&EPA
United States
Environmental Protection
Agency
Office of Research and
Development
Washington, DC 20460
EPA/625/R-94/004
September 1994
Handbook
Recycling and Reuse of
Material Found on
Superfund Sites
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EPA/625/R-94/004
September 1994
Handbook
Recycling and Reuse of
Material Found on Superfund Sites
Center for Environmental Research Information
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
^Printed on Recycled Paper
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Notice
The preparation of this document has been funded wholly or in part by the U.S. Environmental
Protection Agency (EPA). This document has been reviewed in accordance with EPAs peer and
administrative review policies and approved for publication. Mention of trade names or commercial
products does not constitute endorsement or recommendation for use.
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Contents
Page
Figures v
Tables vii
Abbreviations viii
Acknowledgments ix
Chapter 1 Introduction 1
1.1 Purpose 1
1.2 Impetus for Recycling and Reuse 1
1.3 Scope 1
1.4 Organization 2
Chapter 2 Compilation of Technologies and Applications 3
Chapter 3 Description of Recycling Technologies 11
3.1 Distillation 11
3.2 Energy Recovery (General) 12
3.3 Energy Recovery (Cement Kilns) 13
3.4 Decanting 16
3.5 Thermal Desorption 17
3.6 Solvent Extraction 19
3.7 Use as Construction Material 20
3.8 In Situ Vacuum Extraction 21
3.9 Pumping and Recovery 22
3.10 Freeze-Crystallization 23
3.11 Propellant and Explosive Extraction 24
3.12 Propellant and Explosive Reuse 26
3.13 Propellant and Explosive Conversion to Basic Chemicals 27
3.14 Re-Extrusion of Thermoplastics 28
3.15 Chemolysis 29
3.16 Size Reduction and Reutilization of Plastic and Rubber Wastes 30
3.17 Thermolysis 32
3.18 Chemical Precipitation 33
3.19 Ion Exchange 34
3.20 Liquid Ion Exchange 35
3.21 Reverse Osmosis 37
3.22 Diffusion Dialysis 38
3.23 Electrodialysis 39
3.24 Evaporation 40
3.25 Mercury Bioreduction 41
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Contents (continued)
Page
3.26 Amalgamation 42
3.27 Cementation 42
3.28 Electrowinning 43
3.29 Chemical Leaching 44
3.30 Vitrification 46
3.31 Pyrometallurgical Metal Recovery 47
3.32 Cement Raw Materials 49
3.33 Physical Separation 51
3.34 Mercury Roasting and Retorting 51
3.35 Mercury Distillation 53
3.36 Decontamination and Disassembly 53
3.37 Recycling Transformers and Ballasts 55
3.38 References 56
Chapter 4 Product Quality Specifications 63
4.1 Feed Material to Petroleum Refining 63
4.2 Organic Chemicals 63
4.3 Thermoplastic Particulate 64
4.4 Rubber Particulate 64
4.5 Fuels for Energy Recovery 64
4.6 Metals for Reuse 65
4.7 Metal-Containing Sludge or Slag for Feed to Secondary Smelters 65
4.8 Waste Feed to Hydrometallurgical Processing 66
4.9 High-Value Ceramic Products 66
4.10 Inorganic Feed to Cement Kilns 67
4.11 Cement Substitute 67
4.12 Aggregate and Bulk Construction Materials 68
4.13 References 69
Chapter 5 Case Studies 71
5.1 Recycling Spent Abrasive Blasting Media Into Asphalt Concrete 71
5.2 Recycling Spent Abrasive Blasting Media Into Portland Cement 73
5.3 Recovering Lead Particulate from Small-Arms Practice Ranges 75
5.4 Processing of Superfund Wastes in a Secondary Lead Smelter 78
5.5 Treatment Train for Recovery of Petroleum From Oily Sludge 79
5.6 Solvent Recovery by Onsite Distillation 80
5.7 Thermal Desorption To Treat and Reuse Oily Sand 82
5.8 Pumping To Recover Nonaqueous-Phase Liquids 82
5.9 References 83
IV
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Figures
Figure Page
2-1 Recycling technology options at Superfund sites 9
3-1 Batch distillation 12
3-2 Energy recovery application 13
3-3 Energy recovery in a cement kiln 14
3-4 Example of centrifugal decanting 16
3-5 Example of the thermal desorption process 18
3-6 Example of the solvent extraction process 19
3-7 Construction material loader 20
3-8 Example of a vacuum extraction system 21
3-9 Example of a pump and recover system 22
3-10 Example of the freeze-crystallization process 23
3-11 Munition disassembly steps 24
3-12 The ammonium perchlorate reclamation process 27
3-13 The white phosphorus reclamation process 27
3-14 Example of an extruder 29
3-15 Example of a chemolysis reaction 29
3-16 Example of a plastic shredding operation 30
3-17 Example of the pyrolysis process 32
3-18 Solubility of metal ions in equilibrium with a hydroxide precipitate 33
3-19 Example of an ion exchange operation 34
3-20 Liquid ion exchange contacting cell 36
3-21 Example of the reverse osmosis process 37
3-22 Example of a diffusion dialysis cell 38
3-23 Example of an electrodialysis cell 39
3-24 Example of the evaporation process 40
3-25 System to study geochemical cycling of mercury 41
3-26 Example of a mercury amalgamation cell 42
3-27 Example of a cementation cell 43
3-28 Example of an electrowinning cell 43
3-29 Example of the chemical leaching process 45
3-30 Example of the vitrification process 47
3-31 Examples of pyrometallurgical processes 48
3-32 Example of a cement kiln operation 50
3-33 Cross section showing particle distribution in a spiral concentrator channel 51
3-34 Example of the mercury retorting process 52
3-35 Example of the mercury distillation process 53
3-36 Example of decontamination apparatus 54
3-37 Example of a transformer 55
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Figures (continued)
Figure Page
5-1 Abrasive blasting material and the cement-making process 74
5-2 Recovering bullet fragments and reusing berm soil at small-arms practice ranges 76
5-3 Processing lead wastes in a secondary smelter 78
5-4 Vacuum vaporizer for onsite solvent distillation 81
5-5 Coal tar recovery system 83
VI
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Tables
Table Page
2-1 Waste Types and Applicable Recycling Technologies 3
2-2 Summary of Recycling Technology Characteristics 5
3-1 Wastes Suitable for Treatment in a Cement Kiln 15
3-2 Particle Separation Techniques 52
4-1 Approximate Feed Concentration Requirements for Secondary Smelters 62
5-1 Particle Size Range for Application of Separation Techniques 76
5-2 U.S. Secondary Lead Smelters as of November 1993 77
VII
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Abbreviations
AASHTO American Association of State Highway
and Transportation Officials
ABM abrasive blasting media
AP ammonium perchlorate
API American Petroleum Institute
ARRA Asphalt Recycling and Reclaiming
Association
ASTM American Society for Testing and
Materials
BF blast furnace
BMC bulk molding compound
CERI Center for Environmental Research
Information
DBP dibutyl phthalate
DC direct current
DNAPL dense nonaqueous-phase liquid
DNT dinitrotoluene
ED electrodialysis
EDTA ethylenediaminetetraacetic acid
EERC Energy and Environmental Research
Center
EPA U.S. Environmental Protection Agency
ERG Eastern Research Group, Inc.
FHWA Federal Highway Administration
HEX high-blast explosive
HOPE high-density polyethylene
HMX high-melting explosive
HWF hazardous waste fuel
LDPE low-density polyethylene
LIX liquid ion exchange
LNAPL light nonaqueous-phase liquid
MC methylene chloride
MEK methyl ethyl ketone
NAPL nonaqueous-phase liquid
MAS Naval Air Station
NC nitrocellulose
NCP National Contingency Plan
NEESA Naval Energy and Environmental Support
Activity
NG nitroglycerine
PAH polycyclic aromatic hydrocarbon
PC polymer concrete
PCB polychlorinated biphenyl
PE polyethylene
PET polyethylene terephthalate
PM polymer mortar
PP polypropylene
PS polystyrene
PVC polyvinyl chloride
RCRA Resource Conservation and Recovery Act
RDX research department explosive
REV reverberatory furnace
RIM reaction injection molding
RO reverse osmosis
SMC sheet molding compound
SRK short rotary kiln
S/S stabilization/solidification
SSU standard Saybolt unit(s)
STLC Soluble Threshold Limit Concentration
SVOC semivolatile organic compound
TCLP Toxicity Characteristic Leaching
Procedure
tetryl 2,4,6-tetranitro-N-methylaniline
TNT trinitrotoluene
TRI Toxics Release Inventory
TSCA Toxic Substances Control Act
VOC volatile organic compound
WET Waste Extraction Test
VIM
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A cknowledgments
This document provides assistance in identifying potential recycling technologies for a wide variety
of contaminants and matrices. Personnel at Superfund and Resource Conservation and Recovery
Act (RCRA) Corrective Action sites face the challenge of selecting remedial options for wastes that
contain organic and inorganic contaminants.
Recycling contaminated materials may be an efficient method of waste management at contami-
nated sites. Recycling technology converts materials that otherwise would require disposal into
useful commodities. The recycling process can either remove contaminants from the matrix and
collect them in some useful form or can modify the contaminant and matrix to yield a new product
with desirable properties.
Thermal, physical, chemical, and biological mechanisms for waste recycling have been developed
or are being studied at the laboratory scale. This document is designed to increase awareness
among Superfund or RCRA site personnel of the capabilities and limitations of a wide range of
recycling technologies. The handbook describes technologies for recycling organic and inorganic
contaminants in solid and liquid matrices. It also discusses the fundamental principles, maturity,
applications, advantages, limitations, and operating features of commercially available and emerg-
ing recycling technologies. A summary and two summary tables are provided to allow rapid
identification of candidate technologies.
This document was submitted in partial fulfillment of Contract 68-CO-0068 by Eastern Research
Group, Inc. (ERG), Lexington, Massachusetts, under the sponsorship of the U.S. Environmental
Protection Agency (EPA). This document was prepared for EPAs Office of Research and Develop-
ment, Center for Environmental Research Information (CERI), Cincinnati, Ohio. Edwin Earth of
CERI served as the Project Director and provided technical direction and review.
This document was written by personnel at the Battelle Memorial Institute, Columbus, Ohio. The
principal authors were Lawrence Smith and Jeffrey Means. Other authors were Karen Basinger,
Arun Gavaskar, Jody Jones, Prabhat Krishnaswamy, Manfred Luttinger, Bruce Monzyk, Mark
Paisley, and Prakash Palepu. Illustrations were prepared by Loretta Bahn and Erin Sherer. Technical
editing was provided by Lynn Copley-Graves. Paul Queneau of Hazen Research, Inc., provided
advice and consultation on methods for recycling metal-containing wastes. ERG provided project
management, editing, and document preparation support under the direction of Heidi Schultz.
The following individuals peer reviewed this manual:
Ruth Bleyler
Hazardous Waste Division, EPA Region 1
John Blanchard
Office of Emergency and Remedial Response, EPA Headquarters
Albert Kupiec
AWD Technologies
Sally Mansur
Pollution Prevention Division, EPA Region 1
Raymond Regan
Pennsylvania State University
Debbie Sievers
Waste Division, EPA Region 5
IX
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Chapter 1
Introduction
1.1 Purpose
The intent of this handbook is to assist pollution preven-
tion efforts by encouraging recycling and reuse of
wastes found on Superfund or Resource Conservation
and Recovery Act (RCRA) Corrective Action sites. This
handbook outlines specific technologies for recycling
and reuse of materials that require remediation at con-
taminated sites. Case studies within the handbook
document applications of these technologies to real-
world conditions.
The main users of this handbook are expected to be
personnel responsible for remediation of Superfund
sites. Other potential users are personnel involved in
RCRA corrective actions and environmental staff at
facilities that generate industrial wastes.
This handbook is intended to increase the awareness of
recycling options among personnel responsible for site
cleanup by pointing out various technology options. The
technologies in this handbook are described in generic
terms; vendor-specific implementations of the technolo-
gies are not discussed due to the summary nature of the
document. The document does not discuss the detailed
costs or regulatory issues (except in the case studies in
Section 5), as economics and regulations are complex,
change rapidly, are location specific, and thus cannot be
covered in a summary document. The economics and
regulatory compliance of a technology option must be
determined by site personnel based on local conditions.
This document also does not cover risk evaluation to
human health and the environment, which needs to be
a consideration when remediating a site.
The general concept of recycling and reuse is straight-
forwardto find better ways to handle wastes other than
depositing them in waste disposal sites. In practice,
recycling takes on a variety of connotations, depending
on the context and the user. For example, RCRA has
specific regulatory definitions for recycling activities.
Many publications make distinctions among terms such
as reclamation, recovery, and recycling based on the
processing required and the planned use. In this docu-
ment, recycling and reuse are applied as general terms
to indicate a range of activities, from direct reuse in a
similar application to processing to produce a raw ma-
terial for general use.
1.2 Impetus for Recycling and Reuse
Recent Congressional legislation and U.S. Environ-
mental Protection Agency (EPA) policy advocate pollu-
tion prevention, which includes environmentally sound
recycling.
According to the National Contingency Plan (NCP) Pre-
amble, Section 300.430(a)(1), EPA intends to focus
available resources on selection of protective remedies
that provide reliable, effective response over the long
term. Recycling technologies already offer methods to
remediate contaminants and minimize the amount of
waste created. By creating a small volume of residuals
that require subsequent management, the cost effec-
tiveness of a remedy may increase.
The NCP Preamble mandate for remedies that protect
human health and the environment can be accom-
plished through a number of means, including recycling.
The final rule indicates that alternatives shall be devel-
oped to protect human health and the environment by
recycling waste or by eliminating, reducing, and control-
ling risks posed at each pathway at a site. The emphasis
is clear: recycling is an approved means of site reme-
diation.
Another criterion for remedy selection listed in the NCP
is "reduction of toxicity, mobility, or volume through treat-
ment." The regulation states that project managers
should considerthe degree to which alternatives employ
recycling or treatment that reduces toxicity, mobility, or
volume. Here again, emphasis is placed on considera-
tion of remedies that use waste reduction to reduce the
risks that a site poses.
1.3 Scope
This handbook outlines recycling and reuse approaches
for a wide range of waste types. Both organic and
inorganic contaminants in solid and liquid media are
considered.
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The following wastes containing mainly organic con-
taminants are discussed:
Organic liquids
Organic soils, sludges, and sediments
Petroleum-contaminated soils, sludges, and sediments
Solvent-contaminated soils, sludges, and sediments
Propellants and explosives
Rubber goods (e.g., tires and conveyor belts)
Polymers
Wire stripping fluff, plastic fluff, and paint debris
The following wastes containing mainly inorganic con-
taminants are discussed:
Metal-containing solutions
Metal-containing soils, sludges, and sediments
Slags
Mine tailings
Ashes (bottom and fly)
Spent abrasive blasting media
Foundry sands
Batteries
Mercury-containing materials
In addition, the following miscellaneous wastes are
covered:
Chemical tanks and piping
Structures
Demolition debris
Transformers and ballasts
This handbook does not cover wastes with established
recycling markets because information on recycling
these materials is available from other sources. Such
wastes include:
Municipal solid wastes, including nonleaded clear
glass, white goods (e.g., refrigerators, washers, and
dryers), automobiles, paper goods, and aluminum
cans.
Pure metals, including iron, steel, and ferrous alloys;
copper and copper alloys; nickel and nickel alloys;
and precious metals.
Mixed metal wastes with over 40 percent metal
content.
Iron and steel blast furnace slags.
1.4 Organization
The body of this handbook starts, in Chapter 2, with an
illustration of recycling technology options and two sum-
mary tables to help the user quickly identify candidate
recycling technologies for waste materials. The illustra-
tion presents the wide variety of waste types present at
Superfund and RCRA Corrective Action sites, and
shows how recycling and reuse options can be applied
to these wastes. The illustration also provides a quick
overview of the recycling potential of various waste
materials. The first summary table lists wastes and
shows possible recycling technologies for each waste.
The second summary table outlines some of the key
features of each technology.
The technologies shown in the second summary table
are described in Section 3. Process description, sche-
matic illustration, advantages, disadvantages or limita-
tions, and operating features are summarized for each
technology. These brief outlines familiarize the user with
the technology. A listing of reference material for each
technology provides sources of detailed information.
Section 4 reviews the general technical specifications
(but not legal or regulatory requirements) of some typical
end users of waste materials. The section describes the
product characteristics and input material specifications
for the more common users of wastes. The potential
end-user of materials from a Superfund site will have a
high level of concern about toxic contaminants and the
associated potential for adverse health and safety ef-
fects or increased liability. There are few standards for
recycled materials. Working with end-users to under-
stand their process requirements and concerns is es-
sential for developing workable specifications.
The application of recycling to real-world situations is
examined through case studies. Section 5 describes
several specific large-scale or commercial applications
of recycling to waste materials. Site and waste type,
technology application, recycling benefits, economics,
and limitations are discussed for each case study.
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Chapter 2
Compilation of Technologies and Applications
This section summarizes the wastes and technologies
described in the following sections. The overall scope of
the handbook is illustrated in Figure 2-1 (see page 9).
The reader is encouraged to use Figure 2-1 as a starting
point to identify technologies that are suitable for various
waste materials. For situations that contain liquid
wastes, such as lagoons, the reader should refer to the
liquid waste types (shown as tankage) to identify the
applicable technologies. The wastes and applicable re-
cycling technologies are summarized in Table 2-1. The
recycling technology characteristics are summarized in
Table 2-2. The figure and summary tables will help users
to quickly identify technology candidates applicable to
wastes at their sites.
Table 2-1. Waste Types and Applicable Recycling Technologies
Waste Type
Applicable Recycling
Technologies*
Wastes containing mainly organic contaminants
Liquid organic solvent
Liquid petroleum products
Solvent-contaminated
soils, sludges, and
sediments
Petroleum-contaminated
soils, sludges, and
sediments
Organic sludges
Vadose zone volatile
organic compounds
(VOCs)
Nonaqueous-phase
liquids (NAPLs)
Dissolved organics
Propellants and
explosives
Lead/acid battery cases
Distillation (3.1)
Energy recovery (3.2 and 3.3)
Decanting (3.4)
Distillation (3.1)
Energy recovery (3.2 and 3.3)
Decanting (3.4)
Energy recovery (3.2 and 3.3)
Decanting (3.4)
Thermal desorption (3.5)
Solvent extraction (3.6)
Energy recovery (3.2 and 3.3)
Decanting (3.4)
Thermal desorption (3.5)
Solvent extraction (3.6)
Use as asphalt aggregate (3.7)
Energy recovery (3.2 and 3.3)
Decanting (3.4)
Thermal desorption (3.5)
Solvent extraction (3.6)
In situ vacuum extraction (3.8)
Pump and recover (3.9)
> Freeze-crystallization (3.10)
> Energy recovery (3.2 and 3.3)
> Ingredient extraction, reuse, and
conversion to basic chemicals
(3.11-3.13)
1 Energy recovery (ebonite or
polyethylene) (3.2 and 3.3)
> Reuse as thermoplastic
(polyethylene) (3.14-3.17)
Waste Type
Applicable Recycling
Technologies*
Wastes containing mainly organic contaminants (continued)
Rubber goods
(e.g., tires and conveyor
belts)
Liquid monomers
Solid polymers
(low solids content)
Solid polymers (high
solids content, e.g.,
sheet molding
compounds and bulk
molding compounds
[CaCO3, glass fiber, and
other inorganic filler in
the 70% range])
Paint residue and paint
removal debris
Plastic fluff
> Energy recovery (3.2 and 3.3)
> Size reduction and reuse (3.16)
> Thermolysis (thermal conversion to
basic hydrocarbon products) (3.17)
> Distillation (3.1)
> Energy recovery (3.2 and 3.3)
> Energy recovery (3.2 and 3.3)
> Reuse as construction material
(3.7)
< Re-extrusion (thermoplastics) (3.14)
> Chemolysis (chemical conversion
to monomers and oligomers) (3.15)
> Size reduction and reuse (3.16)
> Thermolysis (thermal conversion to
basic hydrocarbon products) (3.17)
> Reuse as construction material
(3.7)
> Size reduction and reuse (3.16)
1 Thermolysis (thermal conversion to
basic hydrocarbon products) (3.17)
Energy recovery (3.2 and 3.3)
Thermolysis (thermal conversion to
basic hydrocarbon products) (3.17)
Energy recovery (3.2 and 3.3)
Thermolysis (thermal conversion to
basic hydrocarbon products) (3.17)
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Table 2-1. Waste Types and Applicable Recycling Technologies (continued)
Waste Type
Applicable Recycling
Technologies*
Waste Type
Applicable Recycling
Technologies*
Wastes containing mainly inorganic contaminants
Low-concentration
metals-containing
solutions
High-concentration
metals-containing
solutions
Low-concentration
metals-containing soils,
sludges, and sediments
High-concentration
metals-containing soils,
sludges, and sediments
Silicate or oxide slags
containing zinc,
cadmium, or lead
Low-concentration
metals-containing
silicate/oxide slag, ash,
dust, or fume
High-concentration
metals-containing silicate
or oxide slag, ash, dust,
or fume
Abrasive blasting media
Foundry sand
Chemical precipitation (3.18)
Ion exchange (3.19)
Liquid ion exchange (3.20)
Reverse osmosis (3.21)
. Dialysis (3.22-3.23)
Evaporation (3.24)
Bioreduction (3.25)
Freeze-crystallization (3.10)
Chemical precipitation (3.18)
Liquid ion exchange (3.20)
Evaporation (3.24)
Amalgamation (3.26)
Cementation (3.27)
Electrowinning (3.28)
Chemical leaching (3.29)
Vitrification (3.30)
Chemical leaching (3.29)
Vitrification (3.30)
Pyrometallurgical processing (3.31)
Chemical leaching (3.29)
Pyrometallurgical processing (oxide
volatilization in a waelz kiln, flame
reactor, or plasma furnace) (3.31)
Use as construction material (3.7)
Vitrification (3.30)
Cement raw materials (3.32)
Chemical leaching (3.29)
Pyrometallurgical processing
(general) (3.31)
Use as construction material (3.7)
Vitrification (3.30)
Cement raw materials (3.32)
Physical separation (3.33)
Use as construction material (3.7)
Vitrification (3.30)
Cement raw materials (3.32)
Physical separation (3.33)
Wastes containing mainly inorganic contaminants (continued)
Firing range soil Chemical leaching (3.29)
Pyrometallurgical processing (lead
smelter) (3.31)
Physical separation (3.33)
Lead/acid battery
internals
Nickel/cadmium batteries
Mercury-containing
batteries
Mercury metal
Mercury-containing soils,
sludges, and sediments
Mercury-containing water
Miscellaneous wastes
Chemical tanks, pipes,
and architectural
materials
Nonmetal structures and
demolition debris
Wood debris
Transformers and
ballasts
Chemical leaching (3.29)
Pyrometallurgical processing (lead
smelter) (3.31)
Physical separation (3.33)
Chemical leaching (3.29)
Pyrometallurgical processing (3.31)
Chemical leaching (3.29)
Roast and retort (3.34)
Mercury distillation (3.35)
Bioreduction (3.25)
Chemical leaching (3.29)
Physical separation (3.33)
Roast and retort (3.34)
Bioreduction (3.25)
Decontamination and disassembly
(3.36)
Bulk metal reuse (3.36)
Use as construction material (3.7)
Decontamination and disassembly
(3.36)
Energy recovery (3.2)
PCB flush and treat (dielectric)
(3.37)
Metal recovery (electrical device)
(3.37)
' Numbers in parentheses refer to the section(s) of this handbook
where the technology is discussed.
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Table 2-2. Summary of Recycling Technology Characteristics*
Technology Contaminant Media
End Use
Limitations
Organic liquid processing
Distillation (3.1)
Energy recovery
(3.2 and 3.3)
Decanting (3.4)
Organic solvents,
petroleum, and
monomers
Organic solvents,
petroleum, monomers,
and wood debris
Organic solvents,
petroleum
Flowable liquids
Flowable liquids
Two immiscible liquid
phases
Organic product
Heating value in
boiler, furnace, or
cement kiln
Organic product
Difference in boiling points
Impurities
Energy content
Ash content
Impurities
May produce toxic byproducts
Waste moisture content
Explosive hazard
Typically produces a mixed
product
Fluid density
Impurities
Organic solids, soil, sludge, and sediment processing
Energy recovery
(3.2 and 3.3)
Decanting (3.4)
Thermal desorption
(3.5)
Solvent extraction (3.6)
Soil vapor extraction
Solvents, petroleum,
propellants and
explosives, thermoplastic
or thermosetting
polymers, rubber goods,
paint debris, or plastic
fluff
Solvent- or petroleum-
contaminated soils,
sludges, or sediments,
or organic sludges
Volatile or semivolatile
organics
Volatile or semivolatile
organics
Volatile organics
Flowable soils, sludges,
sediments, or
particulates
Soils, sludges, or
sediments
Soils, sludges, or
sediments
Soils, sludges, or
sediments
In situ vadose zone soils
Heating value in
boiler, furnace, or
cement kiln
Organic liquid
Organic liquid
Organic liquid
Organic product
Energy content
Ash content
Impurities
May produce toxic byproducts
Waste moisture content
Explosive hazard
Typically produces a mixed
product
Fluid density
Impurities
Typically produces a mixed
organic product
Typically produces a mixed
organic product
Extraction/collection efficiency
(3.8)
Pump and recover (3.9) Nonaqueous-phase
liquids (NAPLs)
In situ soils
Organic product
Propellant and
explosive extraction
(3.11)
Propellant and
explosive reuse (3.12)
Propellant and Energetic materials
explosive conversion to
basic chemicals (3.13)
Energetic materials
Energetic materials
Munitions, rockets, etc. Energetic materials
1 Typically produces a mixed
organic product
Extraction/collection efficiency
Typically produces a mixed
organic product
Pretreatment step for reuse or
chemical recovery
Difficult to extract safely
Re-extrusion (3.14)
Chemolysis (3.15)
Size reduction and
reuse (3.16)
Thermolysis (3.17)
Thermoplastic
Polymers
Thermoplastic,
thermosetting polymer,
or rubber goods
Thermoplastic,
thermosetting polymer,
paint debris, plastic fluff,
or rubber goods
Munitions, rockets, etc.
Munitions, rockets, etc.
Solids with low
concentrations of inert
materials
Solids with low
concentrations of inert
materials
Solids
Solids
Energetic materials Difficult to extract safely
Industrial chemicals
(e.g., ammonium
perchlorate, nitrates,
phosphates)
Plastic products
Organic chemicals
Aggregate, bulk
fillers, or filter media
Liquid or gaseous
hydrocarbon
feedstocks
Difficult to extract safely
Most applicable to single
polymer type
Color and opacity
Impurities
Most applicable to single
polymer types
Type of polymer
Inorganic filler or
reinforcement content
Difficult to extract safely
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Table 2-2. Summary of Recycling Technology Characteristics (continued)
Technology Contaminant Media End Use
Limitations
Water processing
Freeze-crystallization
(3.10)
Precipitation (3.18)
Ion exchange (3.19)
Liquid ion exchange
(3.20)
Metals or dissolved
organics
Metals
Metals
Metals
Reverse osmosis (3.21) Metals
Diffusion dialysis (3.22) Metals
Electrodialysis (3.23) Metals
Evaporation (3.24) Metals
Bioreduction (3.25) Mercury
Amalgamation (3.26) Mercury
Cementation (3.27) Metals
Electrowinning (3.28) Metals
Water
Water
Water
Water
Water
Water
Water
Water
Water
Water
Water
Water
Recovery of metals,
metal salts, or
organics
Recovery of metals
or metal salts
Recovery of metals
or metal salts
Recovery of metals,
metal salts, or metal
concentrates
Recovery of metals
or metal salts
Recovery of metals
or metal salts
Recovery of metals
or metal salts
Recovery of metals
or metal salts
Recovery of mercury
Recovery of mercury
Recovery of metals
Recovery of metals
1 Requires low concentrations
of suspended solids
Typically requires additional
processing to yield marketable
product
Typically requires additional
processing to yield marketable
product
Requires low concentrations
of suspended solids and oil
and grease
Requires low concentrations
of suspended solids
Typically requires additional
processing to yield marketable
product
Requires low concentrations
of suspended solids and oil
and grease
Requires low concentrations
of suspended solids and oil
and grease
Requires low concentrations
of suspended solids and oil
and grease
Energy-intensive process
Requires low concentrations
of suspended solids and oil
and grease
Mercury must be condensed
and refined to produce a
marketable product
No net reduction in metal
content
Mercury/metal amalgam must
be retorted to obtain mercury
metal
Requires low-cost source of
less-noble metal
No net reduction in metal
content
-------
Table 2-2. Summary of Recycling Technology Characteristics (continued)
Technology
Contaminant
Media
End Use
Limitations
Metal-containing soil, sludge, sediment, slag, or other solid processing
Metals or inorganics
Use as construction
material (3.7)
Bioreduction (3.25)
Chemical leaching
(3.29)
Vitrification (3.30)
Pyrometallurgical
processing (3.31)
Feed to cement kiln
(3.32)
Physical separation
(3.33)
Mercury
Metals
Metals or inorganics
Metals, particularly
cadmium, chromium,
lead, nickel, and zinc at
percent concentration
Metals or inorganics
Metals
Mercury roast and Mercury
retort (3.34)
Mercury distillation Mercury
(3.35)
Miscellaneous waste processing
Surface contamination
Decontamination and
disassembly (3.36)
PCB-containing
transformer and ballast
decontamination (3.37)
PCB-containing oil
Petroleum-contaminated
soils, slags, ashes,
dusts, fumes, abrasive
blasting media, foundry
sand, or nonmetal
demolition debris
Mercury-containing
soils, sludges, or
sediments
Soils, sludges,
sediments, slags, ashes,
dusts, fumes, firing
range soils, batteries, or
mercury-containing
wastes
Soils, sludges,
sediments, slags, ashes,
dusts, fumes, abrasive
blasting media, or
foundry sand
Soils, sludges,
sediments, slags, ashes,
dusts, fumes, firing
range soils, or batteries
Slags, ashes, dusts,
fumes, abrasive blasting
media, or foundry sand
Abrasive blasting media,
foundry sand, firing
range soils, lead/acid
battery wastes, or
mercury-containing
soils, sludges, or
sediments
Mercury-containing
soils, sludges,
sediments, or batteries
Free-flowing mercury
liquid
Chemical tanks, pipes,
and architectural
materials
Dielectric oil in electrical
equipment
Low-value structural
product
Recovery of mercury
Recovery of metals
or metal salts
High- or low-value
ceramic product
Recovery of metals
Cement
Recovery of foundry
sand or abrasive
material; recovery of
metals
Recovery of mercury
Leachable metals in waste
1 Typically requires additional
processing to yield marketable
product
1 Leachable metals in treated
residual
> Volume of leaching solution
required
1 Leaching solution must be
regenerated and reused
1 Silica content
> Leachable metals in product
> Slagging conditions
Slagging
Water content
Arsenic
Halides
Silica content
Iron content
Impurities
Typically requires additional
processing to yield marketable
product
Halides
Water content
Recovery of mercury Initial purity of waste mercury
Recovered bulk
metals and
construction materials
Recovery of oil and
metals
> Substrate value
1 Type and concentration of
contaminant
1 Thermal decontamination of
metals can generate products
of incomplete combustion
'Numbers in parentheses refer to the section(s) of this handbook where the technology is discussed.
-------
Liquid L.
Petroleum Products
(DE, DS, ER)
Debris
. TH) Structures/
SI OUII
Jj (CUSP, PH, PY) ____
Liquid
Waste Types
|p^^ Shredded Plastic Ash
P°^me^ Fluff (ER, TH) (AG, CK, CUSP
TH1 I PH, PY. VT)
Foundry Sand
(AG, CK, VT)
Tires and Belts
(ER, RP, TH)
A
ivionumers
(DS, ER)
Liquid
Organic Solvents
(DE, DS, ER)
Battery Metals
(CUSP, PH, PY)
$k
Recycling Technologies
X=Siuu«w3Zrj?i ^ -!i?'
Inorganics-Contaminated
Sediments (CUSP, PY, VT)
tn ^v. ^f.
Organics-Contaminated §
Sediments (DE, ER, SX, TD)§
AG Aggregate/
Construction Uses
BR Bioreduction
^^5 _^f
Inorganics-
Contaminated
Soils and Sludges
* (CUSP, PY, VT)
XXXMiXXXXXXXXXXAXXXJOO
CL Chemical Leaching
SP Solution Processing
(includes a variety of aqueous
processing technologies)
DD Decontamination/
Disassembly
**IH^
Mercury
S Contamination J
g(BR, CUSP, MR, PH)^
EM Energetic Material
Extraction and Reuse
ER Energy Recovery
apEgp ^^X^^^X^
Transformers Propellants and
and Ballasts (TP) Explosives (EM, ER)
Organics-
Contaminated
J Soils and Sludges
S (DE, ER, SX, TD)
Si8»»»$8SS»SSS3S»
Vadose Zone VOCs
PH Physical Separation
PR Pump and Recover
& RP Reuse Plastics
as Particulate
SX Solvent Extraction
Battery Cases
(CH, ER, RE,
RP, TH)
MM
T:
A YY
TP PCB-Containing
Device Processing
VC Vacuum Extraction
CH Chemolysis
CK Cement Raw Material
DE Decanting
DS Distillation
MD Mercury Distillation
MR Mercury Retorting
C±3
PY Pyrometallurgy
RE Polymer Re-extrusion
TD Thermal Desorption
TH Thermolysis
VT Vitrification
Figure 2-1. Recycling technology options at Superfund sites. (Two-letter technology codes appear below the applicable waste types.)
-------
Chapter 3
Description of Recycling Technologies
This section summarizes a wide range of recycling tech-
nologies that can be applied at Superfund or RCRA
Corrective Action sites to obtain reusable materials from
wastes containing organic and/or inorganic contami-
nants. The application of recycling technologies can
increase the effectiveness of a remedial alternative by
reducing the volume, toxicity, and/or mobility of hazard-
ous substances, pollutants, and contaminants. De-
creased site disposal costs and the value of the recycled
product also may provide cost savings.
Each technology description includes seven sections:
Usefulness, which summarizes the applicability of the
particular technology for recycling.
Process Description, which explains how the technol-
ogy works.
Process Maturity, which describes the technology's
commercial availability and potential for implementa-
tion.
Description of Applicable Wastes, which outlines the
characteristics of waste streams typically processed
for recycling using the technology.
Advantages, which describes some of the particularly
favorable aspects of the technology.
Disadvantages and Limitations, which discusses po-
tential challenges that the technology presents.
Operation, which provides information on operating
conditions and general implementation methods.
