EPA 440/1-75/032
Group I, Fhiise II
r.
Development Document for Interim
Final Effluent Limitations. Guidelines
and
Proposed New Source Performance
Standards for the
INC
Segment of the
NONFERROUS METALS
MANUFACTURING
Point Source Category
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
FEBRUARY 1975
-------
EREATA PJ\GE
Primary Zinc Development Document
1. pp 3, 4, 129 and 134—change all pH ranges to read
"pH...Within the range 6.0 to 9.0" and delete Hg
from tables.
2. p 67, third paragraph, last line, delete "of the
discharge" and replace with "during liming and
settling.,"
3. p 124, last paragraph, 9th line, change "270 kkg"
to "222 kkg", change "50 kkg" to "41 kkg".
4. p 125,-top paragraph, 4th line, change "110 kkg"
to "91 kkg".
5. p 65, delete "Mercury" from table.
6. pp 70 and 71 delete last two paragraphs on p 70 and
first three on p 71.
7. p 132—delete first line.
-------
DEVELOPMENT DOCUMENT
for
PROPOSED EFFLUENT LIMITATIONS GUIDELINES
and
NEW SOURCE PERFORMANCE STANDARDS
for the
ZINC SEGMENT
of the
NONFERROUS METALS MANUFACTURING
POINT SOURCE CATEGORY
Russell E. Train
Administrator
James L. Agee
Assistant Administrator for
Water and Hazardous Materials
im
)n Agency
-------
DEVELOPMENT DOCUMENT
for
PROPOSED EFFLUENT LIMITATIONS GUIDELINES
and
NEW SOURCE PERFORMANCE STANDARDS
for the
ZINC SEGMENT
of the
NONFERROUS METALS MANUFACTURING
POINT SOURCE CATEGORY
Russell E. Train
Administrator
James L. Agee
Assistant Administrator for
Water and Hazardous Materials
«**»
Allen Cywin
Director, Effluent Guidelines Division
George S. Thompson, Jr.
Project Officer
November 1974
Effluent Guidelines Division
Office of Water and Hazardous Materials
U.S. Environmental Protection Agency
Washington, D.C. 20460
-------
t' 3. Environmanta! Protection Agency
-------
ABSTRACT
This document presents the findings of an extensive study of
the primary zinc industry by the Environmental Protection
Agency for the purpose of developing effluent limitations
guidelines and standards of performance, to implement
Sections 304, 306, and 307 of the Federal Water Pollution
Control Act, as amended.
Effluent limitations guidelines contained herein set forth
the degree of effluent reduction attainable through the
application of the best practicable control technology
currently available, and the application of the best
available technology economically achievable, which must be
achieved by existing point sources by July 1, 1977, and July
1, 1983, respectively. The standards of performance for new
sources - contained herein set forth the degree of effluent
reduction attainable through the application of the best
available demonstrated control technology, processes,
operating methods, or other alternatives.
The development of data and recommendations in this document
relates the waste water generated by the primary zinc
subcategory to the production of primary zinc at those
facilities defined by this subcategory.
Supporting data and rationale for development of the
proposed effluent limitations guidelines and standards of
performance are contained in this report.
111
-------
CONTENTS
Section
I CONCLUSIONS
II RECOMMENDATIONS
Best Practicable Control Technology
Currently Available
Best Available Technology Economically
Achievable 4
New Source Performance Standards 5
III INTRODUCTION 7
Purpose and Authority 7
Methods Used for Development of
Effluents Limitations Guidelines
and Standards of Performance 8
General Description of the Primary Zinc
Industry 9
IV INDUSTRY CATEGORIZATION 19
Introduction 19
Factors Considered 20
V WASTE CHARACTERIZATION 37
Introduction 37
Sources of Waste Water 37
Waste Water Characteristics 42
VI SELECTION OF POLLUTANT PARAMETERS 65
Introduction 55
Rationale for the Selection of Pollutant
Parameters 65
Rationale for the Rejection of Other Waste
Water Constituents as Pollutant Parameters 74
VII CONTROL AND TREATMENT TECHNOLOGY 81
Introduction 81
Current Control and Treatment Technology 81
Additional Treatment Technology 96
VIII COSTS, ENERGY, AND NONWATER QUALITY ASPECTS 101
Introduction 101
Basis for Cost Estimation 101
Economics of Present Control and
Treatment Practices 102
Economics of Additional Control and
Treatment Practices 116
Nonwater Quality Aspects 122
v
-------
CONTENTS (continued)
Section
IX BEST PRACTICABLE CONTROL TECHNOLOGY CURRENTLY
AVAILABLE—EFFLUENT LIMITATIONS GUIDELINES 127
Introduction 127
Industry Category and Waste Streams 128
Recommended Effluent Limitations 128
Identification of the Best Practicable
Control Technology Currently Available 129
Rationale for the Selection of Best
Practicable Control Technology
Currently Available 132
X BEST AVAILABLE TECHNOLOGY ECONOMICALLY
ACHIEVABLE--EFFLUENT LIMTATIONS GUIDELINES 133
Introduction 133
Recommended Effluent Limitations 134
Identification of Best Available Technology
Economically Achievable 135
Rationale for the Selection of Best Avail-
able Technology Economically Achievable 136
XI NEW SOURCE PERFORMANCE STANDARDS 139
Introduction 139
Recommended Standards 140
XII ACKNOWLEDGEMENTS 141
XIII REFERENCES 143
XIV GLOSSARY 145
VI
-------
FIGURES
Number Title
Pacje
1. Primary Production of Zinc in the World
and in the United States, 1870-1970, and
Consumption of Zinc, Including Scrap,
in the United States, 1938-1970. 12
2. Generalized Flowsheet of Pyrolytic Zinc
Plants. 21
3. Diagram of Electrothermic Zinc Furnace. 24
4. Generalized Diagram of Waste Water Streams
in Primary Zinc Operations. 38
5. Theoretical Solubilities of Metal Ions as a
Function of pH. 86
8. Experimentally Determined Solubilities of
Metal Ions as a Function of pH. 87
7. Concentration of Metals in the Effluent of a
Lime and Settle Treatment Operation. 89
Vil
-------
TABLES
Number Title
1. Twenty-five Leading Zinc Producing Mines in
the United States in 1971, in Order of Output 11
2. Identified and Undiscovered Zinc Resources
of the United States and the World (Estimated
in Millions of Metric Tons) 13
3. Slab Zinc consumption in the United States by
Use in 1971 15
4. Primary Zinc Plants in the United States 16
5. Grades of Commerical Zinc 17
6. General Overall Current Process Waste Water
Discharge Practices in the Primary Zinc Industry 43
7. Waste Effluents From Plant No. B 44
8. Waste Effluents From Plant No. C 45
9. Waste Effluents from Plant No. D 46
10. Waste Effluents From Plant No. F 47
11. waste Effluents From Plant No. G 48
12. waste Effluents From Plant No. H 49
13. Summary of Selected Data on Waste Water From
Primary Zinc Plants 51
14. Waste Effluents From Plant No. B 53
15. Waste Effluents From Plant No. E 54
16. Rates of Flow of Acid Plant Slowdown Streams 56
17. Waste Effluents From Plant No. B 57
18. Characteristics of Gas-Scrubbing Waste Water
(After Settling) 58
19. Characteristics of Gas-Scrubbing Waste Water
(After Scrubbing) 59
Vlll
-------
TABLES (continued)
20. Waste Effluents From Plant No. B 61
21. Waste Effluents From Plant No. B 62
22. Waste Effluents From Plant No. B 63
23. Current and Future Control and Treatment
Practices in the Primary Zinc Industry 82
24. Analyses of Input and Effluent Streams for a
Treatment Plant 91
25. Calculated Effectiveness of Removal of
Various' Constituents 92
26. Effectiveness of Treatment of Acid Plant
Slowdown by Lime and Settle 93
27. Effluent Concentrations From Lime and Settle
Treatment of Mixed Wastes 95
28. Solubilities of Metal Sulfides 97
29. Capital and Operating Costs of Present Waste
Water Treatment Practices in Primary Zinc
Industry 103
30. Additional Control and Treatment Costs 123
31. Conversion Table 155
IX
-------
-------
SECTION I
CONCLUSIONS
The nonferrous metals manufacturing point source category
has been divided into the following subcategories:
(1) Bauxite refining subcategory *
(2) Primary aluminum subcategory
(3) Secondary aluminum subcategory
(4) Primary copper smelting subcategory
(5) Primary copper refining subcategory
(6) Secondary copper subcategory
(7) Primary lead subcategory
(8) Primary zinc subcategory
Each subcategory has been found to be distinctly different
from the standpoints of processes employed, products
produced, and process waste waters generated, as well as
other less significant factors. Effluent limitations and
standards of performance were promulgated on March 26, 1974,
for the first three subcategories listed above. Development
documents supporting the rationale for these regulations
have been published. This development document presents the
rationale for establishing proposed effluent limitations
guidelines and standards of performance for the primary zinc
subcategory.
The consideration of such factors as age and size of plant,
processes employed, geographic location, and wastes
generated, substantiates the treatment of the primary zinc
industry as a single subcategory. However, the recommended
effluent limitations and standards of performance do take
the production level of each specific facility into account.
One conclusion derived by this study is that the combination
of lime and settle treatment technology and a minimized
process waste water flow, achieved through best practicable
and best available control, is considered to be the best
practicable control technology currently available and the
best available technology economically achievable. The best
practicable and best available flow usage values were
determined to be 8,350 1/kkg (2000 gal/ton) and 5,425 1/kkg
(1,300 gal/ton), respectively. The best practicable and
best available effluent concentrations, derived from lime
and settle treatment of zinc plant process waste water
pollutants, as discussed in Section VII, are identical for
each specific significant process waste water pollutant.
-------
The resultant effluent limitations, based upon the best
practicable control technology currently available and the
best available technology economically achievable, are
derived as the product of the respective flow values and
pollutant concentrations. The best demonstrated control
technology is considered to be identical to the best
available technology economically achievable.
It is estimated that for the existing plants to achieve the
levels of control of process waste water pollutants
recommended for July 1, 1977, the capital costs required
will approximate $1,515,000 and annual operating costs
required will be about 458,000. Incremental control and/or
treatment costs of approximately $1,054,000 capital and
$450,000 annual operating will be required of two plants to
achieve the further reductions in discharge of process waste
water pollutants recommended for the best available
technology effluent limitations of 1983. Therefore, the
total estimated capital and annual operating costs to this
industry are $2,569,000 and $908,000, respectively.
-------
SECTION II
RECOMMENDATIONS
Best_Practicable_Control_Technology_
Currently._Available
The recommended effluent limitations for the primary zinc
subcategory to be achieved by July 1, 1977, and attainable
through the application of the best practicable control
technology currently available, are as follows:
_____ Ef fluent_ limit at ions __ _ __
Effluent ~ Average of daily
characteristic Maximum for values for 30
any 1 day consecutive days
shall not exceed
Metric units (kilogram per 1000
TSS
As
Cd
Hg
Se
Zn
PH
English units (pounds per 1000
________ lb_of_p.roduct] _______ "_ ________
TSS 0.42 C.21
As 1.6x10-3 8.0x10-*
Cd 0.008 0.004
Hg 8.0x10-5 4.0x10-5
Se 0.08 0.04
Zn 0.08 0.04
0.42
1.6x10-3
0.008
8.0x10-s
C.08
0.08
Within the ram
0.21
8.0x10-*
0.004
4.0x10-5
0.04
0.04
je 7.0 to 10.0
The best practicable control technology currently available
is considered to include measures to achieve the reuse and
recycle of process waste water to minimize discharge, and
treatment of the remaining waste water by liming and
settling before discharge. The effluent limitations and
their rationale are discussed in detail in Section IX.
-------
The recommended effluent limitations for the primary zinc
subcategory to be achieved by July lr 1983, and attainable
through the application of the best available technology
economically achievable are summarized below:
Effluent_limitations
Effluent Average of daily
characteristic Maximum for values for 30
any 1 day consecutive days
shall not exceed
Metric units (kilogram per 10CO
]£2_of _groduct]
TSS 0.28 0.14
As 1.1x10-3 5.4x10-*
Cd 5.4x10-3 2.7x10-3
Hg 5.0x10-5 2.5x10-5
Se 0.054 0.027
Zn 0.054 0.027
pH _Within_the_ranc[e_7iO_to_1.0iO
English units (Ib per 1000 Ib
of _2£oductJ
TSS 0.28 0.14
As 1.1x10-3 5.4x10-*
Cd 5.4xlO-3 2.7x10-3
Hg 5.0x10-5 2.5x10-5
Se 0.054 0.027
Zn 0.054 0.027
pH _Withi£_the_ranc[e_of_7..0_to_10iO
The best available technology economically achievable re-
presents an incremental improvement and refinement of the
control measures of decreasing process waste water volume
and the treatment technology identified as best practicable
(i.e., lime and settle). The effluent limitations and their
rationale are discussed in detail in Section X.
-------
New Source Performance Standards
The recommended standards of performance for new sources of
the primary zinc subcategory attainable by the application
of the best demonstrated control technology are identical to
the effluent limitations based on the best available
technology economically achievable. These standards of
performance and their rationale are discussed in greater
detail in Section XI.
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-------
SECTION III
INTRODUCTION
Section 301(b) of the Act requires the achievement by not
later than July 1, 1977, of effluent limitations for point
sources, other than publicly owned treatment works, which
are based on the application of the best practicable control
technology currently available as defined by the
Administrator pursuant to Section 304 (b) of the Act.
Section 301 (b) also requires the achievement by not later
than July 1, 1983, of effluent limitations for point
sources, other than publicly owned treatment works, which
are based on the application of the best available
technology economically achievable which will result in
reasonable further progress toward the goal of eliminating
the discharge of all pollutants, as determined in accordance
with regulations issued by the Administrator pursuant to
Section 304 (b) to the Act.
Section 306 of the Act requires the achievement by new
sources of a Federal standard of performance providing for
the control of the discharge of pollutants which reflects
the greatest degree of effluent reduction which the
Administrator determines to be achievable through the
application of the best available demonstrated control
technology, processes, operating methods, or other
alternatives, including, where practicable, a standard
permitting no discharge of pollutants.
Section 30 4 (b) of the Act requires the Administrator to
publish within one year of enactment of the Act, regulations
providing guidelines for effluent limitations setting forth
the degree of effluent reduction attainable through the
application of the best practicable control technology
currently available and the degree of effluent reduction
attainable through the application of the best control
measures and practices achievable, including treatment
techniques, process and procedure innovations, operation
methods and other alternatives. The proposed regulations
contained herein set forth effluent limitations guidelines
pursuant to Section 304 (b) of the Act for the primary zinc
subcategory of the nonferrous metals category.
-------
Methods Used for Development of Effluent
Limitations Guidelines and
Standards of Performance
The effluent limitations guidelines and standards of per-
formance proposed herein for the primary zinc industry v/ere
developed in the following manner. Data were gathered to
create an industry profile. Data sources included the
published literature, telephone survey results, returns from
a limited questionnaire mailing, Corps of Engineers
discharge permit applications, and state weather control
agency records. Contact was made with a representative of
every United States plant or property engaged in zinc smelt-
ing and refining.
The information that was gathered provided an industry pro-
file from which the need for industry subcategorization
could be assessed and the current control and treatment
practices could be identified. Factors considered for sub-
categorization included water usage, process operation,
products, plant age, plant size, rainfall and evaporation
amount, and geographic location.
Visits were made to five locations where smelting and/or
refining are being conducted. These visits produced de-
tailed information covering control and treatment tech-
nologies plus associated costs, as well as identification of
waste water streams and their constituents. Additional data
for four plant sites were obtained from the Corps of
Engineers Permits to Discharge under the Refuse Act Permit
Program (RAPP). These included the varying degrees of
detail composition, temperature, and volume of intake and
effluent water plus a general description of waste water
treatment. Some analysis data were also provided on the
form completed by several companies. At one location, the
visit was followed by sampling and analysis of source
streams, selected internal streams, and the plant outfall.
Several production operations are performed at the location
that was sampled; consequently, a variety of streams could
be analyzed, some segregated and some mixed. The analyses
identified the chemical and physical characteristics of the
streams. On the basis of the above information, the
constituents of the waste water, which should be controlled
by effluent limitations and standards of performance, were
chosen. In addition, the analyses revealed the
effectiveness of any control and treatment technology
applied to the effluent.
Data gathered on control and treatment technologies
currently in use or under test were supplemented by
information covering other control technologies that might
-------
be applicable to the treatment and control of waste water
from the primary zinc industry. Consideration was given to
both in-plant and end-of-process technologies and to
applications for the effluent from the various production
operations. For each of the control or treatment technology
candidates, the resultant waste water constituents were de-
termined and the limitations and problems associated with
each technology were identified. Installation and operation
cost estimates for application of the technologies were
calculated. Possible environmental impacts on air quality,
solid waste disposal, and ambient noise levels were
assessed.
All of the information that had been developed was evaluated
in order to determine what levels of technology constitute
the best practicable control technology currently available,
the best available technology economically achievable, and
the best available demonstrated control technology.
Gen eral_De script ion^ of _ Primary_Zinc_ Indus try
One category of the industry encompassing the primary
smelting and refining of nonferrous metals (Standard
Industrial Classification Number 333) is the primary
smelting and refining of zinc (SIC Number 3333). SIC Number
3333 describes those establishments primarily engaged in
smelting zinc from the ore, or in refining zinc by any
process. Establishments primarily engaged in the mining and
benefication of zinc ore, as well as some lead ores, and the
rolling, drawing, or extruding of zinc are not classified by
this SIC and are not the subject of this development
document. Facilities for the generation of on-site
electrical power, and other ancillary operations are also
not the subject of this report. The process waste water
sources to be covered by the proposed regulations, for which
the rationale is derived in this text, are clearly defined
in later sections.
The U.S. primary zinc industry includes both electrolytic
and pyrometallurgical retort plants. The latter, which
produce zinc by volatilization and condensation, are further
divided by method of operation (i.e., into those using small
horizontal retorts and those using much larger vertical
retorts or furnaces). Because of difficulty in meeting air
pollution control standards, as well as other
considerations, such as labor costs, all of the horizontal
retort plants have closed down or will do so soon. One of
the two remaining plants has a variance to operate until
December 31, 1973; the other until June 30, 1975. As a
-------
consequence, establishing effluent limitations guidelines is
simplified to a consideration of four electrolytic and two
pyrometallurgical plants. There is a possibility that two
new electrolytic plants may be built in the near future.
and Rgsourceg
Of the approximately 500,000 short tons of zinc produced in
the U.S. in 1971, some 51 percent came from zinc ores, 30
percent from lead-zinc ores, 10 percent from lead ores and 7
percent from copper-base ores. Again based on 1971
production, about 24 percent of the zinc came from
Tennessee, 13 percent from New York state, 12 percent from
Colorado, 9 percent each from Missouri and Idaho, and 5
percent each from New Jersey, Pennsylvania, and Utah. About
60 percent of the zinc production has come; from mines east
of the Mississippi. Table 1 shows the location, type of
ore, and producers of the 25 leading zinc mines in the U.S.
These account for about 83 percent of the total mine
production, the first 10 producing 53 percent of the total.
Fifteen mines that produced about 26,000 tons of zinc in
1970 and 20,000 tons in 1971 were shut down by the end of
1971, largely because of the closure of smelters that had
been treating their concentrates (1). This trend has
continued with more mines and smelters closing in 1972.
As shown in Figure 1, U.S. consumption of primary zinc has
exceeded mine production to an increasing extent in the last
20 years. At present about two-thirds of the primary zinc
used in the U.S. is imported, mostly from Canada, Mexico,
and Central and South America. About half of the imported
zinc has been in the form of concentrates purchased on the
world market in competition with companies from other
countries, but, because of diminishing smelter capacity, a
larger proportion of imported slab zinc may be expected in
the next few years.
Estimated resources of zinc by the U.S. Geological Survey
(2) are shown broadly in Table 2. These estimates indicate
that the U.S. has about 18 percent of the world's
"recoverable" zinc and 7 percent of the subeconomic zinc
resources. Most of the identified recoverable resources are
in the Mississippi Valley (Tri State, Upper Mississippi
Valley, Missouri lead belts and Middle Tennessee) districts
and the Appalachian (New Jersey, Pennsylvania, New York,
East Tennessee, and Virginia) districts.
10
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T/iBLB 1. TWENTY-FIVE LEADING ZINC-PRODUCING MINES IN THE
UNITED STATES IN 1971 IN ORDER OF OUTPUT (1)
Rank
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Balmat
Eagle
Sterling Hill
Friedensville
Bunker Hill
Buick
Young
New Market
Zinc Mine Works
Immel
Austinville and
Ivanhoe
Edwards
Star Unit
Ground Hog
Jefferson City
Burgin
Idarado
U.S. and Lark
Flat Gap
Bruce
Shullsburg
Leadville
Coy
Magmont
Ozark
County and State
St. Lawrence,
N, Y.
Eagle, Colo.
Sussex, N. J.
Lehigh, Pa.
Shoshone, Idaho
Iron, Mo.
Jefferson, Tenn.
it
"
Knox, Tenn.
Wythe, Va.
St. Lawrence,
N. Y.
Shoshone, Idaho
Grant, N. Mex.
Jefferson, Tenn.
Utah, Utah
Our ay and San
Miguel, Colo.
Salt Lake, Utah
Hancock, Tenn.
Yavapai, Ariz.
Lafayette, Wis.
Lake, Colo.
Jefferson, Tenn.
Iron, Mo.
Reynolds, Mo.
Operator
St. Joe Minerals Corp.
The New Jersey Zinc Co.
"
it
The Bunker Hill Co.
Missouri Lead Operating Co.
American Zinc Co.^
New Market Zinc Co. '
United States Steel, Corp.
American Zinc Co.
The New Jersey Zinc Co.
St. Joe Minerals Corp.
Bunker Hill Co. and Hecla
Mining Co.
American Smelting and
Refining Co.
The New Jersey Zinc Co.
Kennecott Copper Corp.
Idarado Mining Co.
United States Smelting,
Refining, Mining Co.
The New Jersey Zinc Co.
Cyprus Mines Corp.
Eagle-Picher Industries,
Inc.
American Smelting and
Refining Co.
American Zinc Co. ^a'
Cominco American, Inc.
Ozark Lead Co.
Source of Zinc
Lead-zinc ore
Zinc ore
ti
1 1
Lead-zinc ore,
lead-zinc
tailings
Lead ore
Zinc ore
1 1
it
"
n
1 1
Lead-zinc ore
n
Zinc ore
Lead, lead-
zinc ores
Copper- lead-
zinc ore
Lead, lead-
zinc ores
Zinc ore
Copper-zinc
ore
Zinc ore
Lead-zinc ore
Zinc ore
Lead ore
n
(a) Purchased by the American Smelting and Refining Co., November 29, 1971.
11
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r-5
World production
U.S. consumption
en
C
O
• r-l
CD
C
O
o
•I-t
1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970
Figure 1. Primary production of zinc in the world and in the
United States, 1870-1970, and consultation of zinc,
including scrap, in the United States, 1938-1970.
12
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TABLE 2. IDENTIFIED AND UNDISCOVERED ZINC RESOURCES OF THE
UNITED STATES AND THE WORLD (ESTIMATED IN MILLIONS
OF METRIC TONS)
Identifieda. Undiscovered
Resources Resources Total
UNITED STATES
Recoverable
Subeconomic
Total
45
75(c)
120
60
230
290
105
305
410
REST OF THE WORLD
Recoverable
Subeconomic
Total
190 (b)
1,200 (c>
1,390
285
3,000
3,285
475
4,200
4,675
TOTAL WORLD
Recoverable
Subeconomic
Total
235 (b)
1.275(c)
1,510
345
3,230
3,575
580
4,505
5,085
(a) IDENTIFIED RESOURCES: Specific, identified mineral deposits that
may or may not be evaluated as to extent and grade, and whose
contained minerals may or may not be profitably recoverable with
existing technology and economic conditions.
(b) RESERVES: Identified deposits from which minerals can be extracted
profitably with existing technology and under present economic
conditions.
(c) CONDITIONAL RESOURCES: Specific, identified mineral deposits whose
contained minerals are not profitably recoverable with existing
technology and economic conditions.
13
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Uses and Projected Growth
Zinc is used largely in die casting, galvanizing, and brass
products, as shown in Table 3. About half of the total
production is special high-grade zinc, of which die casting
alloy is the largest application. Prime Western Zinc, used
mostly for galvanizing, accounts for about 30 percent of the
total. This grade, containing up to 2 percent of impurities
(maximum of 1.6 percent lead, 0.5 percent cadmium, and 0.05
percent iron) is commonly produced in pyrometallurgical zinc
plants using a nonselective feed of zinc concentrates
containing appreciable amounts of lead. A similar or
improved quality of zinc, called "Select Grade", is made in
some plants by using a higher grade of zinc and adding
alloying constituents to give desired galvanizing (hot
dipping) characteristics.
Projected growth is a desirable item of knowledge but a most
difficult prognostication, and is mentioned only to show a
possible trend. An estimate made by the staff of the U.S.
Bureau of Mines (3) indicates a need for over 3,000,000
short tons of primary zinc for the year 2000. (Forecast:
low 2,090,000; high, 4,000,000). Since production from U.S.
zinc mines has shown a downward trend in recent years,
projections mean little; projecting the mine production of
the last 7 years shows virtually no zinc production in the
U.S. in the year 2000. Much depends on the price
incentives, availability of smelter capacity within
practical transportation range, and changes in technology.
Zinc Plants
Zinc reduction plants in the U.S. at the end of 1973 are
listed in Table 4. The three electrolytic plants may be
supplemented by one or two additional plants presently under
consideration. Meanwhile, over half of the zinc metal
production capacity is centered in the two large
pyrometallurgical plants of New Jersey Zinc Company and St.
Joe Minerals Company. In the interval 1971-1973
(inclusive), one electrolytic zinc plant (Great Falls,
Montana), two vertical retort plants, and three horizontal
zinc plants have ceased operations. The Sauget, Illinois,
electrolytic plant of American Zinc Company was closed in
June, 1971, but reactivated by Amax in May, 1973.
Since commercial slab zinc of various grades is produced
directly at the zinc reduction plants, as shown in Table 5,
there are no separate primary zinc refineries. What little
refining may be needed is done as an operating step in the
same plant prior to casting. However, in making a higher
14
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TABLL 3. SLAB ZINC CONSUMPTION IN THE UNITED STATES
BY USE IN 1971 (1)
Industry and Product
Galvanizing
Brass products
Zinc-base alloy castings
Rolled-zinc products
Zinc oxide
Other uses lii
Light metal alloys
Other(a)
Total
kkg
430,600
136,491
468,113
35,239
36,319
4,150
26,521
1,137,432
Short Tons
474,752
150,486
516,111
38,852
40,043
4,575
29,240
1,254,059
(a) Includes zinc dust, wet batteries desilverizing of lead, bronze
powder, alloys, chemicals, castings, and miscellaneous uses.
15
-------
TABLE 4, PRIMARY ZINC PLANTS IN THE UNITED STATES
Company
Location TYPe °f Operation
Annual
Zinc Producing Capacity Acid Plant Products Produced
kkg/Yr(Short Tons/YrOperation at Plant Site
American Smelting
and Refining Co.
American Smelting
and Refining Co.
Amax
Bunker Hill
(Gulf Resources
and Chemical Co.)
New Jersey Zinc
(Gulf and Western
Industries)
St. Joe Minerals
Corp.
National Zinc Co.
Amax
Amarillo, Texas Horizontal Retort
Corpus Christi, Electrolytic
Texas
Sauget, Illinois Electrolytic
Wallace, Idaho Electrolytic
Palmerton, Pa. Vertical Retort
Monaca, Pa.
Electrothermic
Bartlesville, Horizontal Retort
Okla.
