EPA
Development Document for
Proposed Effluent Limitations Guidelines
and New Source Performance Standards
for the
PHOSPHORUS DERIVED
CHEMICALS
Segment of the Phosphate
Manufacturing Point Source Cataegory
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
AUGUST 1973
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Pufe 1 icat i.gn_Not ice
This is a development document for proposed effluent limitations
guidelines and new source performance standards. As such, this report
is subject to changes resulting from comments received furing the period
of public comments of the proposed regulations. This document in its
final form will be published at the time the regulations for this
industry are promulgated.
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DEVELOPMENT DOCUMENT
for
PROPOSED EFFLUENT LIMITATIONS GUIDELINES
and
NEW SOURCE PERFORMANCE STANDARDS
for the
PHOSPHORUS DERIVED CHEMICALS SEGMENT OF THE
PHOSPHATE MANUFACTURING
POINT SOURCE CATEGORY
John Quarles
Acting Administrator
Robert L. Sansom
Assistant Administrator for Air & Water Programs
j^'lT1
Allen Cywin
Director, Effluent Guidelines Division
Elwood E. Martin
Project Officer
August, 1973
Effluent Guidelines Division
Office of Air and Water Programs
U.S. Environmental Protection Agency
Washington, D. C. 20U60
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ABSTRACT
A study was made of the phosphate manufacturing point source category by
the General Technologies Corporation for the Environmental Protection
Agency, for the purpose of developing effluent limitation guidelines.
Federal standards of performance, and pretreatment standards for the
industry, to implement Sections 304, 306 and 307 of the Federal Water
Pollution Control Act Amendments of 1972.
For the purpose of this study, the phosphate manufacturing industry was
defined as the manufacture of the following chemicals: phorphorus (and
by-product ferrophosphorus), phosphoric acid (dry process only),
phosphorus pentoxide, phosphorus pentasulfide, phosphorus trichloride,
phosphorus oxychloride, sodium tripolyphosphate and the calcium
phosphates.
Effluent limitation guidelines were developed as a result of this study,
defining the degree of effluent reduction attainable through the
application of the best practicable control technology currently
available and 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, were also defined.
Except for PC13_ and POC13 manufacture, the recommended best practicable
control technologycurrently available for the entire industry is no
discharge of process waste water pollutants to navigable waters. The
guantitative limitations upon each type of pollution parameter permitted
for PC13 and POC13 manufacturing discharges were defined; they are
basically the remaining constituents after waste water neutralization
and removal of suspended solids. No harmful materials may be
discharged.
Application of the best available technology economically achievable and
best demonstrated technology for treating dissolved solids would enable
the PCl3. and POC13_ manufacturing operations to achieve no discharge of
waste water pollutants.
iii
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CONTENTS
Section Page
I CONCLUSIONS 1
II RECOMMENDATIONS 3
III INTRODUCTION 5
IV INDUSTRY CATEGORIZATION 41
V WATER USE AND WASTE CHARACTERIZATION 45
VI SELECTION OF POLLUTION PARAMETERS 69
VII CONTROL AND TREATMENT TECHNOLOGY 77
VIII COST, ENERGY AND NON-WATER QUALITY ASPECTS 107
IX EFFLUENT REDUCTION ATTAINABLE THROUGH THE APPLICATION
OF THE BEST PRACTICABLE CONTROL TECHNOLOGY CURRENTLY
AVAILABLE, EFFLUENT GUIDELINES AND LIMITATIONS 123
X EFFLUENT REDUCTION ATTAINABLE THROUGH THE
APPLICATION OF THE BEST AVAILABLE TECHNOLOGY
ECONOMICALLY ACHIEVABLE EFFLUENT GUIDELINES
AND LIMITATIONS 137
XI NEW SOURCE PERFORMANCE STANDARDS AND PRETREATMENT
RECOMMENDATIONS 143
XII ACKNOWLEDGEMENTS 149
XIII REFERENCES 151
XIV GLOSSARY 157
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FIGURES
Number Title
1 Flow of Materials in the
Phosphates Manufacturing Industry 9
2 Standard Phosphorus Process Flow
Diagram 16
3 Standard Phosphoric Acid Flow
Diagram (Dry Process) 22
i» Variations of Phosphoric Acid
(Dry Process) 24
5 Phosphorus Pentoxide Manufacture
Flow Diagram 27
6 Phosphorus Pentasulfide Manufacture
Flow Diagram 29
7 Phosphorus Trichloride Manufacture
Flow Diagram 31
8 Standard Process for Phosphorus
Oxychloride Manufacture 33
9 Alternate Process for Phosphorus
Oxychloride Manufacture 34
10 Standard Process for Sodium
Tripolyphosphate Manufacture 36
11 Standard Process for Food-Grade
Calcium Phosphates 38
12 Manufacture of Livestock-Feed Calcium
Phosphate Flow Diagram 39
vi
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TABLES
Number Title
1 Recommended Best Practicable Control
Technology Currently Available for the
Manufacture of Phosphorus Trichloride and
Phosphorus Oxychloride 3
2 U.S. Production of Phosphates 12
3 Current Selling Prices of Phosphorus Chemicals 13
4 Producers of Phosphate Products 14
5 Impurities in Phosphoric Acid 21
6 Composition of Commercial Phosphates Rocks 51
7 Summary of Raw Waste from Phosphorus Manufacture 56
8 Minor Wastes from Plant 037 (PC13 and POC13) 61
9 Summary of Raw Wastes from Phosphorus Consuming
Plants 65
10 Summary of Raw Wastes from Phosphate Plants 68
11 Waste Water Constituents of Phosphate Category 74
12 Relative Chemical Costs for Neutralizing Acid Wastes 86
13 Summary of Control and Treatment Techniques at
Phosphorus Producing Plants 88
14 Effluent from Plant 028 89
15 Effluent from Plant 159 90
16 Water Quality Produced by Various Ion
Exchange Systems 100
17 Treatment Alternatives 108
18 Treatment Alternatives, Cost-Effluent Quality
Comparison 109
19 Energy Requirements for Recommended Guidelines 121
20 Metric Units Conversion Table 160
vii
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SECTION I
CONCLUSIONS
For the purpose of establishing effluent limitations guidelines and
standards of performance, the phosphate manufacturing point source
category was divided into the phosphorus production, the phosphorus
consuming subcategory, and the phosphates subcategories.
Phosphorus and phosphoric acid production were included in this study
because they are necessary prequesites to phosphate synthesis. It is
also appropriate from technical standpoints to include these chemicals
in this study rather than in the inorganic chemical point source
category. Other phosphorus consuming chemicals such as PC13 and V2O5
were included for the same reasons. Processes solely concerned with
phosphates to be used as fertilizers are studied under the fertilizer
point source category.
The phosphorus-production subcategory of the industry is characterized
by large guantities of raw process wastes, including highly deleterious
phossy water and highly-acidic scrubber and guenching waste waters, both
containing large guantities of fluorides, other dissolved solids, and
suspended solids. Through a combination of in-process controls and
end-of- process treatment, several plants within this segment have
achieved zero discharge of phossy water, two have achieved zero
discharge of other process waste waters, and one has achieved zero
discharge of any waste water. While other plants now demonstrate
abatement practices resulting in 97 percent or greater reduction in the
raw waste load before discharge, the total recycle of process water
without any discharge has been aptly demonstrated using the best practi-
cable control technology.
The phorphorus-consuming subcategory of the industry is characterized by
the absence of direct process waste water; the chemicals produced are
readily hydrolyzed so that the processes are essentially dry. However,
just because the products are readily hydrolyzed, water is universally
used for air pollution abatement scrubbing of tail gases, for periodic
cleaning of reaction vessels, and for the general washing of shipped
containers; all resulting in acidic waste waters. In addition, water is
used in protecting and transferring the raw material, elemental
phosphorus, and phossy water is therefore a raw waste from this segment.
Except for the manufacture of dry-process phosphoric acid (where in-
process control has been demonstrated to achieve zero discharge of
agueous wastes), this segment has not yet achieved sufficient reduction
of effluents. The application, however, of currently-available
technology is shown by this study to permit total recycle of waste
waters (and so zero discharge) for the manufacture of P2O5 and P2S5; and
to achieve the neutralization and removal of most suspended solids prior
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to discharge for the manufacture of PC13 and POC13. For these latter
two processes, «. more expensive but still economically achievable
technologies are available for treating the chlorides so as to achieve
zero discharge.
