5. Dry Sand Reclamation (Heine, 1983)
SANO
DISCHARGE
VACUUM I VACUUM
RECEIVER T PUMP
HIGHSPEED
P SCRUBBER
CAKE
(UVNDF1LU)
QUENCH Ii _-r.-
Figure 6. Wet Sand Reclamation (Heine, 1983)
' ' ' - ' " . . : ''' 17 -' V
-------
Chapter 3: Ferrous and Non-Ferrous Foundries
different water solubilities of sand and binders to
separate the two. Clay bonded systems work well
with water reclamation processes because the
clays are very soluble in water. Sodium silicate
sand binders can also be removed using wet
reclamation. The sodium silicate dissolves part of
the sand crystal when binding, but can be re-
moved by exposing it to water. After the sand is
soaked in a water bath it is dried and reused.
Although wet reclamation was used in the 1950s
and 1960s, it has been nearly eliminated as a
methpd of sand recovery. Chemical binders are
also no longer sufficiently hydrophilic to dissolve
in water. Further, organic resins that do dissolve
and other water soluble impurities can cause
significant water contamination. The high volume
of waste water and strict environmental regula-
tions can make wet sand reclamation too expen-
sive.
Thermal Sand Reclamation
Thermal reclamation uses heat in a rotary kiln,
multiple-hearth furnaces, or a fluidized bed to
combust binders and contaminants (Figure 7). In
removing binders, the process can cause sand to
change in composition. Combustion products
from the fuel used to heat the sand and thermal
cracking of the sand crystals may occur. The
resulting sand may be significantly different than
the original sand. Depending on the type of
casting, thermally treated sand may or may not be
usable.
Infrared energy can also be used to thermally treat
sand. This method may maintain more of the
sands original composition, while still destroying
binders. Infrared units, called electric sand
reclamation units, are in place in the United
Kingdom and Canada ("Navistar Goes Infrared,"
SOCKET ELEVATORV
RECEIVING HOPPERv
TO EXHAUST SYSTEM
DIRECT FLAMS
BURNER SYSTEM
AUTOMATIC BURNER
CONTROL SYSTEM
fVOTARY SCREEN CONVEYOR
SEPARATES SAND GRAINS
FROM FOREIGN MATERIAL
HIGH EFFICIENCY
RECUPERATOR SYSTEM
/. FIRST STAGE
ROTARY THERMAL UNIT
....
.HYDRAULIC RAM
SANOrcSO
SCREW TYPE
SAND GRAIN FEED
SHAK.EOUT SAND
ELEVATOR FE=(
TO EXHAUSTSVS
-HcATRECUPSRA
DIRECT FLAME
R SYSTEM
SECOND STAGE
ROTARY THESMAL UNIT
HOT SANO
DISCHARGE
CONTINUOUS
SANO SEAL
FINES TO
COLLECTION
SYSTEM
CLEAN SANO DISCHARGE AT
AMBIENT TEMPERATURE
PRIMARY COOLER
TURBO-COMPRESSOR
FOR FLUIOIciNG AIR
OUTPUT TO SANO
DISTRIBUTION SYSTEM
SECONDARY COOLER.
CLASSIFIER. SCRUBBER
Figure 7. Thermal Sand Reclamgtion (Heine, 1983)
18
-------
Chapter 3: Ferrous and Non-Ferrous Foundries
1993), External blowers push the sand through
fluidized beds, allowing the sand to directly
contact the infrared radiation which breaks down
the binders. The electric sand reclamation units
do hot produce the combustion products associ-
ated with traditional thermal reclamation pro-
cesses. - ' .
Sand Recycling
Another option for foundry sand is recycling.
Many, industries use sand as a raw material in their
-processes. As foundry sand is usually not'hazard-
ous, it can serve this purpose. Markets for spent
foundry sand include manufacturing of: cement,
concrete, asphalt, bricks and tiles, flowable fill
(permeable, low-strength concrete), gebtechnical
fill and roadfill, daily landfill cover, and manufap-.
tured topsoil and composting. Liability and local
legislation must, of course, be considered before
selling spent foundry sand.
Spent Slag and Emissions Control
Dust
Slag and emissions control dust constitute the
remainder of the solid waste produced by found-
ries. Not much has been written regarding
process modification to reduce these solid wastes.
However, if the slag or dust contained sufficient
metal content, they can be fed back into the
furnaces to reclaim the remaining metal dust. The
metals can also be recovered from the dust using
electrolytic or other metal recovery techniques.
The recovered metal can either be added to the
molten metal or sold for other uses.
References
Heine, Hans J. "Saving Dollars Through Sand
Reclamation Part I" Foundry Management
and Technology. 111:5 (May, 1983), pp. 22-25..
Leidel, Dieter S. "Pollution Prevention and
Foundries." Industrial Pollution Prevention
Handbook, ed. Harry M.Fre,edman. 1995. ,
McKinley, M.D. etal. "Waste Management .
Study of Foundries Major Waste Streams: Phase
It." HWRIC#TR-016. April 1994.
Shah, D.B. and A.V. Phadke: "Lead Removal of
Foundry Waste By Solvent Extraction." Journal
of Air and Waste Management. 45 (March,
1995), pp. 150-155..
Trombiy, J. "Recasting a Dirty Industry." Envi-
ronmental Science and Technology. 29:1 (1995),
pp.76-78.
Twarog, D.L., et al. "Waste Management Study
of Foundries' Major Waste Streams: Phase I."
HWRIC Project RRT-16, Waste Management and
Research Center, Champaign, Illinois, November,
1992.:
USEPA. Metal Casting and Heat Treating
Industry." EPA/625/R-92/009. September 1992.