Wastes at Superfund or RCRA Corrective Action sites
usually contain a mixture of contaminant and matrix
types (mixtures of chlorinated and nonchlorinated or-
ganic sludges and soils, for example). These complex
mixtures greatly increase the difficulty of processing to
obtain a reusable product. At most sites, the application
of several process options as a treatment train is re-
quired to encompass a remedial alternative for recovery
of a useful product. Treatment trains often involve rough
separation followed by separation and isolation. Rough
separation is used to remove objectionable contami-
nants and to increase the concentration of the valuable
constituents in the matrix. Separation and isolation fur-
ther clean and upgrade the material to produce a useful
product. Some common examples of rough separation
followed by a separation and isolation process are:
Thermal desorption or solvent extraction from soil,
sludge, or sediment to produce a mixed organic liquid
that is then purified and separated into reusable or-
ganic products by distillation.
Precipitation to produce a filter cake followed by
smelting, chemical leaching, and solution processing;
or vitrification to produce useful materials.
The treatment train may require two separate facilities.
For example, a small, onsite thermal desorption unit
could be used to remove an organic contaminant from
soil or sludge. The recovered material could then be
introduced into the physical separation and distillation
operations of a commercial refinery along with the nor-
mal feedstock. The case studies described in Section 5
illustrate the application of several technologies used in
sequence to form a treatment train.
3.1 Distillation
3.1.1 Usefulness
Distillation is a thermal method that separates and con-
centrates volatile organic liquids from less volatile com-
ponents to allow purification and reuse of one or more
components. Desirable properties for feed material to
petroleum distillation processes are given in Section 4.1.
A case study of batch distillation for onsite solvent re-
covery is described in Section 5.6.
3.1.2 Process Description
Distillation involves heating a liquid mixture of volatile
compounds to selectively vaporize part of the mixture.
The vaporized material, which is enriched with more-
volatile compounds, is condensed and collected as dis-
tillate. The residual unvaporized liquid is enriched with
less volatile materials. Distillation usually involves mul-
tiple stages of evaporation and condensation to improve
the separation of target compounds in the distillate and
still bottoms. Distillation may be done as a batch or as
a continuous process. Small volumes of waste are best
11
-------
treated in batch stills, particularly if the composition
varies or if the solids content is high (see Figure 3-1).
Continuous distillation processing can achieve higher
throughput and can be more energy efficient but is more
sensitive to the properties of the input materials (1).
Mercury-
Contaminated
Water
Air-
Off-Gas and
Mercury Vapor
Effluent
Sampling
Figure 3-1. Batch distillation.
3.1.3 Process Maturity
Distillation is a mature technology. The petroleum and
chemical industries have made extensive use of the
process for many years. Small batch stills can conven-
iently recover small batches of spent solvents on site.
Onsite solvent recovery units typically have a capacity
in the range of 11.3 to 378 L (3 to 100 gal) per 8-hr
shift (2).
3.1.4 Description of Applicable Wastes
Distillation is useful for recovering a wide variety of
petroleum and organic solvents from liquid organic
wastes. For example, solvents can be recovered from
wastes generated in paint formulation, metal cleaning
and degreasing, or paint application (3).
Both the physical form and chemical content of the
organic waste influence the ability to recover useful
materials by distillation. Distillation is more effective if
nonhalogenated and halogenated solvents are not com-
bined in the wastes. Wastes with high solids content are
not suitable for continuous distillation. Wastes contain-
ing organic peroxides or pyrophoric materials should not
be processed by distillation. Materials that polymerize
can cause operational problems.
3.1.5 A dvantages
Distillation is a well-established process for recovering
useful materials from contaminated petroleum and sol-
vents. A solvent with a low boiling point (~100°C [212°F])
mixed with significantly less-volatile contaminants can
be recovered with simple distillation equipment (4).
Volatile residue loss in the still bottoms can be as low
as a few percent. Distillation is technically able to reach
any desired level of product purity, although practical
and economic limits apply.
3.1.6 Disadvantages and Limitations
Distillation requires handling heated volatile organic liq-
uids. Possible air emissions of volatile organics from
process equipment and related storage tanks must be
controlled.
Nonvolatile contaminants and low-volatility liquids re-
main in the still bottoms as viscous sludge. This sludge
process residual must be managed, typically by incin-
eration.
Distillation of complex mixtures of organics with similar
boiling points requires expensive, complex equipment
with high capital costs. However, purification of a volatile
solvent contaminated with heavy oil and grease and of
nonvolatile solids can be done in simple batch stills.
3.1.7 Operation
The main components of a distillation system are the
heat source, a distillation vessel (batch) or column (con-
tinuous), and a condenser. The feed material is heated
to vaporize volatiles, which are collected and con-
densed. Some of the condensed material usually is
returned to the still to control distillate purity.
Distillation process equipment can cover an enormous
range of size and complexity depending on the amount
and type of material to be processed (3). Small quanti-
ties of contaminated solvents can be processed in sim-
ple batch stills. Large quantities of material usually are
processed in continuous distillation columns. Dense,
viscous, or high-solids materials require specialized
equipment such as agitated thin film or wiped film heat-
ing systems (1, 5).
3.2 Energy Recovery (General)
3.2.1 Usefulness
A wide variety of organic wastes can be burned to
recover energy in the form of steam or process heat. A
description of desirable properties in feed materials for
combustion to recover energy is given in Section 4.5.
12
-------
To Off-Gas
Treatment
Water
Waste
Fuel
Steam
Figure 3-2. Energy recovery application.
3.2.2 Process Description
Energy recovery systems process waste containing or-
ganic materials in a boiler or other combustion device to
recover energy values (see Figure 3-2). The organic
component in the waste materials has the potential to
serve as fuel in the combustion device and can, depend-
ing on the organic concentration, displace conventional
fossil fuels such as oil or natural gas. Less concentrated
organic materials require the use of a pilot fossil fuel to
sustain combustion within the combustion device (6).
Energy value is recovered from energy recovery sys-
tems by generating steam or by using the hot flue gases
produced for process heating. If temperatures within the
combustion device are maintained above approximately
1,093°C (2,000°F), the more hazardous organic con-
stituents also can be eliminated from the waste stream.
Unlike incineration of the wastes, the major objective in
an energy recovery system is the recovery of the steam
or hot flue gas as a valuable product.
Inorganic portions of the waste materials exit the com-
bustion device as ash that must be disposed of. If heavy
metals are present in the ash, additional treatment may
be necessary before disposal or reuse.
3.2.3 Process Maturity
Energy recovery systems are mature technologies and
are available from many vendors. In some cases, exist-
ing combustion equipment can be used, with modifica-
tion, to recover useful energy products from wastes
containing organic materials. The scale of the equip-
ment is limited only by the supply of material to be
processed and the means of ash disposal.
3.2.4 Description of Applicable Wastes
A wide variety of wastes can be processed and used for
energy recovery. These include petroleum- or solvent-
contaminated soils, propellants, rubber products, solid
polymeric materials, automobile shredder residue,
sludges, and wood debris (7). High-moisture materials
such as sludges may limit the amount of energy that can
be recovered from a particular waste, but any material
with a measurable heating value over approximately
7,000 kJ/kg (3,000 Btu/lb) can be used for energy recov-
ery. Halogenated solvents are poor candidates for en-
ergy recovery.
3.2.5 Advantages
Energy recovery allows for the generation of a useful
product or products (steam, hot flue gas) from the waste
materials. Depending on the design of the specific com-
bustion device, little preparation of the feedstock is re-
quired, resulting in ease of operation.
3.2.6 Disadvantages and Limitations
Combustion processes may produce highly toxic prod-
ucts of incomplete combustion, such as dioxins and
furans. The limitations of energy recovery as a general
technology include the inability to process high-moisture
wastes, such as sludges. In these cases, the attempted
energy recovery is nothing more than incineration. Ash
residue containing metals is another limiting factor in
energy recovery systems. The ash must be treated as
waste material, which in some cases means additional
costs. If halogenated solvents are burned, corrosive
acid vapors are introduced into the off-gas.
3.2.7 Operation
The specific operation of an energy recovery system
varies with the type of combustion device. Boilers and
similar systems usually are fueled at startup by natural
gas or distillate oil; then, the waste material to be used
as fuel is started and the startup fuel is turned off. The
operation becomes routine and continues by feeding
more waste to the boiler. Temperature is controlled by
the airflowrate, fuel feed rate, and steam generation rate.
Other combustor types, such as fluidized beds, use a
bed of inert material that receives the waste for combus-
tion. These reactor systems are more flexible and can
process a wider range of waste materials. Suspension
burners require more tightly sized materials of generally
small particle size, and are typified by pulverized coal
combustion systems. These systems can require the
addition of a pilot fossil fuel to stabilize the flame.
3.3 Energy Recovery (Cement Kilns)
3.3.1 Usefulness
Energy recovery can be particularly valuable when used
in energy-intensive processes, such as the manufacture
of Portland cement (see Figure 3-3). Due to the special
13
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KEY
Gas Flow
Solids Flow
Feed Preheating
Figure 3-3. Energy recovery in a cement kiln (adapted from Gossman [8]).
characteristics for cement kiln combustion and the num-
ber of cement kilns permitted to burn hazardous wastes,
energy recovery in cement kilns is discussed separately. A
description of desirable properties for feed materials for
combustion to recover energy appears in Section 4.5.
A large quantity of combustible waste is burned as fuel
in cement kilns across the United States each year. The
predominant waste fuels are hazardous solvents, waste
oils, and tires. The number of cement kilns permitted to
burn waste fuels has grown significantly since 1985. For
example, in 1990, 6.8 percent of fuel consumption at
cement kilns was hazardous waste fuel (9). EPA data
suggest that 23.6 million metric tons (26 million tons) of
hazardous waste fuel, with a heating value greater than
9,000 kJ (8,500 Btu), is available, but less than 10
percent of this fuel presently is committed to energy
use (10, 11).
3.3.2 Process Description
Cement kiln operation is discussed in greater detail and
is illustrated in Section 5.2. Raw materials such as lime-
stone, clay, sand, and iron ore (perhaps supplemented
by solid wastes of various types) are fed, either wet or
dry, in specific proportions into the back (higher) end of
a long rotary kiln. (Use of inorganic wastes as raw
materials in cement kilns is discussed in Section 3.32.)
Fuel is burned at the front (lower) end so that the hot
combustion gasflow direction in the kiln is that of the
solids. As the raw materials travel toward the front end
of the kiln, they are heated, dehydrated, calcined, and
then combusted and crystallized to form cement clinker.
The process is extremely energy intensive, with maxi-
mum gas temperatures in excess of 2,200°C (3,990°F)
at the front end of the kiln. This is a significantly higher
temperature than in most hazardous waste incinerators,
which typically operate at less than 1,480°C (2,700°F)
and have shorter gas retention times than cement kilns.
The extent of fuel combustion at cement kilns is greater
than in most hazardous waste incinerators, with fewer
emissions (8).
Depending on the waste fuel to be burned, pretreatment
may be necessary, such as mixing, neutralization, dry-
ing, particle sizing, thermal separation or pyrolysis,
and/or pelletization (8). Several different technologies
are used to feed waste fuels into cement kilns, depend-
ing on the type of waste (9). Petroleum and petrochemi-
cal wastes generally can be pneumatically introduced.
3.3.3 Process Maturity
More than 25 cement kilns currently are permitted and
actively burn hazardous waste fuels nationwide, with 10
additional plants soon to follow (9). These 25 plants
represent one-third of all cement plants in the country
and one-quarter of clinker production capacity. At least
seven cement kilns currently are burning tires or tire-de-
rived fuel on an operating basis and another five on an
experimental basis (12).
3.3.4 Description of Applicable Wastes
A wide variety of wastes can be recycled in this manner,
depending on Btu content, physical characteristics, and
chemical composition. Table 3-1 provides some guid-
ance on the acceptability of different wastes based on
14
-------
Table 3-1. Wastes Suitable for Treatment in a Cement Kiln (8)
0% Organics <
Friability
-M00% Organics
<0.1% Organics
5,000 Btu/lb
5,000 Btu/lb
High friability
Solids
Sludges
Liquids
Low friability
Inorganic solids (see Section 3.32)
Suitable for blending into raw feed
Inorganic liquids and sludges
Suitable for blending into
wet-process slurries; probably not
suitable for dry-process kilns
Same as above for sludges
Organic-contaminated solids
and sludges (such as
contaminated soils or filter
cake)
Requires some form of
thermal separation or direct
feed for preheater
Same as above for solids
Organic/water mixtures
Suitable for incineration
Grindable solid waste fuels
(such as spent aluminum pot
liner)
Hazardous waste fuel (HWF)
sludges
Difficult to handle; can be
blended into liquids or
otherwise processed
Liquid hazardous waste fuels
physical characteristics and heat content. The Portland
cement product is tolerant of a wide variety of trace
constituents. As long as harmful constituents are con-
trolled, destroyed, or rendered inert, the advantages of
burning waste fuels are clear (8).
Typical constituents in hazardous waste fuel are xylene,
toluene, mixed aliphatic hydrocarbons, acetone, methyl
ethyl ketone, and a variety of chlorinated solvents. Ap-
plicable solid wastes include tires, shredded plastic
chips, petroleum industry residues, resins, and refuse-
derived fuel (13). Cement kilns are very energy inten-
sive. A single plant can potentially consume up to
several million tires or several million kilograms of waste
solvent and oil per year.
The most desirable waste fuel is relatively low in chlorine
(Cl) content, is liquid, and has a moderately high Btu
content, ranging from 25,600 to 41,900 kJ/kg (11,000 to
18,000 Btu/lb). The total suspended solids content of
liquid fuels should be less than 30 percent to prevent
plugging of the delivery system (14).
3.3.5 Advantages
Hazardous waste fuel generally burns cleaner than coal
in a cement kiln and has lower associated nitrogen oxide
(NOX) and sulfur oxide (SOX) emissions. The high tem-
peratures achieved lead to thorough oxidation of the
combustibles, and refractory contaminants such as non-
volatile metals are immobilized in the clinker's crystalline
structure (8).
Kiln control is generally enhanced when burning even
small quantities of hazardous waste fuel because the
high level of volatiles stabilizes and aids combustion.
The clinker acts as a scrubber for hydrochloric acid
(HCI), and burning chlorinated solvents can enable the
production of low-alkali cement, eliminating the need to
purchase and add calcium chloride (CaCI2) as an addi-
tional raw ingredient. In certain cases, burning hazard-
ous waste fuel enhances cement clinker quenching and
yields a product with higher strength and better grinding
characteristics (8).
Steel from the reinforcing belts in tires does not need to
be removed priorto burning because iron is an essential
ingredient in Portland cement manufacture. Burning
tires can actually reduce or eliminate the need to pur-
chase iron ore to supplement the iron (Fe) content of
quarry rock (12).
Financially, burning hazardous waste fuels at cement
kilns can be profitable to both the waste generator and
the kiln operator. The waste generator has reduced
costs relative to other disposal options; the kiln operator
is paid to burn fuel that would otherwise have to be
purchased. In the case of tires, even if the cement plant
operator pays up to 35 cents per tire, the economics still
may be favorable to the operator (12).
3.3.6 Disadvantages and Limitations
Although a waste fuel recycling program dramatically
reduces fuel costs for the plant operator, it also brings
specific challenges:
At less than 25,600 kJ/kg (11,000 Btu/lb), waste fuel
is not a "hot" fuel; therefore, special attention must
be paid to burner pipe design, optimum clinker cooler
operation, and a tight hood seal (10, 11).
Cement plant operators prefer to develop a uniform
and consistent waste fuel supply so that processing
parameters do not need constant adjustment.
Solid and sludgy wastes present handling difficulties.
15
-------
Excessive Cl levels and the lack of compensating
adjustments in kiln operations can lead to problems
such as plugups, bad product, or kiln brick loss (8).
Cl levels in the total fuel (compared with just the
hazardous waste fuel) should be less than 3 percent
by weight (14).
Cement kilns must meet the stringent air standards
specified in their permits. These standards affect the
type of waste that can be burned.
Cement kilns that burn hazardous waste fuel tend to
produce a disproportionately large amount of cement
kiln dust, which currently is exempted from the re-
quirements of Resource Conservation and Recovery
Act (RCRA) Subtitle C regulation under the Bevill
Amendment, passed on October 12, 1980. Additional
controls and possible regulation under Subtitle C,
however, are being considered that could significantly
affect the economics of burning hazardous waste
fuels at cement kilns (9).
Excessive levels of lead (Pb) and zinc (Zn) in the
waste fuel can reduce product strength; excessive
levels of Pb and chromium (Cr) can lead to safety
hazards (8).
3.3.7 Operation
Cement kiln waste fuel recycling operation is quite sim-
ple for the generator. The waste fuel must be trans-
ported to the cement plant or to a permitted waste fuel
processor (or "blender") as a broker for the kiln operator.
Usually either the processor or the kiln operator per-
forms pretreatmentto prepare the waste fuel for burning.
3.4 Decanting
3.4.1 Usefulness
Decanting is a physical method of separating two immis-
cible liquid phases to allow purification and reuse of one
or more of the phases. A case study of decanting as part
of a treatment train to recover petroleum from an oily
sludge is described in Section 5.5.
3.4.2 Process Description
Decantation is used to remove small quantities of oil
dispersed in water, or small quantities of water dis-
persed in oil (see Figure 3-4). Decantation relies on
gravity to separate dense and light liquid phases. During
the process, one liquid is dispersed as fine droplets in a
second continuous phase. Decanting enhances the coa-
lescence of the droplets of the dispersed phase into
drops large enough to allow gravity to separate the two
phases. Decanting efficiency increases with large drop-
lets and large density differences between the phases
Oil/Water
Mixture
Emulsion
Breaking Agent
Polymer
T
Water
Oil
Solids
Centrifuge
Figure 3-4. Example of centrifugal decanting.
and decreases with increasing viscosity of the continu-
ous phase (15).
3.4.3 Process Maturity
Decanting to separate oil and water is a well-established
technology. A variety of equipment types are available
to efficiently treat a variety of oil and water mixtures.
3.4.4 Description of Applicable Wastes
Decanting is applicable to the separation of immiscible
liquids. Oil can be recovered by treating contaminated
oil, oily water, or oil sludges. Stable emulsions and
suspensions must be broken to allow for efficient physi-
cal separation.
3.4.5 A dvantages
Decanting allows for separation and recovery of oil from
water or sludge. Parallel plate separation can reduce oil
concentration in water from 1 percent to about 20 to 50
mg/L (1.2 to 2.9 grains/gal). Dissolved air flotation pro-
vides about 90-percent effective removal of oil from
water, with residual oil concentrations ranging from 90 to
200 mg/L (5.2 to 12 grains/gal) (15).
16
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3.4.6 Disadvantages and Limitations
Surfactants or fine particulate will stabilize emulsions,
greatly reducing the efficiency of decanting. Chemical
additives are often needed to break stable emulsions
(16). Decanting will only separate immiscible liquids
such as oil and water. Further processing, such as
distillation, is needed to separate mixtures of organics.
3.4.7 Operation
In its simplest form, a decanter is a tank with a large
surface area to volume ratio. The continuous phase
stands in the tank, while droplets of the dispersed phase
combine and rise or sink (depending on density) to form
a second phase that can be decanted. This simple
approach is applicable only when the dispersed phase
is present as large droplets and the speed and efficiency
of separation is not critical.
Decanting works best when the surface area available
for formation of a second phase is large compared with
the volume of fluid. Use of corrugated parallel plates
often yields a large surface area to volume ratio. A
variety of commercial implementations of the parallel
plate separator are available.
Coalescers, hydrocyclones, centrifuges, or air flotation
units are used when the dispersed and continuous
phases are difficult to separate or when a high propor-
tion of solids are present. Coalescers provide a surface
that enhances contact and agglomeration of the dis-
persed phase droplets, thereby improving phase sepa-
ration. The surface can be a packed bed, a fiber mesh,
or a membrane. The surface may be hydrophobic or
hydrophilic, depending on the nature of the dispersed
phase. Hydrocyclones and centrifuges improve phase
separation by centrifugal action, induced by radial flow
(hydrocyclones) or mechanical spinning (centrifuge).
The mechanical centrifuge is particularly useful for
separating light oil, water, and solids. Air flotation units
improve phase separation by forming air bubbles or
introducing them into the continuous phase. The bub-
bles provide a large surface area for collecting the dis-
persed phase droplets. The most common method used
to form bubbles is to saturate water with air at elevated
pressure and then to release the pressure (i.e., dis-
solved air flotation). Bubbles also can be introduced by
gas sparging or electrolysis. Air flotation is used mainly
when the dispersed phase is a low-density hydrophobic
material, such as oil, and when the dispersed phase
concentration is low.
3.5 Thermal Desorption
3.5.1 Usefulness
Thermal desorption is a method used to physically re-
cover volatile and semivolatile organic contaminants
from soils, sediments, sludges, and filter cakes for reuse
of the contaminant constituents. Volatile metals, particu-
larly mercury, can be recovered by a thermal process
similar to thermal desorption, called roasting and retort-
ing (Section 3.34). A case study of thermal desorption
as part of a treatment train to recover petroleum from an
oily sludge is described in Section 5.5. A case study of
thermal desorption to clean oily sand is described in
Section 5.7.
3.5.2 Process Description
Thermal desorption systems heat the contaminated ma-
terial to increase the rate of contaminant volatilization
and cause the organic partition to the vapor phase (see
Figure 3-5). The removal mechanisms are a combina-
tion of decomposition and volatilization. The organic-
laden off-gas stream that volatilization creates is
collected and processed. Unlike incineration, thermal
desorption attempts to remove organics rather than oxi-
dize them into their mineral constituents. As a result,
thermal desorption systems operate at lower tempera-
tures (95°C to 540°C [200°F to 1,000°F]).
3.5.3 Process Maturity
Thermal desorption processing equipment is in com-
mercial operation and can be obtained readily from sev-
eral vendors. Low-temperature treatment units are
available as trailer-mounted or modular units, which can
be transported to sites on standard highway transport
trucks with a maximum gross vehicle weight of 36,300
kg (80,000 Ibs). Thermal desorption has been selected
for remediation of several Superfund sites (18).
3.5.4 Description of Applicable Wastes
Low-temperature systems have been used for the re-
mediation of soil contaminated with a variety of volatile
and semivolatile organic compounds (VOCs and
SVOCs), including halogenated and nonhalogenated
VOCs and SVOCs, polychlorinated biphenyls (PCBs),
pesticides, and dioxins/furans (17, 19). The low-tem-
perature desorption processes are best suited for re-
moval of organics from sand, gravel, or rock fractions.
The high-sorption capacity of clay or humus decreases
the partitioning of organics to the vapor phase.
The heating process evaporates water as well as or-
ganics. Energy used to remove water from high-
moisture-content wastes increases cost and does not
assist in organic removal. Thermal desorption is there-
fore best applied to low-moisture-content wastes.
Thermal treatment units cannot process an unlimited
range of particle sizes in the feed material. Units that
use indirect heating require the presence of smaller
particles to provide sufficient contact surface with the
heated wall. Fluidized bed or rotary kiln units require a
17
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Oversize
Rejects
Clean
Off-Gas
Spent
Carbon
Concentrated
Organics
^ Water
Figure 3-5. Example of the thermal desorption process (17).
reasonably narrow particle size range to control particle
residence time in the heat zone. All units are unable to
process large chunks due to heat transfer limitations and
the potential for mechanical damage to the equipment
from impact. The maximum allowed particle size de-
pends on the unit but typically ranges from 3.8 to 5.1 cm
(1.5 to 2 in.) in diameter.
3.5.5 Advantages
Thermal desorption allows for removal and recovery of
organics from complex solid matrices. Desorption proc-
ess conditions do not encourage chemical oxidation/re-
duction mechanisms, so combustion products are not
produced. Thermal desorption treatment of low-organic-
content streams is less energy intensive than incinera-
tion (20). In some cases, desorbed organics can be
used directly; for example, desorbed petroleum hydro-
carbons can be collected and used as a bitumen substi-
tute in asphalt, or can be injected into a cement kiln or
furnace for energy recovery. The operating temperature
for thermal desorption reduces the partitioning of metals
to the off-gas.
3.5.6 Disadvantages and Limitations
The successful performance of thermal desorption tech-
nology depends on the ability to maintain controlled
heating of the contaminated matrix. The basis of the
process is physical removal by volatilization. Organic
removal is determined directly by the vapor pressure of
the contaminant and the bed temperature. Treated
waste retains traces of organic contaminants (20).
The organics stripped from the solid matrix are collected
as a mixture, which must be distilled or otherwise puri-
fied before it can be reused as a solvent. Mixed petro-
leum products and nonhalogenated solvents can be
used as fuel sources. Treated media typically contain
less than 1 percent moisture. Dust can easily form dur-
ing processing and when treated material is transferred
out of the heating unit.
Thermal desorption is a capital-intensive operation that
requires complex and expensive equipment. Costs can
be controlled to some degree by matching processing
equipment size to the amount of material to be treated.
Low-temperature treatment requires complex equip-
ment operating at elevated temperatures. Equipment
operation involves hazards, but the nature and level of
risk are consistent with industry practice.
3.5.7 Operation
Maximum temperatures and the heating systems used
in commercial thermal desorption processing vary
widely. Operating temperatures range from 95°C to
540°C (200°F to 1,000°F). Heating equipment includes
rotary kilns, internally heated screw augers, externally
heated chambers, and fluidized beds. Some systems
use two-stage heating, where the first stage operates at
low temperature to remove mainly water and the second
stage operates at higher temperature to vaporize
organics (21-23).
Most thermal desorption units use inert carrier gas to
sweep volatilized organics away from the heated media.
Treatment of off-gas from thermal desorption systems
typically requires several steps. First, the hot off-gas is
conditioned for efficient organic collection by removing
particulate impurities. Various combinations of cyclone
separators and baghouse filters remove the particulate
impurities. Scrubbers and the processes of countercur-
rent washing and condensation then collect the or-
ganics. Most of the cleaned carrier gas is recycled to the
heating unit, while carbon adsorption cleans the dis-
charged portion.
18
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3.6 Solvent Extraction
3.6.1 Usefulness
The process of solvent extraction involves using an
organic solvent to recover organic contaminants from
soils, sludges, sediments, or liquids for reuse of the
contaminant constituents.
3.6.2 Process Description
In solvent extraction, a solvent that preferentially re-
moves the organic contaminant is contacted with the
contaminated media (see Figure 3-6). Typical solvents
include liquefied gas (propane or butane), triethylamine,
or proprietary organic fluids. The extraction solvent is
well mixed with the contaminated matrix to allow con-
taminants to transfer to the solvent. The clean matrix
and solvent are then separated by physical methods,
such as gravity decanting or centrifuging. Distillation
regenerates the solvent, which is then reused. Depend-
ing on their characteristics, recovered organic contami-
nants can be collected for reuse, processed to increase
purity, or burned for energy recovery.
3.6.3 Process Maturity
Solvent extraction uses conventional solid/liquid con-
tacting, physical separation, and solvent cleaning equip-
ment. Two systems were tested as part of the Superfund
Innovative Technology Evaluation (SITE) Demonstration
Program (25, 26). Solvent extraction has been selected
to remediate several Superfund sites and emergency
response actions (18).
3.6.4 Description of Applicable Wastes
Solvent extraction is effective in treating sediments,
sludges, and soils containing primarily organic contami-
nants such as PCBs, VOCs, halogenated solvents, and
petroleum (27). Oil concentrations as high as 40 percent
can be processed. Extraction is more effective with
lower molecular-weight hydrophobic compounds. Con-
taminants targeted by solvent extraction include PCBs,
VOCs, and pentachlorophenol (28).
3.6.5 Advantages
Solvent extraction recovers organic contaminants from
an inorganic matrix, thus reducing the waste volume and
preparing the organic for recycling. The treated residual
is a dry solid. Solvent extraction can be used to treat
wastes with high concentrations of organic contaminants.
3.6.6 Disadvantages and Limitations
Organically bound metals can transfer to the solvent
along with the organics and restrict reuse options. Most
extraction solvents are volatile, flammable liquids (20);
as such, these liquid types require design and operating
precautions to reduce risks of fire and explosion.
The liquid collected by solvent extraction processing of
wastes typically contains a large number of different
organics. A mixture composed of nonchlorinated or-
ganics may be suitable for energy recovery or asphalt-
making. For higher-grade uses or when chlorinated
organics also are present, further processing (e.g., dis-
tillation) may be required to separate the various organic
liquids. Detergents and emulsifiers in the waste can
reduce extraction performance. Water-soluble deter-
gents dissolve and retain organic contaminants in the
matrix. Detergents and emulsifiers promote foam forma-
tion, which complicates separation of the matrix and
extraction solvent.
3.6.7 Operation
In solvent extraction processing, excavated waste ma-
terials are contacted with a selected extraction solvent.
Solvent
Recovery
Organics
Recovery
Recovered
Organics
Water
Reclaim
Filtration
System
Treated
^ Cake to
Disposal
Figure 3-6. Example of the solvent extraction process (24).
19
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To be successful, the extraction solvent should have a
high solubility in the contaminant and low solubility in the
waste matrix.
As the process typically exhibits extraction behavior that
is mass transfer limited, thorough mixing of the solvent
and contaminated matrix is required. Some solvent ex-
traction systems require the addition of water if the
waste is a dry, nonflowing solid. In other systems, ex-
traction fluid is added to make the waste flow.
The extraction solvent typically is purified by distillation.
In systems that use pressurized solvents, such as lique-
fied gas or supercritical carbon dioxide (CC^), vaporiza-
tion occurs by pressure release, which causes the
solvent to boil. With higher-boiling solvents, distillation
tanks or towers may be used to separate the extraction
solvent from the organic contaminants.
The triethylamine system extracts both water and or-
ganics. The contaminant/water/solvent mixture is
heated to 55°C (130°F), where separate water and or-
ganic phases form. The phases are separated by de-
canting, and the contaminant and solvent are separated
by distillation.
3.7 Use as Construction Material
3.7.1 Usefulness
Low-value matrices with very low levels of leachable
contaminants are suitable for reuse in construction ap-
plications after minimal processing. Sources for informa-
tion on specifications for construction materials are
given in Sections 4.11 and 4.12. A case study on the use
of spent sand blasting media as aggregate in asphalt is
described in Section 5.1.
3.7.2 Process Description
This category includes a collection of different proc-
esses that all use waste materials as an aggregate,
usually in construction or road paving. Examples include
the use of foundry sand, blasting sand, slag, fly ash, soil,
or some other material as a blender aggregate in ce-
ment concrete, asphalt concrete (see Section 5.1),
grading material, fill, or roadbed (see Figure 3-7). Alter-
natively, monolithic wastes such as plastic or elastomer
wastes, bricks, other ceramics, mortars, or solidified
wastes from stabilization/solidification (S/S) or vitrifica-
tion projects can be crushed to form aggregate for the
above purposes. These materials also can be reused in
monolithic form for erosion control, diking material, arti-
ficial reefs, and other purposes.
Crushed stone also has agricultural applications (e.g.,
as a filler or conditioner in fertilizer and a mineral
additive in animal feeds or poultry grit) and industrial
applications (e.g., as an extender in plastic, rubber,
Figure 3-7. Construction material loader.
paper, or paint). The principal requirements for the use
of waste materials as aggregates or bulk materials are
acceptanceby regulatory agencies, customers, and
the publicand product performance. Typically the
waste material must lend some useful function to the
product and meet leach resistance criteria and specifi-
cations for physical properties (29). The "end use"
should not simply be disposal in another form (termed
"use constituting disposal" or "sham recycling"). Even if
regulatory requirements and technical specifications are
met, customers or the public may be reluctant to accept
the use of those materials.
3.7.3 Process Maturity
The technology for this group of processes is mature
and commercially available. A wide variety of materials
have been used as aggregates in construction projects
for many years.
3.7.4 Description of Applicable Wastes
Applicable wastes include a wide variety of inorganic
waste materials. Pavements, construction materials, ce-
ramics, or glasses that are either aggregates or can be
crushed to form aggregates are typical (30). Some fly
ash and slag wastes can be used to supplement or
replace Portland cement. Reuse usually takes place in
the public domain, so wastes should contain low levels
of relatively low-hazard contaminants.
3.7.5 Advantages
The structural properties of recycling aggregates make
them well suited for the designed end uses. In addition,
turning waste materials into aggregates conserves land-
fill space for higher-hazard waste materials and avoids
disposal costs.
3.7.6 Disadvantages and Limitations
The main disadvantage of recycling aggregates is the risk
or perceived risk of exposure to hazardous materials,
20
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which creates health concerns in the public. The two
principal exposure pathways are inhalation of dusts or
exposure to ground or surface water containing soluble
metals that have leached from the aggregate. Any such
recycling project should be able to demonstrate that no
significant risk is added to either process or product.
There should be negligible incremental risk to the recy-
cling process workforce or to the public potentially ex-
posed to the recycled material. Potential liabilities
relating to the real or perceived health effects of the
recycled material may exist for the waste generator.
Other limitations pertain to product specifications, such
as strength, grading, chemical composition and purity,
and chemical reactivity (31). Section 4.12 summarizes
American Society for Testing and Materials (ASTM)
specifications for aggregates and bulk construction ma-
terials; Section 5.1 describes a number of product ac-
ceptance criteria for recycling waste aggregates into
asphalt concrete. Aggregate for landfill cover should
have low dispersability; otherwise dusting will occur.
Waste aggregate used to produce mortar or other ce-
mentitious products should have a low metallic alumi-
num content because aluminum corrodes and releases
hydrogen gas (H2), which decreases the strength of the
cement.
3.7.7 Operation
This recycling technology is straightforward and in-
volves little in the way of operation. Unless the reuse
location is on site, the waste aggregate must be trans-
ported to the recycler's location. If the aggregate is
going to be used as a construction material or as aggre-
gate in concrete, crushing the waste aggregate and/or
grading it by particle size may be necessary. Storage
requirements in compliance with any pertinent regula-
tions may involve an impervious liner, bins, or hoppers
to prevent leaching. Special handling and worker pro-
tection may be required to minimize exposure to dust.
3.8 In Situ Vacuum Extraction
3.8.1 Usefulness
In situ vacuum extraction removes volatile organics from
the vadose zone without bulk excavation. The extracted
organics can be collected for reuse by condensation or
adsorption/regeneration.
3.8.2 Process Description
In situ soil vapor extraction is the process of removing
VOCs from the unsaturated zone (see Figure 3-8). Blow-
ers attached to extraction wells alone or in combination
with air injection wells induce airflow through the soil
matrix. The airflow strips the VOCs from the soil and
carries them to extraction wells. The process is driven
Condenser
To Off-Gas
Treatment
Figure 3-8. Example of a vacuum extraction system.
by partitioning of volatile materials from solid, dissolved,
or nonaqueous liquid phases into the clean air that the
blowers introduce (32). Air emissions from the systems
typically are controlled aboveground by adsorption of
the volatiles onto activated carbon, by thermal destruc-
tion (incineration or catalytic oxidation), or by condensa-
tion through refrigeration (33).
3.8.3 Process Maturity
Vacuum extraction to remove volatile organics from the
vadose zone is a mature and widely applied technology.