The phosphates segment of the industry, i.e., the group of chemicals
manufactured from phosphoric acid, is characterized by acids and by
finely-divided solids in the raw aqueous wastes. Several plants have
already achieved zero discharge by in- process controls and by end-of-
process treatment; and this study shows how the entire segment may
achieve zero discharge by applying currently available practicable
technology.
The general conclusion reached is that the industry has already solved
its most serious raw waste problem, that is, the abatement of water
pollution from phosphorus-producing facilities; and that the very high-
volume manufacturing processes (phosphorus, phosphoric acid, sodium
tripolyphosphate, and feed-grade calcium phosphate) have already
achieved zero discharge. The remainder of the industry, made up of much
smaller-volume plants, has lagged behind in effluent reduction, but
technology is available to make the entire industry notable.
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SECTION II
RECOMMENDATIONS
The recommended effluent limitations guidelines based upon best
practicable control technology currently available is no discharge of
process waste water pollutants to navigable waters for the manufacture
of the following chemicals:
Phosphorus Production Category
Phosphorus (and Ferrophosphorus)
Phosphorus Consuming Subcategory
Phosphoric Acid (Dry Process)
Phosphorus Pentoxide
Phosphorus Pentasulfide
Phosphate Production Subcategory
Sodium Tripolyphosphate
Calcium Phosphates (Food Grade)
Calcium Phosphates (Animal Feed Grade)
The recommended effluent limitations for this technology for phosphorous
trichloride and phosphorous oxychloride of the phosphorus consuming
Subcategory are given in Table 1.
Table 1. Recommended Best Practicable Control Technology Currently
Available for the Manufacture of Phosphorus Trichloride and Phosphorus
Oxychloride. (Process Water)
The recommended effluent limitations guidelines based upon best
practicable control technology currently available for process water for
the manufacture of PCI3 and POC13 are:
maximum 30 day average
Phosphorus Phosphorus
Trichloride Oxychloride
Total Suspended Solids: kg/kkg 0.7 0.15
(Ib/ton) (1.4) (0.3)
Total Dissolved Solids: kg/kkg 5 3.5
(Ib/ton) (10) (7)
PH 6.0-9.0 6.0-9.0
The above guidelines apply to the maximum average of daily values for
any period of 30 consecutive days. The maximum for for any one day for
of total suspended solids and total dissolved solids are twice the
consecutive 30 day average value. The pH limitation must be met at all
times. It is recommended that noncontact cooling water allowed to be
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discharqed. Effluent limitations for this waste stream are expected to
be covered in future studies. For the purposes of this report, process
water is defined as any water that comes into direct contact with any
raw material, intermediate, product, by-product or gas or liquid that
has accumulated such constituents.
The recommended effluent limitations guidelines based upon best
available technology economically achievable is no diseharqe of process
waste water pollutants for the manufacture of the followinq chemicals:
Phosphorus Consuminq Subcateqory
Phosphorus (and Ferrophosphorus)
Phosphorus Consuminq Subcateqory
Phosphoric Acid (Dry Process)
Phosphorus Pentoxide
Phosphorus Pentasulfide
Phosphorus Trichloride
Phosphorus Oxychloride
Phosphate Subcateqory
Sodium Tripolyphosphate
Calcium Phosphates (Food Grade)
Calcium Phosphates (Animal Feed Grade)
The recommended new source performance standards are the same as the
above recommended best available technoloqy economically achievable.
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SECTION III
INTRODUCTION
PURPOSE AND AUTHORITY
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 national 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 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 304(b) of the Act requires the Administrator to publish within
one year of enactment of the Act, requlations providing guidelines for
effluent limitations setting forth 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
regulations proposed herein set forth effluent limitation guidelines
pursuant to section 304(b) of the Act for the phosphate manufacturing
point source category.
Section 306 of the Act requires the Administrator, within one year after
a category of sources is included in a list published pursuant to
Section 306 (b) (1) (A) of the Act, to propose regulations establishing
Federal standards of performances for new sources within such
categories. The Administrator published in the Federal Register of
January 16, 1973 (38 F.R. 1624), a list of 27 source categories.
Publication of the list constituted announcements of the Administrators
intention of establishing, under Section 306, standards of performance
applicable to new sources within the phosphate manufacturing source
category, which was included within the list published January 16, 1973.
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SUMMARY OF DEVELOPMENT METHODS
The Environmental Protection Agency has determined that a rigorous
approach including plant surveying and verification testing is necessary
for the promulgation of effluent standards from industrial sources. A
systematic approach to the achievement of the reguired guidelines and
standards includes the following:
(a) Categorization of the industry and determination of those industrial
categories for which separate effluent limitations and standards need to
be set;
(b) Characterization of the waste loads resulting from discharge within
industrial categories and sufccategories;
(c) Identification of the range of control and treatment technology
within each industrial category and subcategory;
(d) Identification of those plants having the best practical technology
currently available (notable plants); and
(e) Generation of supporting verification data for the best practical
technology including actual sampling of plant effluents by field teams.
The culmination of these activities is the development of the guidelines
and standards based on the best practicable current technology.
This report describes the results obtained from application of the above
approach to the phosphate manufacturing industry, as defined for the
purpose of this study as the following list of products:
Elemental Phosphorus and Ferrophosphorus
Dry-Process Phosphoric Acid
Phosphorus Pentoxide
Phosphorus Pentasulfide
Phosphorus Trichloride
Phosphorus Oxychloride
Sodium Tripolyphosphate
Calcium Phosphates (Non-Fertilizer)
The effluent limitation guidelines and standards of performance proposed
herein were developed in the following manner. The point source
category was first subcategorized for the purpose of determining whether
separate limitations and standards are appropriate for different
segments within a point source category. Such subcategorization was
based upon raw material used, product produced, manufacturing process
employed, and other factors. The raw waste characteristics for each
subcategory were then identified. This included an analysis of (1) the
source and volume of water used in the process employed and the sources
of waste and waste waters in the plant; and (2) the constituents
(including thermal) of all waste waters including toxic constituents
which result in taste, odor, and color in water or aguatic organisms.
The constituents of waste waters which should be subject to effluent
limitation guidelines and standards of performance were identified.
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The full range of control and treatment technologies existing within
each subcategory was identified. This included an identification of
each distinct control and treatment technology, including both in-plant
and end-of-process technologies, which are existent or capable of being
designed for each subcategory. It also included an identification in
terms of the amount of constituents (including thermal). The chemical,
physical, and biological characteristics of pollutants of the effluent
level resulting from the application of each of the treatment and
control technology and the reguired implementation time were also
identified. In addition, the non-water guality environmental impact,
such as the effects of the application of such technologies upon other
pollution problems, including air, solid waste, noise and radiation,
were also identified. The energy reguirement of each of the control and
treatment technologies was identified as well as the cost of the
application of such technologies.
The information, as outlined above, was then evaluated to determine what
levels of technology constituted the best practicable control technology
currently available, "best available technology economically achievable"
and the "best available demonstrated control technology, processes,
operating methods, or other alternatives". In identifying such
technologies, various factors were considered. These included the total
cost of application of technology in relation to the effluent reduction
benefits to be achieved from such application, the age of eguipment and
facilities involved, the process employed, the engineering aspects,
process changes, non-water guality environmental impact (including
energy requirements), and other factors.
The data for identification and analyses were derived from a number of
sources. These sources included EPA research information, published
literature, previous EPA technical guidance for inorganic chemicals,
alkali and chlorine industries, qualified technical consultation, and
on-site visits and interviews at notable manufacturing plants throughout
the United States. All references used in developing the guidelines for
effluent limitations and standards of performance for new sources re-
ported herein are included in Section XIII of this document. Five
companies in the phosphate manufacturing industry were contacted. A
breakdown of the data base is listed below:
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Chemical Number of Plants in Data Base
Literature Inspected Sampled Permit Application
PJt 132* 2
H3POU 2 1* 2
P205 1 1 1
P2S5 22 2
PC1J3 22 2
POC13 22 2
Na5P3O10 2 1* 1
Calcium Phosphates
(Food Grade) 1 1 1
(Feed Grade) 1 1 1
""Includes verification of plants with no discharge.
In addition much information was obtained from plant personnel at the
time of plant inspections, plant sampling, and company discussions.
GENERAL DESCRIPTION OF THE INDUSTRY
The industry covered by this document is the phosphate manufacturing
source category. It is more descriptively termed the nonfertilizer
phosphorus industry. The following chemicals covered by SIC 2819 were
studied:
phosphorus
ferrophosphorus
phosphoric acid (dry process)
phosphorus pentoxide
phosphorus pentasulfide
phoshporus trichloride
phosphorus oxychloride
sodium tripolyphosphate
calcium phosphates (food grade)
calcium phosphates (animal feed grade)
Other phosphorus and phosphate chemicals are expected to be covered at a
later time.
