EPA-4 50/3-74-009
May 1973
NATIONAL EMISSIONS
INVENTORY
OF SOURCES
AND EMISSIONS
OF
MOLYBDENUM
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-450/3-74-009
NATIONAL EMISSIONS INVENTORY
OF
SOURCES AND EMISSIONS
OF
MOLYBDENUM
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
U.S. Environmental Pr^'' ^' R'
Region 5, Library ^
77 West Jackson i'-' ,-'.•• •~':;or
Chicago, IL 606C-V-. .j
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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-450/3T?4-009
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TABLE OF CONTENTS
SECTION TITLE . PAGE
ACKNOWLEDGEMENT V
ABSTRACT vi
I INTRODUCTION 1
A. PURPOSE AND SCOPE 1
B. CONCLUSIONS 2
II OVERALL U.S. MATERIAL FLOW CHART FOR MOLYBDENUM -
1970 4
A. U.S. PRODUCTION AND ORE PROCESSING 4
B. IMPORTS AND EXPORTS OF MOLYBDENUM CONCENTRATE 4
C. GOVERNMENT AND INDUSTRIAL STOCKPILE CHANGES 4
D. METALLURGICAL USES 4
E. CHEMICAL USES 6
III SOURCES AND ESTIMATES OF MOLYBDENUM-CONTAINING
EMISSIONS 7
A. DATA PRESENTATION AND ACCURACY 7
B. DEVELOPMENT OF EMISSIONS ESTIMATES - 1970 12
C. SUMMARY OF PRINCIPAL EMISSIONS 17
IV REGIONAL DISTRIBUTION OF PRINCIPAL SOURCES AND
EMISSIONS 18
V NATURE OF EMISSIONS 21
VI UPDATING OF EMISSIONS ESTIMATES 25
A. VERIFICATION OF CURRENT ESTIMATES 25
B. PERIODIC REVIEW OF ESTIMATES 25
REFERENCES 27
111
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LIST OF TABLES AND FIGURES
TABLE No. TITLE PAGE
1 SOURCES AND ESTIMATES OF MOLYBDENUM-
CONTAINING EMISSIONS 8
2 SUMMARY OF PRINCIPAL SOURCES AND
EMISSIONS OF MOLYBDENUM 17
3 REGIONAL DISTRIBUTION OF PRINCIPAL
SOURCES AND EMISSIONS 20
4 PHYSICAL PROPERTIES OF MOLYBDENUM
AND COMPOUNDS 21
Figure No.
1 MOLYBDENUM MATERIALS FLOW - 1970
IV
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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. Andrew Kulis,
Commodity Specialist, Bureau of Mines, who provided significant
technical inputs to this program.
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ABSTRACT
A national inventory of the sources and emissions of the
element molybdenum was conducted. The study included the preparation
of an overall material flow chart depicting the quantities of moly-
bdenum moving from sources of mining and importation through all
processing and reprocessing steps to ultimate use and final disposition.
All major sources of molybdenum-containing emissions were identified
and their molybdenum emissions into the atmosphere estimated. A
regional breakdown of these sources and their emissions was also
provided. The physical and chemical nature of the molybdenum-containing
emissions was delineated to the extent that information was available,
and a methodology was recommended for updating the results of the study
every two years.
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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 molyb-
denum. The purpose of the study was to define as accurately as pos-
sible, based on existing and available published and unpublished infor-
mation, the levels, nature and sources of molybdenum containing emis-
sions 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 molybdenum
moving from sources of mining and impor-
tation, through all processing and
reprocessing steps to ultimate use and
final disposition as far as the move-
ments can be treated.
Identify all major potential molybdenum
containing emission sources, and esti-
mate the total quantity of molybdenum
emitted to the atmosphere from each
source. Emission factors, level, and
types of air pollution control will
also be provided for each of these
sources to the extent that available
information permits.
. Define those sources which contribute
at least 80 percent of the total emis-
sions of molybdenum.
Provide a regional breakdown of these
major sources and their emissions.
. Present the nature of the molybdenum con-
taining emissions for each of these major
sources including a delineation of their
physical and chemical form and particle
size distribution to the extent that
information is available.
Provide recommendations as to a methodol-
ogy for updating the results of this
study every two years.
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B. CONCLUSIONS
1. Material Flow
Based on all available data, 34,821 tons of
molybdenum were consumed in the U.S. in 1970. The sources of
molybdenum were imports, releases from government stockpiles, and
domestic mining.
A major portion of the molybdenum ore concentrate was
converted to the oxide. Most of the oxide was consumed in making steel
and other alloys, with only a small portion being used for pigments,
catalysts, lubricants, and other miscellaneous products.