A reference handbook on soil vapor extraction is avail-
able (34). Extracted organics can be recovered as
useable liquid either by chilling to directly condense
liquids or by adsorption onto (and subsequent regenera-
tion of) carbon or other media. Recovery of liquids is
technically feasible, but treatment using thermal de-
struction is more frequently used.
3.8.4 Description of Applicable Wastes
Vacuum extraction has demonstrated its ability to re-
move halogenated and nonhalogenated VOCs and non-
halogenated SVOCs. The process also is potentially
effective for halogenated SVOCs (35).
3.8.5 Advantages
Vacuum extraction allows recovery of organics without
bulk soil excavation.
3.8.6 Disadvantages and Limitations
The organics collected by vacuum extraction typically
contain a large number of different organics. In addition,
the composition changes as extraction proceeds due to
differences in the relative volatility of the organic con-
taminants. A mixture of nonchlorinated organics may be
suitable for energy recovery or for making asphalt. For
higher-grade uses orwhen chlorinated organics also are
21
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present, further processing (e.g., distillation) may be
required to separate the various organic liquids.
Moisture in the extracted vapor stream freezes during
condensation of organic vapors. High moisture content
causes sufficient icing on condenser surfaces to signifi-
cantly reduce the efficiency of chilling for collecting or-
ganic liquids.
3.8.7 Operations
Application of vacuum extraction relies on the ability to
deliver, control the flow of, and collect stripping air. The
main factors favoring application of vacuum extraction
are the contaminant vapor pressure, the air conductivity
of the soil, the soil moisture content, the sorption capac-
ity of the soil, and the solubility of the contaminant in
water. High vapor pressure, high conductivity, low soil
moisture, low sorption, and low water solubility improve
extraction efficiency (35).
3.9 Pumping and Recovery
3.9.1 Usefulness
The pumping and recovery process can be used to
extract immiscible organic liquids in the subsurface,
which can then be reused. A case study of pumping and
recovery of coal tar wastes is described in Section 5.8.
3.9.2 Process Description
Many organic liquids have low solubility in water and can
be present in natural formations as accumulations of
nonaqueous-phase liquids (NAPLs). The location and
configuration of the accumulations depend upon the
density, interfacial tension, and viscosity of the NAPL.
For NAPLs with a density lower than water (LNAPLs),
the NAPL often is found as a layer floating on the top of
the ground water. For NAPLs with a density higher than
water (DNAPLs)for example, some chlorinated sol-
vents, organic wood preservatives, coal tars, pesticides,
or PCBsan organic liquid phase can pool on low-
permeability geologic formations.
The accumulations of organic liquid can be recovered
for reuse by installation of wells and pumps. Recovery
of LNAPLs usually involves a skimming system that
preferentially removes the floating organic liquid (see
Figure 3-9). Ground-water pumping in the LNAPL recov-
ery well can be used to depress the ground-water level,
thus creating a gravity gradient to assist in transport of
LNAPL to the skimming system. DNAPLs can be recov-
ered by pumping from liquid deposits.
3.9.3 Process Maturity
Pump and recover systems use simple, commercially
available well installation and pumping equipment and
LNAPL
Water
LNAPL
Depressed Water Level
Figure 3-9. Example of a pump and recover system.
techniques (36). Pumping and collection of NAPLs are
used to recover either light or dense organics at Super-
fund or RCRA Corrective Action sites (37, 38).
3.9.4 Description of Applicable Wastes
Pump and recover system can be applied to collect
immiscible organic liquid deposits from in situ formations.
3.9.5 Advantages
Deposits of dense or light NAPL floating on ground
water can contribute to ground-water and surface-water
contamination. Pumping and recovery of NAPL pools
represent a low-cost technology to collect and return
organic liquids for reuse.
3.9.6 Disadvantages and Limitations
Placement, installation, and operation of wells must be
done carefully to reduce the risk of promoting NAPL
migration due to pumping operations.
The recovered NAPL typically is a mixture of several
organics and water. Water and NAPL can be separated
by decanting. In many applications, preprocessing is
needed to break emulsions. A mixture of nonchlorinated
organics may be suitable for energy recovery or making
asphalt. For higher-grade uses or when chlorinated or-
ganics are present, further processing (e.g., distillation)
may be required to separate the various organic liquids.
3.9.7 Operations
Mobile NAPLs can be pumped from wells and drains.
Systems may use one pump to withdraw only the NAPL
or the NAPL mixed with water, or they may use two
pumps, one to withdraw NAPL and another to withdraw
water. Wells should be placed in stratigraphic traps to
optimize recovery where NAPL pools are present. Long-
term recovery is increased if maximum thickness and
saturation of NAPL is maintained at well locations (36).
22
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In typical pumping operations, the pumping rate is held
constant. Cyclic pumping may be useful in situations
where slow mass transfer rates reduce the availability
of the contaminant. In cyclic pumping, the removal rate
varies with time by alternating periods of pumping and
no pumping. When pumps are idle, contaminants can
flow out of more restricted low-permeability areas. The
petroleum industry uses cyclic pumping to enhance oil
extraction (32).
3.10 Freeze-Crystallization
3.10.1 Usefulness
Freeze-crystallization is a physical method to recover
concentrated solutions of organic or metal salt contami-
nants for reuse by processing high-concentration water
solutions.
3.10.2 Process Description
Freeze-crystallization is a separation technique used to
separate solids from liquids or liquids from liquids (see
Figure 3-10). For hazardous waste treatment, the proc-
ess is used to separate water from the hazardous com-
ponents. Freeze-crystallization uses a refrigeration
process that causes water in a solution to form into
crystals. The crystals are then separated from the re-
maining material, washed, and melted into a purified
stream. This leaves a concentrated volume of the water-
stripped material to be processed for resource recovery
or, in some cases, used directly. Ferric chloride solution
concentrated by freeze-crystallization treatment of
acid pickling baths can be used in water treatment, for
example.
Feed
Recovered Salt Solution
Figure 3-10. Example of the Freeze-crystallization process
(adapted from Heist [39]).
3.10.3 Process Maturity
Development of the freeze-crystallization process be-
gan in the 1950s, when it was commercialized for frac-
tioning p-xylene from its isomers. The process has been
used to desalt seawater, to purify organic chemicals,
and to concentrate fruit juices, beer, coffee, and vinegar.
In the late 1980s, freeze-crystallization was applied to
the treatment of hazardous wastewaters in the United
States. The newer, direct-contact refrigeration cycles, in
which coolant is mixed directly with the input solution,
have improved the efficiency of the technology (40).
3.10.4 Description of Applicable Wastes
Freeze-crystallization is most effective when used to
treat nonfoamy, nonviscous wastes and liquid wastes
with low suspended solids content. Demonstrated appli-
cations include recycling of acid pickle liquor, recycling
of alkaline baths used in metal finishing, and recovery
of materials from ammunition plant wastewater (5).
3.10.5 A dvantages
The freeze-crystallization process is energy efficient,
closed (no emissions), and flexible enough to adjust to
a wide variety of wastes. Input solutions generally do not
require pretreatment. Contaminants in the crystal melt
contain from 0.01 to 0.1 percent of the contaminants in
the input solution. The residual retains the volatiles that
are in the waste. Low temperatures during operations
help avoid corrosion of metal equipment.
3.10.6 Disadvantages and Limitations
High capital costs are associated with the process, de-
pending on the operation, facility size, and construction
materials. The capital costs can be two or three times
higher than the costs of evaporation or distillation sys-
tems. Production hangups can occur because of the
complexity of the process used to control crystal size
and stability. Eutectic conditions can occur where more
than one material crystallizes at the same time. Buildup
on the vessel walls of the crystallizer, or fouling, even-
tually occurs and requires system shutdown to allow
foulant removal (41).
3.10.7 Operation
The major components of the process are crystal I izers,
separators, melters, and a refrigeration system. A solu-
tion is fed into one or more crystal I izers, where the
solution is either cooled or evaporated. Crystals begin
to form and can be separated from the residual concen-
trate by filtration, hydrocyclones, centrifuges, or wash
columns. The crystals are washed to remove additional
concentrate, then melted. The residual is a concentrated
contaminant stream that can be processed further for
organic or metal recovery or, in some cases, can be reused
directly. Processing capacities range from about 3.78
L/min (1 gal/min) in mobile units to 378 L/min (100 gal/min)
in larger systems. The operating costs primarily reflect
electricity and staffing needs.
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3.11 Propellant and Explosive Extraction
3.11.1 Usefulness
Propellant and explosive extraction applies physical and
chemical methods to remove energetic materials from
metal casings for reuse, conversion to basic chemicals,
or burning for energy recovery.
3.11.2 Process Description
Different energetic materials provide propulsive or ex-
plosive functions in rocket motors, munitions, and simi-
lar devices. These materials are made of different
chemicals and have different characteristics of solubility,
sensitivity to ignition, burn rate, and energy content. The
potential for reuse varies widely depending on the physi-
cal form, chemical content, and reactive characteristics
of the materials.
The energetic materials to be recovered may be present
in obsolete devices or in contaminated soils, sludges,
or manufacturing residues. Obsolete devices may be
refurbished and reused for their original purpose, or may
be disassembled so that the energetic materials can be
removed. The removed energetic materials may be
purified and reused (see Section 3.12), processed to
recover useful chemicals (see Section 3.13), or burned
for energy recovery (see Section 3.2.).
Munitions can contain various primers, igniters, propel-
lants, explosives, and chemicals (see Figure 3-11).
Used to initiate propellant burning, priming and igniting
Explosive
Propellant
compounds often are high-sensitivity materials, such as
metal azides or fulminates. Propellants (usually contain-
ing nitrocellulose, nitroglycerine, and/or nitroguanidine)
burn rapidly to drive the projectile. A fuse and igniters
trigger the projectile. The projectile may be filled with
explosives, pyrotechnic mixtures, or smoke-generating
chemicals. Explosive ingredients include trinitrotoluene
(TNT), high-melting explosives, and ammonium nitrate.
Chemicals frequently used in pyrotechnic and smoke
mixtures include magnesium, zinc, and metal nitrates.
The explosive or chemical fill is usually held in a binder.
Bombs contain materials similar to projectiles but do not
require propellants.
Rocket motors are thin metal casings containing an
energetic material held in place with a binder. The ener-
getic material typically is a mixture of ammonium per-
chlorate oxidizer and aluminum metal fuel, held by a
polymer binder.
3.11.3 Process Maturity
Commercially proven methods are available to extract
many types of energetic materials. Additional extraction
methods are under development to improve on the effi-
ciency of the existing methods and to allow extraction of
energetic materials from previously unprocessable
devices.
3.11.4 Description of Applicable Wastes
Recovery and reuse methods should be applied only to
munitions and rocket motors that have documented
Fuse
Recycling Process
Recycling Process
Recycling Process
Reuse or
Energy Recovery
Figure 3-11. Munition disassembly steps (adapted from Hermann [42]).
24
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histories. Documentation should include the method
of manufacture and the composition of all energetic
materials in the device. Propellants that contain com-
bustion modifiers, such as lead compounds, are difficult
to reuse because of the stringent controls on lead emis-
sions. Primary explosives and initiating explosives, such
as lead azide or metal fulminates, generally are not
candidates for recovery and reuse due to their sensitiv-
ity. Pyrotechnic chemical filling ingredients generally
are not recovered due to the variability of the composi-
tion used, their sensitivity, and the low value of their
ingredients (43).
3.11.5 Advantages
Extraction is a necessary preprocessing step for most
options to reuse or recover energetic materials. With the
exception of devices to be refurbished and reused, the
energetic material first must be removed from the device
to allow additional processing.
3.11.6 Disadvantages and Limitations
Due to the nature of the available energy content and
low activation energy of the materials, all processing of
energetic material requires careful attention to safety
precautions to avoid initiation of high-energy release
events.
Sludges and soils containing less than 10 percent by
weight of energetic materials typically pass the U.S.
Army Environmental Center criteria for nonreactivity and
do not exhibit a RCRA ignitability or reactivity charac-
teristic. Soils containing higher concentrations require
special precautions. Energetic materials extracted from
sludges or soils are likely to be sufficiently concentrated
to require special precautions (43).
Explosives projectiles and the oxidizer and fuel in rocket
motors are held by a binder, which usually is a
crosslinked thermosetting polymer. The binder can com-
plicate solvent extraction of explosives or the aqueous
dissolution of water-soluble oxidizers (44).
3.11.7 Operation
For an energetic material to be recycled, it typically must
be removed from its current container (e.g., projectile
body or rocket motor casing). Conventional techniques
involve some combination of disassembly and punching
or cutting to gain access to the energetic material.
Munition components can be disassembled and sepa-
rated by a process called reverse engineering, which
involves separation of the casing (containing ignition
compounds and propellant) from the projectile ignition
compounds, explosives, and possibly a fuse. The pro-
pellants are easily removed from metal casings, allow-
ing both the energetic materials and metals in the casing
to be reused. Projectiles or bombs can be opened by a
variety of methods. Punching opens small items with
thin- or medium-thick walls, such as pyrotechnic or
smoke munitions. Shearing with a guillotine-like shear
blade removes fuses and cuts rocket motors into smaller
sections. Wet saw cutting or high-pressure water jet
cutting are applicable to a wide variety of munition types
(45). Equipment for reverse engineering can be de-
signed to work well for specific munitions but does not
adapt easily to varying configurations (43).
Once the container is opened, the energetic material
can be removed. For composite rocket motors and other
items containing energetic materials held in place by
binders, high-pressure water washout (hydromining)
and mechanical cutting (machining) are the established
methods to remove the energetic materials from the
container. Hydromining has been in commercial opera-
tion since the mid-1960s to remove energetic materials
from rocket motors and projectile bodies. Propellant
machining is a standard manufacturing technique that
shapes the initial burning surface in a rocket motor to
provide the required ballistics or to remove all of the
propellant from rocket casings (43).
Cryogenic washout is a dry process that uses high-
pressure jets of cryogenic liquid to embrittle and fracture
the energetic material. Bench-scale testing has been
performed with liquid nitrogen and liquid ammonia, and
large-scale tests are planned (43). Removal of energetic
material using CO2 pellet abrasion and critical fluid ex-
traction also is under development (46).
Methods to dissolve the polymer binders used to hold
energetic materials also are being developed. Poly-
urethane-based polymers are commonly used as bind-
ers for propellants and explosives. By undergoing hy-
drolysis at 230°C (445°F), the polyurethane groups in
the binder split. The mixture is then treated by solvent
extraction to recover both polyols and energetic materi-
als from the binder (47). (For more information on the
use of chemolysis to reduce polymers to monomers and
oligomers, see Section 3.15.)
Some munition binders are heat sensitive and degrade
upon heating. Polypropylene-glycol-urethane, for exam-
ple, will degrade when heated to 160°C (320°F) and held
for 10 hours (44).
Melting and steamout are well-established methods for
removing TNT from explosive devices. These processes
use heating to liquefy the TNT, which is then poured out
of the casing. Melting and steamout are in commercial-
scale use at a variety of ammunition plants and at the
U.S. Army's Western Demilitarization Facility in Haw-
thorne, Nevada (43).
An emerging technique uses fracturing at cryogenic
temperatures to open the container and extract ener-
getic materials. Cryogenic fracturing involves cooling
the device with liquid nitrogen followed by crushing in a
25
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hydraulic press (48). Both the metal casing and the
energetic fill are brittle at cryogenic temperatures, so the
device fractures into small pieces when crushed. The
fragments can be processed to recover the energetic
materials by solvent extraction, melting, gravity separa-
tion, or magnetic separation (43).
Solvent extraction is the most appropriate process for
recovery of water-insoluble explosives from contami-
nated soils, sludges, and process wastes. Washing
explosives-contaminated lagoon samples with a 90-
percent acetone and 10-percent water extractant has
been demonstrated to achieve greater than 99-percent
removal. Recovery of the explosives and regeneration
of the extractant, however, present significant chal-
lenges. Distillation is the only currently feasible method
for separating the extracted explosive from the
acetone/water solvent. The distillation process subjects
the acetone to elevated pressure and temperature. Ex-
posing a volatile solvent containing the extracted explo-
sives to distillation conditions raises serious safety
concerns. An alternative solvent regeneration method
would be needed to allow commercial-scale develop-
ment of a solvent extraction system for wastes contami-
nated with explosives (43).
3.12 Propellant and Explosive Reuse
3.12.1 Usefulness
Physical and chemical methods are available to reuse
energetic materials in similar applications.
3.12.2 Process Description
Obsolete munitions and rocket motors can be inspected
and reused for training or similar applications. Explo-
sives and energetic materials can be remanufactured
into new explosive products, or processed to separate
and recover the energetic material for reuse (see Fig-
ure 3-12).
3.12.3 Process Maturity
Munitions and rocket motors have been inspected and
reused on a limited scale. Remanufacture of new devices
from obsolete equipment has been demonstrated on a
small scale, and reuse of separated energetic material
has been demonstrated on a commercial scale (43).
3.12.4 Description of Applicable Wastes
Relatively stable high explosives such as high-melting
explosive (HMX, or octahydro-1,3,5,7-tetranitro-1,3,5,7-
tetrazocine), 2,4,6-tetranitro-N-methylaniline (tetryl), or
TNT can be reliably reclaimed and reused. Propellants
such as nitrocellulose (NC), dinitrotoluene (DNT),
dibutyl phthalate (DBP), and nitroglycerine (NG) and
oxidizers such as ammonium perchlorate (AP) are less
stable and may require significant purification prior to
reuse (44).
3.12.5 A dvantages
Reuse of energetic materials allows potential waste ma-
terial to be recovered as a high-value product and
avoids the necessity of using new resources to manu-
facture explosives.
3.12.6 Disadvantages and Limitations
Due to the nature of the available energy content and
low activation energy of the materials processed, all
processing of energetic materials requires careful atten-
tion to safety precautions to avoid initiation of high-
energy release events.
3.12.7 Operation
Ordnance items and rockets are routinely reinspected
for training and similar applications. Reuse is, of course,
applicable only to devices that are in good condition and
have a well-documented history.
Hazard class 1.1 rocket propellant, containing explo-
sives such as NG, NC, and HMX, has been remanufac-
tured into 2-lb booster charges used to initiate
ammonium nitrate/fuel oil or slurry explosives. Plastic-
bonded explosives have been granulated and reused
to make charges for metal bonding and forming appli-
cations (43).
Energetic compounds can be collected for reuse by
processing to reject binder, impurities, and other inert
components. Explosives such as high-blast explosive
(HEX), HMX, research department explosive (RDX, or
hexahydro-1,3,5-trinitro-1,3,5-triazine), tetryl, TNT, NG,
and NC are dissolved or suspended by steaming, high-
pressure water jet cutting, or solvent extraction (see
Section 3.6). Filtration, selective extraction/precipitation,
vacuum evaporation, and other purification methods
then separate the explosives from the binders and im-
purities, such as metal fragments and decomposition
products (44).
Purified surplus explosive can undergo large-scale com-
mercial reuse in slurry explosives. Slurry explosives are
a saturated aqueous solution of water-soluble oxidizer,
which carries particles of oxidizer and sensitizing "fuel"
in suspension. The most common oxidizer is ammonium
nitrate, and the most common sensitizer is aluminum
powder (49). Sodium nitrate, sodium perchlorate, and
sodium chlorate are possible alternative oxidizers. Pat-
ent literature shows that munition explosives such as
TNT, tetryl, HMX, RDX, and NG are used as sensitizers
in slurry explosives. The reported consumption of slurry
explosives is hundreds of millions of pounds annually (43).
26
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Filters
Propellant
Crystallizers
Heat
Exchanger
T
Centrifuge
^
Ammonium
Perchlorate
(Wet)
Water Residue (Wet)
Figure 3-12. The ammonium perchlorate reclamation process (43).
Water-soluble ammonium perchlorate is recovered from
composite rocket propellants by leaching with hot water.
The propellant mixture, consisting of binder, ammonium
perchlorate, and aluminum, is size reduced and con-
tacted with heated water in a macerator. The ammonium
perchlorate is recovered from the water by crystal-
lization. The recovered ammonium perchlorate is in-
distinguishable from salt made from new materials and
can be reincorporated into rocket propellant (43).
3.13 Propellant and Explosive
Conversion to Basic Chemicals
3.13.1 Usefulness
Chemical processing is used to convert propellants and
explosives to basic chemicals that can be reused.
3.13.2 Process Description
The energetic components of munitions may have com-
mercial use as basic chemicals rather than as explo-
sives (see Figure 3-13).
3.13.3 Process Maturity
Commercial processes are available to recover basic
chemicals from munitions. Applications have been lim-
ited to a few special situations due to the low value of
the basic ingredients.
3.13.4 Description of Applicable Wastes
Energetic materials that contain a high proportion of
ammonia or nitrate are potentially useful for fertilizer
manufacture. Materials such as aluminum in rocket pro-
pellants or zinc, manganese, and phosphorus in pyro-
technic or smoke munitions can be recovered.
3.13.5 A dvantages
Conversion to basic chemicals can open a wider market
for lower value energetic or pyrotechnic materials.
3.13.6 Disadvantages and Limitations
Due to the nature of the available energy content and
low activation energy of the materials processed, all
processing of energetic and pyrotechnic materials re-
quires careful attention to safety precautions to avoid
initiation of high-energy release events.
Fertilizer-Grade
Phosphoric
Acid
Water
Phosphoric
Acid
Collection
i
I
>| Cyclone
Reclaimed
Metal
Figure 3-13. The white phosphorus reclamation process.
27
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3.13.7 Operation
Ammonium nitrate and ammonium perchlorate-based
propellants can be ground to reduce the particle size,
blended with inert carriers, and reused as nitrogen fer-
tilizer (50). Purified nitrocellulose-based propellants can
be used as supplements in animal feed (46).
The Crane Army Ammunition Activity in Crane, Indiana,
recovers white phosphorus from munitions by convert-
ing the phosphorus to phosphoric acid. The process
produces marketable phosphoric acid and metal scrap.
The acid conversion plant processes munitions from
other Army facilities and has sold thousands of tons of
phosphoric acid and scrap metal for its demilitarization
operations (43).
Thermolysis (Section 3.17) using a hydrogenation proc-
ess is being developed to convert propellants and ener-
getic materials to useful chemicals. In this process, the
waste is combined with hydrogen and is heated over a
catalyst in the temperature range of 40°C to 400°C
(100°F to 750°F) at pressures ranging from 1.6 to 8.6
mPa (250 to 1,250 psi) to form recoverable light organic
chemicals, such as methane and ethane (51).
3.14 Re-Extrusion of Thermoplastics
3.14.1 Usefulness
Reprocessing of thermoplastic waste is a method used
to make commercial and industrial polymeric products
from postconsumerand postindustrial commingled plas-
tics. The material is mechanically reground and then
extruded into the required shapes. (Sources for informa-
tion on specifications for thermoplastic material reuse
are given in Section 4.3.)
3.14.2 Process Description
The various stages for recycling thermoplastic wastes
are polymer characterization, collection, separation,
cleaning, regrinding, and extrusion. Postconsumerther-
moplastic products typically are made with extrusion
molds, blow molds, or injection molds (see Figure 3-14).
Extrusion entails rotating a screw in a barrel to melt
plastic pellets and force the molten resin through a die.
Extrusion usually precedes blow/injection molding. The
extrusion process is used to form film plastics (such as
sheet wraps) or profile extrusions (such as pipe). Blow
molding is used for containers (such as bottles),
whereas injection molding is used to form solid parts
(such as bottle caps) that require higher dimensional
precision.
One common structural product made from commingled
(mixed) plastic waste streams is plastic lumber, which is
a flow-molded linear profile. A mixture of films and con-
tainers, as well as some residual impurities known as
tailings, are blended into a compatible raw material and
extruded into large cross-section items that have struc-
tural utility. Blending is enhanced by compatibilizers that
allow bonding between two otherwise unadhering plas-
tics. Other types of impurities are "encapsulated" during
the extrusion of these shapes. Recently, wood, flour, and
glass fibers have been mixed with the recyclate to en-
hance the mechanical properties (such as stiffness and
strength) of the lumber. Production of plastic lumber is
the main focus of this discussion, as plastic lumber is
most amenable to the use of mixed plastics (53).
3.14.3 Process Maturity
Research currently is underway to improve the charac-
terization and separation of various polymers in waste
streams. The technology for regrinding and extruding
products itself is mature. The extruders and molding
equipment that process recyclates are commercially
available. Both structural and nonload-bearing products
made from recycled plastics are in the marketplace.
Only a few companies, however, currently make glass-
and fiber-reinforced plastic lumber with proprietary tech-
nologies.
3.14.4 Description of Applicable Wastes
The six types of plastics currently identified by number
for recycling are polyethylene-terephthalate (PET), high-
density polyethylene (HOPE), polyvinyl chloride (PVC),
low-density polyethylene (LDPE), polypropylene (PP),
and polystyrene (PS). All other plastics are included in
Category 7 for recycling purposes. The polyethylenes
(PEs), PP, and PS seem to be most suitable for plastic
lumber production. Some compatibilizers currently are
available to extrude PE/PVC, PE/PS, and PVC/PS
blends, as well as some specialized plastics. The blends
can be used to extrude plastic lumber. PVC in large
fraction does lead to some stability problems due to
degradation (52, 54, 55).
3.14.5 A dvantages
Mechanical recycling or re-extrusion of thermoplastic
waste has several advantages in addition to reducing
waste disposal volume. First, commingled plastics can
be processed with minimal separation. Next, manufac-
tured plastic lumber has weather-resistant properties
superior to those of traditional wood, as well as sufficient
strength and toughness to replace wood. Furthermore,
the re-extrusion process is a way to use tailings, the
miscellaneous plastics left after the stream has been
mined of HOPE and PET. Finally, certain products (such
as plastic pallets) can be molded directly rather than
fabricated from extruded lumber.
28
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Plastic
Particulate
Extrusion
Screw
L^
1
1
r^
i
i
i
Extrusion
Die
Extruded
Product
Feed
Section
Figure 3-14. Example of an extruder (52).
Compression
Section
3.14.6 Disadvantages and Limitations
The user of materials from Superfund sites will have a
high level of concern about the potential for incorporat-
ing trace contaminants into commercial products. The
primary limitation of re-extrusion of thermoplastic waste
is the variability in the properties of the end product. In
addition, very few specifications for lumber products
currently are available to the buyer to purchase these
products. ASTM Committee D20.95 currently is working
on some of these standards (see Section 4.3). Another
limitation of the lumber seems to be lower stiffness
values compared with wood that sometimes lead to
unacceptable deflection in structural uses. Therefore,
changes in design sometimes are warranted for struc-
tural applications. Several research programs funded
by state and federal agencies currently are under way
to establish material property databases and design
procedures.
3.14.7 Operation
Machinery for extruding and molding currently is avail-
able on a turnkey basis and can be set up for operation.
A directory of equipment manufacturers with a list of
products made from recycled plastics has been com-
piled. The availability and transportation costs of the raw
materials heavily influence the economics of a success-
ful recycling plant, however. Extrusion without separa-
tion leads to products of dark brown, black, or gray
colors; for other colors, separation and sorting are nec-
essary. A manufacturer may require that a municipality
that collects mixed plastics also buy the recycled prod-
uct. Studies have shown that local, state, and federal
governments will be the largest consumers of recycled
plastic lumber products, such as guardrail posts, plastic
pallets, benches, or landscape timbers.
Metering
Section
3.15 Chemolysis
3.15.1 Usefulness
Chemolysis is a chemical method to recover useable
monomers or short-chain polymers from solid polymer
wastes.
3.15.2 Process Description
Chemolysis is a depolymerization reaction to convert
polymers (about 150 repeating units) into monomers or
short-chain oligomers (2 to 10 repeating units). Chemo-
lysis reduces condensed polymers by reversing the pre-
parative chemistry (see Figure 3-15). The polymers
react with water or alcohols at elevated temperature to
break the bonds between units (56).
3.15.3 Process Maturity
Chemolysis is used commercially to recycle clean waste
that contains one type of polymer. In particular, several
companies have commercial processes that recycle
PET wastes by methanolysis, glycolysis, or hydrolysis.
Polymer-
O
I
H
AW-R-NH, + HO-R^M
Monomers
and
Oligomers
Figure 3-15. Example of a Chemolysis reaction.
29
-------
Extension of the process to mixed polymer types will
require significant development (57). Molecular separa-
tion of polymers by selective dissolution has been dem-
onstrated at the bench scale (58).
3.15.4 Description of Applicable Wastes
Condensation polymers such as polyesters and poly-
amides and some multiple addition polymers such as
PEs are created by reversible reactions; therefore,
chemical reaction can convert them back to their imme-
diate precursors. Bulk thermoplastics such as HOPE,
PP, PS, and PVC are not easily broken down by chemi-
cal methods. These bulk plastics are more amenable to
thermal treatment to produce hydrocarbon products
(see Section 3.17) (59, 60).
3.15.5 A dvantages
Converting a solid plastic back into the monomers used
for manufacture creates a high-value chemical product.
Unlike grind and remelt recycling, conversion to mono-
mers and oligomers allows purification and remanufac-
ture of the plastic. Remanufacture avoids problems with
impurities such as copolymers, stabilizers, and pig-
ments, and with heat history and aging effects such as
yellowing or embrittlement (61).
3.15.6 Disadvantages and Limitations
The reaction conditions are specific to one type of poly-
mer and generally do not work well with mixed plastic
types. Chemical recovery of organic chemicals from
plastics requires expensive equipment and therefore
high throughput for economical operation.
3.15.7 Operation
Using glycols as the reaction medium stops short of
complete conversion to monomers. Glycolysis produces
short-chain oligomers consisting of 2 to 10 units. Use of
excess methanol at elevated temperature as the reac-
tion medium results in conversion to monomers. For
example, PET can be heated in contact with methanol
to produce dimethlyterephthalate and ethylene glycol
(62). Recent European patent applications discuss
treatment of PET wastes with alcohol and a barium
hydroxide transesterification catalyst to produce soluble
polyesters. Urethane can be broken down with an al-
kanolamine and catalyst into a concentrated emulsion
of carbamates, ureas, amines, and polyol (59).
Selective dissolution can also separate mixed polymers.
In this process, single polymers are removed from a
mixture by dissolution at a controlled temperature. The
most soluble polymer is removed first, followed by se-
quential dissolution of polymers at increasing tempera-
tures (52, 58).
3.16 Size Reduction and Reutilization of
Plastic and Rubber Wastes
3.16.1 Usefulness
Size reduction and reuse of plastics and rubber wastes
are ways in which waste plastics and rubber are shred-
ded or ground for use as filter media, filler in new
plastics, concrete or asphalt aggregate, and other appli-
cations requiring low-density filler. General require-
ments for rubber particulate for reuse are described in
Section 4.4.
3.16.2 Process Description
Originally, emphasis in plastics recycling was placed
almost entirely on thermoplastic materials because they
could be easily reworked by melt processing (see Sec-
tion 3.14). Thermoplastic materials accounted for the
largest volume of plastics in packaging and durable
goods, encompassing such commodity plastics as PE,
PP, PS, PVC, and PET polyesters. Thermoset plastic
materials have received greater emphasis in recent
years as attention has shifted from packaging to durable
goods, and recycling of thermoset plastics is now feasi-
ble. Thermoset materials can be shredded or ground for
reuse (see Figure 3-16). The focus of recent research is
to allow the plastic particulate to be reclaimed for higher-
value applications.
Mixed
Plastic
Shredder
Shredded Plastic
Figure 3-16. Example of a plastic shredding operation.
30
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3.16.3 Process Maturity
3.16.7 Operation
Clean, single-type thermoset plastic participate is
reused commercially as filler in new plastic products.
Applications for mixed materials require further develop-
ment. Mixed plastic is most likely to be reused as aggre-
gate or as a supplement in cement. The preparation,
characterization, and testing of polymer concrete (PC)
and polymer mortar (PM) are in the research phase.
The use of scrap tire in asphalt pavements is also in the
research stage. Although commercial equipment is
available to grind and separate rubber from scrap tires
and mix it with asphalt, the impact of mixing on pave-
ment performance is not yet certain. Several state gov-
ernments and the Federal Highway Administration
(FHWA) have conducted feasibility studies and trial
tests. All of these studies and tests indicated that this
method is the most effective way to reuse scrap tires.
The effect of rubber in asphalt on pavement perform-
ance is still being evaluated, and a cost-benefit analysis
of this new construction material's use on a large scale
is being conducted. On a more limited scale, recrea-
tional and sport surfaces prepared from this material
have worked quite successfully (54).
3.16.4 Description of Applicable Wastes
Lower-value mixed thermoplastic materials or thermo-
setting materials can be ground and reused as particu-
late. (Extrusion of waste thermoplastics is discussed in
Section 3.14.) Common thermoset polymers include vul-
canized elastomers (both natural and synthetic rub-
bers), epoxies, phenolics, amino resins (e.g., urea and
melamine formaldehyde), polyurethanes, and polyes-
ters (based on unsaturated polyester resins, generally
modified and crosslinked with styrenic monomers).
3.16.5 A dvantages
The main advantage of using waste plastics in PC and
scrap tires in asphalt is that both PC and asphalt con-
sume large quantities of these solid wastes, thereby
reducing waste disposal and alleviating incineration
concerns. Other advantages include enhancement in
the strength-to-weight ratio of concrete and durability
compared with cement-based materials.
3.16.6 Disadvantages and Limitations
One of the main disadvantages of PC and PM is the loss
of strength at high temperatures, which is an important
factor in applications such as precast building panels.
For rubberized asphalt, the problem so far has been
justifying the increased cost of the material, as the bene-
fits of better performance and durability are not yet
established.
Crosslinked polyurethanes are processed by shredding
or grinding for reuse in reaction injection molding (RIM)
or in plastic foam as inert filler or "rebond." Blending
flexible foam crumb waste with 10 to 20 percent by
weight virgin liquid isocyanate/polyol prepolymer and
using the reacted, cast composition as carpet backing
has been commercially successful. On the other hand,
attempts to use polyurethane regrind waste in RIM sys-
tems have been limited to low regrind levels (on the
order of 10 percent by weight), because the viscosity of
the liquid components that carry the regrind quickly
reaches unacceptable levels for the RIM process.
Recycling of sheet molding compounds (SMCs) and
bulk molding compounds (BMCs) differs from polyure-
thane recycling in two important respects: 1) the polyes-
ter/styrene bonds are not thermally reversible below the
degradation temperature of the polymer and 2) SMCs
and BMCs have a very high inorganic filler loading (on
the order of 70 percent by weight). This high filler loading
forestalls the use of incineration as a disposal method
because the recoverable energy content per unit weight
is low, the heat sink burden is high, and the volume of
residue is high.
Early recycling attempts centered on grinding the
crosslinked, filled compounds to a powder for use as an
inert filler. Ground SMC filler could best be incorporated
into the SMC mix by withholding an equivalent amount
of calcium carbonate, resulting in a compound that had
the advantage of a slightly lower density. The monetary
value of the calcium carbonate replaced by ground
SMC, however, is a few cents per pound and cannot
account for the processing costs of grinding SMC.