The flow of materials in the phosphate manufacturing industry is
depicted in Figure 1. This industry is almost entirely based upon the
production of elemental phosphorus from mined phosphate rock. The
economics have dictated that the phosphorus production facilities be
located at the sources of the raw material, which are in three areas in
the United States: Tennessee, the Idaho-Montana area, and Florida. The
key in-plant siting decision is the relative weights of phosphate rock,
elemental phosphorus and phosphoric acid (about 10:1:4). Hence, the
rock is processed close to the mine and the acid is produced close to
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MINED
PHOSPHATE
ROCK
ELEMENTAL
PHOSPHORUS
FERROPHOSPHORUS
t)RY OR FURNACE
PROCESS
PHOSPHORIC
ACID
ANHYDROUS
PHOSPHORUS
COMPOUNDS
SOLUBLE
PHOSPHATES
(SODIUM
TRIPOLYPHOSPHATE)
INSOLUBLE
PHOSPHATES
(CALCIUM
PHOSPHATES)
PHOSPHORUS
PENTASULFIDE
PHOSPHORUS
PENTOXIDE
PHOSPHORUS
TRICHLORIDE
PHOSPHORUS
OXYCHLORIDE
FIGURE I
FLOW OF MATERIALS IN THE NON-FERTILIZER PHOSPHORUS CHEMICALS INDUSTRY
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its consumption point; the relatively low-weight elemental phosphorus is
almost universally the form shipped from place to place.
Ferrophosphorus, widely used in the metallurgical industries, is a
direct by-product of the phosphorus production process, since most
furnace-qrade phosphate rock contains 2 to 6 percent iron oxide.
Over 87 percent of the elemental phosphorus is used to manufacture high-
qrade phosphoric acid by the furnace or "dry" process (as opposed to the
wet process which coverts phosphate rock directly into phosphoric acid;
this lower-grade wet process acid is almost exclusively used in the
fertilizer industry and is separately discussed in another portion of
this EPA effort). The remainder of the elemental phosphorus is either
marketed directly or converted to chemicals such as phosphorus
pentoxide, phosphorus pentasulfide, phosphorus trichloride, and
phosphorus oxychloride. These later chemicals are chiefly used in
synthesis in the organic chemicals industry.
Much of the furnace-grade phosphoric acid is directly marketed, larqely
to the food industry and to the hiqh-grade fertilizer industry.
Phosphoric acid is also used to manufacture two basic classes of
phosphates: water-soluble phosphates used in detergents and for water
treatment, typified by sodium tripolyphosphate; and water-insoluble
phosphates which are used in animal feeds and in foods, typified by the
calcium phosphates.
The process involved in the non-fertilizer phosphorus chemicals industry
are very briefly as follows:
Elemental phosphorus and ferrophosphorus are manufactured by the
reduction of phosphate rock by coke in very large electric furnaces,
using silica as a flux. Very large quantities of water are circulated
for cooling the very hot eguipment, for cooling and granulating the
slag, and for condensing the phosphorus vapor from the furnace. Since
water is both non-reactive and immiscible with liquid phosphorus, water
is used extensively in direct contact with phosphorus for heat transfer,
for materials transfer, for protection from the atmosphere, and for pur-
ification. This study is concerned with manufacturing operations
subsequent to receiving washed phosphate ores at the phosphorus
production facility. Ore benefication is commonly but not exclusively
conducted at a separate off-site location. The huge waste load from
benefication, 7500 kg of gangue per kkg of phosphorus eventually
produced, warrants a separate study as a segment of the mining industry.
Phosphoric acid manufactured by the "dry" or furnace process consists of
the burning of liquid phosphorus in air, the subsequent quenching and
hydrolysis of the P2Of> vapor, and the collection of the phosphoric acid
mists. The operation uses cooling water and process water is consumed
10
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in making the aqueous acid. Solid wastes may be generated should a
plant perform subsequent purification of the acid.
The manufacture of the anhydrous phosphorus chemicals (P2O5, P2S5, and
PC13) is essentially by the direct union of phosphorus with the
corresponding element. Phosphorus oxychloride, PC13, is manufactured
from PC13_ and air or from PC13_, P2Q5, an<^ chlorine. Water use is
limited to cooling water, to water for transferring elemental
phosphorus, to scrubber water, and to wash water for reaction vessels
and shipping containers.
Sodium tripolyphosphate is manufactured by the neutralization of
phosphoric acid with the appropriate proportions of caustic soda and
soda ash in mix tanks. The resulting mixture of monoand di-sodium
phosphates is dried and the crystals calcined to produce the
tripolyphosphate.
The calcium phosphates are similarly made by the neutralization of
phosphoric acid with lime. The amount and type of lime used and the
amount of water in the process determines whether anhydrous monocalcium
phosphate, monocalcium phosphate monohydrate, dicalcium phosphate
dihydrate, or tricalcium phosphate, is the final product. Table 2 lists
production tonnages for these chemicals as reported by the U.S. Bureau
of Census. As seen from this table the industry is relatively small
relative to numbers of plants.
Table 3 lists the current selling prices of the chemicals within this
industry. Table 4 lists the producers of phosphate products.
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TABLE 2. U.S. Production Phosphates
Chemicals
Phosphorus
Ferrophosphorus
Phosphoric Acid
(Furnace Process)
Phosphorus Pentoxide
Phosphorus Pentasulfide
Phosphorus Trichloride
Phosphorus Oxychloride
Sodium Tripolyphosphate
Calcium Phosphates
Metric Tons
495,000
110,000*
Short Tons
545,000
121,000*
1,640,000** 1,810,000**
Number
of Plants
10
25
(withheld)
54,000
50,000
28,000
945,000
536,000
(withheld)
59,000
55,000
31,000
1,040,000
592,000
(withheld)
5
4
4
17
7
independently estimated. (2)
**Estimated as 87 percent of Phosphorus Consumption, usinq
90 percent conversion, and stated as acid of 54 percent P2O5.
The total production of phosphoric acid, both wet and dry was
5,650,000 kkq (6,240,000 short tons).
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TABLE 3. Current Selling Prices of Phosphorus Chemicals
Source: Chemical Marketing Reporter, June 25,
1973
CHEMICAL
White Phosphorus
Phosphoric Acid (Furnace)
Phosphorus Pentoxide
Phosphorus Pentasulfide
Phosphorus Trichloride
Phosphorus Oxychloride
Sodium Tripolyphosphate
Monocalcium Phosphate
Dicalcium Phosphate
Tri calcium Phosphate
GRADE
75% Commercial & Feed
80% Cotrtnercial & Feed
85% National Formulary
Technical
Food
Anhydrous Food
U.S.P Food
Feed
NF Precip.
SELLING PRICE
$/Metric Ton
419
164
176
194
441
299
292
270
179
270
314
286
82
315
$/Short Ton
330
149
160
176
400
271
265
245
162
245
285
259
74
286
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Producers of Phosphate Products
Phosphorous
Holmes Company 0
FMC Corporation 0
Mobil Corporation 0
Monsanto Company 0
Occidental Petroleum Corp. 0
Stauffer Chemical 0
TVA 0
Olin Corporation
Goodpasture, Inc.
American Cyanaciid Co.
Borden, Inc.
Eastman Kodak Co.
Farmland Industries
Int'l. Minerals & Chemical Corp.
Knox Gelatine, Inc
Richardson-Merrell, Inc.
Feedstock
Phosphorous Phosphorous Phosphorous Phosphorous Furnace Sodium Dicalcium
Pentoxide Trichloride Oxychloride Pentasulfide Acid Tripolyphosphate Phosphate
00 00
0 00
0 0 000
000000 0
0 0 0 000
0
0
0
0
0
0
0
Technical
Calcium
Phosphate
0
0
0
0
0
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DETAILED PROCESS DESCRIPTIONS
Following is a description of each process in this industry. Process
flow disgrams are included. In generating the following process
descriptions, emphasis has been placed upon process features which
generate aqueous wastes. The details of the waste stream character,
however, have been left for discussion in Section V.
