NATIONAL EMISSIONS
INVENTORY
OF SOURCES
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Water Programs
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
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EPA-450/3-74-011
NATIONAL EMISSIONS INVENTORY
OF
SOURCES AND EMISSIONS
OF
SILVER
by
GCA Corporation
GCA Technology Division
Bedford, Massachusetts 01730
Contract No. 68-02-0601
EPA Project Officer: David Anderson
Prepared for
ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Water Programs
Office of Air Quality Planning and Standards
Research Triangle Park, N. C. 27711
May 1973
O.S. Pnvirohmental Protection Agency
Region 5, Library f-< ^ "
77 West Jackson F
Chicago, JL 605;.'- . "iCor
-------
This report is issued by the Environmental Protection Agency to report technical
data of interest to a limited number of readers. Copies are available free of
charge to Federal employees, current contractors and grantees, and nonprofit
organizations - as supplies permit - from the Air Pollution Technical Information
Center, Environmental Protection Agency, Research Triangle Park, North
Carolina 27711, or from the National Technical Information Service, 5285 Port
Royal Road, Springfield, Virginia 22151.
This report was furnished to the Environmental Protection Agency by GCA Corp-
oration, Bedford, Massachusetts, in fulfillment of Contract No. 68-02-0601. The
contents of this report are reproduced herein as received from GCA Corporation.
The opinions, findings, and conclusions expressed are those of the author
and not necessarily those of the Environmental Protection Agency. Mention of
company or product names is not to be considered as an endorsement by the
Environmental Protection Agency.
Publication No. EPA-450/3-74-011
11
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ACKNOWLEDGEMENT
The continued cooperation and dedication of Mr. Carl Spangler of
EPA, who served as Program Monitor until his death is deeply appreciated.
GCA would like to extend thanks to Mr. David Anderson and Mr. James
Southerland of EPA for their cooperation in the preparation of this study.
In addition, special thanks are also due to Mr. R. Welch and Mr. J.
West, Commodity Specialists, Bureau of Mines, who provided significant
technical inputs to this program.
111
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TABLE OF CONTENTS
SECTION TITLE PAGE
ABSTRACT vii
I INTRODUCTION 1
A. PURPOSE AND SCOPE 1
TJ. CONCLUSIONS 2
II OVERALL U.S. MATERIAL FLOW CHART FOR SILVER 4
A. U.S. PRODUCTION AND ORE PROCESSING
(45,006,000 ounces) 4
B. IMPORTS AND EXPORTS (Net, 34,671,000 ounces
imported) 4
C. STOCKPILE CHANGES (NET DECREASE, 101,000
ounces) 6
D. SCRAP RECYCLING (49,318,000 ounces) 6
E. PRIMARY SMELTING (81,381,000 ounces) 7
F. SECONDARY REFINING (80,043,000 ounces) 7
G. CONSUMPTION OF SILVER (129,096,000 ounces) 7
III SOURCES AND ESTIMATES OF SILVER-CONTAINING EMISSIONS 9
A. DATA PRESENTATION AND ACCURACY 9
B. DEVELOPMENT OF EMISSIONS ESTIMATES - 1970 14
C. SUMMARY OF PRINCIPAL EMISSIONS 24
IV REGIONAL DISTRIBUTION OF PRINCIPAL SOURCES AND
EMISSIONS 26
V NATURE OF EMISSIONS 30
VI UPDATING OF EMISSIONS ESTIMATES 32
A. VERIFICATION OF CURRENT ESTIMATES 32
B. PERIODIC REVIEW OF ESTIMATES 32
VII REFERENCES 34
V
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LIST OF TABLES AND FIGURES
TABLE NO.
TITLE
SOURCES AND ESTHETES OF SILVER-CONTAINING
EMISSIONS
PRINCIPAL SOURCES OF SILVER-CONTAINING
EMISSIONS - 1970
GEOGRAPHICAL DISTRIBUTION OF EMISSION
SOURCES AND EMISSIONS
PROPERTIES OF METALLIC SILVER
PAGE
10
25
27
30
FIGURE NO.
SILVER MATERIALS FLOW - 1970
VI
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ABSTRACT
A national inventory of the sources and emissions of the element
silver was conducted. The study included the preparation of an overall
material flow chart depicting the quantities of silver moving from
sources of mining and importation through all processing and reprocess-
ing steps to ultimate use and final disposition. All major sources of
silver-containing emissions were identified and their silver emissions
into the atmosphere estimated. A regional breakdown of these sources
and their emissions was also provided. The physical and chemical nature
of the silver-containing emissions was delineated to the extent that in-
formation was available, and a methodology was recommended for updating
the results of the study every two years.
Vii
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I. INTRODUCTION
A. PURPOSE AND SCOPE
The Monitoring and Data Analysis Division, Office of Air Quality
Planning and Standards of the U.S. Environmental Protection Agency (EPA) has
contracted with GCA Technology Division to conduct a national inventory of the
sources and emissions of the element silver. The purpose of the study was to
define as accurately as possible, based on existing and available published
and unpublished information, the levels, nature and sources of silver-contain-
ing emissions for defined geographic regions throughout the United States.
The scope of this program is outlined below:
Develop an overall material flow chart
depicting the quantities of silver
moving from sources of mining and importa-
tion, through all processing and
reprocessing steps to ultimate use and
final disposition as far as the movements
can be traced.
Identify all major potential silver-
containing emissions emitted to the atmos-
phere from each source. Emission factors
and level, and types of air pollution con-
trol will also be provided for each of
these sources to the extent permitted by
available information.
Define those sources which contribute at
least 80% of the total emissions of silver.
Provide a regional breakdown of these major
sources and their emissions.
Present the nature of the silver-containing
emissions for each of these major sources
including a delineation of their physical
and chemical form and particle size distri-
bution, to the extent that information is
available.
Provide recommendations as to a methodology
for updating the results of this study every
two years.
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B. CONCLUSIONS
1. Material Flow
Based on all available data, 105 x 10 troy ounces (29,000
troy ounces = 1 U.S. short ton) of silver was consumed in the U.S. in
1970. As shown in Figure 1, about 25 percent of this was recovered as
old scrap, the remainder being in use or wasted in various ways. The
sources of silver included domestic mining and net imports, in about 4:3
proportion. Approximately 160 x 10 ounces underwent primary or second-
ary refining, of which part was exported and part was recycled as new
scrap.
The principal users of silver were the following industries:
Photography 30 percent
Contacts and conductors ... 20 percent
Sterling and jewelry ... 20 percent
Brazing alloys, solders,
and electroplating ... 20 percent
Other uses ... 10 percent
Certain assumptions made in preparing the above estimates, due to a de-
ficiency of data in certain areas, are explained in detail in Chapter II.
2. Principal Emission Sources
Silver is somewhat unique in that most of the atmospheric
emissions of silver are not associated with the silver industry (Chap-
ter II). The principal sources (after emission control, if any) are the
iron and steel industry (46 percent), cement industry (25.7 percent),
combustion of coal and oil (13.6 percent), and incineration (5.6 percent)
One reason for this is that the silver industry is small in comparison
with the iron and steel and coal industries. A second reason is the
value of silver, which results in close attention to silver processes
in which aerosols containing silver are generated.
Within the silver industry, the most concentrated emission
sources are primary and secondary smelting and refining (1.1 percent).
