EPA/600/R-94/047
January 1994
FINAL REPORT
MERCURY USAGE AND ALTERNATIVES
IN THE ELECTRICAL AND ELECTRONICS INDUSTRIES
by
Bruce M. Sass, Mona A. Salem, and Lawrence A. Smith
Battelle
Columbus, Ohio 43201
Contract No. 68-CO-0003
Work Assignment No. 3-36
Project Officer
Paul Randall
Pollution Prevention Research Branch
Risk Reduction Engineering Laboratory
Cincinnati, Ohio 45268
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
s Printed on Recycled Paper
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NOTICE
This material has been funded wholly or in part by the U.S. Environmental Protection
Agency (EPA) under Contract No. 68-CO-0003 to Battelle. It has been subjected to the Agency's
peer and administrative review and approved for publication as an EPA document. Approval does
not signify that the contents necessarily reflect the views and policies of the EPA or Battelle; nor
does mention of trade names or commercial products constitute endorsement or recommendation
for use. This document is intended as advisory guidance only to the electrical and electronics
industries in developing approaches to pollution prevention. Compliance with environmental and
occupational safety and health laws is the responsibility of each individual business and is not the
focus of this document.
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FOREWORD
Today's rapidly developing and changing technologies and industrial products and
practices frequently carry with them the increased generation of materials that, if improperly dealt
with, can threaten both public health and the environment. The U.S. Environmental Protection
Agency (EPA) is charged by Congress with protecting the Nation's land, air, and water resources.
Under a mandate of national environmental laws, the agency strives to formulate and implement
actions leading to a compatible balance between human activities and the ability of natural systems
to support and nurture life. These laws direct EPA to perform research to define our environmental
problems, measure the impacts, and search for solutions.
The Risk Reduction Engineering Laboratory is responsible for planning, implementing, and
managing research, development, and demonstration programs to provide an authoritative,
defensible engineering basis in support of the policies, programs, and regulations of EPA with
respect to drinking water, wastewater, pesticides, toxic substances, solid and hazardous wastes.
Superfund-related activities, and pollution prevention. This publication is one of the products of
that research and provides a vital communication link between the researcher and the user
community.
Passage of the Pollution Prevention Act of 1990 marked a significant change in the U.S.
policies concerning the generation of hazardous and nonhazardous wastes. This bill implements the
national objective of pollution prevention by establishing a source reduction program at the EPA and
by assisting States in providing information and technical assistance regarding source reduction. In
support of the emphasis on pollution prevention, projects have been designed, with the coordina-
tion and cooperation of the Office of Solid Waste (OSW), to identify and evaluate source reduction
and recycling options for selected RCRA wastestreams. This report describes the current usage of
mercury as well as alternative technologies to reduce mercury use and disposal in the electronics
industry.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
in
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ABSTRACT
Many industries have already found alternatives for mercury or have greatly decreased mercury
use. However, the unique electromechanical and photoelectric properties of mercury and mercury
compounds have made replacement of mercury difficult in some applications. This study was initiated to
identify source reduction and recycling options for mercury in the electrical and electronics industries (SIC
36) and measurement and control instrument manufacture (SIC 382). The project identified trends in
pollution prevention for mercury use throughout the U.S. economy by a review of the sources and use of
mercury in the economy. Regulatory trends encouraging mercury pollution prevention were examined, and
current practices in the electrical and electronics industries were reviewed in detail to identify potential
source reduction and reuse options for mercury. Industrial and economic data suggest that the quantity of
mercury used in electrical and electronic control and switching devices is significant. Opportunities have
been identified to replace mercury-containing devices. For applications where mercury cannot be avoided,
recycling, mainly by vacuum retorting, is commercially available.
This report was submitted in partial fulfillment of Contract Number 68-CO-0003, Work
Assignment 3-36 under the sponsorship of the U.S. Environmental Protection Agency. This report covers a
period from August, 1992, to December, 1993, and the study was completed as of January 31, 1994.
IV
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CONTENTS
Notice • [|
Foreword '"
Abstract • iv.
Acknowledgments . . . vii
SECTION 1: Introduction 1
SECTION 2: Technical Approach • 3
Literature Search 3
Technical Associations • 4
Academia 4
Industry • 4
Battelle Staff • 5
Conferences 5
Site Visits • • 5
tr
SECTION 3: Mercury Economic Data and Regulation 6
Historical Uses 6
Recent Mercury Usage Patterns 6
Mercury Cell Chloralkali Process 9
Batteries 11
Switching Devices and Control Instruments 11
Electrical Lamps 11
Mercury-Cadmium-Telluride Semiconductors 12
Paints 12
Catalysts 12
State and Federal Regulations 12
Mercury Treatment Standards Under RCRA 13
State Regulations 14
SECTION 4: Source Reduction Alternatives for Mercury in the Electrical
and Electronics Industries 17
Electrical Lighting 17
Batteries 18
Switching Devices 1Q
Mercury Electronic Switches 19
Silent Switches 20
Reed Switches 20
Proximity Sensors and Switches 20
Control Instruments • 22
Thermostats 22
Mercury Switch Thermostats 24
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CONTENTS (Continued)
Thermostat Market Assessment 26
Non-Mercury Switch Thermostats 26
Mercury-Cadmium-Telluride Semiconductors 31
MCT Alternative Processes 32
SECTION 5: Recycling Alternatives for Mercury in the Electronics Industry 33
Industry Profile 33
Recycling Case Studies 33
SECTION 6: Conclusions 42
SECTION 7: References 43
APPENDIX: Questionnaire 47
TABLES
Number
1 Mercury consumption in the United States, by use ^ 7
2 U.S. mercury consumption in electronic products (metric tons), 1980-1992 9
3 Discards of mercury in products in the municipal solid wastestream, 1970 to 2000
(in short tons) 10
4 Typical composition range for K106 nonwastewater 10
5 Examples of dry cell-type batteries 11
6 Comparison between the mercury switch and its alternatives 21
7 Market drivers governing thermostat sales 27
8 Comparison between the mercury switch thermostat and its alternatives 27
FIGURES
1 U.S. mercury consumption in electronic products, 1980-1992 8
2 Typical packaged high-speed optical switch has electrical input ports and output
fibers 19
3 Typical bimetal shapes: (a) strip, (b) coil, (c) U-shape, (d) spiral 23
4 Typical diaphragm forms used for temperature sensing 23
5 Mercury tilt switch 24
6 Honeywell T87 thermostat 25
7 Mechanical bimetallic snap switch 28
8 Diagram of magnetic snap switch 29
9 Hot-wire vacuum switch 30
10 Typical fluorescent lamp recovery processing flowchart 34
11 Vacuum retort for mercury recovery 36
12 Reverse distribution scenarios for recycling of thermostats 38
VI
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ACKNOWLEDGMENTS
This report was prepared under the direction and coordination of Paul M. Randall of the
U.S. Environmental Protection Agency (EPA), Office of Research and Development, Risk Reduction
Engineering Laboratory, Pollution Prevention Branch, in Cincinnati, Ohio. Technical review was
provided by
Dr. David Allen
Professor, UCLA
Los Angeles, California
Mr. Rodney Everett
Marketing Manager, HVAC
General Electric Company
Morrison, Illinois
Mr. S. Garry Howell
U.S. Environmental Protection Agency
Risk Reduction Research Engineering Laboratory
Pollution Prevention Research Branch
Cincinnati, Ohio
Mr. Steve Keefe
Director, State Government Affairs
Honeywell, Inc.
Minneapolis, Minnesota
Mr. Richard Robinson
National Electrical Manufacturers Association
Washington, D.C.
Mr. Ronald J. Turner
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Physical/Chemical Separations Branch
Cincinnati, Ohio
VII
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SECTION 1
INTRODUCTION
This study was conducted as part of the U.S. Environmental Protection Agency's (EPA)
effort to develop pollution prevention options for RCRA wastestreams that have been difficult or
expensive to treat. Pollution prevention is the use of materials, processes, or practices that reduce
or eliminate the creation of pollutants or wastes. Pollution prevention should be considered the
first step in a hierarchy of options for reducing the generation of pollution. The next step in the
hierarchy is responsible recycling of any wastes that cannot be reduced or eliminated at the source.
Wastes that cannot be recycled should be treated in accordance with environmental standards.
Finally, any wastes that remain after treatment should be disposed of safely.
The objective of the study and this resulting report has been to identify source reduction
and recycling options for mercury in the electronics industry. To accomplish this objective, the
sources and use of mercury in the U.S. economy were reviewed and regulatory trends encouraging
mercury pollution prevention were examined to provide a background for a detailed review of the
electronics industry. Current practices in the electrical and electronics industries (SIC 36) and
measurement instrument and control instrument and control instrument manufacture (SIC 382)
were reviewed in detail to identify potential source reduction and reuse options for mercury.
Industrial and economic data suggest that the quantity of mercury used in electronic control and
switching devices is significant. Some opportunities were identified to replace mercury-containing
devices. It was found that recycling of mercury, mainly by vacuum retorting, is becoming
commercially available for some electronic components.
The steady decline in mercury consumption in the United States is well documented in
previous studies on mercury usage in batteries and fluorescent lamps; however, details of how the
electronics industry had reduced its need for mercury and what new technologies were involved
were not well known. The data collected identify possible approaches to reduce mercury use and
increase recycling in the subject industries.
Although mercury was known to be toxic for many centuries, the level of health hazard
has come to light only since the 1970s. Metallic mercury, its vapor, and many of its compounds
are protoplasmic poisons, which are toxic to all forms of life. Ingesting sufficient quantities, by
mouth, through the skin, or by inhalation, can cause severe neurological damage and fatality in
humans (Budavari, 1989). The alkyl organic compounds are the most toxic forms of mercury.
Alkyl mercury compounds, such as dimethylmercury, are used as intermediates in some chemical
processes. It is now known that some marine organisms can biologically methylate inorganic
mercury and concentrate it up to 3,000 times.
Mercury-containing RCRA wastes are difficult to treat reliably by conventional techniques
such as solidification/stabilization. This project was undertaken, with the coordination and cooper-
ation of the Office of Solid Waste, to help define pollution prevention technologies for mercury-
containing RCRA problem wastes.
Reduction of mercury disposal is also promoted by the 33/50 Program. The 33/50
Program is EPA's voluntary pollution prevention initiative to reduce national pollution releases and
off-site transfers of 17 toxic chemicals by 33% by the end of 1992 and by 50% by the end of
1995. EPA is asking companies to examine their own industrial processes to identify and
1
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implement cost-effective pollution prevention practices for these chemicals. Company participation
in the 33/50 Program is completely voluntary. The Program aims, through voluntary pollution
prevention activities, to reduce releases and off-site transfers of a targeted set of 17 chemicals
from a national total of 1.4 billion pounds in 1988 to 700 million pounds by 1995, a 50% overall
reduction. The Toxics Release Inventory (TRI) (established by federal law, the Emergency Planning
and Community Right-to-Know Act of 1986) will be used to track these reductions using 1988
data as a baseline. As required by the Pollution Prevention Act of 1990, TRI industrial reporting
requirements were to be expanded, beginning in calendar year 1991, to include information on
pollution prevention.
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SECTION 2
TECHNICAL APPROACH
The study supplemented literature data sources with industry and academic sources to
give insight into current uses for mercury and to identify and evaluate practical alternatives to
reduce mercury use.
LITERATURE SEARCH
Battelle performed an extensive literature search for information on the use of mercury
and its alternatives in the electronics industry. Technical journals were utilized to obtain the
necessary information. A literature search was performed at the Electronic Industries Association.
The U.S. Bureau of Mines database was searched for information quantifying the production and
consumption of mercury. The Electric Power Research Institute (EPRI) database, the Alternative
Treatment Technology Information Center (ATTIC), and the Pollution Prevention Information
Exchange System (PIES) also were employed.