Annotated
Bibliography
Air Quality Committee (1Q-E), "Foundries Face
Stricter Air Quality, PollutionMonitoring,"v
Modern Casting. May 1990. This article pro-
vides a good description of SARA Title III.
Corfiett, Michael J., "Eliminating the Waste
Stream from Your Cold Box Process." Foundry
Management and Technology. 121:12 (Decem-
ber, 1993), pp. 3 8-40. Good information-about
the Isocycle process. Discusses cold box sand
casting briefly.
Douglas, John. "Electrifying the Foundry Fire,"
EPRIJournal. October/November 1991;.pp. 17
-23. This article discusses electric options to
replace coal-fired processes.
East, William, "Solid WasteNo Place to Go,"
Foundry Management and Technology. May .
1991. This article discusses the sources of solid
waste from foundries. -,
Fuller, Robert, "Toxicity: Characteristics Leaching
Procedure Replaces Extraction Procedure Toxic-
ity," -Modern Casting, 80 (November, 1990), pp.
51-53. Discusses changes in EPA methods for
determining toxicity characteristics of industrial
waste. .
*
Gschwandtner, Gerhard and Susan Fairchild,
Emissions Factors for Iron Foundries Criteria
and Toxic Pollutants, EPA-600/2-90-044, US
19
-------
Chapter 3; Ferrous and Non-Ferrous Foundries
Environmental Protection Agency, Washington,
DC, August. 1990. Discussion of air pollution
sources from foundries.
Ham, R.K. and W.C. Boyle. "Research Reveals
Characteristics of Ferrous Foundry Wastes,"
Modern Casting. February, 1990, pp. 37-41.
Discusses the toxicity of liquid foundry wastes.
Jacobs Engineering. Waste Audit Study, Thermal
Metal Working Industry, Jacobs Engineering,
December, 1990. Discussion of waste streams
associated with foundries.
Mosher, Gary E. "EPA Publishes New Land Ban
Regulations." Mo'dern Casting. 80:1 (January,
1990), pp. 40-41. Discussion of the Hazardous
and Solid Waste Amendments of 1984 as they
apply to foundries.
National Renewable Energy Laboratories. "The
Foundry Industry"-In Technology Partnership.
Case Studies
Washington, DC: Department of Energy. April,
1995. Brief discussion of the industry and the
processes. Also a brief discussion of the Metal
Casting Competitiveness Research Act of 1990.
Smith, Virginia D. "Foundries and Clean Air Act:
Several Unanswered Questions." Foundry
Management and Technology. 119:2 (February,
1991), 16-18. This article provides a general
description of how the Clean Air Act of 1990 will
potentially affect the foundry industry.
Summary of Factors Affecting Compliance by
Ferrous Foundries, Volume 1, EPA-340/1-80-
020, US Environmental Protection Agency,
Washington, DC, January, 1981. This article
discusses waste sources associated with foundries.
Trembly, Jeanne. "Recasting a Dirty Industry,"
Environmental Science and Technology. 29:2
(1995), pp. 76-78. Discussion of foundry air
emissions and the Clean Air Act of 1994.
Air Emissions Reduction
Replacing Organic Cleaners with Citrus Based Solvents
Pollution Prevention Case Study, Enviro$en$e, October 31,1995
Northern Precision Castings, Geneva, Wisconsin, is an investment casting operation employing
150 people and casting more than 200,000 pounds of metal per month. The operation uses
ceramic molds and wax patterns. The wax patterns must be cleaned thoroughly for proper
ceramic adhesion. The cleaner used was the solvent 1,1,1 -Trichloroethane (TCA) which
evapoarted to leave the surface clean. The evaporation produced 1 8,000 pounds (1 988) of
'emissions.
Environmental regulations pertaining to TCA caused Northern PercisionCasting to consider
alternatives. They requested alternatives from their solvent supplier. The supplier's first
recommendation was a switch to freon until a better alternative-could be identified. The freon
produced fewer emission man the than TCP and was used for six to nine months. After that
period, freon was replaced with a citrus-based, non-hazardous solvent. The new solvent has
been effectively cleaning the wax assemblies with minimal emissions.
Product quality was a concern prior to the cleaning chemical switch. However, the change
produced no change in mold quality. Initally, the citrus-based solvent produced an odor the
workers found offensive, but the problem has been resolved.
The switch,from organic solvent cleaners to a citrus-based cleaner has required no capital cost
and no signifacant changes in operations and maintenance costs. The fugitive air emissions
prior to the shift were 1 8,000 pounds (1 988). After the move to the citrus-based cleaner,
emissions constituted water-soluble liquid waste which can be discharged to the Publicly-Owned
Treatment Works (POTW). ' ; . ' .
20
-------
Chapter 3: Ferrous and Non-Ferrous Foundries
Foundry Sand Reclamation
Micigan Department of Commerce and Naturla Resources, November 1993,
#9303 ;
Wolverine Bronze or Roseville, Michigan insta'lled-a thermal sand recycling system in an
attempt to cut costs of sand purchases. The system produced sand quailty adequate to meet
the molding needs; however, the system was n9t economically beneficial. As the sand needs at
the facilty varied greatly, use of the machine varied. However, the thermal apparatus required
constant heat to provide quick start up without damage to the system.; With-the heat
requirements, the thermal sand recycling operation did not save signficant amounts of money
'over the purchase of new sand. ' , .
In 1 989, low enery sand recycling sytems were evaluated to replace the thermal system. An
attition sand recovery system Was installed. In the attition system, sand grains rub together at
high speeds to remove residual binders and inorganic contamiants. The system has produced
signifant cost savings over the .use of new sand. The primary savings stems from reduced
energy and maintenance requirements over the thermal recovery system. . .