Although about four times as much silver is emitted in the wearing of
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electrical contacts, this emission is spread geographically over a
very large number of sources.
3. Regional Emissions
The regions of the U.S. in which most of the estimated
emissions of silver occur are Regions 3*and 5, the east central por-
tion of the U.S. The region in which the total emission per square
mile is greatest is Region 3, the Pennsylvania-Virginia portion of
the U.S. As noted above, these estimates result far more from the
geographical distribution and nature of the iron and steel industry
than from the silver industry.
4. Nature of Emissions
The principal emissions of silver are believed to be
elemental silver, with some simple sulphides, oxides, and halides.
This opinion is based on the nature of silver and the characteris-
tics of the high-temperature operations producing the emissions.
Particles containing silver are probably on the order
of one micron diameter (MMD). The particles are expected to travel
considerable distances (miles) before being deposited,
5. Degree of Control
The overall level of control of silver emission is es-
timated to have been about 85 percent in 1970. Large sources under
relatively poor control included open hearth steel production and
municipal incineration. Large sources under relatively good control
included blast furnace iron production and commercial incineration.
6. General Comments
The silver content of coal, oil, and/or incineration
ash may be sufficient to be of commercial value. Investigation of
this might result in added interest in controlling these emissions,
and hence, further documentation of this area is recommended.
See page 26 for a list of regions.
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II. OVERALL U.S. MATERIAL FLOW CHART FOR SILVER
Figure 1* presents a flow diagram depicting the total quantities
of silver products moving from sources of mining and importation
through the processing and reprocessing steps t;o ultimate use and fi-
nal disposition. Each of these sources is discussed below.
A. U.S. PRODUCTION AND ORE PROCESSING (45,Q06,000 ounces)
Silver is produced mainly as a co-product of base metal ores
(66 percent in 1970) and from silver ore (32 percent). ' In 1970,
the separate U.S. sources were (in troy ounces; 29,16? fcroy ounces =
1 U.S. short ton):
16,023,000 - copper ore processing
14,258,000 - silver ore
11,128,000 - copper-lead, lead-zinc, copper-zinc,
and copper-lead-zinc ore processings
2,581,000 - lead ore processing
415,000 - gold ore processing
397,000 - gold-silver ore processing
158,000 - processing of old mine tailings;
also tungsten and uranium ore pro-
cessings
46,000 - zinc ore processing
The Department of Commerce reports the 1970 mining production
(2)
of silver as 47,483,000 ounces.v ' The above sum and figures appear
to be more thoroughly documented, however.
B. IMPORTS AND EXPORTS (Net, 34,671,000 ounces imported)
In 1970 about 40 percent more silver wap imported than mined
(62,300,000 ounces). Of this, about half was in tfce form of bullion
or refined silver (32,600,000 ounces) and half in forms requiring
a 3*1
various types and degrees of refinement (29,700,000 ounces).
*
Data in Figure 1 and in this section are left unrounded for purposes
of information control. On average, the typical statistic is accur-
ate to within 10 percent, in the opinion of the authors.
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Ul
and Processing
Gold Mining
tad Processing
Gold-Silver
Mining & Processing
Copper Mining
Lead Mining
Zinc Mining
and Process ing
Metal Ores
uraniuv & tung-
Treaaury
Release, Net
415
397 ^
»'
2,581 ^
^ J
11.128
15. ,..
62 300
67,900
45,00
r*
Prils
ReEln
(63,
>-
"1
erles
100)
Se
Re
8
on
Fin
81
»
3,0
dir
Ing
,381
224,
43
y
>2|
129
I
09
77
nd
at
f
f
67.799
uBtrlal & Pri-
re«9«. Net
Intermediate
Processing
29
23,999
Nev
Scrap
11,437
\ *"
1
1
24.235 +
1
t
31,044 |
1 *"
1,804
'18i \>
I
i
14,035 T.
1 *
\
6,>42 | _.
1 ^~
I
25.18, ^
1
1
,8, }
1.999
709 | _
4
3.539
I
Sterling
Photographic
Materials
Dental & fedical
Supplies
Mirrors
Brazing Alleys
Contacts and
Bearings
ata jsts
Coinage and
*-
,
*
*
(105,097) 79,778
I ^
i '" ' '
25,319 rji.t.
Sera
i
*GCA Estimate
Figure I SILVER 1970 MATERIALS FLCW
(THOUSANDS OF TROY OUNCES; 29,000 TROY OUNCES « 1 U.S. SHORT TON)
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Total silver exported was roughly one-third of that imported
(27,629,000 ounces). Most of this was refined metal (17,240,000 ounces),
with waste, sweepings, ore and concentrates (10,378,000) comprising the
. , (1)
remainder.
C. STOCKPILE CHANGES (Net Decrease, 101,000 ounces)
About 50 percent more silver entered the domestic supply from
Federal sources than was mined in 1970 (67,900,000 ounces). ' This
was chiefly in the form of coinage silver sold by the Treasury, which
had accumulated in connection with the recent sharp reduction in the
use of silver in coins. This program of large-scale sale of coinage
silver was completed in late 1970. Consequently the 1970 stock deple-
tion should be viewed largely as a non-recurring item. (Note: The
same reference also gives the 1970 depletion of Treasury stock as
79,000,000 ounces, however without documentation.)
The U.S. industrial stockpile is estimated to have increased
(2)
by 43,800,000 ounces in 1970.^ ' This includes the holdings in U.S.
commodity exchanges, but does not include the silver in private hands
and in banks. With the cessation of U.S. silver coinage and the
sharp rise of the price of silver, private speculative holdings may
have increased, although data is not available to support this. We
estimate that in fact the sum of industrial, commodity exchange, and
private holdings increased by the amount 67,799,000 ounces in 1970.
This is approximately the amount of silver released by the Treasury,
which was also an unusual event. This release of Treasury silver and
the proportionate unusual increase in silver holdings tend to cancel,
leaving the imported, produced, and secondary silver flows about the
same as in other recent years.
D. SCRAP RECYCLING (49,318,000 ounces)
The total new silver entering the economy (mined, imported,
and released from the Treasury) was 175,206,000 ounces. Of this, part
entered industrial stockpiles and part was exported, leaving 79,778,000
ounces of new silver for ultimate domestic consumption, after scrap
recycling.
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The amount of new scrap recycled was 23,999,000 ounces.
This is material in relatively pure form requiring a minimum of refine-
ment. The amount of old scrap recycled was 25,319,000 ounces. This
includes salvaged products, chemical waste, precipitates, etc., re-
quiring considerable refining. The total scrap recycled (49,318,000
ounces) combined with the new silver to give a total supply of
224,524,000 ounces. After exports and stockpile changes, this left
129,096,000 ounces as the domestic supply. After new scrap, 105,097,000
ounces remained for use in various products. Old scrap was later re-
covered in the amount of 25,319,000 ounces, leaving 79,778,000 ounces
in the form of new products still in use, discarded products not sal-
vaged, and other wasted silver.
E. PRIMARY SMELTING (8.,381,000 ounces/1'
In addition to the U.S. mining ores and concentrates, U.S.
primary refineries also processed 36,375,000 ounces of silver from im-
ported materials, coinage released by the Treasury (containing 90 per-
cent silver), and recycled materials. In general, the type of mater-
ial to be refined determines whether it requires primary treatment, or
whether it can be processed more simply by a secondary refinery.