The ATTIC network is maintained by the Technical Support Branch of EPA's Risk
Reduction Engineering Laboratory (RREL). This network has four online databases that can be
searched by external users.
• ATTIC Database. Contains abstracts and bibliographic citations to technical
reports, bulletins, and other publications produced by EPA, other federal and
state agencies, and industry dealing with technologies for treatment of
hazardous wastes. Performance and cost data, quality assurance information,
and a contact name and phone number are given for the technologies.
• Risk Reduction Engineering Laboratory (RREL) Treatability Database. Provides
information about contaminants — physicochemical properties, environmental
data, treatment technologies, contaminant concentration, media or matrix,
performance, and quality assurance.
• Technical Assistance Directory. Lists experts from government, universities,
and consulting firms who can provide guidance on technical issues or policy
questions.
• Calendar of Events. Extensive list of conferences, seminars, and workshops on
treatment of hazardous wastes. International as well as U.S. events are
covered.
Two other databases are available through a system operator. The Robert S. Kerr Environmental
Research Laboratory Soil Transport and Fate Database deals with the movement and fate of
contaminants in soil matrices. The Hazardous Waste Collection Database is a collection of reports,
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commercially published books, and directives and legislation on hazardous waste. There is no
charge for the ATTIC service. It is available via modem over standard telephone lines. The phone
number for the ATTIC modem contact is (903) 908-2138 (1200 or 2400 baud), and the modem
settings are no parity, 8 data bits, 1 stop bit, and full duplex. The system operator for ATTIC can
be reached at (908) 321-6677 or by fax at (908) 906-6990. The user's manual (U.S. EPA, ND)
also is available.
PIES is a bulletin board system that links to several databases and provides messaging
capabilities and forums on various topics related to pollution prevention. Through its link to the
United Nation's International Cleaner Production Information Clearinghouse, it provides a communi-
cation link with international users. PIES is part of the Pollution Prevention Information Center
(PPIC), which is supported by EPA's Office of Environmental Engineering and Technology Demon-
stration and Office of Pollution Prevention and Toxics. PIES contains information about current
events and recent publications relating to pollution prevention. Summaries of federal, state, and
corporate pollution prevention programs are provided. The two sections of the database cover
case studies and general publications and can be searched by keywords related to specific
contaminants, pollution prevention technologies, or industries. The phone number for dial-up
access is (703) 506-1025; qualified state and local officials can obtain a toll-free number by calling
PPIC at (703) 821-4800. Modem settings are 2400 baud, no parity, 8 data bits, 1 stop bit, and
full duplex. The system operator for PIES can be reached at (703) 821-4800.
TECHNICAL ASSOCIATIONS
Battelle contacted the following organizations to obtain data on electrical and electronics
industry practices:
American Electronics Institute (AEI)
Chemical Manufacturers Association (CMA)
American Institute of Pollution Prevention (AIPP)
Electronic Industries Association (EIA)
Electric Power Research Institute (EPRI)
Instrument Society of America (ISA)
National Electrical Manufacturers Association (NEMA)
Institute of Electrical and Electronics Engineers, Inc. (IEEE)
American Electronics Association (AEA).
ACADEMIA
Battelle contacted a number of universities to gather information on current research on
alternatives to mercury use. The Electrical Engineering Departments at the University of Illinois and
the University of Missouri were particularly responsive to the information request.
INDUSTRY
Battelle solicited many industry members through phone calls and questionnaires, shown
in the Appendix. The companies contacted were General Electric Company, AT&T, Digital Equip-
ment Corporation, Honeywell, Microswitch, CP Clare, Motorola, Thomson CSF, Lutron, Alph
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International, Leviton, Philips Lighting Company, Hamlen, and Sylvania. Battelle also contacted
waste exchanges in an effort to identify reuse options for mercury-bearing wastes.
BATTELLE STAFF
The Product Design and Engineering and the Electronic Systems Operations staff at
Battelle provided input on the operational characteristics of current mercury-containing electronic
devices and identified alternative technologies to mercury use.
CONFERENCES
Battelle staff attended the National Conference on Minimization and Recycling of
Industrial and Hazardous Waste 92, held in Arlington, Virginia, September 22-24, 1992, and the
First IEEE International Symposium on Electronics and the Environment, held in Arlington, Virginia,
May 10-12, 1993, to review current research into mercury-free or reduced-mercury-content
electrical, electronic, instrument, or control options.
SITE VISITS
Battelle staff visited Honeywell's thermostat manufacturing facilities in Minneapolis,
Minnesota. Honeywell, other thermostat manufacturers, and the National Electrical Manufacturers
Association have worked with the Minnesota Pollution Control Agency to initiate a recycling
program for all brands of mercury-switch thermostats. Battelle staff also visited Honeywell's
recycling pilot facility, also located in Minneapolis.
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SECTION 3
MERCURY ECONOMIC DATA AND REGULATION
Mercury is a shiny metal'and is the only common element that is liquid at room tempera-
ture. The chemical symbol, Hg, is derived from the Greek word hydrargyrum, meaning "liquid sil-
ver." Mercury's atomic number 80, and its atomic weight is 200.59. Mercury has a high density
(13.6g/cm3).
Mercury is an unreactive, corrosion-resistant metal which melts at -38.87°C (-37.97°F)
and boils at 356.58°C (673.84°F). When heated to near its boiling point, mercury oxidizes in air
to form mercuric oxide (HgO). Mercuric oxide decomposes at 500°C (930°F), releasing oxygen
and forming mercury metal.
Mercury is estimated to occur in concentrations of 0.010 to 0.3 mg/kg in typical soils
(Swartzburg et al., 1992 and 1993). By contrast, ore-grade materials average about 0.5% mercury
content.
The primary source of mercury is the sulfide ore, cinnabar. In a few cases, mercury
occurs as the principal ore product. Mercury is more commonly obtained as the by-product of pro-
cessing complex ores that contain mixed sulfides, oxides, and chloride minerals, which are usually
associated with base and precious metals, particularly gold. Native, or metallic, mercury, is found
in very small quantities in some ore sites.
Mercury can be recovered from its ores by relatively simple methods. Some early
methods for purification included leaching the ores in sodium sulfide and sodium hydroxide solu-
tions or in a sodium hypochlorite solution. Today, mercury is recovered from the sulfide ores or
secondary sources by a high-temperature retorting process. The ore is ground and heated to about
580°C (1080°F) in the presence of oxygen. The sulfide ore decomposes to form mercury vapor
and sulfur dioxide. The mercury vapor is condensed and washed with nitric acid. The cleaned
mercury is further purified by single or triple distillation, depending on the grade required.
HISTORICAL USES
Mercury was among the first metals to be identified and used as native metal. Archaeol-
ogists found mercury in an Egyptian tomb dating from 1500 BC. Mercury compounds also have
been in use since early times. The Egyptians and the Chinese are believed to have used cinnabar
as a red pigment. The Greeks used mercury as a medicine.
RECENT MERCURY USAGE PATTERNS
Mercury for domestic use in 1990 came from domestic miries, sales of surplus from
government stocks, imports, and waste recovery. Mercury was produced as the main product of
the McDermitt Mine and as a by-product of eight gold mines in Nevada, California, and Utah. The
McDermitt Mine has since been closed (U.S. Bureau of Mines, 1993). Market expectations indicate
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a continuing decline in mercury use and increased reliance on recycled mercury (Greenberg et'al.,
1993).
Smaller amounts of mercury are produced when secondary sources are reprocessed. In
1992, commercial secondary mercury reprocessors produced 176 metric tons of mercury (U.S.
Bureau of Mines, 1993). Common secondary mercury sources include spent batteries, mercury
vapor and fluorescent lamps, switches, dental amalgams, measuring devices, control instruments,
and laboratory and electrolytic refining wastes. The secondary processors typically use high-
temperature retorting to recover mercury from compounds and distillation to purify the contam-
inated liquid mercury metal.
The main use areas for mercury are chemical production, particularly chlorine/caustic
manufacture; electrical and electronic components; and instruments and related products. Recent
mercury use patterns are indicated by Table 1. As shown in the table, both the supply and the
demand for mercury have declined in response to regulatory pressures particularly in paints and
chemicals. More detail on the annual use in electrical and electronics applications is shown in
Figure 1 and in Table 2. Note that in Figure 1, data for Wiring Devices and Switches, Measuring and
Control Instruments, and Other Electrical and Electronic and Other Instruments (after 1987) have
been combined in bar chart format. This was done because there is some ambiguity regarding how
specific devices may have been placed in any one of these three Standard Industrial Classification
(SIC) categories. The combined data roughly represent mercury consumption in all electrical,
electronic, and instrument applications exclusive of electrical lighting and batteries. Overall, the data
in Table 2 and Figure 1 suggest that mercury usage has declined over the past decade, but aside
from batteries, usage in electrical and electronic devices has remained fairly constant.
TABLE 1. MERCURY CONSUMPTION IN THE UNITED STATES, BY USE
Use
Use in 1989
(WIT)""
Use in 1992
(MT)lal
Chemical and Allied Products
Mercury cell chloralkali process 379
Laboratory uses 18
Paint 192
Other chemical related uses 40
Electrical and Electronics
Electric lights 31
Devices and switches 141
Batteries 250
Instruments and Related Products
Measuring and control instruments. 87
Dental 39
Other 32
Total 1,212
209
18
0
18
55
69
16
52
37
148
621
(a) MT = metric ton (1 MT is equivalent to 1000 kg, 2,205 Ib, 1.102 short tons,
and 29 flasks).
Source: U.S. Bureau of Mines (1993).
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1100
1000 --
900 --
800 --
700 --
i
g
600 --
500
400 --
300 --
200
100
Other Electrical and
Electronic, other
Instruments
Measuring and
Control Instruments
I Wiring Devices and
Switches
Batteries
Electrical Lighting
CD
oo
CO
i
co
oo
CO
s
CO
in
oo
CO
CO
YEAR
CO
oo
oo
CO
CO
oo
CO
o
CO
CO
CO
CO
Figure 1. U.S. mercury consumption in electronic products, 1980-1992.
(Source: U.S. Bureau of Mines Annual Report.)
8
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TABLE 2. U.S. MERCURY CONSUMPTION IN ELECTRONIC PRODUCTS
(METRIC TONS), 1980-1992
Year
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
Electrical
Lighting
SIC
Code 3641
36
36
28
44
51
40
41
45
31
31
33
29
55
Wiring Devices
and Switches
3643
106
91
69
80
94
95
103
131
176
141
70
25
69
Batteries
3692
960
1016
858
806
1025
953
751
533
448
250
106
18
16
Measuring and
Control
Instruments
382
105
196
106
85
99
79
63
59
77
87
108
70
52
Other Electrical and
Electronic, Other
Instruments'3'
Other
_ (b)
_
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TABLE 3. DISCARDS"" OF MERCURY IN PRODUCTS IN THE MUNICIPAL
SOLID WASTESTREAM, 1970 TO 2000 (IN SHORT TONS*1)
Products
Household batteries
Electrical lighting components
Paint residues
Fever thermometers
Thermostats
Pigments
Dental uses
Special paper coating
Mercury light switches
Film pack batteries
Total Discards
1970
310.8
19.1
30.2
12.2
5.3
32.3
9.3
0.1
0.4
2.1
421.8
1980
429.5
24.3
26.7
25.7
7.0
23.0
7.1
1.2
0.4
2.6
547.5
1989
621.2
26.7
18.2
16.3
11.2
10.0
4.0
1.0
0.4
0.0
709.0
2000
98.5
40.9
0.5
16.8
10.3
1.5
2.3
0.0
1.9
0.0
172.7
(a) Discards before recovery.
(b) Weights in this report are converted to short tons of 2,000 pounds.
Source: U.S. EPA, 1992a, EPA/530-R-92-013.