Blackwell,
Okla.
Horizontal Retort
42,303(46,641)
97,956(108,000)
64,149 (70,727)
110,312(121,624)
103,398(114,000)
226,750(250,000)
45,350(50,000)
72,832(80,300)
No
Yes
Yes
Yes
Yes
Yes
Yes
Prime Western Zinc
Slab zinc, zinc
alloys, zinc sulfate,
cadmium, sulfuric acid
Slab zinc, cadmium,
zinc sulfate, sulfuric
acid
Slab zinc, zinc alloy-
cadmium, sulfuric ac:
Slab zinc, zinc allo?
zinc dust and pellet;
zinc oxide, ferroalloy,
sulfuric acid
Slab zinc, zinc alloys,
zinc oxide, cadmium,
ferrosilican, mercury,
sulfuric acid
Zinc
-------
TABLE-J 5, GRADES OF COMMERCIAL ZINC (4)
Composition, percent
Zinc
Lead, Iron, Cadmium, min. by
difference
Special High Grade
High Grade
Intermediate
Brass Special
Prime Western
0.003
0.07
0.20
0.6
1.6
0.003
0.02
0.03
0.03
0.05
0.003
0.03
0.40
0.50
0.50
99.990
99.90
99.5
99.0
98.0
17
-------
quality product than that normally produced, a definite
refining step, such as redistillation, may be necessary.
This is described in more detail in the discussion on plant
operations.
Some zinc producing companies also produce zinc oxide.
Although zinc oxide plants are covered in a separate survey
of chemical plants, consideration is included in this study
where both oxide and metal are produced in the same plant.
Zinc powder is commonly produced, particularly in
electrolytic plants, for internal use in solution
purification. Several other byproducts are listed in Table
4.
18
-------
SECTION IV
INDUSTRY CATEGORIZATION
Introduction
In developing recommended effluent limitations guidelines
and standards of performance for new sources for a given
industry, a judgment must be made as to whether effluent
limitations and standards can be uniformly and equitably
applied to the entire industry, or whether there are
sufficient differences to warrant the establishment of
subcategories. The purpose of effluent limitations
guidelines can be realized only by categorizing the industry
into the ^ minimum number of groups for which separate
effluent limitations guidelines and new source performance
standards must be developed.
The objectives of industry categorization are to allow the
establishment of recommended effluent limitations and
standards of performance that are specific, unambiguous, and
uniformly applicable to a given industry subdivision.
Categorization, therefore, involves the identification and
examination of the factors in an industry which might bear
upon such a classification in terms of the recommended
limitations to be developed.
The factors considered in determining whether additional
subcategories are justified for the primary zinc industry
are:
(1) Process,
(2) Age,
(3) Size,
(4) Location,
(5) Raw materials,
(6) Waste characteristics,
(7) Byproducts and ancillary operations.
As a result of the following analysis of each of these
individual factors, as well as interrelating effects they
may have upon each other, the primary zinc industry is, for
the purposes of establishing effluent limitations and
standards of performance, considered as a single sub-
category, the primary zinc subcategory.
19
-------
Process
£2£_S^li£ii2llj E2^S^iS3« T^e following
discussion of processing is accompanied by the diagram given
in Figure 2. Domestic primary zinc plants treat sulfide
concentrates from various sources. These are stored, dried
if necessary, and blended to give a reasonably uniform
charge to the roasters. The roasting operation to remove
sulfur is carried out as completely as is economically
feasible in the electrolytic plants, since residual zinc
sulfide is insoluble. In the pyrolytic or retort plants,
where roasting is followed by sintering, complete removal of
sulfur is not as necessary in roasting. Sulfur removal is
usually rather complete to recover as much sulfur as
possible in the metallurgical sulfuric acid plant operating
on the roaster offgases. One pyrolytic plant, with a
typical feed of 54 percent zinc and 31 percent sulfur,
removes about 96 percent of the sulfur contained in the
feed.
Various types of roasting are used for zinc concentrates.
Multiple-hearth roasters are versatile and flexible,
permitting different conditions on different hearths. They
are used effectively in deleading. It is not unusual for 90
to 95 percent of the lead in a concentrate containing 0.3 to
0.5 percent lead to be removed in roasting when this is an
important objective. Fluid-bed roasters can be controlled
to give stable operating conditions. An oxidizing
atmosphere is used to quickly volitilize contained sulfur to
sulfur oxides with the flash roaster. Both the fluid-bed
and flash roasters give a steady and comparatively high S02
feed (i.e., about 5.5 to 12 percent SO2, by volume) to the
metallurgical sulfuric acid plant. When using a flash
roaster, the feed must be carefully sized, which may
necessitate additional grinding for proper preparation.
Because of the comparatively high temperatures generated in
flash and fluid-bed roasters, waste heat boilers are
commonly used with them. The roaster offgases, exiting the
roaster at about 1000°C (1800°F), are cooled down to about
400°C (750°F) by heat transfer with the waste heat boilers.
At these lower temperatures, the offgases can be treated for
particulate removal in the dust collection systems.
Roasting eliminates some of the impurities from the zinc
concentrate, other than sulfur and lead. Any mercury that
may be present is volatilized and goes with the gas stream
to scrubbers preceding the acid plant. As much as 20
percent of the cadmium present in the zinc concentrate may
be eliminated. The majority of the input cadmium is
20
-------
ZINC CONCENTRATES
i
Gases to
atmosphere
Storage, drying, blending
*
Secondary or
oxidic materials
Roasting
1
*
Dust collection '
Scrubbing j Acid
Mercury recovery | Plant
I
,.t .
Fumes, dusts,
residues
t
Calcine
acid
Moisture
Preparation
Oxides
Coke
Pelletizing
Sand
Recycle dust
Return
sinter
Dust
Collection
Gases to
atmosphere
uJ
f
Metallics
Coke
T
Cadmium plant
Briquetting
Electrothermic
reduction
Blue powder
\
Vertical retort
reduction
Coal, clay
and binder
Stack
1 Carbon monoxide )
Products of reduction I
SLAB ZINC
lower grades
ZINC OXIDE —
Liquation
Oxidation
/
Plant use
Residue treatment
American
process
SLAB ZINC
special
high grade
ZINC
Refining
(redistillation)
French process
Slag ,
discard
Ferrosilicon
High zinc
concentrate
recycled
Reclaimed coke
recycled
Lead-silver cone.
to lead plant
Figure 2. Generalized flowsheet of pyrolytic zinc plants.
21
-------
generally recovered in solution purification in electrolytic
plants or eliminated to a greater extent in sintering in
pyrometallurgical plants.
Sintering __ §nd_Briguetting __ (Pi£2i£tic_ Processes},. To make a
more compact feed, as well as eliminate more of the
impurities, the roasting product, calcine, is futher
processed pyrometallurgically by sintering (in pyrolytic
plants) . However, since the sulfur has been substantially
removed in roasting, the sinter machine off gases are vented
to the stack after primary particulate removal.
The feed for sintering is made up of calcined concentrates,
return portions for resintering, baghouse or electrostatic
precipitator dusts and various residues and zinc oxide
materials that may be purchased or that originate in the
plant. Fuel, amounting usually to 4 to 5 percent carbon, is
added, and in at least one plant, a small amount of silica
sand is also added to give a hard, semifused sinter. These
constituents are mixed, moisture is added,, and the feed is
pelletized to assure a uniform, permeable bed for sintering.
Where available, zinc sulfate solutions from in-plant
leaching operations are used to moisten the feed for
pelletizing, since this conserves water and enhances zinc
recovery.
Cadmium elimination in sintering is high with as much as a
90 percent removal. Lead elimination may amount to 70 to 80
percent. Consequently, the dust collected from the
sintering machine circuit is greatly enriched in these
impurities. By recycling the dust, the cadmium and lead
content is built up in the flue dust to a level high enough
to permit economical removal of the cadmium in a separate
division of the plant. A representative sinter produced
from low impurity concentrates used in making high grade
metal may run from 58 to 64 percent zinc, 0.005 percent
lead, O.OC5 to 0.01 percent cadmium, and 0.1 to 0.35 percent
sulfur; that for making Prime Western metal may be on the
order of 55 percent zinc, 0.3 percent lead, and 0.01 percent
cadmium.
In one pyrolytic zinc plant, an additional step,
briquetting, is undertaken in preparing the charge for
reduction. Sinter is ground, mixed with pulverized coal
(including a coking type) , clay, moisture, and a binder.
The mixture is then pressed into small briquettes weighing
about 1.5 pounds each. These are fed into a step-grade
autogenous coking furnace where they attain a strong
structure to resist disintegration in handling and
reduction, as well as to keep the reductant and zinc oxide
22
-------
in close contact. Heat for this coking operation is
generated by burning the volatile constituents of the charge
produced inside the furnace.
Ey£2lXtic __ Reduction. Since only two pyrolytic zinc plants
are involved in this discussion and they differ in retort
construction and operation, a description of the reduction
step necessarily becomes specific.
In the vertical retort process, hot briquettes are fed at
regular intervals into tall retorts and pass slowly downward
while undergoing reduction of their zinc oxide content. The
residual or spent briquettes are continuously discharged by
a roll extractor into a quenching compartment, from which
they are removed for further treatment. By use of a venturi
scrubber, all gases are exhausted from the furnace (which
operates with an internal pressure slightly below ambient) .
The gases, principally metallic zinc vapor and carbon
monoxide, pass first through a zinc condenser and then to
the venturi scrubber. By means of a splash system, whereby
a _ mechanically driven device fills the condenser chamber
with a rain of zinc droplets which fall back into a bath of
molten zinc, the zinc vapor from the retorts is condensed
and collected with excellent efficiency. Over 95 percent of
the zinc vapor leaving the retort is condensed to liquid
zinc.
The vertical retort walls are made of silicon carbide brick.
Common dimensions of the retort are a width of 0.3 meter (1
foot), a length of 2.1 meters (7 feet), and a height of 10
meters (35 feet), giving a capacity of about 7.3 kkg (8
short tons) of zinc per retort per day. Heating the charge
to about 1300° C (2400 ° F) is done by gas in chambers
surrounding the retort side walls. Gases from the
combustion chambers are used to preheat incoming air for
combustion by means of recuperators. The carbon monoxide
from the zinc condensation chamber is scrubbed with water
sprays to remove entrained solids, and the gas is used as
part of the fuel for heating the retorts. Blue powder, a
mixture of metallic zinc and zinc oxide, is collected as
residue from the scrubbing system and during the periodic
cleaning of the condenser. This material is recycled.
In the process of electrothermic reduction of zinc, a much-
larger, internally heated retort or furnace is used. Figure
3 shows the general cross section. The largest of such
circular furnaces presently in use are 2.4 meters (5 feet)
inside diameter and 15 meters (50 feet) in height with a
zinc producing capacity of about 90.7 kkg (100 tons/day).
This type of pyrometallurgical retort furnace is constructed
23
-------
les_^
>
f
C
,oke-i
f
/
1
-Br
r
' *"
-q
jets
pSint
Y
\" /
Carbon monoxide
to
vacuum pumps
Carbon monoxide
gas
Batch fed-
dross ^
Rotary
distributor
--^Rotary
preheater
Blue powder
slurry
to ponds
Liquid zinc
Tap hole
Cooling well
Condenser
Water rin
Rotary discharge table
Gamma ray source
Graphite electrodes
,Vapor ring
Water-cooled jackets
raphite electrodes
/7/'Residue
an conveyors to
recovery system
Figure 3. Diagram of electrotherraic zinc furnace.
24
-------
of firebrick; the vapor ring condenser and its cooling well
are lined with silicon bricks for better conductivity.
Water, for cooling, is used in steel jackets surrounding
much of the reduction area of the furnace. Similar
electrothermic furnaces are used to produce zinc oxide, but,
in place of a vapor ring and condenser used to produce
elemental zinc, multiple outlets permit the vapor to enter a
surrounding combustion chamber where oxidation occurs.
Preheated coke and sinter, along with miscellaneous minor
zinc- bearing products, are fed continuously into the top of
the furnace. This charge passes slowly downward where the
coke serves both as reductant and conductor for the electric
current that enters through graphite electrodes positioned
near the top and base of the furnace. Zinc vapor passes
from the main furnace to a vapor ring and thence to a
condenser where it is condensed by bubbling through a bath
of molten zinc. Water cooled hairpin loops at the condenser
cooling well maintain a constant bath temperature of 480 to
500 °C (900 to 930 °F). The gas, mostly carbon monoxide,
passing through the condenser is water scrubbed by impingers
and used as fuel elsewhere in the plant. Some blue powder
or uncondensed zinc-zinc oxide is recovered by settling the
scrubber slurry in ponds. This is dried, briquetted, and
recycled with the furnace feed. Furnace residue after zinc
distillation goes to a reclamation plant where residual coke
and some unreacted zinc are recovered and recycled. In this
plant, where sand may be added to make a hard sinter,
sufficient ferrosilicon is present in some residues to
warrant recovery as a byproduct.
Zinc __ Productioru Recovery of zinc by
hydrometallurgical-electrolytic means has the advantages
over pyrometallurgical methods of being able to more readily
treat lower grade concentrates and attain a high purity
product. Recovery of byproducts and the elimination of dust
and heat from furnaces other than roasters are two
additional advantages. However, the high capital cost of an
electrolytic zinc plant has been an adverse factor.
Charge preparation for an electrolytic zinc plant differs
from that of a retort plant in that a finely calcined feed
is needed, rather than a compact hard-sintered product.
After completely roasting the concentrates, sizing and
regrinding coarse particles may be necessary. Also, since a
high lime-magnesia feed would introduce unwanted magnesium
sulfate into the electrolyte, an acid wash to remove such
solubles is a necessary pretreatment before roasting such
concentrates .
25
-------
The substantially sulfide-free calcine from roasting, along
with other zinc oxide products, are leached with spent
electrolyte, that is, with a sulfuric acid solution
containing residual zinc sulfate. This spent electrolyte
may contain around 200 g/1 of sulfuric acid. The trend in
the United States is to leach continuously or
semicontinuously, rather than batchwise as in the past,
since this practice requires less equipment, space, and
labor, and is considered to be better adapted to automatic
control. Whether by batch or continuously, the spent
electrolyte and calcine are added to leaching tanks under
conditions of acidity control to avoid dissolving an excess
of iron, and to precipitate, finally, the iron that is
dissolved.
The problem is to selectively dissolve as much of the zinc
as possible, precipitating iron and accompanying impurities
(such as arsenic, antimony, silica, and germanium) without
precipitating any of the dissolved zinc. The presence of
iron hydroxide in carrying down impurities is of such
importance that, if there is insufficient iron in the
concentrates treated, scrap iron may be used as an
additional source. When considerable zinc is made
relatively insoluble in roasting by the formation of zinc
ferrites, the practice is to leach with hot, comparatively
strong, spent electrolyte to dissolve both zinc and iron,
and then precipitate the iron as jarosite. This treatment
may also be applied to the leached residue. In double-bath
leaching, calcines are leached with a deficit of spent
electrolyte to keep the solution slightly basic and free of
dissolved iron. Residue from this step is further leached
with excess acid and the resultant solution recirculated to
the first stage. Thus, the leaching of roasted zinc
concentrates is mucn more complicated than would be assumed
by the simple exothermic equation ZnO + H2_S04_ >ZnS04_
+ H20.
After leaching, the neutral or pregnant solution is filtered
and goes to purification. This is usually done in large
drums or filters, but when handling ve^ry hot, highly
concentrated solutions, filters are used.. After washing,
the residue may be processed further to recover residual
zinc (as in the jarosite process, or by flotation), and the
final residue containing lead and precious metals is usually
sent to a lead smelter.
Purification is accomplished largely by additions of zinc
dust, which precipitates copper, cadmium, cobalt, nickel,
and other residuals by replacement. By adding zinc dust in
multiple stages, it is possible to make rough separations,
as a high-copper precipitate and a high-cadmium precipitate,
26
-------
each carrying down some of the other impurities. At times,
copper and arsenic may be purposely added to give more
precipitate in order to bring down obnoxious minor
impurities. In one plant, a semicontinuous purification
step is used. Purified solution is sent to the electrolytic
cells. The high-copper precipitate is treated to remove
most of the zinc and the final copper cake is sent to a
copper smelter. Likewise, the cadmium cake is sent to a
cadmium recovery plant, where cadmium and other byproducts
are recovered.
The electrolytic cell room is a large area containing a
multiplicity of tanks through which the zinc-containing
solution, or electrolyte, slowly flows. Each tank contains
a number of alternate anodes and cathodes (such as 28 anodes
and 27 cathodes), but the number may vary considerably in
different plants. Anodes are rectangular, commonly made of
cast lead containing 0.75 to 1 percent silver, and are 0.95
to 0.79 centimeters (3/8 to 5/16 inch) thick, about 0.76
meters (2-1/2 feet) wide, and 1.2 meters (4 feet) deep.
Cathodes are aluminum, have slightly smaller rectangular
dimensions and are commonly only 0.48 centimeters (3/16
inch) thick.
Zinc is deposited from solution onto the aluminum cathodes
at a rate governed mostly by the current density employed.
Currently in the United States, this is around 750 amp/sq m
(70 amp/sq ft) of cathode area, although in one plant this
density may be as high as 1130 amp/sq m (105 amp/sq ft).
Such comparatively high current density develops
considerable heat in the electrolyte and various means of
cooling and recirculation are used, such as internal cooling
coils or external cooling systems. In one plant, cold well
water passing through lead coils has been used, but this has
recently been successfully replaced by a flash cooler under
reduced pressure. Since current efficiency is less than 100
percent, some oxygen is released at the anodes and hydrogen
at the cathodes. The bursting of these bubbles causes an
acxd spray which can make the cell room uncomfortable, as
well as enhance corrosion of equipment. in addition to
abundant ventilation, various electrolyte covers and
additives are used with variable success to curtail misting.
Strontium carbonate (or barium hydroxide) is added to the
electrolyte in some plants to reduce lead contamination of
the deposited zinc. Glue or gum arabic are among the agents
added to obtain a smoother deposit and less interference by
impurities.
When the deposit attains a desired thickness, for example in
24 hours, the cathodes are removed and zinc is stripped.
27
-------
This stripping is commonly done manually (a considerable
cost item), although various mechanical means and air
blasting have been used at least experimentally. The
cathode zinc is washed and sent to the casting plant.
Electrolyte is recirculated after passing through a series
of cells, and at least a portion of the spent electrolyte is
sent back to the leaching plant continuously.
Refining^ Melting^ and Casting. Cathode zinc sheets from
electrolytic zinc plants are dried, melted, and cast into
various forms of slab zinc. Alloys of zinc, particularly
for die castings, are also prepared and cast. At times,
dependent upon marketing conditions, lead and other desired
constituents are purposely added to a relatively high grade
of electrolytic zinc to make a Select Grade for galvanizing.
Zinc dust is made at the plants for use in purification of
solutions.
Zinc produced in pyrolytic plants is normally less pure than
that produced electrolytically, but this is overcome when
desired by (1) careful selection of raw material and taking
special care in preparation of the charge (roasting and
sintering) to eliminate most of the impurities, and (2) by
refining. Impure hot metal as produced is given a liquation
treatment. It is allowed to cool to just above the melting
point of zinc, whereby the lead and iron present in amounts
exceeding their solubility in zinc separate by precipitation
and can be removed mechanically to a considerable extent.
This dross can be processed in the plant or treated in a
secondary zinc plant for recovery of values. The partially
purified zinc is then cast as slab zinc into Prime Western
grade or higher, depending on purity. By redistillation of
impure zinc, the highest purity commerical grades of zinc
can be produced, depending on the procedure used. The most
common method is to use dual fractionating columns of
silicon carbide, heated externally. Cadmium and zinc are
largely volatilized from the first rectifying column,
leaving lead, iron, and other high-boiling point
constituents, which can be removed from the base.
Condensate from the first column goes to a second, or
cadmium column, where by reflux condensation, cadmium and
the low boiling impurities are removed. These are sent to a
cadmium plant for recovery.
Melting and casting zinc into commercial forms is a
relatively simple operation as the temperature required is
only moderate. Water is used in some plants for rapidly
cooling the molds, but commonly does not come into contact
with the metal. Ammonium chloride flux is usually used on
the molten zinc in the melting furnace to retard oxidation
28
-------
at the surface and to collect any oxides formed. Plants
using air pollution control devices on gases from the zinc
melting operation will collect, in the control device,
solids containing both zinc oxide and chloride compounds.
Any processing to recover the zinc values from this air
pollution control residue must deal with the chloride
content of the residue. This is especially true in
electrolytic zinc plants, because the electrolysis reaction
is very sensitive to the deleterious effects of chloride in
the electrolyte.
Cadmium Recovery. All of the zinc plants produce cadmium.
Although minor compared with the main plant production of
zinc, the U. S. zinc plants are producing about 3.6 to 4.9
million kilograms (8 to 9 million pounds) of cadmium yearly.
Electrostatic precipitator or baghouse dusts from certain of
the roasting or sintering operations in the plant, which
have reached a desired concentration of cadmium by
recycling, are treated hydrometallurgically for cadmium
recovery, along with any high-cadmium dusts from other
sources. High-cadmium zinc from zinc refining operations,
and cadmium precipitated by zinc dust in purifying zinc
solutions constitute important cadmium sources, also.
Although details of operation differ at each zinc plant, the
general procedure in treating dusts has been to leach with a
solvent for the cadmium (and zinc), filter, and send the
residue (containing insoluble lead) to a lead recovery
plant. This solvent usually is dilute sulfuric acid, but in
at least one plant the dust is first given a sulfating roast
and is water leached. The cadmium zinc sulfate solution is
treated with zinc dust to precipitate cadmium as a metallic
sponge and separate it from most of the zinc. This sponge,
or that from electrolytic zinc plant purification residues,
may be dissolved and reprecipitated to achieve an improved
separation. Eventually, the reasonably zinc-free cadmium
sponge is melted directly with a caustic flux or it is
distilled in a graphite furnace. If distilled, the metal
may be further purified by redistillation. An alternative
treatment used, particularly in the electrolytic zinc
plants, is to dissolve the sponge in dilute sulfuric acid
(return electrolyte) and electrolyze the sulfate solution
much as in electrolytic zinc recovery. The cadmium metal is
melted and usually cast in a form convenient for use in
electroplating.
Metallur2ical_Sulfuric_Acid_Plants. Because of its usage at
all but one currently operating primary zinc smelter, the
metallurgical sulfuric acid plant is considered as an
integral part of the primary zinc production process. The
29
-------
one exception to this practice, a horizontal retort plant,
is not considered as an important factor, since it is
currently operating under a variance and is scheduled to
discontinue operation on June 30, 1975.
The offgas from the multiple-hearth, fluid-bed, or flash
roasters of the primary zinc industry contain a sufficient
concentration of SO2 for conventional sulfur oxide control,
such as a metallurgical sulfuric acid plant. After primary
particulate removal in either a hot electrostatic
precipitator or a baghouse, the strong SO2 offgases must be
preconditioned prior to entrance into the acid plant. The
preconditioning operation normally consists of humidifying
and scrubbing the effluent with a weak sulfuric acid
solution in an open tower and a packed tower (or in some
applications, one scrubbing tower with a gas humidifying
section and a scrubbing section); the removing of residual
fume and SO3 particulate in an electrostatic precipitator,
called a mist precipitator; and, finally drying in a drying
tower for removal of entrained moisture. The preconditioned
gas stream then enters the metallurgical sulfuric acid plant
where conversion of SO2 to SO3, in the presence of a
vanadium pentoxide catalyst, and absorption of the S03 to
H2SO4 in the acid towers occurs. The acid plant tail gas
contains about 2000 to 3000 ppm S02, by volume, and some
entrained acid mist. Removal of the acid mist, prior to
atmospheric release of the tail gas, is conventionally
accomplished by mist eliminator. Process waste waters,
termed as the acid plant blowdown, result from the
preconditioning section and the tail gas mist eliminator.
Large volumes of noncontact cooling water are used to
maintain correct operating temperatures within the
metallurgical sulfuric acid plant.
Summary,, _of Process. Two basically different process
approaches~are employed in the primary zinc industry. These
are pyrometallurgical processing and electrolytic
processing. Except for a preleach operation used by the
electrolytic processors, the first step of roasting is
practiced by all, and the offgases produced by the roasting
step are subjected to convental SO2 control by all (i.e., of
consequence to the proposed effluent limitations).
Subsequent processing, sintering, reduction, and refining
(if practiced), for the pyrometallurgical plants and
leaching and electrolysis for the electrolytic plants, do
not produce process waste waters as defined later in this
document. Therefore, for the purposes of establishing
effluent limitations and standards of performance for the
primary zinc industry, this industry, based upon process, is
considered as a single subcategory.
30
-------
Changes and improvements made from time to time may largely
nullify the effects of plant age; hence, the time a plant
has been operating is not necessarily a good criterion for
additional subcategorization. The oldest zinc plant
currently operating was built originally in 1898, a more
modern addition was built in 1910, and the present vertical
retort-type furnaces were put into operation in 1929.
Considering the use of present equipment, the range in
starting time of four of the five plants has been in the
same time frame, 1928 to 1930. The newest plant started in
1941. All the plants, consequently, are 32 to 45 years old
and are considered to be in the same general age category.
Size
Existing electrolytic zinc plants in the United States are
roughly . similar in size. Their production rates, at
present, range only from 63,500 to 109,000 kkg (70,000 to
120,000 tons)/yr. The two pyrolytic plants with capacities
of 99,800 and 227,000 kkg (110,000 and 250,000 tons)/yr
differ in size from each other, but are larger than the
electrolytic zinc plants by a factor of 2. That is, the
average production rate of the two pyrolytic plants is
double that of the average of the three electrolytic plants.
On the basis of size, therefore, the zinc industry can be
classified most logically into pyrolytic and electrolytic
groups.
Location
By location, the pyrolytic zinc plants are grouped together
in Pennsylvania; the electrolytic plants are scattered from
the Mississippi River to the Northwest and Southwest. That
is not a strong factor in determining categories, but again
the differentiation is between pyrolytic and electrolytic
plants.
By climate, there is similarity between the locations of all
the plants, except plants in the Southwest. There is a
remarkable similarity in temperature and solar evaporation
capacity at all the other plants. The plant in the Midwest
has a somewhat higher average temperature and greater water
evaporation capacity, but is not greatly dissimilar in this
respect to the other three. In the Southwest, the higher
average temperature and slightly lower rainfall gives the
capacity for considerably greater evaporation.
31
-------
All the plants are located along rivers or streams where
there is no problem of adequate drainage and little
possibility of flooding. The plant in the Midwest
conceivably could be flooded under exceptional conditions,
and the plant in the Southwest could be inundated to some
extent by extreme hurricane conditions.
As reported by one plant in the geographically-arid
Southwest, land available on the plant site is essentially
non-existent for impoundment of process waste water
pollutants and subsequent disposal through solar
evaporation.
Therefore, additional subcategorization based upon geography
is unwarranted.
Raw Materials
All of the zinc plants use zinc concentrate as their chief
raw material. These may be company owned or purchased on
the world market in competition not only with each other,
but with zinc plants abroad. The need for custom processing
results in a variation in feed characteristics.
Consequently, the effect of the composition of concentrates
used on waste water pollution must be regarded over a
reasonably long time, rather than entirely from the
standpoint the material currently used.
In the purchase of some foreign concentrates, for example,
mercury is sometimes encountered. Mercury is also found in
reasonable trace concentrations (up to about. 400 ppm) in the
domestically mined and milled zinc concentrates of up-state
New York and the Coeur d1 Alene region of the Northwest.
This merely means a quantitative difference in mercury
recovered, either intentionally or unintentionally, as all
the zinc plants take precautions to prevent mercury
contamination of water and air, and all are effected to some
extent by its presence, at least potentially, in zinc
concentrates.