To upgrade the value of recycled SMC, processes were
developed that enable the composite to be broken up
gently, leaving the glass fibers largely intact. SMC or
BMC products prepared with this type of recycled poly-
ester composite benefit from the reinforcement provided
by the salvaged glass fibers. These products can re-
place a portion of both high-quality, primary calcium
carbonate and the glass fibers required for compound-
ing new SMC or BMC materials. Processes along simi-
lar lines are being developed.
Plastic or elastomer particulate also can be reused in
concrete or asphalt. PET and PE chips are mixed with
concrete or mortar to form PC or PM. These composites
are stronger and more durable than conventional cement-
based construction materials (63). Rubber from old tires
can be reused in pavement applications to enhance
pavement performance. Two processes yield this com-
posite material; the "dry" process uses 6.35 mm (V4-in.)
chunks or larger and the "wet" process uses finely
ground particles of rubber (64).
31
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3.17 Thermolysis
3.17.1 Usefulness
Thermolysis (thermal conversion) uses elevated tem-
perature in a controlled atmosphere to produce valuable
chemical monomers by processing liquid or solid or-
ganic wastes.
3.17.2 Process Description
Thermolysis of high-organic solid wastes to basic hydro-
carbon products involves pyrolysis, hydrogenation, or
gasification. Pyrolysis is heating in the absence of air to
produce liquid and gaseous hydrocarbons (see Fig-
ure 3-17). Hydrogenation is the treatment of viscous
organics at high temperature and pressure, typically
with a catalyst, to produce valuable saturated hydrocar-
bons. Gasification is partial oxidation of a range of hy-
drocarbons to produce synthesis gas (carbon monoxide
and hydrogen), used in the production of organic chemi-
cals (56, 57).
^\
Ba
sifier
c
\
\t
Cyclone
J \
^/
= ^
/*
c
XX
A oh -^4
/^
^ F
HE
s.
CFBa
ombust
rlue Gas to
;at Recovery
>r
^ Fuel as
*.
/^ \
Cooler
(^J
Plastic
Particulate
Feed -^-x /
\/ Removal
Mixed
.Monomer
Product
Steam
Steam
_»
Required
'Circulating Fluidized Bed
Figure 3-17. Example of the pyrolysis process.
3.17.3 Process Maturity
In Europe, plastics pyrolysis demonstration plants are
operating in Ebenhausen, Germany, and Linz, Austria.
Development in the United States to date has focused on
treatment of scrap tires. The current development chal-
lenges are process scale-up and improved process effi-
ciency when processing high-solids-content plastics (65).
3.17.4 Description of Applicable Wastes
Thermochemical methods to convert organic solids to
petrochemicals are better able to process mixed mate-
rial and higher inorganic content than re-extrusion or
chemolysis are. Mixed polymeric wastes can be proc-
essed without sorting or significant preparation. Contami-
nation of the plastic wastes also can be tolerated (66).
3.17.5 A dvantages
Thermolysis can treat mixed, coarsely ground plastic
scrap at high throughputs to yield basic hydrocarbon
products. The process can be designed and operated to
limit the production of higher molecular-weight liquids
that can reduce overall process efficiencies.
3.17.6 Disadvantages and Limitations
Chlorine (from PVC wastes) contaminates the liquid
product if not removed. Even low levels of chlorine are
unacceptable for refinery feed or fuel use. Testing of a
thermolysis process at the Energy and Environmental
Research Center (EERC) at the University of North
Dakota targeted a maximum chlorine content of
200 ppm (67). Chlorine can be removed by preprocess-
ing or by retention in fluidized bed material such as
calcium oxide (CaO).
Some nitrogen-containing polymers, such as nylon, can
produce hydrogen cyanide, resulting in potentially haz-
ardous off-gas. The process uses high-temperature
processing equipment, which requires a significant capi-
tal investment to develop a full-scale processing plant.
3.17.7 Operation
Testing at the EERC indicates that thermal decomposi-
tion of polymers is influenced by temperature, fluidized
bed material, fluidization velocity, and feed polymer
composition. Temperature had the strongest effect, but
the effects of bed material, fluidization velocity, and feed
composition were greater than expected. With olefin
polymers, increasing temperature changed the product
liquid composition; lower temperatures yielded olefins
and aliphatics, intermediate temperatures yielded
cyclics and aromatics, and high temperatures yielded
fused-ring aromatic polymers (67).
Atypical process uses circulating fluidized bed reactors
to convert mixed plastic wastes into monomer feed-
stock. The primary product from the process is ethylene,
based on the composition of typical plastic wastes.
A product gas containing about 40 percent ethylene has
been produced from a mixed polymer feedstock. The
product gas could be fed to an ethylene purification plant
to produce the high-purity feedstock necessary for poly-
merization and/or other products. Treatment of coarsely
ground plastic scrap at high throughputs produces the
desired monomer products at low cost. Operation of the
process is expected to be simple, with a startup fuel
used initially to heat the reactors and supply any addi-
tional energy required for the system. Severe operating
conditions (e.g., high temperature and high pressure) allow
conversion of industrial wastes, scrap tires, used oil, or
mixed plastic wastes to basic organic components (68).
32
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3.18 Chemical Precipitation
3.18.1 Usefulness
Precipitation is a chemical method to remove and con-
centrate dissolved inorganics from aqueous materials
with low concentrations of contaminants. The precipi-
tated solid may be a useful product, or it may receive
additional processing (e.g., chemical leaching or smelt-
ing) to recover a salt or metal.
3.18.2 Process Description
In the chemical precipitation process, soluble contami-
nants are removed from a waste stream by their conver-
sion to insoluble substances. Physical methods such as
sedimentation and filtration can then remove these pre-
cipitated solids from solution. The addition of chemical
reagents that alter the physical state of dissolved or
suspended metals initiates precipitation. Reagents also
adjust the pH to a point where the metal is near its
minimum solubility (see Figure 3-18). Standard reagents
include:
Lime (calcium hydroxide)
Caustic (sodium hydroxide)
Magnesium hydroxide
Soda ash (sodium carbonate)
Trisodium phosphate
Sodium sulfide
Ferrous sulfide
These reagents precipitate metals as hydroxides, car-
bonates, phosphates, and sulfides. Metals commonly
removed from solution by precipitation include arsenic,
barium, cadmium, chromium, copper, lead, mercury,
nickel, selenium, silver, thallium, and zinc. Xanthates also
are being evaluated for the precipitation of metals (69).
j= 1,000
10 -
0.1 -
0.001 -
I 0.00001 L
024 6 8 10 12
PH
* Based on Hydroxide as the Solid Phase
Figure 3-18. Solubility of metal ions in equilibrium with a
hydroxide precipitate.
14
The chosen reagent is added to the metal solution by
rapid mixing followed by slow mixing to allow the pre-
cipitate particles to grow and/or flocculate. A floccu-
lant/coagulant reagent often is needed to enhance
particle agglomeration. Sedimentation or clarification,
the next step in precipitation, allows the precipitate to
settle to the bottom of a tank for collection. Typical
settling times for heavy metal particles range between
90 and 150 min (70).
3.18.3 Process Maturity
Industrial use of chemical precipitation of metal-contain-
ing wastewater is widespread. Precipitation is com-
monly used for wastewater treatment at electroplating
facilities, leather tanning shops, electronics industries,
and nonferrous metal production facilities. Precipitation
often is selected for removing metals from ground-water
pump-and-treat operations. Vendor systems are avail-
able for ground-water treatment with design flowrates of
up to 95 L/sec (1,500 gal/min).
Precipitation also is applied to recycling, either to cap-
ture metals in a more concentrated form for subsequent
processing or, less commonly, to form a solid metal salt
product.
3.18.4 Description of Applicable Wastes
Hydroxide precipitation effectively removes cadmium,
chromium (+3), copper (+2), iron (+3), lead, manganese,
nickel, tin (+2), and zinc. Most of these can be removed
to concentrations of less than 1 mg/L (0.06 grains/gal).
For arsenic, cadmium, lead, silver, and zinc, the residual
concentration in solution is significantly lower with sul-
fide precipitation. Sulfide precipitation also is effective
for chromium (+3, +6), copper (+1, +2), iron (+2, +3),
mercury, nickel, and tin (+2). Hydroxide precipitation
generally shows poor metal removal when chelating
agents are present, although these agents have less
effect on the efficiency of sulfide precipitation.
3.18.5 A dvantages
Precipitation collects metals in a concentrated form for
reuse as salts or, with additional processing, for metal
recovery. Precipitation can achieve very low concentra-
tions of metal contaminants in the treated water. Chemi-
cal precipitation is a proven technology for industrial
wastewater treatment with many years of data demon-
strating effectiveness fora wide range of waste streams.
Precipitation uses simple, low-capital-cost, commer-
cially available equipment.
3.18.6 Disadvantages and Limitations
Precipitation usually does not produce a useful product
directly. In most applications, the precipitated sludge
requires further processing to recover the metal. For
33
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example, precipitation may be used to produce a sludge
that is then processed by hydrometallurgical or pyromet-
allurgical methods to recover products. Precipitation
usually requires supplementary processing or chemical
adjustments. For example, physical separation may be
needed to remove suspended solids or oil and grease.
Adjustment of the metal's oxidation state (e.g., reduction
of Cr(VI) to Cr(lll)) may be needed.
Some precipitation processes, particularly the sulfide
system, have the potential to generate undesirable or
toxic sludge or off-gas.
3.18.7 Operation
A typical system may begin with pretreatment steps
such as large solids removal, cyanide destruction,
and/or chemical reduction. Materials then enter a mixing
tank, where the selected reagent is added. A floccula-
tion/coagulation tank may then be needed to allow the
precipitate to settle. Flocculants such as alum, lime, or
polyelectrolytes are added in a slowly stirred tank to
promote agglomeration of the precipitate, yielding
denser particles that settle faster. Settling usually takes
place in a clarifier with a sloped bottom, where the
sludge is collected. In a continuous system, the sludge
is sent to a subsequent settling tank for further settling.
Following settling, the sludge must be dewatered through
vacuum filtration or filter presses prior to recovery.
Treated water effluent from the clarifier can be filtered to
remove fine particulates that did not settle. Other tech-
nologies such as ultrafiltration, reverse osmosis, acti-
vated carbon capture, and ion exchange can be used to
treat the effluent to further reduce concentrations of
metals, if required.
The pH is a critical operating parameter in a chemical
precipitation system. The optimal pH must be first deter-
mined, then maintained. A pH level at which the metal
compound has a low or minimum solubility is desired.
For hydroxides, the pH would range from 9 to 11. Sul-
fides have lower solubilities at similar pH ranges; there-
fore, lower pH levels (pH 8 to 10) can be used to achieve
comparable removal. Selecting the optimal pH is com-
plicated by the fact that metal hydroxides have specific
points of minimum solubility, and these minimums occur
at different points for different metals. Varying solubilities
present a challenge when designing a system to treat a
water stream containing several metals. Including more
than one precipitation stage with different pH points may
be necessary. Sulfide precipitation normally is done at a
pH of greater than 8 to avoid generation of hydrogen
sulfide gas. Other operating parameters include reten-
tion time in various process steps, flowrate of the waste
stream, reagent dose rates, and temperature.
3.19 Ion Exchange
3.19.1 Usefulness
Ion exchange is a physical/chemical method to concen-
trate and recover dissolved inorganics from aqueous
solutions with low concentrations of contaminants.
3.19.2 Process Description
Ion exchange is a technology to remove ionic species,
principally metals ions, from aqueous waste streams.
The process is based on the use of specifically formu-
lated resins having an "exchangeable" ion bound to the
resin with a weak ionic bond. If the electrochemical
potential of the ion to be recovered (contaminant) is
greater than that of the "exchangeable" ion, the ex-
change ion goes into solution, and the metal binds to the
resin (see Figure 3-19).
Influent Water, B+Ions
KEY
+ Sites With A* Ions
* Sites With B* Ions
Exhausted Zone
Ion Exchange
Active Zone
Regenerated Zone
Treated Water, A+ Ions
Figure 3-19. Example of an ion exchange operation.
Resins are separated into two classes: cation and anion.
Cation resins exchange positive ions, such as dissolved
metals, and anion resins exchange negative ions, such
as sulfate or nitrate. Resins have a higher affinity for
some ions than for others. Generally speaking, strong-
acid resins prefer cations with higher ionic charges.
Ion exchange is reversible, so the captured metal ions
are removed from the resin by regeneration using an acid
for cation resins or a base for anion resins. The concen-
tration of contaminants is higher in the regeneration so-
lution than in the treated wastewater. The regeneration
solution is further treated to recover metals or salts.
3.19.3 Process Maturity
Ion exchange technology is fully developed and com-
mercially available, although applications are waste-
stream specific. Applications have included removal of
34
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radionuclides from power plant waste streams, removal
and recovery of metals from electroplating operations,
removal of metals from ground and surface waters,
recovery and removal of chromium, and deionizing/soft-
ening of process water.
3.19.4 Description of Applicable Wastes
Ion exchange systems can effectively remove ionic met-
als such as barium, cadmium, copper, lead, mercury,
nickel, selenium, silver, uranium, and zinc. The technol-
ogy also is applicable to nonmetallic anions such as
halides, and to water-soluble organic ions such as car-
boxylics, sulfonics, and some amines. Ion exchange has
been used to recover chromium and copper from ground
water contaminated with wood-treating chemicals. The
chromium and copper are returned to the wood-treating
plant for reuse (71). Ion exchange in general is applic-
able for recovering metals from solutions containing less
than 200 mg/L (12 grains/gal) of dissolved metal. Solu-
tions with higher concentrations usually are more effi-
ciently concentrated using electrowinning (Section 3.28)
or dialysis methods (Sections 3.22 and 3.23) (70).
3.19.5 A dvantages
Ion exchange is capable of extracting all metals from
dilute wastewater streams and collecting the metals, at
a much higher concentration, in the regeneration solu-
tion. Further processing usually is needed to produce a
product metal or salt, however.
The capital cost of ion exchange equipment is low, and
operating costs are most influenced by chemical use,
cost of resin, and labor for regeneration. The cost to treat
a fixed water flow increases as the dissolved ion con-
centration increases. Therefore, ion exchange is best
suited for removal of metals from waste streams with
lower concentrations of dissolved metals (2).
3.19.6 Disadvantages and Limitations
The ion exchange resin must be regenerated to remove
the metals collected from the wastewater. Most ion ex-
change processes are not selective and thus recover a
mixture of metals. A reusable product is not recovered
directly; the regeneration solution is further processed
to produce a reusable product. A technology such as
dialysis or electrowinning is used to recover metals or
salts from the concentrated regeneration solution.
Ion exchange resins are prone to fouling because of
high concentrations of suspended solids or some or-
ganic substances. Pretreatment such as filtration can
remove some fouling agents. Oxidizers such as chromic
or nitric acid may react with the ion exchange resin,
causing the resin to degrade (70). In some cases, the
reaction may be severe enough to result in serious
safety concerns.
3.19.7 Operation
Ion exchange systems can operate in one of four
modes: batch, fixed bed, fluidized bed, and continuous.
The fixed bed system, the most common, typically in-
cludes four steps: service, backwash, regeneration, and
rinse. During service, the waste stream is passed
through the ion exchange resin, where ionic contami-
nants are adsorbed. When the ion exchange resin is
nearing full capacity (the concentration of dissolved ions
in the effluent begins to increase), the ion exchanger is
taken out of service and backwashed to remove sus-
pended solids. The resin bed is then regenerated by
passing either an acid (for cationic resins) or a caustic
(for anionic resins) through the resin bed. The resultant
low-volume regeneration solution can then be further
processed to recover metals or salts. The resin is then
rinsed of excess regenerant and returned to service (72).
Factors that affect the performance of an ion exchange
system include the concentration and valence of the
contaminants, the concentration of competing ionic spe-
cies or interferences, the concentration of total dissolved
and suspended solids, and the compatibility of the waste
stream to the resin material. Pretreatment techniques
for ion exchange systems (e.g., carbon adsorption,
aeration, or filtration) may be necessary. Cartridge filters
upstream of the resin bed can remove suspended sol-
ids. To prevent iron and manganese precipitation, pre-
aeration followed by flocculation, settling, and filtration
can be used (70).
3.20 Liquid Ion Exchange
3.20.1 Usefulness
Liquid ion exchange (LIX) is a form of solvent extraction
that allows separation, concentration, purification, and
recovery of dissolved contaminants from solutions. The
most common application is recovery of metals dis-
solved in water, but nonmetals and oil-soluble impurities
also can be recovered.
3.20.2 Process Description
The basic principle of solvent extraction applied to re-
cover metal from solution is simple. The process de-
pends on shifting the reaction equilibrium of a system,
usually by adjusting the pH of the aqueous phase. The
organic extractant and operating conditions are selected
to cause metals to partition from the waste stream into
the extractant. A stripping solution is selected to favor
distribution of the metals from the extractant into the
stripping solution. Although real-world applications intro-
duce complications, LIX is an effective method to treat
wastewaters containing metals at low concentration
while recovering a concentrated solution (73).
35
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In the LIX process, an aqueous solution containing met-
al contaminants is contacted with an extractant. The
extractant is immiscible in water and dissolved in high
flashpoint kerosene. Typical extractants include dibutyl
carbitol, organophosphates, methyl isobutyl ketone,
tributyl phosphate, amines, and proprietary ion ex-
change fluids. The metal-containing water and the or-
ganic extractant phases are thoroughly mixed to allow
rapid partitioning of the dissolved metals into the extrac-
tant (see Figure 3-20). After contacting, the mixed
phases enter a settler, where the water and organic
separate.
The organic extractant is then contacted with stripping
solution in a second contacting/settling step. The strip-
ping solution is chemically adjusted so that metals par-
tition out of the organic extractant into the water. This
stripping step regenerates the extractant for reuse and
captures the metal in the aqueous stripping solution.
The stripping water may be a marketable salt solution
or may require further treatment by precipitation, elec-
trowinning, or other processes to recover a salt or metal
product (73).
3.20.3 Process Maturity
Large-scale commercial LIX operations for metal recov-
ery have been in use for over 50 years. Equipment is
available from several vendors, and a wide range of
solvents allow extraction of the desired metals with mini-
mum impurity levels.
The technology was developed initially for recovery and
reprocessing of uranium. Applications have expanded to
primary production of copper, vanadium, cobalt, rare
earth metals, zinc, beryllium, indium, gallium, chromium,
mercury, lead, iron, cadmium, thorium, lithium, gold, and
Organic Phase
Aqueous Phase
r
Metals-Bearing
Water
Organic
Extractant
Treated
Water
Metals-Bearing
Organic
Extractant
palladium. Application to recovery of metals from waste
streams is, however, a recent development (74, 75).
3.20.4 Description of Applicable Wastes
The technology can be used to recover a variety of
dissolved metals at any concentrations. The total
dissolved solid concentration can be any level. The tech-
nology currently is being demonstrated for dissolved
metals concentrations ranging from 1 to 100,000 mg/L
(0.06 to 6,000 grains/gal). The feed stream for an LIX
process is a low-suspended-solids (preferably sus-
pended-solids-free) aqueous fluid containing dissolved
metal contaminants.
LIX can be used to regenerate extractant from chemical
leaching (see Section 3.29). Metal is extracted from a
metal-containing solid by aqueous solvents (acid, neu-
tral, or alkaline solutions). LIX is then used to recover
the metal and regenerate the extraction solution. LIX also
can be used to recover metals from contaminated sur-
face water, ground water, or aqueous process residuals.
LIX can selectively remove a dissolved metal contami-
nant from process brine, thereby allowing discharge or
recycle of the brine. A metal or combination of metals
can be recovered from multicomponent aqueous
streams containing metals in chelated form or com-
plexed by dissolved aqueous organics (e.g., citric acid)
or inorganics (e.g., phosphates). Careful selection of
extractant and process conditions is critical when apply-
ing LIX technology to these complex streams. Extract-
ants also are available for recovery of toxic oxoanions,
such as selenate and chromate.
3.20.5 Advantages
LIX processing recovers metals from solutions as high-
purity, marketable compounds or elements. Extractants
can be chosen to give high selectivity for the desired
metal while rejecting common dissolved cations such as
calcium or sodium and other impurities. Solutions con-
taining as little as 1 mg/L to more than 100,000 mg/L
(0.06 to 6,000 grains/gal) can be concentrated by factors
of 20 to 200.
LIX can achieve high-throughput, continuous operation.
The process is tolerant of variations in feed composition
and flow. The extraction/stripping operations can be
carried out in simple, readily available process equip-
ment at low pressure and temperature (ambient to 80°C
Figure 3-20. Liquid ion exchange contacting cell.
3.20. 6 Disadvantages and Limitations
The LIX process requires low levels of suspended sol-
ids. Suspended solids entering the phase separation
settler may collect at the water/extractant interface, in-
terfering with phase separation.
36
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Complex waste streams can be processed but may
require several extraction stages. Extractant formulation
and process optimization for treating waste streams
containing several metals and contaminants require ex-
perience with LIX processes and treatability testing.
3.20.7 Operation
Feed flowrates from 1 ml to thousands of gallons per
minute can be processed. Various contactor/phase
separation devices are available to allow selection of
optimal equipment for the waste stream, extractant, and
flowrateto be processed. For example, liquid-liquid con-
tacting can be accomplished in mixer-settlers, columns,
centrifuges, and hollow-fiber or spiral-wound membrane
cells. After mixing in the contactor, the water/organic
mixture is allowed to separate in a settler, a relatively
quiescent area in the process equipment where the
immiscible water and oil phases disengage and flow
separately from the unit. The metals are stripped from
the extractant using the same mixing/settling approach.
The stripping solution may be pure water or may contain
acidic, basic, or neutral salts or dissolved complexing
agents. The stripping chemistry is chosen to allow effi-
cient removal of metal from the extractant while produc-
ing a useful product. For example, copper can be
stripped by sulfuric acid to produce a marketable copper
sulfate solution. The metal product from the LIX process
may be a solution, solid salt, elemental metal, or precipi-
tate. The stripping solution may be forwarded to a crys-
tallizer or precipitator/clarifier to form solid salt or may
be electrowon to form elemental metal.
3.21 Reverse Osmosis
3.21.1 Usefulness
Reverse osmosis (RO) is a physical/chemical method to
concentrate and recover dissolved inorganics in aque-
ous solutions with low concentrations of contaminants.
3.21.2 Process Description
Osmosis is the movement of a solvent (typically water)
through a membrane that is impermeable to a solute
(dissolved ions). The normal direction of solvent flow is
from the more dilute to the more concentrated solution
(see Figure 3-21). RO reverses the normal direction of
flow by applying pressure on the concentrated solution.
The semipermeable membrane acts as a filter to retain
the ions and particles on the concentrate side while
allowing water to pass through. The cleaned water pass-
ing through the membrane is called the permeate. The
liquid containing the constituents that do not pass
through the membrane (i.e., metals) is called the con-
centrate. Metal or salt products are recovered from the
Waste_
Feed
Permeate
High-Pressure
Pump
Figure 3-21. Example of the reverse osmosis process.
concentrate by techniques such as evaporation, electro-
winning, or precipitation.
For RO applications, membranes that have high water
permeability and low salt permeability are ideal. The
three most commonly used RO membrane materials are
cellulose acetate, aromatic polyamide, and thin-film
composites, which consist of a thin film of a salt-rejecting
membrane on the surface of a porous support polymer.
3.21.3 Process Maturity
RO has long been used to desalinate water. The proc-
ess is beginning to be applied in the electroplating in-
dustry for the recovery of plating chemicals in rinse
water.
3.21.4 Description of Applicable Wastes
RO can be applied to concentrate most dissolved metal
salts in aqueous solution. Electrolytes and water-soluble
organics with molecular weights greater than 300 are
stopped by the membrane and collect in the concen-
trate. Most metals in solution (e.g., nickel, copper,
cadmium, zinc) can be concentrated to about 2 to 5
percent in the concentrate (76, 77). Waste solutions
containing high suspended solids, high or low pH, oxi-
dizers, or nonpolar organics typically are not suitable for
RO processing.
3.21.5 Advantages
RO separates a waste stream into two streams: the
cleaned permeate and the concentrate, which may con-
tain percent concentrations of dissolved salts. The
cleaned permeate can be reused as process water, and
the concentrate can be further treated to recover metal
or can be reused as a metal salt solution. RO is less
energy intensive than distillation or evaporation.
3.21.6 Disadvantages and Limitations
RO membranes are sensitive to fouling and degrada-
tion. Even trace concentrations of nonpolar organics or
37
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moderate to high levels of suspended solids will foul the
membranes. Pretreatment can be used to condition the
waste and reduce fouling problems. Extreme pH condi-
tions or oxidizers in the waste solution will degrade the
membrane (70).
The ability of the membrane to retain dissolved contami-
nants is based on molecule size, weight, and electrical
charge, as well as variations of maximum pore size of
the membrane; therefore retention may be difficult to
predict. RO seldom exhibits "absolute" retention (77).
Evaporation produces more concentrated solutions than
does RO, which is frequently used to preconcentrate
waste streams prior to evaporation.
3.21.7 Operation
Performance of the RO system typically is measured by
three parameters: flux, product recovery, and rejection
(78). Flux is the flowrate of permeate per unit area of
membrane measured as liters persquare meter (gallons
per square foot) per day. The major factors influencing
the sustainable flux are the physical and chemical sta-
bility of the membrane, fouling rate, and flow limits due
to concentration polarization at the membrane.
Product recovery is the ratio of permeate flow to feed
flow and typically is controlled by adjusting the flowrate
of the reject stream leaving the RO module. Low product
recoveries result in a low concentration of the metals.
As product recovery increases, the metals concentra-
tion of the concentrate increases, requiring an increase
in pressure from the pump to overcome the osmotic
pressure.
Rejection measures the degree to which the metal is
prevented from passing through the membrane. Rejec-
tion increases with the ionic size and charge of the
metals in the feed. Rejection is dependent on the oper-
ating pressure, conversion, and feed concentration.
Typically, metals removal by RO is greater than 95
percent.
3.22 Diffusion Dialysis
3.22.1 Usefulness
Diffusion dialysis is a method to recover acids or bases
for reuse by processing waste aqueous solutions that
contain acids or bases contaminated with dissolved
metals and organics, particulate and colloidal matter,
and other dissolved or suspended nonionic species.
3.22.2 Process Description
Diffusion dialysis is a simple ionic exchange membrane
technology that uses the concentration gradient as the
driving force to achieve separation of acids or bases
from waste solutions (see Figure 3-22). Anion exchange
KEY
~\A)~ ~ Anionic Selective Membrane
M+ Cationic Metal
W Aqueous Wastestream
P Product Acid
Depleted
Waste *
Water-
M+
Acid
1
^
Acid
W
M+
W
Waste
Acid
Product
Acid
Figure 3-22. Example of a diffusion dialysis cell.
membranes allow the passage of anions only (e.g., Cl,
NO3, F, SO4 2~), and cation exchange membranes allow
the passage of cations only (e.g., Na+, NH4+). The
membranes are impermeable to nonionic species, par-
ticulates, colloids, and even organics. The only excep-
tion to the impermeability is the passage of hydrogen
(H+) and hydroxyl (OH) ions. Because of their small size
and high mobility, hydrogen ions can pass through an
anion exchange membrane that is impermeable to all
other positively charged ions, and hydroxyl ions can
pass through a cation exchange membrane. The process
unit consists of a stack of anion exchange membranes
(in acid recovery) or cation exchange membranes (in
base recovery) with spaces between them (79).
3.22.3 Process Maturity
Large-scale diffusion dialysis units (760 to 7,600 L/day
[200 to 2,000 gal/day]) for acid or base recovery are
available and in commercial operation at several sites in
the United States. Several vendors also supply small-
scale (38 to 380 L/day [10 to 100 gal/day]) portable
units. The units are modular, and increases in size or
flowrate involve adding membranes to the stack.
3.22.4 Description of Applicable Wastes
The most frequent uses of diffusion dialysis have been
to recover acid values from spent pickling liquor in steel
plants and spent aluminum anodizing baths, to recover
mineral acids from battery waste, and to recover caustic
38
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from chemical milling waste. Diffusion dialysis can re-
cover acids or bases from solutions containing particu-
lates, colloidal suspensions, dissolved metals, and
dissolved organics. Dissolved organics are either non-
ionic or positively charged in acidic waste streams or
negatively charged in basic waste streams, and they are
rejected by the anion exchange or cation exchange
membranes used in the recovery of acids and bases,
respectively. The acid or base concentration in the feed
waste streams can be as high as 30 percent by weight
in diffusion dialysis. Waste solutions containing mixed
acids (e.g., HF and nitric acid) also can be recovered.
3.22.5 Advantages
Diffusion dialysis is a low-pressure, low-temperature
process that does not require the addition of treatment
chemicals. Power is needed to run the pumps, a minimal
requirement. Skid-mounted, modular, portable diffusion
dialysis units are available, allowing convenient applica-
tion on site. The modular design provides the ability to
adjust capacity as needed. The process can handle
acidic or base streams in small, drummed batches or as
a continuous stream from a process. Operating costs
are minimal.
3.22.6 Disadvantages and Limitations
Diffusion dialysis uses water in quantities equal to the
volume of the waste stream. The product stream con-
taining the acid or base values must be used on site or
shipped for sale. The capital costs are high compared
with conventional wastewater treatment equipment. The
capital cost of a small (38 L/day [100 gal/day]) diffusion
dialysis unit is $25,000. Membranes are susceptible to
scaling and biological fouling. The overall process eco-
nomics depend on the usable membrane life (80).
3.22.7 Operation
The aqueous waste stream and water are fed counter-
currently into alternate compartments in the membrane
stack. Underthe influence of the concentration gradient,
the acid values (consisting of H+ ions and anions) from
the waste stream pass through the anion exchange
membrane and migrate to the water stream, forming the
product acid. The acid-depleted waste stream contain-
ing the dissolved metals, particulates, and other non-
ionic species (e.g., organics) is sent for disposal. The
recovered acid is either sold or used in the plant. The
acid recovery rate typically is 90 to 99 percent. The
flowrates of the waste stream and water stream usually
are comparable. Similar flowrates and countercurrent
flow assure minor or no dilution of acid concentration in
the product stream relative to the feed waste stream.
The unit for base recovery is similar to that for the acid
system except that cation exchange membranes are
used and alkali values from the waste stream migrate
across the membrane to the product stream.
3.23 Electrodialysis
3.23.7 Usefulness
Electrodialysis (ED) is a method to recover acids or
bases for reuse by processing aqueous waste streams,
or to concentrate and recover selected ions from aque-
ous waste streams containing other dissolved or sus-
pended contaminants.
3.23.2 Process Description
In ED, ions in solution are selectively transported across
ion exchange membranes under the influence of an
applied direct-current field (see Figure 3-23). The ion
exchange membranes are either anion selective (i.e.,
permeable to anions such as Cl~, SO4 2~) or cation se-
lective (i.e., permeable to positive ions). The membrane
itself acts as a barrier to the solution, to suspended
particles, and to other dissolved nonionic species. An
ED unit consists of hundreds of alternating anion and
cation exchange membranes with spacers between
them. Water and the feed containing dissolved ions and
other contaminants are introduced into adjacent com-
partments in alternating fashion. Under the imposed
polarity, the anions and cations from the feed migrate in
opposite directions and concentrate in the two adjacent
water-filled compartments. Because of the alternating
arrangement of cation and anion membranes, the ions
KEY
- -(A) - Anionic Selective Membrane
© Cationic Selective Membrane
© Cation
© Anion
Anode
Rinse
Anode +
\
Feed
Cathode
Rinse
5T
Concentrate
Product
VVater
T
1 Cathode -
Figure 3-23. Example of an electrodialysis cell.
39
-------
pass through the first membrane they encounter but are
blocked by the next membrane because of their charge.
The combination of migration due to the electric field and
the arrangement of ion-selective membranes allows
ions to concentrate in the water-filled compartments. ED
units are capable of concentration factors of 10 or more.
The concentrate and the diluate (feed solution depleted
of most of its ions) are collected and reused (79).
3.23.3 Process Maturity
ED units are used in commercial operations to recover
metal plating baths (80). Small units (38 to 190 L/day
[10 to 50 gal/day]) are used in small plating job shops,
and large units (380 to 3,800 L/day [100 to 1,000 gal/day])
are used in larger applications such as at aircraft main-
tenance depots.
3.23.4 Description of Applicable Wastes
ED is used to recover caustic from spent chemical mill-
ing solutions, metal values from plating rinse water, and
acid from spent etchants and pickling liquors (5). ED
units separate chemical values from solutions con-
taining particulates and colloid suspensions. The acid or
base concentrations in the feed and concentrate
streams can be as high as 25 percent by weight in
electrodialysis.
2.23.5 Advantages
The concentrate stream volume is small relative to the
feed stream volume (by a factor of 10 or more), resulting
in the recovery of chemical values in a concentrated
form. Skid-mounted, modular, portable electrodialysis
units are available that allow convenient application on
site. The modular design provides the ability to adjust
capacity as needed.
3.23.6 Disadvantages and Limitations
Electrodialysis requires a source of power (10 to 200 kW)
to effect the separation. The diluate (feed depleted of its
chemical values) may not meet primary treatment stand-
ards and may require additional cleanup prior to dis-
posal. The capital costs are high compared with those
for conventional wastewater treatment equipment. The
membranes are susceptible to scaling and biological
fouling. The overall process economics depend on the
usable membrane life (80).
3.23.7 Operation
Waste stream (feed) and water are fed into alternate
compartments in the ED stack. The dissolved ions (ac-
ids, bases, or metal salts) migrate from the waste stream
under the influence of the electric field and concentrate
in the water stream. The water stream flowrate is sub-
stantially smaller than the waste stream flowrate. The
concentrate containing the recovered chemical values
is collected. The ion-depleted waste stream may be
reused as rinsewater or discarded, depending on the
application.
3.24 Evaporation
3.24.1 Usefulness
Evaporation is a thermal method to concentrate and
recover dissolved inorganics in aqueous materials with
low concentrations of contaminants.
3.24.2 Process Description
Evaporation takes place when a liquid is heated and
converts to vapor, with the liquid boiled away to leave a
concentrated salt solution or slurry (see Figure 3-24).
Evaporation processes may be used to recover the
vaporized liquid, to form a concentrated salt solution for
reuse, or to preconcentrate a salt solution for additional
processing for recovery of a metal or salt (81).
3.24.3 Process Maturity
Evaporation is used commercially to reduce the volume
of aqueous solutions produced by a wide variety of
processes (80). Applications for reuse or recovery of
valuable products are less common but have been com-
mercialized to recover dragout from plating baths, re-
cover contaminated acids, and produce ferric chloride
from steel pickling baths (82).
3.24.4 Description of Applicable Wastes
Evaporation is best suited to processing waters contain-
ing moderate starting concentrations of dissolved salts.
Waste streams containing more than about 4,000 mg/L
(230 grains/gal) of metal usually can be efficiently
evaporated to as high as 20 percent solids (76).
Evaporation is used to treat a variety of wastewater
streams containing dissolved metal salt contaminants.