2- Principal Emission Sources
Two thirds of the estimated atmospheric emissions of
molybdenum are not associated with the molybdenum industry, but result
from the combustion of coal. Coal is far the largest source of
emissions. Despite a relatively small concentration of molybdenum in
coal, there was sufficient quantity of coal burned to produce about 610
tons of emitted molybdenum in 1970.
Within the molybdenum industry, several sources were
identified as being of approximately similar consequence: the mining of
ore; the production of ferromolybdenum; the production of steel con-
taining molybdenum as an alloying ingredient; and the roasting of ore
concentrate. Together these are estimated to produce about 29% of all
U. S. emissions.
3. Regional Emissions
The region of the U. S. in which most of the molybdenum
is estimated to be emitted is Region 5* (Ohio and vicinity). This is
partly due to the large emission from coal combustion. In the absence
of this, the molybdenum industry alone would produce the largest
total emission in Region 9, princpally Arizona, based on certain
assumptions set forth in Chapter IV.
*See page 18 for a list of regions.
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4. Nature of Emissions
Based on the physical properties of molybdenum
and its compounds, most of its emissions are estimated to be in
particulate form ranging from submicrometer to micrometer sized
particles. The chemical forms are believed to be largely simple oxides
and sulphides, with little elemental molybdenum being emitted.
5. Degree of Control
The overall level of control of molybdenum emission is
estimated to have been about 86 percent in 1970. The degree of control
would have been greater, but for the relatively poor control of coal
flyash (82 percent estimated), which sharply lowered the overall
average.
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11' OVERALL U. S. MATERIAL FLOW CHART FOR MOLYBDENUM - 1970
The molybdenum industry uses mining, co-product, and import
sources of molybdenum disulphide concentrate. This material, for the
most part, is roasted to molybdenum oxide, most of which is consumed in
steelmaking and other metallurgical processes. The industry is
described in more detail below and in Section III. Figure 1* presents
a flow diagram depicting the total quantities of molybdenum products
moving from sources through the processing and reprocessing steps to
ultimate use and final disposition.
A. U. S. PRODUCTION AND ORE PROCESSING
Molybdenum is produced in the U. S. both as a primary yield
and as a co-product yield from copper, tungsten, and uranium operations.
Of the 55,676 tons of molybdenum produced from these sources in 1970,
68 percent was as a primary yield. The primary ore contains typically
only 0.3 percent molybdenum disulphide, and thus requires extensive
beneficiating operations including flotation. Similar beneficiating
processes are used in producing co-product concentrates.(1)
B. IMPORTS AND EXPORTS OF MOLYBDENUM CONCENTRATE
Due to high import tariffs for molybdenum products and a
self-sufficiency in production, only 12 tons were imported into the
United States in 1970. Total exports of ore and concentrates totaled
27,800 tons of contained molybdenum.^
C. GOVERNMENT AND INDUSTRIAL STOCKPILES CHANGES
The Bureau of Mines reports that inventories of industrial
stocks increased by 658 tons in 1970. GCA, however, in their prepara-
tion of Figure 1, estimates a decrease of 4,533 tons in industrial
stockpiles in order to supply the necessary raw material for reported
consumption levels. The National Government Stockpile was reduced by
2,400 tons in 1970.^
*Note. Data in Figure 1 and in this section are left unrounded, for
purposes of information control. On the average, the typical
statistic is accurate to within 10%, in the opinion of the
investigators.
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D. METALLURGICAL USES
Almost all the concentrate is roasted to the oxide except
for a very minimal amount which remains as the sulfide and is purified
for use as a lubricant. The principal primary products from the
roasted concentrate used by the metallurgical industries are
molybdenum oxide and ferromolybdenum. A small amount of metal power,
about 3% of total, was used predominantly in mill products. '
Almost 90 percent of exports of primary products (8,365 tons) were
roasted concentrate or molybdenum oxide. The domestic use by the
metallurgical industry totals 20,806, tons or 91.7 percent of domestic
molybdenum/ ' Of this, steel production is by far the major
consumer (71 percent).
E. CHEMICAL USES
Although the principal primary product used in the chemical
industries is molybdic oxide, ammonium and sodium molybdates are used
in the production of pigments, catalysts and other miscellaneous
chemicals. In 1970, 1,342 tons of molybdic oxide, 805 tons of
ammonium molybdate and 343 tons of sodium molybdate were used to
produce 529 tons of pigments, 906 tons of catalysts, and 426 tons of
other products (mainly ceramics). ' All weights expressed are in terms
of contained molybdenum content.
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HI. SOURCES AND ESTIMATES OF MOLYBDENUM - 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
columns 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
category varying by more than an order of magnitude from the value
presented. 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 Factors":
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
accuracy is not stated.