F. SECONDARY REFINING (80,043,000 ounces)^'
In addition to old and new scrap, secondary refineries also
processed various amounts of imported materials and Treasury coinage
silver. There are many such refineries handling a wide variety of
scrap and byproducts. The material may pass through several hands
and stages of refining before attaining a useful form and purity. The
above figure is therefore an estimate, based on the refineries that
were considered in the references utilized.
G. CONSUMPTION OF SILVER (129,096,000 ounces)
Purchases of silver were reported as follows:
38,044,000 - photographic materials
25,183,000 - contractors and conductors
24,235,000 - sterling and jewelry
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14,035,000 - brazing alloys and solders
11,437,000 - electroplating
6,342,000 - batteries
1,999,000 - catalysts
1,804,000 - dental and medical supplies
1,386,000 - mirrors
709,000 - government coinage
383,000 - bearings
3,539.000 - miscellaneous
Total 129,096,000 ounces
Whether or not these reported purchases include or exclude new scrap
is a matter of some uncertainty in the silver industry. The Bureau
of Mines and the Department of Commerce both publish "industrial
consumption" figures, which however, differ approximately by the
amount of new scrap. ( ' It is probable that the above figures
include new scrap, and that the remainder, 105,097,000 ounces, was
actually made into products by the above "consuming" markets. Figure
1 is based on this assumption. After new scrap, 25,319,000 ounces
was subsequently salvaged as old scrap from expired products as low-
grade wastes, leaving 79,778,000 ounces for ultimate disposal by buri-
al or incineration.
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III. SOURCES AND ESTIMATES OF SILVER-CONTAINING EMISSIONS
A. DATA PRESENTATION AND ACCURACY
Table 1 presents a summary of the data from which emissions
were estimated for all major potential sources. Each of the six col-
umns comprising this table will be discussed below.
1. Emission Factors
Except where indicated, this gives the pounds of total
particulates emitted per ton of production. Such considerations as:
. variations in process conditions among
individual plants comprising a source
category
. inaccuracies in existing data
. a limited quantity of existing data,
may, however, result in an average emission factor for a source cate-
gory varying by more than an order of magnitude from the value pre-
sented. In recognizing the need to indicate the level of accuracy of
these emission factors, a reliability code is presented along with
each emission factor value appearing in the table. This reliability
code system is described below and is based on the system utilized in
EPA Document No. AP-42, "Compilation of Air Pollutant Emission Fac-
tors":
A: Excellent
This value is based on field measurements
of a large number of sources.
B: Above Average
This value is based on a limited number
of field measurements.
C: Average
This value is based on limited data and/or
published emission factors where the ac-
curacy is not stated.
D: Below Average
This emission factor is based on engineering
estimates made by knowledgeable personnel.
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TABLE 1
SOURCES AND ESTIMATES OF SILVER-CONTAINING EMISSIONS
o
Source
Iron and Steel
Sinter Process
Blast Furnace
Open Hearth
Basic Oxygen
Electric Arc
Iron Foundry
Coal
Oil
Gasoline, etc.
[ncineration
Municipal
Commercial
Cement
Uncontrolled
Particulate
Emission
Factor
Ib/ton
20
Sinter
130
Pig Irop
17
Steel
40
Steel
10
Steel
20
NA
HA
NA
NA
--
NA
kg/10\g
10
65
8.5
20
9
10
NA
NA
NA
NA
--
NA
Reliability
1 Code
C
C
C
C
C
C
.
-
Production
Level
(tons/yr)
51,000,000
88,800,000
65,800,000
48,000,000
16,800,000
22,000,000
33,800,000a
287,000°
450,000,000
ioo,oooa
7,790,000C
7. Ag in
Emissions
0.01
0.01
0.05
0.004
0.05
0.008
0.0007
0.005
o.oooooib
0.037
(0.008-
0.015)
0.01e
Reliability
Code
D
D
C
D
D
D
A
A
B
B
B
Ag Emissions
Before Controls
tons/yr
51
578
280
38
42
18
236
14
4.5
37
220
896d
106oz/yr
1.5
16.8
8.2
1.1
1.2
0.5
6.9
0.41
0.13
1.1
6.5
26. Od
Estimated
Level of
Emission
Control
(%)
90
99
40
99
78
75
82
0
0
37
99
88
Ag Emissions
After Controls
tons/yr
5.1
5.8
168.0
0.38
9.2
4.5
42.5
14.0
4.5
23.0
2.2
107.0
106oz/yr
0.15
0.17
4.90
0.01
0.27
0.13
1.24
0.41
0.13
0.68
0.07
3.1d
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2- Level of Production Activity
This column depicts the quantity of material produced
(unless otherwise stated) annually. When multiplied by the emission
factor, an estimate of the total particulate emissions for that source
in pounds per year is obtained.
The values in this column are based on the material flow
calculations presented in Section II. Consequently, they have the
same accuracy as those material flow values which is estimated at
+ 10 percent.
3- Percent Metal in Emissions
The method of analyzing or assaying a dust sample for
the amount of metal it contains determines to a large extent the re-
liability of the data. For example, analytical chemistry techniques
for dust containing substantial fractions of metal can be accurate to
within a small percentage. On the other hand, optical spectroscopy
methods for determining concentrations on the order of parts per mil-
lion can be inaccurate by a factor of 2. Because of this variability,
the reliability codes discussed above for the emission factors are
also utilized to estimate the relative accuracy of the percentage
values listed in column 3.
4- Level of Emissions Before Control
The values in this column are derived by multiplying
the values in columns 1 through 3. The result is converted to tons/
year of emissions before control.
5. Estimated Level of Emission Control
The overall effectiveness of control for a source cate-
gory is based on two factors:
. the portion of the processes which are under control
. the typical degree of control
For example, if 60 percent of vertical roasters have some type of
particulate emission control, and these include both scrubbers and
12
-------
precipitators such that the apparent weighted average efficiency of
control is 85 percent, the overall control effectiveness is estimated
60 x 85 = 51 percent.
The accuracy of control efficiency data varies with the
degree of control. For a wet scrubber operating at 80 percent effi-
ciency; i.e., passing 20 percent material, the actual emission may
safely be assumed to be between 15 and 25 percent because of the rela-
tive ease of making determinations at this level. Thus the emissions
after control may be assumed to be accurate within + 5/20 or 25 per-
cent. On the other hand, for a baghouse reported as being 99 percent
efficient, or passing only 1 percent of the material, the actual emis-
sion may vary from 0.5 percent to perhaps 2 percent because it is fre-
quently difficult to make low-level measurements with accuracy. In
such case, the resulting emission data could be in error by a factor
of 2.
Unless otherwise specified, it is assumed that the re-
ported overall level of particulate control applies equally to all
silver-containing particles, independent of size, resistance and other
important collection parameters. This assumption results in a correct
estimate of silver emissions after control when the particulate is
chemically homogeneous; i.e., silver is contained in the same concen-
tration in all particles. If however, silver is concentrated in cer-
tain particles and in addition the efficiency of the control equip-
ment is not uniform for all particles, then the utilization of an
average control level is less valid for calculating silver emissions
after control. Data on the preferential control of silver-containing
particles is seldom available, but is included in this report when
possible.