For example, plating rinse wastes can be concentrated
Condenser
To Off-Gas
Treatment
Waste _
Feed
Concentrate
Figure 3-24. Example of the evaporation process.
40
-------
by evaporation. The evaporated water is reused for
rinsing, and the concentrate is returned to the plating bath.
Concentration by evaporation is more difficult for wastes
containing foam-stabilizing impurities such as surfac-
tants, fine particulates, or proteins; salts that have re-
duced solubility at elevated temperature (e.g., calcium
carbonate); compounds that decompose at elevated
temperature; and high-suspended-solids concentra-
tions.
3.24.5 Advantages
Evaporation concentrates dilute solutions of soluble
salts. Volume reductions of 80 to 99 percent are pos-
sible, depending on the initial salt and suspended solids
concentration and the salt solubility. The concentrated
solution may be reused directly but usually is further
treated by cementation, precipitation, electrowinning, or
other processes to produce useable salts, metals, or
brines. Evaporated water can be condensed and reused
as onsite process water (5).
3.24.6 Disadvantages and Limitations
Evaporation systems generally have high capital costs
and require both a significant energy input and a system
to collect and treat off-gas. Suspended solids, oil, and
grease cause foaming, which increases the difficulty of
process operations.
3.24.7 Operation
Evaporation processes require sufficient heat energy to
vaporize the liquid waste matrix. Evaporation usually is
carried out either by boiling heat transfer or flash evapo-
ration. In boiling heat transfer, steam, hot oil, or another
heat transfer source is applied to transfer heat through
a coil or vessel wall into the waste material. Boiling of
the waste occurs at the heated wall. In flash evapora-
tion, the waste is heated under pressure and then flows
by pumping or natural circulation to a vessel at lower
pressure, where boiling occurs. Common examples of
evaporators using boiling heat transfer are rising film,
falling film, and wiped film evaporators. Flash evapora-
tion is accomplished in forced or natural circulation
evaporators.
During the past decade, the use of atmospheric evapo-
rators has increased for recovery of plating chemicals.
The atmospheric evaporator contacts an airstream with
heated solution. The air humidifies and removes water,
concentrating the solution. The atmospheric evapora-
tors have lower processing rates than conventional
evaporators but use simpler, less expensive equipment
and are suitable for onsite processing of small volumes
of aqueous waste.
3.25 Mercury Bioreduction
3.25.7 Usefulness
Mercury bioreduction is a biochemical method to re-
cover mercury metal for reuse by processing mercury-
contaminated soils, sludges, sediments, and liquids.
3.25.2 Process Description
Bacterially mediated reduction of ionic mercury to mer-
cury metal plays an important role in the geochemical
cycle of mercury in the environment (83, 84). Two orga-
nisms, Pseudomonas putida (85) and Thiobacillus ferro-
oxidans (86), have been tested for their application to
the reduction and recovery of mercury wastewater. Bio-
logical activity can reduce mercury salts to metal (see
Figure 3-25). Elemental mercury metal is a dense liquid
with a relatively high vapor pressure, so low-energy
separation methods can recover the mercury after bio-
reduction. In most concepts, the bioreduced mercury
metal is removed from the waste matrix by airflow, then
captured on activated carbon. Mercury metal is then
recovered by retorting (Section 3.34). When the waste
matrix viscosity is low, mercury metal may be recovered
directly by gravity separation (Section 3.33).
3.25.3 Process Maturity
Bioreduction of mercury salts to metal is being explored
in the laboratory (87). There is no field experience with
the technology.
3.25.4 Description of Applicable Wastes
The bioreduction process is potentially applicable to
removal of mercury from solid or liquid wastes.
3.25.5 Advantages
Bioreduction allows mercury recovery to occur without
application of heat or use of potentially hazardous
chemical leaching agents.
Mercury-
Contaminated
Water
Air-
Off-Gas and
Mercury Vapor
Effluent
Sampling
Figure 3-25. System to study geochemical cycling of mercury
(adapted from Barkay et al. [83]).
41
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3.25.6 Disadvantages and Limitations
3.26.3 Process Maturity
Organisms can tolerate only low concentrations of mer-
cury. Biological reactions typically proceed at slower
rates than analogous chemical reactions, so longer resi-
dence times and larger reactor volumes are needed.
3.25.7 Operation
Biological detoxification of mercury-contaminated waste
could be carried out in a well-mixed aerobic reactor
system. The reaction is an enzyme-catalyzed reduction
of ionic mercury to mercury metal. The elemental mer-
cury could be removed from the reaction media by air
stripping or gravimetric separation. If air stripping is
used, mercury is captured on activated carbon, which
can be treated by retorting for mercury recovery.
3.26 Amalgamation
3.26.7 Usefulness
Amalgamation is a chemical method to recover mercury
for reuse by processing solutions of mercury salts in
water.
3.26.2 Process Description
Amalgamation depends on the ability of mercury to form
low-melting-point alloys with a wide variety of metals. A
metal, typically zinc, that is thermodynamically able to
decompose mercury compounds is contacted with a
solution of mercury salt (see Figure 3-26). A chemical
reaction occurs, reducing the mercury ions to mercury
metal, which then combines with the zinc to form a solid
alloy. The zinc/mercury amalgam is treated by retorting
to recover the mercury (88).
Zinc
Particulate
Mercury-
Contaminated
Water
Mercury-Zinc
Amalgam
to Retorting
Treated
Effluent
Figure 3-26. Example of a mercury amalgamation cell.
In the past, mercury amalgamation was used to extract
gold and silver from ores by formation of an amalgam.
Mercury was retorted from the amalgam for reuse in the
process, leaving gold or silver metal (89). Amalgamation
currently is not applied for removal or recovery of mer-
cury from wastewaters.
3.26.4 Description of Applicable Wastes
Amalgamation of mercury with zinc recovers mercury
from salts or elemental mercury in water solution.
3.26.5 Advantages
Amalgamation recovers elemental mercury, produces
an easily recoverable solid, and gives rapid reaction
rates if a large surface area of sacrificial metal is avail-
able.
3.26.6 Disadvantages and Limitations
Amalgamation does not reduce the total metal content
of the wastewater. The solution must be clear and free
of oil, grease, and emulsified or suspended matter.
Noble metals in solution are precipitated by cementation
and increase zinc consumption.
3.26.7 Operation
In practice, finely divided zinc is mixed with the mercury-
containing solution. Good agitation is needed to ensure
contact between the zinc particles and the solution.
Sufficient excess zinc is required to ensure that all mer-
cury ions are reduced and that a mercury/zinc amalgam
forms. The amalgam is separated from the treated water
and retorted to recover mercury metal.
3.27 Cementation
3.27.1 Usefulness
Cementation is an electrochemical method to recover
metals for reuse by processing from aqueous solutions.
3.27.2 Process Description
Cementation is the precipitation of a metal in solution
from its salts by a displacement reaction using another,
more electropositive metal (see Figure 3-27). For ex-
ample, copper or silver can be displaced from solution
by elemental iron.
3.27.3 Process Maturity
Cementation is a mature process used for the produc-
tion of copper metal. Cementation has also been applied
for the removal of copper from acid mine waters (80).
42
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Less-Noble
Metal
Particulate
Metal-
Contaminated
Water
Treated
Effluent
Precipitated
More-Noble
Metal
Figure 3-27. Example of a cementation cell.
3.27.4 Description of Applicable Wastes
Cementation is applicable to recovery of dissolved noble
metals from aqueous solutions. Use of aluminum to
displace more-noble metals was tested and indicated
the potential for removal of many salts of copper, tin and
lead. The test solutions contained about 200 mg/L
(12 grains/gal) of metal at a pH of 2.5. Recovery of
copper complexed by ethylenediaminetetraacetic acid
(EDTA) was only 51 percent. No copper was displaced
from the nitrate solutions, apparently due to the acidic
pH (90).
3.27.5 Advantages
Cementation recovers elemental metal, produces an
easily filterable precipitate, and gives rapid reaction
rates if a large surface area of sacrificial metal is
available.
3.27.6 Disadvantages and Limitations
Cementation does not reduce the total metal content of
the wastewater. The more-noble metal that precipitates
is replaced by dissolution of the less-noble metal. Eco-
nomic recovery requires an inexpensive source of less-
noble metal in fine particulate form.
These disadvantages can be offset by combining ce-
mentation with electrowinning. For example, zinc can be
used to electrochemically precipitate (cement) lead,
copper, and cadmium from solution. The zinc is then
recovered by electrowinning (Section 3.28).
3.27.7 Operation
A solution of noble metal (e.g., copper) is contacted with
a less-noble metal (e.g., zinc or iron). Thorough agitation
during treatment is critical for effective removal (90). The
noble metal is displaced from the solution as elemental
metal and is collected by filtration. Automobile shredder
scrap is a common source of iron for commercial copper
cementation.
3.28 Electrowinning
3.28.1 Usefulness
Electrowinning is an electrochemical method to recover
elemental metal for reuse by processing moderate- to
high-concentration aqueous solutions.
3.28.2 Process Description
Electrowinning uses direct current (DC) electricity ap-
plied to electrodes immersed in an aqueous solution to
convert dissolved metal ions to elemental metal (see
Figure 3-28). Positively charged metal ions migrate to
the negative electrode, where the metal ions are re-
duced to elemental metal. The metal plates out on the
electrode for subsequent collection and reuse.
3.28.3 Process Maturity
Electrowinning applies principles and equipment similar
to those of commercial electroplating but differs in its
goal: to recover metals rather than form a decorative or
protective coating. In electrowinning, the metal coating
appearance is unimportant, so thicker coats can be
allowed to accumulate. Electrowinning is applied com-
mercially in the mineral refining industry and for recovery
of metals from spent electroplating baths.
Negative Electrode
Collecting
Plated Metal
Positive
Electrode
Figure 3-28. Example of an electrowinning cell.
43
-------
3.28.4 Description of Applicable Wastes
Electrowinning is most effective for recovery of more-
noble metals. Metals with a high electrode potential are
easily reduced and deposited on the cathode. Gold and
silver are ideal candidates, but cadmium, chromium,
copper, lead, nickel, tin, and zinc also can be recovered
using a higher voltage (80, 91). Electrowinning will re-
move metals from solutions containing chelating agents,
which are difficult to recover by physical or chemical
processes (70).
3.28.5 Advantages
Electrowinning recovers metals from aqueous solutions
without requiring further processing and without gener-
ating any metal-containing sludge or process residuals.
The residual metal in the liquid effluent from a well-
designed and well-operated electrowinning cell is signifi-
cantly reduced, but ion exchange polishing of the efflu-
ent may be required (70, 92).
3.28.6 Disadvantages and Limitations
Electrowinning is most efficient when applied to concen-
trated solutions. For example, ion exchange resins can
be used to remove metals, which are then concentrated
in the solution used to regenerate the resin (Section
3.19). The regeneration solution is treated by electro-
winning to recover the metal.
Electrowinning typically does not remove metals in so-
lution to acceptable limits for discharge. Ion exchange
often is used to further reduce the metal concentration
in a solution after electrowinning. The regeneration
chemicals from the ion exchange process also are
treated in the electrowinning cell to complete metal re-
covery (93). Cementation (Section 3.27) also is used to
polish water treated by electrowinning (91).
Electrowinning is best applied to solutions with one
metal contaminant. Selecting the electrode potential can
control the type of metal deposited on the cathode. For
example, more-noble metals are removed at lower ap-
plied voltage. Noble metals can be recovered from
mixed-metal baths, but base metals are more difficult to
separate. Electrowinning from mixed-metal systems in-
creases the complexity of operation.
Adverse reactions can occur in an electrochemical cell
depending on the impurities present in the waste (80).
An acid mist is generated over the electrowinning cell.
The acid off-gas must be collected and treated (70).
3.28.7 Operation
An electrowinning metal recovery system requires an
electroplating tank, a direct current power source, elec-
trodes, and support equipment. Solution flow should be
maintained past the cathode by either rotating the cath-
ode or moving the solution by pumping or air agitation
(94). The cathode is often a thin sheet of the metal being
recovered and may be reticulated to increase electrode
surface area. High electrode surface area decreases the
local current density, increases current efficiency, and
reduces electrode corrosion. When a cathode is loaded
with recovered metal, it is removed and replaced. The
metal-coated cathode is sold for the metal value. Flat
titanium cathodes also are used. With titanium cath-
odes, the electrowon metal is stripped off in thin sheets.
Less expensive cathode designs such as metal-coated
plastic sheet or mesh may be used, but the value of the
recovered metal is reduced by embedded plastic. The
anode is made of a conductive and corrosion-resistant
material such as stainless steel or carbon (5).
Electrowinning from dilute solutions is less efficient due
to low ion diffusion rates. The efficiency of electrowin-
ning metals from dilute solutions can be improved by
heating the solution, by agitation, and by using a large
cathode area. Salt may need to be added to maintain
minimal conductivity in the solution being treated (82).
3.29 Chemical Leaching
3.29.1 Usefulness
Leaching is a chemical method to recover metals or
metal compounds for reuse by processing solids and
sludges containing low to moderate concentrations of
contaminants. Adescription of desirable properties forfeed
materials to chemical leaching is given in Section 4.8.
3.29.2 Process Description
Chemical leaching transfers metals from a solid matrix
into the leaching solution (see Figure 3-29). Solution
processing methods are then used to regenerate the
leachant and recover a useful metal or salt. The combi-
nation of chemical leaching and leachant regeneration
is known as hydrometallurgical processing. Hydromet-
allurgical processing typically includes one or more of
the following four steps:
Dissolution of the desired metal
Purification and/or concentration of the metal
Recovery of the metal or a metal salt
Regeneration of the leaching solution
3.29.3 Process Maturity
Chemical leaching is developed at the commercial scale
for recovery of metals from various sludges, catalysts,
and other solid matrices. Several RCRA-permitted facili-
ties are available for processing leachable metal char-
acteristic wastes and listed wastewater treatment
sludges (95). Pilot-scale tests have demonstrated lead
44
-------
Soil
I
I Grizzly |
Leachant
V
Wet
>.
Tromrr
Clean
Oversize
Classifica
S
el S
Clean
Rock,
Gravel
tion Silt, Clay
d"d Leachant 1
crew |
i
Silt, Clay
Clean Leaching Mucr
Sand
^ Dr\A
I A Regenerated
| Leachant
Metal
_r t
Olarifier | Leachant
r
i
ater
Clean
Silt, Clay
>.
Recovered
Metal
r
Remix
>. Soil
^ P
^ Adj
>.
H Clean
ust Soil
Figure 3-29. Example of the chemical leaching process (adapted from U.S. EPA [24]).
recovery from contaminated soil at Superfund sites by
acid extraction followed by regeneration of the extrac-
tion solution (96-98).
3.29.4 Description of Applicable Wastes
Chemical leaching and hydrometallurgical processing
can be applied to a variety of solid and sludge wastes.
Wastes containing a high concentration of one metal in
one valence state are preferred (99). Waste streams
processed include wastewater treatment sludges (e.g.,
plating operations [F006], metal finishing, and electronic
circuit board etching), baghouse dust, and spent cata-
lyst. The metals reclaimed include chromium, nickel,
copper, zinc, lead, cadmium, tin, cobalt, vanadium, tita-
nium, molybdenum, gold, silver, palladium, and platinum.
Chemical leaching for mercury recovery is a new and
growing technology area. Several chemical leaching for-
mulations have been developed to remove mercury
from contaminated soils (87). Processes to recover lead
by acid leaching followed by electrowinning are being
developed (100, 101).
Products are often metal salts. For example, hydroxide
plating or etching sludge can be converted to metal salts
such as copper chloride, copper ammonium chloride, or
nickel carbonate (102). For catalysts, metals and sub-
strate materials can be converted by leaching and
solution processing into products such as nickel-copper-
cobalt concentrate, alumina trihydrate, chromium oxide,
molybdenum trioxide, and vanadium pentoxide (103).
3.29.5 Advantages
Hydrometallurgical processes recover metal contami-
nants to produce metal or metal salts directly or upgrade
low-concentration materials to allow metal recovery in
secondary smelters. For some wastes, the process also
may recover the matrix in a useful form, leaving no
residue requiring disposal. Hydrometallurgy usually is
more efficient than pyrometallurgy if the metal concen-
tration is low (from the percent range down to parts per
million). Hydrometallurgical processing can require less-
capital-intensive facilities than pyrometallurgical proc-
essing, but economies of scale still apply.
3.29.6 Disadvantages and Limitations
The chemical leaching operation produces large vol-
umes of leach solution. These solutions typically are
regenerated for reuse to leach the next batch of mate-
rial. Reuse is required both to recover the economic
value of the leaching chemicals and to avoid the envi-
ronmental impacts associated with treatment and dis-
charge of waste solutions.
Leaching of soils with a high clay content leaves fine,
suspended particulate in the leachant. This fine particu-
late complicates further processing of the leachant and
is difficult to remove.
45
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3.29.7 Operation
Hydrometallurgy uses aqueous and/or organic solvents
to dissolve a metal from the solid matrix. (For more
information on liquid ion exchange/solvent extraction of
metals, see Section 3.20.) The dissolution process is
called leaching. The leaching solution is chosen, based
on the types of metals and compounds present in the
matrix being treated, to maximize recovery of valuable
metals while minimizing dissolution of unwanted species
in the matrix. The leaching chemistry often relies on
formation of metal complexes. However, a newly devel-
oping branch of hydrometallurgy, called supercritical ex-
traction, relies on the unusual solvent power of water,
CO2, and organics above the critical pressure and tem-
perature to affect the selective dissolution.
Once the metal is in solution, further processing typically
is required to remove impurities, increase the metal
concentration, or both. The full range of classical solu-
tion processing methods is available for upgrading
the leach solution. The most commonly used methods
are precipitation (Section 3.18), liquid ion exchange
(Section 3.20), and conventional resin ion exchange
(Section 3.19).
The concentrated and purified metal-containing solution
typically requires further treatment to produce a market-
able product. In some cases, the metal salt or complex
is reduced to native metal. Reduction to metal can be
accomplished by electrowinning or by reducing the met-
al using a reducing gas such as hydrogen. Alternatively,
the end product of the hydrometallurgical process may
be a metal salt. Chemical processing converts the com-
pound in solution to a more marketable oxide or salt
form.
3.30 Vitrification
3.30.1 Usefulness
Conversion to a ceramic product is a thermal method to
form useful products from slags and sludges with low
concentrations of metal contaminants alone or mixed
with organics. Ceramic products can range from high-
value materials such as abrasives or architectural stone
to low-value materials such as aggregate. Some char-
acteristics of high- and low-value ceramic products are
outlined in Sections 4.9 and 4.12, respectively.
3.30.2 Process Description
This technology uses heating to promote oxidation, sin-
tering, and melting, thus transforming a broad spectrum
of wastes into a glasslike or rocklike material. The melt-
ing energy can be derived from the oxidation of materi-
als in the feed supplemented by combustion of fossil
fuels or electrical heating. The process typically collects
particulate in the off-gas system and returns the particu-
late to the melter feed so secondary waste generation
is minimized. The discharged solid can be formed into
ceramic products (see Figure 3-30).
3.30.3 Process Maturity
Vitrification/sintering to form a stable glasslike or rock-
like solid is a commercially available technology (105).
3.30.4 Description of Applicable Wastes
Waste materials amenable to treatment include filter
cakes, foundry sand, ash, and sludge. The process
treats inorganic wastes containing cadmium, chromium,
cobalt, copper, lead, nickel, vanadium, or zinc. Exam-
ples of suitable wastes include sludge from wastewater
treatment, electric arc furnace off-gas treatment resi-
dues, and baghouse dust (104).
The presence of volatile metals in the waste complicates
vitrification processing due to production of metal vapors
in the off-gas. Metals such as mercury or beryllium that
volatilize under process conditions may not be amen-
able to treatment. Wastes containing arsenic require
some combination of pretreatment and special process-
ing conditions and off-gas treatment systems to mini-
mize arsenic volatilization.
Selected waste streams can be converted into high-
value ceramic products such as abrasives, decorative
architectural stone, or refractory. Wastes suitable for
these processes typically are hydroxide sludge from
treatment of plating or etching baths containing a single
metal contaminant. The process has been applied com-
mercially to F006 wastes (106).
Processes have been demonstrated for thermal conver-
sion of a variety of silicate matrices containing metal and
organic contaminants into intermediate-value ceramic
products. For example, fly ash (107), incinerator ash
(108), iron foundry slag (109), and petroleum-contami-
nated soils (110, 111) have been used for the manufac-
ture of bricks. In addition, spent abrasive blasting media
have been used to replace sand in the manufacture of
bricks and mortar.
Low-value construction aggregate and stone can be
produced from a variety of waste materials. Examples
include concrete aggregate produced from fly ash (112,
113) or fill material produced by vitrification of metal-
containing wastes.
3.30.5 Advantages
The discharged product is a chemically durable material
that typically passes the Toxicity Characteristic Leaching
Procedure (TCLP) test as nonhazardous. The process
provides volume reduction (40 percent for soils to
greater than 99 percent for combustibles). The high
46
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Chemicals
Metals-Bearing Waste
Silicates
Air Pollution
Control System
Flue Gas
T
Product Exit
Figure 3-30. Example of the vitrification process (adapted from U.S. Air Force [103]).
Kiln
operating temperature destroys organic contaminants in
the waste (70).
3.30.6 Disadvantages and Limitations
The thermal conversion process is capital and energy
intensive. Revenue is unlikely to equal processing costs,
even for waste streams that form a high-value product.
The main economic advantage is avoided disposal
costs.
Thermal processing generates large volumes of off-gas
that must be controlled and cleaned. Volatile metals in
the waste, particularly arsenic, beryllium, or mercury,
complicate processing.
3.30.7 Operation
Ceramic products may be formed by either sintering or
melting. In both processes, prepared waste material is
heated to form the ceramic. Most thermal treatment
processes require feed material to be within a narrow
particle size range. Size reduction, pelletization, or both
processes usually are needed to obtain the required
size.
In sintering, the waste is prepared by mixing with clay
or other silicate and possibly water and additives. The
resulting mix is pressed or extruded to form pellets,
which are treated at high temperature but below the
bulk melting temperature. Particles join to form a solid
ceramic piece.
Vitrification processes also require feed preparation.
Chemical additions and mixing may be used to promote
oxidation-reduction reactions that improve the proper-
ties and stability of the final product. Silica sources such
as sand or clay also may be needed. Vitrification proc-
esses operate by heating the pretreated waste to melt-
ing temperatures. The molten, treated waste flow exits
from the melter into a waste forming or quenching step.
The melt can be formed in a sand-coated mold or
quenched in a water bath, depending on the type of
product required.
Gases released from the thermal treatment unit are
processed through an emission control system. Particu-
lates may form due to carryover, metal fuming, or anion
fuming. The particulates are removed by knockout
boxes, scrubbers, and/or venturi separators. Particu-
lates are separated from the scrubbing fluid by filtration
and are returned to the treatment system. Acid gases,
such as sulfur dioxide from sulfates, are removed by
scrubbing with sodium hydroxide.
3.31 Pyrometallurgical Metal Recovery
3.31.1 Usefulness
Pyrometallurgical processing is a thermal method to
recover metals or metal compounds for reuse by proc-
essing solids and sludges with percent concentrations
of metal contaminants. A description of desirable prop-
erties for feed material to a Pyrometallurgical metal re-
covery process is given in Section 4.7. A case study of
processing Superfund site wastes in a secondary lead
smelter is described in Section 5.4.
3.31.2 Process Description
Pyrometallurgy is a broad term covering techniques for
processing metals at elevated temperature. Processing
at elevated temperature increases the rate of reaction
47
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and reduces the reactor volume per unit output (see
Figure 3-31). Elevated temperature also may benefit
the reaction equilibrium. Pyrometallurgy offers a well-
developed and powerful collection of tools for recovery
of metals from waste materials. Three general types of
pyrometallurgical processes are in use:
Pretreatment of material as preparation for further
processing.
Treatment of material to convert metal compounds to
elemental metal or matte and to reject undesirable
components.
Subsequent treatment to upgrade the metals or
matte.
These operations may be used singly, in sequence, or
in combination with physical, hydrometallurgical, bio-
logical, orelectrometallurgical processing depending on
the types of material processed. The three types of
pyrometallurgical processes generally use different
equipment and approaches.
3.31.3 Process Maturity
Pyrometallurgical processing is developed at the com-
mercial scale for recovery of cadmium, lead, and zinc
from K061 (RCRA waste code for Electric Arc Furnace
emission control dust/sludge) and a variety of metal-
containing silicate and sludge wastes.
3.31.4 Description of Applicable Wastes
Pyrometallurgical processing typically is used to process
large volumes of solid or low-moisture sludge containing
percent levels of metals. Processing capacity is available
for a variety of metal leachability characteristic wastes,
F006-listed waste, and other metal-containing soils,
slags, dusts, sludges, ashes, or catalysts. The types of
materials processed include wastes from electroplating,
electropolishing, metal finishing, brass and steel foun-
dries, galvanizing, zinc diecasting, nickel-cadmium and
iron-nickel batteries, chromium-magnesite refractories,
waste magnesium powders and machinings, and pot
liner from aluminum smelters (114-119).
Some facilities may accept wastes containing trace
quantities of metals if the matrix is a good source of
silica or alkali for flux or a carbon source for metal
reduction. Processing ash from incineration of municipal
wastewater treatment sludge provides silica as a flux
and allows recovery of trace quantities of gold and silver.
Pyrometallurgical processors also may accept used
foundry sand for metals and silica, lime residues from
boiler cleaning or dolomitic refractories for metals and
alkali, or carbon brick and coke fines for carbon.
3.31.5 Advantages
Pyrometallurgy is an extractive treatment approach that
can recover metals or metal salts for reuse. The high
operating temperature destroys organic contaminants in
the waste (70). The volume of slag residual resulting
OXIDATION SMELTING
Combustion Gases
(Cd, As, Hg, Pb*)
> Liquid Slag
(Ba, Cr, Zn, Pb)
Fluxes
Heat
Liquid Metal
(Ag)
*lf Temperature Is Sufficiently High (1,400-1600°C),
Pb Will Volatilize as PbO
Figure 3-31. Examples of pyrometallurgical processes.
REDUCTION SMELTING
Reduction Gases
(Hg, Cd, As, Zn)
Liquid Slag
(Ba, Cr)
Reductant
(Coal, Oil, Gas)
Liquid Metals
(Ag, Pb, Cr*)
"Chromium Will Distribute Between Metal and Slag
48
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from the process typically is smallerthan the initial waste
volume. In most cases, the hazardous metal concentra-
tion in the slag is low and the slag is leach resistant, so
it may be reused as a low-value aggregate product.
3.31.6 Disadvantages and Limitations
Pyrometallurgical processing is applicable only to spe-
cific types of wastes. Success depends both on the
types and concentrations of metals present and the
physical and chemical form of the matrix.
The process is capital and energy intensive. Processing
can be profitable or break even when the waste contains
a high concentration of valuable metal or can be proc-
essed as a small addition to an existing feedstream. For
other waste types, pyrometallurgical processing is costly.
Pyrometallurgical processing generates large volumes
of off-gas that must be controlled and cleaned. Volatile
metals in the waste, particularly arsenic, complicate
processing.
3.317 Operation
Oxidation is often used as a pyrometallurgical pretreat-
ment to convert sulfide materials to oxides. Normally
oxidation is carried out as a gas-solid phase contact of
air passing over fine particulate material in a multihearth
or fluidized bed reactor. Pretreatment also is used to
selectively metallize the feed for subsequent leaching.
Pyrometallurgical processing to convert metal com-
pounds to metal usually requires a reducing agent, flux-
ing agents to facilitate melting and slag off impurities,
and a heat source. The fluid mass often is called a melt,
although the operating temperature, while quite high,
often is below the melting points of the refractory
compounds being processed. The fluid forms as a low-
melting-point material due to the chemistry of the melt.
An acceptable melting point is achieved by addition of
fluxing agents, such as calcium oxide, or by appropriate
blending of feedstocks.
Carbon is the most commonly used reducing agent for
base metal compounds. The carbon typically reacts to
produce carbon monoxide and carbon dioxide while
forming free metal or matte. Combustion of the carbon
also can provide the required heat input. Feedstocks,
such as sulfides or organic-laden wastes, react exother-
mically, thus providing some heat input as well.
The most common fluxing agents in mineral smelting are
silica and limestone. The flux is added along with the
reducing agent to produce a molten mass. A wide variety
of molten salts, molten metals, or other fluxing systems
are used for special processing situations.
Separation of the metal from the undesirable waste
components typically is accomplished by physical action
based on phase separations. As the metal salts react
with the reducing agent to form metal or matte, the
nonmetallic portions of the ore combine with the flux to
form a slag. Volatile metals such as zinc or cadmium
vaporize and are collected by condensation or oxidation
from the off-gas, usually as oxides due to combustion of
metal fume in the flue. Dense, nonvolatile metals can be
separated from the less dense silicate slag by gravity
draining of metallics from the bottom of the reaction
vessel. Slag oxides are tapped from a more elevated
taphole.
Pyrometallurgical processes for final purification (refin-
ing) usually take the form of selective volatilization,
dressing, or liquation. In some cases, ores consist of
less-volatile metals such as lead and iron mixed with
volatile metals such as zinc, cadmium, or arsenic. For
other metal systems, chemical reactions are needed to
form volatile species to allow separation of product met-
als and impurities.
3.32 Cement Raw Materials
3.32.1 Usefulness
Use of inorganic wastes as raw material in cement
manufacture is a thermal method to recover inorganics,
mainly aluminum, iron, or silica, from solid materials with
low concentrations of contaminants. Burning of mainly
organic-containing materials in a cement kiln for heating
value is discussed in Section 3.3. Adescription of desirable
properties for cement raw materials is given in Section
4.10. A case study using spent sand blasting media for
cement raw materials is described in Section 5.2.
3.32.2 Process Description
In this process, waste materials are fed to a cement kiln
as a substitute for raw materials such as limestone,
shale, clay, or sand. The primary constituents of cement
are silica, calcium, aluminum, and iron. Inside the ce-
ment kiln, the raw material substitutes undergo chemical
and physical reactions at temperatures that progres-
sively reach 1,480°C (2,700°F) to form cement clinker
(see Figure 3-32). Inorganic contaminants are bound
into the lattice structure of the cement crystals.
3.32.3 Process Maturity
Nonhazardous silicate and aluminate wastes are used
as raw material substitutes in Portland cement manufac-
ture on a commercial scale. Application to wastes con-
taining RCRA metals may be possible, but commercial
application is limited by the requirements of the Boiler
and Industrial Furnace regulations.
3.32.4 Description of Applicable Wastes
The primary raw materials of interest are silica, calcium,
aluminum, and iron. Good candidates for raw materials
49
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Clay, Shale,
and Limestone
Cooling Fans
To Gypsum Addition
and Grinding
Figure 3-32. Example of a cement kiln operation.
substitution typically contain 95 percent or more of these
constituents. Examples of acceptable feed materials in-
clude the following sources:
Alumina sources:
Catalysts
Ceramics and refractories
Coal ash
Adsorbents for gases and vapors
Aluminum potliner waste
Calcium sources:
Lime sludges
Iron sources:
Foundry baghouse residuals
Iron mill scale
Silica sources:
Abrasives
Ceramics
Clay filters and sludges
Foundry sand
Sand blast media
Water filtration media
3.32.5 Advantages
Cement kilns provide high operating temperatures and
long residence times to maximize the immobilization of
metal contaminants into the cement mineral structure.
The high-alkali reserve of the cement clinker reacts to
form alkali chlorides (sodium, potassium, calcium) that
prevent the evolution of acidic vapors in the off-gas. The
chloride content must be limited, however, to avoid va-
por production and to prevent soluble chlorides from
degrading the setting rate of the cement product (119).
3.32.6 Disadvantages and Limitations
Both combustion to heat the raw materials and decom-
position reactions during formation of cement clinker
generate large volumes of off-gas that must be controlled
and cleaned.
3.32.7 Operation
Raw material burning typically is done in a rotary kiln.
The kiln rotates around an inclined axis. The raw mate-
rials enter the raised end of the kiln and travel down the
incline to the lower end. The kiln is heated by combus-
tion of coal, gas, or oil in the kiln. As the raw materials
move through the inclined, rotating kiln, they heat to
temperatures in the area of 1,480°C (2,700°F). The high
temperature causes physical and chemical changes,
such as (8):
Partial fusion of the feed materials
Evaporation of free water
Evolution of carbon dioxide from carbonates
During burning, lime combines with silica, alumina, and
iron to form the desired cement compounds. The heat-
ing results in the cement clinker. Clinker consists of
granular solids with sizes ranging from fine sand to
walnut size. The clinker is rapidly cooled, mixed with
additives such as gypsum, and ground to a fine powder
to produce the final cement product.
Portland cement product is produced by heating mix-
tures containing lime, silica, alumina, and iron oxide to
form clinker, which is then ground. About 3 to 5 percent
of calcium sulfate, usually as gypsum or anhydrite, is
added during grinding of the clinker. The gypsum aids
the grinding process and helps control the curing rate of
the cement product (120). The gypsum is intermixed
during grinding of the clinker. The main constituents of
Portland cement typically are tricalcium silicate, dical-
cium silicate, tricalcium aluminate, and tetracalcium alu-
minoferrite.
50
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3.33 Physical Separation
3.33.1 Usefulness
Physical separation uses physical differences to con-
centrate and recover solids suspended in water or mixed
with other solids. A case study of lead recovery from soil
at a small-arms practice range using physical separation
is described in Section 5.3.
3.33.2 Process Description
Physical separation/concentration involves separating
different types of particles based on physical character-
istics. Most physical separation operations are based on
one of four characteristics:
Particle size (filtration or microfiltration)
Particle density (sedimentation or centrifugation)
Magnetic properties (magnetic separation)
Surface properties (flotation)
3.33.3 Process Maturity
Application of physical separation methods is well
established in the ore-processing industry. Physical
separation provides a low-cost means of rejecting unde-
sirable rock and debris, thus increasing the concentra-
tion of metal and reducing the volume to process (see
Figure 3-33). Mining experience is now being extended
to full-scale application of physical separation at Super-
fund sites.
3.33.4 Description of Applicable Wastes
Physical separation is applicable to recovery of metals
from soils, sediments, or slags in either of two situations.
First, discrete metal particles in soil can be recovered
based on size, density, or other properties. For example,
mercury metal can be recovered by gravity separation,
lead fragments can be separated by screening or by
gravity methods, and high-value metals (e.g., gold or
KEY
Small, Dense Particles
0 Coarse, Dense Particles
o Small, Light Particles
Q Coarse, Light Particles
Washwater
Material Distribution in
the Channel of a Spiral,
Concentrator
iira]X
Tailings
Middlings
Concentrate i
Figure 3-33. Cross section showing particle distribution in a
spiral concentrator channel.
silver) can be recovered by membrane filtration. The
most common applications are size and gravity recovery
of lead in firing range or battery breaking site soils and
gravity recovery of elemental mercury from contami-
nated soils (87, 97, 121).