D: Below Average
This emission factor is based on
engineering estimates made by know-
ledgeable personnel.
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TABLE I
SOURCES AND ESTIMATES OF MOLYBDENUM-CONTAINING EMISSIONS
Source
MINING
Open Pit
Underground
Copper Open Pit
BENEFICIATION
ROASTING
METALLURGICAL
Ferromolybdenum-
Electric Arc
Molybdenum Metal
CHEMICAL PRODUCTION
STEEL & ALLOY PRODUC-
TION
Steel
Cast Iron
Super Alloys
Alloys
Mill Products
Particulate
Emission
Factor ,
(Ib/ton)
10
0.5
10
52
100
200
2000
Nil
25
15
200
25
0.5
(kg/kgxlO )
15
0.25
5
26
50
100
1000
Nil
12.5
7.5
100
12.5
0.25
Reliability
Code
D
D
D
D
C
D
B
C
C
C
C
C
Production
Level
(tons/yr)
13,000
25,986
16,690
34,821
34,821
6,221
803
1,148
14,712
1,958
1,254
395
858
% Mo in
Emissions
*
*
*
*
*
*
*
*
*
*
*
*
*
Mo
Emissions
Before
Controls
(tons/yr)
65
6
83
906
1,740
622
803
Nil
184
15
126
5
0
Estimatec
Level of
Emissions
Control
0
0
0
98. 8Z
98%
90%
99.9%
Nil
787.
997.
787.
78%
-
j Mo
Emissions
Following
Controls
(tons/yr)
65
6
83
11
35
62
1.0
Nil
41
0.1
28
1
0
00
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TABLE I (cont.)
Source
NON-METALLURGICAL USES
INADVERTENT SOURCES
Coal burning
Oil combustion
Mineral Processing
TOTALS
Uncontrolled
Particulate
Emission
Factor ,
2
NA
HA
NA
1
NA
NA
NA
Reliability
Code
D
Production
Level
(tons/Yr)
1,861
33,800,000
(uncontrolled
emissions)
287,000
(uncontrolled
emissions)
6.9 x 106
(controlled
emissions)
% Mo in
Emiss ions
*
.01 (B)
.01 (C)
.00023 (D)
Mo
Emissions
Before
Controls
(tons/yr)
2
3,380
29
16
7,179
Estimated
Level of
Emissions
Control
0
82%
0
NA
86%
Mo
Jmissions
Following
Controls
(tons/yr)
2
610
29
16
990
NOTE: NA = Not Applicable
Emission factor multiplier equal to tons of Mo processed annually
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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
Ibs 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%.
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
reliability 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
million 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 III.
4. Level of Emissions Before Control
The values in this column are derived by multiplying
the values in columns 1-3. 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
category is based on two factors:
the portion of the processes which
are under control
the typical degree of control
For example if 60% of vertical roasters have some type of particulate
emission control, and these include both scrubbers and precipitators
10
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such that the apparent weighted average efficiency of control is 85%,
the overall control effectiveness is estimated to be 60 x 85 = 51%.
The accuracy of control efficiency data varies with the
degree of control. For a wet scrubber operating at 80% efficiency, i.e.
passing 20% material, the actual emission may safely be assumed to be
between 15 and 25% because of the relative ease of making determinations
at this level. Thus the emissions after control may be assumed to be
accurate within + 5/20 or 25%. On the other hand, for a baghouse
reported as being 99% efficient, or passing only 1% of the material, the
actual emission may vary from 0.5 to perhaps 2% because it is
frequently 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
reported overall level of particulate control applies equally to all
molybdenum-containing particles, independent of size, resistance and
other important collection parameters. This assumption results in a
correct estimate of molybdenum emissions after control when the parti-
culate is chemically homogenious, i.e. molybdenum is contained in the
same concentration in all particles. If however, molybdenum is con-
centrated in certain particles and in addition the efficiency of the
control equipment is not uniform for all particles, then the
utilization of an average control level is less valid for calculating
molybdenum emissions after control. Data on the preferential control
of molybdenum-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 emission estimates within
+ 25 percent.
6. Level of Metal Emissions After Control
The values in this column are derived by multiplying
11
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the values in Column 4 by the value (100 minus estimated Level of
Control).
B. DEVELOPMENT OF EMISSIONS ESTIMATES - 1970
Estimates of particulate emissions containing molybdenum
in the U. S. atmosphere are developed in the following paragraphs and in
Table 1. The Table indicates that a substantial portion of the
emissions is due to inadvertent sources, i.e. those not directly a
part of the molybdenum industry.
Molybdenum ore is presently recovered from mines as a
major ore and as a byproduct or co-product from copper, tungsten and
uranium mining. The only significant sources of ore are the
molybdenum and copper mines/ >3^ The ore is presently recovered by
both open-pit and underground methods. The portion of production from
each method shifts significantly from year to year and present trends
indicate an increase in open-pit excavation in the future.