The accuracy of estimating the level of control for a
specific source category is dependent on the quality of available data.
The investigators feel that, in general, the level of control data
will contribute an accuracy to the resulting emissions estimates with-
in + 25 percent.
13
-------
6> Level of Metal Emissions After Control
The values in this column are derived by multiplying the
values in column 4 by the value (100 minus estimated Level of Control).
B. DEVELOPMENT OF EMISSIONS ESTIMATES - 1970
Due to the value of silver, careful control of all processes
involving silver is standard practice. Wasting of silver, including
airborne particulate, is tolerated only as an economic or practical
necessity. Consequently, the emissions containing silver, listed in
Table 1, tend to be smaller in proportion, as well as in magnitude,
than have been identified for the other metals in this review. The
largest silver emissions (iron and steel processing; coal combustion;
incineration) comprising about 85 percent of all silver emission, are
not a part of the silver industry, but are the inadvertent results of
other practices. Data pertaining to these largest emissions are lim-
ited for two reasons: The silver industry has not been interested in
them as economic sources of silver; and silver has thus far had a low
priority as an air pollutant.
1. Iron and Steel Production
Very little information has been found giving typical
Ag contents of the emissions from the common iron and steel manufac-
turing processes. Orban, et al.(4) found a "trace" of Ag20 in the
emission from a Bessemer converter, with an apparent resolution of his
tests of about 0.02 percent. Hammond, et al.(5> reports 0.05 percent
Ag in the particulate discharge from an open hearth furnace, based
on "qualitative" spectrographic analysis with an apparent test resolu-
tion of 0.01 percent. The same authors also give an average of 0.0091
percent Ag in samples from a baghouse serving a gray iron cupola
furnace, based on a qualitative analysis. No other directly useful
data was found.
Additional perspective is gained indirectly, however,
in other ways. The average concentration of Ag in the earth is
0.000002 percent;(6) and in coal ash, 0.0007 percent (see below). Ag
14
-------
tends to occur naturally with some other metals, zinc in particular,
and also copper, aluminum, and manganese. These metals bracket the
melting and vaporizing temperatures of Ag (960 C and 1950 C, respec-
tively, see Section V). Because they are usually emitted in larger
concentrations, they are more easily measured and more often reported.
Because of their similarity to silver's thermal characteristics, the
ratio of silver to these metals may tend to be preserved in emissions
from high temperature processes. In those iron and steel emissions
for which data is available, the ratio of silver to zinc appears to
be of the order of 0.003, and of silver to copper, 0.10. Data on zinc
and copper emissions from all processes listed in Table 1 are general-
ly available. ' Using these known emissions and the apparent ratios,
plus the actual silver emission data cited above, estimates of silver
emission were made as given in the table. They vary from 0.004 to
0.05 percent.
Table 1 indicates that the iron ore blast furnace gener-
ates one of the largest quantities of silver, equal in magnitude to
one-third of all the silver mined in the U.S. annually. Because the
blast furnace is well controlled, however, the final silver emission
is not outstanding. The open hearth furnace, on the other hand, be-
cause of a lower level of particulate control, emits approximately 37
percent of all Ag emissions in the U.S. This quantity is equivalent
to about 10 percent of the silver mined domestically.
Iron and steel production as a whole is estimated to
contribute 58 percent of the silver emission. It is noteworthy that
the silver content of these emissions is estimated to be similar to
those of copper and lead refinery emissions. The latter are collected
when possible and processed for their valuable metal contents. A
silver content of 0.01 percent is equivalent to 2.9 ounces/ton, a
marginal concentration in ore form, but perhaps more attractive in
fume form. Current prices of refined silver are approximately $2.00/
ounce.
15
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2- Coal and Oil Combustion
Silver and coal sometimes occur together in nature. For
example, in Utah in the 1870's, thin scales of silver were found along
with small deposits of minable lignite in sandstone. Evidently almost
any concentration of Ag in coal could be encountered depending on the
size of the coal sample and its source. Abernathy and Gibson,(9) in
a survey of trace metals in coal, cites reports of maximum silver con-
tents of 0.0001 to 0.0084 percent in the ash of a variety of western
and West Virginia coals. The geometric mean is about 0.0009 percent.
n (")
Brown gives the maximum silver content of coal ash as 5 to 10 ppm,
equivalent to 0.0005 to 0.0010 percent silver. Accordingly, the av-
erage of 0.0007 percent is used in Table 1
Table 1 estimates that slightly less silver emission is
developed from coal combustion than from the open hearth process.
Furthermore, coal power plants are controlled about three times as well
as the open hearth process (82 percent(32) versus 40 percent control).
Thus, controlled silver emissions from coal burning contributes about
15 percent of the U.S. silver emissions.
The above references indicate that the ratio of
silver to copper in both the earth, and in coal, is about 0.002;
and of silver to zinc, about 0.0005. These ratios may be useful
in arriving at order of magnitude estimates of the silver content
of other samples of coal ash that have been tested for copper or zinc,
but not for silver.
Gerstle, Cuffe, et al.(10>11) report the emissions of
numerous other trace metals in coal ash, but not silver. Their data
give the efficiency of an electrostatic precipitator on each of the
metals. The copper-zinc ratio in the ash was reduced by one-half in
passing through the precipitator. This suggests that silver may also
be differentially controlled by the equipment in use. We have used
the average 82 percent level of control, however.
The combustion temperatures of coal are in the vicinity
of 1700 C, approaching the vaporization temperature of silver. Thus,
16
-------
part of the silver in the coal may be vaporized within the firebox.
It is probable that this silver vapor condenses into the ash as the
combustion products cool. Thus, we have assumed that the ash assay,
as reported above, includes essentially all of the silver emitted by
the process. The same assumption applies to iron and steel and other
high temperature process emissions in Table 1.
Analysis of the ash from fuel oil would be expected to
be similar to that from coal, in the sense that both are fossil fuels.
Comparisons of typical analyses of each show similar concentrations
of copper and zinc. Levy, et al.(21) report a concentration of 0.0018
percent silver in oil ash (optical emissions spectroscopy), moderately
higher than the coal ash assay. On the other hand, Walsh reports
a concentration of 0.03 percent silver in oil ash (spectrographic
analysis). Trace metal content of oil is known to vary by factors
(13)
of 25 or more, depending upon the type of oil.v All factors
considered, an average of 0.005 percent is used in Table 1. Oil
combustion emissions are uncontrolled, resulting in a level of
silver emissions from fuel oil combustion (0.41 x 106 ounces)
which is about one-third the level emitted from coal firing.
3. Gasoline and Other Light Fuels
Analyses of premium and low-lead gasolines indicated
silver concentrations ranging from less than 0.001 to 0.4 ppm with
apparently reliable data of 0.002 ppm (neutron activation), 0.02 ppm
(spark source mass spectroscopy), and 0.05 ppm (spark source mass
spectroscopy), being reported.<23> An average content of 0.01 ppm
is assumed. The silver contents of other light fuels were not
available, and were assumed to be the same as for gasoline. It
is further assumed that the silver in these fuels is entirely emit-
ted to the atmosphere. Including kerosene, light distillates, and
jet fuels with gasoline, 3.4 x 109 barrels or about 450 x 10 tons^
were burned in 1970. The resulting emission estimate of 0.13 x 10
ounces of silver is shown in Table 1.