Cupola Slag Reduction
Iowa Waste Reduction Assistance Program, Cast Study #94-20
Quinn Machine and Foundry of Boone, Iowa produces concrete pipe forms our of iron. Slag
from the cupola furnace was being produced at a rate of approximately 8,000 pounds per
day. Quinn sought to reduce the slag production and, in turn, reduce thier volume of waste.
They first attempted to locate a metal recovery operation for the slag. However, metal
recovery did not prove economical for the facility. .
After further evatuatipn, itwasdetermined that a smaller charge in the furnace would increase.
the yield and reduce slag formation." The change has resulted in the predicted reductions.
From the changes, landfill costs have been reduced by approximately $1,275 peryear.
21
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22
-------
Aluminum Smelting and
Refining
A .luminum is primarily used to produce pistons,
/Vengine and body parts for cars, beverage
cans, doors, siding and aluminum foil. It may also
be used as sheet metal, aluminum plate and foil,
rods, bars and wire, aircraft components, win-
dows and door frames. The leading users of
aluminum include-the container and packaging
Industry, the transportation industry, and the
building and construction industry.
Aluminum can either be produced from bauxite
ore or from aluminum scrap. Refinement of
aluminum ore is sufficiently expensive that the
secondary production industry commands much
of the market. About 40% of aluminum in the US
is recovered for secondary refining (USEPA,
1995). .
Due to high energy requirements, thCmajor
primary aluminum producers tend to locate in
areas with low energy costs, including the North-
west and Ohio River Valley. .Secondary producers
tend to locate near industrial centers, including
southern California and the Great-Lakes.'
Both primary and secondary aluminum producers
refine and melt the aluminum and pour it into bars
called ingots. The ingots are shipped to metal
casting plants or other shaping plants for molding
or rolling.
Primary Aluminum
Refining
Aluminum production from bauxite ore is a three
step process. First the alumina is extracted from
bauxite ore usually using the Bayer Process. In
the Bayer Process, finely crushed bauxite is mixed
with sodium hydroxide and placed in a 'digester.'
High temperatures and pressures in the digester
cause reactions in the ore / sodium hydroxide
mixture. The result is dissolved aluminum oxide.
and ore residue, The residues,'which include
silicon; lead, titanium, and calcium oxides, form a
sludge in the bottom of the digester. The alumi-
num oxide is evaporated off and condensed.
Starches and other ingredients are added to
remove any remaining impurities from the oxide.
The solution is then moved to a precipitation tank
where the aluminum oxide is crystallized. Alumi-
num hydroxide and sodium hydrizide are the
products of the crystallization. The crystals are
washed, vacuum dewatered and sent to a
calculator for further dewatering.
Aluminum oxide from the Bayer Process is then
reduced to aluminum metal usually using the Hall-
Heroult process. In this process the aluminum
oxide is placed in a electrolytic .cell with molten
cryolite! A carbon rod in the cell is charged and
the reaction results in carbon monoxide, carbon
dioxide and aluminum. The aluminum sinks to .
the bottom where it is removed from the tank and
sent to a melting or holding furnace.
The molten aluminum is then mixed with desired
alloys to obtain specific characteristics and cast '
into ingots for transport to fabricating shops. In
the fabrication shops, the molten aluminum or
aluminum alloys are remelted and poured into
casts and cooled. Molten aluminum may be , ..
further heated to remove oxides, impurities and
other active metals such as sodium and magne-
sium, before casting. Chlorine may also be
bubbled through the molten aluminum to further
remove impurities.
Waste Sources and Pollution
Prevention Opportunities
Air emissions come from a number of sources.
The grinding of the bauxite, calcinating the
aluminum oxide, and handling materials produce
particulates. Air emissions equipment is used
extensively to capture these particulates.'
23
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Chjocer 4: Afummum Smelting and Refining
The participates may be metal rich. If the metallic
content is sufficient, the emissions control dust
can be remelted to capture any remaining metals
or it may be otherwise reused or sold for its
metallic content. If the dust is not sufficiently
metal rich, it usually landfilled.
Another source of air emissions from primary
aluminum production processes occurs during the
reduction of aluminum oxide to aluminum metal.
Hydrogen fluoride gases and particulates, fluo-
rides, alumina, carbon monoxide, sulfur dioxide
and volatile organics are produced. Electrolytic
baths often use anode pastes in the cell. The
paste must be continually fed into the cell through
a steel sheet with an opening. This continual feed
allows the gas to escape.
One method fdr reducing gas emissions is the use
of pre-baked anodes. Pre-baked anodes must be
manufactured in an on-site plant. The pre-baked
anodes allow the electrolytic bath to be sealed,
allowing gas to be captured. The anodes are then
replaced every 14-20 days, containing the gasses
for collection. Anode baking furnaces produce
fluorides, vaporized organics and sulfur dioxide
emissions. The emissions are often controlled
using wet scrubbers.
Liquid waste is not a great concern in aluminum
processing. Wastewater is produced during
clarification and precipitation; however, much of
the water is directly reused.
Solid phase wastes include bauxite refining waste,
called red mud, and reduction waste from spent
pot liners. Red mud contains iron,.aluminum,
silica, calcium and sodium, depending on the ore
used. Usually red mud is managed on site and is
not hazardous.
The refractory lining from the pots used to refine
the aluminum are the other solid waste concern.
The refractory breaks down with contini-ous use
to produce RCRA K088 hazardous waste.
Secondary Aluminum
Production .
In the secondary aluminum production industry,
scrap aluminum is melted in gas- or oil-fired
reverberatory or hearth furnaces. Impurities are
removed using.chlorine or other fluxes until the
aluminum reaches the desired purity.