At one electrolytic plant, deleaded zinc oxide fume from
lead blast furnace-slag treatment forms an important part of
the zinc raw material. Similar oxide, presently not
deleaded, is produced at another electrolytic plant and sold
as such, but it may be used as part of the zinc plant feed
at times. At another plant, considerable crude zinc oxide
is added to the charge. This is partially from Waelz-kiln
treatment of low-grade zinc products.
32
-------
Miscellaneous secondary zinc and interplant products are
treated from time to time by some of the plants. Such
secondary material may include galvanizing byproducts, which
introduce substantial amounts of chlorides (mostly zinc
chloride and ammonium chloride) into the waste water.
One electrolytic plant expects to be treating their company
owned concentrates, presently processed at a horizontal
retort plant. These concentrates are high in magnesium
carbonate. Leaching the untreated roasted calcine from this
source would introduce a very undesirable quantity of
magnesium salts into the electrolytic plant; hence, a
preparatory acid leach of the concentrates to remove the
magnesium is necessary, and this introduces an unusually
high amount of magnesium sulfate into the process waste
water circuit.
Although other raw materials are used, besides zinc
concentrates, oxides, or secondary zinc materials, they do
not exert significant influence over the quantity or quality
of waste water produced. Thus, the coal, clay and binder
used in briquetting and coke and sand in pelletizing in
electrothermic reduction are minor contaminants. However,
some coke, such as that currently used, does contain
considerable chlorides, which add to the chloride content of
the waste water stream. In the electrolytic plants,
additives used, such as glue, gum arabic, strontium
carbonate or barium hydroxide, recycled manganese dioxide,
and zinc dust, have minor effect on the waste water.
Altogether, no sharp distinction for the purposes of
additional subcategorization can be drawn between the
various plants on the basis of raw materials. Different feed
materials affect the amounts of pollutants entering the
waste water stream. In general, all the plants have
substantially the same problems, with added emphasis on
chlorides introduced in raw materials in one or two plants
and on sulfates in another.
Waste_Characteristics
Presented in the next section of this report (Section V) are
data on waste characteristics of the primary zinc smelters,
the characteristics, in so far as they are known, of unit
process waste water streams, and the current status of the
industry with regard to present and planned waste water
treatment and control practices. On the basis of the
industry's current method of response to water pollution
control needs, the primary zinc industry is considered as a
single category of point sources in terms of recommended
33
-------
effluent limitations guidelines. That is, the waste water
characteristics and quantities associated with unit
operations, as associated with present or planned control or
treatment practices, are a more common feature of the plants
in this industry, than are any of the factors described
above.
Byproducts §nd_ Ancillary Operations
Some of the byproducts produced at the domestic primary zinc
facilities, as a result of the primary zinc process, include
commercial grade sulfuric acid, cadmium, and metallurgical
fumes, which are either shipped out for further processing
or recycled internally. Zinc oxide, an inorganic chemical,
is recovered at several of the primary facilities.
Spiegeleisen, a low content ferromanganese, is produced at a
plant, but is considered as an ancillary operation. Other
chemicals are produced on-site, such as fertilizers, but
again, are considered as ancillary operations. A primary
lead smelter and refinery, as well as an integrated mining
and milling operation, are all co-located with one
electrolytic zinc plant. Facilities for the production of
power are located on-site at several of the smelters, both
pyrometallurgical and electrolytic. Mercury was at one time
recovered at one facility as a byproduct through the use of
an indirectly-fired rotary kiln and condensor system. From
the standpoint of effluent limitations for the process waste
waters of the primary zinc industry, the only known
byproducts of consequence are sulfuric acid and cadmium,
both of which are produced on-site at all facilities.
Summary
The factors of process, age, size, location, raw materials,
waste characteristics, and byproducts and ancillary
operations have been discussed to determine the need for
further subcategorization of the primary zinc industry. As
illustrated under the discussion of size, the two pyro-
metallurgical plants are considerably larger in production
capacity than the three electrolytic zinc plants. This
difference in size could produce larger magnitudes of
process waste water from such sources as acid plant
blowdown. Some electrolytic facilities use a preleach
operation to limit the introduction of magnesium sulfate
into the electrolyte. The process waste water volume from
this source should counterbalance any possible waste water
volume effects produced from size differential.
34
-------
Therefore, for the purposes of establishing effluent
limitations guidelines and standards of performance, the
primary zinc industry is considered as a single subcategory.
35
-------
-------
SECTION V
WASTE CHARACTERIZATION
Introduction
The following discussion first covers the sources of waste
water identifiable within plants in the primary zinc
industry and then presents waste characteristics in terms of
data showing quantities of flow and the contained
constituents. Waste waters are characterized in terms of
both total discharges and unit process operations. Waste
characteristics are further related to past and present
control and treatment practices.
Source s_g_f., Wag t e_ Wat er
The sources of waste water identified in primary zinc plants
may be described in terms of two overall classes, noncontact
cooling water and process waste water.
Noncontact cooling waters are considered to be those which
are used for cooling in heat exchangers and do not contact
any of the raw materials, intermediate or final products, or
byproducts, or any process or waste material characterizable
in terms of thermal load and pollutants associated with the
cooling circuit (e.g., suspended solids, oil and grease, and
additives such as water-softening compounds or corrosion
inhibitors). These streams are not included in the
definition of this development document and are dealt with
here only as necessary to define other streams.
Process waste waters are considered as those waste water
streams which have contacted some material characteristic of
the process of the industry and, thereby, are considered to
have the opportunity to be potentially polluted in terms of
constituents contained in those materials. These process
waste water streams are the subject of this document and are
those considered in terms of recommended effluent
limitations guidelines and standards of performance.
In examining the unit process operations of the primary zinc
industry, the following associated waste water streams were
identified: (streams are indicated in the diagram given as
Figure 4)
37
-------
Roaster
Waste
Heat
Boilers
oo
oo
Noncontact
Cooling
Slowdown
t
Cooling Tower(s)
for Noncontact
Cooling Waters
i L
Sintering
Machines
Reduction
Furnaces
Gas Cleaning,
Spray Chambers
Scrubbers
Acid-
>lant
Acid
Plant
Metal
Casting
Cooling
Electrolysis |
Recycle
Reservoir
1_
Slowdown
Cadmium
Plant
Miscellaneous
Scrubbers
and
Residue
Treatments
Contact
Cooling
Water
Figure 4. Generalized diagram of waste water streams in primary zinc operations.
-------
Roasting - noncontact cooling water,
• Roaster-gas cleaning train - bleed streams from
gas cooling spray chambers or wet scrubbers
(i.e., acid plant blowdown),
Metallurgical sulfuric acid plant - noncontact cooling
water,
Reduction furnaces - noncontact cooling water,
• Reduction furnace gas cleaning operations - bleed
streams or once-through water streams,
Electrolysis (of zinc) - noncontact cooling water,
• Metal casting cooling - direct contact cooling
waste water streams,
• Cadmium production - spent process liquor,
Rectifier cooling - noncontact cooling water,
Boiler operations - boiler blowdown,
Miscellaneous cooling waters from pump seals,
bearing cooling, vacuum pumps, etc.,
• Auxiliary air pollution control operations -
including dust control and/or wet processing
of air pollution control residues to reclaim
metal values,
• Electrolytic purification, washwater, and spills,
• Preleaching of zinc concentrates.
In the following discussion, the specific origins of those
waste streams considered as process waste waters (in above
listing, preceeded by "•'?) are identified.
Ac id_ PIant_BIgwdgwn
As discussed in Section IV, zinc sulfide concentrates are
roasted to remove the sulfur by the oxidation of zinc to
zinc oxide and sulfur oxide. The roaster gas generally
passes through a series of facilities which may be typified
by the sequence: waste heat boiler, cyclones, hot
electrostatic precipitators, gas conditioning
(humidification) spray tower, (or open and packed towers),
electrostatic precipitator (mist precipitator), dryer,
contact acid plant, and tail gas mist eliminator. As
indicated in the diagram, the identifiable process waste
water streams issuing from this sequence of operations are a
stream from the gas humidification chamber and a bleed
stream from the wet scrubber. These two streams may be in a
common circuit with recirculation capacity, and are
generally referred to collectively as "acid plant blowdown".
Interviews with operating personnel established the
following three bases for the existence of acid plant
blowdown.
(1) Control of temperature of the gases, and.
39
-------
implicitly, the recirculating stream, involving,
for example, the use of cool makeup water
as the means of temperature control.
(2) The prevention of buildup of chloride
concentration in the recirculating stream
to a level which would produce significantly
accelerated corrosion of the materials of
construction. For example, a level of
O.C02 weight percent chloride in the
recirculating stream was considered tolerable
in terms of stainless steel equipment;
whereas, a chloride level of 0.2 weight
percent would be considered a level to
justify an increased bleed rate.
(3) The maintenance of a tolerable level of suspended
solids in the recirculating system. The
tolerable level would be defined as that at
which the system functioned continuously,
and would vary with pipe sizes and pump
characteristics, but may be characterized
as having a maximum in the range of 2 to 3
weight percent solids. The origin of the
suspended solids is the particulates in the
gas stream entering the hot electrostatic pre-
cipitator and subsequently the wet scrubber. This
particulate level is a dependent on the number
and performance level of the preceding dust
control devices (i.e., waste heat boiler,
cyclones, and electrostatic precipitator).
Performance levels of these devices may vary
with time, maintenance, and charge material,
or even ambient atmospheric conditions.
Various aspects of the acid plant blowdown stream, such as
its connection with air pollution control, its
characteristics, and its treatment will be presented in
detail in later discussion. Acid plant blowdown was
identified as a component of discharge streams in all plants
but one, where it was routed to a cadmium byproduct
operation specifically for reuse. As discussed below, a
subsequent chloride bleed stream was necessary.
Metaj._C^sting Cooling Water Stream
The other process waste water stream identified as common to
all zinc producing plants is a metal casting cooling water
stream. This stream results from the spraying or immersion
of cast metal to cool the metal to insure complete
solidification and to produce a temperature suitable for
handling of the product (ingots, slabs, pigs, etc.). Metal
40
-------
cooling waste water generally contains suspended solids and
oil and grease in terms of metal oxides, mold washes, and
lubricants from casting equipment.
Miscellaneous^Sourcgs
Reduction_Furnace_Gas_Scrubber. In the case of pyrolytic
plants, the gases drawn from reduction furnaces are, after
condensation of zinc, washed with water to permit use of the
carbon monoxide as a fuel. The gas washing water may be
characterized as generally involving high volumes of use and
as containing zinc and metal oxides, possibly hydrocarbons,
and various particulates (as suspended solids), and the
corresponding products of hydrolysis.
Dust Control Operations. In the same area of waste stream
production, there exist auxiliary dust control operations
using wet scrubbers or auxiliary operations treating air
pollution control residues. A stream which will be
considered related will be that issuing from the aqueous
processing of zinc melting dross, treated to reclaim the
contained zinc (oxide). The dust control-related streams
are from the wet scrubbing of dusts generated in the
grinding and processing of secondary (scrap) materials. The
baghouse dusts (from melting operations), drosses, and
secondary (scrap) materials all bear the common
characteristics of producing, principally, zinc oxides and
chlorides in the waste streams. One common factor
identifiable here is the ammonium chloride or zinc chloride
flue components associated with each of the materials.
Cadmium Processing. All the existing zinc plants produce
byproduct cadmium. All cadmium processing circuits except
one were operated in a closed-loop fashion with regard to
aqueous effluents. The single open circuit was that case,
wherein acid plant blowdown was used for the cadmium
leaching operation and the spent liquor from the cadmium
circuit, while subjected to special cadmium control steps,
including liming and settling, served as an outlet for
chlorides from the zinc circuit.
The closed-loop operation characteristic of most cadmium
producing operations is achieved by virtue of the fact that
the circuit intrinsically contains chemical precipitation
and filtration steps, termed purifications, which result in
"bleed" streams in the form of filter cakes, which may be
variously recycled within the plant operation, shipped as
intermediate product, or disposed of as waste. Some
elements found in these cakes include iron, arsenic, indium,
lead, mercury, and copper, as well as zinc and cadmium.
41
-------
Electrolytic Processing. It is noteworthy that no discharge
exists from electrolytic process streams. Again, the
process circuit intrinsically contains purification steps of
chemical precipitation and solids separaition, with filter
cakes providing the outlet for impurities, and with
recirculation of spent electrolyte to the leach step.
Careful control of the input of chlorides and fluorides to
the circuit is necessary to maintain control of both the
electrolysis reaction and product quality (e.g., the
prevention of pitting and nonuniform deposition of the
zinc). Special make-up water quality is usually provided by
special wells. The electrolyte composition may be
maintained by special means such as extraction of byproduct
compounds (dependent on concentrate source) such as spray
drying. Zinc electrolysis is exothermic, and has associated
appropriate cooling loops in heat exchangers or flash
cooling capability for the electrolyte circuit. All spills
and wash water are considered valuable metal-bearing
material and are recycled to the leach-purification circuit.
The above are the process waste water streams whose
contributions are of principal significance in the following
discussion of the qualitative data assembled on waste water
characteristics.
Waste Water Characteristics
Overall Plant Effluents
As a first measure of waste characterization, the range of
characteristics and quantities, of past and existing
discharges from zinc plants, as available from various
sources, are presented in the following discussion.
Some general characteristics of current industry practice
are listed in Table 6. The volumetric flow rate of
discharges vary from zero at one plant in the southwestern
United States, which is able to practice complete disposal
by means of solar evaporation, to 4,060 cu in/day (1.07 mgd) .
Treatment practices at plants discharging waste water varied
from simple settling to lime-and-settle treatments applied
to either component streams or to the total plant effluent.
The characteristics of total plant effluents are given in
Tables 7 through 12. In this series of tables, the basic
concentration, flow, and production rate data are shown to
indicate the details of methodology of waste
42
-------
TABLE 6. GENERAL OVERALL CURRENT PROCESS WASTE WATER DISCHARGE
PRACTICES IN THE PRIMARY ZINC INDUSTRY^1)
Volume of Discharge
Plant Type of Operation J&/day (gal/day)
A Pyrolytic 0 (0)
B Electrolytic 1,310,000 (346,000)
C Electrolytic 1,140,000 (300,000)
D Electrolytic 4,060,000 (1,070,000)
E Pyrolytic 2,400,000 (633,000)
F Pyrolytic 2,460,000 (650,000)
G Pyrolytic 1,255,000 (331,000)
H Pyrolytic 69,200 (18,300)
(2)
Degree of Treatment
Solar Evaporation
Complete lime and settle
Settle
Mix and Settle
Partial Lime and Settle
Partial Lime and Settle
Complete Lime and Settle
(Lime and Settle)
(1) Sources: verbal and written information submitted by producers.
(2) Complete lime and settle indicates that all waste streams are treated;
partial lime and settle indicates that one or more component streams
are so treated.
43
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TABU: 7. WASTE EFFLUENTS FROM PLANT NO. B
Outfall No.: Total Plant (Treated) Discharge
Contributing Operations: Roasting Acid Plant, Electrolytic Zinc,
all associated operations
Total
Plant
Intake,
Parameter mg/1
pH 7.9
Alkalinity no
COD
Total Solids
Dissolved Solids 575
Suspended Solids °
Oil sr\d Grease
Sulfafp (as S) 80
Chloride 106
Cyanide
A I ijTYi-f PUTT]
Cadmi,™
Calcium 64
Chromium
lr™ 3.4
Lead
Magnesium 1'
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Sodium
Tellurium
Zinc
Phenols
Flow,
1/t'flV
gal /day
Prodr:*"1 f "i on ,
kkg/day 272
short, tons/day 300
Total
Plant
Discharge,
mg/1
8.6
17
--
4485
249
4
2221
171
<0.1
<0. 1
<0.02
<0.02
0.06
0.15
0.004
0.13
1.8
50
<0.1
2,763,050
730,000
Change
mg/1
17 (G)
--
+3910 (N)
+ 249 (N)
4 (G)
2141 (N)
65 (N)
<0.01 (G)
<0.01 (G)
<0.02 (G)
<0.02 (G)
-3.3 (N)
0.15 (G)
0.004 (G)
0.13 (G)
1.8 (G)
50 (G)
<0.1 (G)
kg/day
--
46.97
-"*
10,303
688
11.05
5,916
179.6
<0.028
<0.028
<0.056
--
<0.056
NLC
0.414
0.011
0.359
--
4.97
_ —
~~
~~
138.2
Net Loading
kg/kkg
--
0.173
— -
39.72
2.53
0.041
21.76
0.66
<1.0 x 10 4
-A
<1.0 x 10 ^
<2.0 x 10"4
~ ~
<2 x 10~4
NLC
0.0015
4.1 x 10"5
0.0013
~-
0.018
—, _
0.508
Ib/S.Ton
--
0.345
— ~
79.44
5.06
0.081
43.5
1.32
<2.0 x 10 ^
-L
<2.0 x 10 ^
<4 x 10~4
— —
<4 x 10'4
NLC
0.003
8.1 x 10"5
0.0026
~~
0.037
""
1.02
Source: Plant Data
44
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TABLL 8. WASTE EFFLUENTS FROM PLANT NO. C
Outfall No.:
Contributing Operations: Electrolytic Zinc Production
Parameter
Total Total
Plant Plant
Intake, Discharge,
mg/1 mg/1
Net
Change
mg/1
Net Loading
kg/day kg/kkg
Ib/S.Ton
Alkalinity
COD
Total Solids
Dissolved Solids
Suspended Solids
Oil and Grease
Sulfate (as S)
Chloride
Cyanide
Aluminum
Arsenic
Cadmium
Calcium
Chromium
Copper
Iron
Lead
Magnesium
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Sodium
Tellurium
Zinc
0.00030
0.00005
-0.00025
80
125
45
81.76
0.472
0.944
Flow,
I/day
gal/day
Production,
kkg/day
short tons/day
18,168,000
4,800,000
173.2
194
Source: Plant Data
45
-------
TABLU 9. WASTE EFFLUENTS FROM PLANT NO.D
Outfall No.: 004
Contributing Operations:
Roasting, leaching, electrolysis,
melting, and casting of Zinc
(Gross Discharge)
Parameter
PH
Alkalinity
COD
Total Solids
Dissolved Solids
Suspended Solids
Oil and Grease
SuUate (as S)
Chloride
Cyr.nide
Aluminum
Arsenic
Cadmium
Calcium
Chromium
Copper
Ir<~>n
Le.-d
Magnesium
MercMry
Molvbdenum
Nickel
Potassium
Selenium
Silver
Sodium
Tellurium
Zinc
Ammonia
Flow,
I/day
gal/day
Production,
kkg/day
short tons/day
Total Total
Plant Plant Net
Intake, Discharge, Change
mg/1 mg/1 mg/1
3.3
NA 416 NA
4
1133
1107
26
750
100
0.68
2.4
32
0.002
0.34
1.93
1.35
208
0.003
8.55
75
243
2
5,450,400
1,440,000
297.3
333
kg/day
2267
268
6175
6033
142
~~
4088
545
--
3.7
13.1
174.4
0.0109
L.85
10.5
7.36
1134
0.016
46.6
408.8
1324
10.9
Net Loading
kg/kkg
7.63
0.07
20.8
20.3
0.48
~~
13.8
1.8
--
0.01
0.044
0.59
0.00004
0.006
0.035
0.02
3.8
0.00005
0.16
1.4
4.45
0.037
Ib/S.Ton
15.3
0.14
41.6
40.6
0.96
27.6
3.6
--
0.02
0.088
0.12
0.00008
0.012
0.07
0.04
7.6
0.0001
0.32
2.8
8.9
Source: RAPP Data (1971)
46
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TABLE 10. WASTE EFFLUENTS FROM PLANT NO. F
Outfall No.: 001
Contributing Operations: Pyrolytic Zinc Smelting Operations
Parameter
PH
Alkalinity
COD
Total Solids
Dissolved Solids
Suspended Solids
Oil and Grease
Sulfate (as S)
Chloride
Cyanide
Aluninuni
Arsenic
Cadmium
Calcium
Chromium
Copper
Iron
Lead
Magnesium
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Sodium
Tellurium
Zinc
Ammonia (as N)
F
Flow,
I/day
gal/day
Production,
kkg/day
short tons/day
Total
Plant
Intake,
ma/1
7.7
75
6
260
250
5
5
125
16
<0.001
<0.0001
0.002
58
<0.1
<0.01
0.02
0.01
<0.001
<0.1
<0.1
3.5
0.002
<0.01
0.03
1.05
0.5
44,965,800
11,800,000
611.6
685
Total
Plant
Discharge,
rag/1
7.6
70
12
460
455
10
8
175
60
0.08
0.003
0.2
100
<0.1
<0.01
0.08
0.08
<0.001
<0.1
<0.1
11
0.007
<0.01
5
1.75
2.0
Net
Change
mg/1
-5
6
200
205
5
3
50
44
0.08
0.003
0.2
42
0
0
0.06
0,07
7.5
0.005
5
0.7
1.5
Net Loading
kg/day
NLC
269
8,990
9,217
225
134.9
2,248
1,978
3.6
0.13
9
1,888
2.7
3.1
337
0 0.22
224.8
31.5
67.4
kg/kkg
--
0.44
14.7
15.1
0.37
0.22
3.7
3.2
0.006
0.0002
0.01
3.1
0.004
0.005
0.55
0.0004
0.37
0.05
0.11
Ib/S.Ton
--
0.88
29.4
30.2
0.74
0.44
7.4
6.8
0.012
0.0004
0.02
6.2
0.008
0.01
1.10
0.0008
0.74
0.1
0.22
Source: 1972 RAPP Data
47
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TABLL 11. WASTE EFFLUENTS FROM PLANT NO. G
Outfall No.: 001
Contributing Operations: Horizontal Retort Zinc Plant
including Sulfuric Acid Plant
Parameter
pH
Alkalinity
COD
Total Solids
Dissolved Solids
Suspended Solids
Oil and Grease
Sulfate (as S)
Chloride
Cyanide
Ali.TnJn.ra
Cadmium
Calcium
Chromium
Copper
Iron
Lead
Magnesium
Mercury
Molybdenum
Nickel
Potassium
SeleTiT u^
Sodium
Tellurium
Zinc
Ammonia
Flow,
I/day
gal/day
Production,
kkg/day
short tons/day
Total Total
Plant Plant Net
Intake, Discharge, Change
mg/1 ms/l mg/1
NA 8.5 NA
48
73
2750
2748
2.5
1.2
360
347
50
0.56
710
0.7
0.044
1.6
1.04
1.9
0.001
40
1.4
0.01
110
11
7.6
1,078,725
285,000
124
137
kg/ day
51.8
51.8
78.8
2967
29.65
2.7
1.3
388
374
54.0
0.60
766
0.8
0.047
1.7
1.12
2.05
0.001
43.16
1.5
0.01
118.7
11.9
8.2
Net Loading
kg/kkg
0.42
0.42
0.64
23.93
0.24
0.02
0.01
3.13
3.02
0.44
0.005
6.18
0.006
0.0004
0.014
0.009
0.017
0.000008
0.35
0.012
0.00008
0.96
0.096
0.66
Ib/S.Ton
0.84
0.84
1.28
47.86
0.48
0.04
0.02
6.26
6.04
0.88
0.010
12.36
0.012
0.0008
0.028
0.018
0.034
0.000016
0.70
0.024
0.00016
1.92
0.192
1.32
48
-------
TABU; 12. WASTE EFFLUENTS FROM PLANT NO. i;
Outfall No.: 001
Contributing Operations: Horizontal Retort Zinc Production
Mixed Wastes
Total
Plant
Intake,
Parameter mg/1
PH
Alkalinity
COD
Total Solids
Dissolved Solids
Suspended Solids
Oil and Grease
Sulfate (as S)
Chloride
Cyanide
Aluminum
Arsenic
Cadmium
Calcium
Chromium
Copper
Iron
Lead
Magnesium
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Sodium
Tellurium
Zinc
Floxj,
I/day
gal/day
Production,
kkg/day
short tons/day
Total
Plant Net
Discharge, Change
mg/1 mg/1
6.7
13 NA
6
1500
1500
13
251
620
0.010
0.010
4.4
44
0.05
0.06
0.02
0.02
12.6
.001
81.5
144
120
69,220
18,288
181.4
220
kg/day
0.9
0.42
103.8
103.8
0.9
17.4
42.9
0.0007
0.0007
0.30
3.0
0.003
0.004
0.0014
0.0014
0.87
0.00007
5.64
9.96
8.3
Net Loading
kg/kkg
0.005
0.002
0.57
0.57
0.005
0.096
0.24
0.000004
0.000004
0.0017
0.017
0.000017
0.00002
0.000008
0.000008
0.0048
4 x 10"6
0.031
0.055
0.046
Ib/S.Ton
0.01
0.004
1.14
1.14
0.01
0.192
0.48
-6
8 x 10
8 x 10"6
0.0034
0.034
3.4 x 10"5
4 x 10"5
1.6 x 10"5
1.6 x 10"5
0.0096
8 x 10"6
0.062
0.11
0.092
Source: 1971 RAPP Data
49
-------
characterization. Where both intake and discharge
concentrations were available, intake concentrations were
subtracted from discharge concentrations to produce an
arithmetic net concentration, which may be taken as
indicating the contribution of the zinc producing operation
to the water. Where the arithmetic net value was negative,
no meaningful loading was considered calculable, and the
entry NLC, meaning no load calculable, was made. Where only
discharge concentrations were available, a gross discharge
characteristic was determined. Using discharge
concentrations (net or gross), unit waste loads were
calculated using the concentration, the flow, and production
rate data as given at the bottom of the tables. The data
given are drawn from various sources covering the time
period 1971 to 1973. Recent or planned changes in discharge
practices are discussed in various later portions of this
document.
A summary table of selected data is presented in Table 13 to
allow a comparison of unit waste loads expressed in units of
a constituent per unit of zinc production (i.e., kg/kkg and
lbs/1000 Ibs). Plant A is not included in these tabulations
because there is no discharge; Plant E is omitted in that no
meaningful overall unit waste load data could be developed
for the zinc smelting operation, due to the combination of
the multiplicity of (nonzinc) operations and outfalls.
In general, the data given in Table 7 through 13 exhibit a
considerable range of practices, waste water constituent
levels, flows, and other factors. Plants G and H exhibit
low production rates, minimum discharge flows, and minimum
calculated unit waste loads, with low discharge flows being
considered the most important factor in making these the
lowest unit waste loads.
In terms of gross concentrations contained in the discharge
streams, the ranges encountered in the available data for
some of the constituents given in the tables may be
summarized as:
Dissolved Solids 455-4485 mg/1
Suspended Solids 25-249 mg/1
Sulfates 175-2221 mg/1
Chlorides 60-620 mg/1
Arsenic 0.1-0.68 mg/1
Cadmium 0.02-2.4 mg/1
Copper 0.01-0.34 mg/1
Iron 0.02-1.93 mg/1
Lead 0.02-1.35 mg/1
Mercury 0.00005 - 0.004 mg/1
50
-------
TABLE 13. SUIMARY OF SULCTLD DATA W 17STL
PRIfiAMT ZINC PI/OTS (Waste loads
pound/1000 pounds)
QIAPACTLPISTICS FRCT
units of Kg/iacg or
y
Plant
Production Rate, kkg/day
„ (tons/day)
Discharge Rate, A/day
Treatment Practifeeal/da>')
Basis
Source
pH
COD
Dissolved Solids
Suspended Solids
Oil and Grease
Sulfate
Chloride
Arsenic
Cadmium
Copper
Iron
Lead
Mercury
Nickel
Selenium
Zinc
B
272
(300)
2 763,000
^730,000} .