In 1970, of the 55,676 tons of molybdenum contained in
concentrate mined, 24 percent (13,000 tons) is estimated to have come
from non-copper open pit mines, 46 percent (25,986 tons) from underground
molybdenum mines, and 30 percent (16,690 tons) from open pit copper
mining. The emission factors used in Table 1 are based on emission
factors for other similar operations^ The resulting estimate is that
154 tons of molybdenum were released by mining of all types in 1970.
2. Beneficiation Operation
Due to the low concentrations of MoS in the ore
(0.37o average), beneficiation to a concentrate is necessary before
comsumption. The operations involved include crushing, grinding, classi-
fication, flotation, filtration and drying. Recovery from copper ore
is generally of the same nature; however, different flotation agents are
used due to the necessity of also maximizing the recovery of the copper.
Recovery from ore generally runs between 70 and 90 percent although
recovery from copper ore has been reported as low as 50 percent. The
12
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concentrate itself is about 98 percent MoS^ Although no data were
found on emissions from beneficiation, the general procedures are wet,
except for material handling, crushing, and drying. Emissions from
handling and crushing are frequently estimated for other industries at
2 Ibs/ton of feed and, in the case of molybdenum, are estimated to be
controlled at 95 percent.(4) The same identical emission factor can be
reasoned to yield Ibs. of molybdenum emitted per ton of molybdenum
produced, assuming the emitted particles contain the same concentration
as the feed. Emissions from drying processes in other industries are
generally on the order of 50 Ibs. per ton of feed and are typically
well controlled at about 99 percent.(4) The resulting emissions for
handling and crushing are 50 tons and for drying 1240 tons. After con-
trol, emissions are estimated at 15 tons/yr.
3. Roasting Concentrate
Virtually all MoS concentrate is roasted to the oxide
before consumption. A minor amount is purified and used as a lubricant,
but neither the quantity of material not the estimated emissions are
significant. All roasting in 1970 was accomplished by multiple hearth
Nichols-Herschoff furnaces, although more recently these are being
replaced by fluid bed roasters in the copper industry. The latter
method will be expected to generate more emissions until the point of
control.
An emission factor of 168 Ibs. of particulate per ton of
metal is reported for multiple hearth furnaces in the copper
industry(4) which is equivalent to 100 Ibs. of molybdenum per ton of
molybdenum, assuming the particulate is MoS2- Since approximately
34,821 tons of molybdenum in concentrate form was roasted, this gives
an emission of 1,740 tons before control. Reference (4) indicates a
control effectiveness of 85 percent for copper roasting. However,
discussion with the molybdenum industry suggests that a better
estimate of molybdenum roasting control is 98 percent, producing a net
emission of 35 tons.
13
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4. Ferromolybdenum Production
Production of ferromolybdenum amounted to approximately
6,221 tons in 1970, or about 18 percent of the molybdenum consumption.
Molybdenum oxide is the raw material for making ferromolybdenum. Two
processes are in use, electric arc furnaces, and a silico-thermite pro-
cess. For the former, emissions factors and controls applicable to a
variety of ferroalloy production processes indicate typical values of
200 Ibs/ton and 80 percent control efficiency.(4^ In the four years
since these control estimates were made, however, we believe that the
level of control for ferromolybdenum production has improved to at least
90 percent. For the silico-thermite process, no information was found.
It is suspected that the process generates substantially more emission
initially but is enclosed to a greater extent and under better emission
control. It is assumed that 200 Ibs/ton and 90 percent control apply
effectively to the entire ferromolybdenum production, giving an
estimated emission of 70 tons after control.
Slag from some ferromolybdenum furnaces is crushed, a
process which produces some emissions. In one instance, the material
is crushed to 320 mesh (about 50 microns) with a substantial portion of
the material finer than this. The material is dry, and is used for
landfill. The molybdenum content of slag, and emissions factors, were
not available. This source is assumed to be of negligible consequence
relative to the major sources listed in Table 1.
5. Molybdenum Metal Production
About 2.3 percent of the roasted concentrate was used to
produce metallic molybdenum. Two processes were used, the more common
being the reduction of MoS2 in a hydrogen atmosphere. The molybdenum
sublimes and is carefully collected as a fine power. It is subsequently
sintered in various forms for ultimate use. The second process pro-
duced a higher purity metal, by reducing ammonium molybdate in an
electric furnace. An emission estimate was made by assuming that 100
percent of the material is emitted initially, and that control is an
14
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excellent 99.9 percent. This results in an estimated 1.0 ton of
molybdenum emitted to the atmosphere.