Second, metals present in elemental or salt form may
be sorbed or otherwise associated with a particular size
fraction of soil material. Materials tend to sorb onto the
fine clay and silt in soil. Physical separation can divide
sand and gravel from clay and silt, yielding a smaller
volume of material with a higher contaminant concentra-
tion. The upgraded material can then be processed by
techniques such as pyrometallurgy or chemical leaching
to recover products.
3.33.5 Advantages
Physical separation allows recovery of metals or reduc-
tion of the volume to be treated using simple, low-cost
equipment that is easily available from a wide variety of
vendors.
3.33.6 Disadvantages and Limitations
Physical separation requires that the desired compo-
nent be present in higher concentration in a phase
having different physical properties than the bulk mate-
rial. Separation methods applied to dry the material
(e.g., screening) generate dust.
3.33.7 Operation
The general characteristics of some common particle
separation techniques are summarized in Table 3-2.
3.34 Mercury Roasting and Retorting
3.34.7 Usefulness
Mercury roasting and retorting is a thermal method to
recover mercury metal for reuse by processing mercury-
containing solids and sludges.
3.34.2 Process Description
Relatively few metal oxides convert easily to the metallic
state in the presence of oxygen. Reduction to metal
typically requires the presence of a reducing agent such
as carbon, as well as elevated temperatures; mercury is
one of the few exceptions. Many mercury compounds
convert to metal at an atmospheric pressure and tem-
perature of 300°C (570°F) or less. Mercury also is sub-
stantially more volatile than most metals, with a boiling
point of 357°C (675°F). As a result, mercury and inor-
ganic mercury compounds can be separated from solids
by roasting and retorting more easily than most metals
can (87).
51
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Table 3-2. Particle Separation Techniques (122, 123)
Technique
Screen Sizing
Basic Principle Various diameter
openings allowing
passage of particles
with different effective
sizes
Classification by
Settling Velocity
Different settling
rates due to particle
density, size, or
shape
Gravity Separation
Separation due to
density differences
Magnetic
Separation
Magnetic
susceptibility
Flotation
Particle attraction to
bubbles due to their
surface properties
Major
Advantage
Limitations
Typical
Implementation
High-throughput
continuous processing
with simple, inexpensive
equipment
Screens can plug; fine
screens are fragile; dry
screening produces dust
Screens, sieves, or
trommels (wet or dry)
High-throughput
continuous
processing with
simple, inexpensive
equipment
Process is difficult
when high
proportions of clay,
silt, and humic
materials are present
Clarifier, elutriator,
hydrocyclone
High-throughput
continuous
processing with
simple, inexpensive
equipment
Process is difficult
when high
proportions of clay,
silt, and humic
materials are present
Shaking table, spiral
concentrator, jig
Recovery of a wide
variety of materials
when high gradient
fields are used
Process entails high
capital and
operating costs
Electromagnets,
magnetic filters
Effectiveness for fine
particles
Particulate must be
present at low
concentrations
Air flotation columns
or cells
Retorting is a decomposition and volatilization process
to form and then volatilize elemental mercury (see
Figure 3-34). Waste is heated in a vacuum chamber,
usually indirectly, in the absence of air to a temperature
above the boiling point of mercury. Heating normally is
done as a batch process. The exhausted mercury is
collected by condensation, water scrubbing, or carbon
adsorption. Mercury roasting is the process of heating
mercury-containing materials in air, typically to convert
sulfides to oxides in preparation for retorting.
3.34.3 Process Maturity
A commercial infrastructure has been established for
recycling mercury-containing scrap and waste materials
(125). Recovery of mercury from soils by thermal treat-
ment has been practiced on a commercial scale (87,
126). Industrial production of mercury from recycling of
secondary sources amounted to 176 metric tons (194
tons) in 1990(127).
3.34.4 Description of Applicable Wastes
Dirt, soils, and sludge-like material can be processed if
the water content is below about 40 percent. If the
mercury is in solution, the mercury must be collected as
a solid by precipitation or adsorption onto activated
carbon. As with the sludge feed, the collected solids
must contain less than about 40 percent water. Land
Disposal Restriction treatment standards for various
RCRA nonwastewater mercury-containing wastes with
concentrations of more than 260 mg/kg (260 ppm) mer-
cury were developed based on thermal treatment to
recover mercury as the Best Demonstrated Treatment
Technology.
Mercury-Containing
Waste
Carbon F
Treatmer
'*
rrom Waste
it
-\ ^x
^ ^ , J
Indirectly Heated
Vacuum Retort
i iii i
Carbon Absorption
of Mercury From
Wastewater
Treated
Wastewater
T
Water-Chilled
Condenser
*-
1
Particulate 1- liter
and Water Trap
Condensed
Mercury to
Distillation
Off-Gas Treatment
Exhaust Gas
Figure 3-34. Example of the mercury retorting process (adapted
from Lawrence [123]).
52
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3.34.5 Advantages
Roasting and retorting each provide an effective means
to recover mercury from a variety of mercury-containing
solids. Both fixed facilities and transportable units are
available (128).
3.34.6 Disadvantages and Limitations
Roasting and retorting generate an off-gas stream that
must be controlled and cleaned. Volatile metals in the
waste, particularly arsenic, complicate processing.
3.34.7 Operation
In the retorting process, solids contaminated with mer-
cury are placed in a vacuum-tight chamber. Following
closure of the chamber, a vacuum is established and
heat is applied. Operating the retort under vacuum helps
collect and control mercury emissions from the process.
The materials in the chamber are subjected to tempera-
tures in excess of 700°C (1,300°F). Mercury is vapor-
ized from the material, withdrawn, and collected. The
mercury can be further purified by distillation. The
mercury-free solids are transported to other facilities for
recovery of other metals, if possible.
Typical feed materials include metal and glass materi-
als. Most plastics can be processed, but PVC and other
halogen-containing materials must be minimized due to
the potential for generating corrosive or volatile materi-
als during heating in the retort. Volatile or reactive met-
als such as lithium, arsenic, and thallium also are not
allowed in the process (124).
3.35 Mercury Distillation
3.35.7 Usefulness
Mercury distillation is a thermal method to recover high-
purity mercury metal for reuse by processing slightly
contaminated liquid elemental mercury.
3.35.2 Process Description
Mercury distillation relies on mercury's relatively low
boiling point to allow purification of slightly contaminated
liquid mercury to very high levels of purity. Mercury and
volatile impurities boil off in a vacuum retort, leaving
nonvolatile impurities in the retort. The mercury vapors
are then distilled to concentrate volatile impurities in a
mercury heel to produce high-purity mercury (see Figure
3-35). Multiple passes through retorting and distillation can
produce 99.9999 percent or higher purity mercury (125).
3.35.3 Process Maturity
Distillation is commercially available for final cleanup of
slightly contaminated liquid mercury metal.
Mercury Distillation Units
Mercury
Feed
Wasted
Figure 3-35. Example of the mercury distillation
(adapted from Lawrence [123]).
Purified
Mercury
Product
process
3.35.4 Description of Applicable Wastes
Feed to a mercury distillation process typically is free-
flowing mercury liquid showing a shiny surface and no
visible water, glass fragments, or other solids. Physical
separation may be used to remove solids to allow distil-
lation of the mercury. Wastes containing lead, cadmium,
or arsenic usually are unacceptable for distillation.
Typical waste sources are mercury metal liberated from
solid by retorting, electronic scrap, and impure, used
mercury.
3.35.5 Advantages
Distillation can be applied to clean mercury recovered
by roasting or retorting (Section 3.34).
3.35.6 Disadvantages and Limitations
The process generates an off-gas stream that must be
controlled and cleaned. Volatile metals in the waste,
particularly arsenic, complicate processing.
3.35.7 Operation
Mercury distillation typically is carried out in small batch
vacuum systems. Vacuum distillation reduces the re-
quired operating temperatures and helps collect and
control mercury emissions from the process. The usual
processing capacity for a batch is 208 L (55 gal). Higher
purity mercury is produced by redistillation and/or wash-
ing. Specially designed distillation operations can pro-
duce 99.99999 percent ("7 nines") pure mercury with
quadruple distillation. The more common approach is
triple distillation followed by washing the mercury with
dilute nitric acid to yield 99.9999 percent ("6 nines") pure
mercury.
3.36 Decontamination and Disassembly
3.36.1 Usefulness
Decontamination and disassembly uses mechanical
and chemical methods to clean and disassemble proc-
ess equipment and structures to allow recovery of met-
als or inorganic materials for reuse. A source for
53
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specifications describing bulk metals for recycling is
given in Section 4.6.
3.36.2 Process Description
The process includes the dismantling of equipment; de-
contamination of walls, ceilings, and floors; and the
cleaning or removal of utilities such as drains, ductwork,
filters, vents, and electrical conduits. The building then
may be either reused or dismantled. The major steps in
decontamination and disassembly include:
Preparation of equipment for removal.
Disassembly of equipment and fixtures.
Equipment decontamination.
Metal cutting, including electrical conduit, drains, and
vent systems.
Metal decontamination.
Floor tile removal.
Decontamination of floors, walls, and ceilings.
Concrete floor cutting and excavation of soil to remove
subfloor drains (if necessary).
3.36.3 Process Maturity
A multitude of cleaning and disassembly methods are
commercially available for equipment, metals, and other
materials such as glass, brick, wood, rubber, and con-
crete. Cleaning technologies range from detergents and
water, grinding methods, and chemical treatments to the
use of lasers, CO2 pellet blasting (see Figure 3-36), and
other methods that produce a minimum of additional
waste. Disassembly methods include wire, flame, and
water cutters; saws; shears; nibblers; and large impact
equipment. Disposal options for waste can be costly;
therefore, waste minimization increases in importance.
Cleaning methods should be selected to avoid produc-
tion of or to minimize the volume of hazardous waste.
An understanding of the Land Disposal Restrictions can
assist facility management in the selection of the most
effective treatment and/or disposal methods (129).
3.36.4 Description of Applicable Wastes
Different methods are effective on different contami-
nated materials. Typical methods for cleaning metals are
high-pressure water blasting, solvents, and other media
blasting (plastic, wheat starch, sodium bicarbonate,
carbon dioxide pellets, ice pellets), cryogenic, and ther-
mal treatments. Advanced paint removal technologies
were reviewed in a recent EPA report (130). The CO2
blasting method was used successfully at a Superfund
site to clean building and tank surfaces contaminated
with mercury and heavy metals (131). Concrete can be
cleaned with these methods and others, such as by
grinding and milling, or using strippable coatings and
foam cleaners. The strippable coatings, foams, and
blasting methods are effective on painted metal and
concrete surfaces, but electrical conduit is most effec-
tively cleaned with a dry method. Drains and complex,
hard-to-reach surfaces can be cleaned with solvents
and foams.
Concrete cutting methods include core stitch drilling,
diamond wire cutting, flame and water cutting, sawing,
and use of impact equipment, such as a backhoe-
mounted ram or paving breaker (hammer-like devices).
Metal and equipment can be decommissioned using arc
saws, shears, nibblers, torches, water cutting equip-
ment, power saws, band saws, or guillotine saws.
3.36.5 Advantages
Surface decontamination methods, such as carbon di-
oxide pellet blasting and laser heating, add a minimum
amount of waste to the pretreated quantity. Abrasive
blasting and thermal cleaning methods provide high
throughput rates. For cutting structures, wire cutting is a
faster, more precise cutting method than traditional cut-
ting methods. Saws provide versatility by using specific
blades for various materials.
3.36.6 Disadvantages and Limitations
Abrasive blasting methods can damage the underlying
surface. Most cleaning techniques require varying levels
of training and respiratory, eye, skin, and ear protection.
Water blasting, plastic media blasting, solvents, foams,
Figure 3-36. Example of decontamination apparatus.
54
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and detergents all add to the pretreated quantity of
waste. Most cutting techniques also require dust and
contamination control before, during, and/or after cutting
operations. Some equipment, such as large saws, wire
cutters, shears, and coring machines, can be heavy and
cumbersome to use.
Decontamination and disassembly processing can re-
veal asbestos in many forms. Asbestos-containing ma-
terial was used as insulation, in siding and shingles, and
in laboratory hood and equipment linings (transite). Site
surveys should include identification and charac-
terization of asbestos-containing materials and appro-
priate planning for decontamination and disassembly
operations.
3.36.7 Operation
The types of equipment and materials and the time
required for decontamination vary depending on which
method is used. Solvents may be used in a self-con-
tained unit or may be circulated through pipes and
drains. Cleaning times range from a few minutes to a
few days. Blasting equipment generally consists of a
pumping mechanism, vacuum mechanism, and possibly
a treatment system for recycling the blasting media.
Cleaning times range from 0.5 to 35 nf/hr (5 to 350 ft2/hr).
Cutting and grinding techniques may require pretreat-
ment or a tent for dust control, as well as stabilization of
surrounding material. A vacuum system also may be
used for cleanup and containment of the waste. The
time required for operation depends on the material and
the equipment chosen, and can range from 0.1 to
1.8 m2/hr (1 to 20 ft2/hr).
3.37 Recycling Transformers and Ballasts
3.37.7 Usefulness
Electrical equipment containing PCB-dielectric oils can
be processed to destroy the PCBs, allowing continued
use of the device, or can be disassembled to recover
the metals in the device. A source for specifications
describing bulk metals for recycling is given in Section
4.6.
3.37.2 Process Description
Recycling of electrical devices using PCB-containing
dielectric oils such as transformers (see Figure 3-37)
involves a combination of mechanical disassembly and
chemical and thermal treatment to recover metals and,
in some cases, the dielectric oil. The recycling of trans-
formers and ballasts is a concern because older electri-
cal equipment commonly used oils containing PCBs.
Recycling a transformer involves three major steps: test-
ing the oil for PCB content, removing the oil from the
transformer, and disassembling the transformer. Once
r li
f
l?v
^L
=rr
.---
^
3
^c
LJ
L
X
^
/
/
/
- v
""" d
&V
I
S|
J)
Figure 3-37. Example of a transformer
the transformer is disassembled, its components can be
decontaminated, and salvageable materials can be re-
cycled (132, 133).
3.37.3 Process Maturity
Since the initial PCB Marking and Disposal Rule in
1978, technologies have emerged to improve the effi-
ciency of cleaning and recycling PCB oils and transform-
ers with less risk to the public. Methods to dechlorinate
the transformer oils were in place by the early 1980s.
Technologies have emerged for cleaning the oil using a
mobile unit while the transformer is operating (134). For
transformers that are replaced with newer, more efficient
models, an estimated 90 to 95 percent of the trans-
former metal is recyclable (135).
3.37.4 Description of Applicable Wastes
Recovery of metals and dielectric oils is applicable to a
variety of electric equipment, mainly transformers and
ballast inductors. The components of the transformers
include oil, tanks, cores, coils, valves, insulating materi-
als, bushings, and other fittings, such as gauges and
switches.
3.37.5 Advantages
Replacing or decontaminating transformers containing
PCB fluids can reduce the costs associated with fluid
testing, regulatory inspection recordkeeping, and poten-
tial spill cleanup. Metals can be salvaged from obsolete
transformers. In some cases, PCB-containing dielectric
oil may be dechlorinated and reused. Dechlorinated
dielectric oil that is unsuitable for reuse can be treated
by incineration. Incineration of transformer fluids and
insulation materials from PCB transformers destroys
the material and the PCBs, and the use of a metals
reclamation furnace can yield even cleaner metals for
55
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recycling. Surface contamination of metal and ceramic
components can sometimes be removed with the use of
solvents so that the materials can be reused.
3.37.6 Disadvantages and Limitations
Thermal destruction of PCBs can create products of
incomplete combustion, such as dioxins or dibenzo-
furans. Solvents used for surface cleaning of metal parts
are distilled for reuse, but a PCB residue remains that
is treated by incineration (136). Discarded materials
must be carefully monitored so that Toxic Substances
Control Act (TSCA) disposal requirements are not vio-
lated and no contamination of the disposal facility oc-
curs. Materials disposed of in a landfill also continue to
carry a liability, i.e., they are still the responsibility of the
generator (137).
3.37.7 Operation
The actual decommissioning process starts by testing
the filling oil. When handling PCB-contaminated materi-
als, the recycling contractor implements measures to
prevent, contain, and clean up spills. The oil is tested to
determine the level of personal protection clothing and
equipment required.
Once the oil is properly drained from the transformer, the
transformer is disassembled. The transformer body,
core steel, copper, aluminum, brass, and other metal
components of the disassembled transformer are then
accessible for recycling. Some processors clean the
metal parts with solvent and transfer the metals to a
smelter for recycling. Other processors use onsite incin-
erators, ovens, or furnaces to burn unwanted insulating
materials and the adhering PCB contaminants from the
transformer internals. Onsite incineration results in de-
contaminated metal scrap but can produce products of
incomplete combustion from trace residual PCBs.
The dielectric oil typically is treated by a chemical
dechlorination process. The dechlorinated oil may be
either reused or destroyed by incineration.
Decontaminated materials with no commercial value,
such as ceramic bushings, are sent to a landfill for
disposal.
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When an NTIS number is cited in a reference, that
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National Technical Information Service
5285 Port Royal Road
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132. Dougherty, J. 1993. Transformer decommission-
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136. Laskin, D. 1993. What's hot and what's not: An 137. Kelly, J., and R. Stebbins. 1993. PCB regulations
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Chapter 4
Product Quality Specifications
Recycled materials are commodities in a competitive
marketplace. Recycling is most successful where the
supplier is aware of the needs of the end user. The end
user is best served by a reliable supply of material
conforming to an established specification. Given the
variability of wastes, uniformity seldom is achieved but
should be approached as closely as possible.
The volume of material available influences its recycling
potential. Larger volumes of uniform material generally
are more desirable. In a few special cases, however, the
waste material inventory can exceed the short-term de-
mand. Sudden appearance of a large supply in a small
market depresses the value of the potentially recyclable
material.
A few waste types may be profitable to recycle. Alumi-
num and copper metal demolition debris can be recycled
profitably if sufficient volumes of clean material are avail-
able. In most cases, significant onsite processing is
needed, or a processor requires a fee to accept waste
as a feedstock to an offsite recycling process.
4.1 Feed Material to Petroleum Refining
Petroleum hydrocarbons recovered at Superfund or Re-
source Conservation and Recovery Act (RCRA) Correc-
tive Action sites by nonaqueous-phase liquid (NAPL)
pumping (Section 3.9), thermal desorption (Section 3.5),
solvent extraction (Section 3.6), or other processes
often require additional processing to produce a market-
able petroleum product. When materials are suitable, a
conventional refinery can efficiently carry out process-
ing. This section outlines some of the key properties for
determining the suitability of recovered petroleum for
upgrading by conventional refinery separation processes.
The main consideration for successful refinery distilla-
tion (Section 3.1) is the difference in volatility of the
components. A low boiling point mixture can be distilled
at low temperature to reduce the complexity and cost of
the still. When the component to be recovered is much
more volatile than the contaminants, distillation can be
accomplished with simple equipment.
The thermal properties (heat capacity, heat of vaporiza-
tion, thermal conductivity, and heat transfer coefficient)
of the material also are important. Low heat capacity and
heat of vaporization indicate that low heat input is re-
quired to affect the distillation. High thermal conductivity
and high heat transfer coefficient indicate that heating
the waste can be accomplished with relative ease.
The physical properties must be compatible with pump-
ing and heating the waste. A tendency to produce foam,
indicated by a high surface tension, is undesirable. A
waste containing high concentrations of suspended sol-
ids can form a dense, viscous sludge and clog distillation
columns. High-viscosity materials are difficult to proc-
ess. Organics that tend to form polymers can polymer-
ize, clogging the column or coating the heat transfer
surfaces (1).
To simplify distillation and maximize product quality, the
waste solvent streams should be segregated as much
as possible. Separating chlorinated from nonchlorinated
and aliphatic from aromatic solvents is particularly bene-
ficial (2).
4.2 Organic Chemicals
Organic liquids and gases can be recovered from soils
by processes such as thermal desorption (Section 3.5),
solvent extraction (Section 3.6), or NAPL pumping (Sec-
tion 3.9), or can be produced from solid materials by
chemolysis (Section 3.15) orthermolysis (Section 3.17).
These organic fluids are then marketed as feedstock for
refineries or chemical plants. Onsite recovery of petro-
leum from RCRA K wastes is occurring more frequently
(3, 4). For onsite recovery of plant wastes, the source of
the material is known, so less documentation is needed
to gain plant acceptance of the recovered feedstock.
Use of materials recovered from offsite sources raises
concerns for chemical processors. Small quantities of
certain impurities can poison catalysts, increase corro-
sion, or generate acidic off-gas. Because even small
amounts of the impurities are potentially damaging, sat-
isfactory demonstration of acceptable quality requires
sophisticated sampling and analysis (5). Particularly un-
desirable contaminants include metals and chlorine (6).
Refineries and chemical processors also require low
suspended solids levels and ash content (7).
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4.3 Thermoplastic Particulate
Thermoplastic particulate can be re-extruded into new
products (Section 3.14). American Society for Testing
and Materials (ASTM) Standard Guide D 5033, "The
Development of Standards Relating to the Proper Use
of Recycled Plastics," provides definitions of terms, de-
scribes four general types of plastic recycling, and out-
lines factors important in developing standards for
recycling plastic. The Standard Guide notes that, unless
an existing standard specifically restricts the use of
recycled plastic based on performance standards,
recycled plastic can be used as feedstock. Specifically
mentioning recycled plastic in the specification is unnec-
essary. ASTM Standard Specification D 5033, "Poly-
ethylene Plastics Molding and Extrusion Materials From
Recycled Postconsumer (HOPE) Sources," defines and
specifies recycled postconsumer high-density polyeth-
lene (HOPE) chips or pellets for molding and extrusion.
The polymer type and purity control the value of the
particulate. The best candidates for reuse are single
polymer types containing no impurities. Mixtures of dif-
ferent types of polymers, polymers containing coloring,
solid additives, or impurities are much less valuable.
The properties vary substantially among the seven major
polymer categoriespolyethylene-terephthalate (PET),
high-density polyethylene (HOPE), polyvinyl chloride
(PVC), low-density polyethylene (LDPE), polypropylene
(PP), polystyrene (PS), and all others. Even within a
single category, polymers can have significantly different
properties. For example, HOPE polymers with different
molecular weights have different properties and applica-
tions. The low-molecular-weight, low-viscosity, injec-
tion-molded base cup for soft drink bottles is not
interchangeable with the high-molecular-weight, high-
viscosity material used in milk bottles (8). Achieving a
finer separation of resin types increases the value of the
recycled thermoplastic.
The price for granulated plastic typically is higher to
adjust for the cost of granulation. However, users often
accept only baled plastics to enable verification of impu-
rity levels. The typical desired levels for nonplastic con-
taminants are either no metals or less than 3 percent
nonplastic (9).
4.4 Rubber Particulate
Tires and similar rubber goods are composed mainly of
polymers, carbon black, and softeners. The softeners
are primarily aromatic hydrocarbons. The typical com-
position of a tire casing is 83 percent total carbon, 7
percent hydrogen, 2.5 percent oxygen, 1.2 percent sul-
fur, 0.3 percent nitrogen, and 6 percent ash (10).
Of the 278,000,000 tires discarded in 1990, about 34.5
percent were recycled, with the reuse options being
retreading (13.7 percent), energy recovery (9.4 per-
cent), fabricated products (4.3 percent), export (4.3 per-
cent), asphalt (0.9 percent), and miscellaneous (1.9
percent) (10). Some energy recovery applications con-
sume whole tires. Tires also can be cut into shapes or
strips to make sandals, floor mats, washers, insulators,
or dock bumpers (11).
For most reuse options, however, the tires must first be
reduced to particulate. Particulate may be used to fab-
ricate new rubber products or to make asphalt, or par-
ticulate can be burned to produce energy. The success
of recycling and most appropriate reuse applications
depends on the particle size and particle size distribu-
tion; the strength, elasticity, impurity content, and other
properties; and the cost of the particulate produced.
Rubber particulate can be used to fabricate athletic field
surfaces, carpet underlayment, parking bumpers, and
railroad crossing beds (Section 3.16). Fine particulate
rubber for these applications is produced by mechanical
grinding with an abrasive or by cryogenically fracturing
the material after cooling it in liquid nitrogen. Steel or
fabric is separated from the rubber fragments by mag-
netic and/or gravity separation. The quality of the re-
claimed rubber is lower than that of newly manufactured
rubber because aging and treatment in the recycling
process reduce elasticity.
In asphalt concrete, ground tire rubber replaces some
of the aggregate in asphalt (Section 3.16). Section 1038
of the Intermodal Surface Transportation Efficiency Act
of 1991 (Public Law #102-240) includes provisions to
increase the number of tires used in asphalt for highway
pavement.
Discarded tires are shredded to 2-in. and smaller chips
for use as a fuel (Sections 3.2 and 3.3). The typical
heating value is 32,500 kJ/kg (14,000 Btu/lb) for whole
tire chips or 36,000 kJ/kg (15,500 Btu/lb) for steel-free
tire chips. When used as fuel in cement kilns, iron from
the tire belts and beads supplements the iron required
for cement making. For other furnace types, the wire
pieces from belts and beads are undesirable; the wires
clog furnace feed equipment and generate ash. With the
exception of cement kilns, most furnaces that use shred-
ded tire fuels require dewired rubber particulate. Proc-
essing to remove the metals is commercially feasible but
increases the cost of tire-derived fuel particulate.
4.5 Fuels for Energy Recovery
Substituting waste materials for fuel is an approach
frequently applied to recover value from the waste
(Sections 3.2 and 3.3). The ideal energy recovery fuel
should be as similar to conventional fuels as possible.
Most conventional boilers are fueled with coal, oil, or
gas. ASTM D-396, "Standard Specification for Fuel
Oils," divides fuel oils into grades based on suitability for
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specific burner types. The specification places limiting
values on properties such as flashpoint, pour point,
water and sediment content, carbon residue content,
ash content, vaporization characteristics, viscosity, den-
sity, corrosivity, and nitrogen content. ASTM D-388,
"Classification of Coal by Rank," describes classifica-
tions of coal based on factors such as carbon content,
gross heat content, and agglomeration characteristics.
A high proportion of carbon and hydrogen present as
organic compounds, low water content, and low ash
content are the ideal conditions for a fuel material. High
water content wastes heat due to the energy removed
in the combustion gas by the heated water. High ash
content increases the complexity of bottom ash and fly
ash handling in the boiler. Specific impurities bring other
possible complications. The presence of halogenated
solvents in the fuel is highly undesirable because the
combustion process produces acidic vapors.
Various impurities can volatilize, increasing the com-
plexity of air pollution control requirements. High con-
centrations of volatile metals (arsenic, cadmium, lead,
selenium, and mercury) may cause excessive concen-
trations of these metals to enter the combustion gases.
Nonvolatile metals remain in the ash and may cause
unacceptable levels of leachable metals. Halides, nitro-
gen, phosphorus, or sulfur can react to form corrosive
gasses. Halides in the waste can combine with metals
such as lead, nickel, and silver, forming volatile metal
halides (12). Highly toxic chlorinated organics such as
polychlorinated biphenyls (PCBs) or pesticides require
high combustion temperatures and high destruction ef-
ficiencies (13).
The viscosity of liquid fuels is an important physical
parameter. Liquid waste must be amenable to atomiza-
tion at acceptable pressures. Liquids with a dynamic
viscosity less than 10,000 standard Saybolt units (SSU)
are considered pumpable. The optimum viscosity for
atomization is about 750 SSU (13).
Pulp and paper making require significant energy input.
To conserve resources, heat typically is supplied by
onsite boilers burning wood waste (hog fuel). Hog fuel
shows substantial variations in heat content and mois-
ture. Because the hog fuel boilers are designed to feed
solid wood and operate with varying quality feed, they
can use solid waste materials such as broken pallets or
rubber particulate more easily than conventional utility
boilers can (10).
Off-specification production batches or outdated explo-
sives contain chemical energy that can be recovered.
For example, the approximate heating values of trinitro-
toluene (TNT) and research department explosive (RDX)
are 15,000 to 9,000 kJ/kg (6,460 and 3,900 Btu/lb), re-
spectively (14). The use of energetic materials as fuel
raises three main issues.
The reactivity of the energetic materials must be ac-
counted for in the design of fuel-handling and burning
systems. Either the material must be dissolved in fuel
oil to eliminate the possibility of explosion or the fur-
nace must be designed to contain the largest possi-
ble explosion. TNT and RDX have low solubility in
fuel oil and typically are dissolved in a solvent, such
as toluene, before being mixed with fuel oil (14).
Energetic materials contain more bound nitrogen
than typical fuels, increasing the quantity of nitrogen
oxide (NOX) generated during combustion. The fur-
nace off-gas treatment system may require special
provisions to curtail or treat NOX.
Explosives dissolved in fuel oil increase viscosity. As
discussed above, viscosity is a key parameter in the
selection and design of the fuel oil atomizing nozzle.
Up to limits imposed by reactivity, TNT does not sig-
nificantly increase the viscosity of No. 2 fuel oil. A
viscosity increase due to the addition of TNT to No.
6 fuel oil, however, is significant and may be more
limiting than reactivity constraints (14).
4.6 Metals for Reuse
Site cleanup activities such as storage tank removal,
building demolition (Section 3.36), and transformer dis-
assembly (Section 3.37) can produce bulk metals for
reuse. Iron, steel, aluminum, and copper shapes can be
recycled through existing scrap recovery channels. The
Institute of Scrap Recycling Industries (15) provides
guideline specifications for nonferrous scrap, including
copper, brass, bronze, lead, zinc, aluminum, magne-
sium, nickel, copper-nickel alloys, and stainless steel.
These guidelines describe minimum metal content,
maximum impurity levels, density, surface contamina-
tion, and other physical conditions defining various
grades of metal scrap. For example, more than 30 cate-
gories of aluminum scrap are described.
For recycling of bulk metal from demolition, surface
contaminants such as welds, rust, scale, paint, or coat-
ings generally are acceptable. Hazardous contaminants
must be removed, however (16). Mixtures of alloy types
of the same metal also reduce value. Paradoxically, very
expensive specialty stainless steels or aluminum alloys
may be less valuable in the recycling market than low-
alloy materials; the added alloying metals are viewed as
impurities in the recycling process.
4.7 Metal-Containing Sludge or Slag for
Feed to Secondary Smelters
Waste materials at Superfund or RCRA Corrective Ac-
tion sites may contain a sufficiently high concentration
of metals to be suitable for processing in a smelter
(Section 3.31). Lower-concentration wastes may be ame-
nable to processing by another method (e.g., physical
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separation [Section 3.33] or chemical leaching [Section
3.29]/precipitation [Section 3.18]) that would produce a
smaller volume of residual with a metals content high
enough to warrant smelting. The metal types and con-
centrations, matrix properties, and impurities control the
suitability of wastes for processing in secondary smelt-
ers. The typically desired minimum concentrations of six
metals for secondary smelters are indicated in Table 4-1.
The waste matrix also may contribute constituents
needed to form slag. The main slag-forming compo-
nents are silica, iron, and calcium. A waste matrix with
high thermal conductivity is desirable. High thermal con-
ductivity indicates that the matrix can be heated more
quickly and uniformly (19).
Impurities that volatilize or react to form volatile products
increase the complexity and expense of off-gas treat-
ment. Examples include mercury, arsenic, nitrates, sul-
fates, sulfides, phosphates, and halides. Mercury and
arsenic are amenable to pyrometallurgical processing
but require special off-gas treatment provisions (1). Ex-
cept for arsenic in lead battery alloys, arsenic- and
mercury-containing materials are incompatible with
most existing secondary smelters in the United States.
Pyrometallurgical processing relies on partitioning of
different metals to vapor, slag, and molten metal phases
to form purified products. Impurities that partition to the
same phase as the target metal are undesirable. Incom-
patibilities are process specific. Volatile metals such as
arsenic and antimony tend to contaminate the zinc oxide
product fumed from a waelz kiln. Silver and bismuth are
difficult to separate from lead in secondary refining be-
cause they tend to remain in the metal rather than
partition to the slag.
Alkaline metals such as sodium and potassium de-
crease the viscosity and increase the corrosiveness of
slag formed in a pyrometallurgical reactor. Excessive
levels of alkaline metals increase the difficulty in control-
ling slag properties and may cause the slag to damage
the reactor lining (20).
Table 4-1. Approximate Feed Concentration Requirements
for Secondary Smelters (13, 17, 18)
Metal
Approximate Minimum
Concentration for
Pyrometallurgical Recovery
Cadmium
Chromium
Copper
Lead
Nickel
Zinc
2%
5%
30%
55%
1.3%
8%
4.8 Waste Feed to Hydrometallurgical
Processing
Hydrometallurgical processes, such as acid leaching
(Section 3.29), precipitation (Section 3.18), reverse os-
mosis (Section 3.21), or ion exchange (Section 3.19) are
not highly selective. The difficulty of recovering products
from mixed metal wastes increases as the number of
metal contaminants present increases. Segregating
spent processing solutions greatly enhances their com-
patibility with recycling processes. The waste stream
should not be mixed or diluted. The highest concentra-
tion of metal possible should be maintained (21).
Typical parameters of interest for hydrometallurgical
processing include calcium, cadmium, chromium, cop-
per, iron, mercury, magnesium, nickel, phosphorus,
lead, tin, zinc, organic content, color, smell, acid insol-
ubles, moisture, cyanide, and filtration rate. Organics
interfere with chemical leaching and many of the solu-
tion processing techniques used to recover metals from
the leaching solution. Organic contaminants in wastes
to be treated by hydrometallurgical methods should,
therefore, be minimized (19). Thespeciation of the metal
contaminants in the waste is an important factor. The
valence state and counter ion affect the ability to dis-
solve the metal. Chelating agents or metal complexing
anions can greatly increase the difficulty of recovering
metals from solutions (22). Wastes with high pH and
high alkalinity are difficult to treat by acid leaching due
to the high consumption of acid by the reserve alkalinity.
4.9 High-Value Ceramic Products
Some waste streams can be treated at high temperature
to produce valuable ceramic products (Section 3.30).
For example, vitrified waste can be fritted to make abra-
sives, cast from a melt, or formed and sintered into
products such as bricks or architectural dimension stone.
The waste also may be converted to a frit for use as feed
material in the manufacture of ceramics. Ceramic materi-
als are products manufactured by high-temperature treat-
ment of raw materials of mainly earthy origin. The main
components of ceramics are silicon, silica, and/or silicate.
The variety of possible products includes:
Structural clay products, which include burned clay prod-
ucts such as brick, roof tile, and ceramic tile and pipe.
Refractories, which include special materials for high-
temperature applications such as kiln-lining bricks,
high-temperature insulation materials, and castable
refractories.
Abrasives, which include particulate material (along
with any supporting materials and binders) used for
cutting, grinding, or polishing; common abrasives are
fused alumina, silicon carbide, silica, alumina, and
emery.
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Architectural products, which include decorative and
structural ceramics such as brick, blocks, patio
stones, wall and floor tile, art pottery, and chemical
and electrical porcelain.