Complete Lime
and Settle
Net &. Gross
Plant Data
8.6
0.173
39.7
2.53
0.04
21.8
0.66
< 1 x 10'4
< 2 x 10"4
< 2 x 10'4
NLC
0.0015
4.1 x 10"J
0.001
0.018
0.508
C
173
(194)
18,168,000
(4,800,000)
Settle
Net
Plant Data
-_
--
-_
—
--
__
__
—
--
--
--
NLC
-._
--
0.472
D
297
5,450,400
(1,440,000)
Partial
Lime &
Settle
Gross
1971 RAPP
Data
3.3
0.07
20.3
0.48
__
13.8
1.8
0.01
0.044
0.006
0.035
0.02
5 x 10'5
__
4,45
F
611
44,965,800
(11,800,000)
Lime & Settle
Net
1972 RAPP
Data
7.6
0.44
15.1
0.37
0.22
3.7
3.2 ,
2 x 10'4
0.01
__
0.004
0.005
__
__
__
0.37
G
124
1,078,^)
5285,000)
Lime and Settle
Gross
RAPP Data
8.5
0.64
0.24
0.02
0.01
3.13
3.02
0.005
4 x 10"4
0.014
0.009
8 ;< 10"6
0.012
0.096
H
181
(220)
69,220
(18,288)
1971 RAPP
Data
6.7
0.002
0.57
0.005
0.096
n ?A
u. ^M-
4 x 10"6
0.002
1 x 10"5
8 x 10"6
8 x 10"6
4 x 10"6
_ —
0.046
-------
Selenium 0.007-1.8 mg/1
Zinc 5-243 mg/1.
It must be noted that these generalized discharge
characteristics include all streams (i.e., noncontact
cooling water, water from auxiliary operations, etc.).
Thus, dilution of process waste water with all other waters
will produce low values of pollutant concentrations.
Thus, wastes from primary zinc plants, on the most general
basis, may be characterized as containing, not unexpectedly,
noteworthy levels of zinc and sulfates, accompanied by
typically associated elements of cadmium, lead, and, less
significantly, arsenic and selenium.
The unit waste loads given in Tables 7 to 13 represent both
treated and untreated waste waters, and show the range of
waste characteristics produced by combinations of many
factors of flow, treatment effectiveness, different types
and combinations of plant operations, production rates, etc.
More detailed discussion of these individual factors will be
given in the following paragraphs and sections. It may be
noted here that the waste loads of Plant G represent a
combination of relatively low flow, low production, and
moderately high effectiveness of a lime and settle
treatment. These waste loads may be compared with those of
Plant D where higher production and flow rates and simple
settling treatment pertain, resulting in higher unit waste
loadings of all constituents. Plant H is soon to be closed
and little information was available on factors contributing
to the very low waste loads, although the very low flow is
considered the major influence.
Unit Process Waste Streams
Both existing plant data and field verification sampling
provided some basis for the analysis of flows of waste water
streams from unit process operations.
Acid Plant Blowdown. The information developed on the
characteristics of acid plant blowdown is given in Tables 14
and 15. These streams typically contain high sulfates, low
pH, and relatively high levels of lead, cadmium, selenium,
zinc, and, depending on the concentrate fed to the roasters,
varying amounts of mercury.
52
-------
T/ABIJ: 14. WASTE EFFLUENTS FROM PLANT NO. B
Outfall No.:
Contributing Operations: Scrubber Bleed + ESP Sump (Acid Plant Slowdown)
Total
Plant
Intake,
Paraneter mg/1
pH 7.9
Alkalinity 110
COD
Total Solids
Dissolved Solids 575
Suspended Solids 0
Oil and Grease
Sulfate (as S) 80
Chloride 106
Cyanide
Aluminum
Arsenic
Cadmium
Calcium 64
Chromium
Copper
Iron 3.4
Lead
Magnesium 17
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Sodiuro
Tellurium
Zinc
Flow,
I/day
gal /day
Production,
kkg/dsy 272
short tons/day 300
Slowdown,
mg/1
23.0
135
8
5.0
4572
105
1
0.6
0.2
19
2
0.006
0.26
13
25
Net
Change
mg/1
23.0 (G)
-440 (N)
8 (N)
5.0 (G)
4492 (N)
-1 (N)
1 (G)
0.6 (G)
-64 (G)
0.2 (G)
15.6 (N)
2 (G)
-17 (G)
0.006 (G)
0.26 (G)
13 (G)
25 (G)
47,840
224,000
kg/day
19.50
.
NLC
6.78
4.24
3809
NLC
0.848
0.509
NLC
0.17
13.2
1.7
NLC
0.0051
0.22
11.0
21.2
Net Loading
ks/kkg
0.072
NLC
0.025
0.016
14.004
NLC
0.003
0.0019
NLC
0.0006
0.0485
0.0063
NLC
1.87 x 10"5
/
8 xllO"^
00.0404
0.078
Ib/S.Ton
0.144
NLC
0.05
0.032
28.0
NLC
0.006
0.004
NLC
0.0012
0.097
0.0126
NLC
3.7 x 10"5
16 x 10~4
0.081
0.156
53
-------
TALLL 15. WASTE EFFLUENTS FROM PLANT NO. E
Outfall No.:
Contributing Operations: Acid Plant Effluent (Untreated)
Discharge,
Parameter ms,/l
pH 2.8
Alkalinity
COD
Total Solids
Dissolved Solids 5400
Suspended Solids 200
Oil and Grease
Sulfate (as S)
Chloride
Cyanide
Aluminum
Arsenic
Cadmium 33
Calcium
Chromium
Copper
Iron
Lead 48
Magnesium
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Sodium
Tellurium
Zinc 1500
CrO, 0.10
Flow,
I/day 1,308,096
gal/day 345,600
Production,
kkg/dsy 321-4
short tons/day 3°°
. Loading
kg/day kg/kkg Ib/S.Ton
7063 21.98 43.95
261.6 0.814 1.628
43.16 0.134 0.268
62.8 0.195 0.391
1962 o.lOS 12.2
0.1308 0.0004 0.0008
54
-------
The data given in Tables 14 and 15 are for untreated streams
(i.e., raw waste) and are not, in themselves, representative
of discharge streams.
Of some interest also are the flow rates for acid plant
blowdown streams. Rates of flow for a number of such
streams are given in Table 16, based on internal stream flow
rate data supplied by the indicated plants. In terms of
ranges of flow, the range for the five plants varies from
741,000 I/day (195,000 gal/day) to 2,400,000 I/day (633,600
gal/day). On the basis of product (shown for both zinc and
sulfuric acid) the range of flows varies for zinc, for
example, from 3170 1/kkg (760 gal/ton) to 7900 1/kkg (1890
gal/ton). The range for this particular stream, thus,
varies less than the overall discharge rates given
previously.
The values given are flows representing mid-range values or
average values of the flows reported by the various
producers and are subject to variations due to a large
number of factors such as ambient temperature, feed
materials, operating conditions, etc.
Metal Cooling Water.A waste water stream in zinc producing
operations is from the cooling of the cast metal product,
usually in the forms of slabs, ingots, pigs, etc. Data
obtained on such a stream is given in Table 17. The
principal constituents apparently contributed by the use of
water for direct contact cooling of the cast products
include oil and grease, suspended solids, and zinc, although
the latter is a contribution appearing at much lower levels
in this stream than in, for example, acid plant blowdown.
The data given were obtained by field sampling and represent
the average of samples obtained from sampling two separate
casting operations for two days. This particular waste
water stream had an average flow rate of 231,112 I/day
(61,060 gal/day) or, expressed in terms of flow per unit of
zinc metal product, 850 1/kkg (203 gal/ton).
Other P£2£ess Waste Waters. Among other process waste
waters identifiable in the existing primary zinc industry
are various internal streams associated with either dust
control devices, gas washing (i.e., associated with recovery
of retort gas fuel values) or streams resulting from the
treatment of pollution control residues for the recovery of
metal values.
The characteristics of streams from gas scrubbing operations
are given in Tables 18 and 19. The gases are from reduction
furnaces and the streams referred to are internal process
55
-------
TABLE 16. RATES OF FLOW OF ACID PLANT
SLOWDOWN STREAMS
Plant
B
C
D
E
e
Acid Plant Slowdown
Flow Rates
I/day
850,300
741,300
2,180,000
2,400,000
980,000
(gal/day)
(224,660)
(195,800)
(576,000)
(633,600)
(259,000)
Flow Per Unit of
Zinc Produced
1/kkg
3170
4220
7220
7300
7900
(gal/ton)
(76C)
(1010)
(1720)
(1760)
(1890)
Flow Per Unit of
Sulfuric Acid Produced
1/kkg
4900
1960
6850
5300
3920
(gal/ton)
(1180)
(470)
(1640)
(1270)
(940)
56
-------
TABLE 17. WASTE EFFLUENTS FROM PLANT NO. B
Outfall No.:
Contributing Operations: Metal Casting Cooling
Total
Plant
Intake ,
Parameter mg/1
pH 7.9
Alkalinity 110
COD
Total Solids
Dissolved Solids 575
Suspended Solids 0
Oil and Grease
Sulfate (as S) 80
Chloride 106
Cyanide
Aluminum
Arsenic
Ca dmium
Calcium 64
Chromium
Copper
Iron 3 -4
i tUll
Lead
Magnesium 17
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Sodium
Tellurium
Zinc
Flow,
I/day
gal /day
Production,
kkg/day 2T2.1
short tons/day 30°
Discharge,
ms;/l
8.4
14
14
340
5
13
37
95
1
"
<0.02
<0.02
0.05
0.05
<0.002
<0.02
0.03
1.1
231,112
61,060
Net
Change
mg/1
14 (G)
-235 (N)
5 (G)
13 (G)
-43 (N)
-11 (N)
<0.1 (G)
<0.1 (G)
<0.02 (G)
-64 (G)
<0.02 (G)
-3.35 (N)
0.05 (G)
-17 (G)
<0.002 (G)
<0.02 (G)
0.03 (G)
1.1 (G)
Net Loading
kg/day
3.23
-54.3
1.16
3.0
-9.9
-2.54
<0.023
<0.023
<0.046
-14.8
<0.046
-0.77
0.012
3.93
<0.0005
<0.005
'0.007
0.25
kg/kkg
0.012
NLC
0.0043
0.011
NLC
NLC
<0. 00008
<0. 00008
<0. 00017
NLC
<0. 00017
NLC
0.00004
NLC
<1.8 x 10"6
<0. 000018
0.000026
0.00092
Ib/S.Ton
0.024
NLC
0.0086
0.022
NLC
NLC
<0.0002
<0.0002
<0.0003
NLC
<0.0003
NLC
0.00008
NLC
<3.6 x 10'6
<3.6 x 10"5
0.000052
0.00184
57
-------
TABLE 18. QIARACTERISTICS OF GAS SCRUBBING IZASTE vCVTER (AFTER SETTLING)
Concentrations ,
Calculated
mg/Ji Raw Waste Load (Combined Streams)
Constituent
pH
Dissolved Solids
Suspended Solids
Sulfate
Chloride
Cadmium
Zinc
Stream 1
--
490
50
150
40
0.05
2
Stream 2
7.8
800
20
100
150
0.3
2
kg/ day
9,788
327
1,417
1,722
3.4
26.16
Ibs/day
21,530
720
3,120
3,790
7, .5
57 .,6
kg/kkg(2) lb/ton(2)
--
16.0
1.17
5.10
6.20
0.012
0.094
(1) Not a discharge stream, i.e., an internal-process stream; total flow of
combined streams averaged 13,081,000 i/day (3,376,000 gal/day), equiva-
lent to 21,388 A/kkg (4,930 gal/ton) of zinc produced; data supplied by
plant operators.
(2) Metal concentrations reported on the basis of soluble metals.
58
-------
TABLE 19. aiARACTERISTICS OF GAS SCRUBBING V?ASTE WATER (AFTER SCRUBBING)
Concentrations ,
Constituent tng/jj
PH
Dissolved Solids 7.2
Suspended Solids 220
Cadmium 0.15
Lead 58
Cyanide 12
Calculated Raw Waste Load
kg/day
45.5
10.4
0.031
12
2.48
Ibs/day kg/kkg
0.170
0.039
0.00012
0.045
0.009
Ib/ton
0.34
0.077
0.00023
1.5 x 10"4
0.019
(1) A scrubber-bleed stream; not a discharge stream; average flow value of
207,100 A/day (54,720 gal/day), equivalent to 761 4/kkg (182 gal/ton)
of zinc produced.
(2) Metals concentrations based on total metals.
59
-------
streams (i.e., they are not discharged as characterized, but
pass through other steps of production processes, waste
treatment, or mixing before becoming a component of
discharge). The characteristics listed were reported by
producers, and the constituents for which data were
available are those considered of significant interest by
the producer. It should be noted that characteristics are
reported after settling and the metal concentrations are
reported in terms of soluble metals in one case (Table 18)
and total metals in the other case (Table 19). Water use
levels in the two applications were calculated to be 21,400
1/kkg (4,900 gal/ton) of zinc produced, and 461 1/kkg (182
gal/ton) in the other case, with the difference being that
the first case represents once through water use and the
second case represents a system involving recycle with a
bleed amounting to approximately 0.1 percent of the total
recirculating flow. Efforts to completely close this
scrubber circuit, have caused problems with spray nozzles to
such an extent as to seriously interfere with plant
operation.
Characteristics of waste waters from auxiliary unit process
operations are given in Tables 20 through 22. In the first
two cases, the waste waters are produced by auxiliary
operations treating air pollution control or other residues
to allow reclamation of zinc values. The principal
characteristic of these streams are relatively high levels
of dissolved solids (sulfates and chlorides). They also
contain varying, but significant levels of the previously
discussed constituents arsenic, cadmium, copper, zinc, and
lead. Again, the two streams characterized in Tables 20 and
21 are internal process streams and are subject to mixing
and treatment before discharge. The average flow rates
associated with these two streams were i?4 1/kkg (42
gal/ton) and 353 1/kkg (85 gal/ton) calculated on the basis
of zinc production for the plant.
Another stream encountered within the industry was from a
unique chemical conversion operation associated with the
production of an additive to the electrolyte. The
characteristics of this waste water are given in Table 22 in
terms of grab samples from two days of batch-type
operations. The principal constituents of those identified
are an alkaline pH (11) and a high level of dissolved
solids. The other characteristics reflect the separate
nature of the chemicals involved and do not correspond to
the previous streams discussed. The average flow associated
with this waste water stream was calculated as 4150 1/kkg
(900 gal/ton) on the basis of the plant zinc production.
The stream was subsequently treated before discharge.
60
-------
TABLE 20. WASTE EFFLUENTS FROM PLANT NO. B
Outfall No.:
Contributing Operations: Auxilary Metal Reclamation Operation
Parameter
PH
Alkalinity
COD
Total Solids
Dissolved Solids
Suspended Solids
Oil and Grease
Sulfate (as S)
Chloride
Cyanide
Aluminum
Arsenic
Ca'dmium
Calcium
Chromium
Copper
Ircr
Lead
Magnesium
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Sodium
Tellurium
Zinc
Phenols
Flow,
I/day
gal/day
Production,
kkg/day
short tons/day
Total Total
Plant Plant
Intake, Discharge,
mg/1 mg/1
6.3
110
4
575 4060
0 9
1
80 33
106 1542
<0.1
0.10
64
<0.02
3.4 0.48
1.8
17
0.003
<0.02
0.01
1300
<0.1
Net
Change
mg/1
4 (G)
3485 (N)
9 (N)
1 (G)
-47 (N)
1436 (N)
<0.1 (G)
0.1 (G)
0.10 (G)
NLC
<0.02 (G)
-2.92 (N)
1.8 (G)
-17 (N)
0.003 (G)
<0.02 (G)
0.01 (G)
1300 (G)
<0.1 (G)
47,464
12,540
272.1
300
Net Loading
kg /day
0.19
,
165.5
10.43
0.048
NLC
68.21
<0.0048
0.0048
0.0048
NLC
<9.5 x 10
NLC
0.086
NLC
kg/kkg Ib/S.Ton
6.99 x
0.61
0.0016
1.7 x
NLC
0.251
<1.7 x
1.7 x
1.7 x
NLC
-4 <3.4
NLC
3.1
NLC
1.4 x
<9.5 x 10-4 0.4
'0.0048
61.75
<0.0048
1.7 x
0.227
<1.7 x
10"4 0.0014
1.2
0.0032
10"4 3.4 x 10-4
NLC
0.502
10-5 <3.4 x 10"5
c . _ c
10 5 3.4 x 10 5
10"5 3.4 x ID'5
NLC
xlO-6 <6.8 x 10"6
NLC
x 10'4 6.2 x 10'4
NLC
10"4 1 x 10-
x ID'6 <6.8 x 10'6
10"5 3.4 x ID'5
0.454
ID'5 <3.4 x 10"5
61
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TALLL 21. WASTE EFFLUENTS FROM PLANT NO. B
Outfall >'o.:
Contributing Operations: Auxilary Metal Reclamation Operation
Parameter
p'H
Alkalinity
COD
Total Solids
Dissolved Solids
Suspended Solids
Oil and Grease
Sulfate (as S)
Chloride
Cyanide
Aluminum
Arspn1" c
Cadmium
Calcium
Chromium
Copper
Iron
Lead
Magnesium
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Sodium
Tellurium
Zinc
Phenols
Flow,
1/d.nv
gel/day
Production,
kkg/day
short tons/day
Intake, Discharge,
mg/1 tng/1
7.9 5.2
110
56
575 146,130
0 1,338
10
80 9,259
106 160
<0.1
3.0
<0.02
64
8.0
3.4 33.0
300
17
0.003
1.0
-------
T/U3LL, 22. WASTE EFFLUENTS FROM PLANT NO. B
Outfall No.:
Contributing Operations: Auxilary Process Ooeration
Total
Plant
Intake ,
Parameter mg/1
pH 7.9
Alkalinity 110
COD
Total Solids
Dissolved Solids 575
Suspended Solids 0
Oil xr,d Grease
Sulfat* (as S) 80
Chloride 106
Cyanide
Aluminum
Arsenic
Cadmium
Calcium ,.
^ • 64
Chromium
Copper
Iron 2 4
Les d
Magnesium ^7
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Sodium
Tellurium
Zinc
Flow,
I/flay
gal/day
Production,
kkg/day 272.1
short tens/day 300
Discharge ,
rng/1
11.0
34
135970
1447
5
10947
295
<0.1
0.1
0.1
<0.02
0.04
1.6
0.05
<0.002
0.02
<0.01
3.5
Net Change
mg/1
34(G)
134595(N)
1447(N)
5(G)
10867(N)
189 (N)
<0.1(G)
O.l(G)
<0.02(G)
0.04(G)
-1.8(N)
0.05(G)
<0.002(G)
0.02(G)
<0.01(G)
3.5(G)
113,020
29,860
ks/day
3.84
15209
163.5
0.565
1228.0
21.357
<0.011
0.011
0.0023
0.0046
NLC
0.0057
NLC
0.0023
0.0011
0.396
kg/M ton
0.0141
55.89
0.601
0.0021
4.513
0.0785
0.00004
0.00004
0.000008
0.000016
NLC
0.0002
NLC
9 x 10"7
0.000008
0.000004
0.0014
Ib/S.Ton
0.0282
111.78
1.202
0.0042
9.026
0.1570
0.00008
0.00008
0.000016
0.000032
NLC
0.0004
NLC
18 x 107
0.000016
0.000008
0.00292
63
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Summary
The waste characteristics of the primary zinc industry have
been shown in terms of concentration and unit waste load.
The noteworthy characteristics in the waste waters have been
identified as dissolved solids, most commonly sulfates,
metals such as lead, cadmium, zinc, copper, selenium, and
arsenic. Characteristics of internal process streams have
been similarly identified in terms of the common component
process waste water streams of acid plant blowdown,_metal
casting cooling water, and streams arising from auxiliary
operations such as air pollution control or treatment of
residues for recovery of zinc values.
64
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SECTION VI
SELECTION OF POLLUTANT PARAMETERS
Introduction
The following waste water parameters, which have been
determined to be present in the process waste waters of the
primary zinc industry in sufficient quantities to warrant
there control and treatment, are as follows:
Total suspended solids
Arsenic
Cadmium
Mercury
Selenium
Zinc
PH
The rationale for the designation of these parameters and
for the rejection of other parameters are presented in the
following paragraphs.
Sltiona^_fo^_the_Selection_of_Pollutant_Parameters
The control and treatment technologies discussed in Section
VII describe the current practices, as well as those which
are under construction, by the industry which are used to
treat and control the selected pollutants. From these
discussions, it was concluded that the discharge of total
suspended solids and heavy (trace) metals can be controlled
by pH adjustment and suspended solids removal.
Setting effluent limitations on the prescribed heavy metals,
which are the principal pollutant metals in the process
waste waters from the primary zinc industry, and specifying
a pH range will in turn limit the other trace metals found
in these waste waters. Such metals include aluminum,
magnesium, antimony, chromium, cobalt, copper, iron
manganese, nickel, silver, and tin.
There is an optimum pH for precipitation of each metal,
which results in its greatest reduction by solids removal
(settling or filtration). The pH selected for the mixture
of metals associated with the primary zinc industry is a
compromise between the maximum removal of cadmium and zinc,
as hydroxides, and that suited for the maximum removal of
65
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the other metals associated with the process waste waters.
Coprecipitation of these heavy metal hydroxides with cadmium
and zinc hydroxide (and also aluminum, copper, iron, and
magnesium hydroxide, if they are present in the waste
waters) at a pH at which optimum coprecipitation occurs is
used in good water treatment practice. Therefore, an
appropriate pH adjustment, followed by solids removal will
reduce all the metals to levels consistent with the best
practicable control technology currently available.
Acidity and alkalinity are reciprocal terms. Acidity is
produced by substances that yield hydrogen ions upon
hydrolysis and alkalinity is produced by substances that
yield hydroxyl ions. The terms "total acidity" and "total
alkalinity" are often used to express the buffering capacity
of a solution. Acidity in natural waters is caused by
carbon dioxide mineral acids, weakly dissociated acids, and
the salts of strong acids and weak bases. Alkalinity is
caused by strong bases and the salts of strong alkalies and
weak acids.
The term pH is a logarithmic expression of the concentration
of hydrogen ions. At a pH of 7, the hydrogen and hydroxyl
ion concentrations are essentially equal and the water is
neutral. Lower pH values indicate acidity while higher
values indicate alkalinity. The relationship between pH and
acidity or alkalinity is not necessarily linear or direct.
Waters with a pH below 6.0 are corrosive to water works
structures, distribution lines, and household plumbing
fixtures and can thus add such constituents to drinking
water as iron, copper, zinc, cadmium and lead. The hydrogen
ion concentration can affect the "taste" of the water. At a
low pH, water tastes "sour". The bactericidal effect of
chlorine is weakened as the pH increases, and it is
advantageous to keep the pH close to 7. This is very
significant for providing safe drinking water.
Extremes of pH or rapid pH changes can exert stress
conditions or kill aquatic life outright. Dead fish,
associated algal blooms, and foul stenches are aesthetic
liabilities of any waterway. Even moderate changes from
"acceptable" criteria limits of pH are deleterious to some
species. The relative toxicity to aquatic life of many
materials is increased by changes in the water pH.
Metalocyanide complexes can increase a thousand- fold in
toxicity with a drop of 1.5 pH units. The availability of
66
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many nutrient substances varies with the alkalinity and
acidity. Ammonia is more lethal with a higher pH.
The lacrirnal fluid of the human eye has a pH of
approximately 7.0 and a deviation of 0.1 pH unit from the
norm may result in eye irritation for the swimmer.
Appreciable irritation will cause severe pain.
The parameter of pH is considered essential as a
characteristic of waste water. Since it is the major
control parameter in neutralization treatment, the
pertinency has been indicated in terms of current waste
characteristics in Section IV and is further discussed in
subsequent sections of this document. When in the range of
pH 7 to ]0, the acid wastes have been neutralized, but are
not excessively alkaline. Overall concentrations of
dissolved metals can be expected to be at a minimum when the
pH of the discharge is maintained in this range.
Total Suspended Solids
Suspended solids include both organic and inorganic
materials. The inorganic components include sand, silt, and
clay. The organic fraction includes such materials as
grease, oil, tar, animal and vegetable fats, various fibers,
sawdust, hair, and various materials from sewers. These
solids may settle out rapidly and bottom deposits are often
a mixture of both organic and inorganic solids. They
adversely affect fisheries by covering the bottom of the
stream or lake with a blanket of material that destroys the
fish-food bottom fauna or the spawning ground of fish.
Deposits containing organic materials may deplete bottom
oxygen supplies and produce hydrogen sulfide, carbon
dioxide, methane, and other noxious gases.
In raw water sources for domestic use, state and regional
agencies generally specify that suspended solids in streams
shall not be present in sufficient concentration to be
objectionable or to interfere with normal treatment
processes. Suspended solids in water may interfere with
many industrial processes, and cause foaming in boilers, or
encrustations on equipment exposed to water, especially as
the temperature rises. Suspended solids are undesirable in
water for textile industries, paper and pulp, beverages,
dairy products, laundries, dyeing, photography, cooling
systems, and power plants. Suspended particles also serve
as a transport mechanism for pesticides and other
substances, which are readily sorbed into or onto clay
particles.
67
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Solids may be suspended in water for a time, and then settle
to the bed of the stream or lake. These settleable solids
discharged with man's wastes may be inert, slowly
biodegradable materials, or rapidly decomposable substances.
While in suspension, they increase the turbidity of the
water, reduce light penetration and impair the
photosynthetic activity of aquatic plants.
Solids in suspension are aesthetically displeasing. When
they settle to form sludge deposits on the stream or lake
bed, they are often much more damaging to the life in water,
and they retain the capacity to displease the senses.
Solids, when transformed to sludge deposits, may do a
variety of damaging things, including blanketing the stream
or lake bed and thereby destroying the living spaces for
those benthic organisms that would otherwise occupy the
habitat. When of an organic and therefore decomposable
nature, solids use a portion or all of the dissolved oxygen
available in the area. Organic materials also serve as a
seemingly inexhaustible food source for sludgeworms and
associated organisms.
Turbidity is principally a measure of the light absorbing
properties of suspended solids. It is frequently used as a
substitute method of quickly estimating the total suspended
solids when the concentration is relatively low.
Total suspended solids is a gross measure of the solids
remaining in suspension following treatment of precipitated
dissolved metals. Compliance with a TSS limitation insures
that effective phase separation has been achieved.
Relatively unsophisticated methods, the simplest of which is
provision for adequate settling time in a settling pond, are
available for the treatment of waste water to decrease the
suspended solids content.
Arsenic
Arsenic is found to a small extent in nature in the
elemental form. It occurs mostly in the form of arsenites
of metals or as pyrites.
Arsenic is normally present in sea water at concentrations
of 2 to 3 ug/1 and tends to be accumulated by oysters and
other shellfish. Concentrations of 100 mg/kg have been
reported in certain shellfish. Arsenic is a cumulative
poison with long-term chronic effects on both aquatic
organisms and on mammalian species and a succession of small
doses may add up to a final lethal dose. It is moderately
68
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toxic to plants and highly toxic to animals especially as
AsH3.
Arsenic trioxide, which also is exceedingly toxic, was
studied in concentrations of 1.96 to 40 mg/1 and found to be
harmful in that range to fish and other aquatic life. Work
by the Washington Department of Fisheries on pink salmon has
shown that at a level of 5.3 mg/1 of As£O3 for 8 days,
arsenic trioxide was extremely harmful to this species; on
mussels, a level of 16 mg/1 was lethal in 3 to 16 days.
Severe human poisoning can result from 100 mg
concentrations, and 130 mg has proved fatal. Arsenic can
accumulate in the body faster than it is excreted and can
build to toxic levels, from small amounts taken periodically
through lung and intestinal walls from the air, water and
food.