Other aluminum production plants use dross in
addition to scrap. Dross is a by-product of
primary aluminum melting. This process further
reduces the pollution resulting from primary
aluminum production. It contains fluxes and
varying concentrations of aluminum. "Skim,"
"rich," or "white dross" refer to aluminum dross
with high aluminum content. "Black dross" or
"salt cakes" refer to aluminum dross from prac-
tices that use salt fluxes.
The dross is crushed, screened and melted in. a
rotary furnace where the molten aluminum is
collected in the bottom. The resulting salt slag is a
waste product. To reduce this waste more of the
remaining metallics may be leached into water and
collected.- .
To eliminate the need for salt fluxes., a new
plasma torch treatment has been developed to
heat the rotary furnace. High concentrations of
aluminum are recovered from this procedure.
Pollution Prevention in
Secondary Aluminum Processing
Air emissions and solid-phase wastes are the
primary concerns in the aluminum processing
.industry. Air emissions depend largely on the
quality of scrap used. Emissions can come from .
smelting, refining, and the furnace effluent gases.
Gases can include combustion products, hydrogen
chloride and metal chlorides, aluminum oxide
metals and metal compounds. To reduce emis-
sions regardless of the type of scrap used, alumi-
num fluoride can be substituted for chlorine to
remove impurities from the molten metal. All
systems are usually connected to emissions ;
control equipment, typically a baghouse for
collecting fluorine and other gases. ,
Solid-phase waste from secondary aluminum
production is slag formed during smelting. The
slag contains chlorides, fluxes and magnesium.
The metallics may be separated and reused or
sold.
24
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Chapter 4: Aluminum Smelting and Refining
Liquid wastes include water that is added to the
.slag to help separate the different metals. The .
waste water may be contaminated with salt and ,,
fluxes, but can often be recovered and reused.
Annotated
Bibliography
USE? A., Profile of The Nonferrous Metals .
Industry. EPA 31O-R-95-010. This document . .
discusses uses, processes and pollution prevention ,
opportunities associated with aluminum produc- .
tion'i
Case Study ,
Replacement of Organic Solvents with Water-Based Coatings for
Sand Cores
Minnesota Tehcnical Assistance Program/ 1994, 6/94-93
The Progress Casting Group, Inc., of Plymouth, Minnesota, is an aluminum foundry. Progress
Casting used 1,1,1 -trichloroethane (TCA) to coat sand cores for use in parts molding. The TCA
prevented the molten metal from penetrating the cores and left a smooth finish on the finished
metal piece. ' ,
Replacment of TCA with an alternative coating was promfed by environmental commitments,
economics of compliance and customer demands. Alternatives were evaluated for thier ability
to withstand the pressure and temperatures of the molten aluminum. The alternative coating
also posed problems assocated with consistent solid suspension, even application of the
coating, and quick drying methods.- . , -
The alternative selected was a water- and isopropyl alcohol- (IPA) based coating. To apply the
coating in a quick and even manner; Progress Casting worked with vendors to develop an .
automated dipping and drying system. The IPA coating requires repeated dipping, as opposed
to the one application needed for TCA. The application includes a dip tank containing the .IPA
solution, two infrared ovens and four rotating racks to hold and lower the cores through the
system! The infrared ovens were selected to dry the coating as theyprovided adequate time
requirements and coating thickness. One problem with IPA, is the fire hazard associated with
IPA's flamabiltiy.' . ' :
The switch from TCA to IPA based coatings has resulted in a $59,000 savings in TCA purchase
costs. These costs have been replace with 35,000 pounds of the IPA coating per year at an
estimated cost of.$1 4,500. Progress Casting has also satisfied customer demands to reduce
TCA and has complied with CAM programs. .' . ' .
25
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Chapter 4: Aluminum Smelting and Refining
Heat Transfer Applications
"Pollution Prevention Success Stories/' WMRC, 1994
Chicago Whifemetal Casting of Chicago,'Illinois casts aluminum, magnesium and zinc using die
casts. To reduce costs, the casting operation evaluated possible energy reduction methods.
They installed a head cogeneration system to recover heat from the aluminum remelt furnace.
After recovery, the heat is used in zinc and aluminum operations. The initial system cost ..
$70,000, but is estimated to have saved the company 20% of the natural gas it would have
used and $1 80,000 in energy bills over a ten year period.
Waste water reduction was also evaluated at the plant. Quench water was originally hauled
away weekly at a cost of $62,000 per year. A water filtration system was installed at the plant.
The system removes impurities and returns the water for reuse. The filtration system is estimated
to have saved the plant $744,000 over its 1 2 year life in disposal costs. .Additionally, a "savings
of $72,000 in water usage is estimated.
.26
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Copper Processing
The copper processing industry refines copper
from metal ores or scrap copper. The leading
consumers of copper are wire mills and brass
mills, which use the copper to produce copper
Wire and copper alloys, respectively. End uses of
copper include construction materials, electronic
' products, and transportation equipment. Once
refined, copper can be used as a powder in
automotive, aerospace, electrical and electronics
equipment, in anti-fouling compounds, various
chemicals and medical processes. Compounds of
copper include fungicides, wood preservatives,
copper plating, pigments, electronic applications
and specialized chemicals.
Copper can be produced as either a primary
product or as a co-product of gold, lead, zinc or
silver. It is mined in both the Northern and
Southern Hemisphere and primarily consumed in
the Northern Hemisphere with the U.S. as a
primary producer and consumer.
Primary Production
of Copper
Copper is mined in open pits and below ground.
The ore usually contains less than 1% copper and
is often associated with sulfideminerals. The ore
is ground, concentrated, and slurried with water
and chemical reagents. Air blown through the
mixture attaches to the copper, causing it to float
to the top of the slurry. The copper is/then
removed with a skimmer. The tailings remain and
are dewatered and disposed of in tailing ponds.