A mercury-bearing sludge results from treatment of effluents from electrolytic processing
to generate chlorine gas and sodium hydroxide. This sludge is a Resource Conservation and
Recovery Act (RCRA)-listed waste with the waste code K106. A typical composition range for
K106 nonwastewater is shown in Table 4 (Dungan, 1992).
TABLE 4. TYPICAL COMPOSITION RANGE FOR
K106 NONWASTEWATER
Component
Composition
Mercury
Sulfur
Inorganic salts, mainly
sodium chloride
Water
1 to 12% (dry basis)
0.4 to 15% (dry basis)
3 to 15% (dry basis)
24 to 57%
Source: Dungan, 1992.
10
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Batteries
Batteries make up a significant but decreasing use of mercury. Mercury historically has
been used to coat the zinc anode (negative electrode) in nonrechargeable household batteries. A
few examples of these dry cell-type batteries are listed in Table 5.
Mercury is used to prevent the evolution of hydrogen gas from the battery, which results
from internal chemical reactions. Hydrogen may pressurize the cell and cause internal leaking or
explosion; blowout valves are now installed at the tips to minimize this possibility. In the alkaline-
manganese battery, zinc anodic material is added as a powder. In the past, 1 to 3% mercury was
mixed with the powdered zinc to form a mercury-zinc amalgam that inhibits zinc oxidation caused
by chemical reactions with other components in the battery. The proportion of mercury in the
amalgam decreases the rate of oxidation. Because alternatives to mercury have been identified by
the battery manufacturing industry, mercury use in this industry is declining.
Switching Devices and Control Instruments
Mercury is used in both high-voltage and low-voltage mercury-arc rectifiers, oscillators,
power control switches for motors, phanatrons, thyratrons, ignitrons, reed switches, silent switch-
es, thermostats, and cathode tubes in radios, radar, and telecommunications equipment. Current
rectifiers use electron tubes that consist of a metal, ceramic, or glass shell containing electrodes
that maintain and control current flow. Electron tubes are used to generate, rectify, amplify, or
convert electrical signals. Electron tubes are classified as vacuum and gas-filled tubes. In practice,
the distinction is not absolute as the degree of vacuum and the amount and type of gas may vary
widely. In general, gas-filled tubes permit higher currents than do vacuum tubes due to ionization
of mercury vapor in the tube.
Mercury also is used in many medical and industrial instruments to control or measure
reactions and equipment functions. This list includes mostly metallic mercury equipment, such as
thermometers, manometers, barometers, and other pressure-sensing devices, gauges, valves, seals,
and controls. The calomel (mercurous chloride) electrode commonly is used in conjunction with
glass electrodes to measure hydrogen ion (pH) and other ion activities.
Electrical Lamps
Mercury vapor is used in both low-pressure "fluorescent" lamps and high-pressure mercu-
ry lamps. Fluorescent lamps commonly are used for indoor lighting, whereas high-pressure mercury
TABLE 5. EXAMPLES OF DRY CELL-TYPE BATTERIES
Battery Type
Size/Configuration
Zinc-carbon
Alkaline-manganese dioxide
Mercuric oxide
Zinc-silver oxide
Carbon-zinc air
AAA, AA, C, D, 9V
AAA, AA, C, D, 9V
Button cells (hearing aids)
Button cells
Button cells (hearing aids
and pagers)
11
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lamps are used for street lighting, industrial work areas, aircraft hangers, and floodlighting. Other
mercury-vapor lamps are used for photographic purposes, including motion picture projection, and
for heat therapy.
Mercury-Cadmium-Telluride Semiconductors
Mercury-cadmium-telluride (MCT) is an important semiconducting material used for
infrared (IR) detection. Its photoconductive and photovoltaic properties rival those of more mature
lll-V semiconductors such as GaAs, GaP, and InSb. Other potential uses for MCT are in IR lasers
(Mahavadi et al., 1990) and /-ray detectors (Mullin et al., 1985). The bulk composition of the
MCT alloy is Hg^Cd^Te (0
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Mercury Treatment Standards Under RCRA
In the mid-1980s to early 1990, the EPA collected and evaluated process performance
data to identify Best Demonstrated Available Technologies (BDATs) for the treatment of RCRA-
listed wastes. These studies collected performance data for industrial applications of recycling for
a wide range of metals-contaminated wastes including mercury-bearing wastes. The EPA BOAT
process considered recycling as a treatment alternative for many nonwastewater streams and
identified recycling as the BOAT for some nonwastewater subcategories.
Recycling of mercury received increased momentum from the development of land ban
restrictions on mercury-containing wastes. Like other metals, mercury cannot be destroyed. Fur-
ther, EPA review of treatment data for the development of BOAT indicated that mercury is difficult
to reliably stabilize when present either at high concentrations or in elemental form. The analysis
of treatability data did, however, indicate that low concentrations of elemental mercury could be
stabilized to meet the leachability levels acceptable for land disposal. Applicable technologies for
the low-concentration mercury wastes were stabilization, amalgamation, or acid leaching followed
by sulfide precipitation.
Due to the concerns about the ability to stabilize wastes containing high levels of
mercury, the EPA examined a range of extraction and concentration techniques for recovering
mercury for reuse. The classical technologies for recovery of mercury from sludges are the thermal
processes of roasting and retorting. These processes sublimate mercury from metal-bearing wastes
and capture the mercury, which require further refining prior to reuse.
Aqueous-based mercury recovery methods also were considered. These included acid
leaching to form a solution that further concentrated by precipitation, amalgamation, ion exchange,
electrodialysis, or electrowinning. Mercury concentrated by precipitation, amalgamation, or ion
exchange will require further treatment such as roasting followed by triple vacuum distillation to
produce a refined product.
BOAT treatment standards for organomercury wastes require pretreatment to remove or
destroy the organic material(s). The organic constituents may interfere with the recovery or
treatment of mercury-bearing wastes.
Due to a lack of data on mercury waste treatment by acid leaching followed by solution
processing, the EPA established roasting and retorting as the BOAT for all mercury nonwastewaters
having total mercury concentrations above 260 mg/kg, except for radioactive mixed wastes. The
affected RCRA wastes are D009 (mercury characteristic), P065 (mercury fulminate), P092 (phenyl
mercury acetate), U151 (mercury), and K106 (wastewater treatment sludge from the mercury cell
process in chlorine production). The EPA also established incineration as a pretreatment step for
P065, P092, and D009 (organics) prior to retorting in its June 1, 1990 rule (June 1, 1990,
55 FR 22572 and 22626).
The regulated community has expressed concern over lack of capacity, particularly for
incineration of pretreatment of organomercury wastes. At least 17,260 metric tons of nonwaste-
water forms of D009, K106, P065, P092, and U151 were generated in 1988 (Labiosa, 1992). By
1994, the estimated capacity for commercial processing of mercury-containing wastes is about
1,140 metric tons per year. Also, the operating commercial retorting facilities for RCRA wastes are
permitted only for D009 wastes except for one facility that is permitted to retort K151 wastes.
New capacity is planned for retorting of K106 and D009 wastes. However, these
facilities will be located at chloralkali plants and will be used to treat only plant waste on site.
Operators of existing hazardous waste incinerators are reluctant to accept mercury-containing
wastes. There is concern that existing provisions of 40 CFR 268.42(a) will cause the incinerator
ashes and wastewater treatment sludges to be regulated as high-content mercury wastes that will
require retorting.
13
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Despite the short-term capacity shortage, the EPA concluded that maintaining retorting
and roasting as the BDATs for mercury waste is sound and consistent with the EPA methods for
establishing BDATs (Labiosa, 1992). Roasting and retorting are demonstrated for a variety of
mercury species such as sulfides in ore concentrates and mixed materials in sludge and for solid
wastes such as batteries and wastewater treatment sludge. Although the commercial capacity for
mercury roasting and retorting is limited, equipment is available for purchase. In addition, new
technologies for mercury recovery are being developed and source reduction efforts are reducing
mercury waste production {Dungan, 1992).
The BOAT technology code RMERC is defined as retorting or roasting in a thermal
processing unit capable of volatilizing mercury and subsequently condensing the volatilized mercury
for recovery. The retorting or roasting unit {or facility) must be subject to one or more of the
following:
• a National Emissions Standard for Hazardous Air Pollutants (NESHAP)
for mercury
• a Best Available Control Technology (BACT) or a Lowest Achievable
Emission Rate (LAER) standard for mercury imposed pursuant to a
Prevention of Significant Deterioration (PSD) permit
• a state permit that establishes emission limitations (within the meaning of
Section 302 of the Clean Air Act) for mercury.
All wastewater and nonwastewater residues derived from the RMERC process must comply with
the corresponding treatment standards for the applicable waste code, including consideration of
any applicable subcategories (e.g., high or low mercury subcategories).
State Regulations
Several states have enacted or are considering legislation to prohibit mercury disposal in
municipal waste, discourage or prohibit mercury use, or encourage mercury recycling.
California
Under California's hazardous waste regulations (Title 22, Hazardous Waste Control Law,
Health and Safety Code, Division 20), used fluorescent bulbs are considered hazardous because
their mercury content exceeds the state's Total Threshold Limit Concentration (TTLC) for mercury
(20 mg/kg). Although California does not have a "conditionally exempt small quantity generator"
classification, CaliforniaisJDepartment of Health Services (DHS) has instituted a policy (not a
regulation), that limits the disposal of fluorescent bulbs by'a generator to hb"rribfe'than 25" used
tubes and/or mercury vapor lamps "at any one time in one day. . ." (about 7 kg/day, or
210 kg/month). This policy was developed to allow small-quantity generators (e.g., individuals,
small businesses) to dispose of their bulbs in the Subtitle D wastestream, while still regulating
large-quantity generators (e.g., large companies, relamping companies) under the state's hazardous
waste program.
However, some larger generators apparently have misinterpreted the policy. Anecdotal
reports indicate that some companies are disposing of the first 25 bulbs a day in municipal solid
waste, with the rest going to recycling facilities, or are storing used bulbs and gradually disposing
of them 25 bulbs at a time in their municipal solid waste. Since such practices are not within the
intent of California's regulatory policy, the DHS currently is reviewing the policy to eliminate such
abuses (U.S. EPA, 1992b).
14
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Connecticut
A recent bill passed by the legislature in Connecticut, PA91-377, requires the Public
Works Commissioner to establish a pilot program for pollecting and recycling fluorescent bulbs at a
state facility. The bill also requires that a report be prepared, by January 1993, for the legislature's
Environment Committee that will address the feasibility and costs associated with such programs.
To date, the Public Works Department has initiated neither a pilot program nor a formal study (U.S.
EPA, 1992b).
Florida
Florida state law 93-207 section 55, "environmentally sound management of mercury-
containing devices and lamps," has been approved by the governor. The law prohibits incineration
or disposal to a landfill of mercury-containing devices after January 1, 1996. The prohibition may
be applied as early as July 1, 1994 on a local basis if recycling capacity is available. A mercury-
containing device is any electrical product, other than batteries or lamps, that is determined by the
Florida Department of Environmental Protection as proven to release mercury into the environment.
Incineration or landfill disposal of mercury-containing lamps is prohibited after July 1,
1994. Recycling rather than disposal in a permitted facility may be required as of July 1, 1994 on
a local basis if recycling capacity is available.
Michigan
Proposed legislation in Michigan (Senate Bill 583), if passed, would prohibit the sale of
any product that contains lead, mercury, or cadmium that was intentionally introduced into the
product unless the product or the product's packaging is labeled with the statement, "This product
contains heavy metals that may be hazardous to human health and the environment."
Minnesota
The Minnesota legislature has recently enacted a law (1992 Minnesota Law Chapter 560)
regulating the disposal of mercury-containing products. The new law limits sales and use of
mercury, and bans placing mercury and mercury-containing articles in solid waste or wastewater
streams. Sellers of mercury must obtain the buyer's written agreement to use the mercury only for
certain purposes and to abide by the disposal regulations. Buyers must certify that the mercury
will be used only for medical, dental, instructional, research, or manufacturing purposes.