Arsenic is a normal constituent of most soils, with
concentrations ranging up to 500 mg/kg. Although very low
concentrations of arsenates may actually stimulate plant
growth, the presence of excessive soluble arsenic in
irrigation waters will reduce the yield of crops, the main
effect appearing to be the destruction of chlorophyll in the
foliage. Plants grown in water containing one mg/1 of
arsenic trioxide showed a blackening of the vascular
bundles in the leaves. Beans and cucumbers are very
sensitive, while turnips, cereals, and grasses are
relatively resistant. Old orchard soils in Washington that
contained 4 to 12 mg/kg of arsenic trioxide in the top soil
were found to have become unproductive.
Arsenic is also identifiable as a characteristic process
waste water pollutant contributed by primary zinc operations
and is also not proven to be reliably controlled by common
practicable control or treatment methods such as lime and
settle. In order to achieve the desired goal of improved
control and reduction of the discharge of pollutants, it is
deemed necessary to select arsenic as a specific parameter.
Cadmium
Cadmium in drinking water supplies is extremely hazardous to
humans, and conventional treatment, as practiced in the
United States, does not remove it. Cadmium is cumulative in
the liver, kidney, pancreas, and thyroid of humans and other
animals. A severe bone and kidney syndrome in Japan has
been associated with the ingestion of as little as 600
ug/day of cadmium.
69
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Cadmium is an extremely dangerous cumulative toxicant,
causing insidious progressive chronic poisoning in mammals,
fish, and probably other animals because the metal is not
excreted. Cadmium could form organic compounds which might
lead to mutagenic or teratogenic effects. Cadmium is known
to have marked acute and chronic effects on aquatic
organisms also.
Cadmium acts synergistically with other metals. Copper and
zinc substantially increase its toxicity. Cadmium is
concentrated by marine organisms, particularly molluscs,
which accumulate cadmium in calcareous tissues and in the
viscera. A concentration factor of 1000 for cadmium in fish
muscle has been reported, as have concentration factors of
3000 in marine plants, and up to 29,600 in certain marine
animals. The eggs and larvae of fish are; apparently more
sensitive than adult fish to poisoning by cadmium, and
crustaceans appear to be more sensitive than fish eggs and
larvae.
Cadmium is identifiable as a characteristic component of
process waste water in the primary zinc industry and is a
characteristic byproduct of zinc production. The chemical
behavior in lime-and-settle treatment processes varies
considerably from that of zinc and its selection as a
pollutant parameter for purposes of establishing effluent
limitations provides another parameter indicating the level
of performance achieved in any control and treatment
technology.
Mercury
Although elemental mercury occurs as a free metal in some
parts of the world, it is rather inert chemically and
insoluble in water; hence, it is not likely to occur as a
water pollutant. It is used in scientific and electrical
instruments, in dentistry, in power generation, in solders,
and in the manufacture of lamps. Mercuric salts occur in
nature chiefly as the sulfide HgS, known as cinnabar, but
numerous synthetic organic and inorganic salts of mercury
are used commercially and industrially. Many of the
mercuric and mercurous salts are highly soluble in water.
Mercury and mercuric salts are considered to be highly toxic
to humans. They are readily absorbed by way of the
gastrointestinal tract, and fatal doses for man vary from 3
to 30 grams. Adults may safely drink water containing about
4 to 12 mg of Hg per day and a fatal does of such water
would be about 75 to 300 mg per day.
70
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Mercuric ions are considered to be highly toxic to aquatic
life. For freshwater fish, concentrations of 0.004 to 0.02
mg/1 of Hg have been reported harmful.
Mercury salts, such as the unstable compounds mercuric
sulfate and nitrate, have killed minnows at a concentration
of 0.01 mg/1 as mercury, after 80-92 days. At
concentrations of 0.05 and 0.1 mg/1 as mercury, fish were
killed in 6 to 12 days. For phytoplankton, the minimum
lethal concentration of mercury salts has been reported to
range from 0.9 to 60 mg/1 of Hg. The toxic effects of
mercuric salts are accentuated by the presence of trace
amounts of copper.
The available information serves to identify mercury as a
process waste water pollutant characteristic of the zinc
industry. Further, mercury is currently the subject of
control and treatment efforts including methods other than
lime-and-settle treatment. The chemical behavior of mercury
in a lime-and-settle treatment process is not currently
demonstrated conclusively. Thus, the selection of mercury
as a process waste water pollutant parameter is deemed
appropriate in that it is characteristic of zinc operations,
but not automatically or concurrently controlled by control
and treatment technology applicable to other constituents.
Selenium
Analogous to sulfur in many of its chemical combinations,
selenium is used in its elemental form and as several salts
in a variety of industrial applications, such as
pigmentation in paints, dyes, and glass production; as a
component of rectifiers, semiconductors, photo-electric
cells, and other electrical apparatus; as a supplement to
sulfur in the rubber industry; as a component of alloys; and
for insecticide sprays. Selenium occurs in some soils as
basic ferric selenite, as calcium selenate, as elemental
selenium, and in organic compounds derived from decayed
plant tissue. In some areas of South Dakota and Wyoming,
soils may contain up to 30 mg/kg of selenium. Selenium may
be expected in trace quantities in the municipal sewage from
industrial communities.
Proof of human injury by selenium is scanty and definite
symptoms of selenium poisoning have not been identified; but
it is widely believed that selenium is highly toxic to man.
It has been stated that the symptoms of selenium poisoning
are similar to those of arsenic poisoning. Mild chronic
selenium poisoning has been observed in humans living in
areas where the soil and produce are rich in selenium. In
71
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addition, there have been cases of selenosis at industrial
establishments that use or produce selenium compounds.
Selenium in trace amounts appears to be essential for the
nutrition of animals, including man, although very little is
known about the mechanism of its action. Arsenic and
selenium are apparently antagonistic in their toxicity,
tending to counteract each other. Selenium salts are
rapidly and efficiently absorbed from the gastro-intestinal
tract and excreted largely through the urine. Retention is
highest in the liver and kidney. Surveys have shown that
dental caries rates of permanent teeth were significantly
higher in seleniferous areas than in non-seleniferous areas.
There is also a tendency for increased malocclusion and
gingivitis in seleniferous areas. The USPHS Drinking Water
Standards have restricted selenium to 0.05 mg/1 on a
mandatory basis for many years. In 1962, however, the new
standards lowered the mandatory limit to 0.01 mg/1. The WHO
International and European Drinking Water Standards
prescribe a mandatory limit of 0.05 mg/1. These strict
standards were undoubtedly set because of the similarity
between arsenic and selenium poisoning, the dental effect,
and the known toxicity to livestock, as described below.
In general, the soil in parts of the world where selenium
poisoning occurs naturally contains 1 to 6 mg/kg of selenium
in the top eight inches. However, plants vary in their
ability to absorb selenium; the final selenium
concentrations in the plant will be determined by many
factors, including the species and age of the plant, season
of the year, and the concentration of soluble selenium
compounds in the root zone.
Selenium poisoning ("alkali disease" or "blind staggers")
occurs frequently among livestock in the Great Plains
regions of the United States and Canada, and also in Mexico.
It can be produced in laboratory rats, as well as livestock,
by feeding abnormal amounts or inorganic selenium compounds
of seleniferous feed. Selenium poisoning occurs naturally
among cattle, sheep, horses, pigs, and even poultry, in both
chronic and acute forms. It is characterized by loss of
hair from mane and tail and soreness of the feet, as well as
by deformity, loss of condition, and emaciation. Among
poultry, the eggs give rise to abnormal or weak chicks.
Impairment of vision, weakness of limbs, and respiratory
death have resulted from livestock feeding on plants
containing ICO to 1000 mg/kg of selenium.
Added as a sodium selenite, 2.0 mg/1 of selenium has been
toxic to goldfish in eight days, and lethal in 18 to 46
days. Minute concentrations of selenium appear not to be
72
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harmful to fish during an exposure period of several days;
however, constant exposure to traces of selenium has caused
disturbances of appetite and equilibrium, pathological
changes, and even deaths of fish after several weeks.
Concentrations considered safe for human beings over a
period of weeks have been toxic to fish.
The rationale for the selection of selenium as a process
waste water pollutant parameter is based on the same
considerations as for mercury and arsenic (i.e., it is
identifiable as a characteristic contribution of zinc
producing operations, but exhibits chemical behavior such
that it is not automatically removed concurrently with other
constituents by current treatment practices.
Zinc
Occurring abundantly in rocks and ores, zinc is readily
refined into a stable pure metal and is used extensively for
galvanizing, in alloys, for electrical purposes, in printing
plates, for dye-manufacture and for dyeing processes, and
for many other industrial purposes. Zinc salts are used in
paint pigments, cosmetics, pharmaceuticals, dyes,
insecticides, and other products too numerous to list
herein. Many of these salts (e.g., zinc chloride and zinc
sulfate) are highly soluble in water; hence it is to be
expected that zinc might occur in many industrial wastes.
On the other hand, some zinc salts (zinc carbonate, zinc
oxide, zinc sulfide) are insoluble in water and consequently
it is to be expected that some zinc will precipitate and be
removed readily in most natural waters.
In zinc mining areas, zinc has been found in waters in
concentrations as high as 50 mg/1. In most surface and
ground waters, it is present only in trace amounts. There
is some evidence that zinc ions are adsorbed strongly and
permanently on silt, resulting in inactivation of the zinc.
Concentrations of zinc in excess of 5 mg/1 in raw water used
for drinking water supplies cause an undesirable taste which
persists through conventional treatment. Zinc can have an
adverse effect on man and animals at high concentrations.
In soft water, concentrations of zinc ranging from 0.1 to
1.0 mg/1 have been reported to be lethal to fish. Zinc is
thought to exert its toxic action by forming insoluble
compounds with the mucous that covers the gills, by damage
to the gill epithelium, or possibly by acting as an internal
poison. The sensitivity of fish to zinc varies with
species, age and condition, as well as with the physical and
73
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chemical characteristics of the water. Some acclimatization
to the presence of zinc is possible. It has also been
observed that the effects of zinc poisoning may not become
apparent immediately, so that fish removed from zinc-
contaminated to zinc-free water (after 4-6 hours of exposure
to zinc) may die 48 hours later. The presence of copper in
water may increase the toxicity of zinc to aquatic
organisms, but the presence of calcium or hardness may
decrease the relative toxicity.
Observed values for the distribution of zinc in ocean waters
vary widely. The major concern with zinc compounds in
marine waters is not one of acute toxicity, but rather of
the long-term sub-lethal effects of the metallic compounds
and complexes. From an acute toxicity point of view,
invertebrate marine animals seem to be the most sensitive
organisms tested. The growth of the sea urchin, for
example, has been retarded by as little as 30 ug/1 of zinc.
Zinc sulfate has also been found to be lethal to many
plants, and it could impair agricultural uses.
Zinc has, not unexpectedly, been identified as a process
waste water pollutant characteristically contributed t>y the
zinc industry. As will be developed in more detail later,
the chemical behavior of zinc makes it a component of
special nature in current lime-and-settle treatment
technology and is, thus, a critical indicator of the level
of performance achieved in treatment operations.
Siii2nale_for_Rejection_of_Other_Waste_Water
£onstituents_as_PoJLlutant_Parameters
Dissolved Solids
In natural waters the dissolved solids consist mainly of
carbonates, chlorides, sulfates, phosphates, and possibly
nitrates of calcium, magnesium, sodium, and potassium, with
traces of iron, manganese and other substances.
Many communities in the United States and in other countries
use water supplies containing 2000 to 4000 mg/1 of dissolved
salts, when no better water is available. Such waters are
not palatable, may not quench thirst, and may have a
laxative action on new users. Waters containing more than
4000 mg/1 of total salts are generally considered unfit for
human use, although in hot climates such higher salt
74
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concentrations can be tolerated; whereas, they could not be
in temperate climates. Waters containing 5COO mg/1 or more
are reported to be bitter and act as bladder and intestinal
irritants. It is generally agreed that the salt
concentration of good, palatable water should not exceed 500
mg/1.
Limiting concentrations of dissolved solids for fresh-water
fish may range from 5,000 to 10,000 mg/1, according to
species and prior acclimatization. Some fish are adapted to
living in more saline waters, and a few species of fresh-
water forms have been found in natural waters with a salt
concentration of 15,000 to 20,000 mg/1. Fish can slowly
become acclimatized to higher salinities, but fish in waters
of low salinity cannot survive sudden exposure to high
salinities, such as those resulting from discharges of oil-
well brines. Dissolved solids may influence the toxicity of
heavy metals and organic compounds to fish and other aquatic
life, primarily because of the antagonistic effect of
hardness on metals.
Waters with total dissolved solids over 500 mg/1 have
decreasing utility as irrigation water. At 5,000 mg/1,
water has little or no value for irrigation.
Dissolved solids in industrial waters can cause foaming in
boilers and interference with cleanliness, color, or taste
of many finished products. High contents of dissolved
solids also tend to accelerate corrosion.
Specific conductance is a measure of the capacity of water
to convey an electric current. This property is related to
the total concentration of ionized substances in water and
water temperature. This property is frequently used as a
substitute method of quickly estimating the dissolved solids
concentration.
From the standpoint of quantity discharged, dissolved solids
could have been considered a pollutant parameter. However,
there is no readily available treatment for significantly
decreasing dissolved solids beyond the levels achieved by
the limitations on metals content and pH. Energy
requirements, especially for evaporation, are such as to
preclude limiting dissolved solids at this time. Operators
should, however, be encouraged to minimize discharge of
excessive dissolved solids by intelligent management of
those plant operations resulting in the contribution of
additional dissolved solids to the waste effluents.
75
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Lead, Nickel, and Copper
Lead has been identified as a constituent in process waste
waters, but is considered to be responsive to the control
technologies applicable to the control of cadmium
Specifically, a lime-and-settle treatment operated to
produce optimum values of zinc and cadmium (both selected
above) will necessarily result in associated degrees of
reduction of lead, copper, nickel, and some other metals.
Chemical Oxygen Demand
The chemical oxygen demand is a measure of the quantity of
the oxidizable materials present in water and varies with
water composition, temperature, and other functions.
Dissolved oxygen (DO) is a water quality constituent that,
in appropriate concentrations, is essential not only to keep
organisms living but also to sustain species reproduction,
vigor, and the development of populations. Organisms
undergo stress at reduced DO concentrations that make them
less competitive and able to sustain their species within
the aquatic environment. For example, reduced DO
concentrations have been shown to interfere with fish
population through delayed hatching of eggs, reduced size
and vigor of embryos, production of deformities in young,
interference with food digestion, acceleration of blood
clotting, decreased tolerance to certain toxicants, reduced
food efficiency and growth rate, and reduced maximum
sustained swimming speed. Fish food organisms are likewise
affected adversely in conditions with suppressed DO. Since
all aerobic aquatic organisms need a certain amount of
oxygen, the consequences of total lack of dissolved oxyaen
due to a high COD can kill all inhabitants of the affected
area.
If a high COD is present, the quality of the water is
usually visually degraded by the presence of decomposing
materials and algae blooms due to the uptake of degraded
materials that form the foodstuffs of the algal populations.
The low concentration of oil and grease found in the process
waste waters of this industry will minimize the organic
sources of COD. Limitations on pli will control ferrous-iron
content of effluents.
Cyanide
Cyanides in water derive their toxicity primarily from
undissolved hydrogen cyanide (HCN) rather than from the
cyanide ion (CN~). HCN dissociates in water into H+ and CN~
in a pH dependent reaction. At a pH of 7 or below, less
than 1 percent of the cyanide is present as CN~; at a ph of 8,
76
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6.7 percent; at a pH of 9, 42 percent; and at a pH of 10, 87
percent of the cyanide is dissociated. The toxicity of
cyanides is also increased by increases in temperature and
reductions in oxygen tensions. A temperature rise of 10°C
produced a two- to threefold increase in the rate of the
lethal action of cyanide.
Cyanide has been shown to be poisonous to humans; amounts
over 18 ppm can have adverse effects. A single dose of
about 50-60 mg is reported to be fatal.
Trout and other aquatic organisms are extremely sensitive to
cyanide. Amounts as small as 0.1 part per million can kill
them. Certain metals, such as nickel, may complex with
cyanide to reduce lethality especially at higher pH values,
but zinc and cadmium cyanide complexes are exceedingly
toxic.
When fish are poisoned by cyanide, the gills become
considerably brighter in color than those of normal fish,
owing to the inhibition by cyanide of the oxidase
responsible for oxygen transfer from the blood to the
tissues.
While cyanides are used in the concentrating of zinc ores by
floatation, they are not used in zinc smelting or refining,
nor are they formed by any of the processing operations, and
no need exists for cyanide limitations.
Temperature
Temperature is one of the most important and influential
v/ater quality characteristics. Temperature determines those
species that may be present; it activates the hatching of
young, regulates their activity, and stimulates or
suppresses their growth and development; it attracts, and
may kill when the water becomes too hot or becomes chilled
too suddenly. Colder water generally suppresses
development. Warmer water generally accelerates activity
and may be a primary cause of aquatic plant nuisances when
other environmental factors are suitable.
Temperature is a prime regulator of natural processes within
the water environment. It governs physiological functions
in organisms and, acting directly or indirectly in
combination with other water quality constituents, it
affects aquatic life with each change. These effects
include chemical reaction rates, enzymatic functions,
molecular movements, and molecular exchanges between
77
-------
membranes within and between the physiological systems and
the organs of an animal.
Chemical reaction rates vary with temperature and generally
increase as the temperature is increased. The solubility of
gases in water varies with temperature. Dissolved oxygen is
decreased by the decay or decomposition of dissolved organic
substances and the decay rate increases as the temperature
of the water increases reaching a maximum at about 30°C
(86°F). The temperature of stream water, even during
summer, is below the optimum for pollution-associated
bacteria. Increasing the water temperature increases the
bacterial multiplication rate when the environment is
favorable and the food supply is abundant.
Reproduction cycles may be changed significantly by
increased temperature because this function takes place
under restricted temperature ranges. Spawning may not occur
at all because temperatures are too high. Thus, a fish
population may exist in a heated area only by continued
immigration. Disregarding the decreased reproductive
potential, water temperatures need not reach lethal levels
to decimate a species. Temperatures that favor competitors,
predators, parasites, and disease can destroy a species at
levels far below those that are lethal.
Fish food organisms are altered severely when temperatures
approach or exceed 90°F. Predominant algal species change,
primary production is decreased, and bottom associated
organisms may be depleted or altered drastically in numbers
and distribution. Increased water temperatures may cause
aquatic plant nuisances when other environmental factors are
favorable.
Synergistic actions of pollutants are more severe at higher
water temperatures. Given amounts of domestic sewage,
refinery wastes, oils, tars, insecticides, detergents, and
fertilizers more rapidly deplete oxygen in water at higher
temperatures, and the respective toxicities are likewise
increased.
When water temperatures increase, the predominant algal
species may change from diatoms to green algae, and finally
at high temperatures to blue-green algae, because of species
temperature preferentials. Blue-green algae can cause
serious odor problems. The number and distribution of
benthic organisms decreases as water temperatures increase
above 90°F, which is close to the tolerance limit for the
population. This could seriously affect certain fish that
depend on benthic organisms as a food source.
78
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The cost of fish being attracted to heated water in winter
months may be considerable, due to fish mortalities that may
result when the fish return to the cooler water.
Rising temperatures stimulate the decomposition of sludge,
formation of sludge gas, multiplication of saprophytic
bacteria and fungi (particularly in the presence of organic
wastes), and the consumption of oxygen by putrefactive
processes, thus affecting the esthetic value of a water
course.
In general, marine water temperatures do not change as
rapidly or range as widely as those of freshwaters. Marine
and estuarine fishes, therefore, are less tolerant of
temperature variation. Although this limited tolerance is
greater in estuarine than in open water marine species,
temperature changes are more important to those fishes in
estuaries and bays than to those in open marine areas,
because of the nursery and replenishment functions of the
estuary that can be adversely affected by extreme
temperature changes.
Temperature is an indicator of unusual thermal loads where
waste heat is rejected from a process. Excess thermal
loads, even in noncontact cooling operations, have not been
and are not expected to be a significant problem in the
primary zinc industry. In most fresh water operations, the
cooling water is used in closed circuit with a cooling pond
or cooling tower; in seawater applications, where a once-
through scheme is used, flows are so large that temperature
rise is insignificant.
79
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SECTION VII
CONTROL AND TREATMENT TECHNOLOGY
Introduction
The current treatment practices applied to process waste
water streams in the primary zinc industry include both
settling and lime-and-settle of either segregated unit
process streams or total plant effluents. control measures
currently used include recycle with bleed and reuse of waste
water.
In the context of this report the term "control technology"
refers to any practice applied in order to reduce the volume
of waste water discharged. "Treatment technolgoy" refers to
any practice applied to a waste water stream to reduce the
concentration of pollutants in the stream before discharge.
Information on planned treatment serves to identify
increased applications of the same measures, or the
application of refined lime-and-settle treatments of
considerably increased performance. The application of
sulfide-precipitation treatment is a possible future
development. Other alternatives, such as reverse osmosis,
are not currently considered applicable.
Current Contrgl_and_rTreatment_Technolggy
Of the eight plants discussed in Section IV, one exhibits no
discharge by virtue of location (i.e., solar evaporation),
and one is so near to closure that no meaningful information
was obtained on treatment or control practices. The current
practices of the remainder of the industry are briefly
summarized in Table 23.
The specific streams to which various control or treatment
measures are applied consist of the following cases:
Acid plant blowdown (i.e., wet scrubber bleed streams and
gas-humidification chamber) effluents are treated in the
following ways:
Individually treated
by liming and settling 1 plant
Reuse 1 plant
Mixed with other streams
liming and settling 2 plants
81
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TABLE 23. CURRENT A11D FUTURE CONTROL AMD TP£ATMENT
PRACTICES Hi TIiE PRIMARY ZINC IIOJSTRY
Current Practices
Future Practices
Plant
Internal
Streams
Total Plant
Effluent
Internal
Streams
Total Plant
Effluent
Some recycle Lime and
settle
No change announced
Settle, lime
and settle
Settle
Mix and
settle
pH adjustment
Recycle Lime and
settle (and
other)
Lime and
settle
Various changes considered
Reuse, settle
lime and
settle
Settle
Increased
recycle
Lime and
settle
82
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Mixed and settled 2 plants
Metal casting cooling waste water is currently only settled,
with various degrees of recycle practiced in the industry.
In two pyrolytic zinc plants using major amounts of water
for the cleaning of CO-bearing retort exhaust gases, one
plant practices recycle using associated pH control and
settling, and the other plant uses settling and mixing
of wastes to achieve control over final plant effluents.
No other significant control, recycle, or treatment measures
may be identified in terms of internal, unit process waste
water streams; it may be noted that mixed plant waste
treatments are eventually applied to some streams, with
usually some reduction of pollutant loads occurring as a
result of mixing and settling.
Lime and Settle Treatment
As a requisite part of developing information on waste
characteristics and control and treatment technology, the
technical and practical aspects of lime and settle treatment
technology assume considerable importance.
The choice of lime as a reagent for treating plant waste
water is generally based on economics. Caustic soda, (NaOH)
and soda ash, (Na2C03_) are possible substitutes, but both
are more costly alkalies, and both are currently in short
supply. Also, neither forms an insoluble sulfate, so
neutralization with these alkalies does nothing for sulfate
concentrations. Ammonia, NH3_, an alkali easy to handle and
convenient to use in automatic neutralization systems, does
not reliably precipitate all metals. Also, addition of
nitrates to receiving bodies of water is not currently
recommended, in view of the deleterious effects associated
with them; they are, themselves, pollutants.
There is no "typical" waste stream; characteristically, the
important waste streams from a plant will contain some
sulfuric acid and may have a pH of less than two, and there
will be trace-level concentrations of a number of pollutants
associated with ores (e.g., arsenic, selenium, lead, nickel,
or zinc).
Addition of a lime slurry ("milk of lime") to such a
solution will precipitate the hydroxides of several of the
metals and will reduce dissolved sulfate concentrations
83
-------
through the formation of gypsum, CaSOU.2H2O. (Formation of
gypsum is, in some respects, a disadvantage. The treated
effluent from such a system can well exist in a condition of
supersaturation with respect to gypsum and can readily
precipitate when conditions are favorable, sometimes
plugging large pipes with surprising rapidity.)
Iron hydroxide is a good flocculant and "collector" for
scavenging other ions from solution, and the formation of
iron hydroxide by the addition of a soluble iron salt to a
solution already basic or to be made basic by the addition
of an alkali is widely practiced, both in the laboratory and
in practice. The addition of ferric chloride, for example,
is a standard procedure in the treatment of sanitary wastes.
The natural presence of iron in effluents results in
percentage removals of some ions by neutralization and
precipitation better than would be expected in pure chemical
systems. Iron may have other beneficial effects too,
although these are difficult to document in the very complex
ionic solutions involved.
In treating an effluent stream, sufficient lime will be
added to raise the pH to between 10 and 11.5, and the closed
stream will normally be conveyed to a settling pond to
settle out suspended solids. Upon exposure to the air,
carbon dioxide is absorbed, gradually reducing the pH. If
the retention time in the pond is long enough, this
carbonation will reduce the pH to 9.5 or below. During this
time the precipitated solids will be settling out, so that a
final effluent containing less than 10 ppm (10 mg/1) of
total suspended solids (TSS) can be achieved.
Some of the solids are colloidal in nature. If the
retention time is not long enough, or if wind and wave
action in the pond stir up the sediments, the desired low
total suspended solids levels may not be aichieved. In such
situations, another treatment technology can be applied.
There are now available a number of organic polyelectrolytes
which, though costly per pound, are very effective at very
low concentrations in providing additional flocculation and
clarification.
Achieving a low total suspended solids content is not
generally a major problem in treating effluents from primary
zinc facilities. Neutralization, precipitation, and
settling should reduce total suspended solids to
satisfactory levels in almost all situations. The principal
problems with effluents from zinc smelters are related to
dissolved metals, most of which are precipitated as
hydroxides and anions, especially sulfate. Removal of
84
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suspended solids is a problem only with respect to the
removal of these precipitates after neutralization.
It has long been known that the solubilities of many metal
hydroxides and hydrated oxides is markedly influenced by pH.
Pourbaix (7) has calculated and compiled "Potential - pH
Diagrams" and solubility curves for many elements, based on
theoretical considerations. Curves based on Pourbaix1s
results are shown in Figure 5 for Ag, As, Cd, Cu, Fe, Hg,
Ni, Pbr Te, and Zn. These curves are, of course,
equilibrium curves for pure compounds in simple systems, and
cannot be extrapolated to the complex multi-ion systems of
zinc plant waste waters.
While they cannot be extrapolated directly to practical
solutions, they do show that there is no single pH at which
minimum concentrations will be achieved for all elements,
and also that in the pH range of interest, pH 6 to 12,
nearly all of the elements pass through a minimum, most of
them in the pH range 9 to 11.
Arsenic has a high solubility plateau, 17 g/1, up through pH
9, and increases rapidly beyond this point. The solubility
of mercury is also constant, over an even wider range, (pH
3.04 to 14.88), and is also so high, 47 g/1, that it too
does not appear in the graph.
Experimental values of metal solubilities as a function of
pH have been presented by Hartinger (8). Data from
Hartinger for several metals are plotted in Figure 6.
Although they differ somewhat from the theoretical values in
Figure 5, including generally having a higher solubility at
a given pH, the general shapes of the curve are similar, and
again suggest that optimum pH's are in the 9 to 11 range.
These data are for simple pure systems. Solubilities of
mixed systems as a function of pH are not given.
Information in the literature indicates that cadmium
concentrations can be greatly reduced by precipitation with
lime. Jenkins et al. (9) report that freshly precipitated
cadium hydroxide leaves approximately 1 mg/1 of cadmium in
solution at pH 8, but this then is reduced to 0.1 mg/1 at pH
10. Hartinger shows even lower values, 0.002 mg/1, at pH 11
(Figure 6). High levels of iron appear beneficial for the
removal of cadmium when liming; evidence for the beneficial
effects of iron has been presented by Marayama, et al. (10).