Much of the process data in this section was acquired by discussions
with industry personnel and by observations of existing facilities. A
large body of data also exists in the published literature, and was used
extensively in the following discussion. Of particular usefulness were
the publications of Beveridge and Hill, (4) of Barber,(5,6) Barber and
Farr,(7) and LeMay and Metcalf(8) of The Tennessee Valley Authority,
which supplied very specific operating details of TVA's facilities; of
Ellwood, (9) and of Bryant, Holloway and Silber(lO) of the Mobil Chemical
Company. Standard reference books such as Faith, Keyes and Clark, (11)
Kirk and Othmer, (12) and Shreve, (13) were also useful.
THE PHOSPHORUS PRODUCTION SEGMENT
Phosphorus is manufactured by the reduction of mined phosphate rock by
coke in an electric furnace, with silica used as a flux. Slag,
ferrophosphorus (from iron in the phosphate rock) and carbon monoxide
are reaction by-products. The simplified overall reaction may be
written:
2Ca3(P04)2 + 10 C + 6SiO2 1250_-_1500£C_^ P4 + 10 CO + 6CaSiO3.
A typical material balance for the process is:
Raw_Materials Products
Phosphate Rock 10.0 kkg Phosphorus 1.0 kkg
Silica 1.5 Ferrophosphorus 0.3
Coke 1.5 Slag 8.9
Carbon Monoxide 2.8
Total TJTo kkg Total IITo kkg
The electrical power consumption is approximately 15,400 KWH/kkg (14,000
KWH/ton) of phosphorus produced; part of this supplies the endothermic
heat of reaction of 6,200 KWH/kkg of P.4.
The standard process, as pictured in Figure 2, consists of three basic
parts: phosphate rock preparation, smelting in the electric furnace, and
recovery of phosphorus.
15
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BURN
FIGURE 2
STANDARD PHOSPHORUS PROCESS FLOW DIAGRAM
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Phosphate rock ores are first blended so that the furnace feed is of
uniform composition. The silica composition is important since the
overall furnace feed must have a Si<32/CaO ratio close to the eutectic
composition for desired slag flow properties. The blended phosphate
rock is carefully pretreated by drying, by agglomerating the particles,
and by heat treating.
After the raw phosphate rock is dried, sizing or agglomeration is
accomplished by pelletizing, briquetting, flaking, or "nodulizing", and
pre-formed agglomerates are then calcined in a rotary kiln. The
nodulizing operation performs simultaneous agglomeration and calcining
by heating the rock to its incipient fusion point, with subsequent
crushing, sizing, and recycling of fines. Sizing promotes the even
distribution of gas flow within the furnace and results in more
efficient heat transfer and lower total energy costs. The size of the
furnaces has dramatically increased in recent years, accentuating the
needs for stoichiometric balance and thermal homogeneity within the
charge (or "burden"). Heat treatment or calcining of the feed increases
the strength and hardness of the particles, preventing large quantities
of fines from being formed by attrition.
The calcining, at 1000 to 1400°C, also liberates water of hydration,
organics, carbon dioxide, and fluorine at a much lower energy cost than
would be required in the subsequent electric furnace operation. Since
25 percent of the manufacturing costs of phosphorus are for electric
power, considerable effort is made to conserve this power. Moreover,
by-product carbon monoxide from the smelting operation is available as a
source of auxiliary energy.
The sizing and calcining operations are sources of dust and of fluorine
fumes. The dust may be electrostatically precipitated, and the gases
are scrubbed with water, removing fluorine as HF and E2SiF6. The dry
dusts collected are normally recycled to the nodulizing operation.
The burden of treated phosphate rock, coke, and sand is charged to the
furnace by incrementally adding weighed quantities of each of the three
materials to a common belt conveyor. The furnace itself has a carbon
crucible and carbon-lined steel sidewalls, with a two-foot-thick self-
supporting cast concrete roof. In an effort to eliminate periodic roof
replacement due to excessive cracking of the concrete, some newer
furnaces have anti-magnetic (to avoid induction heating) stainless steel
roof structures. Penetrations in the furnace are for feed chutes, for
carbon electrodes, for tap holes, for slag (upper liquid layer) and for
ferrophosphorus (lower liquid layer), and for exhaust gases.
Electric furnaces for phosphorus production have been dramatically
increasing in size to achieve operating economies:
17
-------
Size of Largest. Furnace in Operation
Year Megawatts kkg/Year Tons/Year
1950
1960
1970
25
50
65
13,600
27,200
36,300
15,000
30,000
40,000
The smallest furnaces produce 9,100 kkg (10,000 tons) of phosphorus per
year.
An appreciation of the physical size may be attained from the fact that
the largest carbon electrodes used are 1.5 to 1.8 meters (5 to 6 feet)
in diameter and carry 50,000 amps each.
The furnace is extensively water-cooled. Cooling water is used for the
electrical transformer, for the furnace shell, for the crucible bottom,
for the fume hood, for the tapholes, and for electrode joints. Newer
furnaces use telescoping water seals on furnace electrodes; and for TVA-
type furnaces with rotating crucibles, a water seal is provided between
the crucible and the stationary roof.
The 2 to 6 percent Fe2O3 in the furnace-grade phosphate rock is reduced,
with the iron recovered as the f errophosphorus alloy:
Fe2Q3 + 3C->2Fe + 3CO
8Fe + P4-
The f errophosphorus typically contains 59 percent iron and 22 percent
phosphorus and is marketed for the production of phosphorus alloys. The
vanadium content of ferrophosphorus adds to its value. Should the
marketplace be favorable for ferrophosphorus, iron slugs can be added to
the furnace charge. Alternately, should a soft market for
ferrophosphorus occur, the ferrophosphorus can be converted into high-
grade metallurgical iron and fertilizer phosphates. An important degree
of freedom is in the ore blending operation, where ores of appropriate
iron content may be selected depending upon the ferrophosphorus market.
Slag and ferrophosphorus are tapped periodically. The air cooled
ferrophosphorus is sold in lumps to the metallurgical industry; no water
is involved either in ferrophosphorus cooling or in subseguent product
preparation.
The slag may typically contain 38 percent SiO.2 and 48 percent CaO, and
also contain considerable quantities (depending of course upon the ore
composition) of A12O3, CaF2, K2O, and MgO, with traces of uranium and
other heavy metals. The slag may be air-cooled, but water guenching is
more typical. High-density slag is produced by adding water to molten
slag in a pit, and by subseguently breaking it up and shipping aggregate
for railroad bed or roadbed construction. Alternately, a high-velocity
18
-------
water stream may be used upon the molten slaq to produce a low density
expanded or granulated slag, which has a market in concrete formulation.
In either event, some of the fluorides from the slag are captured by the
quenching water, either as soluble fluorides or as suspended solids.
There are numerous sources of fumes from the furnace operation. The
feeding operation is a source of dust, and fumes are emitted from the
electrode penetrations and from the tapping operations. These fumes,
consisting of dust, phosphorus vapor (which is immediately oxidized to
phosphorus pentoxide), and carbon monoxide are often collected and
scrubbed.
The hot furnace gases, consisting of 90 percent CO and 10 percent P4,
pass through an electrostatic precipitator to remove the dust prior to
phosphorus condensation. Unless this dust were removed, it would later
be emulsified by liquid phosphorus and water, forming large amounts of
"phosphorus mud" or sludge which would be difficult and costly to
handle.
The precipitator is a most unusual piece of eguipment. In the
phosphorus process, the precipitator is in the main process stream, as
opposed to its usual application in an exhaust stream. Because of this,
it is gas-tight (especially since any air would cause phosphorus
combustion). It operates at very high temperatures with the inlet gas
approaching 540°C (1000°F), and its surfaces must be maintained hot to
prevent phosphorus condensation (the dew point of phosphorus is 180°C
(356°F)). The precipitator is typically a tube bundle, with the gas
passing through the tubes, and with a high-voltage wire along the axis
of each tube. Both the wire and the tube are mechanically shaken to
release the dust into a hopper. In some installations, the dust is
slurried in water, pumped to a settling pond, and the solids are
recycled to the raw feed for recovery of phosphates values (the
clarified pond effluent is reused in the slurrying operation).
The high-voltage wires may be insulated from the shell with an oil seal;
contaminated oil is periodically replaced with fresh oil. Alternately,
a quartz seal may be used. The entire unit is heated either
electrically or by an inert gas jacket of by- product carbon monoxide
combustion gases.
Downstream of the precipitator, the phosphorus is condensed by direct
impingement of a hot water spray, which is sometimes augmented by heat-
transfer through water-cooled condenser walls. The liquid phosphorus
(freezing point 44°C (111°F)) drains into a water sump, where the water
maintains a seal from the atmosphere. This water is partially
neutralized by addition of ammonia or caustic to minimize corrosion, and
then is recirculated from the sump to the phosphorus condenser.