Mercury-containing products (i.e., thermostats, thermometers, electric switches,
appliances, and medical or scientific instruments) must be clearly labeled as to their mercury
content and to the fact that their disposal is now regulated. When such items are removed from
use, the mercury must be reused, recycled, or otherwise managed so that it does not enter the
municipal solid waste stream or wastewater disposal system. Thermostat manufacturers must
provide incentives and sufficient information to ensure that thermostats being removed from
service are so reused, recycled, or otherwise managed. The act also includes limits on distribution
of thermometers and bans games and toys containing mercury.
In addition, the Minnesota Pollution Control Agency (MPCA) is charged with conducting a
study to propose waste management rules that address the disposal of mercury-containing light
bulbs (U.S. EPA, 1992b), See Section 5 for a discussion of MPCA's participation in a thermostat
recycling program.
New Jersey
Proposed legislation in New Jersey (Assembly Bill 2046), if passed, would limit develop-
ment of new solid waste incinerators and prohibit incineration or disposal in sanitary landfill of
15
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metal containers, chlorinated plastics, scrap iron, glass, plastic beverage containers, batteries, used
tires, scrapped corrugated cardboard, yard waste, vegetative waste, food waste, newsprint, office
paper, and any other material deemed reusable, compostable, or recyclable. The list of proscribed
items may be expanded to include any other material in the solid wastestream that is a source of
cadmium, lead, dioxin, mercury, chlorine, or halogens -for which removal would reduce the heavy
metal content of residual ash from combustion of solid waste.
New York
New York State's Energy, Resources, and Development Agency is working with Mercury
Refining (a processor of general mercury wastes near Albany) to increase their capacity for
handling and treating various mercury-containing wastes. The state is concerned in general with
reducing mercury wastes in municipal wastestreams; fluorescent bulbs are only one of several
products of concern.
Mercury Refining is one of a few companies in the United States that reclaims mercury
from various wastes. Their retorting process will be expanded to handle batteries and other
household waste products. The State of New York and Mercury Refining are investigating various
bulb-handling systems for the process (U.S. EPA, 1992b).
Vermont
In Vermont, a bill recently has been introduced to bar the disposal of fluorescent lamps,
motor oil, antifreeze, and organic solvents. The bill would require manufacturers to ensure that a
collection system is available and to publicize its existence (U.S. EPA, 1992b).
16
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SECTION 4
SOURCE REDUCTION ALTERNATIVES FOR MERCURY
IN THE ELECTRICAL AND ELECTRONICS INDUSTRIES
The industry sectors covered by this report are electrical and electronic device manufac-
ture (SIC 36) and measuring and control instrument manufacture (SIC 382). Source reduction
alternatives to mercury use are being sought and have been used in the electrical lighting, battery,
switching device, instrument, and thermostat manufacturing areas. These alternatives are
discussed in the following sections.
ELECTRICAL LIGHTING
In 1992, approximately 55 metric tons of mercury were consumed by the electrical
lighting industry. Mercury-containing lamps include fluorescent lamps and high-intensity discharge
(HID) lamps. Examples of HID lamps include mercury vapor, metal halide, and high-pressure sodi-
um lamps. Today, fluorescent lamps and HID fluorescent lamps are the second largest source of
mercury in municipal solid waste, as shown in Table 3 (U.S. EPA 1992a). By the year 2000, mer-
cury contamination resulting from the disposal of fluorescent lamps to municipal solid waste is pro-
jected to increase to 40.9 short tons. Although manufacturers are working to reduce the mercury
content of each lamp, increased fluorescent lamp usage is expected due to their energy efficiency.
The average life of an electrical fluorescent lamp is 4 years, whereas that of a HID lamp is less than
1 year. More than 550 million fluorescent lamps were used in 1992 (information obtained from
NEMA). The input of mercury to municipal solid waste from the primary source — household
batteries — is projected to decline from 621.2 short tons in 1989 to 98.5 short tons in 2000.
All fluorescent lamps contain mercury. Mercury acts as a multiphoton source in fluor-
escent lamps. The mercury content typically ranges from 20 to 50 mg per tube depending on the
size. Ultraviolet (UV) light is produced by mercury when it is bombarded by electrons produced by
current flowing through the tube. Phosphor powders coated on the inside glass tube convert the
UV light to visible light.
Major lighting companies such as General Electric, Sylvania, Philips, and Siemens have
expended serious efforts to identify alternatives to mercury as a photon source in lighting. The
U.S. Department of Energy (DOE) funded a multimillion dollar contract with Sylvania to find a
multiphoton phosphor to provide an alternative to mercury use as a photon source. The project
terminated last year without success.
Most of the alternatives tested have failed the performance tests. Cesium and cadmium
have good discharges but are not economical. They also are hazardous and thus offer no pollution
prevention advantage. The use of alternative phosphors would require changes to the design of
the lamp power supply. The new lamp design would require changing the ballast and fixture struc-
ture, which in turn would require the disposal of millions of ballasts and fixtures, thus contributing
to the solid and hazardous wastestreams.
The research to date shows that there is no economically feasible alternative to mercury
in fluorescent lighting. However, research is being done to find a way to reduce the amount of
17
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mercury used in electrical lighting (Meyer, 1992). Light bulbs produced today contain 60% less
mercury than those manufactured 10 years ago. Today a standard fluorescent lamp contains
0.05 mg/m3 mercury, approximately 0.02% of the total weight of the bulb.
A low-energy mercury vapor light bulb was developed by two companies in California.
This bulb has an operating life of 20,000 hours, or 20 times that of an incandescent bulb. The
mercury vapor is excited using a high-frequency radio wave to give off UV light, which then strikes
the phosphor coating on the inside of bulb walls to produce visible light.
Although reduction of mercury in lamps has reached practical limits, there is a growing
market for recycling the mercury, glass, and aluminum from fluorescent and mercury vapor lamps.
A standard fluorescent lamp contains up to 80% glass by weight. The end assemblies constitute
about 15% of the total tube weight. These end pieces are aluminum with a coated tungsten fila-
ment held in a glass mount. The filling gas is argon, or in the case of energy-conserving models,
argon and krypton. The inside surface of the tube is coated with a phosphor powder to produce
light. The powder is mostly calcium phosphate plus trace quantities of activators such as manga-
nese, antimony, chloride, fluoride, tin, yttrium, or titanium. The aptivators control the color of the
light.
Prior to 1988, cadmium was used to increase light output efficiency. Because cadmium-
containing lamps still exist in the inventories of suppliers, some mercury waste processors will not
accept any fluorescent lamps.
Fluorescent lamps can be processed to recover several valuable resources. The recovery
process typically involves crushing the tube and separating the metal end pieces from the glass.
Metal components such as the end caps often are sent to other recyclers for recovery. The tube
components are then roasted and retorted to recover mercury. The glass, phosphor, and mercury
may be treated together, or the glass may be separated and only the phosphor treated. The
resulting glass often is recycled. Mercury recovered by retorting is purified by distillation for reuse.
Processing typically costs 10 cents per foot of tube for standard tubes. The cost covers
shipping to the processing facility. High-pressure mercury vapor lamps and U-tube fluorescent
lamps or other lamps with ceramic bases require some hand disassembly. It typically costs about
50 cents per lamp to process these items (Watson, 1992).
Some states such as California and Minnesota have passed legislation restricting the
disposal of fluorescent lamps containing 40 to 50 mg of mercury per tube, depending on the size.
In California, more than 25 types of fluorescent lamps have been classified as hazardous waste. In
Minnesota, all lamps discarded from commercial sources are considered hazardous. Such legisla-
tion has caused several companies to start recovering mercury from spent lamps.
Other states are suggesting similar regulations. Currently, there are no federal regulations
for the disposal of fluorescent lamps. Used fluorescent lamps that show a toxic teachable charac-
teristic by the TCLP test are considered RCRA hazardous waste and are subject to RCRA Subtitle C
regulations.
BATTERIES
In 1992, approximately 16 metric tons of mercury were consumed in the United States
by the battery manufacture industry. In the past, mercury was added to alkaline-manganese and
zinc-carbon batteries to control gassing. U.S. manufacturers were successful in reducing the mer-
cury content to below 250 ppm (Balfour, 1992). In 1992 U.S. manufacturers started producing
mercury-free alkaline-manganese batteries. Most zinc-carbon batteries manufactured in the United
States no longer contain any mercury.
Batteries represent the largest current source of mercury in municipal solid waste, as
shown in Table 3 (U.S. EPA, 1992a). In 1989, household batteries accounted for 621.2 short tons
18
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of the mercury discarded in municipal solid waste. It is estimated that by the year 2000,
household batteries will be responsible for only 98.5 short tons of the mercury discarded in
municipal solid waste.
Beginning in 1992, several battery manufacturers began selling mercury-free alkaline
batteries. Other metals such as indium, gallium, and magnesium are used as substitutes for
mercury (U.S. Bureau of Mines, 1993). In addition, the use of mercuric oxide batteries, primarily
for hearing aids and pagers, is being replaced by zinc-air batteries. However, mercuric oxide
batteries will continue to be used for medical and military applications because, currently, there are
no acceptable substitutes (U.S. Bureau of Mines, 1993).
Many states, such as Minnesota, New Jersey, and Connecticut, have passed legislation
targeting the recovery of household batteries. As a result, battery collection and recycling pro-
grams have been implemented. Mercury recovery rates from household batteries are improving.
Currently, nearly 6% of the mercury in batteries is recovered.
SWITCHING DEVICES
Industrial and economic data suggest that the quantity of mercury used in electronic
control and switching devices is significant. Research shows that mercury is still used in the
devices described below.
Mercury Electronic Switches
Ignitrons, thyratrons, and trigger-tubes containing mercury are applied as an electronic
switch via grid control. The thyratron is adapted to control a moderate amount of power in an
on/off switching operation. This type of switch is used in communications and has been replaced
largely by solid-state alternatives. The communications industry currently is performing much
research in the fiber optic switch field. Optical switching technology is especially suited for appli-
cation in the communications industry. Much research is being done in this area, and new appli-
cations are still developing (Korotky, 1989; Hinton, 1992). Figure 2 illustrates an example of a
high-speed optical switch.
The transistor, •developed in 1947, has replaced most vacuum tubes and some gas-filled
tubes. Some tubes, however, have not been replaced by solid-state devices, although inroads are
RFandDC
Input
Silicon
V-Groova
Array
Lithium
Nlobato
Crystal
Cabtod
Slntfa Mod*
Housing
TI-Dtffusad
Wavaguld*
A*ymm*trte CNracUoiMl
Coptonar Couptor
StrlpHM
Figure 2. Typical packaged high-speed optical switch has electrical input ports and output fibers
(after Korotky, 1989).
19
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being made. Special-purpose transistors now are available to amplify signals in the microwave
region of frequencies. Applications requiring the ability to amplify high-power signals, however,
still require gas-filled tubes. Examples of such applications include microwave ovens, radar instal-
lations, X-ray machines, or mercury-arc rectifiers.
The few remaining applications of gas-filled tubes use mercury vapor tubes. Gas-filled
mercury tubes use a pool of mercury as the cold cathode pool. In the excitron type, a small arc is
continually maintained between the cathode and an auxiliary excitation anode. When the main
anode is positive, current is carried through the tube by transport of ionized mercury vapor. The
ignitron-type tube is similar, except that a spark is created during each positive cycle by a flash of
current passed between an ignitor electrode and the pool of mercury at the cathode. The mercury
vapor becomes ionized because of electron emissions caused by the spark, and an arc is estab-
lished between the cathode and anode.