The water is recovered and recycled.
' One of two processing methods are used to refine
concentrated copper. Pyrometallurgy, or smelting,
is used on ore with copper sulfide and iron sulfide
minerals, the concentrate is dried and fed into a
furnace. The minerals are partially oxidized and
melted, resulting in segregated layers. .'The matte,
layer refers to the iron-copper sulfide mixture
which sinks to the bottom. .The slag, which refers
to the remaining impurities, floats on top of the
matte. The slag is .discarded on site or sold as .
railroad ballast and sand blasting grit.. Sulfur
dioxide gases ,are also collected and made into
sulfiiric acid for use in hydrometallurgical leaching
(discussed below) or sold off-site.
i .
The matte is recovered and moved to the con-
verter, a cylindrical vessel into which the copper is
poured. Air, lime and silica are added to react
with the metal oxide. Scrap copper may also be
added. Iron slag is removed and often recycled
back into the furnace. Sulfur dioxide is captured
and converted into sulfuric acid. The converted
copper, known as "blister copper," is recovered.
f
The blister copper then undergoes "fire refining." .
Air and natural gas are blown through the copper
to remove any remaining sulfur and oxygen. The
copper is cast into copper anodes and placed in an
electrolytic cell. Once charged; the pure copper
collects on the cathode and is removed as 99%
pure. The copper can be sold to wire-rod mills or
further processed into rods. Anode slime refers to
impurities that sink to the bottom of the electro-
lytic cell. .-'..
The second method for refining copper is called
the hydrometallurgical process. This process
begins with oxidized copper ores or oxidized
copper wastes. The oxidized material is leached
with sulfuric acid from the smelting process. The
sulfuric acid is percolated through piles of oxidized
metal and collected with acid resistant liners.
Further refining may be performed using one of
two processes. In cementation, the acidic solution
of copper is deposited on to scrap iron in an
oxidation-reduction reaction. After sufficient
amounts of copper have been plated, the copper is
further refined using the pyroinetaliurgical pro-
cess. However, this process is rarely used.
27
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Chapter 5: Copper Processing
Solvent extraction is more commonly used to
refine copper. An organic solvent in which copper
is soluble islntroduced. As the copper is more
soluble in the organic layer than the aqueous, it
enters an organic-copper solution and is separated.
Sulfuric acid is added to strip the copper from the
organic solvent into an electrolytic solution.
In the electrolytic process, called electrowinning,
the copper plates out onto the cathode. The
cathodes are sold as-is or made into rods on-site
or made into starting sheets for other electrolytic
cells.
All remaining organics and acids are reused.
Further, sulfur is fixed throughout the process to
meet Clean Air Act Standards. If the sulfur
content of the gas is over 4%, the sulfur com-
pounds are made into sulfuric acid for use in the
process or for sale to fertilizer manufacturers.
Slurries with less than 4% sulfur are classified as
RCRA hazardous" wastes because of sulfur,
cadmium, lead and other metals.
Secondary Copper
Processing
Secondary copper processing involves two steps:
metal pretreatment and smelting. Pretreatment
includes cleaning and concentrating the copper.
Concentrating is done manually or mechanically
and includes sorting, stripping, shredding and
magnetic separation. The metal can be further
refined using pyrometallurgical methods
including sweating, insulation burning, or drying
or hydrometallurgical methodsincluding
flotation and leaching. The concentrated metal is
then smelted. Generally, copper is fire refined,
similar to primary copper smelting operations
although the exact procedure depends on the
quality of copper scrap. .
Pollution Output and Prevention
in Copper Processing
Primary and secondary copper processing produce
similar pollutants with similar pollution prevention
opportunities. Air emissions include particulates
" and sulfur dioxide. Particulate air emissions
usually include iron and copper oxides, but many
contain other metal oxides, sulfates or sulfuric
acid. Particulates are usually captured using
emissions control equipment. Depending on the
composition of the emissions some recovery of
heavy metals may be possible.
In addition, secondary copper processing produces
air emissions from the removal of excess oils and
cutting fluids. The air emissions are usually
captured using baghouses. After-burners may also
be used to fully combust products.
. - j* ' J
Sulfur dioxide is usually captured using single
stage electrostatic precipitation. Once captured,
the sulfur dioxide is converted into sulfuric acid
and sold or reused in process.
Liquid wastes from the copper processing plant
include large quantities of water. Most of the
water can be reused with minimal refinement.
The leaching process creates some sulfuric acid
liquid waste. The sulfuric acid is almost always
directly reused. Electrolytic refining procedures
also produce some'liquid waste. This waste is
usually sent to waste water treatment facilities and
discharged.
Annotated
Bibliography
USEPA, Profile of The Nonferrous Metals
Industry. EPA 310-R-95-010. This document
discusses uses, processes and pollution prevention
opportunities associated with copper processing.
28
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Lead Processing
The US is the third largest producer of primary
lead, with most coming from Missouri. The
primary end users of lead are batteries and
ammunition. Consumers of lead include TV glass,
computer glass, construction (including radiation
shields), and protective coatings.
Primary Lead
Processing
Primary lead production begins with sintering.
Concentrated lead ore is fed into a sintering
machine with iron, silica, limestone fluxes, coke,
soda ash, pyrite, zinc, caustics or pollution control
particulates. The mixture is blasted with hot air to
burn off the sulfur and sent to the smelter.
Lead is usually smelted in a blast furnace using the
carbon from, the sintering machine to provide the
heat source. As melting occurs, several layers
form in the furnace. The molten lead layer sinks
to the bottom of the furnace. A layer of the
lightest elements, including arsenic and antimony,
floats to the top and is referred to as the "speiss."