19
-------
Liquid phosphorus is stored in steam-heated tanks under a water blanket.
and is transferred into tank cars by pumping or by hot water
displacement. The tank cars also have a protective blanket of water and
are equipped with steam coils for remelting at the destination.
Despite very hiqh precipitator removal efficiencies, enouqh dust reaches
the condensers to form some phosphorus mud, which is typically 10
percent dust, 30 percent water, and 60 percent phosphorus.
The condenser exhaust qases are mainly carbon monoxide, which is either
burned in a flare or utilized for heating elsewhere in the plant.
20
-------
THE PHOSPHORUS-CONSUMING SEGMENT
Phosphoric Acid (Dry Process)
Phosphoric acid is made from elemental phosphorus in the "dry" process,
as opposed to the acidulation of phosphate rock in the "wet" process.
The wet process is discussed in a separate report, dealing with the
fertilizer industry, in this overall EPA effort. Furnace acid, as dry-
process phosphoric acid is called, is relatively pure compared to wet-
process acid, as Table 5 indicates. Consequently, the furnace acid is
primarily used for preparing foodstuffs, detergents, and other high-
grade products; while wet acid is primarily used for preparing
fertilizers and animal feed supplements.
TABLE 5. Impurities in Phosphoric Acid (54* P2O5)
Total Impurities, wt %
Wet Process
Acid
6.2 - 6.6
Furnace
Acid
F, wt %
SO3, wt %
A12O3, wt %
Fe203, wt X
Water insolubles, wt %
0.6 - 1.0
2.7
0.9
1.2
0.8
0.007
0.003
0.001
0.0007
0.012
Density, kg/1 (Ib/gal)
9 27°C (80°F)
Viscosity, cp 3 27°C (80°F)
Color
1.72 (14.3)
85
Black
1.57 (13.1)
18
Colorless
In the standard dry process illustrated in Figure 3, liguid
phosphorus is burned in air, the resulting gaseous phosphorus
pentoxide is absorbed and hydrated in a spray of water, and
the mist is collected with an electrostatic precipitator.
The standard reaction may be written:
PU + 502->2P205 + 6H20-* 4H3PO4
21
-------
S3
N3
LIQUID
PHOSPHORUS"
VENT
JL
ELECTROSTATIC
PRECIPITATION
AIR
i.
WATER
COMBUSTION
FURNACE
P2°5
GASES
HYDRATION
_y
>DUST WASTE
NoSH
WATER
PURIFICATION
FILTRATION
T
PHOSPHORIC
->ACID
STORAGE
WASTE
FIGURE 3
STANDARD PHOSPHORIC ACID FLOW DIAGRAM (DRY PROCESS)
-------
Liquid phosphorus is stored under water in tanks heated with steam coils
(the freezing point of phosphorus is U4°c (111°F)). The phosphorus may
be fed to the burner by hot-water displacement in a feed tank, in a loop
with a steam-heated displacement water tank and water pump.
Alternately, the liquid phosphorus may be pumped directly.
There are variations in the desiqn of the liquid phosphorus injector.
Some producers achieve fine atomization using air in a dual-fluid
injector (where the injection orifice can be large enough to prevent
plugging). To prevent freezing of the phosphorus in upstream portions
of the injector and yet to keep the injector tip cool, intricate use of
both steam and cooling water has been simultaneously applied. Other
designs have proven successful for phosphorus atomization, including the
exploitation of extreme turbulence in a pre-combustion zone. Some form
of temperature control is required, since red phosphorus formed at
combustion temperatures much higher than 1650°C (3000°F) would color the
resulting acid and would plug injector orifices.
In the combustion chamber, corrosion by V205 vapors and by hot
phosphoric acid (formed from the moisture in the air) is countered by
using a graphite lining. The steel shell of the combustion chamber is
cooled by running water down its exterior surfaces. This mode of heat
transfer is standard, pressurized cooling water is avoided since any
leaks would result in premature hydration. Recent plants have been
constructed with stainless steel combustion chambers.
The gas exiting from the combustion chamber is typically 540°C (1000°F),
and is then hydrated with direct water sprays, which also reduces the
temperature to 120°C (250°F) or less.
A variation of the standard process, illustrated in Figure 4, uses
dilute acid for hydration instead of water. In this case, the make-up
water is added in the vapor-liquid separation step. The rationale is
that PK>5 vapor is absorbed more easily as the concentration of
absorbing acid is increased. Another deviation from the standard
process, also shown in Figure 4, is the use of a high-pressure-drop
venturi scrubber to complete the somewhat difficult hydration, and a
screen-type demister and separation tower instead of an electrostatic
precipitator to free the tail gases of the persistent acid mist.
When an electrostatic precipitator is used for collection of the
phosphoric acid mist, the corrosivity requires the use of carbon tubes
and stainless steel high-voltage wires. Those plants using a high-
pressure-drop venturi scrubber and a screen type demister with a
separation tower utilize stainless steel construction. Where dilute
phosphoric acid is used in the hydrator, the make-up water is added in
the separation tower. Regardless of process variation, phosphoric acid
23
-------
to
LIQUID
PHOSPHORUS
COMBUSTION
AIR BLOWER
COMBUSTION
CHAMBER
TO STORAGE<-
_V
HYDRATOR
PRODUCT
ACID
COOLER
VENT
t
DEMISTER
PRODUCT
ACID
\
MAKE-UP
SEPARATOR
TOWER
WATER
DILUTE
ACID
FIGURE 4
VARIATIONS OF PHOSPHORIC ACID (DRY) PROCESS
-------
is made with a consumption of water; no aqueous waste streams are
generated by the process.
The product acid is quite pure, but for the manufacture of foodgrade
acid, traces of arsenic must be removed. Arsenic occurs naturally with
phosphorus in the ore (they are both Group V-A elements) at a level of
about 0.075 kg of arsenic per kkg of phosphorus (0.15 Ib/ton). The
arsenic is quantitatively carried through into the acid, and is commonly
removed by treatment with a soluble sulfide followed by filtration of
the insoluble arsenic sulfide.
Phosphorus Pentoxide
The manufacture of solid anhydrous phosphorus pentoxide is similar to
the first stages of phosphoric acid manufacture. Liquid phosphorus is
burned in an excess of air:
P4(l) + 502->2P205(s)
Figure 5 is a flow diagram for a standard phosphorus pentoxide
manufacturing facility. A significant difference between the two
processes is that in the anhydrous phosphorus pentoxide process, the air
is dried to an extremely low dew point, since any moisture results in a
lumpy and agglomerated product not suited for its uses as a reactive
drying agent and as a reactive condensing agent in organic synthesis.
Typically, the ambient air is filtered, then refrigerated to achieve a
dew point of -18 to -7°C (0 to 20°F), and then dried to a dew point of
-46°C (-50°F) with silica gel.
After reaction of liquid phosphorus with excess dried air in the
combustion chamber, the P2O.5 vapor is condensed to a solid in a "barn",
which is a room-like structure. Some installations utilize a more
conventional tower for condensation. Both the combustion chamber and
the barn (or tower) are cooled by an external flow of water down the
surfaces; pressurized cooling water is avoided since any leaks would
result in lumpy, unacceptable product.
Condensed phosphorus pentoxide solid is mechanically scraped from the
walls using moving chains, and is discharged from the bottom of the barn
or tower with a screw-type conveyor. The gases are vented to the
atmosphere through a tail-gas water seal which absorbs any P2O5 vapor or
solid carry-over. There is usually continuous water addition and
overflow for the tail gas seal.
The product particle size is sensitive to the rate of cooling and
condensation in the barn or tower. In a barn, the external surface-to-
volume ratio is small, a relatively high temperature is maintained in
the condensing unit, and rather large crystals may grow. In a tower,
heat transfer is more rapid, and the product is very finely divided.
25
-------
One installation uses two towers in series; the first has much higher
heat transfer rates and results in a coarser product than the second,
and the products from the two towers are separately packaged.
26
-------
AIR
AIR FILTER
AIR DRYER
V
WATER
LIQUID PHOSPHORUS STORAGE
ro
COMBUSTION
CHAMBER
BARN
.PRODUCT
P2°5
WATER SEAL
FIGURE 5
PHOSPHORUS PENTOXIDE MANUFACTURE FUDW DIAGRAM
-------
Phosphorus Pentasulfide
The standard process for the manufacture of phosphorus pentasulfide,
shown in Figure 6, is by direct union of the elements, both in liquid
form:
P4(l) + 10S(1)-»2P2S5(1)
The largest use of phosphorus pentasulfide is for the manufacture of
lubricating oil additives.