Silent Switches
Silent switches using mercury are small tubes with electrical contacts at one end of the
tube. As the tube tilts, the mercury collects at the lower end, providing a conductive path to
complete the circuit. Mercury switches are available in voltage ratings up to 250 volts and current
ratings up to a maximum of 45 amps. This type of switch is used in numerous applications. For
example, in the electrical light switch, when the switch is tilted it makes the circuit and when it is
tilted back it breaks it. These switches also are used in such diverse applications as sump pump
float controls, automobile trunk lamps, and washing machine lift covers. Silent switches are
referred to as such because they prevent electrical noise from occurring. When the contact is
made the electrical flow is smooth.
There are several alternatives to mercury switches. One alternative is the micro switch;
this is a quick-acting snap switch that is actuated by a small travel distance of 1/16 inch or less. It
is used to shut off the power that drives a traveling mechanism when the traveling unit reaches a
predetermined point. It is operated either manually or mechanically. This switch is a good replace-
ment in case of safety switch application or when sudden power interruption is desired, but is not
suitable for all mercury switch applications. The primary disadvantage of all hard contact switches
is that they may fail due to contamination or corrosion in the contacts. Table 6 compares switches
that use mercury with alternative switch types.
Reed Switches
Reed switches are small circuit controls that are used in electronic devices. Their
electrical contacts are wetted with mercury to provide an instantaneous circuit when the switch is
closed and to permit instantaneous current interruption when the circuit is broken. Reed switches
eliminate the static produced in ordinary hard-contact-type switches. Reed switches are used in
applications where static would impair the operation of the electronic device.
Alternatives to reed switches are being found in solid-state and electro-optical switches
(Table 6). Reed switches are less expensive than solid-state alternatives and therefore still hold a
significant place in the market. However, the trend is for solid-state relays to steadily replace
mercury-wetted switches.
Proximity Sensors and Switches
An area of growth in the solid-state switch market is in proximity sensors and switches
(Engineering Materials and Design, 1989). One design uses an inductive coil to sense motion and
is used to detect prop shaft rotation and movement of conveyors. Sensing distances are as yet
20
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TABLE 6. COMPARISON BETWEEN THE MERCURY SWITCH AND ITS ALTERNATIVES
Type
Properties
Application
Hazardous
Content"1
Mercury switch Smooth contact, simple in design. On/off relay, thermostats,
versatile, inexpensive circuit control
Hard-contact Metal-to-metal contact, may be
switch open or sealed, versatile,
inexpensive
.On/off relay, general circuit.con-
trols, high or low voltage
Mercury
None
Arsenic,
gallium
Lithium
niobate
None
None
III-V semi-
conductor
materials
None
Solid-state switch More sophisticated design features. Communications, circuit control,
versatile electronic thermostats
Electro-optical Higher speed, expensive, multiple Communications
switch user
Inductive Senses metal targets, 10 to 20 mm Shaft rotation, conveyors
sensor detection
Capacitive Senses mass Conveyors
sensor
Photoelectric Senses nontransparent. Conveyors
sensor nonreflective materials, up to 50 m
away; high speed
Ultrasonic sensor Senses all objects, range of about Conveyors
0.5 m; high speed
(a) Indicates hazardous materials other than lead which may be used in solder.
fairly short, in the neighborhood of 10 to 20 mm. Work is in progress by major companies to
increase the sensing distance without significantly increasing switch size. Other problems are that
the coil detects only metal targets, temperature affects performance, and hysteresis may not allow
opening and closing at the same switch position.
An alternative design uses capacitive sensors to detect mass, so the target may be
metallic or nonmetallic targets. However, they may be affected adversely by electromagnetic and
radiofrequency interference, as well as by moisture and dust.
Photoelectric sensors also are undergoing expanding development. Typiqally, they use
either a consolidated light beam or a diffuse light source. Distances range from up to 20 to 50 m
by beam methods and 2 m by diffuse methods. Fiber optics can be added to detect objects as
small as 0.1 mm. Disadvantages are that target materials cannot be transparent or reflective.
Other problems are dust, moisture, and ambient light.
Ultrasonic sensors are gaining new ground because they overcome many problems
endemic to other kinds of sensors. Ultrasonic sensing does not depend on color, optical reflectivity,
shape, or material. Its sensitivity is not diminished by dust or moisture. However, audible noise
from machinery may cause misreads. Initially, ultrasonic sensors operated in the 20 to 30 kHz
band, but some now operate above 200 kHz. Their sensing range typically is around 0.5 m.
Still more specialized applications such as in telecommunications systems, may employ
electro-optical switches. Research in electro-optical switches, or photonics, in proceeding along two
21
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paths. Guided-wave photonics is the more highly developed of the two. It combines a large number
of signals into a single physical channel within optical fibers and other structures. Free-space pho-
tonics, the newer technology, processes signals in parallel using structures such as lenses, mirrors,
holograms, and arrays of optical logic gates or electro-optical integrated circuits (Hinton, 1992).
CONTROL INSTRUMENTS
Mercury is used in many instrumentation devices such as thermometers and mercury
manometers. Mercury manometers are considered reliable absolute-pressure gages, and they
provide the accuracy needed for a system analysis. A common application is in the steam jet air
ejectors used in process plants th'at have a supply of available steam. However, some mercury-free
units such as electronic vacuum gages are accurate, portable pressure-measuring instruments.
Formerly, gas regulators used mercury in a safety device that was designed to divert gas flow
outside of a building if the gas line pressure became too high. This device consisted of a U-shape
tube with mercury at the base of the tube. If the pressure were to exceed a safe value, a weighed
amount of mercury would be ejected through an outside vent, subsequently relieving gas pressure.
Modern gas regulators use a mechanical spring mechanism instead of mercury. Older homes may
still have gas regulators that contain mercury.
THERMOSTATS
Thermostats are temperature control devices that usually consist of a temperature-
sensing element, an electrical switch that activates heating and cooling equipment, and a mecha-
nism for adjusting nominal temperature. Thermostats are used to control temperature in large
building spaces, individual rooms, and appliances. Some types of thermostats use mercury in the
switch mechanism. Historically, mercury switches have proved to be quite reliable, accurate, long-
lived, and cost efficient. These are important qualities because thermostats control the dispensa-
tion of large amounts of electrical power and their operational efficiency has a large impact on fuel
consumption., Unoptimized thermostatic control can lead to many times more energy consumption
than necessary. Poor performance may be caused by one of several reasons. The main reason is
due to hysteresis in the temperature-sensing component, the electrical switch, or both. Hysteresis
may lead to large differentials, or swings, in room temperature.
Most residential and appliance thermostats are two-wire, or on/off, type electromechan-
ical devices. They contain a temperature-sensing element that mechanically moves an electrical
switch into a position where it can be energized. The temperature-sensing device most commonly
used in the United States is a bimetal element, which operates on the principle of differential
expansion of materials (Haines, 1961). It is composed of two thin layers of dissimilar metals,
which have different coefficients of thermal expansion, either welded or brazed together. Bimetals
can have many different shapes, such as a strip, coil, U-shape, and spiral, as shown in Figure 3.
When heated, the bimetal bends toward the metal which has the lower of the two rates of thermal
expansion, and when cooled it bends the opposite direction. Another type of temperature-sensing
element is a gas-filled diaphragm. Diaphragm sensors employ a gas- or liquid-filled form that
expands when heated and contracts when cooled (Figure 4). Normally, a refrigerant gas is used.
Replacement gases that are hon-ozone-depleting are being investigated. These types of sensors
are used in some air-conditioning equipment, but less in heating equipment. Diaphragm sensors are
more popular in Canada and Europe than in the United States. Their tolerances are not as great as,
for example, the mercury tilt switch, and they are relatively expensive because they require more
engineering design and calibration prior to sale.
22
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(c)
fcfc:
Figure 3. Typical bimetal shapes: (a) strip, (b) coil, (c) U-shape, (d) spiral.
Thermostat switches are mounted on a temperature-sensing element such that they can
be energized or de-energized at certain temperatures above a nominal setting, known as the control
point. The maximum difference between the minimum and maximum operating temperatures is the
temperature differential, which normally should be within 2°F of the control point for comfort
heating. Larger temperature differentials would be too noticeable, whereas smaller differentials
would cause a heating or cooling system to run more frequently than necessary and would be
uneconomical. Another problem that affects system performance is control hunt. If the heating or
cooling equipment is mismatched with the room size, temperature may vary widely about the
control point. Then, the problem of undershooting or overshooting the control point temperature
will result. Control hunt is associated with the heating or cooling system, whereas temperature
differential is particular to the thermostat itself.
To achieve better control of temperature differentials, manufacturers fit most all types of
thermostats with a component to achieve heat leveling (Haines, 1961). Heat leveling prevents
room overheating and is accomplished in either of two ways. One method, called heat anticipation,
uses a small resistance element to heat a bimetal sensor at the beginning of the call-for-heat cycle.
This method normally is applied to two-wire circuits, that are typical of single-stage switches. The
second method, called heat acceleration, is used in series with the common wire in three-wire
circuits. A heat accelerator does not cause the full effect of the artificial heat to be felt by the
thermostat until the room temperature has risen enough to break the low-temperature contact. The
effect of the heat accelerator is to accelerate shutdown of a burner after it has been running. In
either case, the resistance heat element is located below and close to the bimetal sensor, so that
artificial heat is quickly detected by the heat-sensing element.
In modern residential heating, electromechanical thermostats operate at 24 VAC.
However, line voltage may be used in older equipment, in electric strip heating, and in inductive
circuits such as the kind used to activate ventilation fans in attics and other semiclosed spaces.
Figure 4. Typical diaphragm forms used for temperature sensing (after Miles, 1965).
23
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Conversion from line voltage (nominally 115 VAC) to 24 VAC usually is accomplished by rewiring
the thermostat to a transformer supply. Newer, fully electronic thermostats operate at 5 VDC
Internally. Conversion from 24 VAC to 5 VDC usually is done within the thermostat assembly
Itself. Commercial heating and cooling equipment often uses fully electronic or pneumatic controls,
neither of which utilize mercury.
Mercury Switch Thermostats
The mercury tilt switch is a type of electrical switch that is commonly used in thermo-
stats. Mercury's unique natural properties make it extremely effective in mercury switch thermo-
stats, and it has been used in thermostats for more than 40 years. At room temperature mercury
has excellent conductivity and its high surface tension enables the mercury to move freely in a
cohesive mass within the switch assembly (Figure 5). Each bulb contains approximately 3 grams
of mercury. Normally, a mercury tilt switch is mounted to a piece of bimetal. The switch follows
the motion of the bimetal as it responds to changes in room temperature by rotating one way or
another. The switch thus controls a circuit by being moved to an opened or closed position. A
drop of mercury within a sealed glass or metallic tube moves under the force of gravity, where it
either makes or breaks an electrical circuit. Mercury's physical properties, particularly high density
and surface tension, are such that the mercury tilt switch performs exceptionally well. As the
mercury drop flows down the tube, its weight shifts past the center of the tube to accelerate the
tilting motion. Temperature differentials normally may be within 1 to 1.5°F for mercury switch
thermostats, which is optimal for most heating or cooling system. Thus, thermostats containing
mercury provide accurate and reliable temperature control. A schematic showing the components
of the popular Honeywell T87 thermostat is shown in Figure 6.
Mercury switch thermostats operate quietly and efficiently, do not require a power
source, and require little or no maintenance. The typical service life of a mercury thermostat is
20 to 40 years. They are sufficiently accurate for residential heating/cooling systems and, by
reducing temperature differentials, they provide highly economic temperature control. Mercury tilt
switches are sold by suppliers at $0.75 to $1.45 each. The primary markets for mercury thermo-
stats are single-stage heating/cooling systems and multistage systems such as heat pumps for resi-
dential applications. Single-stage systems, where a thermostat controls either heating or cooling,
normally require one mercury tilt switch per thermostat. Multistage heating and cooling systems,
such as are used in residential heat pumps, commonly require 2 to 6 mercury tilt switches per
Wira
Drop of
Mercury
Contacts
Figure 5. Mercury tilt switch.