17
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4' Incineration
Assays of samples of fly ash from refuge combugtion have
indicated a silver conf-pnt- of > »-~ n
content of 2 to 9 ounces per ton of ash (equivalent
to 0.006 to 0.028 percent As)(14) A^ q«"-vaient
percenc AS;- Another source reports a content of
19 ounces per ton (0.059 percent Ag).<15)
An estimated average value of 12 ounces per ton of fly-
ash, or 0.037 percent Ag, is used in Table 1. Note that at this rate
the recovery value of the silver is about 14 times greater than the
cost of disposal of the ash that was recently estimated to be $1.50/
The net emission of 0.68 x 106 ounces is the third highest
emission in the table.
Recently, special purpose commercial incinerators have
been developed specifically to recover the silver used in photographic
materials.* Of the 38 x 106 ounces of silver used annually by the
mdustry, it is estimated that 14 x 106 ounces is recycled as preci-
pxtates from photographic processing solutions. Of the remainder it
is estimated that 6.5 x 106 ounces is processed by the special incin-
erators, the rest being burned in municipal incineratprs or wasted in
various other forms. The special incinerators are reported to recover
at least 99 percent of the silver, resulting in a net emission of only
0.07 x 10 ounces from commercial incinerating operations.
5. Cement
Assays of dust from three cement plant clinker coolers
indicated 0.015 percent silver (spectrographic analysis) according to
a review of EPA data.< 2> Assays of dust from thre£ air separators
indicated 0.008 percent silver, also from EPA data. Based on these
Percentages (0.008 to 0.015 percent), the range of silver emissions
xs 75 to 140 tons/year after 88 percent control with an intermediate
value of 107 tons/year in this survey. The resulting emission esti-
mate of 0.32 x 10 ounces is only about 3 percent of the total U.S.
silver emission.
18
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6. Production of Non-Ferrous Metals
a. Mining
Mining and milling operations are estimated to gen-
erate 200 pounds of emissions per 1,000 tons of production, for each
of several non-ferrous metals.<17'18) If one assumes that the concen-
tration of silver in the emitted dust is the same as in the ore being
processed, then 200 pounds of silver emissions are generated for each
1,000 tons of silver produced. In 1970, 45 x 10 ounces of silver
were produced. Thus the estimated emission of silver from all non-
ferrous mining and milling operations generating silver as a co-product
is 4,500 ounces. This is after particulate control, which is minimal.
b. Primary Smelting
In the case of copper smelting, Davis reports 10.1
ounces of silver per ton of emitted dust (0.035 percent Ag), and 10
pounds of emitted dust per ton of copper produced, after control by
an electrostatic precipitator at about 97 percent efficiency.
This measurement was made at the stack, where effluents from various
operations had been combined, notably, roasting, reverberatory furnace
smelting, and converting. This indicates an effective before-control
generation of 333 pounds of dust per ton of copper. In other plants,
it was reported that emission factors of 704 pounds of dust per ton
of product was generated in smelting before 99 percent control; 1833
pounds per ton of product in smelting before 99 percent control; and 3.1
pounds per ton of product in unspecified processes before control.
Using an average 1,000 pounds per ton generated, with a copper produc-
tion of 1,765,000 tons in 1970 and a control efficiency of 99 percent,
results in approximately 90,000 ounces of emission as shown in Table 1.
In the smelting of other ores, an estimated 50 per-
cent of the 1970 U.S. silver production was derived through lead,
zinc, lead-zinc, and silver ores.(1) The silver content in these ores
averages about 8.7 ounces per ton, whereas in copper ore the content
is only about 0.07 ounces per ton (1963 data).(19) The ore is first
19
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concentrated by flotation in which little aerosol is generated. After-
ward, there is still a much higher proportion of silver along with
these other metals than with copper. A limited amount of emission data
(24)
is available. Sintering and sinter crushing at a lead smelter is
reported to generate 0.3 pounds of dust per ton of product before an
average control of 92 percent. For a lead blast furnace and a rever-
beratory furnace, emissions are reported to be 20 and 36 pounds per
ton, respectively, before 95 percent control. Zinc smelting in gener-
al is reported to emit 7.0 pounds per ton before an average 90 percent
control.
In none of these cases is the silver content of the
emitted particulate reported. Since the data base is insufficient
for a complete computation of silver emission, the following estimates
are made: particulate emission averages 25 pounds per ton, on a base
of 1,460,000 tons of heavy metal produced in 1970; the average assay
of the particulate is five times greater than for copper due to the
higher proportion of silver present; and control efficiences average
95 percent. As a result, 45,000 ounces are estimated to be emitted
after control.
Less than 1 percent of the silver produced in the
U.S. in 1970 was produced by the processes of amalgamation and cyani-
dation. In the former process, after crushing, washing and drying of
the ore, it is mixed with mercury and then heated in a retort furnace.
In the latter process, the crushed ore is leached, after occasional
roasting, and the silver is precipitated from the leachate before en-
tering a reverberatory furnace. It is estimated that 1 percent of
the silver produced by these two processes escapes as aerosol, or
1,200 ounces.
c. Secondary Refining
The refining of scrap metals other than silver scrap
is believed to be relatively free of silver emissions since most
scrap has a low silver content. One possible exception is copper
scrap from electrical products, which contains considerable silver in
20
-------
the form of electrical contacts and conductors. The 1970 consumption
of silver for contacts and conductors was 25 x 10 ounces; and the con-
sumption of copper by the electrical industry, about 50 percent of the
U.S. copper consumption was 1.0 x 10 tons. The resulting ratio is
25 ounces of silver per ton of copper. Emissions of copper from sec-
ondary copper refining after controls have been estimated at 210 tons
per year. If the consumption ratio applies to these emissions,
then it is estimated that up to 5,250 ounces of silver is emitted
during secondary copper refining. At 97 percent control efficiency,
this would be 167,000 ounces before control.
Emissions from the secondary refining of lead in
(22)
blast furnaces are reported in two cases. One furnace controlled
by scrubber (estimated efficiency 90 percent) produced 1.14 pounds per
ton of particulate after control, containing approximately 30 ppm of
silver. The second furnace controlled by cyclone and fabric filter
(estimated efficiency 99 percent) produced 0.17 pounds per ton of par-
ticulate after control containing about 170 ppm of silver. The com-
puted pre-control emission factors average about 15 pounds per ton,
and the post control assays average 0.01 percent. Only about 75,000
tons of scrap lead were refined in 1970, resulting in a negligible
0.05 tons of silver generated before control.
Other than the commercial incineration of photo-
graphic materials included above, silver scrap is generally refined
by melting followed by electrolytic refining. A typical reverbera-
tory furnace may emit 30 pounds per ton of metal, and an electrolytic
cell, 2 pounds per ton, for a total emission of 32 pounds per ton.
These emissions are controlled at an estimated 98.5 percent. Since
only 80,043,000 ounces of silver underwent secondary refining in 1970,
the emission is estimated to have been 1,280,000 ounces before control,
and 19,200 ounces after control.