A "matte" layer also forms from the copper and
metal sulfides. Finally, a layer of blast furnace
slag, which contains mostly silicates, also forms.
The speiss and the matte are usually sold to
copper smelters where they are refined for copper
processing. The slag is stored and partially
recycled, if the metaLcontent is sufficient.
The lead from the blast furnace, called lead
bullion, then undergoes the dressing process. The
bullion is agitated in kettles then cooled to 700-
800 degrees.- This process results in molten lead
and dross. Dross refers to the lead oxides,
copper, antimony and other elements that float to
the top of the lead. Dross is usually skimmed off
and sent to. a dross furnace to recover the non-
lead components which are sold to other metal
manufactures.
Finally, the molten lead is refined. Pyrometallurgi-
cal methods are usually used to remove the
remaining non-lead components of the mixture.
The non-lead metals are usually sold to other
metal processing plants. The refined lead may be
made into alloys or directly cast.
Pollution Sources and Prevention.
Primary lead production produces air emissions,
process wastes and solid wastes. Air emissions
consist primarily of sulfur oxides and particulates. .
Sintering plant air emissions include sulfur and
particulates. These emissions are usually burned
in the blast furnace and eliminated. Paniculate
emissions from blastfurnaces include lead oxides,
quartz, limestone, iron pyrites, iron-limestone-
silicate slag, arsenic and other metallic com-
pounds. The exact type and amount of
particulates depends largely on the input material.
Emissions control equipment, usually a baghouse,
is most often used to control particulates.
Blast furnaces also produce slag. The slag
consists primarily of iron and silicon oxides,
aluminum and calcium oxides, and other metals,
depending on inputs. The slag can either be
reused in the process to capture more metals or
disposed of on site. If the slag is not reused, it
may be treated-to recover the metals for sale.
Liquid wastes from primary lead production
include wastewater and slurries. Acid plant
blowout from sulfuric acid production plants, slag
granulation water from slag disposal, and plant.
'wash down water from housekeeping are the
prim?ry types of liquid wastes. The water is
considered RCRA K065 hazardous waste due to
the lead content.
29
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Cuoter 6: Lead Processing
Secondary Lead
Processing
Most of the lead produced comes from secondary
sources. Lead scrap includes lead acetate batter-
ies, cable coverings, pipes, sheets and lead coated,
or terne bearing, metals. Solder, product waste '
and dross may also be recovered for its small lead
content. Most secondary lead is used in batteries.
To recover lead from a battery, the battery is
broken and the components are classified. The
lead containing components are processed in blast
furnaces for hard lead or rotary reverberatory
furnaces for fine particles. The blast furnace is
similar in structure to a cupola furnace used in
iron foundries. The furnace is charged with slag,
scrap iron, limestone, coke, oxides, dross, and
reverberatory slag. The coke is used to melt and
reduce the lead. Limestone reacts with impurities
and floats to the top. This process also keeps the
lead from oxidizing. The molten lead flows from
the blast furnace into holding pots. Lead may be
mixed with alloys, including antimony, tin, arsenic,
copper and nickel. It is then cast into ingots.
Pollution Sources and Prevention
Air ernissions and solid waste are the primary
pollution concerns for secondary lead producers.
Reverberatory or blast furnaces produce most of
the lead waste. Products can include sulfur
oxides, nitrogen oxides, antimony, arsenic, copper,
or tin, depending on inputs. Lead paste desulfur-
ization is a process used by new lead processing
plants to reduce the sulfur dioxide emissions and
waste sludge. The air emissions in older plants
are usually controlled with settling and cooling
chambers and with baghouse emissions control .
equipment.
.The battery breaking process contributes sulfuric
acid, dust, battery cases and lead compounds.
The solid emissions include emissions control dust
and slag from smelting. They are considered
K.069 hazardous wastes.
Annotated
Bibliography
USEPA, Profile of The Nonferrous Metals
Industry. EPA310-R-95-010. This document
discusses uses, processes and pollution prevention
opportunities associated with lead production.
30
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Zinc Processing
Zinc is the fourth most widely used metal,
following iron, aluminum, and copper. Zinc is
mined mostly in Canada, the former USSR,
Austral ia, Peru, Mexico and the US. In 1993,
about 50% of the zinc mined came from Alaska.
Tennessee, New York and Missouri are the top
producers of zinc metal. -
The US is the worlds largest consumer of zinc. ^
Eighty percent is consumed in slab format, while
20%. is consumed in compounds. Most zinc is
used in the galvanizing steel process. Other uses
include the automotive, construction, electrical
and machinery industries. Zinc compounds
include agricultural chemicals, paints, pharmaceu-
ticals, and rubber.
Primary Zinc
Processing
Zinc concentration is usually done at the mine site,
prior to reaching the zinc processing plant. The
concentration includes crushing and flotation
techniques. At the zinc processing plant, the zinc
is first reduced using pyrometailurgical methods,
including distillation, or hydrometallurgical meth-
ods, including eleetrowinning, calcination, leach-
ing, or purification. The eleetrowinning process is
most commonly used.
Eleetrowinning uses an electrolytic cell to reduce
the zinc. An electric current is run from a lead-
silver anode through a zinc solution. The zinc
deposits on an aluminum cathode and is har-
yested. The zinc is then melted and cast into
ingots. ...
Pollution Sources and Prevention
Primary zinc production produces air emissions,
process wastes and solid-phase wastes. Air
. emissions come primarily from the zinc roasting
process and consist primarily of sulfur dioxide
emissions. Most emissions are recovered on site
in sulfuric acid production plants, where sulfuric
acid is produced.
Zinc roasters also produce particulate emissions.
Particulate air emissions from primary zinc
production often contain cadmium, lead and other
compounds, depending on inputs. The slurry
formed from the emissions control equipment is
K066 hazardous waste.