24
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COVER
WIPER
RETAINER
OS
NUMBER
PINION
WIPER
&
HEATER BRACKET
JUMPERS
(UNDERNEATH
BASE)
Figure 6. Honeywell T87 thermostat. (Courtesy of
Honeywell, Inc., Minneapolis, Minnesota.)
25
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thermostat, depending on the type of system controlled. Residential heat pumps commonly use
2 mercury tilt switches for 3-stage operation (2 heating stages, 1 cooling stage).
Thermostat Market Assessment
Analysis of thermostat markets indicates that approximately 10 to 15 metric tons of
mercury are consumed annually in the United States for the production of thermostats, primarily for
home heating and cooling applications. Today, about 70 million thermostats are in residential use
in the United States1. It is estimated that 90% use mercury. Thermostat manufacturers estimate
that 2 to 3 million thermostats are brought out of service each year. Most of these thermostats are
replaced by the homeowner or contractor.
There are three main market drivers governing U.S. purchases of thermostats, which are
summarized in Table 7. One force driving the market is that existing equipment may require ser-
vice. This could occur for several reasons. If the heating system in a home is changed, and/or if
the thermostat is old, the homeowner may elect to replace the thermostat. Thermostats usually
are installed by the HVAC dealer who purchases the equipment through a wholesaler. A second
driver is that the homeowner may choose to modernize existing thermostats that are still in working
order. This decision may be motivated by interest in achieving fuel cost savings through purchase
of a more efficient thermostat, or for convenience features such as time-temperature programmabil-
ity. The third market driver is the purchase of new equipment for a new house or for remodeling
or additions in an existing house. Table 7 also shows estimated annual U.S. consumption of
thermostats.
Non-Mercury Switch Thermostats
Alternative devices to replace mercury tilt switches would have to address the issues of
cost, performance, fuel management, and environmental concerns. For example, if conventional
mercury switch thermostats were no longer available, they might be replaced with switches of
similar cost. Market research by thermostat manufacturers shows that consumers are driven pri-
marily by price and that the majority of consumers will select a replacement thermostat of equiva-
lent cost to the original, even if it offers substantially greater temperature differential swings. This
would increase the amount of unnecessary energy used to heat buildings. The net environmental
impact of energy consumption would have to be compared with the environmental impact of using
mercury. For example, burning fossil fuels releases air pollutants, including mercury. Borrowing
from studies on fluorescent lamps, which have shown that if they were replaced by incandescent
lamps (which would require more energy to produce the same amount of light), the increased
mercury entering the environment from burning coal would exceed the amount of mercury con-
tained in fluorescent lamps. Although no similar studies have been performed on mercury switch
thermostats, thermostats control a much larger amount of energy and have a much longer life than
fluorescent lamps, so the results could be even more pronounced. Most important, mercury switch
thermostats are relatively easy to recycle, so that the mercury never need enter the environment.
Section 5 of this report discusses current recycling efforts by Honeywell, the largest U.S. supplier
of mercury switch thermostats.
Several alternatives to mercury switches are available in the market. With the exception
of the fully electronic type, the switch technologies discussed below are mature, and each is used
today in particular niche applications. All thermostat switches, including the mercury tilt switch
1 Estimate based on consultations with thermostat manufacturers and on housing data from U.S. Bureau of
the Census, 1993.
26
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TABLE 7. MARKET DRIVERS GOVERNING THERMOSTAT SALES
Market Driver
Installer
End Use/Need
U.S. Annual
Consumption
Service call
Replace/modernize
thermostat
New equipment (includ-
ing new thermostat)
Dealer
Homeowner
Dealer
Maintenance of
existing equipment
Fuel/cost savings
Convenience features
Weather change""
New construction
Home remodeling
2 to 3 M""
1 to 2 Mlb)
2 to 3 M{c)
(a) First week of sustained cold or hot weather prompts purchases of new thermostats.
(b) Consumption rate based on survey of thermostat manufacturers.
(c) Based on new housing starts, which ranged from 1.2 to 1.8 million/yr in the period 1980 to
1992, with corrections for multiple thermostats per housing unit and replacements during
remodeling. (Housing data from U.S. Bureau of the Census, 1993.)
(Figure 5), have the basic function of transmitting movement of a thermal sensor to a control
component, which then will be regulated with respect to further changes in the thermal sensing
unit. The control component is a switch in an electrical circuit, an amplifier in an electronic circuit,
and a pressure-actuated valve in a pneumatic system. The electrical and electronic types are
summarized in Table 8 and discussed below.
TABLE 8. COMPARISON BETWEEN THE MERCURY SWITCH THERMOSTAT
AND ITS ALTERNATIVES
Switch Type
Mercury tilt switch
Mechanical snap-acting
switch
Open-contact magnetic
snap switch
Sealed-contact magnetic
snap switch
Electronic thermostat
Performance
Accurate, reliable, long
service life
Inexpensive, less reliable
Accurate, moderate
service life
Accurate, reliable, long
service life
Accurate, reliable.
unproven service life
Applications
Premium residential
heating/cooling
Electric strip heating,
ventilation (a)
Standard residential
heating/cooling
Premium residential
heating/cooling
Premium residential
heating/cooling
Thermostat
Price11"
$40-80
$10-30
$30-50
$60-100
$70-140(c)
(a) Primarily used on line-voltage equipment.
(b) Manufacturer's list price; includes thermostat unit, without clock or other options available in product line.
(c) Includes programmable features.
27
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Open-Contact Mechanical Snap Switch
The mechanical snap switch is perhaps the simplest example of how movement of the
bimetal can be transmitted to activate an electrical switch. The example shown in Figure 7 uses
the Otter principle (Miles, 1965). Thin bimetal of large surface area is held under tension due to a
crimp placed in the metal. This enables the center leg of the device to snap downward as the
bimetal expands due to increasing temperature and to snap upward as the temperature declines.
An electric circuit is completed by means of a stationary contact above the moving contact.
Mechanical snap switches press their contacts together and open them instantaneously (hence the
term "snap"), which ensures positive electrical contact with minimum contact wear, and eliminates
the need for a separate switch. The primary use of the open-contact snap switch for heating
purposes is in electric strip heating, which operates on line voltage rather than on 24 VAC. Fewer
than 5% of homes in the United States use electric strip heating, which is mainly confined to areas
in the Pacific Northwest and New England. In addition, three-season porches sometimes are
heated by electric strip units.
In addition to use in thermostats for home heating, mechanical snap switches can be
used as temperature regulators for electric irons, flame-failure devices, and overtemperature
controls for electric motors. Advantages of the mechanical snap switch over other types of
thermostats include low cost, light weight, design simplicity, and orientation independence. Disad-
vantages over other types include lower accuracy, higher temperature differential, shorter life under
continuous use, and failure if contacts become dirty.
Open-Contact Magnetic Snap Switch
The magnetic snap switch uses a thermal sensing element, such as a bimetal or gas-filled
diaphragm, to, act against an armature which is poised to bring a movable contact into position
with a fixed contact, as shown in Figure 8. As this occurs, the armature responds to the force of a
magnet and suddenly is drawn toward it. The purpose of the magnet is to prevent the contacts
from arcing and chattering as they are drawn closer together. The mechanism is designed such
that with the contacts engaged, the magnetic armature still is slightly separated from the magnet.
Then, as the temperature increases, a spring exerts a restoring force away from the magnet to the
point where the armature's attraction to the magnet is overcome, and the moving blade snaps
away from the fixed contact. Advantages of the open-contact magnetic snap switch over other
types of thermostats are low to moderate cost, good precision, and orientation independence.
Moving
Contact
Crimp
Figure 7. Mechanical bimetallic snap switch.
28
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Fixed
Contacts
\
cfl
Magnet
I
Restoring
Force
Armature
Thermal
Sensor
Pivot
Figure 8. Diagram of magnetic snap switch.
It is an alternative that already is used in many low-end, single-stage thermostats. A primary
disadvantage is that this type of switch is easily contaminated and subject to failure due to
common household items such as dust that prevent the contacts from closing properly. This type
of switch is not acceptable in premium equipment such as heat pumps.
Sealed Magnetic Snap Switches
The sealed magnetic snap switch is similar to the open-contact magnetic switch de-
scribed above, except that the contacts and armature assembly are sealed in a canister to prevent
contamination by dust. This type has been used in single-stage heating/cooling systems for more
than 20 years. It is considered a higher cost alternative to other types of switches. However,
recent cost increases in manufacturing all types of switches have brought these two types into
closer alignment. The sealed magnetic snap switch offers superior performance when used with a
U-shaped bimetal rather than a spiral bimetal. It has the advantages of not being position-sensitive
and of being resistant to chattering due to wall vibration. One problem is that the spacing required
to eliminate magnetic interference between switches is difficult to overcome in multistage thermo-
stats. The major problem in staging of snap switches is being able to stage the switches without
cascading through the small interstage differentials required.
Electronic Control Systems
Fully electronic thermostats use all solid-state electronic components for sensing tempera-
ture and for switching the heating or cooling circuit. The primary temperature sensing element is the
thermistor. The cost of employing electronic control systems in low-end and single-stage applica-
tions is high. However, electronic switch costs are declining and the mercury switch cost is steady,
causing the gap to narrow. Unlike mercury-containing thermostats, electronic thermostats require a
power source. Power can be provided directly from a 24-VAC source or from self-contained
29
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batteries. The primary advantage of electronic thermostats is programmability and the fuel cost
savings that can result by lowering room temperature automatically at preset times. Disadvantages
are higher cost and possible shorter lifetimes than electromechanical thermostats. However, it
remains to be seen if electronic thermostats produced today will operate with as few needs for
repairs as have been documented for electromechanical types. One disadvantage of the battery-
powered units is that the batteries require periodic changing and may create a different
environmental concernl Older electronic units had a tendency to be larger than any of the electro-
mechanical units. Because the thermostat market is price-sensitive at the different performance
levels, the penetration of electronics into the middle- and low-end portions of the markets has been
prevented. Current manufacturer's estimates for the single-stage electronic thermostats indicate a
retail price increase of 35% to 100% over the electromechanical units, with the cost differential for
multistage units in the 20% to 50% range.
Hot-WIre Vacuum Switch
The hot-wire vacuum switch is a secondary relay that operates on the principle that no
arc is formed in a vacuum when an electric circuit is made or broken. This allows even highly
inductive loads, such as motors, to be switched. Electrical loads up to 25 amps at line voltage can
be accommodated with appropriate surge suppression, with temperature differentials of only about
0.1 °C (Miles, 1965). A schematic of this switch is shown in Figure 9. The distance between the
Spring Lawai
Qap Between
Contacts
taMUtaHnff
Bobbin
Fulcrum
Reaiatanea
Wire
Main
o o
Hot-WIra
Terminate
Figure 9. Hot-wire vacuum switch.
30
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contacts may be very small, typically on the order of 0.001 inch. A resistance wire is wound
around an insulating bobbin and is rigidly fixed to its terminals. Tension on the resistance wire
forces the level to rotate about a fulcrum and compress a spring. If a small current is passed
through the wire it is. heated and expands, which allows the spring to force the level, thus closing
the gap and completing a circuit between the main terminals. The hot-wire vacuum switch is ideal
for applications where fine temperature control is needed. One unusual feature of this relay is that
after the primary control circuit is made, some time is taken before the resistance wire expands and
the load circuit is made. The time delay may be made up to 20 seconds. The primary control
device may be a hard contact bimetal switch. The hot-wire vacuum switch is used for temperature
control in some luxury automobiles.