7. Intermediate Silver Products
Practically all of the 129,096,000 ounces of silver con-
sumed by the various markets first passes through intermediate hands,
21
-------
where it is processed in various ways/20) The metal, in various de-
grees of purity, may be alloyed; shaped into wire, sheet, powder, etc;
or converted chemically or electrochemically. Few, if any, of these '
processes emit significant amounts of silver, because relatively few
firms convert most of the silver. Also, these processes usually in-
volve limited amounts of silver and are closely supervised.
In forming powdered silver, a jet of molten metal is
combined with a high velocity air jet. From 40 to 90 percent of the
particles thus formed are 50 microns or under. It is unlikely that
any appreciable number of particles 5 microns or smaller are produced
by this process. Since larger particles will be well controlled, it
is assumed that the resulting emission of silver is negligible.
Nearly all silver for photographic consumption is first
converted to silver nitrate by dissolving the metal in hot nitric acid
in an enclosed vessel. The fumes that escape this vigorous reaction
are scrubbed to control the nitrogen oxides produced. The literature
on this process is preoccupied with gaseous control problems rather
than silver loss. It is unlikely that any appreciable quantity of
silver escapes. Similarly, electrochemical conversion of silver into
silver sulphate may involve the boiling of hydrogen gas, with possible
minor emission of silver. Silver sulphate, chloride, cyanide, and
oxides are produced in relatively small quantities compared to silver
nitrate.
Little aerosol is emitted in shaping silver. The various
steps may include weighing and charging a crucible for melting; poring
and casting into molds; rolling, slitting, drawing. As a percentage
of all U.S. emission of silver, these sources are estimated to be
negligible.
8. Consumption of Silver
a. Electrical Contacts
About one-half of the 25,183,000 ounces of silver
used for contacts and conductors, or 12,000,000 ounces is estimated to
22
-------
be used annually for solid (cast or machined) and composite (laminar)
contacts. Although silver is used because it withstands sparking and
mechanical wear well, it is evident that the contacts do nevertheless
undergo wear. It is assumed that the contacts are designed to last
the life of the rest of the electrical equipment, which is typically
about 20 years. That is, it is estimated that 5 percent of the silver
consumed annually is worn away in the form of aerosol. This results
in 600,000 ounces of emission per year. This is spread over a very
large number of locations, as most appliances, automobiles, telephones,
etc. use some silver contacts.
b. Brazing and Soldering
About 14,000,000 ounces of silver are consumed by
brazing. Although the production of these alloys is relatively non-
emitting and easily controlled, the brazing process emits a consider-
able amount of fume. An estimated 1 percent of silver in these alloys
is emitted, the rest of the metal remaining at the point of joining.
Most of the brazing is done in specialized locations (air conditioning
and refrigeration is estimated to consume 20 percent; automotive and
aircraft, 30 percent) which permits these emissions to be better con-
trolled than others (plumbing and heating, and electrical appliance
brazing tend to be non-concentrated). Assuming that emissions from
brazing and soldering are 50 percent controlled, the net emission es-
timate is 70,000 ounces of silver.
9. Other Sources
GCA estimates that these sources contribute 43,000
ounces of silver emissions, or about one-half percent of the total.
The following minor sources have been considered:
Emission Estimates
Silver Consumption (ounces)
Conductors, spray painting 10,000
Bearings and lubricants, loss of
flake silver lubricant in use 2,000
Mirrors, spraying of solutions 1,500
Batteries, sintering, electrolytic
processes, chemical losses 900
23
-------
Silver Consumption
Electroplating, chemical and liquid
spills
Catalysts, preparation, regenera-
tion and erosion
Sterling and jewelry, buffing and
polishing
Brazing alloys and solder, production
Medicine and dentistry, preparation of
materials
Miscellaneous Sources
Non-metallic mineral operations emit-
ting dust with trace silver
Forestry and agricultural burning of
unwanted waste containing trace silver
(Note: Forest fires not included)
Cloud seeding
Wear of coinage
Emission Estimates
(ounces)
250
250
200
150
100
20,000
7,500
negligible
negligible
C. SUMMARY OF PRINCIPAL EMISSIONS
TOTAL 42,850
Table 2 summarizes the largest 1970 emissions of silver, as
the estimates were developed in Table 1. These are grouped into in-
dustrial sources, those directly associated with the silver industry,
and inadvertent sources, those having little to do with the silver in-
dustry. In the case of silver, the latter category is the larger.
24
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TABLE 2
PRINCIPAL SOURCES OF SILVER-CONTAINING EMISSIONS - 1970
Source
Inadvertent Sources
Iron and steel production
Cement production
Coal burning
Municipal incineration
Oil burning
Silver Industry Sources
Electrical contacts
Primary smelting
Percent of U.S. Total
Ounces /year
5,630,000
3,100,000
1,240,000
680,000
410,000
600,00
133,000
Tons /year
193.0
107.0
42.5
23.3
14.0
20.6
4.5
Percent*
46.3
25.7
10.2
5.6
3.4
4.9
1.1
97.2
Percent of Table 1 total, 12,100,000 ounces/year.
25
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IV. REGIONAL DISTRIBUTION OF PRINCIPAL SOURCES AND EMISSIONS
For purposes of showing geographical distribution, the U.S. was
divided into ten regions identical to the Regional Branches of EPA:
States
Connecticut, Maine, Massachusetts, New Hampshire
Rhode Island, Vermont
II New Jersey, New York, Puerto Rico, Virgin Islands
III Delaware, Maryland, Pennsylvania, Virginia, West
Virginia, District of Cplumbia
IV Alabama, Florida, Georgia, Kentucky, Mississippi,
North Carolina, South Carolina, Tennessee
V Illinois, Indiana, Michigan, Minnesota, Ohio,
Wisconsin
VI Arkansas, Louisiana, New Mexico, Oklahoma, Texas
VII Iowa, Kansas, Missouri, Nebraska
VIII Colorado, Montana, North Dakota, South Dakpta,
Utah, Wyoming
IX Arizona, California, Nevada, Hawaii and the South
Pacific
X Alaska, Idaho^, Oregon, Washington
Emissions from the principal sources listed in Table 2 are.distributed
among these ten regions as shown in Table 3. Also, the number of plants
producing the emissions i.s shown in the table when such information is
available.