Nickel is also precipitated by neutralizing with lime. The
nickel hydroxide has a minimum theoretical solubility of
0.01 mg/1 at pH 10, according to Jenkins et al. (9).
85
-------
1
E
o
C/)
0.01
0.001
0.0001
Figure 5. Theoretical solubilities of netal ions as a function of
86
-------
0.01
7 8 9 10
pH(After 2-hr Standing)
Figure 6. Experimentally determined solubilities
of metal ions as a function of pH.
87
-------
Kantawala and Tomlinson have reported the reduction of
nickel concentration from 100 mg/1 to 1.5 mg/1 (pH 9.9) by
the addition of 250 mg/1 of lime. (11)
Upon neutralization, coprecipitation and adsorption may or
may not bring the concentration of a metal below its
equilibrium value for the adjusted pH. Little research has
been published on the role of such parameters as pH, Eh
(oxidation potential), noncommon ions, and complexing agents
upon the solubilities of the metals found in plant waste
streams. For this reason, waste water treatment by
neutralization and precipitation (liming and settling) is
largely empirical at the present time, although it is
generally known that many metals can be reduced in
concentration to low values by neutralization, while others
are not dependably reduced.
Data on concentrations of metals in treated waste water are
plotted in Figure 7. These data were supplied by a zinc
producer operating a lime and settle treatment facility for
mixed plant wastes. The data represent daily averages of pH
and soluble metal analyses in 24-hour composite samples.
The treatment facility operates with effluent ranging from
pH 6.5 to 10.5 and a level of suspended solids ranging from
nil to a daily maximum of 64 mg/1. The data plotted
represented 29 daily determinations over a period of two
months of continuous operation with an average treated
volume of 2,650 cu m/day (0.7 mgd). The data fell into
various bands as indicated in the figure. The lowest
concentration band developed was that for copper, with the
concentration band descending to the maximum pH included,
giving levels of 0.05 to 0.15 mg/1 of copper at pH 10.5. A
band of data for lead showed a similar behavior, covering a
range of maximum values of about 0.6 mg/1 at pH 6.5 to 0.05
to 0.2 mg/1 at pH 10.5. Zinc and cadmium showed somewhat
different behavior with a band of data descending from
concentrations including single values on the order of 30 to
100 mg/1 at pH 6.5 to 7.0 to the minimum values recorded
(i.e., 0.1 to 0.3 at pH 10.5). The plant data for complex
waste water show a general trend in agreement with theory
and experiment in that concentration limits appear changed
in complex coprecipitation compared with theoretical values,
and the increase in concentrations of lead and zinc above a
pH of about 9.2 is not evident in the scatter bands based on
the plant data. Both of these differences may well be
attributable to the differences between static (equilibrium)
and dynamic systems. In the latter, precipitation may be
accompanied by instantaneous variations in pH and continuing
separation of precipitate and supernatant so that solid-
liquid equilibrium is not possible. The role of complex-
88
-------
_1.2
20
o
c
•H
tSI
C
O
C
-------
compound formation and the solubility effects thereof remain
unknown in practical operations.
An indication of the effectiveness and performance of this
treatment plant is given in Tables 24 and 25. The data
given are based on composited grab samples taken over a two
day period. The concentrations of constituents of two input
streams to the treatment, and the concentrations in the
effluent are given in Table 24. The effectiveness of the
treatment in removing various constituents is given in Table
25, which also shows the mass balance type data used to
derive the effectiveness level. All data are based on a two
day sample period, an average operating pH level of 8.2, and
a suspended solids level of about 25 mg/1 in the final
effluent.
The positive values given for a few of the constituents are
subject to some interpretation. The positive change in
suspended solids is atypical of plant opercition according to
prior operational data, and represents only the sampling
period. The increase in oil and grease is considered an
artifact of sampling and calculation, as all input and
output concentrations are near the practical minimums. The
calculated positive change in dissolved solids may be a
result of grab sampling or may well be realistic.
Both sulfates and chlorides, components of dissolved solids,
showed net decreases due to the treatment. Insufficient
data are available on all cations or anions to provide any
confirmation of the observed dissolved solids data. All
other constituents were removed to some degree by the lime
and settle treatment. Over 90 percent removal was observed
for iron, zinc, and cadmium.
Data on the removal of selected constituents from acid plant
blowdown by a lime and settle treatment are given in Table
26. It may be noted that a pH of 11.8 is maintained in the
effluent from this plant. While no net change in suspended
solids is indicated by the data, considerable reductions in
cadmium, lead, and zinc concentrations are achieved. It may
be noted that the concentrations of lead and zinc associated
with the pH of 11.8 are above those shown in the data for
the treatment plant operating up to a pH of 10.5. These
data would seem compatible with the trends in theoretical
data, although practical differences among plants may
overshadow equilibrium considerations. The high pH of 11.8
is maintained to achieve improved settling of fine suspended
solids associated with the presence of zinc (i.e., the high
pH represents an optimum balance, for this effluent, between
metals concentrations and suspended solids)„
90
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TAbLE 24. ANALYSES OF INPUT AND EFFLUENT STREAMS FOR A
TREATMENT PLANT
Inputs to Treatment Plant
Parameter
PH
Alkalinity
COD
Total Solids
Dissolved Solids
Suspended Solids
Oil and Grease
Sulfate (as S)
Chloride
Cyanide
Aluminum
Arsenic
Cadmium
Calcium
Chromium
Copper
Iron
Lead
Magnesium
Mercury
Molybdenum
Nickel
Potassium
Selenium
S i Ive r
Sodium
Tellurium
Zinc
Flow,
I/day
(gal/day)
Stream 1,
mg/1
2.5
23.0
135
8
5.0
4,572
105
1
0.6
0.2
19
2
0.00&
0.26
13
25
847,840
( 224,000)
Stream 2,
mg/1
0.5
15
5,o50
13
-------
TABLE 25. CALCULATED EFFECTIVENESS OF REMOVAL OF VARIOUS CONSTITUENTS^
Parameter
pH
Alkalinity
CCD
Total Solids
Dissolved Solids
Suspended Solids
Oil and Grease
Sulfate (as S)
Chloride
Cyanide
Aluminum
Arsenic
Cadmium
Calcium
Chromium
Copper
Iron
Lead
Magnesium
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Sodium
Tellurium
Zinr
Flow,
I/day
(gal/day)
Input
Stream 1,
kg/day
2.5
--
19.50
--
114.46
6.78
4.24
3,876.
89.02
--
—
0.85
0.51
~
—
0.17
16.11
1.70
—
0.005
-—
0.22
--
11.02
--
—
—
21.20
847,840
(224,000)
Input
Stream 2,
kg /day
6.7
--
28.73
—
10,820.94
24.90
1.92-5.75
4,290.07
463.48
0.19
--
0.19
0.31
--
--
0.06
0.33
3.44
--
0.008
— *•
0.59
--
1.03
—
—
—
2,035.87
1,915,210 2
(506,000)
Total
Input ,
kg /day
„.
--
48.23
--
10,935.40
31.68
6.16-9.99
8,166.07
552.50
0.19
--
1.04
0.82
--
--
0.23
16.44
2.14
--
0.013
--
0.81
—
12.05
—
--
—
2,056.89
,763,050
(730,000)
Total
Output ,
kg/day
—
46.97
--
12,392.28
688.00
11.05
6,136.73
472.48
0.28
--
0.28
0.06
--
—
0.06
0.17
0.41
—
0.010
_-
0.36
—
4.97
--
--
—
138.15
2,763,050
(730,000)
Net
Change (-b-)
kg /day
--
-1.26
--
+1,456.88
+657.00
1.06-+4.89
-2,029.34
-80.02
—
--
-0.76
-0.76
—
--
-0.17
-16.27
-1.73
—
-0.003
--
-0.45
—
-7.08
—
--
--
-1,918.74
—
— —
Net
, Change (b)
percent
--
-2.6
—
+13.3
+2,070.
+49-+17
-24.8
-14.5
--
—
-73.1
-92.7
_.
—
-73.9
-98.97
-80.8
--
-23.1
~ ~
-55.6
—
-58.8
—
--
--
-93.3
--
™" ™
(-a' Calculations for each entry = -Sp x -^— x 1 x 10
' ' Negative numbers indicate removal by treatment.
"6
= kg/day; see Table 24 for mg/1 values.
92
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TABLE 26. EFFECTIVENESS OF TKLJffiMtNT OF ACID PLAOT
BY LIME >\ND SETTLE
t ct Lo£.diir.
fret
Parameter
I nt ake, D i s ch ax vs., Ch ar<;,»
o/I
^c-, kg/Metric Ib/Short
per cert ton ton
pH 2.8
Alkalinity
COD
Total Solids
Dissolved Solids 5,400
Suspended Solids 2CO
Oil and Grease
Sulfate (as S)
Chloride
Cyanide
Aluminum
Arsenic
Cadmium 33
Calcium
Chromium
Copper
Iron
Lead 48
Magnesium
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Sodium
Tellurium
Zinc 1,500
Flow,
I/day 1,308,096
(gal/day) (345,600)
_1LJ' i- -_r . - _ -^.- . - -—,-... . -..„.— ....i. — ... : «... — — — .. -
11.3
2,500 -2,900 -53.7
100 0 C
0.03 -32.97 -99.9
6.9 -41.1 -35.6
2.6 -1,497.4 -99.3
93
-------
The concentrations of various constituents from a lime and
settle treatment plant treating mixed plant wastes are given
in Table 27. Here the average value of pH is 9.6, and the
average values for zinc and cadmium fall within the range
previously indicated by the plot of data in Figure 7. The
values for lead fall somewhat above the prior data.
A new treatment facility at one domestic primary zinc
smelter is currently being lined-out. This new facility
will use a lime and settle method on the total plant waste
water, which includes the primary zinc plant process waste
waters (745 gpm), the waste water of its primary lead
smelter, and the waste water from integrated mining and
milling operations. The anticipated concentrations of
selected process waste water pollutants from this facility
are as follows:
Process waste water Concentration
pollutant (212/1)
TSS 60
Cd 0.5
Hg 0.006
Pb 1.0
Zn 1.7
Except for the higher value indicated for total suspended
solids, the anticipated concentrations for the remaining
pollutant characteristics fall within the range shown in
Table 27.
Mercury and Selenium Removal
Some domestic and imported zinc concentrates contain
appreciable trace quantities of mercury. Operating
experience at several currently operating primary zinc
smelters, which either routinely or occasionally process
these high mercury-content concentrates, has shown that most
of the mercury is volitilized during the first
pyrometallurgical step. This step is roasting, the offgases
from which conventionally proceed to a metallurgical
sulfuric acid plant. Two smelters have found that much of
this mercury accumulates in the acid plant-gas
preconditioning equipment of the open and packed weak acid
scrubber and the mist precipitators (coke boxes at older
acid plants).
One smelter developed a mercury recovery facility, comprised
essentially of an indirectly-fired, continuous-feed rotary
kiln with a condenser system. The charge material to the
94
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TABLE 27. EFFLUENT CONCENTRATIONS FROM LIME AND SETTLE
TREATMENT OF MIXED WASTES
Concentrations^ mg/l^a)
Constituent
PH
Total Solids
Sulfur
Chloride
Cadmium
Lead
Selenium
Zinc
Minimum
9.3
1430
250
140
0.03
0.5
0.8
1.0
Maximum
10.8
4050
730
490
0.7
1.8
5.0
8.8
Average
9.6
-
650
480
0.3
0.7
-
2.0
(a) Except for pH .
95
-------
kiln was spent coke, taken from the coke boxes of the older
metallurgical sufluric acid plants. Another currently
operating smelter removes a "high-mercury" purge from its
acid plant scrubber (i.e., a scrubber having two sections,
one for gas humidification and the other for scrubbing) and
washdown from its mist precipitators, holds this effluent in
a tank, and adds zinc dust to precipitate out the vast
majority of both mercury and selenium. A similar practice
is used by an European company.
Additional Treatment Technology
Additional treatment methods, which could be employed for
further reduction of pollutants from process waste water
discharges include: (1) hydrogen sulfide treatment, (2)
reverse osmosis, (3) evaporation, and (4) chemical fixation.
Hydrogen Sulfide Treatment
Hydrogen-sulfide treatment would be an effective method for
the removal of heavy metals as sulfide precipitates, which
are known to have extremely low solubility. Solubilities of
the sulfides of typical heavy metals found in the waste
water discharges from the primary zinc industry are shown in
Table 28. Since the solubilities of the sulfides are higher
at low pH, the precipitation reaction should be carried out
at a neutral or alkaline pH.
Some investigative studies involving the basic application
of the hydrogen sulfide (H2S) precipitation process to zinc
smelter process waste waters are being performed by one
domestic primary zinc company. Even though no pilot plant
studies have, as yet, been conducted, the bench scale
experimental data to date have indicated that the following
treated pollutant parameter concentrations could be
achievable:
Process waste water
TSS
As
Cd
Hg
Se
Zn
pH
Treated concentration
0.01
0.01
0.0005
0.10
1 . 0
6.0 - 6.4
96
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TABLE 28. SOLUBILITIES OF METAL SULFIDES
Solubility,
Metal Neutral Solution Low pH
Ni < 1 100,000
Cd < 1 5,000
Pb < 1 70
Cu < 1 < 1
Hg < 1 < 1
97
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The company considers this potential application to be
specific to its own zinc concentrates, which have a high
magnesium content. Problems associated with this treatment
process are stated by the company to be based upon the
complexity of the process, as well as the resultant high
economics.
Reverse Osmosis
Reverse osmosis (RO) is a process, whereby a waste water
stream is passed at pressures from 34 to 136 atm (500 to
2000 psia) over a membrane. The membrane is cast from a
solution of cellulose acetate and has the property of
allowing passage of water through the film, but rejecting
ions. The permeate is almost completely of ionic material,
while the concentrate having almost all of the ions must be
further treated. The advantage of RO is that recoveries of
75 to 90 percent of the inlet water can be obtained, which
results in only a small fraction of the stream needing to be
treated further by chemical means or by evaporation.
Unfortunately, the application of RO can be done only under
fairly stringent waste water conditions. The suspended
solids content of the inlet water should be low (probably
less than 200 ppm), otherwise/ a coating will develop on
the membrane surface, slowing down the process. The pH of
the inlet water is fairly critical and should be from 6 to
7.5 for optimum results. Waste water outside of this range
will tend to cause rapid hydrolysis of the acetate groups in
the membrane and subsequent failure of the film. In
addition, quantities of slightly soluble materials must be
kept low to prevent fouling of the film by precipitation of
these materials on the film.
In the case of the waste water from the zinc smelters, the
concentration of ions, with the possible exception of zinc,
is low enough for reverse osmosis treatment to be
considered.
A test program to determine the applicability of RO to the
waste stream would be required prior to the application of
this technique. At present, RO must be considered as
unproven technology.
Evaporation
Evaporation is comparable with reverse osmosis in cost and
effectiveness for waste water treatment. The technology is
more advanced for evaporation than for reverse osmosis.
98
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Evaporation is currently used on a commercial scale for
desalination of brackish water or seawater and for waste
water treatment. The process used most commonly for the
above applications is the multiple-effect evaporation/
distillation process. With appropriate control of pH and
suspended solids to minimize the fouling of heat transfer
surfaces, this type of evaporation process can be employed
for waste water treatment with an economic usage of fuel.
Evaporative treatment usually produces concentrated waste
liquor, which must be disposed of by complete evaporation
using a separate evaporator or by some other means, such as
chemical fixation, which is discussed below.
Chemical^Fixation
Chemical fixation is a process for detoxifying hazardous
liquid wastes by means of the reaction of chemical additions
with the waste material to form a chemically and
mechanically stable solid. The process can be used for the
chemical fixation of polyvalent metal ions in stable and
insoluble inorganic compounds. Monovalent cations and many
anions are physically entrapped in the matrix structure
resulting from the reaction process. Chemical fixation is
costly when compared with the treatment methods discussed
thus far and probably would rarely be used for directly
treating the large volume of process waste water effluents
from the primary zinc operations. The process, however,
might prove useful and economic for the ultimate disposal of
concentrated liquor wastes generated from reverse osmosis or
evaporative treatment.
99
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SECTION VIII
COSTS, ENERGY, AND NONWATER QUALITY ASPECTS
Introduction
This section deals with the costs associated with the
various treatment methods available to the primary zinc
industry for the reduction of the pollutant load in the
process waste water effluents. In addition, other nonwater
quality aspects of waste water treatment are discussed.
The treatment cost study was performed on a plant-by-plant
basis on six (Plants B, C, D, E, F, and G) of the existing
primary zinc plants. One plant (Plant A), excluded from the
cost study, is a plant located in the Southwest, where the
arid climate permits this plant to operate with no discharge
of process waste water through solar evaporation.
The costs for the present treatment practices in the
industry were obtained directly from the six plants. The
costs for additional waste water treatment beyond the
current practices were estimated by using published cost
data, rather than the cost data supplied by the plants.
This approach was considered necessary in view of the
findings from the plant survey that either the pertinent
cost data were not available from the plants or the cost
data supplied by the plants show substantial variation owing
to the differences among the plants with respect to water
usage, treatment, and cost reporting procedure.
Basis for Cost Estimation
Data on capital costs and annual costs for present control
practices were obtained from selected zinc plants. These
data were modified, as needed, in the following manner to
put all costs on a common basis.
(1) The capital costs reported were converted
to 1971 dollars by using the Marshall &
Swift Index (quarterly values of this
index appear in the publication Chemical
Engineering, McGraw Hill).
(2) The annual costs were recalculated to
reflect common capitalized charges.
To do this, the annual costs were
101
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calculated by using a factor method
as described below:
Operating and maintenance - as
reported by plants,
Administrative overhead - 4 percent
of operating and maintenance,
Depreciation - 5 percent of the 1971
capital.
Property tax and insurance - 0.8
percent of 1971 capital.
Interest - 8 percent of the 1971
capital.
Other - as reported by plants.
In the following discussion, capital costs are expressed in
$/annual kkg ($/annual ton) and annual costs in $/kkg
($/ton) based on annual production capacity of zinc metal or
its equivalent.
Economics of Pgesent_Control and
Treatment Practices
The cost data supplied by the plants on current control and
treatment practices in the primary zinc industry are
summarized in Table 29. Data reflects the difference among
the plants with respect to processes, water usage and
conservation, waste water treatment, extent of plant water
circuit revisions, and cost reporting procedures employed.
A description of present treatment practices and associated
costs are given below for each plant.
Plant B
Discharges of process waste water from this plant were
reported as follows:
Di sc ha r ge_ Rates
E_ff luent u
1. Acid plant blowdown 850 (156)
2. Celestite conversion
a. sulfide circuit 33 (6)
b. oxide circuit 82 (15)
3. Metal cooling 76 (14)
4. Dust washing 49 (9)
102
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TABLE 29. CAPITAL AND ANNUAL COSTS OF PRESENT WASTE WATER
TREATMENT PRACTICES IN PRIMARY ZINC INDUSTRY
Annual Zinc
Production, Capital
Plant kkg Total, $
Designation (tons)
M
S B 97
(108
C 64
(70
D 110
(121
E 104
(115
F 226
(250
G 45
(50
,956 3,176,000
,000)
,149 3,580,000
,727)
,313 306,900
,624)
,300 492,000
,000)
,750 3,113,600
,000)
,350 328,000
,000)
Cos t s
$ / annual kkg
($/annual ton)
32 .42
(29.40)
55. 81
(50.61)
2.78
(2.53)
4. 72
(4.28)
13.73
(12.45)
7.23
(6.56)
Annual Costs
Total, $/year $/kkg
($/ton)
828,000 8.45
(7.66)
567,000 8.83
(8.01)
112,500 1.02
(0.12)
233,000 2.23
(2.02)
677,900 2.99
(2.72)
98,600 2.17
(1.97)
-------
5. Dross leaching
6. Baghouse dust leaching
TOTAL
98
J.20.
1,308
(18)
_I221
(240)
Waste water treatment processes include settling in a
central lagoon and heavy metal removal by lime treatment.
The acid plant blowdown is discharged directly to the lime
treatment plant. All other process waste water effluents
are discharged first to the central lagoon. The central
lagoon also receives indirect cooling water, boiler
blowdown, and treated sanitary waste water, with a combined
discharge rate reported at 1,466 cu m/day (269 gpm). The
overflow from the central lagoon, with a combined output at
1,924 cu m/day (353 gpm), is discharged to the lime
treatment plant. The total inflow to the lime treatment
plant is 2,774 cu m/day (509 gpm).
Cost data were supplied by the plant on capital costs,
operating, and maintenance costs. Cost data are summarized
below.
Basis: Zinc Production = 97,956 kkg/yr (108,000 tons/yr)
£a£ital_Costs 1971 $
Lime treatment plant 496,000
Central settling lagoon 595,000
Plant water circuit revisions 1,496,000
Miscellaneous 589,000
Total Capital Costs 3,176,000
Jf/Annual kkg 32.42
($/Annual ton) (29.40)
Annual_Costs
Operating and maintenance
Overhead
Depreciaiton
374,800
15,000
157,000
104
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Interest 251,000
Tax and insurance 2^xl££
Total Annual Costs $828,000
$/kkg 8.45
($/ton) (7.66)
Plant C
This plant indicated that it was planning a major
modification of plant water usage and process waste water
treatment. A mercury-selenium removal system is currently
in operation. Conservation of process waste water measures
include the conversion of vacuum evaporators, operating on
electrolyte cooling, to a cooling tower; a cooling tower to
minimize the blowdown from casting; and the minimization of
acid plant blowdown by efficient cooling tower operation.
The status of this company's progress toward a new process
waste water treatment facility does not allow the listing of
the possible economics as "present control and treatment
practices." The two alternatives, which have been
investigated include a lime and settle treatment and a
hydrogen sulfide precipitation treatment. Currently, the
company is investigating the possibility of lime treatment
with a sodium silicate flocculent.
The waste water conservation modifications, scheduled for
implementation in 1974, will reduce current plant process
waste water sources to the following:
Discharge Rates
Process, WasteTTWaterr Effluent cujoQ/day _(ggm)
1. Acid plant blowdown 741 136
2. Preleaching liquor bleed 392 H!l_
TOTAL 1,133 (208)
The current "control and treatment practice" economics for
both the mercury-selenium collection system and the process
waste water flow volume reduction are presented below:
Basis: Zinc Production = 64,149 kkg/yr (70,727 ton/yr)
105
-------
Capital Costs 1971 $
Mercury-selenium removal 65,000
Electrolyte cooling (conversion
to cooling tower) 2,460,000
Other water conservation
Total capital costs $2,935,000
$/Annual kkg 45.90
($/Annual ton) (41.40)
Annual Cost s
Water conservation 41,000
Mercury- selenium removal 16,000
Overhead 3,000
Depreciation 148,000
Interest 235,000
Tax and insurance ____ S^CKM)
Total Annual Costs $467,000
$/kkg $7.29
($/ton) ($6.58)
Plant D
This zinc plant is a part of a complex operation. The
entire plant complex is currently in the process of
extensive modificiation of water usage and treatment with
the installation of a new central waste water treatment
facility, which will serve the entire plant complex. The
modification is scheduled to be completed in 1974.
Under the modified plan for waste water treatment, the zinc
plant will discharge 4,060 cu m/day (745 gpm) of process
106
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waste water to the central treatment facility, consisting of
the following effluents:
Discharge_Rate
Process Waste Water Effluents SU—JS/d^i JL2S21L
1. Acid plant blowdown 2,180 (400)
2. Miscellaneous wet scrubbers 1,090 (200)
3. Preleaching liquor bleed 545 (100)
4. Miscellaneous drainages __ 245 ___ [IJil
TOTAL 4,060 (745)
In addition to the above plant discharges destined for the
central treatment facilities, the zinc plant will also
discharge 1,362 cu m/day (250 gpm) of indirect cooling water
to a nearby operation and an additional 4,115 cu m/day (755
gpm) of indirect cooling water to a creek without treatment.
The central treatment facility consists of a 117 acre
central impoundment area and a central treatment plant.
Waste water discharges from the plant complex, including the
zinc plant, are collected in the central impoundment area.
The combined waste water is withdrawn from the pond and
treated in the central treatment plant. The treatment
process employed is lime addition and liquid/solid
separation by settling in a thickener. The underflow sludge
from the thickener is returned to the central impoundment
area for permanent disposal. The clarified overflow from
the thickener is both discharged to a creek and recirculated
to the plant's concentrator.
The costs for the central treatment facility assigned to the
zinc plant include: (1) the retrofit cost for the water
circuit revisions in the zinc plant, (2) the cost for the
central impoundment area apportioned to the zinc plant, and
(3) the cost for the central treatment plant apportioned to
the zinc plant. Since only the total costs are known or can
be calculated for the central impoundment area and the
central treatment plant, the costs assigned to the zinc
plant were estimated by multiplying the total costs by the
ratio of the waste water discharge from the zinc plant and
the total waste water discharge from the plant complex to
the central impoundment area. The total waste water input
to the central impoundment area is estimated at 31,174 cu
m/day (5,720 gpm), which consists of: (1) 4,060 cu m/day
(745 gpm) from the zinc plant, (2) 572 cu m/day (105 gpm)
from a lead smelter, (3) 6,595 cu m/day (1,210 gpm) from a
mill concentrator, and (4) 16,568 cu m/day (3,040 gpm) from
a mine.
107
-------
Under the above assumption, the capital and annual costs for
the zinc plant portion of the central treatment facility
were estimated as follows from the data supplied by the
plant.
Basis: Zinc Production = 110,313 kkg/yr
(121,624 tons/yr)
Capital Costs
Central treatment plant
Total
Zinc plant portion
Central Impoundment Area
Total
Zinc plant portion
Zinc plant retrofit costs
Total Zinc Plant Portion
$/Annual kkg
($/Annual ton)
&Qnual_Costs
Central treatment plant and
impoundment area
Total Operating and
Maintenance
Zinc plant portion
Overhead
Depreciation
Interest
Tax and insurance
Total Operating Costs
$/kkg
($/ton)
1971 $
$518,000
75,600
$644,000
94,000
_ 112x3 00.,
f306,900
2.78
(2.53)
$/Year
$656,000
95,500
3,800
4,800
7,600
800
$112,500
1.02
(0.92)
108
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This plant comprises two production facilities located at
two separate sites with separate water circuits. The two
facilities are designated as Plant E-l and Plant E-2. The
two plants are discussed separately.
fiant^EXL . Discharges of process water from Plant E-l were
reported as follows.
Discharge_Rate
P£2£§ss_Waste_Water_Ef fluent £U_m/daY _IH£J2}L_
1. Acid plant blowdown 1,090-3270 (200-600)
2. Sinter plant humidifier _ 16 3-27 2_ _J3_0;-50l_
TOTAL 1,253-3,542 (23C-650)
The above process waste water effluents are combined and
treated by lime precipitation. Indirect cooling water and
plant runoff water are discharged without treatment to a
creek.
Lime treatment of the process water effluents consists of
precipitation of metal hydroxides by lime addition followed
by clarification in a thickener and settling lagoons. The
underflow sludge from the thickener, containing metal
hydroxide precipitate, is either returned to the process
(roaster or sinter plant) or discarded on land within the
plant.
The costs for the lime treatment process were estimated from
the cost data supplied by the plant.