6. Chemical Molybdates Production
About 3 percent of the roasted concentrate was used to
produce compounds of molybdenum. The production of sodium molybdate and
ammonium molybdate is accomplished by dissolving molybdic oxide in
either sodium hydroxide or ammonium hydroxide, precipitation, recrystal-
lization and drying. Calcium molybdate is produced by mixing pulverized
limestone with molybdic oxide to produce a product analyzing 46.3 to
46.6 percent molybdenum. Mo emissions primarily would be from handling,
and are assumed to be negligible.
7. Steel and Alloy Production
About 57 percent of the U. S. molybdenum was consumed
in the production of steel, cast iron, and various alloys (Figure 1).
The emissions from these processes have apparently not been analyzed in
in any detail for molybdenum content, however. One approach to making
estimates is to assume that the emissions will contain the same per-
centage of molybdenum as the feed. This is partly justified by the
fact that the vaporization temperature of molybdenum is at least 3700 C,
far above the operating temperature of all types of furnaces with the
possible exception of an electric arc furnace. This means that
molybdenum should not be concentrated in the emission particulate.
There is no apparent reason for the particulate to be low in molybdenum
content, either. Therefore, it is assumed that the emission factor of
pounds of molybdenum per tons of molybdenum feed, is the same as the
emission factor of pounds of particulate per ton of steel, alloy, etc.,
produced. These are given in Table 1 along with control effectiveness
factors for the various processes. The total emission estimate after
control is 70 tons, of which steels and super alloys are estimated to
be responsible for the greatest proportion as shown in Table 1.
8. Non-Metallurgical Uses
About 8 percent of all molybdendum is used for pigments ,
15
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catalysts, and other chemical and ceramic purposes. Emisssions from
these sources are believed to be almost entirely from material
handling. Using a typical emission factor of 2 Ibs/ton, the emissions
are shown in Table 1 to be negligible.
9. Inadvertent Sources
a. Coal Combustion
Coal consumption in 1970 amounted to about
(12)
517,000,000 tons. The particulate generated has been estimated at
33,800,000 tons of which 82% was controlled.^ The concentration of
molybdenum in coal ash has been reported as 0.011 percent (73 samples of
Appalachian coal ash, spectrographic analyses),^ as 0.003 percent
(13 samples of coal ash, semi quant a tive determinations)^ and as about
.002 percent (17 samples of flyash).(8' The weighted average is about
0.01 percent, resulting in a net molybdenum emission after control of
610 tons.
b. Oil Combustion
The concentration of molybdenum in residual oil ash
has been reported as 0.00093 (at least 3 samples of ash)^ and as
0.025 (two samples of ash), giving an average of about 0.01 percent,
the same as for coal. (See also Reference 11 for variations.) An
estimated 287,000 tons of oil ash particulate is generated^ which is
practically not controlled. This results is an estimate of about 29
tons of molybdenum released to the atmosphere.
c. Non-Ferrous Minerals
A large quantity of rock, cement, fertilizer, clay,
and lime dust is released into the atmosphere in the U. S., estimated
to be 6,900,000 tons after control. No data on the concentration of
molybdenum in these dusts has been found, however. The earth's crust
is estimated to contain about 2.3 ppm of molybdenum/11^ If this con-
centration applies to the mineral emission above, 16 tons of molybdenum
would be the estimated emission. This first approximation is included
in Table 1.
16
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C. SUMMARY OF PRINCIPAL EMISSIONS
Table 2 summarizes the major sources and estimated emissions
of molybdenum, as developed in Table 1 and accompanying discussion.
The sources are grouped in two categories; those directly originating
with the molybdenum industry or industries using molybdenum, and those
having no relationship to the molybdenum industry, called inadvertent
sources. Due to the content of molybdenum in coal, the latter
category is larger.
These prinicpal estimates are examined further in later
sections of this report.
TABLE 2
SUMMARY OF PRINCIPAL SOURCES AND EMISSIONS OF MOLYBDENUM
Inadvertant Sources
Coal combustion
Molybdenum Industry Sources
Mining, copper open pit
Mining, Molybdenum open pit
Ferromolybdenum production
Steel production using Molybdenum
Roasting concentrate
U.S. Tons /year of Mo.
610
83
65
62
41
35
% of U.S.
61.6
8.4
6.6
6.3
4.1
3.5
90.5
17
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IV. REGIONAL DISTRIBUTION OF PRINCIPAL SOURCES AND EMISSIONS
For purpose of showing geographical distribution, the U.S. was
divided into ten regions identical to the Regional Branches of EPA:
Region State
I Conn., Me., Mass., N.H., R.I., Vt.
II N.J., N.Y., P.R., V.I.
HI Del., Md., Pa., Va., W.Va., B.C.