Liquid sulfur (melting point 113°C (230°F)) is transferred from a steam-
heated storage tank using submerged pumps, and liquid phosphorus
(melting point 4U°C (111°F)) is transferred by hotwater displacement.
The highly exothermic reaction is usually carried out as a batch
operation in stirred cast-iron pots. A "heel" cf molten P.2S5 (melting
point 282°C (5UO°F)) from the previous batch is used to absorb the
initial heat of reaction. Liquid phosphorus and liquid sulfur are
incrementally added, since the reactants and the product are extremely
flammable at the reaction temperature, the reactor is continuously
purqed with nitrogen. A water seal is used in the vent line.
The batches from multiple reactors are forced into an electrically-
heated (300°C (570°F)) P2S5 holding tank by nitrogen pressure. Some of
the P2SJ5 is converted directly into product, while the rest is purified.
Liquid P2S.5 from the holding tank that is to be sold is cast directly
into drums or into cones. When the molten product contacts air during
casting, it ignites and fumes of P2O5 and SO2 are generated. A fume
hood and water scrubber are used. The cones, after cooling, are crushed
and packaged; solid P2S5 does not auto-ignite in air. The dust from the
crushing operation is removed in a dry separation system such as a
cyclone.
The liquid P2S.5 that is to be purified may be vacuum distilled (normal
boiling point is 515°C (960°F)) in a continuous system. The condenser
is cooled by a high-temperature heat transfer fluid, which in turn is
cooled in a water-cooled heat exchanger. The condenser is operated
between the melting and boiling points of the product. Molten purified
P2S5 is then cast and crushed, sharing the fume scrubber and dust
collection systems with the impure product operation.
An alternate mode of purification is the washing of crushed P2SJ5 with
carbon disulfide, in which by-product phosphorus sesquisulfide (P4.S3)
and free sulfur are soluble.
28
-------
WATER VENT
N3
VD
t
SULFUR
STORAGE
TANK
N2 PURGE
LIQUID
PHOSPHORUS
STORAGE
TANK
-
BA1
REAC
\
PCH
TOR
/
WATER
SEAL
•s.
S
P2S5
HOLDING
TANK
VENT
^
s
PI
SCRUBBER
/
S
CASTING
\
RODUCT
STILL POT
/
> WASTE
VENT
t
^ rciicuiKir >. DUST
> CRUSHING — ^ COLLECTOR
4 1
PRODUCT WASTE
C
nMn^KIOC'D \ ^^1 1^ TD A D
JNUtlMoLK ^ LULU 1 nAr
/^
S/ V
HEAT VACUUM
EXCHANGER PUMP
FIGURE 6
PHOSPHORUS PENTASULFIDE MANUFACTURE FLOW DIAGRAM
-------
Phosphorus Trichloride
Phosphorus trichloride, used extensively in organic synthesis, is
manufactured directly from the elements:
P4(l) + 6Cl2(g)->4PCl3(l)
The standard process is shown in Figure 7. Liguid phosphorus is charged
to a jacketed batch reactor. Chlorine is bubbled through the charge,
and phosphorus trichloride product (melting point -112°C (-173°F)),
boiling point 74°C (165°F) is refluxed until all of the phosphorus is
consumed. Some cooling water is used in the reactor jacket since the
formation of PCI3 is exothermic. Care is taken to avoid an excess of
chlorine; otherwise, phosphorus pentachloride is formed.
When the reaction is complete, the cooling water to the reflux condenser
is turned off, steam is supplied to the reactor jacket, and the product
of the batch distillation is condensed and collected.
A water scrubber collects hydrochloric acid and phosphorous acid, the
hydrolysis products of PC13 vapors:
PC13 + 3H20-»3HC1 + H3PO3
The vapor pressure of the product is sufficiently high so that the fumes
from transferring the product into shipping containers are also
collected and scrubbed.
In a variation of the standard process, the reaction is conducted semi-
continuously instead of batch-wise. The reflux condenser of Figure 7 is
tailored so that only a small fraction of the PC13_ is withdrawn as
product; the larger fraction of condensed PC13 returns to the reactor
and serves as the working fluid and heat sink for the reaction, since
elemental phosphorus is somewhat soluble in PC13. Gaseous chlorine is
added continuously, and liquid phosphorus is added incrementally.
No provision is generally made for continuous cr frequent withdrawal of
residue from the reactor either in the batch process or in the semi-
continuous process. Instead, the residue is permitted to accumulate,
and the reactor is shut down for cleanout at infrequent intervals.
Phosphorus trichloride is corrosive and is often shipped in returnable
nickel drums. Prior to use, these drums are thoroughly washed with
water and steam-cleaned. Some recent use has been made of non-
returnable epoxy-lined steel drums.
30
-------
CHLORINE
LIQUID
PHOSPHORUS
STORAGE
TANK
BATCH
REACTOR
x
s
REFLUX
CONDENSER
CONDENSER
•^
s
V
HOLDING
TANK
/ATER
\^
v^
J>
TRANSFER
TO
CONTAINERS
VENT WATER
,\ K
SCRUBBER
VENT
,t
SCRUBBER
-^PRODUCT
\
^STE
WASTE
\
&STE
WASTE
FIGURE 7
PHOSPHORUS TRICHLORIDE MANUFACTURE FLOW DIAGRAM
-------
Phosphorus Oxychloride
Phosphorus oxychloride, used in the preparation of organic phosphate
esters and Pharmaceuticals, is manufactured by the reaction of liquid
phosphorus trichloride, chlorine, and solid phosphorus pentoxide:
3 PCI 3(1) + 3 Cl2(g) + P205(s)->-5 POC13 (1)
The standard process, illustrated in Figure 8, is carried out in a batch
reactor and still very similar to the standard phosphorus trichloride
equipment. Liquid phosphorus trichloride is charged to the reactor,
solid phosphorus pentoxide is added, and chlorine is bubbled through the
mixture while the PC13 (boiling point 74°C (165°F)) and later the POC13
(boiling point 105°C (221°F)) are refluxed. When the reaction is
complete, steam is supplied to the reactor jacket, the water to the re-
flux condenser is shut off, and the product is distilled over and
collected.
An alternate process for the manufacture of phosphorus oxychloride from
phosphorus trichloride is also in commercial use. As is shown in Figure
9, dried air is used as the oxidant in a batch process. A water-cooled
reflux condenser is used as in the standard process, except that a
refrigerated condenser is added in series to ensure total reflux of the
PC13 upstream of a water scrubber for the tail gas. The significant
difference is that in the air-oxidation process, a large quantity of
non-condensible gas (nitrogen and excess oxygen) is involved.
Instead of a final distillation step, the product POC13_ is filtered,
with periodic changing of the cartridge filter elements.
Water scrubbers collect hydrochloric acid and phosphoric acid, the
hydrolysis products of POC13 vapors, from both the reaction/
distillation equipment and from transferring operations (for either
process) :
POC13 + 3H20-»3HC1 * H3PO4
Like phosphorus trichloride, phosphorus oxychloride is extremely
corrosive and is shipped in returnable nickel drums. Prior to reuse,
these drums are thoroughly washed with water and steam cleaned. Some
recent use has been made of non-returnable epoxy lined steel drums.
32
-------
VENT WATER
t I
SCRUBBER
WASTE
PCI3 P205 CI2
V V V
BATCH
REACTOF
REFLUX
CONDENSER
V
CONDENSER
HOLDING
TANK
TRANSFER
TO
CONTAINERS
PRODUCT
VENT WATER
t I
SCRUBBER
T
WASTE
FIGURE 8
STANDARD PROCESS FOR
PHOSPHORUS OXYCHLORIDE MANUFACTURE
33
-------
_y
REFLUX
CONDENSER
_y
REFRIGERATED
CONDENSER
PCI,
AIR
1
AIR DRYER
BATCH
REACTORS
SOLID WASTED
WATER VENT
SCRUBBER
WASTE
WATER VENT
SCRUBBER
WASTE
FILTER
_V
HOLDING
TANK
TRANSFER
TO
CONTAINERS
PRODUCT
FIGURE 9
ALTERNATE PROCESS FOR
PHOSPHORUS OXYCHLORIDE MANUFACTURE
34
-------
THE PHOSPHATE SEGMENT
Sodium Tripolyphosphate
Sodium tripolyphosphate is manufactured by the neutralization in mix
tanks of phorphoric acid by soda ash or by caustic soda and soda ash,
with the subsequent calcining of the dried mono and di-sodium phosphates
crystals. Figure 10 is a flow diagram of the standard process. The
sodium tripolyphosphate product is widely used in detergents and in
water-softening applications. In the neutralization step, the amount of
raw materials is measured and controlled to yield monosodium
orthophosphate and disodium orthophosphate in a 1:2 mole ratio:
6H3P04 + 5Na2C03->2NaH2P04 + UNa2HPO4 + 5H2O + 5CO2,
or
9H3P04 + SNaOH + 5Na2C03-*-3NaH2POJi + 6Na2HPOU + 10H2O + 5CO2
In either process variation, the final pH in the mix tank is very
carefully adjusted by small additions of either phosphoric acid or
caustic soda solution.