MERCURY-CADMIUM-TELLURIDE SEMICONDUCTORS
The potential health and environmental hazards of preparing mercury-cadmium-telluride
(MCT) materials is well recognized in the electronics industry. Although method improvements
have led to a decrease in the amount of mercury used, difficulties involved in preparing MCT are
such that efficiency has not been a primary consideration. Production of MCT requires very con-
trolled conditions. Although MCT can be made in bulk, it is more successfully prepared using
epitaxial growth techniques (Liu et al., 1991). Bulk methods require high Hg partial pressure at the
maximum melting point, which is approximately 35 atm for x = 0.2 compositions, where x is a com-
position variable in the formula Hg.,.xCdxTe. Bulk methods of preparation also tend to yield crystals
that are nonuniform in x, due to segregation effects in the melt (Irvine and Mullin, 1981). For use
in IR detectors, x should vary by no more than 0.5% over 1 cm. High-temperature epitaxial tech-
niques also must maintain relatively high Hg partial pressures. A successful technique is to grow
epitaxial layers of MCT by transport of Hg and Te, followed by interdiffusion with a CdTe sub-
strate. This method, done at high temperatures (500-600°C), can result in a large interdiffusion
region and uncertain layer composition. Low-temperature growth «150°C) has been achieved by
vacuum deposition, but with low growth rates «0.6 //m/h).
More modern growth techniques use organometallic vapor-phase epitaxy (OMVPE) to
transport less stable Cd and Te alkyls to an interface at temperatures between 375 and 425°C.
The alkyls form an adduct that must be completely converted to a film by pyrolysis on the sub-
strate. For example, epitaxial layers of MCT can be grown onto CdTe substrates using dimethyl-
cadmium and diethyltelluride, diisopropyltelluride, methylallyltelluride, or ditertiarybutyltelluride in a
low vapor pressure of elemental mercury {Irvine and Mullin, 1981). High-purity hydrogen at
atmospheric pressure is used as the carrier gas. In addition, dimethylmercury has been used as the
Hg source for growing MCT (Bhat et al., 1990); however, its toxicity and atmospheric stability
have prompted the use of elemental mercury instead (Mullin et al., 1985). The growth rate of MCT
by OMVPE methods may be on the order of about 10 jt/m/h using Hg partial pressures below
0.1 atm. The minimum temperature for efficient pyrolysis increases with the flow velocity of the
carrier gas. The mercury pressure must be high enough so that it is not depleted in the growth
layer. However, the temperature of the reactor wall and the mercury also are critical, because if
the temperature is too high, the organometallic Cd/Te adduct could decompose prematurely,
coating the reactor and altering the concentration on the substrate (Tunnicliffe et al., 1984). To
achieve better compositional uniformity, multiple layers of epitaxial films are grown which are then
annealed at the growth temperature (Tunnicliffe et al., 1984).
Another difficulty in making MCT is that CdTe cannot be obtained in large wafers, unlike
GaAs or Si, so the size is incompatible with standard processing equipment. One approach to
circumvent this problem is to deposit a buffer layer of CdTe onto GaAs, then use OMVPE to create
31
-------
r
the MCT. However, this approach suffers from incorporation of Ga into the MCT, the severity of
which depends on the CdTe/GaAs crystal face used (Korenstein et al., 1990).
MCT Alternative Processes
Mercury usage in MCT manufacturing may be attained by developing more efficient
processes. In principle, still lower mercury vapor pressures could be used, providing they are above
the thermodynamic minimum pressures (fugacities) needed to satisfy the chemical reactions.
However, kinetically favored side reactions make it necessary to use higher vapor pressures than
thermodynamics would predict. At present, concern over mercury usage and, hence, possible
waste, are overshadowed by technical difficulties involved in producing MCT materials of accept-
able homogeneity. However, the widespread use of elemental mercury instead of the more
hazardous dimethylmercury can be seen as an.environmentally improved process.
Still other II-VI compounds can be prepared by OMVPE techniques, some of which may
have the necessary photoelectric properties, and which also may be produced with lower or no
mercury. Examples of other II-VI compounds are HgTe, CdTe, CdSe, ZnSe, ZnTe, ZnS,
ZnO, and CdS (Mullin et al., 1985).
32
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SECTION 5
RECYCLING ALTERNATIVES FOR MERCURY
IN THE ELECTRONICS INDUSTRY
Mercury is one of the most easily recovered metals. There exists a well-established and
growing infrastructure for recycling of mercury-contaminated wastes spurred by both economic and
regulatory pressures.
INDUSTRY PROFILE
There is a well-established infrastructure for recycling mercury-containing scrap and
waste materials. Industrial production of mercury from recycling of secondary sources amounted
to 176 metric tons in 1992 (U.S. Bureau of Mines, 1993).
Relatively few metal oxides convert easily to the metallic state in the presence of oxygen.
As a result, reduction reactions typically require the presence of both a reducing agent such as
carbon and elevated temperatures. Mercury is one of the few exceptions. Many mercury
compounds will convert to metal at atmospheric pressure and 300°C or lower temperature by
direct dissociation (Perry et al., 1963).
Mercury also is substantially more volatile than most metals with its boiling point of
357°C (Chase et al., 1985). As a result, mercury and mercury compounds can be separated by
roasting and retorting more easily than most metals, making it an ideal candidate for recycling from
a wide variety of waste materials. A U.S. Bureau of Mines study showed that thermal desorption
processes are potentially cost effective for recovery of mercury from a wide variety of electrical
manufacturing wastes (Dewing and Schluter, 1992).
RECYCLING CASE STUDIES
The following sections describe applications for recycling mercury-contaminated solid
wastes. The U.S. Bureau of Mines (1993), EPA reports (Labiosa, 1992), and literature sources
(Watson, 1992) discuss companies that recover mercury from scrap materials or RCRA wastes by
roasting/retorting or from liquid mercury wastes by distillation. The reported capabilities and feed
material requirements of these companies are summarized below.
Adrow Chemical Company
Wanaque, NJ
(201) 839-2372
Adrow Chemical Company is a redistiller of liquid metal mercury waste. The feed'
material requirement is a free-flowing liquid showing a shiny surface and no visible water, glass
fragments, or other solids. They prefer lots of >15 Ib and typically require a Vz-\b sample for
analysis prior to accepting liquid mercury for distillation.
33
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Advance Environmental Recycling Corporation
2591 Mitchell Avenue
Allentown, PA 18103
Jane E. Buzzard
(215) 797-7608, fax (215) 797-7696
Advance Environmental Recycling Corporation (AERC) indicates capabilities in retorting
and other techniques for mercury recycling. AERC provides separation and recycling of glass,
metal, and phosphor powder from fluorescent lamps. The overall process steps are illustrated in
Figure 10. In addition to processing fluorescent lamps, AERC refines mercury metal for reuse by
distillation.
A variety of processing capabilities are reported to be under development. Equipment
should be available in early 1993 to expand the range of material types covered. Capability will
include processing mercury metal-containing solids exhibiting the D009 characteristic, mercury
Spent Fluorescent Lamps
Crasher
Separator
Glass
Metal
Recycle
Phosphor Powder
Metallic Mercury
Recycle
Thermal Separation
"Roast & Retort"
1
Mercury
Phosphor
Powder
Triple
Distillation
I
Re-Use
Recycle
Figure 10. Typical fluorescent lamp recovery processing flowchart (AERC literature).
34
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vapor lamps, sodium vapor lamps, and alkaline and other mercury-containing batteries. Acceptable
D009 mercury-containing solids include thermometers, manometers, switches, spill collection kits,
amalgams, and mercury-contaminated debris. Soil and sludge materials exhibiting the D009
characteristic are not included.
AERC also indicates the capability to perform treatability tests on mercury-bearing
wastes. Inorganic mercury compounds exhibiting the D009 characteristic are accepted for treat-
ability testing. Quantities must be consistent with 40 CFR 261.4{e) and (f) and with Pennsylvania
Title 25 Section 26,1.4(c), "samples undergoing treatability studies." AERC plans to begin
accepting organpmercury compounds for processing under the treatability testing provisions after
January 1, 1993.
Bethlehem Apparatus Company
890 Front Street
Hellertown, PA 18055
Bruce Lawrence
(215) 838-7034
Bethlehem Apparatus Company retorts solids contaminated with mercury. The process
applied for mercury recovery is vacuum retorting as illustrated in Figure 11. The mercury-bearing
material is placed in a stainless steel chamber. Following closure of the chamber, a vacuum is
established and heat is applied. The materials in the chamber are subjected to temperatures in
excess of 700°C (1300°F). Mercury is vaporized 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.
The facility is permitted to process characteristic RCRA waste D009. An input concen-
tration of 5% mercury is preferred. Typical feed materials include metal and glass materials. Most
plastics can be processed, but polyvinyl chloride and other halogen-containing materials must be
minimized due to the potential for generation of corrosive or volatile materials during heating in the
retort. Volatile or reactive metals such as lithium, arsenic, and thallium are not allowed in the
process. Quartz containers can be processed but must be crushed.
Dirt, soils, and sludge-like material can be processed if the water content is below about
40%. 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 solid must contain less
than about 40% water.
Permitting requirements and process features are reported to place limits on the types of
material accepted. Mercury-bearing materials that cannot be accepted for recovery/recycling in-
clude, but are not limited to, mercuric chloride; organomercurials; mercury solutions; and all
mercury compounds other than mercuric oxide, sulfide, or iodide. Radioactive materials, explosives
or reactives, acids, and alkalis cannot be processed. Due to permitting requirements, wastes listed
with K, U, and P codes and organomercurials cannot be accepted (Lawrence, 1992).
GZA GeoEnvironmental/Hunter Mining Corporation
141 East Palm Lane
Phoenix, AZ 85004
Michael W. Chintis
(602) 495-1833
GZA has performed preliminary demonstration tests and treatability studies for a physical
gravimetric process to remove mercury from contaminated soils. The first step is material sizing to
prepare the feed. The material entering the system must have a uniform size to allow the varying
35
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Mercury Vfepor*
L
Vacuum Retort
Heating Chamber
Water Chilled
Condenser
Condensed Mercury
Particle
. j_ ^| hiwi v
I RIter/Water Trap
Waste I vacuum Pump
Water
Mercury
Vapor
Absorption
Exhaust
to Room
Chlorine and Acid
Vapor Absorption
«—o
Odor Absorption
Exhaust
Vacuum Pump
Single
Distillation
1
Triple
Distillation
1
Triple
Distilled
Mercury
Customers
Charcoal Absorption
of Mercury from
Waste Water
To
Wastewater
Treatment
Figure 11. Vacuum retort for mercury recovery (adapted from Lawrence, 1992).
36
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specific gravities of the components to be efficiently separated by gravimetric methods. The
contaminated soil is washed and screened to produce the uniform matrix required by the separation
equipment. The washing and screening operations are reported to separate soil that is not
contaminated with mercury and to condition the feed material.
The washed and screen feed enters a gravimetric separation system consisting of two
vessels operated in series. Each vessel consists of dual rotating bowls contained in a housing. The
inner walls of the bowls are rubber or plastic spirals designed to capture the dense elemental
mercury. The feed slurry is fed to the center of the bottom bowl. The heavier elemental mercury
and insoluble mercury salts are caught in the lower riffles of the bowl. The lighter components of
the soil waste overflow the top of the bowl. The heavier material containing mercury, mercury
salts, and black sand is discharged from the bottom of the bowl. The elemental mercury is
siphoned off, and the remaining material is passed to the second stage for further separation.
The process produces four effluent streams. Cleaned soil is produced both from the
initial washing and screening and from overflow of the rotating bowls. The typical soil mercury
concentration is reported to be 11 ppm after treatment. Elemental mercury is recovered from the
gravimetric separator. Heavy sands containing small particles of mercury metal plus mercuric
oxides in a magnetite matrix are recovered from the gravimetric separator. This material can be
retorted for mercury recovery. Process wastewater results from the washing and separation steps.
The wastewater mercury content is reported to be nondetectable (Chintis, 1992).
Hazen Research, Inc.