Basis: Total Zinc Production = 104,300 kkg/yr
(115,000 tons/yr)
Ca£ital_Costs 1221-Jl
Total Capital Costs $220,000
Annual_costs
Operating and maintenance 117,000
109
-------
Overhead
Depreciation
Interest
Tax and insurance
Total Annual Costs
Plant ___ E-2. The only source of process water discharge from
Plant E-2 is a bleed from scrubbers used in the retort
operation. The scrubber water is recycled. The bleed from
the recycle circuit reported at 136 to 272 cu m/day (25 to
50 gpm) is treated by settling in a pair of concrete bins
and discharging to a creek. Indirect cooling water and
plant runoff water are discharged without treatment.
The water treatment system includes recycling of the
scrubber water and settling of the scrubber bleed, as well
as recycling of water used for quenching of spent furnace
charge. Data were supplied by the plant on the capital
costs for the treatment system, excluding the two concrete
settling bins, and annual operating and maintenance costs.
Treatment costs are summarized below:
Basis: Zinc Production = 104,300 kkg/yr
(115,000 tons/yr)
Ca£ital_Costs
Treatment system 216,000
Concrete bins 56,000
Total Capital Costs 272,000
Annual^Cgjjts
Operating and maintenance 41,700
Overhead 1,700
Depreciation 13,600
Interest 21,800
Tax and insurance _____ 2X20_0_
Total Annual Costs $ 81,000
110
-------
Total E-1 and E-2.
Capital Costs (E-l+E-2)
$/annual kkg
($/Annual ton)
Annual Costs (E-l+E-2)
$/kkg
($/ton)
492,000
4.72
(4.28)
233,000
2.23
(2.02)
Plant F
Discharges of process waste water from this plant were
reported as follows:
Discharge^Rate
Effluents
1. Scrubbers (2 streams)
a. first scrubber (High grade)
b. second scrubber (P.W.-*-
Intermediate)
2. Dust Control Scrubber
3. Gas cooling and scrubbing
4. A bleed of spent liquor from
cadmium leaching
TOTAL
2,180
10,900
708
2,180
218
16,186
(400)
(2,000)
(130)
(400)
140).
(2,970)
Process water effluents are currently treated by various
chemical and physical methods, which include pH adjustment
with lime or sodium hydroxide and settling in a series of
concrete basins, ponds, and lagoons. All of the process
water effluents after treatment are impounded in a final
settling lagoon. The latter also receives indirect cooling
water and plant runoff water, neither of which is treated.
An overflow from the lagoon is discharged to a river.
Ill
-------
There are two furnace offgas scrubbers, designated as first
and second, producing separate effluents on a once-through
basis. The effluent from the first furnace scrubber is
combined with the effluent from the dust control scrubber,
and the combined stream is treated by a combination of pH
adjustment with sodium hydroxide and settling before
discharge to the final settling lagoon.
The spent leach liquor bleed from the cadmium leaching
operation is first treated for cadmium and zinc
precipitation by lime addition and seguently for residual
cadmium by cementation. The spent leach liquor is combined
with the effluent from the second furnace scrubber, and the
combined stream undergoes settling before discharge to the
final settling lagoon. (The effluent used as the cadmium
leach liquor was originally the acid plant blowdown).
The effluent from the gas scrubber (3 above) is discharged
directly on a once-through basis without treatment to the
final settling lagoon.
Data were supplied by the plant on the capital costs and
operating and maintenance costs for various components of
the present treatment system. Cost data are summarized
below:
Basis: Zinc Production = 226,750 kkg/yr (250,000 tons/yr)
SsMtaijCpjsts .JL22I-IL
Settling ponds 440,000
Slag plant water recirculation 33,800
Cadmium control treatment 131,2CO
Final settling lagoon 328,000
Cooling facilities 662,600
Effluent monitoring 103,100
Miscellaneous system 22j.HQ.Q.
Total Capital Costs 1,778,100
$/Annual kkg 7.84
($/Annual ton) (7.11)
112
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£nnual_Costs
Operating and maintenance 184,600
Overhead 7,400
Depreciation 88,900
Interest 142,200
Tax and insurance ___ .Iii.c20p_
Total Annual Costs 437,300
$/kkg 1.93
($/ton) (1-75)
Plant F is currently in the process of reducing its process
waste water usage from 26,000 1/kkg (6,250 gal/ton) , based
on 16,200 cu m/day (2,970 gpm) and 620 kkg/day (685
tons/day) zinc, to 3,945 1/kkg (945 gal/ton) , based on 2,450
cu m/day (450 gpm) and the same zinc production rate. This
reduction will be achieved through a 90 percent
recirculation of the prime western and intermediate furnace
washer water, the high-grade furnace washer water, and the
carbon monoxide scrubber water. The costs for this flow
reduction scheme follow:
Piping and pumping of 90 percent
recycle of:
High-grade furnace scrubbers 75,500
P-W and Intermediate furnace scrubbers 135,000
CO scrubber 75, COO
Clarification of recirculated flow 1,000,000
Oil and Grease removal from CO water ____ 50^000
Total Capital Costs 1,335,500
^/Annual kkg 5.89
($/Annual ton) (5.34)
113
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Annual Costs
Operating and maintenance:
Recycle, pumping and piping 14,000
Recycle, clarification 40,000
Overhead 2,200
Depreciation 66,700
Interest 107,000
Tax and insurance __ .HLt.2CK)
Total Annual Costs 240,600
$/kkg 1.06
($/ton) (0.97)
Total CurrentContrglandTreatment Costs .
Plant_G
Grand Total 3,113,600
$/Annual kkg 13.73
(I/Annual ton) (12.45)
Operating Costs 1971$
Grand Total 677,900
$/kkg 2.99
($/ton) (2.72)
This plant is currently converting its horizontal retort
plant to an electrolytic zinc plant. Its existing roasters
114
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and acid plant will remain in use. Discharges of process
water from this plant were reported as follows:
Process_Wagte Water Effluents
1. Roaster gas sprays
2. Storage pond overflow
TOTAL
Discharge_Rate
cu_m/day
817 - 1,226
0_- 545
817 - 1,771
(150 - 225)
IO_Z_1CO)_
(150 - 325)
The process water effluent is treated by lime addition to
remove heavy metals as a hydroxide precipitate. The sludge
produced from lime treatment is currently dewatered by
filtration and returned to the sinter plant.
Cost data were supplied by the plant on the capital costs
and the operating and maintenence costs for the lime
treatment plant. Treatment costs are summarized below:
Basis: Zinc Production = 45,350 kkg/yr
(50,000 tons/yr)
Cagital^Costs
Total Capital Costs
$/annual kkg
(^/annual ton)
.1971 $_
$328,000
7.23
(6.56)
Annuaj._Cgsts
Operating and maintenance
Overhead
Depreciation
Interest
Tax and insurance
Total Annual Costs
$/kkg
($/ton)
51,300
2,100
16,400
26,200
-2x600
98,60C
2.17
(1.97)
115
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Economics of Additional_Control_and
Treatment^Practiceg
Of the six primary zinc facilities which should be operating
in 1977, one plant, by virtue of current control and
treatment practices, meets the proposed effluent limitations
guidelines derived in this development document. This one
plant, therefore, is not economically impacted by the
proposed limitations. One other plant currently meets the
1977 recommendations, but must resort to additional control
and/or treatment practices to comply to the proposed 1983
limitations.
The economics of the necessary additional control and
treatment practices for the remaining facilities are
discussed in the ensuing paragraphs.
Plant B
This electrolytic zinc plant generates 1,308 cu m/day (240
gpm) of process waste water. Liming and settling is the
treatment practice employed on this effluent. Based on a
production rate of 268 kkg (296 tons)/day, this plant
currently has a process waste water discharge rate of 4,880
1/kkg (1,170 gal/ton), which is below the 1977 and 1983
recommendations of 8,350 1/kkg (2,000 gal/ton) and 5,425
1/kkg (1,300 gal/ton), respectively. As shown in this
document, zinc concentrations after treatment have been
reported to be high. Plant personnel indicate that low zinc
concentrations are difficult to maintain primarily because
of low pH (acidic) surges entering the treatment facility as
acid plant blowdown. One possible solution to this problem
is the addition of a surge tank to the plant's lime and
settle treatment facility. Costs for this tank, which is
lined and has a one-week capacity, are:
Ca2ital_Costs _12Zi_JL
Surge tank (241,000 cu ft cap.) 33,000
$/Annual kkg 0.34
($/Annual ton) (0.30)
Operating Costs
Total (25% of capital) 8,300
116
-------
$/kkg 0.08
($/ton) (0.08)
Plant C
Plant C is an electrolytic zinc plant which is currently
reducing the volumetric flow rate of its process waste
water. After the new control practices have been
implemented, the anticipated production of process waste
water will be about 6,440 1/kkg (1,550 gal/ton). These
control practices, the economics of which were discussed
previously in this section, are considered as current
practice for this plant and are also considered to be
specific to this one plant, due to the usage of vacuum
evaporators. The plant is anticipating the possible
application of either a lime and settle treatment with a
sodium silicate flocculent, or a sulfide precipitation
treatment. Resulting effluent data from these potential
applications are not yet to pilot plant stage, but economic
investigations have been conducted for each treatment
system. The results are tabulated below:
Lime and Settle Treatment.
Capital Costs 1971 $
Lime facility 1,230,000
$/Annual kkg $19.20
($/Annual ton) ($17.30)
Annual Costs
Lime treatment 503,000
$/kkg $7.85
($/ton) ($7.10)
Sulfide Precipitation Treatment.
Capital Costs 1971 $
H2_S treatment 2,620,000
$/Annual kkg $41.00
117
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($/Annual ton) ($37.00)
Annual Costs
H2_S treatment 777,000
$/kkg $12.20
($/ton) ($11.00)
The above cost estimates have been made by the smelter
operators and are considered to be highly conservative.
Utilizing the costs of other lime and settle treatment
facilities, such as those for Plant F, the following costs
for Plant C, which are used in this analysis, have been
estimated:
Capital Costs " 1971 $
Lime and settle facility 500,000
$/Annual kkg $7.80
($/Annual ton) ($7.04)
Annual Costs
Lime and settle facility 152,000
$Akg $2.37
($/ton) ($2.16)
Plant D
Current data indicate that Plant D's new lime and settle
treatment plant receives 4,060 cu m/day (745 gpm) of process
waste water from its electrolytic zinc operation. After
passage through the treatment plant, approximately 35
percent of the total input flow is recycled to the
integrated flotation operation. Based upon a production
rate of 302 kkg (333 tons)/day, the process waste water
discharge rate is about 8,350 1/kkg (2,000 gal/ton), which,
along with lime and settle pollutant parameter
concentrations, indicates compliance to the 1977 criteria.
A flow value reduction to 5,425 1/kkg (1,300 gal/ton) and/or
pollutant concentration values less than those recommended
for lime and settle by this document would have to be
achieved in order to comply to the recommended 1983 effluent
118
-------
limitations. From a control technology standpoint, this
reduction could be achieved through increased recycle and
reuse in other on-site operations, such as the mill
concentrator and the fertilizer plant. Replacement of wet
scrubbing devices with dry collection devices would also
ensure compliance. Since cost data are not currently
available for these control measures, the costs of
artificially evaporating the necessary flow value decrease
(i.e., (2,000 minus 700 equals 1,300)gal/ton, as
recommended) are used to typify the highest compliance cost
which this plant should have:
Cap,ital_Costs _19jU_!_
Incremental control and/or treatment $909,000
$/Annual kkg $8.25
($/Annual ton) ($7.45)
Annual Costs
Incremental control and/or treatment $414,000
$/kkg 3.76
($/ton) (3.40)
Portion E-1 of Plant E produces calcine and sinter. Two
process waste water streams, the acid plant blowdown and the
sinter plant humidifier, account for a range of 1,253 to
3,542 cu in/day (230 to 650 gpm) . After lime precipitation
of this effluent, data indicate a high total suspended
solids concentration. Therefore, further clarification to
reduce the TSS concentration to the recommended value of 25
mg/1 may be in order. Portion E-2 of Plant E contains a
small process waste water source, the vertical retort
scrubber purge. This effluent, ranging from 136 to 272 cu
m/day (25 to 50 gpm) has high metal values. Therefore,
liming and settling of this small stream may be in order.
The treatment technologies recommended above for Plant E
should aid in complying to the 1977 effluent limitations.
Costs for such actions are given below:
119
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Ca£ital_Costs ___
Clarifiers, two each, 38 ft drain,
for Plant E-1 effluent 96,000
Lime and settle treatment plant
for Plant E-2 effluent _86^000^
Total 182,000
S/Annual kkg 1.75
(S/Annual ton) (1.58)
Annual Costs
Clarifier operating costs 24,000
Lime and settle operating costs
Operating and maintenance 50,600
Depreciation, taxes and insurance,
and interest J.lxj600_
Total 89,200
$/kkg 0.86
($/ton) (0.78)
Various methods exist for Plant E's achievement of the
recommended 1983 effluent limitations. The one method used
in this analysis is by means of flow reduction of process
waste waters. By 1983, the flow rates for each of the three
process waste water sources should approach the lower end of
the indicated flow ranges. The largest of the three
sources, acid plant blowdown, can be greatly reduced by the
addition of a cooling tower, so that temperature will not be
the major reason for a large blowdown. The costs for such a
cooling tower follow:
Cagjtal Costs _J.9_21 JL
Cooling tower 145,000
$/Annual kkg 1.39
($/Annual ton) (1.26)
120
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Annual Costs
Total
$/kkg
($/ton)
36,000
0.35
(0.32)
The total costs attributable to the recommended effluent
limitations for Plant E are:
^/Annual kkg
($/Annual ton)
To tal_ Ajinual_Cos t s
$/kkg
($/ton)
327,000
3. 14
(2.84)
125,200
1.21
(1-10)
Plant F
Current control technology for Plant F has permitted a
volumetric flow reduction so that the discharge, considered
as current, is about 2,450 cu m/day (450 gpm) . In order to
assure compliance to both the 1977 and the 1983 recommended
effluent limitations, this flow, equivalent to 3,945 1/kkg
(945 gal/ton) , should be subjected to lime and settle
treatment. Plant personnel indicate that some noncontact
cooling water must also be segregated from the process waste
water prior to treatment. The costs for these measures are
as follows:
Capital Costs
Segregation of noncontact
cooling water
Lime and settle treatment
of 2,450 cu m/day (450 gpm)
Total
$/ Annual kkg
_12!1_J
250,000
55.0X000
800,000
3.52
121
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(S/Annual ton) (3.20)
Annual^Cpgts
Lime treatment 57,000
Overhead, depreciation, taxes and
insurance, interest
Total
$/kkg
($/ton)
Plant G
Data used for this plant indicate a current flow value of
9,940 1/kkg (2,360 gal/ton) and an anticipated flow value
for 1983 of 6,900 1/kkg (1,570 gal/ton). Plant personnel
indicate that minor reductions in the usage of roaster gas
spray blowdown will allow the achievement of the selected
flow values. Current effluent data from the lime and settle
treatment facility indicate good significant pollutant
concentrations. Therefore, no additional costs should be
incurred by this plant for achieving compliance to the
recommended effluent limitations guidelines.
Tota.j._Costs
The total estimated costs to Plants B, C, E, and F, on the
basis of 1971 dollars, for achievement of the recommended
1977 effluent limitations, are $1,515,000 capital and
$458,000 annual. The costs for compliance to the 1983
recommendations for Plants D and E are $1,054,000 capital
and $450,000 annual. Therefore, the total estimated capital
and annual costs to this industry are $2,569,000 and
$908,000, respectively. A summary of these costs are
shown in Table 30.
Nonwater,Quality Aspects
Energy Requirements
Specific data on energy requirements were not available from
most of the plants surveyed. The current waste water treat-
122
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TABLE 30. ADDITIONAL CONTROL Aid TREATMENT COSTS (1971 $)
00
Plant
Designation
B
C
D
E
F
G
1977
Capital
$ 33,000
500,000
0
182,000
800,000
0
Costs
Annual
$ 8,000
152,000
0
89,000
209,000
0
1983
Capital
0
0
$909,000
145,000
0
0
Costs
Annual
0
0
$414,000
36,000
0
0
Total
Capital
$ 33,000
500,000
909,000
327,000
800,000
0
Costs
Annual
$ 8,000
152,000
414,000
125,000
209,000
0
TOTAL
$1,515,000 $458,000
$1,054,000 $450,000
$2,569,000 $ 908,000
-------
ment practices are confined to cooling towers, settling
ponds, and lime treatment, which require an insignificant
amount of electrical and thermal energy. Data supplied by
Plant E-l on lime treatment indicate a power consumption
estimated at about 4.3 kwhr/kkg (3.9 kwhr/ton) of zinc
production.
Two zinc plants reported that the zinc production process
consumed approximately 99 percent of all plant power needs.
The remaining one percent is the energy value necessary for
all other plant needs, including water pollution control. A
new waste water treatment facility which limes and settles
the combined effluents from a lead-zinc mining, milling, and
smelting complex employs about lOO horsepower-worth of power
equipment. This power need is considered negligible in
comparison to total plant needs.
Solid Waste Generation
When the process waste waters of the primary zinc industry
are neutralized with lime, a sludge will be produced. The
volume of this sludge will primarily be dependent upon the
desired pH adjustment (i.e., the higher the value of pH, the
larger the volume of generated sludge).
Plant C, while investigating the potential application of a
lime treatment facility to its process waste water effluent,
characterized both the probable volume of generated waste
and its constituents. The approach taken was a two step
neutralization of approximately 800 1/min (210 gpm) of
process waste water with 10 percent milk of lime. The first
stage of pH was assumed to reach 9.5, while the second stage
reached 10.7. The resulting sludge calculated out to
approximately 270 kkg (245 tons)/day or (50 kkg (45
tons)/day dry weight). The primary constituent of this
sludge was gypsum, CaS04_ 2H2_0. Other major constituents
were the hydroxides of magnesium, zinc, iron, and manganese.
Since the large volume of this sludge would present a
disposal problem at this facility, plant personnel are
conducting waste water treatment studies by the application
of sulfide precipitation, as well as lime treatment with a
sodium silicate flocculent. With the possible usage of
sulfide precipitation, a smaller volume of gypsum sludge
would be produced and a sulfide cake, containing the major
heavy metal values, would also be generated. The latter
material would be recirculated in the smelting system,
either as feed to the roasters or through a separate
leaching step. Recent studies using sodium silicate as a
flocculent have shown a much smaller generation of sludge.
124
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Because of the addition of the flocculent, a lower pH (about
9.5) can be used to acheive similar effluent results as with
the higher pH achieved through simple liming.
Approximately, one-third (about ]]0 kkg (100 tons)/day) of
sludge would be generated by this application of liming with
flocculent addition.
A new treatment facility, employing milk of lime, ferric
chloride, and a polyelectrolyte to neutralize and settle
68,400 cu m/day (18 mgd) of commingled process waste water
from an integrated domestic primary copper smelter, is
currently preceding through start-up. Approximately 36 kkg
(40 tons)/day of sludge, by dry weight, will be generated.
One currently operating primary electrolytic zinc facility,
(Plant B) neutralizes 2,774 cu m/day (509 gpm) of total
plant effluent with lime. A large volume of sludge is
generated. Approximately half of the influent to the
treatment facility is comprised of noncontact cooling water,
boiler blowdown, and treated sanitary waste water. The
reported volumetric flow rate of process waste water, as
defined by this document, is 1,300 cu m/day (240 gpm). If
the two flows (i.e., process waste water from zinc
production and other plant water) were segregrated, the
generation of sludge due to the treatment recommended by
this document would be much smaller. The operators at Plant
B are currently reducing the water content of the "lime and
settle" sludge generated by their treatment practice by
solar evaporation. Nearly 7,000 wet tons (64 percent
moisture) of this solid waste have been shipped to one of
the company's primary lead smelters, where the sludge is
charged to a zinc (lead slag) fuming furnace. As reported
by this company, the zinc content of the sludge, as shipped,
is averaging about 25 percent (range of 15 to 30 percent).
Thus, sludge generation volume can be reduced by one or a
combination of the following:
(1) Usage of lower neutralization pH, by addition of
flocculents;
(2) Segregation of non-process waste water effluents
from treatment plant influent;
(3) Minimize process waste water volume by maximization
of internal reuse and recycle;
(4) Application of dewatering techniques, such as
centrifuging.
125
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SECTION IX
BEST PRACTICABLE CONTROL TECHNOLOGY CURRENTLY
AVAILABLE—EFFLUENT LIMITATIONS GUIDELINES
Introduction
The effluent limitations that must be achieved by July 1,
1977 are to specify the degree of effluent reduction
attainable through the application of the best practicable
control technology currently available. Such control
technology is based on the average of the best performance
by plants of various sizes and ages, as well as the unit
processes within the industrial category. This average is
not based upon a broad range of plants within the primary
zinc industry, but upon the performance levels achieved by
the exemplary plants. Additional consideration was also
given to:
(1) The total cost of application of
technology in relation to the effluent
reduction benefits to be achieved
from such application.
(2) The size and age of the equipment and
plant facilities involved.
(3) The process employed.
(U) The engineering aspects of the
application of various types of
control techniques.
(5) Process changes.
(6) Nonwater quality environmental
impact (including energy requirements).
The best practical control technology currently available
emphasizes effluent treatment at the end of a manufacturing
process. It includes the control technology within the
process itself when the latter is considered to be normal
practice within the industry.
A further consideration is the degree of economic and
engineering reliability, which must be established for the
technology to be currently available. As a result of
demonstration projects, pilot plants, and general use, there
must exist a high degree of confidence in the engineering
and economic practicability of the technology at the time of
commencement of construction or installation of the control
or treatment facilities.
127
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Industry Category and Waste Water Streams
One category of the industry encompassing the primary
smelting and refining of nonferrous metals (Standard
Industrial Classification Number 333) is the primary
smelting and refining of zinc (SIC Number 3333). SIC Number
3333 describes those establishments primarily engaged in
smelting zinc from the ore, or in refining zinc by any
process. Establishments primarily engaged in the mining and
benefication of zinc ore, as well as some lead ores, and the
rolling, drawing, or extruding of zinc are not classified by
this SIC and are not the subject of this development
document. Facilities for the generation of on-site
electrical power, and other ancilliary operations are also
not the subject of this report. The process waste water
sources to be covered by the proposed regulations, the
rationale for which is derived in this section, have been
clearly defined in past sections.
As developed in previous sections of this document, the
primary zinc industry is considered, for the purpose of
establishing recommended effluent limitations guidelines, as
a single subcategory. The principal basis for this
consideration is the similarities in process waste water
characteristics and applicable control, and treatment
technologies.
The process waste water sources from the primary zinc
industry include acid plant blowdown, reduction furnace
offgas scrubbing, metal casting cooling, cadmium leaching,
dust control scrubbers, offgas humidification, and
preleaching operations.
Recommended Effluent Limitations
The recommended effluent limitations based on the
application of the best practicable control technology
currently available for the primary zinc subcategory are:
Effluent limitations
Effluent Average of daily
characteristic Maximum for values for 30
any 1 day consecutive days
shall not exceed
Metric units (kilograms per 1000
kg of product)
128
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TSS 0.42 0.21
As 1.6x10-3 8.0x10-*
Cd 0.008 0.004
Hg 8.0x10-5 4.0x1C-5
Se C.08 0.04
Zn 0.08 0.04
pH
English units (pounds per 1COO
______ lb_of_eroduct]
TSS 0.42 0.21
As 1.6x10-3 8.0x10-*
Cd 0.008 0.004
Hg 8.0x10-5 4.0x10-5
Se 0.08 0.04
Zn 0.08 0.04
pH _Within_the_range_7iO_to_^£iO
Identification^of_the_Best_ Practicable
Control^ TechnglogY_Currently Available
The best practicable control technology currently available
is identified as the minimization of discharge or process
waste water by the practices of recycle, reuse, segregation,
and, finally, chemical treatment to achieve controlled
precipitation followed by sedimentation (lime and settle).
The review of water use practices in various plant systems
has shown that in specific cases, some process waste waters
are currently being used on a once-through basis; whereas,
in other existing plants, the discharge from the same
process operation is considerably lower on a unit-product
basis by virtue of recycle. Further, various examples of
reuse of process waste water (e.g., acid plant blowdown used
for cadmium leaching) were also identified. Further
evidence of potential reductions in process waste water
volume is given in various proposed plans for decreased
discharge of process waste waters. However, internal
streams in zinc smelters vary considerably with differences
in plant operations, and no specific list of control
measures may be presented for all plants. Those measures
that have been identified include:
The minimization of acid plant blowdown by
appropriate proper operation of prescrubber gas
cleaning facilities to minimize particulate
loadings into the wet scrubbers, cooling capacity
129
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and provisions for settling in the scrubber liquor
recycle circuit, and possibly reuse of the scrubber
bleed stream in other plant operations.
• The minimization of metal casting cooling water
discharge by recycle, possibly including provisions
in the circuit for removal of suspended solids, oil
and grease, and thermal load.
• The exploitation of the evaporative capacity of hot
gases or hot metal for inplant disposal of waste
water.
The end-of-pipe treatment identified as part of the best
practicable control technology currently available is the
lime-and-settle treatment. Currently, some form of this
treatment is applied to some portion of process waste water
at five of the eight (soon to be six) plants in this
industry. The principles of the lime-and-settle treatment
technology are thus known to most of the industry; however,
the current application of the technology is extended, in
some cases to considerably less than all of the process
waste water streams, and, as reflected in Section V of this
document, the technology is applied with varying degrees of
effectiveness. The lime-and-settle treatment identified
herein implicitly includes a "best practicable" level of
performance, described below in terms of effluent
concentrations.
The combination of neutralization and clarification is
required to achieve the best practicable control technology
currently available. Clarification alone will reduce only
total suspended solids; neutralization without clarification
will reduce dissolved metals, but not suspended ones, and
will not provide an effluent of satisfactory quality.
Neutralization with lime to a pH in the 8 to 11 range will
reduce the concentrations of those metals precipitable as
hydroxides, and with properly designed retention facilities
will also reduce total suspended solids to below the
recommended effluent limitations guidelines. Use of lime
has the further advantage that it, unlike sodium-based
alkalies, forms a relatively insoluble sulfate, CaSO4, which
will tend to also reduce the concentrations of dissolved
sulfate in the effluent. Neutralization will not
significantly reduce concentrations of those parameters that
are soluble at an alkaline pH.
In order to achieve the desired concentrations, indications
are that the pH of the solution should be raised to the 10
to 11 range. As discussed in Section VII, arsenic and
selenium are not effectively removed at pH's above 7, and
their removal depends upon absorption and coprecipitation.
130
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In spite of this deficiency, neutralization with lime and
settling of the reaction mixture seems to represent the best
practicable control technology currently available. There
is not the requisite high degree of confidence in the
engineering and economic practicability of the alternative
control and treatment technologies to warrant their
recommendation at this time.
The selection of recommended effluent concentrations and
flows was made on the basis of the information presented in
Sections V, VII, and VIII of this document. Specifically,
the flow rates of discharges of process waste waters
presented in Section VIII of this document were inspected to
determine the range of current effluent rates. As discussed
in Section VIII, these rates do not include those for
noncontact cooling water, and reflect the assumption of the
institution of recycle practices in one plant (Plant F) with
an exceptionally high rate of process waste water, because
of present once-through practice. Hence, this range of
flows as detailed in Section VIII, (1) is based on process
waste water only and (2) includes projected decreases in
flows as reported by industry; that is, the flows reflect
"best practicable control" measures. Average flow rates of
process waste water effluents were converted to discharge
rates per unit of product to obtain the following values:
Flow Production Discharge Rate
£iili£ cu_m/day iSSffll kJS2/day. (£°.S/<2£Y.L 1/kkg (gal/ton)
B 1,308 (240) 268 (296) 4,880 (1,170)
C 1,134 (208) 176 (194) 6,440 (1,550)
D 4,060 (745) 302 (333) 13,440 (3,220)
E 2,400 (440) 285 (315) 8,415 (2,01C)
F 2,450 (450) 621 (685) 3,945 (945)
G 1,250 (230) 124 (137) 9,940 (2,360)
Taking the average of the above six flow values produces a
selected value of 8,350 1/kkg (2,000 gal/ton). This value
is slightly rounded-up, primarily because Plant F reuses its
acid plant blowdown for cadmium leaching.