Glass products, which include vitreous silicate prod-
ucts such as window glass, container glass, and
glass fibers.
Porcelain enamel products, which include products
with a ceramic coating on a metal substrate such as
sink and bathroom fixtures, architectural panels, and
specialty heat and chemical-resistant equipment.
A variety of organizations publish specifications for ce-
ramic feed materials or products. Example sources of
specifications for ceramic products include ASTM, the
American National Standards Institute, the U.S. Navy
(MIL-A-22262(SH) for sandblasting media), and the
Steel Structures Painting Council (SSPC-XAB1X for
mineral and slag abrasives).
4.10 Inorganic Feed to Cement Kilns
Manufacture of hydraulic cement, a conventional build-
ing material, offers possibilities for recycling of contami-
nated waste materials (Section 3.32). Making hydraulic
cement requires a significant input of energy and raw
materials. Opportunities exist for input of nonhazardous
metals-contaminated solids to cement kilns. Of particu-
lar interest to the recycling of metals-contaminated
waste is the need for silica, iron, and alumina.
In raw material grinding, the input materials are ground
so that 75 to 90 percent of the material passes through
a 0.074-mm (2.9 in.) (200-mesh) sieve. The grinding
may be done either wet or dry. In wet milling, water is
added with the mill feed to produce a slurry containing
about 65 percent solids.
Specifications for limestone feed for cement making
require that the calcium carbonate (CaCO3) content be
greater than 75 percent and the magnesium carbonate
(MgCO3) content be less than 3 percent. Because the
raw materials must be finely ground, chert nodules or
coarse quartz grains are undesirable (23).
ASTM specifies five basic types of Portland cement.
Type I is intended for use when the special properties of
the other types are not required. Type IA is for the same
uses as Type I where air entrainment is desired. Air
entrainment is a technique to improve freeze/thaw resis-
tance of the concrete and reduce the mix viscosity with-
out increasing water addition. Type II also is a
general-use cement but offers increased sulfate resis-
tance and lower heat generation. Type IIA is similar to
Type II but is intended for use where air entrainment is
desired. Type III is formulated to maximize early strength
production. Type MIA is the air entrainment version of
Type III. Type IV is intended for use where the heat
generation must be minimized. Type V is for use when
sulfate resistance is desired. The main constituents of
Portland cement typically are tricalcium silicate (CaS),
dicalcium silicate (C2S), tricalcium aluminate (C3A), and
tetracalcium aluminoferrite (C4AF).
The U.S. production of Portland and masonry cement in
1991 was about 70,000,000 metric tons (77,000,000
tons). Portland cement makes up 96 percent of the total
U.S. cement output. Types I and II account for about 92
percent of Portland cement production.
4.11 Cement Substitute
Use as a cement supplement or substitute is a viable
option for some fly ash and slag wastes (Section 3.7).
Fly ash is used in large quantities to stabilize sulfate
sludge, and it can replace cement in construction appli-
cations. Construction applications require selection of fly
ash that is low in sulfate impurity and consists of small,
generally spherical particles. Spherical particles act to
reduce the mix viscosity and thus allow preparation of
concrete with less water addition (25). In mass concrete
pours, excessive temperature increases may occur due
to the heat of hydration released as the concrete sets.
Replacement of some cement by a pozzolan can reduce
the generation of this heat. Fly ash addition also can be
valuable in reducing heat generation (26).
Slag cooled with sufficient speed to retain a largely
vitreous structure exhibits cementitious properties when
hydroxide activators are present. Blast furnace slag
from iron production is the most commonly used slag
pozzolan, but other types are used if they contain limited
quantities of free calcium oxide (CaO) or magnesium
oxide (MgO). Free alkaline earth oxides may reduce
strength due to delayed hydration. Steel-making slags
are reportedly poor candidates due to their high calcium
content (26). However, magnesium slags are reported
to be good candidates (27). In waste solidification/stabi-
lization treatment, replacing some cement with blast
furnace slag provides reducing power to help hold met-
als in a less mobile chemical state (28).
Portland cement is the most commonly used type of
hydraulic cement. Recent environmental regulations
and increased energy costs have increased the cost of
cement making, which has increased the attractiveness
of substituting slag pozzolans for conventional cement
(29). Blended cements are available and may be used
to reduce costs or for special purposes.
The U.S. Environmental Protection Agency (EPA) has
developed guidelines to assist agencies in the procure-
ment of cements and concretes that contain fly ash (40
CFR Part 249). Subpart B of this guide describes the
development of the guide and contract specifications
to allow use of cement containing fly ash, as well as
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provides specific recommendations for material specifi-
cations. For cement, these recommendations are:
ASTM C 595Standard Specification for Blended
Hydraulic Cements.
Federal Specification SS-S-1960/4BCement, Hy-
draulic, Blended.
ASTM C 150Standard Specification for Portland
Cement and Federal Specification SS-C-1960/
General (appropriate when fly ash is used as a raw
material in the production of cement).
For concrete, these recommendations are:
ASTM C 618Standard Specification for Fly Ash and
Raw Calcined Natural Pozzolan for Use as a Mineral
Admixture in Portland Cement Concrete.
Federal Specification SS-C-1960/5APozzolan for
Use in Portland Cement Concrete.
ASTM C 311Standard Methods of Sampling and
Testing Fly Ash and Natural Pozzolans for Use as a
Mineral Admixture in Portland Cement Concrete.
Subpart C describes recommended approaches to
bidding and price analysis. Subpart D describes recom-
mended certification procedures including measure-
ment, documentation, and quality control.
4.12 Aggregate and Bulk Construction
Materials
Sand and slag wastes can be used directly for various
construction purposes (Section 3.7). Other inorganic
wastes can be vitrified to produce rock-like materials
(Section 3.30). The main requirements in using waste
materials as aggregates or bulk materials are regulatory
acceptance, customer acceptance, and performance.
The waste material must meet the required leach resist-
ance criteria and provide some useful function in the
product; the end use should not be simply disposal in
another form. Even if regulatory requirements are met,
construction companies and local citizens are reluctant
to accept the use of waste materials. Therefore, leach
resistance and durability testing may be required be-
yond those specified in the regulations; the reused
waste should meet the performance requirements of
new materials. Some sources of information on perform-
ance of aggregate and construction materials are out-
lined below.
Aggregate is a mineral product from natural or manufac-
tured sources used in concrete making. The specifica-
tions for fine and coarse aggregate are described in
ASTM 33. The important features of aggregate are size
grading; freedom from deleterious materials such as
clay lumps, friable particles, and organic materials; and
soundness.
The alkali reactivity of the cement and aggregate is an
important factor in selecting an aggregate. The concern
is reaction of an alkali with the aggregate, causing a
volume increase and/or loss of concrete strength. The
alkali causing the reaction usually is the calcium hydrox-
ide released as the cement cures. In some cases, how-
ever, the alkali may come from external sources, such
as ground water. There are two basic types of alkali-
aggregate reactions:
Reaction of alkali with siliceous rocks or glasses.
Reaction of alkali with dolomite in some carbonate
rocks.
Some waste slags can exhibit excessive reactivity. For
example, four zinc smelter slag samples tested by Okla-
homa State University were found to be unsuitable as
aggregate for Portland cement because of excessive
expansion during curing caused by alkali aggregate re-
actions (30).
One of several tests can determine the alkali activity
of a potential aggregate, depending on the type of ag-
gregate to be tested. The applicable tests or guides
are ASTM C 227, "Test Method for Potential Alkali Re-
activity of Cement-Aggregate Combinations (Mortar-Bar
Method)"; ASTM C 289, "Potential Reactivity of Aggre-
gates (Chemical Method)"; ASTM C 295, "Petrographic
Examination of Aggregates for Concrete"; ASTM C 342,
"Standard Test Method for Potential Volume Change of
Cement-Aggregate Combinations"; and ASTM C 586,
"Potential Alkali Reactivity of Carbonate Rocks for
Concrete Aggregates (Rock Cylinder Method)." Guid-
ance for selecting the appropriate test method is given
in ASTM C 33, "Standard Specification for Concrete
Aggregates."
Coarse aggregate for bituminous paving mixtures is
specified in ASTM D 692. This specification covers
crushed stone, crushed hydraulic-cement concrete,
crushed blast-furnace slag, and crushed gravel for use
in bituminous paving mixtures specified in ASTM D 3515
or D 4215. Air-cooled blast-furnace slag is required to
have a compacted density of not less than 1120 kg/m3
(70 Ib/ft3) when sizes number 57 [25 to 4.75 mm (1 to
0.19 in.)] or 8 [9.5 to 2.36 mm (0.38 to 0.09 in.)] (ASTM
C 448) are tested. Additional guidance on polishing
characteristics, soundness, and degradation is given.
The ASTM and the American Association of State High-
way and Transportation Officials (AASHTO) are the
main national organizations setting specifications re-
garding crushed stone for use in construction. However,
states or localities develop many specifications for con-
struction aggregates based on their specific needs.
Most common specifications control size grades, sound-
ness, shape, abrasion resistance, porosity, chemical
compatibility, and content of soft particles. Due to the
skid resistance imparted to road surfaces when blast
68
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furnace or steel furnace slag is used as the aggregate,
many state agencies specify that slag aggregate for
asphalt be applied to roads with high traffic volume (29).
The American Railroad Engineering Association sets
standards for railroad ballast. The general charac-
teristics of a good ballast material are strength, tough-
ness, durability, stability, drainability, cleanability,
workability, and resistance to deformation.
Limestone for lime manufacture should contain more
than 90 percent CaCO3, less than 5 percent MgCO3,
and less than 3 percent other impurities. Feed to vertical
limestone kilns should be 12.7 to 20.3 cm (5 to 8 in.) in
size. A size range of 9.5 to 64 mm (% to 2V2 in.) is
acceptable for limestone feed to rotary kilns.
Specifications for limestone or dolomite for fluxing met-
allurgical processes depend on the type of ore to be
processed and the intended end use of the slag. A silica
content of less than 2 to 5 percent, a magnesia content
in the range of 4 to 15 percent, and a sulfur content
of less than 0.1 percent are typical for fluxstone specifi-
cations.
Limestone or dolomite for glass manufacture should
contain more than 98 percent CaCO3 or MgCO3, respec-
tively. The iron limit for glass-making input typically is
0.05 to 0.02 percent.
The American Water Works Association established
specification B100-94, "Standards for Filtering Materi-
als," for particulate used in filtration operations. The
specification describes criteria affecting the acceptability
of filtration media such as particle shape, specific grav-
ity, effective grain size and uniformity, acid soluble im-
purity content, and radioactive and heavy metal content.
4.13 References
1. U.S. EPA. 1991. Treatment technology background
document. Washington, DC.
2. California Department of Health Services. 1990.
Alternative technologies for the minimization of haz-
ardous waste. California Department of Health
Services, Toxic Substances Control Program (July).
3. Home, B., and Z.A. Jan. 1994. Hazardous waste
recycling of MGP site by HT-6 high temperature
thermal distillation. Proceedings of Superfund XIV
Conference and Exhibition, Washington, DC
(November 30 to December 2, 1993). Rockville,
MD: Hazardous Materials Control Resources Insti-
tute, pp. 438-444.
4. Miller, B.H. 1993. Thermal desorption experience in
treating refinery wastes to BOAT standards. Incinera-
tion Conference Proceedings, Knoxville, TN (May).
5. Randall, J.C. 1992. Chemical recycling. Mod. Plas-
tics 69(13):54-58.
6. Reinink, A. 1993. Chemical recycling: Back to feed-
stock. Plastics, Rubber, and Composites Process-
ing and Applications 20(5):259-264.
7. Morgan, T.A., S.D. Richards, and W Dimoplon.
1992. Hydrocarbon recovery from an oil refinery
pitch pit. Proceedings of National Conference: Mini-
mization and Recycling of Industrial and Hazardous
Waste '92. Rockville, MD: Hazardous Materials
Control Resources Institute.
8. Pearson, W. 1993. Plastics. In: Lund, H.F., ed. The
McGraw-Hill recycling handbook. New York, NY:
McGraw-Hill.
9. Hegberg, B.A., G.R. Brenniman, and WH. Hallen-
beck. 1991. Technologies for recycling post-
consumer mixed plastics. Report No. OTT-8. Uni-
versity of Illinois, Center for Solid Waste Manage-
ment and Research.
10. Blumenthal, M.H. 1993. Tires. In: Lund, H.F., ed.
The McGraw-Hill recycling handbook. New York,
NY: McGraw-Hill.
11. Carless, J. 1992. Taking out the trash. Washington,
DC: Island Press.
12. U.S. EPA. 1992. Superfund engineering issue: Con-
siderations for evaluating the impact of metals par-
titioning during the incineration of contaminated
soils from Superfund sites. EPA/540/S-92/014.
Washington, DC.
13. Versar Inc. 1988. Decision criteria for recovering
CERCLA wastes. Draft report prepared for U.S.
EPA Office of Emergency and Remedial Response.
Springfield, VA: Versar Inc.
14. Myler, C.A., WM. Bradshaw, and M.G. Cosmos. 1991.
Use of waste energetic materials as a fuel supple-
ment in utility boilers. J. Haz. Mat. 26(3):333-341.
15. Institute of Scrap Recycling Industries. 1991. Scrap
specifications circular. 1991 guidelines for nonfer-
rous scrap: NF-91. Washington, DC.
16. von Stein, E.L. 1993. Construction and demolition
debris. In: Lund, H.F., ed. The McGraw-Hill recy-
cling handbook. New York, NY: McGraw-Hill.
17. Hanewald, R.H., WA. Munson, and D.L. Schweyer.
1992. Processing EAF dusts and other nickel-
chromium waste materials pyrometallurgically at IN-
METCO. Minerals and Metallurgical Processing
9(4):169-173.
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18. James, S.E., and C.O. Bounds. 1990. Recycling
lead and cadmium, as well as zinc, from EAF dust.
In: Mackey, T.S., and R.D. Prengaman, eds. Lead-
zinc '90. Warrendale, PA: The Minerals, Metals, and
Materials Society.
19. U.S. EPA. 1991. Recovery of metals from sludges
and wastewater. EPA/600/2-91/041. Cincinnati, OH.
20. Queneau, P.B., L.D. May, and D.E. Cregar. 1991.
Application of slag technology to recycling of solid
wastes. Presented at the 1991 Incineration Confer-
ence, Knoxville, TN (May).
21. Edelstein, P. 1993. Printed-circuit-board manufac-
turer maximizes recycling opportunities. HazMat
World 6(2):24.
22. St. Clair, J.D., W.B. Bolden, E.B. Keough, R.A.
Pease, N.F. Massouda, N.C. Scrivner, and J.M.
Williams. 1993. Removal of nickel from a complex
chemical process waste. In: Hager, J.P., B.J. Han-
sen, J.F. Pusateri, WP. Imrie, and V. Ramachan-
dran, eds. Extraction and processing for the
treatment and minimization of wastes. Warrendale,
PA: The Minerals, Metals, and Materials Society.
pp. 299-321.
23. Tepordei, V.V. 1992. Crushed stone annual report
1990. Washington, DC: U.S. Department of the In-
terior, Bureau of Mines (April).
24. Johnson, W 1992. Cement annual report 1990.
Washington, DC: U.S. Department of the Interior,
Bureau of Mines.
25. Horiuchi, S., T Odawara, and H. Takiwaki. 1991.
Coal fly ash slurries for backfilling. In: Goumans,
J.J.J.M., H.A. van der Sloot, and T.G. Aalbers, eds.
Waste materials in construction. Studies in environ-
mental science 48. New York, NY: Elsevier.
pp. 545-552.
26. Popovic, K., N. Kamenic, B. Tkalcic-Ciboci, and V.
Soukup. 1991. Technical experience in the use of
industrial waste for building materials production
and environmental impact. In: Goumans, J.J.J.M.,
H.A. van der Sloot, and T.G. Aalbers, eds. Waste
materials in construction. Studies in environmental
science 48. New York, NY: Elsevier. pp. 479-490.
27. Courtial, M., R. Cabrillac, and R. Duval. 1991. Fea-
sibility of the manufacturing of building materials
from magnesium slag. In: Goumans, J.J.J.M., H.A.
van der Sloot, and T.G. Aalbers, eds. Waste mate-
rials in construction. Studies in environmental sci-
ence 48. New York, NY: Elsevier. pp. 491-498.
28. Bostick, W.D., J.L. Shoemaker, R.L. Fellows, R.D.
Spence, T.M. Gilliam, E.W McDaniel, and
B.S. Evans-Brown. 1988. Blast furnace slag: Ce-
ment blends for the immobilization of technetium-
containing wastes. K/QT-203. Oak Ridge, TN: Oak
Ridge Gaseous Diffusion Plant.
29. Solomon, C.C. 1992. Slag-iron and steel annual
report 1990. Washington, DC: U.S. Department of
the Interior, Bureau of Mines (April).
30. U.S. EPA. 1990. Report to Congress on special
wastes from mineral processing. EPA/530/SW-
90/070C. Washington, DC.
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Chapter 5
Case Studies
This chapter highlights specific case studies of success-
ful examples of commercial recycling of complex waste
materials. Eight case studies were selected to illustrate
applications of a variety of recycling technologies cov-
ering a wide range of contaminant and matrix types. The
case studies describe:
Use of spent abrasive blasting media as aggregate
in asphalt.
Use of spent abrasive blasting media as a raw ma-
terial for Portland cement making.
Physical separation to recover lead particulate from
soils at small-arms practice ranges.
Processing lead-containing wastes from Superfund
sites in a secondary smelter.
A treatment train for recovery of petroleum from an
oily sludge.
Solvent recovery using small onsite distillation units.
Thermal desorption to clean soil for reuse.
Pumping to recover coal tar liquids.
Each case study includes sections on site and waste
description, technology description, recycling benefits,
economic characteristics, and limitations.
These case studies show real-world examples of ways
to overcome the challenges of implementing recycling
technologies, as well as demonstrate the application of
treatment trains to produce useful products from com-
plex waste mixtures.
5.1 Recycling Spent Abrasive Blasting
Media Into Asphalt Concrete
Reuse as asphalt aggregate may be feasible for a wide
variety of petroleum or metals-contaminated soils,
slags, or sands (Section 3.7). The Naval Facilities Engi-
neering Services Center in Port Hueneme, California,
has been studying the recycling of spent abrasive blast-
ing media (ABM), or sandblasting grit, into asphalt con-
crete for commercial paving purposes. The sandblasting
grit is used as a "blender sand" for a portion of the
fine-grained aggregate that is used to produce the
asphalt concrete. This section briefly describes a case
history for an ongoing "ABM-to-asphalt" recycling pro-
ject in Hunters Point, California.
5.1.1 Site and Waste Description
The spent ABM at Hunters Point is composed of a
2,300-m3 (3,000-yd3) pile of Monterey Beach sand con-
taminated with small amounts of paint chips. The spent
ABM was generated in shipcleaning operations con-
ducted at Naval Station, Treasure Island, Hunters Point
Annex, by Triple AAA Shipcleaning during the 1970s and
1980s. The spent ABM grades as a coarse sand and
contains relatively low concentrations of metals. Aver-
age copper, zinc, lead, and chromium concentrations
are 1,800, 1,100, 200, and 100 mg/kg (105, 64, 12, and
6 grains/gal), respectively. Leachable metals concentra-
tions using the California Waste Extraction Test (WET)
methodology average 140, 150, 20, and 2 mg/L (8.2,
8.8, 1.2, 0.12 grains/gal), respectively, for copper, zinc,
lead, and chromium. The WET test is California's ver-
sion of the U.S. Environmental Protection Agency's
(EPA's) Toxicity Characteristic Leaching Procedure
(TCLP). The spent ABM at Hunters Point is considered
hazardous because of soluble threshold limit concentra-
tion (STLC) exceedances on the WET test for copper
and lead but is not an EPA hazardous waste because it
passes the TCLP.
Different types of spent ABM otherthan Monterey Beach
sand can be recycled into asphalt concrete. A coal slag-
derived ABM from shipcleaning operations has been
recycled successfully in Maine. A variety of ABM prod-
ucts derived from both primary and secondary smelter
slags also are recyclable, including copper and nickel
slags.
Waste types otherthan spent ABM also can be recycled
into asphalt concrete as a substitute for a portion of the
aggregate. For example, spent foundry sand and sandy
or gravelly textured soils have been successfully recy-
cled (1, 2). Mixed colored glass is being recycled into
asphalt in New Jersey, and the product has been termed
"glassphalt" (3). Numerous permitted facilities recycle
petroleum-contaminated soils into asphalt concrete;
EPA (4) provides a directory of these facilities. Rubber
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from tires can be pyrolized and substituted for a portion
of the bitumen in the asphalt concrete. Tire particulate
can be used as aggregate in asphalt concrete (5). Also,
worn-out asphalt pavement can be crushed, graded,
and recycled as aggregate in asphalt concrete (6).
5.1.2 Technology Description
The ABM-to-asphalt recycling technology involves sub-
stituting the ABM for a portion of the fine-size aggregate
in asphalt concrete. As long as the metal concentrations
in the spent ABM are not excessively high, the metal
concentrations in the asphalt concrete product should
be very low, and any metals present must be physically
and chemically immobilized in the asphalt binder. Typi-
cally, asphalt concrete consists of approximately 5 per-
cent bitumen and 95 percent graded aggregate. The
graded aggregate includes particles varying from fine
sand to 12- to 25-mm (V2- to 1-in.) gravel. Depending on
the mix design and the ultimate strength requirements
of the product, the fine-size particle fraction may com-
prise 25 to 35 percent of the asphalt concrete. In the
ABM-to-asphalt technology demonstration at Hunters
Point, an ABM concentration of 5 percent by weight of
the final asphalt concrete is being used. In other words,
spent ABM equals 5 percent of the asphalt concrete and
approximately one-seventh to one-fifth of the normal
fine fraction component of the asphalt concrete. Higher
ABM contents are possible; theoretically, the entire fine
fraction of the mix design could be composed of ABM.
At higher ABM concentrations, however, a greater po-
tential exists for adverse impact on product quality
and/or elevated metals concentrations in the product.
ABM recycling is applicable to both cold- and hot-mix
asphalt processes. At Hunters Point, the ABM is being
recycled into hot-mix asphalt for normal commercial
paving applications, yielding high-strength asphalt
concrete for heavily used highways. ABM can be recy-
cled into both a base coarse layer or any subsequent
lifts applied to the base coarse. ABM also can be recy-
cled into cold-mix processes, which yield a lower-grade
product for road repair or lower-traffic-area applications.
5.1.3 Recycling Benefits
The spent ABM at Hunters Point is hazardous in the
state of California and, if no recycling and reuse option
were available, would have to be treated by stabiliza-
tion/solidification and disposed of in a hazardous waste
landfill. This technology makes beneficial reuse of the
ABM by incorporating it into asphalt concrete, where
resulting metal concentrations are low and the metals
have been immobilized in the asphalt concrete matrix.
Millions of tons of asphalt concrete are produced in the
United States annually; therefore, there is a consider-
able demand for aggregate for asphalt pavement.
5.1.4 Economic Characteristics
The cost of an ABM-to-asphalt recycling project de-
pends on a number of factors, particularly:
Tippage rate charged by the asphalt plant.
Distance from the generator to the asphalt plant,
which affects transportation costs.
Required amount of planning, regulatory interactions,
reporting, and program management.
In addition, the following factors affect cost to a lesser
degree:
Analytical fees for chemical and physical analyses of
asphalt test cores to show compliance with any regu-
latory or institutional requirements.
ABM pretreatment, such as screening and debris
disposal.
In the Hunters Point project, the tippage rate charged by
the asphalt plant is $44 per metric ton ($40 per ton) of
ABM recycled. The overall cost is approximately $155
per metric ton ($140 per ton), including significant costs
for transportation to the asphalt plant, regulatory compli-
ance, and analytical testing of core specimens produced
in the laboratory prior to full-scale recycling. In general,
the recycling costs decrease on a per-ton basis with
increasing amounts of spent ABM recycled. The follow-
ing ranges are typical for most projects:
Amount of ABM
(Tons)
500-1,500
1,500-3,000
3,000-6,000
Estimated Costs of
Recycling (per Ton)
$125-$175
$100-$150
$ 50-$100
Therefore, the ABM-to-asphalt recycling approach is
economically beneficial for both the asphalt plant and
the ABM generator. The generator pays significantly less
per ton than it would for disposal in a hazardous landfill
and probably less than it would cost for onsite treatment
and disposal, and the asphalt plant receives payment
for a raw material for which it ordinarily has to pay.
5.1.5 Limitations
The asphalt recycling approach is viable for only certain
types of aggregates. The aggregate must comply with
both performance and environmental standards such as
durability, stability, chemical resistance, biological resis-
tance, permeability, and leachability (7). The principal
limitations pertain to risk, regulatory considerations, or
technical considerations pertaining to the integrity of the
asphalt concrete product. For example:
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ABM-containing solvents or other particularly hazard-
ous or toxic constituents should not be recycled in
this manner.
ABM with high metal contents (percent level or
greater) may pose hazards either to workers at the
asphalt plant due to dust exposure or to the public in
the asphalt product because of metals leaching.
The presence of sulfate or metallic iron is undesirable
because these materials swell upon hydration of sul-
fates or oxidation of iron. Reduced forms of trace
metals may cause similar problems, which, however,
may be avoidable by recycling the ABM into a base
coarse layer, where there is minimal contact with air.
High concentrations of silt and smaller size particles
are undesirable because they have poor wetting
characteristics in the bitumen matrix and may gener-
ate dusts.
Highly rounded aggregates are not compatible with
good vehicular traction in the asphalt concrete
product.
The chief chemist or engineer at the asphalt plant must
ensure that the ABM is compatible with the production
of a high-integrity asphalt concrete product.
Cognizant regulators should be contacted prior to pro-
ceeding with the recycling project. RCRA regulations
discourage the land application of recycled hazardous
materials (8). In most cases, special wastes or state-
regulated wastes may be recyclable, subject to state or
local restrictions or policies.
5.2 Recycling Spent Abrasive Blasting
Media Into Portland Cement
Silicate matrices containing iron or aluminum are good
candidates for reuse as cement raw materials (Section
3.32). The Naval Facilities Engineering Services Center
in Port Hueneme, California, along with Southwestern
Portland Cement Co., Mare Island Naval Shipyard, Ra-
dian Corporation, and Battelle, has been studying the
recycling of spent ABM, or "sandblasting grit," as a raw
material for the manufacture of Portland Type I cement
for construction purposes. The ABM is a silicate slag
containing moderate levels of iron and is being used as
a substitute for the iron ore that normally is used in
cement manufacture. The silica and alumina in the ABM
are also useful ingredients in the cement product. This
section briefly describes a case history for an ongoing
"ABM-to-Portland-cement" recycling project being con-
ducted at Southwestern Portland Cement in Victorville,
California.
5.2.1 Site and Waste Description
The source of the ABM is Mare Island Naval Shipyard
in Vallejo, California, which generates approximately
1,800 metric tons (2,000 tons) of spent ABM per year
from sandblasting submarines. The ABM recycled in this
demonstration project is derived from a slag from copper
smelting. The average bulk elemental composition of
this slag-derived abrasive is as follows:
Iron oxide as Fe2O323 percent
Silica as SiO245 percent
Alumina as AI2O37 percent
Calcium as CaO19 percent
Sodium as Na2Oless than 0.2 percent
Potassium as K2Oless than 0.1 percent
Magnesium as MgO6 percent
The abrasive has a total copper concentration of ap-
proximately 0.2 percent. In addition, the ABM becomes
contaminated with additional copper and other metals
during sandblasting. The types and concentrations of
metals depend on the types of paints and coatings being
removed. Typical metal concentrations in the spent ABM
recycled in this demonstration are shown below (mg/kg):
Copper3,120
Barium1,080
Zinc197
Vanadium118
Chromium90
Cobalt70
Nickel62
Lead33
Arsenic25
The spent ABM is considered hazardous in the state of
California because of its copper content but is not a
hazardous waste under Resource Conservation and
Recovery Act (RCRA) definitions. Consequently, this
recycling demonstration is being conducted under a
research and development variance issued by the Cali-
fornia Environmental Protection Agency.
Several waste types other than spent ABM also are
good candidates for recycling in this manner, particularly
wastes high in alumina (such as bottom or fly ash,
ceramics, and aluminum potliner) and/or iron (e.g., iron
mill scale and foundry waste). Silica and calcium also
are beneficial ingredients but usually are provided in
sufficient quantities by the quarry rock; therefore, they
are not as much in demand.
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5.2.2 Technology Description
The manufacture of Portland cement includes prepara-
tion, grinding, and exact proportional mixing of mineral
feedstocks, followed by heating and chemical process-
ing in the kiln. The raw materials necessary for cement
production include limestone (or another source of cal-
cium carbonate), silica, alumina, and iron oxides that
can be provided by clay, diatomaceous earth, inorganic
wastes, or other sources. The feedstocks are tested for
chemical and physical constituents and are mixed in
exact proportions to obtain the required properties of the
produced cement (see also Section 3.32).
In the more energy-saving kiln operations, the raw ma-
terials are fed through a "calciner." This process uses
residual heat from the kiln and adds additional heat to
begin the important calcining reaction orthe dissociation
of carbon dioxide from the calcium carbonate to form
calcium oxide or "quicklime." Figure 5-1 presents a sim-
plified diagram of the cement manufacturing process for
a kiln equipped with a precalciner. In older cement
manufacturing operations, the process is somewhat
simplified and limited to a single rotating kiln in which all
calcining and chemical reactions occur.
Regardless of the process, the material is passed
through the rotary kiln, which heats the mixture up to
1,480°C (2,700°F). At this temperature, the calcium ox-
ide reacts with silica and alumina to form calcium sili-
cates and aluminates, the primary components of
cement. The resulting products at the end of the kiln are
the hardened nodules known as clinker. These nodules
are allowed to cool, then finely ground and combined
with gypsum to create the final product, Portland cement (9).
During the demonstration tests, ABM was introduced as
approximately 1 percent of the total feedstock of the kiln,
and emissions monitoring was conducted to identify any
fluctuations in the air emissions concentrations from the
process. The final product was then subjected to physi-
cal and chemical analysis to determine the structural
integrity of the product and whether the metals are
bound in the crystalline structure of the cement. The
results of these tests showed that the ABM in these
proportions did not significantly increase the metals con-
tent of the clinker or lead to undesirable air emissions (9).
5.2.3 Recycling Benefits
The spent ABM at Mare Island Naval Shipyard is haz-
ardous in the state of California and, if no recycling and
reuse options were available, would have to be treated
by stabilization/solidification and disposed of in a haz-
ardous waste landfill. This technology makes beneficial
reuse of the ABM by incorporating it into Portland
cement, where resulting metal concentrations are low
and the metals are physically and chemically immobi-
lized in the cement chemical matrix. Tens of millions of
tons of Portland cement are produced in the United
States annually; therefore, there is a considerable de-
mand for iron- and aluminum-rich feedstock for cement
production.
For example, 11 cement manufacturers currently oper-
ate 20 Portland cement kilns in the state of California.
In 1989 alone, these operations reported the cumulative
production of more than 9.4 million metric tons (10.4
million tons) of cement clinker. Due to gaseous losses
during the calcining reaction, approximately 12.2 million
metric tons (13.5 million tons) of feedstock were
required to generate the cement. Therefore, if only one-
tenth of 1 percent of the required feedstock for each
of these kilns were dedicated to recycling of metal-
containing wastes, up to 12,200 metric tons (13,500
tons) of hazardous waste could be diverted from landfill
disposal in just the state of California each year (9).
5.2.4 Economic Characteristics
ABM use in cement manufacturing presents a positive
economic opportunity to both the waste generator and
the operator of the cement kiln. In this demonstration,
the total fee charged by the kiln operator has been about
$215 per metric ton ($195 per ton), and approximately
3,630 metric tons (4,000 tons) of spent ABM have been
recycled thus far. This fee covers a number of different
costs on the part of the kiln operator, including:
, To Off-Gas
Raw
Materials/ABM
I
Crushed
Limestone
Air Blowers
Finished
Portland
Cement
Figure 5-1. Abrasive blasting material and the cement-making process.
74
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The cost of transporting the spent ABM from the
generator's site in northern California to the cement
plant in southern California.
Costs incurred by the kiln operator for determining
feedstock proportions and for process modifications
to accommodate the waste materials.
The cost of sampling and analyzing both the clinker
and the air emissions from the stock to ensure that
elevated metals concentrations are not being gener-
ated in either medium.
Costs associated with regulatory compliance and any
necessary permits or variances.
The only significant cost element not included in the
$215 per metric ton ($195 per ton) figure is the cost of
ABM screening and debris disposal, which was borne
by the shipyard and probably amounted to less than $11
per metric ton ($10 per ton).
Up to the point of the initiation of this recycling project,
Mare Island Naval Shipyard was spending approxi-
mately $730 per metric ton ($660 per ton) to manage
this waste stream, including characterization, transpor-
tation, and disposal in a hazardous waste landfill (includ-
ing any treatment required by the landfill operator).
Therefore, the cost savings to the generator are obvious
and significant, and the kiln operator is being paid to
take a raw material for which the cement plant usually
has to pay.
5.2.5 Limitations
Recycling into Portland cement is applicable to only
certain types of wastes, based on chemical composition,
contaminant levels, and other criteria (10, 11):
Aluminum, iron, and sometimes silica are the primary
constituents that the kiln operator needs to purchase
to supplement the naturally occurring concentrations
in the quarry rock. Ores typically comprise 40 to 50
percent by weight of these constituents. Therefore,
waste materials should contain at least 20 percent or
more of these constituents to be attractive substitutes
for the ore materials.
Combustion to heat the raw materials and decompo-
sition reactions during formation of cement clinker
generate large volumes of off-gas, which must be
controlled and cleaned.
Elevated concentrations of volatiles such as sodium,
potassium, sulfur, chlorine, magnesium, and barium
are adverse to cement production and can lead to
problems such as premature oxidation or the produc-
tion of excess quantities of kiln dust or acidic volatiles
such as hydrochloric acid. Product quality specifica-
tions for inorganic feed to cement kilns are discussed
in Section 4.10. The plant chemist is the final author-
ity on whether a given waste material is compatible
with the mix design.
Recycling operations must not create a significant
risk due to elevated metals concentrations in the
clinker or off-gas. Total metals concentrations in the
recycled wastes should in general be less than 1 per-
cent, and the clinker must be tested to ensure that
metals present are not highly leachable. Waste with
highly toxic and volatile metals such as arsenic or
mercury should not be recycled in this manner.
Cognizant regulators should be contacted prior to pro-
ceeding with the recycling project. RCRA regulations
discourage the land application of recycled hazardous
materials (8). In most cases, special wastes or state-
regulated wastes may be recyclable, subject to state or
local restrictions or policies.
5.3 Recovering Lead Particulate From
Small-Arms Practice Ranges
Between the armed services, municipalities, and private
clubs, there are tens of thousands of outdoor small-arms
ranges, either active or abandoned, in the United States.