The eleetrowinning process produces waste heat.
Rather than letting the hot gas escape into the .
environment, some is recovered and sent to
cooling towers where the steam is collected for
reuse.
Wastewater is produced from leaching, purifica-
tion and eleetrowinning. The water is usually
treated and discharged. Reuse opportunities may
be available.
Solid wastes include acid plant slurries, sludge
from electrolytic cells and copper cakes, a by-
product of zinc production, from the purification
cells. Much of the waste is considered RCRA
hazardous waste. Anode slime from electrolytic
cells consists of impurities not captured prior to
the eleetrowinning process. The composition
usually makes the slime a RCRA hazardous
waste. Copper cakes are captured and sold to
copper processing plants.
Secondary Zinc
Processing
Secondary zinc production uses process scrap
from zinc slabs, zinc oxides and zinc dust. Selec-
tive melting may also be used to capture zinc if
the zinc is mixed with other non-ferrous metals
with higher melting points. Zinc is also often
recovered from the furnace dust of galvanized
31 ..
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Chapter 7; Zinc Processing
steel making plants. Using pyrometallurgical
refinement techniques, the zinc can be recovered.
Once obtained, secondary zinc first undergoes a
separation process. Magnetic separation, sink-
float and hand sorting are usually used to remove
the zinc from unwanted components.
After separation, the zinc is melted with new scrap .
from brass plants, rolling zinc clippings or die
casting. The zinc is melted in a kettle, crucible,
reverberatory furnace or electric induction fur-
nace. Flux is used to trap impurities and produces
dross that is skimmed from the surface of the
molten zinc. The zinc is then either poured into
molds or sent to refiners. ;
High quality scrap from dross, diecastings, and
other zinc rich sources usually can be remelted
without further refinement. The recovered metal
can become galvanized brighten or alloy materials
in copper, aluminum, magnesium, iron, lead,
cadmium or tin production. Zinc helps to make
the metals stronger.
Medium to low grade skims, oxide dusts, ash and
residues containing zinc require more refinement
before melting. These may undergo reduction, or
distillation using pyrometallurgical processes. The
reduction upgrades the zinc for further processing
to reach the desired standards.
Pollution Sources and Prevention
Secondary zinc processing produces air emissions
and solid waste emissions. Air emissions come
from sweating and melting. The emissions include
particulates, zinc fumes, volatile metals, flux
fumes and stnoke, rubber, plastics and zinc scrap.
Incomplete combustion products are also emitted,
but are eliminated when passed through an after
burner. Particulates are collected in emissions
control equipment such as baghouses. The
particulates are often refined for the metals.
In distillation and oxidation processes, zinc
oxides in the form of dust are produced. The
oxides are collected in baghouse emissions control
systems.
Air emissions are also common from the pyromet-
allurgical processes. If simple remelting of the
zinc is required, the emissions are not high.
However, if the zinc requires reduction or other
refinement, emissions are likely. The lower the
quality of zinc scrap, the more air emission
produced in the process. Air emissions are usually
collected in ventilation systems. The emissions
control dust is usually sold as fertilizer or animal
feed.
Solid waste is present in the form of slag. The
slag from secondary zinc production usually
contains copper, aluminum, iron and lead. Slag.is
generated during pyrometallurgical processes and
may be hazardous.
Annotated
Bibliography
USEPA, Profile of The Nonferrous Metals
Industry. EPA310-R-95-010. This document
discusses uses, processes and pollution prevention
opportunities for the zinc processing industry.
32
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Glossary
Aluminum Dross; Dross is a by-product of
primary aluminum melting. It consists of alumi-
num metal and other impurities and is frequently
used in secondary aluminum production.
Attrition Sand Reclamation: Attrition sand
reclamation technology spins two streams of sand
in opposite directions in the presence of heat. The
combination of sand abrasion and binder combus-
tion free the sand particles from some binders.
Basic Oxide Furnace (BOF): Molten iron from
the blast furnace is sent to a basic oxide furnace,
which is used for the final refinement of the iron
into steel. High purity oxygen is blown into the
furnace and combusts carbon and silicon in the
molten iron. Alloy materials may be added to
enhance the characteristics of the steel.
Bayer Process: The process by which alumina is
extracted from bauxite ore in primary.aluminum
production.
Cast Making: The process used to make the
molds into which molten metal will be poured.
t . - - ... ' .
Coke: Coke is a solid carbon fuel and carbon
source used to melt and reduce iron ore
Cokemaking: The processess used to make coke.
The process begins with pulverized, bituminous
coal. The coal is fed into a coke oven which is
sealed and heated to..very high temperatures for
14 to 36 hours. After completion, the coke is
moved to quenching towers and stored until it is
needed. '
Continuous Casting: A siicessive series of
operations that used to produce metal pieces.
These operations often replace batch processes
which are done in stages, leaving some equipment
idle while others are in operation. .
'Cores: Cores are pieces that fit into the mold to
create detailed internal passages in the metal piece.
Cores mustbe strong and hard to .withstand the
molten metal, and collapsible so they can be
removed from the metal piece after it has cooled.
To obtain these properties, resins or chemical
binders are usually-added to sand mixtures.
Cupola Furnace: Cupola furnaces are tall,
cylindrical furnaces used to melt iron and ferro
alloys in foundry operations. Alternating layers of
metal and ferro alloys, coke, and limestone are fed
into the furnace from the top. :
Direct Iron Ore Smelting (DIGS): The DIGS
process is a cokeless irohmaking procedure.
Molten iron is produced from coal and previously
melted ores. In this process, coal and other ores
can produce enough heat to melt ore, replacing
coke completely (USEPA, 1995).