As developed in Sections V and VII, current lime-and-settle
treatment operations (Figure 7 and Tables 24 and 27) for
which reasonable amounts of data are available show the
following concentrations of constituents to be achievable in
effluents.
Total Suspended Solids 25 mg/1
Zinc 5 mg/1
Cadmium 0.5 mg/1
131
-------
Mercury 0.005 mg/1
Selenium 5 mg/1
Arsenic 0.1 mg/1
These demonstrated levels of concentrations were applied,
together with the selected flow value,, to derive the
recommended effluent limitations.
Rationale for the_Selectj,ori_of_Best_Practicable
£gntrol_Technology CurrentlY_AvajJ.able
(1) The selected lime-and-settle technology is capable
of achieving significant reductions in discharge of
pollutants, as indicated by industry-supplied data
and as verified by the analysis of samples
collected on-site at plants where the technology
was applied.
(2) The technology is compatible with industry
variations, including age and size of plant,
processes employed, raw material variations, plant
location, and nonwater quality environmental
impact.
(3) The technology, as an end-of-pipe treatment, can be
an add-on to existing plants, and need not affect
existing internal process and equipment
arrangements.
(4) The ratios of recommended maximum daily values to
30-day averages are based on an analysis of the
RAPP data reported by the producers, from which an
average ratio of maximum concentrations to average
concentrations was derived. This analysis showed
that some parameters, suspended solids for example,
exhibited a fairly narrow and consistent maximum:
average ratio of between 1 and 2; whereas, trace
elements covered a much wider span, and the
differences between plants were greater. A
maximum: average ratio of 2:1 appeared to represent
a fair central value for the pollutants of
interest.
(5) It is concluded that the effluent-reduction
benefits balance the costs of the technology. On
the basis of the information contained in Section
VIII, those plants not presently achieving the
recommended 1977 effluent limitations would require
an estimated capital investment of $1,515,000 and
an increase in annual operating cost of about
$458,000 to achieve the recommended limitations.
132
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SECTION X
BEST AVAILABLE TECHNOLOGY ECONOMICALLY
ACHIEVABLE—EFFLUENT LIMITATIONS GUIDELINES
Introduction
The effluent limitations that must be achieved by July 1,
1983, are to specify the degree of effluent reduction
attainable through the application of the best available
technology economically achievable. The best available
technology economically achievable is not based upon an
average of the best performance within an industrial
category, but is to be determined by identifying the very
best control and treatment technology employed by a specific
point source within the industrial category or subcategory,
or where it is readily transferable from one industrial
process to another. A specific finding must be made as to
the availability of control measures and practices to
eliminate the discharge of pollutants, taking into account
the cost of such elimination.
Consideration must also be given to:
(a) The age of equipment and facilities
involved,
(b) The process employed,
(c) The engineering aspects of the applica-
tion of various types of control
techniques,
(d) Process changes
(e) Cost of achieving the effluent reduction
resulting from application of the best
economically achievable technology,
(f) Nonwater quality environmental impact
(including energy requirements).
In contrast to the best practicable control technology
currently available, the best available technology
economically achievable assesses the availability in all
cases of inprocess controls, as well as control or
additional treatment techniques employed at the end of a
production process.
The best available technology economically achievable is the
highest degree of control technology that has been achieved
or has been demonstrated to be capable of being designed for
plant-scale operation up to and including "no discharge" of
process waste water pollutants. Although economic factors
are considered in this development, the costs for this level
133
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of control are intended to be the top-of-the-line of current
technology subject to limitations imposed by economic and
engineering feasibility. However, the best available
technology economically achievable may be characterized by
some technical risk with respect to performance and with
respect to certainty of costs. Therefore, the best
available technology economically achievable may necessitate
some industrially sponsored development work prior to its
application.
Recommended_Effluent_Limitations
The recommended effluent limitations based on the
application of the best available technology economically
achievable for the primary zinc subcategory are:
Effluent
characteristic
TSS
As
Cd
Hg
Se
Zn
pH
TSS
As
Cd
Hg
Se
Zn
pH
Ef f 1 u en t 1 im j. t a t ions _________
Average of~daily"
Maximum for values for 30
any 1 day consecutive days
shall not exceed
Metric units (kilogram per 1,000
0.14
5.4x10-*
2.7x10-3
2.5x10-5
0.027
0.027
0.28
1.1x10-3
5.4x10-3
5.0x10-5
0.054
0.054
Within_the_ranae_7_iO_to_JJ)iO _______
English units (Ib per 1000 Ib
of_2roduct] ______
0.28
1.1x10-3
5.4x10-3
5.0x10-5
0.054
0.054
0.14
5.4x10-*
2.7x10-3
2.5x10-5
0.027
0.027
134
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Identification of Best Available Technology
Economically Achjeyable
The identification of the best available technology
economically achievable is analogous to the technology
defined in Section IX, and includes control measures to
further minimize the volume of process waste water streams
by additional recycle, reuse, segregation, and the
application of chemical treatment to achieve controlled
precipitation followed by sedimentation.
The control measures identified as part of the applicable
technology include the following:
o Minimization of acid plant blowdown
streams by appropriate measures of
cooling (i.e., by cooling towers or ponds),
control of particulate loadings entering
gas scrubbers, recycle, and/or reuse of
the stream within the plant;
o Minimization of metal casting cooling
waste water discharge by recycle, reuse,
or treatment allowing reuse or recycle
within the operation or the plant;
o Exploitation of evaporative capacity
wirhin the plant in terms of hot gas,
hot metal, or evaporative equipment
operations to maximize inplant disposal of
waste waters;
o Process modifications to maximize the
reuse of water within the processes
at each specific plant.
The selection of recommended effluent concentrations and
flows was made on the basis of information presented in
Section V, VII, and VIII of the document. Specifically, the
flow rates of current and potential discharges of process
waste waters, as discussed in Section VIII, were inspected
to determine the best available technology flow value. The
data used to develop this value follows:
Flow Production Discharge Rate
Plant cu_m/day. __ (2J22J1
B 1,3C8 (240) 268 (296) 4,880 (1,170)
C 1,134 (208) 176 (194) 6,470 (1,550)
135
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D 4,060 (745) 302 (333) 13,400 (3,210)
E 1,390 (255) 285 (315) 4,880 (1,170)
F 2,450 (450) 621 (685) 3,945 (945)
G 818 (150) 124 (137) 6,900 (1,570)
The selected value of 5425 1/kkg (1300 gal/ton) was
developed by averaging the best discharge rates shown in the
above tabulation, namely those from Plants B, C, E, F, and
G. Plant B is currently operating at its indicated value;
Plant C will shortly reduce its flow value to its indicated
value; Plants E and G indicated flow ranges, so the
indicated values for these two plants were taken at the
bottom of each range; Plant F has indicated a method of
process waste water effluent minimization through recycle
and reuse; and, finally, the current value for Plant D is
not used.
The same treatment technology pollutant concentrations, as
were used' in the calculations of the best practicable
effluent limitations, were considered as those achievable
through the application of the best available technology.
These concentrations are achievable by means of lime-and-
settle technology. Values for pollutant concentrations from
such possible technologies as sulfide precipitation or
others, as described in Section VII, cannot, as yet, be used
for the derivation of the best available effluent
limitations.
£ationale_fgr^the_SelectiQn_of_Best_Available
Numerous methods of control and treatment technology are, or
should shortly be available, which would enable compliance
to the proposed effluent limitations based on the best
available technology economically achievable. The best
available limitations are principally based upon the control
technology of maximum reuse and recycle of process waste
water and the treatment technology of lime and settle. The
Idential treatment technology was used in Section IX as part
of the best practicable effluent limitations rationale.
Compliance to the proposed best available limitations can
also be achieved by either employing better treatment
technology (lower pollutant concentrations than used in
calculations) and a lesser degree of control technology
(less recycle and reuse, producing a higher flow usage
value, as used in the calculations) or better control
technology and a lesser degree of treatment technology.
136
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Current industrial research on the application of sulfide
precipitation, flocculent additions, polyelectrolyte
additions, and other treatment methods will undoubtedly lead
to both lower pollutant discharge concentrations and lower
sludge volume generation.
Incremental capital and annual operating costs for the two
primary zinc plants, which would need incremental control
and treatment practices to comply to the recommended 1983
effluent limitations, are approximately $1,054,000 and
$450,000, respectively.
137
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SECTION XI
NEW SOURCE PERFORMANCE STANDARDS
Introduction
In addition to guidelines reflecting the best practicable
control technology currently available and the best avail-
able technology economically achievable, applicable to
existing point source discharges by July 1, 1977, and July
1, 1983, respectively, the Act requires that performance
standards be established for new sources. The term "new
source" is defined in the Act to mean "any source, the
construction of which is commenced after the publication of
proposed regulations prescribing a standard of performance".
New source technology shall be evaluated by adding to the
consideration underlying the identification of best
available technology economically achievable a determination
of what higher levels of pollution control and treatment are
available through the use of improved production processes
and/or treatment techniques. Thus, in addition to
considering the best inplant and end-of-process control
technology, identified in best available technology
economically achievable, new source technology is to be
based upon an analysis of how the level of effluent may be
reduced by changing the production process itself. Al-
ternative processes, operating methods, or other
alternatives must be considered. However, the end result of
the analysis will be to identify effluent standards, which
reflect levels of control achievable through the use of
improved production processes (as well as control
technology), rather than the prescription of a particular
type of process or technology which must be employed. A
further determination that must be made for new source
technology is whether a standard calling for no discharge of
process waste water pollutants to navigable waters is
applicable.
The following factors should be considered with respect to
production processes which are to be analyzed in assessing
new source technology:
(a) The type of process employed and process
changes
(b) Operating methods
(c) Batch as opposed to continuous operations
(d) Use of alternative raw materials and mixes
of raw materials
(e) Use of dry rather than wet processes (in-
cluding substitution of recoverable solvents
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for water)
(f) Recovery of pollutants as byproducts.
Consideration must also be given to the fact that new source
performance standards could require compliance at a much
earlier time than the effluent limitations to be achieved by
existing sources by July 1, 1977.
Recommended Standards
The best available demonstrated control technology,
processes, operating methods, or other alternatives are
identical to the best available technology economically
achievable. The corresponding standard of performance is
identical to the effluent limitations guidelines established
from usage of the best available technology economically
achievable.
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SECTION XII
ACKNOWLEDGMENTS
This document was developed by the Environmental Protection
Agency. The original contractor's draft report, dated
December 1973 was prepared by Eattelle Memorial Institute,
Columbus, Ohio, under contract no. 68-01-1518. Mr. John B.
Hallowell prepared this original (contractor's) draft
report.
This study was conducted under the supervision and guidance
of Mr. George S. Thompson, Jr., Project Officer.
Preparation, organizing, editing, and final rewriting of
this report was accomplished by Mr. Thompson.
The following members of the EPA working group/steering
committee provided detailed review, advice and assistance:
W.J. Hunt, Chairman
G.S. Thompson, Jr.,
Project Officer
S. Davis
D. Fink
J. Ciancia
T. Powers
Effluent Guidelines Division
Effluent Guidelines Division
Office of Planning and Evaluation
Office of Planning and Evaluation
National Environmental Research
Center, Edison
National Field Investigation Center,
Cincinnati
Excellent guidance and assistance were provided to the
Project Officer by his associates in the Effluent Guidelines
Division, particularly Messrs. Allen Cywin, Director,
Effluent Guidelines Division, Ernst P. Hall, Deputy
Director, and Walter J. Hunt, Branch Chief.
The cooperation of individual primary zinc companies, who
offered their plants for survey and contributed pertinent
data, is greatly appreciated. These include:
American Smelting and Refining Company
St. Joe Minerals Corporation
New Jersey Zinc company
Amax Zinc Company, Inc.
Bunker Hill Company
The cooperation of the Water Pollution Control Subcommittee
of the American Mining Congress is also appreciated.
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Acknowledgmenr and appreciation is also given to Ms. Kay
Starr, Ms. Nancy Zrubek, and Ms. Brenda Holmone of the
Effluent Guidelines Division secretarial staff.
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SECTION XIII
REFERENCES
1. Brobst, Donald A., and Pratt, Walden P., editors,
United States Mineral Resources, Geological Survey
Professional Paper, United States Government Printing
Office, Washington, D. C., 1973.
2. Bureau of Mines, Minerals Yearbook, 1971, "Volume I,
Metals, Minerals, and Fuels", United States Depart-
ment of the Interior, Bureau of Mines, U. S. Govern-
ment Printing Office, Washington, D. C. (1973).
3. Bureau of Mines, "mineral Facts and Problems, 1970
Edition", Bureau of Mines Bulletin 650, U. S. Depart-
ment of the Interior, Bureau of Mines, U. S. Govern-
ment Printing Office, Washington, D. C. (1970).
4. cotterill, C. H., and Cigan, J. M. .(editors), AIME
World Symposium of Mining and Metallurgy of Lead and
Zinc, "Volume II, Extractive Metallurgy of Lead and
Zinc", The American Institute of Mining, Metallurgical,
and Petroleum Engineers Inc., Port City Press,
Baltimore, Maryland (1970).
5. 1970 E/MJ International Directory of Mining and
Mineral Processing Operations, Published by Mining
Informational Services, Engineering and Mining
Journal, McGraw-Hill, New York (1970).
6. 1973 Annual Book of ASTM Standards, Part 7, Nonferrous
Metals and Alloys, "Standard Specification for Lead",
B29-55 (Reapproved 1971), pp 30-32.
7. Pourbaix, Marcel, "Atlas_gf_Electrochemical_Eguilibria
in Aqueous Solutions", Pergamon Press, New York
(1966)".~
8. Hartinger, Ludwig; "Waste Water Purification in the
Metalworking Industries, Precipitation of Heavy
Metals:, Part 1, Problems, Bander Bleche Rohre
Dusseldorf, October, 1963, pp 535-540.
9. Jenkins, S. N. Knight, D. G., and Humphreys, R. E.,
"The Solubility of Heavy Metal Hydroxides in Water,
Sewage, and Sewage Sludge, I. The Solubility of
Some Metal Hydroxides:, Int. Jour. Air & Water
Pollutionn 8, 537-556 (1964).
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10. Maruyama, T., S. A. Hannah, and J. M. Cohen,
"Removal of Heavy Metals by Physical and Chemical
Treatment Processes", presented at 45th Annual
Water Pollution Control Federation Meeting (1972).
11. Kantawala, D., and H. D. Tomlinson, "Comparative
Study of Recovery of Zinc and Nickel by Ion Exchange
Media and Chemical Precipitation", Water, Sew Works,
111 R-281 - R 286 (1964).
12. Kolthoff, I. M., and Sandell, E. B., Textbook of
Quantitative Inorganic Analysis, 3rd Ed., The
McMillan Company, New York (1952).
13. "Ultimate Disposal of Liquid Wastes by Chemical
Fixation", Chemfix Division, Environmental Sciences,
Inc., Pittsburgh, Pa. (1973).
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SECTION XIV
GLOSSARY
Acid Plant
In primary zinc reduction operations, an adjoining
metallurgical plant which utilizes the sulfur oxide offgases
from the roasters to produce sulfuric acid.
Act
The Federal Water Pollution Control Act Amendments of 1972.
A term representing the presence of salts of weak acids.
The hydroxides, carbonates, and bicarbonates of calcium,
sodium, and magnesium are the common impurities that cause
alkalinity. An alkaline solution has a pH greater than 7.
Anc ilia ry Oper ation s
Operations which are often carried out at primary zinc
plants but are not an essential part of the processing, for
example, power generation.
Anode
The positive electrode in electrolysis; electrode through
which a current enters an electrolytic cell from an external
electro-motive furnace. In zinc electrolytic practice,
insoluble rectangular lead anodes are used.
Large chamber for holding bags used in the filtration of
gases from a furnace, for the recovery of metal oxides,
dust, and similar solids suspended in the gases.
Best Available Technology, Eggnomically Achievable
Level of technology applicable to effluent limitations to be
achieved by July 1, 1983 for industrial discharges to
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surface waters as defined by Section 3Cl(b) (2)(A) of the
a «—+•
Act.
Level of technology applicable to effluent limitations to be
achieved by July 1, 1977, for industrial discharges to
surface water as defined by Section 301(b) (1) (A) of the
Act.
Slowdown
A discharge from a system, designed to prevent a buildup of
some material, as in a boiler to control dissolved solids.
Brass
An alloy consisting mainly of copper (over 50 percent) and
zinc, to which smaller amounts of other metals may be added.
Calcination
Heating of a solid to a temperature below its melting point
to bring about a state of thermal decomposition or phase
transition other than melting.
Calcine
The impure zinc oxide product of the roasting operations.
Capital Costs
Financial charges which are computed as the cost of capital
times the capital expenditures for pollution control. The
cost of capital is based upon a weighted average of the
separate costs of debt and equity.
CategorY^and^Subcategory
Divisions of a particular industry which possess different
traits affecting waste treatability and requiring different
effluent limitations.
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Cathode
The negative electrode in electrolysis; the electrode
through which a current leaves an electrolytic cell to
return an external source of electromotive force. In zinc
electrolytic practice, rectangular aluminum cathodes are
used.
Cathode Deposit
Metal formed on a cathode during electrolysis. In zinc
electrolysis, zinc is deposited onto aluminum rectangular
cathodes from which it is stripped at regular intervals.
Clarifi cation
Process of removing turbidity and suspended solids by
settling. Chemicals can be added to improve and speed up
the settling process through coagulation.
Cooling Tower
A device in which hot water is pumped to the top of a rower
and cooled by allowing it to flow downward in thin streams
from one container to another.
Concentrates
The product of milling operations in which the ore values,
usually after grinding, are separated and concentrated.
Custom Smelt_er
A smelter processing zinc concentrates purchased from other
sources. These different concentrates are specifically
blended to produce a specific quality "custom" product.
Depreciation
Accounting charges reflecting the deterioration of a capital
asset over its useful life.
Dewat.ering_Classif igr
(Sometimes referred to as a dewatering bin or tank). A
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settling tank for clarifying process water; the tank may
have a continuously operating rake at the bottom which moves
the settled solids or sludge towards an outlet pipe in the
bottom.
Die Casting
A casting process where a molten metal such as zinc is
forced under high pressure into the cavity of a metal mold.
Dust Collector
An air pollution control device for removing dust from air
streams. Filtration, electrostatic precipitation, or
cyclonic principles may be utilized, but the term usually
infers a dry system, not involving a water stream.
Effluent
The waste water discharged from a point source to navigable
waters.
Effluent Limitation
A maximum amount per unit of production of each specific
constituent of the effluent that is subject to limitation in
the discharge from a point source.
Effluent Loading
The quantity or concentration of specified materials in the
water stream from a unit or plant.
Electrolyte Purification
Removal of impurities, copper, cadmium, cobalt, nickel, and
other residuals from the electrolyte by means of replacement
through additions of zinc dust.
Electrolytic Refining
Recovery of metal from concentrates in an aqueous solution
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by electrolysis, and the concomitant separation of
impurities from solution as sludge.
Electrolytic Zinc
Zinc produced from its ores by roasting (to convert sulfide
to oxide), solution of the oxide in sulfuric acid,
precipitation of impurities by adding zinc dust, and final
electrolytic deposition of zinc on aluminum cathodes. The
product has a purity of 99.9 +• percent.
Electrostatic Precipitator
A gas cleaning device using the principle of placing an
electrical charge on a particle, which is then attracted to
oppositely charged plates or wires. The device uses a d-c
potential approaching 40,000 volts to ionize and collect the
particulate matter. The collector plates are intermittently
rapped to discharge the collected dust into a hopper below.
The system may operate dry or the plates may be continuously
cleaned by a falling film of water.
Electrothermic Reduction
A continuous reduction-volatilization process in which the
internal heating of a large vertical cylindrical retort is
supplied by electrical energy; the feed materials,
consisting of sinter and coke, set up resistance to the
electrical current and serve as a heating element. The zinc
vapor and carbon monoxide produced are collected in an
annular ring encircling the furnace at mid-height, from
which they pass into a u-shaped condenser, where the zinc
vapor is condensed to zinc metal, and the carbon monoxide is
caught, cleaned, and compressed for use as fuel.
Flash Roasting
Rapid removal of sulfur from sulfide mineral concentrates by
allowing the concentrates to fall through a heated oxiding
atmosphere. Alternatively, dried and finely ground
concentrates may be blown into a combustion chamber and
burned to calcine and sulfur dioxide.
Flotation
A method of mineral separation in which a froth, created in
water by air bubbles and a variety of reagents, selectively
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float some minerals (in a finely divided condition) by means
of adherence to film bubbles, while other minerals are not
so wetted and sink.
Fluidized-Bed Roasting
A roasting process in which concentrates are fed into a
cylindrical combustion chamber when they become suspended in
a bed supported on an air column. After oxidation of the
finely ground sulfide concentrate occurs, the calcine
overflows a retaining wall inside the roaster. Separation
of the calcine and sulfur dioxide is accomplished in hot
cycles.
Flux
A substance added to a retort or furnace charge that
promotes fusing of minerals or metals, or prevents the
formation of oxides.
Galvanizing
Tne coating of steel with zinc, which may be done by either
not dip or electrolytic methods.
Horizontal Retort Process
A batch reduction-volatilization process in which clay
retorts filled with sinter, zinc oxide, coal or coke, and
small amounts of dross are placed in banks in a furnace,
where the zinc oxide constituent is reduced to zinc,
volatilized, and the evolved zinc vapor is subsequently
condensed to metallic zinc in refractory condensers.
Indirect Cooling
Water cooling in which water is not in contact with any
material in process; jacket cooling of pyrothermic equipment
is an example.
Jarosite
A hydrated sulfate of iron and potassium crystallizing in
the rhombohedral system.
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Jarosite Process
A process of treating concentrates of leached residues in
which the iron impurity present is precipitated as jarosite.
Leaching
The extraction of a soluble metal (or metals) by dissolving
in a solvent. In electrolytic zinc recovery, the
concentrates are leached with spent electrolyte until all
the zinc is dissolved in a still slightly acid (H2S04_)
medium.
Lime Sump
A pit or tank to which lime is added to precipitate out
dissolved metallic impurities from plant waste water.
Multiple-Hearth Roas ting
A roasting process in which the concentrates enter at the
top of a multiple hearth roaster and drop from hearth to
hearth in succession until discharged at the bottom. The
concentrates are raked over each hearth by rubble arms.
Concentrates are first dried on the upper hearth, then
roasted in heated air, as they progress downward through the
roaster. In addition to removing sulfur as S02_, multiple-
hearth roasters are effective in removing lead.
New Source
Any building, structure, facility, or installation from
which there is or may be a discharge of pollutants and whose
construction is commenced after the publication of the
proposed regulations.
New Source Performance Standards
Performance standards for the industry and applicable new
sources as defined by Section 306 of the Act.
Ore
A natural mineral from which materials such as metals can be
economically extracted.
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A measure of the alkalinity or acidity of a solution,
numerically equal to 7 for neutral solutions, increasing
with increasing alkalinity and decreasing with increasing
acidity. A one unit change in pH indicates a tenfold change
in acidity or alkalinity.
Point Source
A single source of water discharge such as an individual
plant.
Pollutant Parameters
Those constituents of waste water determined to be
detrimental and therefore requiring control.
Prime Western Zinc
A commercial grade of zinc containing at least 98 percent
zinc. Maximum limits of impurities are lead, 1.6 percent
iron 0.05 percent; and cadmium, 0.50 percent. It is used
mostly for galvanizing.
Prolongs
In a horizontal retort plant, metal extensions to the
refractory condensers used to collect zinc vapor that escape
the condensers.
Pyrolytic Reduction of Zinc
Recovery of zinc by either the horizontal retort, vertical
retort, or electrothermic processes.
Roasting
In zinc plants, the operation of heating sulfide ores in air
to convert them to oxides; lead may or may not be removed in
this operation depending on specifications of the finished
product.
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Select Grade
A grade of zinc for use in galvanizing made from high-grade
zinc and added constituents to give desired hot-dipping
(galvanizing) characteristics.
Settling Pond
A pond, natural or artificial, used for settling out solids
by gravity from waste water effluents.,
Sinter
The product of the sintering process; agglomerated masses of
relatively sulfur free concentrates of suitable size for
subsequent pyrothermic plant processing, in which some of
the impurities such as arsenic and cadmium have been
removed, at least partially, by volatilization.
Sintering
A process for agglomerating calcine into masses suitable for
subsequent processing in pyrothermic plants, and at the same
time removing volatile impurities such as cadmium and
arsenic.
Sintering Machine
A horizontal sintering furnace containing traveling
articulated grates, which move the feed continuously in belt
conveyor fashion under controlled conditions of combustion
to produce sulfur free sinter of a size suitable for
subsequent, pyrothermic plant processing.
Special High-Grade Zinc
High purity, 99.990 percent zinc, with a maximum limit of
lead, iron, and cadmium of 0.003 percent each. Tin, if
present, should not exceed 0.001 percent. Die casting is
the largest application for this grade.
Spent Electrolyte
In the electrolytic recovery of zinc, the electrolyte after
recovery of zinc by electrolysis; a sulfuric acid solution
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of about 200 grams per liter of sulfuric acid containing
some residual zinc sulfate.
Sphalerite
Zn S, the principal ore mineral of zinc. A maximum weight
discharged per unit of production for each, constituent that
is subject to limitation and applicable to new sources, as
opposed to existing sources, which are subject to effluent
limitations.
Suspension Roasting
(See Flash Roasting)
Thickener
A vessel or apparatus for separating waste solids from waste
water.
Vertical Retort Process
A continuous reduction-volatilization process in which
briquettes of a zinc calcine-anthracite coal mixture pass
downward through vertical silicon-carbide retorts, while
undergoing a reduction of their zinc oxide contents. Zinc
vapor formed during the downward passage flows upward with
the carbon monoxide gas formed in the redxiction to a water
cooled condenser.
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TABLE 31
CONVERSION TABLE
MULTIPLY (ENGLISH UNITS)
ENGLISH UNIT ABBREVIATION
acre ac
acre - feet ac ft
British Thermal
Unit BTU
British Thermal
Unit/pound BTU/lb
cubic feet/tninute cfm
cubic feet/second cfs
cubic feet cu ft
cubic feet cu ft
cubic inches cu in
degree Fahrenheit %F
feet ft
gallon gal
gallon/minute gpm
horsepower hp
inches in
inches of mercury in Hg
pounds Ib
million gallons/day mgd
mile mi
pound/square
inch (gauge) psig
square feet sq ft
square inches sq in
ton (short) ton
yard yd
by TO OBTAIN (METRIC UNITS)
CONVERSION ABBREVIATION METRIC UNIT
0.405
1233.5
0.252
ha
cu m
kg cal
0.555
0.028
1.7
0.028
28.32
16.39
0.555&F-32)*
0.3048
3.785
0.0631
0.7457
2.54
0.03342
0.454
3,785
1.609
kg cal/kg
cu m/min
cu m/min
cu m
1
cu cm
%e
m
1
I/sec
kw
cm
atm
kg
cu m/day
km
(0.06805 psig +1)* atm
0.0929 sq m
6.452 sq cm
0.907 kkg
0.9144 m
hectares
cubic meters
kilogram - calories
kilogram calories/kilogram
cubic meters/minute
cubic meters/minute
cubic meters
liters
cubic centimeters
degree Centigrade
meters
liters
liters/second
killowatts
centimeters
atmospheres
kilograms
cubic meters/day
kilometer
atmospheres (absolute)
square meters
square centimeters
metric ton (1000 kilograms)
meter
* Actual conversion, not a multiplier
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