IV Ala., Fla., Ga., Ky., Miss., N.C., S.C., Tenn.
V 111., Ind., Mich., Minn., Ohio, Wis.
VI Ark., La., N.M., Okla., Texas
VII Iowa, Kans., Mo., Nebr.
VHI Colo., Mont., N. Dak., S. Dak., Utah, Wyo.
IX Ariz., Calif., Nev., Hawaii and the So. Pacific
X Alaska, Idaho, Oreg., Wash.
Emissions from the principal emission sources listed in Table 2 are
distributed among these ten regions, as shown in Table 3. Also, the
number of plants producing the emissions is shown in the table when such
information was available.
The accuracy of the distribution by region varies with the
category. The number of plants per category varied from 1 to several
thousand in this study. When the number of plants was less than
100, an attempt was made to identify each plant and plant location, and
include 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 emissions were distributed by
the number of plants in each region. If the number of plants was very
small or there was reason to believe that certain plants were larger or
produced more emission, distributions were weighted accordingly.
18
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When the estimated number of plants was greater than 100, and the
distribution of plants was not known, the regional 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 emission estimates listed in Table 2 are distributed in Table 3
on the following basis:
Coal combustion: proportional to coal shipped
by state of destination
Mining, copper pit: 14 mines, assumed to have
equal emissions
Mining, molybdenum open pit: two mines, assumed
to have equal emissions
Ferromolybdenum: five companies at five locations,
assumed to have equal emissions
Steel production: 41 companies producing
molybdenum alloys, and stainless and tool
steels containing molybdenum; assumed to
have equal emissions
Roasting concentrate: nine companies at nine
locations, assumed to have equal emissions.
The overall distribution of emissions by region is shown in Table
3, along with the distribution of plant sources. Region 5 is estimated
to have the largest total emission of molybdenum, followed by Region 3
(approximately that area bound by Pennsylvania, Virginia, and Illinois).
However, this appearance is partly due to the large amount of molybdenum
emitted with coal flyash. In the absence of this large source, Region
9 (mostly in Arizona) would be estimated to produce the largest emission,
with Region 3 next.
Considering the geographical areas of these regions, Region 3
has the most concentrated emissions, with .0019 tons of molybdenum
emitted to the atmosphere per square mile-yr.
19
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S3
o
TABLE 3
REGIONAL DISTRIBUTION OF PRINCIPAL SOURCES AND EMISSIONS
r
Principal Sources
Inadvertent
Sources
Coal Burning
Molybdenum
Industry Sources
Mining, Copper
Mining, Molyb.
Ferromolyb.
Steel Prod'n
Roasting
TOTAL
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V. NATURE OF EMISSIONS
Very little data describing the physical or chemical properties of
the molybdenum-containing participate were obtained. Some deductions
regarding the probable character of the emissions may be drawn from the
physical properties of molybdenum and its compounds which are presented in
Table 4 and Figure 2.
TABLE 4
PHYSICAL PROPERTIES OF MOLYBDENUM AND COMPOUNDS
(*)
1
Melting Point
Boiling Point
Density
Atomic Weight
Heat of Vaporization
Hardness (Std.
Miner o logy Scale)
Mo lybdenum
2610 °C
5560 °C
3
10. 2 grams /cm
95.94 a.w.u.
128 kg-cal/g-atom
--
Mo^0?
(sublimes)
1155 °C
--
240 a.w.u.
--
™ ™
MoS0
(sublimes)
450 °C
160 a.w.u.
— —
. 2
* Perry's Chemical Engineers Handbook, 4th Edn, Table 3-169 (Ref. 17)
For example, flyash is the result of combustion temperatures in
the vicinity of 1700°C. The metal molybdenum begins to oxidize above
20°C in air, and at 600°C oxidizes rapidly to Mo03 especially in the
presence of SO-. Thus it is doubtful that any molybdenum in elemental
form is released in the combustion of coal. The oxide and the
sulphide forms sublime well below the combustion temperature of coal,
and consequently may be expected to be released either as extremely
small particles or molecules of oxide or sulphide; or as condensed thin
layers on the surface of other larger flyash particles.
Molybdenum in sulphide form is mined in extremely small concen-
trations. Dust emitted in mining is expected to consist of the
21
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FIGURE 2
VAPOR PRESSURE OF
MOLYBDENUM IN VACUUM
versus
TEMPERATURE
i:8 3.0 2.2 2.4 2.6 2.8 3.0
. V' I I 't' " I ' «• Temperature
* *- 2.« 2.25 2.5 2.75 T . .3
CxlO
APPLICATIONS OF MOLYBDENUM
POWDER
(1) Spray metallizing
(2) Glass to ceramic seals
(3) Alloy additions
(4) Specialized melting techniques
PRESSED AND SINTERED INGOTS
(1) Machined parts
(2) Forged parts
(3) Consumable vacuum arc-cast
electrodes
(4) Contact disks
(5) Alloy additions
(6) Special forms such as rings,
boats, etc.