Small arms are pistols, rifles, and machine guns with
calibers of 15 mm (0.6 in.) or less. Because of the
inevitable buildup of bullets in the target and impact
berms, these ranges are potential source areas for met-
als contamination. These sites also are excellent candi-
dates for metals recovery and recycling because a major
portion of the bullets can be easily removed by separa-
tion technologies based on differences in size and/or
density (Section 3.33). The U.S. Naval Facilities Engi-
neering Services Center in Port Hueneme, together with
Battelle and the U.S. Bureau of Mines, has been study-
ing technologies for recycling lead and other metals from
small-arms impact berms. One recycling demonstration
has been completed at Naval Air Station Mayport, Flor-
ida, and others have been undertaken at Camp Pendle-
ton, California; Quantico, Virginia; and other bases.
5.3.1 Site and Waste Description
Impact berms of small arms ranges come in various
sizes. The height of the berm may vary from 1.5 m (5 ft)
to as high as 15 m (50 ft), and lengths may vary from
4.6 m to 1.609 km (15 ft to 1 mile). The "average"
volume of a berm, based on a survey (12), is about
3,100 yd3. The estimated "average" volume of contami-
nated berm soil is 627 m3 (820 yd3), assuming a 0.9-m
(3-ft) depth of contamination on the impact side of
the berm.
The average mass of lead accumulated in an impact
berm is about 3,190 kg (7,030 Ibs) per year and can
reach as high as 9,000 kg (19,850 Ibs) per year. The
average fraction of lead by volume in the contaminated
soil is about 1 to 2 percent, but localized pockets can
75
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contain up to 30 percent or more by volume. Most of the
lead is in the form of large pieces of bullets and can be
separated from the berm soil using physical separation
techniques such as screening. Bullet fragments typically
will be retained by a 3.5-mesh (5.66-mm [0.22-in.])
screen. For example, in a test run for lead-containing
soil at the Camp Pendleton site, a 3.5-mesh screen
retained 8.5 percent of the 1.36 metric tons (1.5 tons)
screened but collected 59.4 percent of the 143 kg (316
Ibs) of the total lead contaminant. Other metals such as
copper, zinc, tin, and antimony are also frequently pre-
sent due to their occurrence in lead alloys and copper
or brass jackets. Removing the pieces of bullets usually
will not render the soil clean, however, because a pro-
portion of the metal contamination also exists in the form
of small fragments and weathering products or lead ions
adsorbed onto the soil matrix. For example, in one study
the total elemental lead concentration in a berm soil was
23,000 ppm, even after sieving the soil with an 80-mesh
(0.117-mm [0.005-in.]) screen (12).
5.3.2 Technology Description
A flowchart for the technology is shown in Figure 5-2.
Simple screening, either dry or wet, usually can remove
80 to 90 percent or more of the bullet fragments present.
Dry screening is a simple operation and is effective on
most dry and coarse soils. Wet screening can separate
smaller bullet fragments and, therefore, remove a
greater fraction of the lead; also, wet screening is more
effective on wet or clayey soils and does not generate
dust. Wet screening is more complex, however, and
involves peripheral equipment such as mixing tanks,
pumps, thickeners, and possibly chemical additives.
Also, an additional waste stream of water that may be
contaminated with lead is generated and must be
dealt with.
Screening usually is effective at removing the majority
of the recyclable metal present; however, depending on
the site, the use of classification or gravity concentration
technology may be warranted if a significant fraction
of the metal has a fine particle size that is not recover-
able by screening, for example at rifle (as opposed to
pistol) ranges, where bullets tend to fragment more
upon impact. Because both the soil materials and the
bullet fragments can have a range of particle sizes, the
separation equipment should be selected based on
site-specific conditions. Table 5-1 lists some typical
separation processes and applicable particle-size
ranges. Note, however, that advanced separation tech-
nology is not fully demonstrated at small range sites and
can be very time-consuming and expensive to implement.
The lead-rich fractions from processing the impact berm
soil can be recycled to a primary or secondary lead
smelter. Primary smelters (e.g., Doe Run in Boss, Mis-
souri, or ASARCO in Helena, Montana) accept small
Excavate Contaminated
Soil From Impact Berm
Screen out Bullets and
Larger Bullet Fragments
(Wet or Dry)
>_.
*
Recycle
Bullet Fraction
Use Classification Technology To Remove
Smaller Bullet Fragments (Optional:
Technology Developed but Not Yet Fully
Demonstrated for This Application)
>_.
'
Recycle
Bullet Fraction
Stabilize Remaining
Soil To Immobilize
Metal Contaminants
Return Stabilized
Soil to the Impact
Berm for Reuse
Figure 5-2. Recovering bullet fragments and reusing berm soil
at small-arms practice ranges.
range soils with relatively low lead levels (several
percent by weight), whereas secondary lead smelters
prefer 40 percent lead or more.
Even after recovering the majority of the elemental lead
and other metals from the berm soil, there is a good
Table 5-1. Particle Size Range for Application of Separation
Techniques (13,14)
Separation Process
Particle Size Range
Screening
Dry screen
Wet screen
Hydrodynamic classifiers
Elutriator
Hydrocyclone
Mechanical classifier
Gravity concentrators
Jig
Spiral concentrator
Shaking table
Bartles-Mozley table
Froth flotation
>3,000 |
>150 |
>50 |im
5-1 50 urn
5-1 00 |im
>1 50 |im
75-3,000 |im
75-3,000 |im
5-1 00 urn
5-500 |im
76
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possibility that the berm soil will fail the TCLP test
and therefore require further treatment. If this is the
case, the soil can be treated using stabilization/solidifi-
cation (S/S) technology to immobilize the remaining
metals. The treated soil can then be returned to the berm
for reuse or be disposed of in accordance with applica-
ble regulations.
5.3.3 Recycling Benefits
This recycling process treats the impact berm as a
mineral deposit to be mined for lead and other metals.
As indicated above, a majority of the lead can be re-
moved easily by screening, resulting in a concentrate
that is acceptable for recycling to a primary or secondary
lead smelter. Removal of lead simultaneously greatly
reduces the lead content of the berm soil and the risk to
human or ecological receptors. After treatment by S/S
technology, the berm soil can be returned to the impact
berm for future use. The presence of S/S chemicals in
the treated berm soil acts as a "chemical buffer" to inhibit
any future leaching of lead or other metals that are
introduced into the berm during future use.
5.3.4 Economic Characteristics
Dry screening is relatively inexpensive and usually can
be performed for $11 to $22 per metric ton ($10 to $20
per ton). Wet screening and classification or gravity
concentration technology have higher capital and oper-
ating costs because of the auxiliary equipment and may
produce a secondary wastewater stream that requires
additional cost to treat. S/S treatment averages approxi-
mately $165 per metric ton ($150 per ton), depending
on the cost of the treatment chemicals and the tonnage
of soil to be stabilized (15). The lead-rich concentrate
can be sent to a recycler, who will charge a tippage fee
of between $130 to $440 per metric ton ($120 to $400
per ton) provided the concentrate contains at least 10
percent lead by weight. If the lead content is high
enough (typically over 70 percent) and concentrations
of other metallic impurities such as copper and zinc are
low enough (less than 5 to 10 percent), the recycler pays
up to $155 per metric ton ($140 per ton) to receive the
material. A list of secondary lead smelters in the United
States is provided in Table 5-2. Several primary lead
smelters also are operating in the United States and
Canada. Another significant cost element for recycling
the lead concentrate is shipping, which averages ap-
proximately $0.17 per metric ton per loaded kilometer
($0.25 per ton per loaded mile).
Therefore, the overall cost of this impact berm recycling
per remediation technology for the typical size impact
berm, assuming the stabilized berm soil can be reused
in the impact berm, averages $110 to $275 per metric
ton ($100 to $250 per ton), depending on the volume of
soil to be stabilized and whether the recycler pays or
Table 5-2. U.S. Secondary Lead Smelters as of November
1993 (adapted from Queneau and Troutman [16])
Smelter Location
Ponchatoula, LA
Boss, MO
Lyon Station, PA
Muncie, IN
Reading, PA
College Grove, TN
Eagan, MN
Tampa, FL
Columbus, GA
Frisco, TX
Los Angeles, CA
Rossville, TN
City of Industry, CA
Indianapolis, IN
Wallkill, NY
Troy, AL
Baton Rouge, LA
Forest City, MO
Total secondary lead
capacity
Year
Built
1987
1991
1964
1989
1972
1953
1948
1952
1964
1978
1981
1979
1950
1972
1972
1969
1960
1978
smelting
Approximate
Capacity
mtpya
8,000
65,000
54,000
70,000
65,000
10,000
55,000
18,000
22,000
55,000
90,000
9,000
110,000
110,000
70,000
110,000
70,000
27,000
1 ,023,000
Furnace
Type
BF-SRK
REV (paste)
SRK (metal)
REV-BF
REV-BF
REV-BF
BF
REV-BF
BF
BF
REV-BF
REV-BF
BF
REV
REV-BF
REV
REV
REV-BF
BF
BF = blast furnace; REV = reverberatory furnace; SRK = short
rotary kiln
aAs lead metal
charges for taking the lead bullets. This compares favor-
ably with disposal in a hazardous waste landfill.
5.3.5 Limitations
Bullet concentrate containing less than 10 percent lead
is not attractive to a secondary lead smelter but can
probably be recycled to a primary smelter, assuming
transportation costs are not excessive. Copper and zinc
are not desirable but should not cause the soil to be
unacceptable as long as the concentrations of these
metals are below the lead concentration. Soils with ex-
cessive sodium, potassium, sulfur, and per or chloride
can pose complications due to volatility in the blast
furnace and off-gassing. The secondary smelter should
be contacted prior to initiating the project to ensure that
the lead concentrate meets the smelter's acceptance
criteria.
In certain areas, the regulators may not permit the sta-
bilized soil to be returned to the impact berm or to be
disposed of on site. If this is the case and the impact
berm soil must be disposed of in a hazardous landfill,
then there may be little incentive to recover and recycle
77
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the lead concentrate prior to disposing of the waste in
the hazardous landfill.
5.4 Processing of Superfund Wastes in a
Secondary Lead Smelter
The Center for Hazardous Materials Research and an
industrial partner are testing methods to recover lead
from Superfund site wastes by processing in conven-
tional secondary lead smelters (Section 3.31).
5.4.1 Site and Waste Description
The demonstration has researched the potential for lead
recovery from a variety of waste matrices containing
less than 50 percent lead. The typically desired concen-
tration for feed to a secondary smelter is 50 percent. The
waste types tested in the program include battery cases
with 3 to 10 percent lead; lead drosses, residues, and
debris containing 30 to 40 percent lead; and lead paint
removal debris containing 1 percent lead (17).
5.4.2 Technology Description
As shown in Figure 5-3, a typical secondary lead smelter
upgrades lead-bearing feed in a two-step process. Most
of the feed to secondary lead smelters is from recycled
lead products, mainly spent lead-acid batteries. In 1992,
about 75 percent of U.S. lead production came from
recycle of old scrap (16).
In the conventional lead smelting process, batteries are
broken up and processed by gravity separation. Poly-
propylene case material often is recycled to make new
battery cases. Older hard rubber cases are used as fuel
in the reverberatory furnace. The lead plates and lead-
containing paste are processed in the smelter.
The first stage of pyrometallurgical treatment in the re-
verberatory furnace selectively reduces the feed mate-
rial to produce a relatively pure soft lead metal product
and a lead oxide slag containing about 60 to 70 percent
lead. The slag also contains battery alloy elements such
as antimony, arsenic, and tin, as well as impurities. Any
sulfur in the feed exits the reverberatory furnace in the
off-gas as sulfur dioxide (SO2). Solids in the off-gas are
removed by filtration and are returned to the furnace.
The lead-oxide-rich slag is reduced in the blast furnace
to produce hard-lead bullion and waste slag. Iron and
limestone are added to enhance the lead purification
process. Lead metal is cast for reuse. The slag, contain-
ing about 1 to 4 percent lead, is disposed of in a RCRA-
permitted landfill.
As shown in Figure 5-3, wastes containing 5 to 25
percent lead are added to the reverberatory furnace,
and wastes containing 10 to 40 percent lead are added
to the blast furnace. The lower grade wastes were pro-
portioned in with normal higher-grade feed materials.
Modifications were required to reduce the particle size
Experimental
Waste Feed
(5-25% Lead)
Fuel and
Oxygen
Soft Lead
Product
Experimental
Waste Feed -
(10-40% Lead)
Coke, Iron, Air,
and Oxygen
Secondary
Lead Scrap
Reverberatory
Furnace
V V
Lead-Rich
Oxide
Slag
Blast
Furnace
Hard Lead
Product
Afterburner
Furnace
Gases
Gas
Treatment
T
Emissions
CaS04
Sludge
Slag
(1 -4% Lead)
Figure 5-3. Processing lead wastes in a secondary smelter (18).
78
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of some wastes and to incorporate the wastes in with
the normal feed materials.
5.4.3 Recycling Benefits
This recycling process removes lead from wastes at the
Superfund site and returns the metal to commercial use.
Although some lead remains in the slag, the total quan-
tity of lead entering landfills is reduced. Increasing the
reuse of old scrap decreases the demand for lead ore,
thus reducing the environmental degradation due to
mining and smelting of primary lead ores.
5.4.4 Economic Characteristics
The test program demonstrated that the costs for treat-
ing materials containing 10 to 40 percent lead range
from $165 to $275 per metric ton ($150 to $250 per ton).
These costs are competitive with S/S treatment and
landfill disposal (19). Treatment of material with lower
lead concentration typically is not economical for a sec-
ondary smelter (17).
Transportation costs can be significant when large vol-
umes of material must be moved over long distances.
Table 5-2 indicates the locations, capacities, and proc-
essing systems of secondary lead smelters in the United
States.
5.4.5 Limitations
Wastes containing a low lead concentration and a high
proportion of silica reduce the pollution prevention bene-
fit due to increased slag production. Slag from the blast
furnace contains 1 to 4 percent lead. Wastes with little
or no combustible content and lead concentrations less
than about 10 percent will provide little or no net lead
recovery.
Wastes containing significant concentrations of chlo-
rides may increase the concentration of lead in the flue
dust due to formation of volatile PbCI4.
5.5 Treatment Train for Recovery of
Petroleum From Oily Sludge
A combination of decanting (Section 3.4) and thermal
desorption (Section 3.5) is being applied on a commer-
cial scale to recover petroleum products from oily sludge
wastes at refineries (20, 21). These techniques can be
applied to recovery of petroleum or solvents from wastes
at Superfund or RCRA Corrective Action sites.
5.5.1 Site and Waste Description
The oil recycling system is a permanently installed capi-
tal addition at a petroleum refinery. The material being
processed is listed RCRA waste with codes in the range
of K048 to K052. These are source-specific wastes from
petroleum refining, including dissolved air flotation
sludge, oil emulsion, heat exchanger cleaning sludge,
API separator sludge, and tank bottoms. The land
disposal restriction contaminants of concern in these
waste streams include benzene, toluene, ethylbenzene,
xylene, anthracene, benz(a)anthracene, benzo(a)pyrene,
£>/s(2-ethylhexyl)phthalate, naphthalene, phenanthrene,
pyrene, cresol, and phenol. The boiling points of the
organic constituents of the waste range from about 80°C
to390°C (175°Fto730°F).
5.5.2 Technology Description
The oil recovery process uses physical decanting (Sec-
tion 3.4) and thermal desorption (Section 3.5) in se-
quence to recover the petroleum. The listed K wastes
are collected in feed tanks, where diatomaceous earth
may be added if a bulking agent is needed. The mixed
oil, water, and solids stream is then passed through a
centrifuge.
Treatment in the centrifuge produces a mixed oil per
water stream and a sludge stream. The oil per water
stream is separated in an oil per water separator. The
oil returns to the refinery, and the water is treated for
discharge. The sludge stream is treated by drying and
thermal desorption to recover additional petroleum and
reduce the levels of organic contaminants in the treated
residue to below concentrations specified by the treat-
ment standards of the Land Disposal Restrictions.
Thermal treatment of the solids from the centrifuge oc-
curs in two stages. The solids are first processed in a
steam-heated screw dryer operating about 80°C to
110°C (175°F to 230°F) to remove water. The dried
solids are then processed in a hot oil-heated screw
thermal desorption unit to vaporize the organic contami-
nants. The operating temperature of the thermal desor-
ber is 425°C to 450°C (800°F to 840°F), and the
residence time is about 1 hr.
Off-gas from the dryer, desorber, and the enclosed con-
veyor systems connecting the process units is collected
and treated with a water scrubber followed by final
cleanup with granular activated carbon. The scrubber
water is routed to the oil per water separator to recover
the desorbed petroleum products.
5.5.3 Recycling Benefits
The recycling process treats about 2,360 to 3,150 wet
metric tons per month (2,600 to 3,470 wet tons per
month) of oily sludge waste to recover petroleum for
return to the refinery. The output from the thermal desor-
ber is about 90.8 metric tons (100 tons) of dry solid. The
organic content is reduced to meet the requirements of
the Land Disposal Restrictions. The dry solids are fur-
ther treated in a permitted onsite land farm to remove
the trace levels of organics remaining.
79
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5.5.4 Economic Characteristics
The process is estimated to save $40,000 per month
compared with reuse of the sludge for energy recovery,
or $100,000 per month compared with incineration.
5.5.5 Limitations
The desorbed organic is mainly high-boiling-point mate-
rial with a high viscosity. For the application described
in the case study, the high viscosity is not a problem.
Because the process operates at a refinery, the recov-
ered material is added to the refinery input stream. In
other applications, a local use for the heavy oil, such as
at an asphalt plant, would be needed or the recovered
material would have to be shipped to a refinery for
additional processing.
5.6 Solvent Recovery by Onsite
Distillation
Solvent distillation is a widely applied technology for
recovering a reusable product from wastes containing
significant amounts of solvent (Section 3.1). Although
this case study describes a process application, the
approach also could be applied to cleanup of organic
liquids in abandoned tanks or drums, or to liquids ob-
tained by nonaqueous phase liquid (NAPL) pumping
(Section 3.9), thermal desorption (Section 3.5), or sol-
vent extraction (Section 3.6).
5.6.1 Site and Waste Description
Two types of small, onsite distillation units were tested.
An atmospheric batch still was tested on spent methyl
ethyl ketone (MEK) at a site where MEK is being used
to clean the spray painting lines between colors. The
recycled solvent was reused for the same purpose, and
the residue was shipped off as hazardous waste. The
vacuum still was tested on spent methylene chloride
(MC) at a site where wires and cables are manufactured.
The MC is being used for cold (immersion) cleaning of
wires and cables to remove ink markings.
In appearance and color, the spent samples were vastly
different from the recycled and virgin samples. The re-
cycled samples were relatively similar in appearance
and color to the virgin samples, giving the first indication
that contamination had been reduced during recycling.
The specific gravity value of the recycled samples fell
between those of the spent and virgin samples. Absor-
bance measurements indicated sharp differences be-
tween the spent solvent and the recycled solvent. There
was little difference between absorbance measure-
ments on the recycled and virgin samples. Therefore,
appearance, color, specific gravity, and absorbance
could serve as quick indicators of solvent quality for
onsite operators.
Nonvolatile matter (contamination) accounted for nearly
7 percent of the spent MEK sample. This was reduced
to approximately 0.002 percent in the recycled sample.
The conductivity and acidity values of the recycled sam-
ples fell between those of the spent and virgin samples,
indicating some improvement in these parameters. The
water content increased from approximately 1.9 percent
in the spent sample to approximately 5.5 percent in the
recycled samples. This increase indicates that water
contamination present in the spent solvent transfers to
the distillate. However, the fact that the volume of the
distillate is roughly 30 percent lower than the total vol-
ume of the initial spent batch explains only a part of this
increase in water concentration. The remaining water
must have entered the recycled solvent during the recy-
cling process itself, possibly due to a slight leakage from
the water-cooled condenser that was worn out from
several months of use.
The purity of the recycled MEK sample showed a sub-
stantial improvement from the spent sample, increasing
from 78 percent to about 85 percent. The large decrease
in nonvolatile matter during recycling (discussed above)
accounts for most of this increase in purity. Of the 15
percent impurity in the recycled sample, 5 percent is
water, as discussed above. The remaining 10 percent
impurity is probably due to the co-distilling out of paint
thinner solvents (proprietary blends) present in the
spent solvent.
5.6.2 Technology Description
This case study evaluated two different technologies for
recovering and reusing waste solvent on site. The two
technologies tested were atmospheric batch distillation
and vacuum heat-pump distillation. In each technology
category, a specific unit offered by a specific manufac-
turer was tested. However, other variations of these
units (with varying capabilities) are available from sev-
eral vendors.
5.6.2.1 Atmospheric Batch Distillation
This is the simplest technology available for recovering
liquid spent solvents. Units that can distill as little as 19 L
(5 gal) or as much as 208 L (55 gal) per batch are
available. Some of these units can be modified to oper-
ate under vacuum for higher-boiling solvents (150°C
[SOOT] or higher). Contaminant components that have
lower boiling points than the solvent or that form an
azeotrope with the solvent cannot be separated (without
fractionation features) and may end up in the distillate.
The distillation residue, which often is a relatively small
fraction of the spent solvent, is then disposed of as
hazardous waste.
The unit has several safety features, including explo-
sion-proof design. A water flow switch per interlock en-
sures that the unit shuts off if water supply to the
80
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condenser is interrupted. The still has to be installed in
an area with explosion-proof electrical components.
Generally, solvent users already have a flammables
storage area where the still can be installed. Insurers
occasionally may require additional safety features,
such as explosion-proof roofing.
5.6.2.2 Continuous Vacuum Distillation
As shown in Figure 5-4, the configuration is similar to
that of a conventional vacuum distillation system except
that the pump, in addition to drawing a vacuum, func-
tions as a heat pump. No external heating or cooling is
applied. The heat pump generates a vacuum for distil-
lation and compresses vapors for condensation. The
model used in the testing is suitable for solvents with
boiling points up to 80°C (175°F). The spent solvent is
continuously sucked into the evaporator by a special
filling valve. The vacuum drawn generates vapors,
which are sucked into the heat pump, compressed, and
sent to the condenser. The still operating temperature
stabilizes automatically according to the specific solvent
and the ambient temperature. The condenser surrounds
the evaporator, allowing heat exchange between the
cool spent solvent and the warm condensing vapors.
The heat pump is a single-stage rotary vacuum pump,
modified to operate in a solvent atmosphere. The pump
oil is a type that is insoluble in solvent. Solvent vapor
entering the pump is kept free of solid and liquid impu-
rities by a vapor filter and condensate trap. An overflow
protection device guards against foaming in the evapo-
rator by releasing the vacuum. A continuous distillate is
produced and can be collected in a clean tank or drum.
The residue at the bottom of the still can be intermittently
drained for spent solvents containing less than 5 percent
solids. For spent solvents with a higher solids content,
continuous draining by means of a discharge pump may
be necessary.
5.6.3 Recycling Benefits
Described below is the waste reduction achieved at the
test site by the two distillation technologies at the re-
spective sites. Through recycling, large volumes of
spent solvent waste were reduced to small volumes of
distillation residue, which is disposed of as RCRA haz-
ardous waste. In the case of the vacuum unit, a very
small sidestream of used oil is generated through a
routine oil change on the vacuum pump. This oil is
combined with other waste oil generated on the site and
disposed of according to state regulations for used oil
disposal. According to the manufacturer, air emissions
due to the recycling process itself are largely avoidable,
provided that the operating procedures recommended
by the manufacturer are followed. This site has modified
the unit to process faster, however, and this results in
some air emissions (825 L/yr [218 gal/yr]) due to incom-
plete condensation of the vapors.
Both MEK and MC are hazardous chemicals listed on
the Toxics Release Inventory (TRI). These solvents are
Condensate
Trap
Spent
Solvent
Recovered
Solvent
Figure 5-4. Vacuum vaporizer for onsite solvent distillation.
Residue
81
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also on EPA's list of 17 chemicals targeted for 50 percent
reduction by 1995.
5.6.4 Economic Characteristics
The economic evaluation compares the costs of onsite
solvent recycling versus purchase of new solvent and
disposal of spent solvent.
The atmospheric distillation case study indicated that
annual solvent use decreased from 3,330 to 927 L
(880 to 245 gal), and that the volume of solvent residue
requiring disposal decreased from 3,400 to 980 L
(900 to 260 gal). Solvent recycling resulted in savings
of $10,011 per year. The purchase price of the atmos-
pheric batch unit is $12,995. A detailed calculation
based on worksheets provided in the Facility Pollution
Prevention Guide (22) indicated a payback period of
less than 2 years.
The vacuum distillation unit reduced solvent use from
11,350 to 950 L (3,000 to 250 gal) per year. The solvent
volume requiring disposal dropped from 11,350 to 515 L
(3,000 to 136 gal). The savings due to recycling
amounted to $18,283 per year. The purchase price of
the vacuum unit is $23,500 for the explosion-proof
model. The payback period for this unit also was less
than 2 years.
5.6.5 Limitations
Solvent distillation is a versatile technology that can be
used in a number of different applications. The main
limitation of this technology comes into effect if the
solvent to be recovered and the contaminants have
similar boiling characteristics (vapor pressures). When
the liquids have similar boiling characteristics, simple
distillation equipment will not allow a good separation.
The waste solvent would then have to be taken to an
offsite location, where facilities for fractional distillation
are available.
5.7 Thermal Desorption To Treat and
Reuse Oily Sand
A thermal desorption (Section 3.5) unit is processing
abrasive sand contaminated with diesel fuel to remove
the oily contaminant and allow reuse of the treated sand
as fill for new construction at the site (23).
5.7.1 Site and Waste Description
The waste matrix is an abrasive silica sand located at
the Los Angeles Port Authority San Pedro Harbor. The
sand is contaminated with marine diesel fuel that has
petroleum hydrocarbon levels as high as 30,000 mg/kg.
5.7.2 Technology Description
Sand is first screened to remove large debris, then fed
through a counterflow kiln where it is heated to 427°C
(800°F). Organics are vaporized and treated in a thermal
oxidizer. The hydrocarbons also act as supplemental
fuel in the oxidizer. A cyclone and baghouse filter system
collects the fine particulates. Collected particulate is
returned to the kiln for treatment. A lining of refractory
ceramic tiles has been provided in the unit's ducting and
cyclone to protect against the abrasive sand.
5.7.3 Recycling Benefits
The thermal desorption process will produce 272,340
metric tons (300,000 tons) of clean sand. The sand will
be used as fill during the construction of a new container
storage facility, thus avoiding the environmental impact
and cost of disposal. Residual petroleum hydrocarbon
levels following treatment average 71 mg/kg, as meas-
ured by EPA SW-846 method 8015M. The site require-
ment called for reducing hydrocarbons to 1,000 mg/kg
or below. To allow reuse at the site, the total polycyclic
aromatic hydrocarbon (PAH) concentration must be be-
low 1 mg/kg. The thermal desorption process is remov-
ing PAH compounds to nondetectable concentrations.
5.7.4 Economic Characteristics
Cleanup and reuse of the soil avoids the costs for pur-
chase and transport to the site of clean fill and the cost
for disposal of a large volume of sand. The ceramic
lining requires inspection and minor refurbishment for
each 90,780 metric tons (100,000 tons) of sand proc-
essed.
5.7.5 Limitations
Thermal treatment of the desorbed organic generates
some NOX. Small amounts of particulate also are re-
leased, even with the off-gas treatment filtration system.
5.8 Pumping To Recover Nonaqueous-
Phase Liquids
Free product can be recovered from in situ formations
by pumping (Section 3.9) followed by decanting (Section
3.4). Nine months of operation with an in situ pumping
system recovered more than 26,500 L (7,000 gal) of
virtually water-free, high-Btu-content product (24).
5.8.1 Site and Waste Description
The site was a former coal gasification plant located in
the borough of Stroudsburg, Pennsylvania. Coal tar,
produced as a byproduct of coal gasification, had been
discharged through trenches, wells, and the ground sur-
face at the site. The site investigation indicated that up
to 6.8 million L (1.8 million gal) of free coal tar had been
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distributed over about 3.2 hectares (8 acres). The coal
tar extended from the surface down to a silty sand
deposit but was not able to penetrate that layer. An
accumulation of up to 132,000 L (35,000 gal) of nearly
pure coal tar was held in a stratigraphic depression.
5.8.2 Technology Description
Coal tar was recovered using a well cluster 76 cm
(30 in.) in diameter installed at the deepest point of the
depression. The cluster consisted of four wells 15 cm
(6 in.) in diameter screened only in the coal tar layer and
one central well 10 cm (4 in.) in diameter screened over
its entire length.
Initially, coal tar was recovered by pumping from the four
wells at a slow rate. The center well was used for
monitoring. About 380 L (100 gal) per day of nearly pure
product was recovered at the start of pumping, but the
withdrawal rate declined rapidly overtime.
The system was modified, as shown in Figure 5-5, to
increase the product withdrawal rate. The center well
was modified by installing a plug at a depth between the
static ground-water and static coal tar levels. The central
well was then used to remove ground water. Ground
water was reinjected in a gravel-filled leaching field
located about 19.8 m (65 ft) upgradient. The resulting
reduction in ground-water pressure over the pumping
well caused an upwelling of the coal tar. Cyclic pumping
of the coal tarwas used, with pump operation controlled
by two conductivity sensors. One conductivity sensor
was located at the maximum upwelling level and the
other at the static (per pumping) coal tar level. Coal tar
pumping cycled on when the coal tar level reached the
upper conductivity sensor, and cycled off when pumping
had lowered the coal tar level back to the static level.
5.8.3 Recycling Benefits
Nine months of pumping collected about 26,500 L
(7,000 gal) of coal tar containing less than 1 percent
water, with a heating value of 40,700 kJ/kg (17,500
Btu/lb). The recovered coal tarwas used as supplemen-
tal fuel and potentially could have been used as a chemi-
cal feedstock.
5.8.4 Economic Characteristics
The coal tar recovery system was designed for unat-
tended operations and functioned well in that mode. The
major operating costs were electrical service for the
pumps and rental fees for pumps and storage tanks.
Maintenance requirements were minimal and involved
periodic replacement of product recovery pump impel-
lers and cracked polyvinyl chloride (PVC) piping. Waste
disposal was minimal due to the essentially closed-loop
operation. The operating and maintenance costs typi-
cally were $1,000 per month.
5.8.5 Limitations
The most significant problem encountered during pump-
ing operations was attack of well equipment by the
coal tar. The coal tar embrittled plastics such as PVC
piping, electrical insulation, and other equipment, caus-
ing cracking.
5.9 References
1. New England Waste Resources. 1991. Remedia-
tion saves Worcester site. New Eng. Waste Res.
(March), pp. 12-13.
2. Testa, S.M., and D.L. Patton. 1992. Add zinc and
lead to pavement recipe. Soils (May), pp. 22-35.
Recovered
Coal Tar
Leaching
Field
Static Ground-Water Level
Packer
Static Coal Tar Level
Depressed Water Level
Elevated Coal Tar Level
Figure 5-5. Coal tar recovery system (adapted from Villaume et al. [24]).
83
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3. Monroe, C.K. 1990. Laboratory investigation 88-
3/59-R-323, bituminous concrete glassphalt
route 37-86. New Jersey Department of Transpor-
tation, Bureau of Materials.
4. U.S. EPA. 1992. Potential reuse of petroleum-
contaminated soil: A directory of permitted recycling
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5. Blumenthal, M.H. 1993. Tires. In: Lund, H.F., ed.
The McGraw-Hill recycling handbook. New York,
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6. ARRA. 1992. 39 ARRA contractors save the tax-
payer $664,184,838.50 in 1991 (pressrelease). As-
phalt Recycling and Reclaiming Association, 3
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via environmentally processed asphalt. In: Hager,
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Society, pp. 461-485.
8. U.S. EPA. 1990. Current status of the definition of
solid waste as it pertains to secondary materials
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and J.C. Heath. 1992. California hazardous waste
minimization through alternative utilization of abra-
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CA (November).
10. Bouse, E.F., Jr., and J.W Kamas. 1988. Update on
waste as kiln fuel. Rock Products 91:43-47.
11. Bouse, E.F., Jr., and J.W. Kamas. 1988. Waste as
kiln fuel, part II. Rock Products 91:59-64.
12. Heath, J.C., L. Karr, V. Novstrup, B. Nelson, S.K.
Ong, P. Aggarwal, J. Means, S. Pomeroy, and S.
Clark. 1991. Environmental effects of small arms
ranges. NCEL Technical Note N-1836. Port Hue-
neme, CA: Naval Civil Engineering Laboratory.
13. Perry, R.H., and C.H. Chilton. 1984. Chemical
engineers' handbook, 6th ed. New York, NY:
McGraw-Hill.
14. Wills, B.A. 1985. Mineral processing technology,
3rd ed. New York, NY: Pergamon Press.
15. U.S. EPA. 1993. Technical resource document: So-
lidification/stabilization and its application to waste
materials. EPA/530/R-93/012. Cincinnati, OH.
16. Queneau, P.B., and A.L. Troutman. 1993. Waste
minimization charges up recycling of spent lead-
acid batteries. HazMat World 6(8):34-37.
17. Timm, S.A., and K. Elliot. 1993. Secondary lead
smelting doubles as recycling, site cleanup tool.
HazMat World 6(4):64, 66.
18. U.S. EPA. 1992. The Superfund innovative technol-
ogy evaluation program: Technology profiles,
5th ed. EPA/540/R-92/077. Washington, DC.
19. Paff, S.W, and B. Bosilovich. 1993. Remediation of
lead-contaminated Superfund sites using secon-
dary lead smelting, soil washing, and other tech-
nologies. In: Hager, J.P, B.J. Hansen, J.F. Pusateri,
W.P. Imrie, and V. Ramachandran, eds. Extraction
and processing for the treatment and minimization
of wastes. Warrendale, PA: The Minerals, Metals,
and Materials Society, pp. 181-200.
20. Home, B., and Z.A. Jan. 1994. Hazardous waste
recycling of MGP site by HT-6 high temperature
thermal distillation. Proceedings of Superfund XIV
Conference and Exhibition, Washington, DC (No-
vember 30 to December 2, 1993). Rockville, MD:
Hazardous Materials Control Resources Institute.
pp. 438-444.
21. Miller, B.H. 1993. Thermal desorption experience in
treating refinery wastes to BOAT standards. Incinera-
tion Conference Proceedings, Knoxville, TN (May).
22. U.S. EPA. 1992. Facility pollution prevention guide.
EPA/600/R-92/088. Cincinnati, OH.
23. Krukowski, J. 1994. Thermal desorber treats oily
sand for L.A. port authority. Poll. Eng. 26(4):71.
24. Villaume, J.F, PC. Lowe, and D.F. Unites. 1983.
Recovery of coal gasification wastes: An innovative
approach. Proceedings of the National Water Well
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Restoration and Ground-water Monitoring.
Worthington, OH: Water Well Journal Publishing
Company.
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