The mixture of sodium orthophosphates is spray-dried or drum dried and
the solids calcined to produce the sodium tripolyphosphate:
NaH2P04 * 2 Na2HPO4->Na5P301.0 + 2 H2O
The product is then slowly cooled or tempered to preserve the condensed
form of the phosphates. If the product is chilled too rapidly, it will
revert to a mixture of the meta- and polyphosphates:
Na5P30lO-»Na3PO3 +
35
-------
50%
CAUSTIC
TANK
PHOSPHORIC ^
ACID ^
C02-<
(SALE)
SODA
ASH
SILO
SLURRY TANK
MIX TANKS
SEPARATOR
V
CO 2
RELEASE
TANK
SPRAY
DRYING
TOWER
CALCINER
V
PRODUCT
COOLER
(TEMPERING)
PRODUCT
MILLING
AND SIZING
T
PRODUCT
FINES
STACK
4
DEMISTER
1
SCRUBBER
WATER
DUST
COLLECTOR
FIGURE 10
STANDARD PROCESS FOR
SODIUM TRIPOLYPHOSPHATE MANUFACTURE
36
-------
Calcium Phosphates
The non-fertilizer calcium phosphates are made by the neutralization of
phosphoric acid with lime. Although the reactions are chemically
similar, the processes for manufacturing the different calcium
phosphates differ substantially from one another in the amount and type
of lime used and the amount of process water used (See Figures 11 and
12).
Relatively pure, food-grade monocalcium phosphate (MCP) is made in a
stirred batch reactor from furnace acid and lime slurry:
2H3PO4 + Ca(OH) 2->Ca(H2POU) 2 . H2O + H2O
An excess of phosphoric acid maintained during the batch addition cycle
inhibits the formation of dicalcium phosphate. A minimum guantity of
process water is used. The heat of reaction liberates some water as
steam in the reactor, and the remaining water is evaporated in a vacuum
dryer, a steam-heated drum dryer, or in a spray-dryer. The anhydrous
MCP is produced by using CaO (guicklime) and in carrying out the
reaction at 140°C (310°F) so that water is driven off as it is produced.
Relatively pure, food-grade tricalcium phosphate (TCP) is made in a
similar manner to MCP, except that an excess of lime slurry maintained
during the batch addition cycle inhibits formation of dicalcium
phosphate:
2H3PO4 + 3Ca(OH) 2->Ca3(PO4) 2 + 6H20
Like MCP, the TCP is dried to prevent excessive product temperatures.
Relatively pure, food-grade dicalcium phosphate (DCP) is made in batch
stirred reactors, but with much more process water than for either MCP
or TCP:
H3POU + Ca (OH) 2-^CaHPO4 . 2H20
The stoichiometry for DCP manufacture is critical; any excess H3PO.4
during the batch addition cycle would result in some MCP and any excess
Ca (OH)2 would result in some TCP. The excess water in the DCP reactor
is to ensure homogeneity so that the local stoichiometry is as balanced
as the overall reactor stoichiometry.
As a result of the excess of water used, the reaction mixture is a
pumpable slurry as opposed to the pasty consistency for MCP and TCP.
This DCP is mechanically dewatered prior to drying.
37
-------
LIME
WATER
X L
\
/
MCP
MIX
TANK
\
1
SLURRY
HOLD
TANK
V
HOT GAS
W
SPRAY
TOWER
\
f
SIZING
V
PRODUCT
MCP
LIME
SLURRY
TANK
\
/
\
PHOSPHORIC
ACID
TANK
\
/
\
/
1
DCP
MIX
TANK
^
/
SLURRY
HOLD
TANK
WATER VENT
I t
**r
bl
;RUBBER
1
WASTE
WATER VENT
I t
SCRUBBER
I
CENTRIFUGE
WASTE
\l
HOT
' \
GAS
I
KILN
MILL
\
f
CYCLONE
^
/
TCP
MIX
TANK
\
/
SLURRY
HOLD
TANK
STEAM
J, V
VENT
/ t
DRUM
DRYER
\
/
SIZING
PRODUCT
TCP
1
1
WASTE
PRODUCT
DCP
FIGURE 1
STANDARD PROCESS FOR
FOOD-GRADE CALCIUM PHOSPHATES
38
-------
PHOSPHORIC
ACID
J
\S1
WATER VENT
I t
AIR
4
SILICA
4
DEFLUORINATION
WATER
1 X
VENT
/ t
SCRUBBER
LIME
i
^
s
PUG MILL
REACTOR
WATER
si x
VENT
/ I
SCRUBBER
PYPI OMF ^ ^PRURRFR
\
WASTE
v. ROTARY \/ >, PRODUCT ^
•> DRYtR > COOLER >
WASTE
PRODUCT
WASTE
FIGURE 12
MANUFACTURE OF LIVESTOCK-FEED CALCIUM PHOSPHATE
FLOW DIAGRAM
-------
Dicalcium phosphate (DCP) is also manufactured for livestock feed
supplement use, with much lower specifications on product purity.
Hence, the reaction can be conducted without excess water, since some
MCP and/or TCP in the DCP product is perfectly tolerable. The pasty
reaction product is normally dried in a rotary dryer. Powdered
limestone, CaCO3, may be used instead of lime. If quicklime is used,
the drying step may be bypassed.
Another significant process difference is that non-food grade wet-
process phosphoric acid is normally used for this product. The DCP
plants defluorinate the acid unless this step was accomplished by the
acid producer. Wet process phosphoric acid contains approximately one
percent fluoride in various forms. The defluorination consists of
treating the heated acid with finely-divided silica and steaming or
aerating, which liberates silicon tetraf luoride gas:
SiO2 + UHF->SiF4 + 2H2O
Wet scrubbers then hydrolyze and collect this gas as fluosilicic acid
and silicic acid:
3 SiFj* + 3H20- »2H2SiF6 + H2SiO3
The hot defluorinated phosphoric acid is then charged to the reactor to
make dicalcium phosphate.
-------
SECTION IV
INDUSTRY CATEGORIZATION
INTRODUCTION
In developing effluent limitations guidelines and standards of
performance for new sources for a given industry, a judgment must be
made by the Environmental Protection Agency as to whether effluent
limitations and standards are appropriate for different segments
(subcategories) within the industry. The factors considered in
determining whether such subcategories are justified for the phosphate
category of point sources are:
wastes generated
treatability of waste waters
manufacturing process
raw materials
plant size and age
product
land availability
air pollution control eguipment
WASTES GENERATED
Tables 7, 8, and 9 in section V compile the raw waste loads for the
phosphate category. Suspended solids and dissolved phosphates are
common raw waste water constituents for phosphorus, food grade calcium
phosphates, and feed grade calcium phosphates. Dissolved solids are
present in concentrations significantly above background for all the
chemicals studied. Elemental phosphorus can be a waste water
constituent common to all of the phosphate manufacturing industry if the
phossy transport water is not returned to the phosphorus producing
plant. Sulfates, fluorides, and alkalinity are constituents specific to
phosphorus production. Furthermore, the amount of waste water (425,000
1/kkg of P.4) resulting from the production of phosphorus is several
orders of magnitude greater than that generated from any of the other
processes. The chemicals H3PO4, P2O5, P2Sj>, PC13, and POC13 commonly
generate acidic wastes and phosphates.
TREATABILITY OF WASTE WATERS
Phosphorus production clearly stands alone on the basis of waste water
treatability. The large amounts of waste water produced (425,000 1/kkg
Pit) present special problems. It is commonly practiced within the
industry to return phossy transport water to the phosphorus plant.