SHEET
(1) Heat radiation shields
(2) Arch supports for high-tempera-
ture furnaces
(3) Boats for heat treating and
process equipment
(4) Stamped, deep drawn and spun
parts, anodes and other
elements for electronic tubes
(5) Stampings for semi-conductor
application
(6) Aircraft and missile structural
and surface parts
(7) Electronic tube cathode sleeves
ROD
(1) Electronic tube leads - where glass
to metal vacuum seal required
(2) Internal supports for vacuum tubes
(3) Contact disks for "make or break
circuits"
(4) Machined parts
(5) Welding electrodes
(6) Electrodes and stirring rods in
glass manufacture
WIRE
(1) Grid and internal supports for
electronic tubes
(2) Support parts in lamps (hook and
anchor wire)
(3) Mandrel for winding tungsten coils
(4) Wire cloth
(5) Furnace heating elements
(6) Thermocouples
(7) Spray bonding bearing and heat
resistant surfaces
(8) Electrode wire for glass to metal
seals
22
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common rock with included or attached MoS2> Since the sulphide is soft,
it is not expected to fracture to fine particles. Possibly for this
reason most of the dust emitted in mining will consist of rock, with
most of the MoS2 remaining behind in larger particles.
In the production of ferromolybdenum, and in the production of
steel alloys containing molybdenum, the comments made above in discussing
the combustion of coal are partly applicable. However, oxygen and sul-
phurous gases are relatively deficient in these metallurgical operations,
and molybdenum is less apt to oxidize and then sublime as a fume. It
is more probable that particulate emitted from these processes will
contain entrapped molybdenum in metallic form. The molybdenum will
partially oxidize following emission, and remain relatively stable as
an oxide.
Roasting operations, at temperatures up to about 700 C, must
produce some MoS2 fume since the concentrate material begins to sublime
at about 450°C. Probably a portion of these fumes will oxidize
following emission. Thus, particulate emissions from roasting
operations are expected to consist of submicrometer particles in both
the sulphide and oxide forms.
One other source of emissions, developed in Table 1 but excluded in
the list of principal sources, is oil burning, which produces submicro-
meter and micrometer sized particulate. A substantial portion of the
nation's sub-micrometer particulate containing molybdenum may be expected
to originate in the combustion of residual oils.
Submicrometer particulate and particles up to a few micrometers
in diameter may be expected to travel considerable distances from the
source before being deposited or washed out of the air by natural pro-
cesses. Particles of one or two micrometers in diameter will behave
almost as gas molecules in their mixing and traveling. Thus, one would
expect to find molybdenum widespread as a background constituent of air.
(19)
The air in three cities has been tested for molybdenum content.
q
The average concentration was 0.013 micrograms/m . The particulate
containing the molybdenum had an average diameter of 1.16 micrometers,
23
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and the distribution of sizes followed a normal aerosol distribution.
About 70 percent of the particulate was contained in particles less than
2 micrometers.
Molybdenum may be a moderately toxic material, although, at present,
the evidence is not well developed. It is reported that cattle in the
vicinity of a western molybdenum plant were recently found to be
suffering from an unusual ailment, and a cause-and-effect relationship
was implied. Flyash which explicitly contained molybdenum was found
to be a useful soil additive in growing alafalfa, although the benefit
was more likely the change of pH in the soil than due to the molybdenum^
24
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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. Verify that the principal molybdenum processes, the
roasting of concentrate and ferromolybdenum production, are adequately
represented by these estimates. If possible, emissions data should be
obtained from the molybdenum industry rather than by extrapolation
from other processes believed to be similar because of the individual
nature of molybdenum and its compounds.
2. The production of steel alloys containing molybdenum
as an alloying ingredient should be investigated to ascertain that
the emissions of molybdenum are in fact proportional to the feed of
molybdenum. Steel production is a potentially large source of
molybdenum emission, if the emission factor should in fact be larger
than assumed.
3. Crushed rock, lime, clay, fertilizer, and cement dusts
are of sufficient quantity that even slight molybdenum content could be
significant. Typical analyses of these dusts should be made for moly-
bdenum content to verify that the content is in fact as low as assumed.
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 (4).
b. The Source Test Program, in which specific
individual plant emissions are measured. This information provides
25
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emission factors for specific examples of typical, industrial operations
and also provides some analyses of the particulate,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 con-
trol equipment in use, and the actual, or estimated, control efficiency.
The system may eventually be expanded to include description of the
emissions.
