Aluminum Recycling

229 Pages·2006·21.618 MB·English

by  Mark E. Schlesinger

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Aluminum
Recycling
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Aluminum
Recycling
Mark E. Schlesinger
University of Missouri-Rolla
Rolla, MO, U.S.A.
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CRC Press
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Library of Congress Cataloging-in-Publication Data
Schlesinger, Mark.
Aluminum recycling / Mark Schlesinger.
p. cm.
Includes bibliographical references and index.
ISBN 0-8493-9662-X (alk. paper)
1. Aluminum--Recycling. 2. Scrap metals--Recycling. 3. Extraction (Chemis-
try) 4. Aluminum--Metallurgy. I. Title.
TD812.5.A48S35 2006
673’.7220286--dc22 2006043686
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Preface
I wrote this book because I could not find one like it.
I am one of a vanishing breed in North America — professors who teach
extractive metallurgy. Extractive metallurgy used to be defined as the winning of
metals or alloys from naturally occurring ores, but over the past half-century this
has changed. Increasingly, the ore body is now found on the ground, rather than in
it. The majority of iron and steel produced in North America is now obtained from
recycled material, as are 40% of the copper, 80% of the lead — and more than 50%
of the aluminum. As a result, extractive metallurgy instruction now includes significant
exposure to recycling technology and the unique processes used to recover metal
from this strange type of “ore.”
Since most extractive metallurgy textbooks do not include recycling technology
in their discussion of “minerals processing,” and discuss molten-metal refining in a
way that excludes the refining of recycled metal, I went searching for a text that
focused on metals recycling. Although several conference proceedings on the subject
have been published, and some books (in particular Nijkerk and Dalmijn’s Handbook
of Recycling Techniques) have dealt with one or more parts of the recycling process,
there is no treatment of the overall process. This matters, because decisions made
during the collection and upgrading of scrap metals often have an impact on the
melting and refining strategies employed later. As a result, an integrated treatment
of the recycling process is needed.
This turned out to be particularly true for aluminum. Monographs dealing with
aluminum extractive metallurgy in general are uncommon and usually include no
more than a few pages on recycling. The last (and possibly the only) English-
language book to specifically address aluminum recycling was Anderson’s Second-
ary Aluminum, published in 1931. More than one-third of the aluminum produced
worldwide comes from recycled material, but the operations of the recycling industry
are not well known to the general public or to the metallurgical community in general.
This is not to say that information is lacking on aluminum recycling technology.
There are literally thousands of documents and Web pages pertaining to every aspect
of the industry from sources around the globe. Unfortunately, this information is as
scattered as its sources. Much of it has appeared in the annual Light Metals symposia
proceedings published each year by the American Minerals, Metals & Materials
Society of the American Institute of Mining, Metallurgical, and Petroleum Engineers
(TMS-AIME) and more in the proceedings of Australian and Canadian symposia.
Other sources include aluminum industry journals such as Aluminium and Light
Metal Age and recycling industry magazines such as Recycling Today and Scrap.
The burgeoning presence of industry associations, recycling firms, and equipment
suppliers on the Web is also an increasingly good source of information. However,
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this information has not been gathered in one place or synthesized to show the entire
picture. This book is an attempt to produce that picture.
Since the recycling of aluminum is a type of extractive metallurgy, the structure
of this book follows the traditional extractive metallurgy sequence. This begins with
a description of the ore body and the type of minerals (aluminum alloys) it contains,
the mining technology and infrastructure used to obtain it, the mineral-processing
equipment used to beneficiate it, initial thermal processing to remove coatings and
other metals, melting furnaces and practice, and refining technology. Additional
chapters introduce other important elements of the story: the economics of scrap
recycling, the structure of the recycling industry, and the ongoing effort to make
aluminum recycling safer and more environmentally benign. For those interested in
more in-depth information about the material in a particular chapter, a short list of
recommended additional sources is provided.
I owe a tremendous debt to two individuals who shared my vision and were
willing to share their knowledge and expertise to help me get it right. Don Stewart
of Alcoa and Ray Peterson of Aleris International spent much of their time straight-
ening me out on the differences between what I had read and what I should know,
and the book reflects their efforts. David Roth and the staff at Altek/MDY subse-
quently added their expertise to the editing enterprise and found several more
“whoppers” to eliminate. Greg Gelles of the economics department at the University
of Missouri–Rolla graciously agreed to contribute the chapter on recycling economics.
Others who lent their time to looking over parts of the material include Mike
Skillingberg of the Aluminum Association, Adam Gesing of HVSC, and John Green.
Their assistance has helped turn my sow’s ear of a manuscript into Naugahyde, if
not a silk purse.
There are others who helped make this book a reality as well. The staffs of the
University of Missouri–Rolla and Linda Hall Libraries were invaluable in obtaining
information for me from obscure and distant sources. Jason Harris redrew many of
the figures, reducing my dependence on the scanner. Finally, my appreciation goes
out to all the organizations that allowed me to reproduce their illustrations, either
on-line or in print. If a picture is worth a thousand words, their permission is worth
much of this book.
Aluminum recycling is a dynamic industry, with constantly changing technology
and business strategies. As a result, judgments about the advantages and disadvan-
tages of various equipment and operating methods written months ago may be invalid
by the time you see this. In some cases, I may have made a judgment that was wrong
under any circumstances. In any case, any errors you may see are my responsibility.
The number of such errors is undoubtedly greater than I would desire; my hope is
that it is fewer than it might have been.
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About the Author
Mark E. Schlesinger is professor of metallurgical engineering at the University of
Missouri–Rolla, where he has been since 1990. His teaching and research interests
are centered around the production of metals and their alloys, in particular their
extraction from ores and secondary materials. His previous books include Mass and
Energy Balances in Materials Engineering and the coauthored Extractive Metallurgy
of Copper (4th ed.).
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Contributor
Gregory M. Gelles
University of Missouri–Rolla
Rolla, Missouri
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Table of Contents
Chapter 1 Introduction..........................................................................................1
A Brief History of Aluminum Recycling..................................................................2
Advantages (and Challenges) of Recycling..............................................................4
Recommended Reading.............................................................................................8
References..................................................................................................................8
Chapter 2 The Ore Body.......................................................................................9
The Wrought Aluminum Alloy System....................................................................9
The Cast Aluminum Alloy System.........................................................................14
The Product Mix......................................................................................................18
Recommended Reading...........................................................................................23
References................................................................................................................23
Chapter 3 Scrap Collection.................................................................................25
The Materials Life Cycle........................................................................................25
Scrap Collection Practice........................................................................................29
New Scrap......................................................................................................29
Old Scrap........................................................................................................30
Transportation....................................................................................31
Building..............................................................................................32
Packaging...........................................................................................32
Wire and Cable..................................................................................37
Recommended Reading...........................................................................................37
References................................................................................................................37