Dry Sand Reclamation: Dry sand reclamation
relies on mechanical and pneumatic scrubbers to
remove lumps and binders from sand. Mechani-
cal scrubbing moves each sand grain through a
sand-to-metal or sand-to-sand interface to remove
impurities. Pneumatic scrubbers use air to propel
sand between baffles. These scrubbers are .
particularly good for removing clay from molding
sands and binders in systems that are not baked.
Electric Arc Furnaces (EAFs): Electric arc
furnaces are often used in large steel foundries
and steel mills. The metal is charged into the
furnace, with additives to make recovery of slag
easier, and heat to melt the metal is produced with
an electric arc from three carbon ur granite
electrodes. Frequently mills producing steel with
EAF technology are called mini-mills. , '
Energy Optimizing Furnace (EOF): EOF was
developed to replace the electric arc and other
steelmaking furnaces. The EOF is an oxygen
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steelmaking process. Carbon and oxygen react to
preheat scrap metal, hot metal and/or pig iron.
Foundries: Foundries specialize in melting and
casting metal into desired shapes. Foundry
products are most often used in automobiles,
plumbing fixtures, train locomotives, airplanes and
as metal pieces in other kinds of equipment.
Green Sand Molds: Green sand molds, used in
85% of foundries, are a mixture of sand, clay,
carbonaceous material and water. The sand
provides the structure for the mold, the clay binds
the sand together and the carbonaceous materials
prevent rust. Water is used to activate the clay.
Hall-Heroult Process: The process by which
aluminum oxide'from the Bayer Process is
reduced to aluminum metal.
Hearth Furnaces: Hearth furnaces are used in
batch melting of non-ferrous metals. The hearth
can be heated by either electric or natural gas
methods. Hearth furnaces are used to produce
small quantities of metal, usually for art and
similar industries.
HiSmelt Process: The HISmelt process, named
after the HISmelt Corporation of Australia, is
another cokeless iron melting-process being tested.
In this process, ore fines and coal are manipulated
to melt iron ore.
Induction Furnaces: Induction furnaces are the
most widely used type of furnace for melting iron
and are increasingly popular for melting non-
ferrous metals (USEP A, 1992). They are popular
because they provide excellent metallurgical
control and are relatively pollution free.
Ingots: Convenient shapes into which newly
refined, molten metal is poured fpr storage. The
ingots are then remelted and cast into desired
molds.
Integrated Steel Mills: Integrated steel mills
produce steel by refining iron ore.' They produce
very high quality steel with well controlled chemi-
cal compositions.
Investment Molds: Investment molds are made
from ceramic.substances called refractories. They
are used in high precision metal castings.
Iron Carbide Production Plants: Iron carbide
production plants can be an alternative to the
Basic Oxide Furnace. These plants use iron
carbide, an iron ore that contains 6% carbon
rather than 1.5-1.8% of regular iron ore . The
additional carbon ignites in the presence of oxygen
and contributes heat to the iron melting process,
reducing energy requirements (Ritt, 1996).
Iron making: During ironmaking, iron ore, coke,
heated air and limestone or other fluxes are fed
into a blast furnace to produce molten iron that is
free from impurities.
Mini-Mills: Steel production plants that rely on
steelscrap as a base material rather than ore.
Products do not have the tight chemical
composistion of integrated plaints and have
narrower product lines.
Non-Recovery Coke Battery: In non-recovery
batteries, coke oven slag and other by-products
are sent to the.battery where they are combusted.
This technique consumes the by-products,
eliminating much of the air and water pollution.
Permanent Molds: Permanent molds are made
from metal or other resistant material. The molds
are used multiple time by industries, that produce
large numbers of the same piece.
Primary Metal Industries: Industries that
produce ferrous or non-ferrous metal products
from metal ore and / or scrap metal. Plants may
refine metals, cast molten metal into desired
shapes, or produce the inputs for the refining or
casting process.
Pulverized Coal Injections: Pulverized coal can
be substituted for coke at nearly a 1:1 ratio and
can replace 25 - 40% of coke traditionally used in
furnaces (USEPA, 1995). Pulverized coal injec-
tions are used to reduce pollution by reducing the
volume of coke production.
Refractory: Hard, heat resistant substances such
as fire clay, bricks or blocks. The refractory
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protects a furnace shell From abrasion, heat a'nd
oxidation.
Sand Reclamation: "the physical, chemical or
thermal treatment of a refractory aggregate to
allow its reuse without significantly lowering its
original useful properties as required.for the
. application involved" American Foundrymen's
Society. , ''
Sintering: S intering is a process in which solid
wastes are combined into a porous mass that can
then be added to the blast furnace. These wastes
include iron ore fines, pollution control dust, coke
breeze, water treatment plant sludge, and flux.
Shell Molds: Shell molds use chemically bonded
sand to make the molds into which molten metal
will be poured. . .
Slag: Impurities in the iron ore that have been
captured by limestone or other fluxes.
Steel: Steel is an alloy of iron usually containing
less than 1% carbon which is used most fre-
quently in the automotive and construction
industries or is cast into bars, strips, sheets, nails,
spikes, wire, rods or pipes as needed by the
intended user.
Thermal Sand Reclamation: Thermal reclama-
tion uses heat in a rotary kiln, multiple-hearth*
furnaces, or a fluidized bed to combust binders
and contaminants
Wet Sand Reclamation: Wet reclamation uses
water to remove sand binders. The process uses
on the different water solubilities of sand and
binders to separate the two. Clay bonded systems
work well with water reclamation processes
because the clays are very soluble in water.
Sodium silicate sand binders can also be removed
using wet reclamation. Other less soluble binders
may hot be as effective. After the sand is soaked
in a water bath it is dried and reused. .
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