The accuracy of the distributions by region varies^ with the cate-
gory. The number of plants per category ranged from one to several thou-
sand in this study. When the number of plants was less than about 100,
an attempt was made to identify each plant and plant location, and in-
clude it in one of the ten regions. When production or capacity figures
for these plants were available, total production or capacity for each
region was computed, and the U.S. emission estimate for that category
was distributed by region accordingly. When production or capacity
figures were not available, the emission was distributed by the number
of plants in each region. If the number of plants was very small or
26
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TABLE 3
GEOGRAPHICAL DISTRIBUTION OF EMISSION SOURCE AND EMISSIONS
Emission Source
Inadvertent Sources
Iron and Steel
Open Hearth
Other
Coal Burning
Municipal Incineration
Oil Burning
Cement Production
Silver Industry Sources
Electrical Contacts
Primary Smelting
Totals
EPA Regions
1
3.7
1
1.4
23
0.3
0.7
3.8
16.6
2.5
18.0
0.6
1
1.2
5.8
0
0
13.0
2
3.7
1
2.0
33
2.4
5.7
5.5
24.2
4.1
29.1
7.7
13
2.6
12.5
0.2
2
28.2
3
65.7
18
6.7
111
9.3
21.8
4.1
17.7
2.1
15.0
16.8
28
2.4
11.5
0.4
4
107.5
4
7.3
2
2.4
39
9.1
21.1
2.7
11.8
1.3
9.6
15.8
27
3.2
15.7
0.2
2
42.0
5
62.3
17
8.8
146
17.6
41.3
5.5
24.0
1.1
7.6
17.9
30
4.4
21.6
0.4
4
118.0
6
7.3
2
1.2
20
0.6
1.4
0.8
3.5
0.5
3.7
15.8
27
2.0
10.0
1.1
11
29.3
7
0
0
0.3
5
1.7
4.1
0.3
1.4
0.1
0.9
11.8
20
1.1
5.5
0.3
3
15.6
8
7.3
2
0.1
2
1.4
3.3
0.1
0.3
0.3
1.8
5.3
9
0.5
2.7
0.7
7
15.7
9
11.0
3
1.7
29
0.3
0.7
0.1
0.5
1.6
11.6
11.2
19
2.3
11.3
1.0
10
29.2
10
0
0
0.4
7
0.1
0.3
0
0
0.4
2.7
4.1
7
0.7
3.2
.0.4
4
6.1
Totals
168
46
25
415
42.5
100
23
100
14
100
107
181
20.6
100
4.5
47
405
Units
(TPY)
(O.H. Plants
(TPY)
(All types
Plants)
(TPY)
(Percent
Coal)
(TPY)
(Percent
Capacity)
(TPY)
(Percent Oil)
(TPY)
(Plants)
(TPY)
(Percent
Population)
(TPY)
(Plants)
(TPY)
Reference
25
25
1
26
27
28
29
30,20
-------
there was reason to believe that certain plants were larger or produced
more emission, distributions were weighted accordingly.
On the other hand, when the estimated number of plants was greater
than about 100, and the distribution of plants was not known, the re-
gional breakdown was made on a different basis, such as population,
geographical area, or shipments reported, as most appropriate for that
category. Whether the distribution was by plant size, number of plants,
or another statistic, the distribution is believed to be accurate to
within 10 percent in most cases.
The emissions distributions in Table 3 are made on the following
basis:
Inadvertent Sources
Iron and Steel Production: Proportional to the percentage of
U.S. plants in each region
Coal Burning: Proportional to coal shipments, by
state of destination
Municipal Incineration: Proportional to incinerator capacity,
by state
Oil Burning: Proportional to percentage of re-
sidual oil burned
Cement Production: Proportional to number of plants,
by state
Silver Industry Sources
Electrical Contacts: Proportional to population; i.e.,
consumption of equipment containing
contacts
Primary Smelting: Proportional to number of smelters
of all types, by state
The largest emissions of silver in 1970 are estimated to have been
in Regions 3 and 5 (the east central portion of the U.S.). This con-
clusion is strongly influenced by the production of steel by the open
hearth process in these regions, and by the concentration of silver re-
ported in open hearth fumes. Since this concentration report was ap-
parently based on a single measurement of questionable reliability, it
is urged that further tests be made of open hearth fumes before these
estimates be widely adopted.
28
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Region 3 has the smallest geographical area in relation to the
emission of silver in that area (123,000 square miles), or in other
-3
words, the greatest emission of silver per square mile (0.88 x 10
tons of silver per square mile-year). Again, this is largely the re-
sult of the estimates of silver emissions from open hearth steel pro-
duction.
29
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V. NATURE OF EMISSIONS
Practically no data describing the particulate containing silver
has been found. It is, therefore, necessary to estimate the character-
istics of these particles based on the nature of silver and the processes
that generate the emissions.
Table 4 lists some physical characteristics of silver, the most
important of which may be the boiling point, 2210°C. Elemental silver,
because of its high boiling point, will not be emitted in significant
quantities as a vapor by processes operating at lower temperatures.
Simple silver salts (halides, sulphides) and oxides are the most proba-
ble forms of silver.
TABLE 4
PROPERTIES OF METALLIC SILVER*
Melting point:
Boiling point:
Density:
Atomic weight:
Heat of vaporization:
Hardness:
961°C
2210°C
Q
10.5 grams/cm
108 awu
60.7 kg-cal/g-atom
2.8 (standard minerology
scale)
*
Reference 30, Table 3-169. See also Table 3-1.
Whether these compound forms are produced from elemental silver at
high temperatures, or the reverse, depends on the excess oxygen, sulphur,
chlorine, etc., and also on the presence of cyanide ions.
Iron and steel producing processes are typically on the order of
1000°C, although in an electric furnace local temperatures must be ex-
tremely high due to the concentrated electric current. Particulates
from these processes range in size from submicrometer to 5 micrometers.
30
-------
There is no data to indicate the size of the silver-containing
particles within this range. After release from a stack, any of
these particles are capable of traveling long distances before
settling to earth.
Combustion processes (coal, oil, or incineration) tend to be at
lower temperatures. The particulate produced, however, is somewhat
larger, ranging up to approximately 25 microns. Although the largest
particles will settle out fairly quickly, smaller particles including
a small fraction of submicroraeter ones will remain airborne for long
periods.
Since metallic silver is a relatively stable material, there is no
reason to expect significant chemical changes following emission.
Likewise there is no reason to expect unusual physical behavior of par-
ticles containing silver. Dispersion, agglomeration, and settling may
be presumed to proceed at normal rates for these particles.
Silver is not widely known as a toxic material. In nitrate form
it is applied to the eyes of babies, and is used externally in cases of
severe burn. In the vicinity of non-ferrous smelters where the toxic
effects of zinc and lead are well known, emissions of silver have not
been reported as problematic. The extent to which silver, as an air
pollutant, might be considered hazardous has not yet been established.
31
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VI. UPDATING OF EMISSIONS ESTIMATES
The following recommendations are made for periodically updating
the estimates made in this study.
A. VERIFICATION OF CURRENT ESTIMATES
1. Because the estimated high emissions levels from open
hearth steel production significantly influence the conclusions of this
report, improved data for this emissions source should be obtained.
2. Within the silver industry, the emission of silver from
non-ferrous smelters and refineries constitutes the most concentrated
source, i.e., significant emissions from a small number of sources.
Therefore, within the industry, these sources offer the most obvious
opportunities for improved emission control. Compilation of additional
data is recommended to supplement the estimated emissions data from
these sources.
B. PERIODIC REVIEW OF ESTIMATES
1. The Bureau of Mines' estimates for material flow, industry
practices, and trends provide the best estimates of the size of the
industry.
2. EPA activities are currently generating the best emissions
data and should be reviewed using:
a. Overall industry studies; e.g., Reference 31;
b. The Source Test Program in which specific in-
dividual plant emissions are measured. This
information provides emission factors for spe-
cific examples of typical industry operations;
and also provides some analyses of the partic-
ulate, usually including trace metal content
and particle size;
c. NEDS (National Emissions Data System) is steadily
being enlarged and improved. This system can
provide emission factors for specific plants
and plant operations, the type of particulate
control equipment in use, and the actual, or
estimated, control efficiency. The system may
eventually be expanded to include description
of the emissions.
32
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3. The silver industry should be consulted for its opinion and
suggestions regarding the most recently published estimates. This may be
best accomplished by interviewing the Silver Commodity Specialist, Division
of Non-ferrous Metals, Bureau of Mines in Washington; or by interviewing
one or more of the principal companies in the industry.