3. The molybdenum industry should be consulted for its
opinion and suggestions on the most recently published estimates. This
may be best accomplished by interviewing the Molybdenum 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) evironmental 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 problem of obtaining fresh information due to
the natural reluctance of the plants to discuss environmental problems.
However, data thus obtained 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.
26
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REFERENCES
1. Preprint from Minerals Yearbook, Molybdenum, U. S. Bureau of Mines,
Washington, D. C. (1971).
2. Mclnnis, Wilbur, Molybdenum: A Material Survey. U. S. Bureau of
Mines Information Circular IC7784, Washington, D. C. (1957).
3. Economic Analysis of the Molybdenum Industry, Charles River
Associates, Inc., Cambridge, Mass. (1967).
4. Vandegrift, A. D., et. aL, Particulate Pollutant Systems Study.
Vol I, II, III, Report by Midwest Research Institute, St. Louis,
Mo., to EPA, Contract No. CPA 22-69-104, May 1971.
5. Personal Communication with members of the Molybdenum Industry.
6. Zubovic, P., et. al., Distribution of Minor Elements in Coate of the
Appalachian Region. Geological Survey Bulletin No. 1117-C, U. S.
Bureau of Mines, Washington, D. C., 1966.
7. Kessler, et. a., Analysis of Trace Elements in Coal by Spark-
Source Mass Spectroscopy. Bulletin No. 7714, U. S. Bureau of Mines,
Washington, D. C., 1971 Approx.
8. Doran, J. W., and Martens, D. C. "Molybdenum Availability as
Influenced by Application of Fly Ash to Soil," J. of
Environmental Air Quality. 1 (2) 186 April-June 1972.
9. Levy, A., et. al., A Field Investigation of Emissions from Fuel Oil
Combustion for Space Heating, Report by Battelle Inst., Columbus,
Ohio to American Petroleum Institute, API Proj. SS-5, 1 Nov. 1971.
10. Smith, W. S., Atmospheric Emissions from Fuel Oil Combustion,
999 AP-2, U. S. Dept. of H. E. W., 1967.
11. Fairbridge, R. W., ed., The Encyclopedia of Geochemistry and
Environmental Sciences Series, Vol. IVA. Van Nostrand Reinhold Co.,
N. W., 1972.
12, Minerals Yearbook. U. S. Bureau of Mines, Washington, D. C., 1967
1968, 1969, and 1970.
13. Charles River Assosciates, Inc., Cambridge, Mass., Economic Analysis,
of the Silver Industry. Report to the General Services Administration
Wash., D. C. Contract No. GS-OO-DS (P)-85005, WA 68-22, Sept. 1969.
14. Gousseland, Pierre, Molybdenum, Engineering and Mining Journal,
p. 153-156 (March 1972).
27
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15. Personal Communication, Molybdenum Commodity Specialist, Division of
Non-ferrous Metals, U. S. Bureau of Mines, Washington, D. C., 1973.
16. Alloys Digest, a series of descriptions of individual products and
manufacturers, pub. since 1952, by Engineering Alloys Digest Inc
Upper Monclair, N. J. ''
17. Perry. R. H., ejL. al,, Perry's Chemical Engineers Handbook. 4th
Edition, McGraw Hill, Inc., New York, 1963.
18. Philips Elmet Corp., Lewiston, Maine, a brochure or report
containing descriptions of Molybdenum and Tungsten properties and
uses.
19. Lee, R. E., et. al., "Molybdenum Particle Sizes" in Environmental
Science and Technology 6. (12) 1025 Nov. 1972.
28
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA-450/3-74-009
2.
3. RECIPIENT'S ACCESSION-NO.
TITLE AND SUBTITLE
National Emissions Inventory of Sources and
Emissions of Molybdenum
REPORT DATE
May 1973
6. PERFORMING ORGANIZATION CODE
AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
PERFORMING ORGANIZATION NAME AND ADDRESS
GCA Corporation
GCA Technology Division
Bedford, Massachusetts 01730
10. 1
?AF132
11. CONTRACT/GRANT NO.
68-02-0601
2. SPONSORING AGENCY NAME AND ADDRESS
Environmental Protection Agency
Research Triangle Park, N. C. 27711
13. TYPE OF REPORT AND PERIOD
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A national inventory of the sources and emissions of the element molybdenum
was conducted. All major sources of molybdenum-containing emissions were iden-
tified and their molybdenum emissions into the atmosphere estimated. Also, a
method for updating the results of the study every two years was recommended.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
IDENTIFIERS/OPEN ENDED TERMS
COS AT I Field/Group
Molybdenum
Air Pollution
Emission
Inventories
Sources
13. DISTRIBUTION STATEMENT
Release Unlimited
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Unclassified
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