Chapter 4 Aluminum Recycling Economics......................................................41
History of Aluminum Production............................................................................41
Production of Primary Aluminum...........................................................................42
Uses..........................................................................................................................43
Aluminum Recycling...............................................................................................43
Recycling of Used Aluminum Beverage Cans.......................................................45
Aluminum Recycling: An Economic Perspective...................................................48
Conclusion...............................................................................................................51
Recommended Reading...........................................................................................53
References................................................................................................................53
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Chapter 5 BeneficiationTechnology...................................................................55
Comminution...........................................................................................................55
Separation................................................................................................................62
Hand Sorting..................................................................................................62
Air Classification............................................................................................63
Magnetic Separation......................................................................................65
Eddy-Current Sorting.....................................................................................67
Heavy-Media Separation (HMS)...................................................................71
The Alloy Separation Problem................................................................................75
Thermal Processing.................................................................................................78
Decoating.......................................................................................................78
Pyrolysis of Composite Packaging................................................................85
Paint Removal................................................................................................85
Partial Melting................................................................................................86
Sweat Melting................................................................................................86
Agglomeration.........................................................................................................87
Balers ............................................................................................................87
Briquetting......................................................................................................88
Recommended Reading...........................................................................................89
References................................................................................................................90
Chapter 6 Beneficiation Practice........................................................................93
New Scrap................................................................................................................93
Municipal Solid Waste...........................................................................................100
UBCs and Other Packaging..................................................................................102
Automotive Scrap..................................................................................................105
Electrical and Electronic Scrap.............................................................................107
Recommended Reading.........................................................................................111
References..............................................................................................................111
Chapter 7 Melting Furnace Fundamentals.......................................................113
Heat-Transfer Kinetics...........................................................................................113
Combustion............................................................................................................115
The Chemistry of Fluxing.....................................................................................117
Refractory Interactions..........................................................................................118
Recommended Reading.........................................................................................120
References..............................................................................................................120
Chapter 8 Melting Furnace Parts and Accessories...........................................123
Burners...................................................................................................................123
Use of Enriched Air.....................................................................................123
Regeneration.................................................................................................125
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Flame Manipulation.....................................................................................126
Baffles..........................................................................................................126
Recuperators..........................................................................................................127
Refractories............................................................................................................128
Stirring...................................................................................................................129
Environmental Equipment.....................................................................................133
Recommended Reading.........................................................................................135
References..............................................................................................................135
Chapter 9 Fossil-Fuel Furnaces........................................................................137
Single-Chamber Designs.......................................................................................137
Multiple-Chamber Furnaces..................................................................................141
Small-Volume Melters...........................................................................................145
Rotary Furnaces.....................................................................................................145
Holding and Dosing Furnaces...............................................................................146
Recommended Reading.........................................................................................147
References..............................................................................................................147
Chapter 10 Electric Furnace Melting.................................................................151
Induction Furnaces................................................................................................152
Coreless Furnaces........................................................................................152
Channel Furnaces.........................................................................................158
Resistance Furnaces...............................................................................................160
Recommended Reading.........................................................................................161
References..............................................................................................................161
Chapter 11 The Recycling Industry....................................................................163
Who Recycles Aluminum?....................................................................................163
Influences on the Aluminum Recycling Industry.................................................165
The Impact of Government..........................................................................165
The Impact of Demand................................................................................166
The Impact of Cost......................................................................................167
The Impact of Technology...........................................................................168
Recommended Reading.........................................................................................168
References..............................................................................................................169
Chapter 12 Metal Refining and Purification.......................................................171
Common Impurities in Molten Aluminum...........................................................171
Hydrogen......................................................................................................171
Reactive Metals............................................................................................173
Inclusions.....................................................................................................174
The Fourth Class of Impurities....................................................................176
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