4601 Indiana Street
Golden, CO 80403
Barry J. Hansen
(303) 279-4501
The process, developed jointly by Hazen Research, Inc., and the Chlorine Institute, Inc.,
thermally treats mercury-containing wastes to produce a treated residue, elemental mercury for
recycle, and a cleaned off-gas. The technology is owned by the Chlorine Institute, which has
applied for a patent.
The process consists of a thermal processor, afterburner, off-gas handling system, and a
process water treatment system. The thermal processor configuration depends on the physical
characteristics of the waste feed. Feed usually is introduced through a sealed screw or ram feeder.
A stationary hearth or a rotary furnace may be used depending on the nature of the waste feed.
Conditions inside the thermal processor (temperature, atmosphere, and residence time) are con-
trolled carefu|ly to achieve the desired off-gas composition and residue characteristics. An after-
burner ensures complete oxidation of the off-gas products, including mercury compounds and any
residual organics. Solid residue from the thermal processor is reported to be suitable for disposal as
a nonhazardous waste.
The off-gas processing system is designed for compliance with air emission regulations
and is determined by the characteristics of the particular waste. Metallic mercury is recovered
through a series of condensation or scrubbing steps. Any acid gases (HCI, SO2) and particulates
are also removed.
Water containing particulates and soluble mercury is processed in a treatment system.
Residues from the process water treatment system are recycled to the thermal processor. Process
water is recycled to the off-gas handling system or discharged.
Honeywell Inc.
Honeywell Plaza
P.O. Box 524
Minneapolis, MM 55440
37
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Honeywell is working to develop a nationwide recycling program for mercury switch
thermostats. For the last few years, Honeywell, with the support of other thermostat manufac-
turers and the National Electrical Manufacturers Association (NEMA), has been working closely
with the Minnesota Pollution Control Agency (MPCA) to initiate a pilot recycling program in
Minnesota for all brands of mercury switch thermostats. The pilot recycling program, modeled
after a successful program under which Honeywell handles thermostats returned under warranty,
will begin in January, 1994. During the pilot phase, Honeywell will ship mercury switches from
thermostats received through its recycling program network to the Bethlehem Apparatus recycling
facility. Honeywell's intent is to expand this program nationally. However, this can be done only if
an extensive number of approvals are received from the U.S. Environmental Protection Agency
(EPA) and other federal, state, and local agencies. These regulatory requirement pose a substantial
obstacle to establishing a nationwide recycling program.
Because mercury-containing thermostats present no environmental hazard while in opera-
tion, and because of their very large installed base and long service life, Honeywell believes a focus
on preventing these devices from entering the wastestream will be a highly effective approach.
The recycling strategy of reverse distribution is illustrated in Figure 12. One mechanism of reverse
distribution is the heating, ventilating, and air conditioning industry itself, which has the infra-
structure with the potential to recycle a large percentage of these thermostats. Return of used
thermostats by contractors could be encouraged by business incentives. Contractors already must
return broken controls under warranty to Honeywell to receive credit for replacements. This
reverse distribution process could also be used for returning out-of-warranty thermostats. A
second mechanism being considered is homeowner initiative to return out-of-service thermostats to
Honeywell. Honeywell believes this approach has merit based on their experience of receiving
frequent telephone inquiries from consumers relating to thermostat disposal. Methods of packaging
and returning unneeded thermostats by consumers are now being explored. Honeywell is currently
Contractor
Business
Wholesaler
Honeywell
Detl'ilshein
Apparatus
Figure 12. Reverse distribution scenarios fpr recycling of thermostats.
38
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planning to work primarily through county household hazardous waste collection programs for the
Minnesota pilot program.
Innochem Engineering, Ltd.
#850-1441 Creekside Drive
Vancouver, BC
Canada V6J4V3
Michael Rockandel
(604) 736-3381
Electrolytic mercury cell chlorine producers use sulfide precipitation to remove mercury
from wastewaters prior to discharge. The sulfide treatment process generates a sludge designated
as K106-listed RCRA hazardous waste. The composition of K106 wastewater treatment sludge
can vary substantially depending on the design and operation of the chloralkali plant and the quality
of the sodium chloride feed. The K106 waste can be contaminated with soil, carbon filter back-
flush material, and brine. Mercury occurs mainly as mercuric sulfide. Mercuric and mercurous
chloride, elemental mercury, and species adsorbed on clay and activated carbon particles often are
present. The mercury content varies from below 1 % up to 20% with typical values in the 1 to
5% range.
The presence of impurities, particularly chloride salts, can cause difficulties with retorting.
Also, retorting of materials with less than about 5% mercury is inefficient, (nnochem has described
pilot testing of a hydrometallurgical process for pretreatrhent of K106 wastes to separate the
mercury from impurities. The process uses a two-stage leach to remove mercury from the sludge.
The resulting solution is then contacted with an iron surface to cement out mercury and dissolve
iron. The cementation reaction produces a soft mercury/iron amalgam product that is reported to
contain about 40 to 50% mercury. The rest of the product is essentially iron and its alloying
agents. The mercury/iron amalgam is then refined by standard thermal treatment for mercury
recovery (Rockandel, 1992).
Mercury Recovery Services
f 2021 South Myrtle
Monrovia, CA 91016
Bob Roberts
(818) 303-2053, fax (818) 358-2703
Mercury Recovery Services reclaims mercury from fluorescent tubes, mercury vapor
lamps, high-pressure sodium lamps, and metal halide lamps.
Mercury Refining Company, Inc.
1218 Central Avenue
Albany, NY 12205
Alan Winds
(518)459-0820
Mercury Refining Company (MERECO) operates indirectly fired retorts to recover mercury.
Mercury-bearing materials are heated to about 540 to 815°C (1,000 to 1,500°F) to vaporize
mercury. The mercury typically is expected to vaporize at temperatures above 350°C (670°F),
The collected mercury vapors may be further purified by distillation for sale as high-purity mercury
(Hart, 1992). The company processes mercury-containing products (mercury-wetted relays.
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mercury switches, fluorescent lamps, dental amalgams, batteries, etc.), liquid mercury materials,
and contaminated mercury materials (U151 and D009).
Mercury Technologies International
30677 Huntwood Avenue
Hayward, CA 94544
Paul Abernathy
(510) 429-1129, fax (510) 499-1498
Mercury Technologies will accept only fluorescent lamps for reprocessing. The plant
opened in April 1991 and is currently processing about 250,000 lamps per month, charging $0.34
per 4-foot tube. Glass and aluminum end caps from the structure are recycled. The fluorescent
powder removed in processing is thermally treated to recover mercury.
NSSI/Sources and Services
P.O. Box 34042
Houston, TX 77234
(713) 641-0391, fax (713) 641-6153
NSSI is reported to hold a RCRA Part B permit allowing distillation of mercury-containing
radioactive materials to separate the hazardous and radioactive materials and allow recycling of the
mercury.
Pittsburgh Mineral and Environmental Technology
700 Fifth Avenue
New Brighton, PA 15066-1837
William F. Sutton
(412) 843-5000, fax (412) 843-5353
Pittsburgh Mineral and Environmental Technology (PMET) owns and operates mobile units
for recovery of mercury from soil by retorting. The mobile unit is set up and operated on site to
process 6-ton batches of mercury-contaminated soil or sludge. Contaminated material, after blend-
ing with a proprietary (nonsolvent/nonchlorinated) additive, is indirectly heated in a retorting
furnace to volatilize mercury. Mercury in the off-gas is condensed and collected for refining and
reuse. The off-gas is further cleaned by a carbon filter. Mercury also is recovered from the carbon
filter, so the process is reported to generate no mercury-bearing wastes.
The PMET mercury recovery process reportedly is accepted as a recycling process for
soils with D009 toxicity hazard characteristic by U.S. EPA Region III and the Pennsylvania
Department of Environmental Resources. The process also is reported to be applicable to K106
(wastewater treatment sludge from the mercury cell process in chlorine production).
Quicksilver Products, Inc.
200 Valley Drive, Suite #1
Brisbane, CA 94005
Ritchey Vaughn
(415) 468-2000
1-800-275-2554-
Quicksilver Products is described in the literature as. a refiner and distributor of various
grades of metallic mercury. They are reported to provide recycling services for metallic mercury
40
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and mercury-contaminated waste. They will process mercury vapor lamps; thermometers,
barometers, and other mercury metering devices; mercury-contaminated rags, clothing, and debris;
batteries, switches, relays, and other mercury-encapsulated devices; mercury-contaminated soil;
and waste metallic mercury.
Recyclights
2010 East Hennepin Avenue
Minneapolis, MN 55413
(612) 378-9568
Recyclights uses a crush and sieve unit and distillation process to recover mercury from
fluorescent lamps and mercury vapor lamps.
Superior Lamp Recycling Inc.
Port Washington, Wl
Paul Vanderbloemen
(608) 252-7004
Superior Lamp Recycling Inc. has been formed by Madison Gas & Electric and Superior
Environmental Services Hazardous Waste Group Inc. to recycle used fluorescent lamps. The firm
will process lamps in a closed environment, separating mercury, aluminum, phosphor powder,
glass, and plastic for reuse.
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SECTION 6
CONCLUSIONS
This study has identified mercury sources and consumption patterns, and has identified
source reduction and recycling options for mercury in the electronics industry.
Overall, mercury usage has diminished over the past decade, but aside from batteries,
usage in electrical and electronic devices has remained fairly constant. Both the supply and the
demand for mercury have declined in response to regulatory pressures. Industry expectations are
for an increasing proportion of mercury to be supplied by recycled sources (Greenberg et al.,
1993).
Alternatives for mercury-containing electronic devices were presented and compared to
mercury-containing devices. The survey of alternatives shows that many nonmercury options are
available for the diverse applications that make up the electronics industry. Overall, it can be said
that while mercury has had an important role in manufacturing of high-quality electromechanical
products, it undoubtedly will be replaced by more versatile and faster fully electronic equivalents in
the future. The shift from mercury-containing to nonmercury-containing devices is governed as
much by natural evolution of technology as by environmental awareness. Devices based on newer
technologies continually become more cost competitive with former mainstay devices which may
contain mercury. For the present, environmental awareness plays a key role among industries that
use mercury in their products and processes. In these industries, pollution prevention and recycling
are viable means for preventing mercury escape to the environment.
Finally, recycling alternatives for mercury in electronic products were presented. It was
found that vacuum retorting is a viable means of recycling mercury that is becoming commercially
available. However, these recycling programs are unlikely to be available nationwide unless a
means is found to streamline the federal, state, and local approval processes necessary for
implementation.
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SECTION 7
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46
•ArU.S. GOVERNMENT PRINTING OFFICE: MM - 550401/MBM
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APPENDIX
QUESTIONNAIRE
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llBaltelle
. . . Putting Technology To Work
PLEASE ANSWER THE QUESTIONS INDICATED ON THIS FORM AND RETURN TO:
BRUCE SASS, BATTELLE, 505 KING AVENUE, COLUMBUS, OHIO 43201-2693
I. Product Profile.
1. Please describe any products your company manufactures that contain mercury.
Each description should include the following information:
D Product name and function
a Name of specific components that contain mercury
n Name of manufacturer of these components
n Unit cost of these components
D How does the mercury component determine
your product's performance?
2. Have alternatives to the mercury component been identified?
If so, please describe them.
What are the physical and electrical characteristics of these alternatives?
3. If mercury-free alternatives have been identified, are they economically feasible?
Please estimate how the difference in cost (actual or percent difference) would
affect the final cost of producing your product.
4. Is your company currently investigating other alternatives to mercury?
How would you characterize your progress in this area?
What are the primary motives behind this research (e.g., environmental,
technological, economic)?
II. Environmental Corporate Structure.
5. Describe your company's environmental corporate structure.
6. Which departments are responsible for establishing and implementing
environmental policies within your corporation?
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