4. The literature should be reviewed using (a) industrial
views as published from time to time in Chemical Engineering, for example,
and (b) environmental views as summarized in Pollution Abstracts, for example.
5. Individual companies or plants may be approached for opinions,
data, or cooperative tests of their own operations. This is a difficult
approach to the obtaining of fresh information due to the natural reluctance
of the plants to discuss environmental problems. However, data thus obtained
can have a relatively high degree of reliability.
6. State agencies in which specific plants are located may be
able to provide useful information and should be contacted.
33
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VII. REFERENCES
1. West, J. M., "Silver", Minerals Yearbook, 1970, Bureau of Mines,
U. S. Dept. of Interior.
2. Survey of Current Business, Bureau of Economic Analysis, U. S. Dept.
of Commerce.
3. Personal communication regarding the commodity "Silver", Paul Zinner,
U. S. Bureau of Mines, Wash., D. C., November, 1972.
4. Orban, A. R., et. al., "Research on Control of Emissions from Bessemer
Converters" J.A.P.C.A.. 11(3) 103-13, March 1961.
5. Hammond, W. F., et al., "Steel Manufacturing Processes", in Air Pollu-
tion Engineering Manual, 999 AP-40, U.S.D. H. E. W., 1967.
6. Fairbridge, R. W., ed., The Encyclopedia of Geochemistry and Environ-
mental Sciences Series, Vol. IVA, Van Nostrand Reinhold Co., N.Y., 1972.
7. Varga, J., et. al., A Systems Analysis Study of the Integrated Iron and
Steel Industry, Battelle Memorial Institute, Columbus, Ohio, Report to
N.A.P.C.A., U.S. Dept. of Health, Education and Welfare, 15 May 1969.
(PB 184 577)
8. Kearney, A.T., and Co., Systems Analysis of Emissions and Emissions
Control in the Iron Foundry Industry, 3 Volumes, Chicago, 111., Report
to E.P.A., Contract No. CPA 22-69-106, February 1971 (PB 198 348).
9. Abernathy, R.F., and Gibson, F.H., Rare Elements in Coal, U. S. Bureau
of Mines circular No. 8163, 1963.
10. Gerstle, R.W., et al., "Air Pollution Emissions from Coal-Fired Power
Plants", Report No. 2, J.A.P.C.A.. 15(2)59-64, February.
11. Cuffe, S.T., et. al., "Emissions from Coal-Fired Power Plants, A Compre-
hensive Summary," N.A.P.C.A., U.S. Dept. of H.E.W., 1967 (PB 174 708).
12. Walsh, R. T., "Gaseous and Liquid Fuels", in Air Pollution Engineering
Manual, 999 AP-40, U.S. D. H.E.W., 1967.
13. Smith, W. S., Atmospheric Emissions from Fuel Oil Combustion, 999 AP-2,
U.S. D. H.E.W., 1962.
14. Anon., "Gold, Silver Content Seen at $14 per Ton", Solid Wastes Manage-
ment, Refuse Removal Journal, 11^:78, May 1968.
15. Wilson, E.B., and Akers, D.J., "Chemical and Physical Characterization
of Metropolitan Incinerator Refuse and Fly Ash", Second Mineral Waste
Utilization Symposium, Chicago, U.S. Bureau of Mines, March 1970.
16. Ewell, T.W., and Piper, J., "Design of New Silver-Recovery Incinerator",
A.S.M.E., New York, Incinerator Div., Proc. National Incinerator Conf.,
Cincinnati, Ohio, 1970.
17. Davis, W.E., National Inventory of Sources and Emissions: Barium, Boron,
Copper, and Zinc, Section III, Copper,, Report to EPA Office of Air
Programs, Contract No. 68-02-0100, April, 1972.
34
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18. Ibid., Section V, Zinc, May 1972.
19. Butts, A., and Coxe, C.D., Silver: Economics, Metallurgy, and Use,
Van Nostrand, 1967.
20. Charles River Associates, Inc., Economic Analysis of the Silver Industry,
Report to the General Services Admin., Contract No. GS-OO-DS-(P)-85005,
Sept. 1969. (PB 191 464)
21. Levy, A., et al., A Field Investigation of Emissions From Fuel Oil
Combustion for Space Heating, report by Battelle Institute, Columbus,
Ohio, to American Petroleum Institute, API Proj. SS-5, 1 Nov. 1971.
22. EPA Source Test Reports. From analysis of selected test reports,
emission factors and/or particulate analysis data were obtained to
supplement the data found in the literature.
23. Lehmden, D.J., Jungers, R.H., and Lee, R.E., The Determination of Trace
Elements in Coal, Fly Ash, Fuel Oil, and Gasoline, Part I, presented
at the American Chemical Soc. Mtg., Dallas, Texas, April 1973.
24. National Emissions Data System (NEDS) information, based on reports
made by individual plants. Only reliability code (1) and (2) data
is used in the present study. Information furnished by EPA.
25. American Iron and Steel Institute, "Iron and Steel Producing and
Finishing Works of the U.S.", in Directory of I & S Works of the
U.S. and Canada, 1970.
26. Arthur D. Little, Inc., Cambridge, Mass., Systems Study of Air Pol-
lution from Municipal Incinerators, 1970.
27. American Petroleum Institute, "Total Sales of Residual Fuel Oils (Ail
Uses) by States, 1934-1969", Petroleum Facts and Figures, 1971.
28. Pit and Quarry Publications, Inc., Chicago, 111., Portland Cement
Plants, (map), 1969.
29. Bureau of Census, U.S. Dept. of Commerce, Statistical Abstracts of the
U.S.
30. Perry's Chemical Engineer Handbook, 4th Edition, McGraw-Hill, New
York, 1963.
31. A.G. McKee and Co., San Francisco, Calif., Systems Study for Control
of Emissions, Primary Non-ferrous Smelting Industry, 1969.
32. Vandegrift, A.E., et al., Particulate Pollutant System Study, Vol. Ill,
Handbook of Emission Properties, EPA Contract No. CPA 22-69-104.
35
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
* 1 PKPORT NO.
EPA-45n/3-74-011
3. RECIPIENT'S ACCESSION-NO.
p 1. ri TLE AND SUBTITLE
National Emissions Inventory of Sources and
Emissions of Silver
5. REPORT DATE
May 1973
6. PERFORMING ORGANIZATION CODE
AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
^FORMING ORGANIZATION NAME AND ADDRESS
GCA Corporation
GCA Technology Division
Bedford, Massachusetts 01730
10. PROGRAM ELEMENT NO.
2AE132
11. CONTRACT/GRANT NO.
68-02-0601
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Protection Agency
Research Triangle Park, N. C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
A national inventory of the sources and emissions of the element silver
was conducted. All major sources of silver-containing emissions were iden-
tified and their silver emissions into the atmosphere estimated. Also, a
method for updating the results of the study every two years was recommended.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Silver
Air Pollution
Emission
Inventories
Sources
b.lDENTIFIERS/OPEN ENDED TERMS C. COS AT I Field/Group
STATEMENT
19. SECURITY CLASS (ThisReport)
21. NO. OF PAGES
Release Unlimited
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
36
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