Therefore, the problem of treating elemental phosphorus is only a
phosphorus plant problem, or can be so handled, that it will be a
problem unique to phosphorus plants.
-------
The chemicals H3POU, P2Q5» p2S5, PC13, and POC13 present similar
treatability problems in that acidic wastes are encountered. PC1.3 and
POC1J3 present more difficult problems because the resultant chloride
ions are difficult to remove.
The calcium phosphates involve similar treatment problems (suspended
solids and phosphates) . De flu or in at ion of animal feed grade calcium
phosphates will produce fluoride wastes, but the proposed treatment
schemes will handle this waste constituent.
MANUFACTURING PROCESS
Manufacturing process is the principal factor used to determine
subcategories. Phosphorus production is an ore reduction process
involving large electric furnaces and large amounts of raw material and
slag. Ferrophosphorus is a byproduct in the phosphorus reaction and is
always considered along with phosphorus when considering effluent
guality.
The chemicals H3PO4., P2QS, PCL3, and POC13 are all similar in that a
gaseous phase intermediate or product is encountered somewhere in the
reaction sequence. The synthesis of P2S.5 resembles the above in that
water and air must be completely absent in the whole or parts of the
reaction sequence.
Sodium tripoly phosphate and the calcium phosphates are produced by the
neutralization of phosphoric acid by alkaline slurries.
RAW MATERIALS
The following raw materials are used for each process:
Chemical Raw Materials
P± & Fe£P Phosphate Ore Coke(C) SiO2
H3POJ4 Pjt 02
P205 Pjt 02
P2S5 PI S
PC13 Pjt C12
POC13 PC13 C12 (P205)
Na5P30JO H3PO4 Na2C03 (NaOH)
Calcium Phosphates H^POjt Ca(OH)2
When the nonphosphorus compounds are excluded, four subcategories become
evident on the basis of raw material. The POClJ process is so like the
PC13 process, however, that it is included in the latter subcategory.
-------
PLANT SIZE AND AGE
Plant size will not affect the quantities of wastes produced (kg per kkg
of product) to such a degree that subcategorization would be warranted.
The same basic production processes for each chemical are used
throughout the phosphate industry. Plant age will not affect the
quantities of wastes produced to the degree where subcategorization is
warranted. Another point is that there are no really new plants, and
consequently the situation does not exist where new technologies make
older technologies obsolete. With respect to economics it is
particularly difficult to access the effects of waste water treatment.
These chemicals serve as raw materials or intermediates for other
products produced by the same company. The theoretical profitability of
a single plant may well not decide if operations are to continue at that
site. With this in mind it would be difficult if not impossible to
establish criteria based upon the economics of plant size or age for the
purpose of subcategorization.
PRODUCT
The product does have some bearing on the waste water quality when the
product or vapors from the product or intermediate come into contact
with water. This topic has already been indirectly discussed under
wastes generated. In summary, phosphorus production is associated with
elemental phosphorus, phosphates, fluoride, suspended and dissolved
solids. H2JP04., P2O5, P2S5t PC13, and POC13 result in phosphates,
dissolved solids, and acids in the waste waters. Na.2P3_O.1() and the
calcium phosphates result in phosphates, suspended and dissolved solids.
LAND AVAILABILITY
Removal of suspended solids from raw waste waters is most easily
accomplished by use of large settling ponds. This will be the principle
concern for land availability. However, the plants in this category are
located in rural sites when the problem of land availability is
minimized.
AIR POLLUTION CONTROL EQUIPMENT
All of the chemicals covered in this study use wet scrubbers or water
systems in the process itself which amount to scrubbers. Therefore this
is not a topic for subcategorization. Furthermore dry air pollution
control equipment is recommended to either precede or replace wet
scrubbers in order to reduce scrubber water contamination.
Volitilization of hazardous substances such as fluorine from
neutralization and settling ponds is insignificantly small.
-------
SUECATEGORIES
The factors that entered into the selection of subcateqories are: wastes
generated, treatability of waste waters, product, and particularly raw
material and manufacturing process. Three subcateqories were considered
necessary for purposes of establishing effluent guidelines:
a. Phosphorus Production
1. phosphorus
2. ferrophosphorus
b. Phosphorus Consuming
1. phosphoric acid (dry process)
2. phosphorus pentoxide
3. phosphorus pentasulfide
4. phosphorus trichloride
5. phosphorus oxychloride
c. Phosphate
1. sodium tripolyphosphate
2. Calcium phosphates
i. animal feed grade
ii. food grade
-------
SECTION V
WATER USE AND WASTE CHARACTERIZATION
INTRODUCTION
With the background of manufacturing technology discussed in Section
III, this Section discusses the specific water uses in the phosphate
manufacturing industry and the raw wastes from this industry prior to
control and/or treatment of these wastes. Both Section III and Section
V are intended to be generally descriptive of the industry; i.e., they
outline the standard manufacturing processes and the standard raw waste
loads that are common to the great bulk of plants in the industry. It
is not until Section VII, Control and Treatment Technology, and Section
IX, Best Practicable Control Technology Currently Available, that
distinctions are made (and quantitatively supported by independently-
verified sampling data of plant effluents) within the industry, pointing
out those notable plants which have already achieved significant
reduction or total elimination of polluting discharges.
The discussion to fellow this Section, therefore, should not be taken as
implying that the raw waste loads guoted are always actual plant
discharges. Rather, they are intended to describe the total waste
management problem originally faced by any plant in the industry. In
actuality, significant abatement steps have been taken by some plants
within the industry. By fully explaining the total waste management
problem (in terms of raw waste loads), the control and treatment steps
can be later explained and evaluated.
SPECIFIC WATER USES
Water is primarily used in the phosphate manufacturing industry for
eight principal purposes:
Non-contact Cooling Water
Process and Product Water
Transport Water
Contact Cooling or Heating Water
Atmospheric Seal Water
Scrubber Water
Auxiliary Process Water
Miscellaneous Uses
Non-Contact Cooling Water
Water used without contacting the reactants, such as in a tube-in-shell
heat exchanger, is not contaminated with process effluent. If, however,
the water contacts the reactants, then contamination of the water
results and the waste load increases. Probably the single most
45
-------
important process waste control technique, particularly for subsequent
treatment feasibility and economics, is seqreqation of non-contact
cooling water from process water.
Non-contact coolinq water is generally of two types in the industry.
The first type is recycled coolinq water which is cooled by coolinq
towers or spray ponds. The second type is once-through coolinq water
whose source is qenerally a river, lake or tidal estuary, and the water
is returned to the same source from which it was taken.
The only waste effluent from the recycled water would be water treatment
chemicals and the coolinq tower blowdown which qenerally is discharqed
with the coolinq water. The only waste effluent from the once-throuqh
coolinq water would be water treatment chemicals which are qenerally
discharqed with the coolinq water. The coolinq tower blowdown may
contain phosphates, nitrates, nitrites, sulfates and chromates. The
water treatment chemicals may consist of alum, hydrated lime, and alkali
metals such as sodium and potassium produced by ion exchanqe units.
Reqeneration of the ion exchanqe units is generally accomplished with
sodium chloride or sulfuric acid, depending upon the type of unit
employed in the plant.
Process and Product Water
The process or product water generally is that which comes in contact
with the product and stays with the product as an integral part, such as
the quenchinq, hydrolysis and dilution water used in phosphoric acid
manufacture, or the water used as a reaction medium in food-qrade
dicalcium phosphate manufacture.
Transport Water
Water may be used for transportinq reactants or products between unit
operations. A pure example is in the use of water for transferrinq (by
displacement) liquid phosphorus. Another example is the transfer of
electrostatic precipitator dust in phosphorus manufacture as a slurry in
water.
Since intimate contact between the process materials and transport water
occurs, this water may qenerally contain dissolved or suspended
materials and so is classified as process water.
Contact Coolinq or Heatinq Water
This water comes under the general headinq of process water because it
comes in direct contact with process waters. A prime example is the
larqe quantity of water used to quench the slaq from phosphorus
furnaces; another is the water used to condense the qaseous phosphorus
after it is produced in the furnaces.
46
-------
Other direct contact cooling or heating water usage such as that for
contact steam heating and/or drying, steam distillation, pump and
furnace seals, etc., is generally of much lower volume than the
barometric condenser water and is easier to treat for waste effluents.
Atmospheric Seal Water
Because some of the materials in this industry spontaneously ignite upon
contact with the oxygen in air, the air is kept out of reaction vessels
using a water seal. Liguid phosphorus is universally protected by
storing under a water blanket. These seal waters are considered as
process waters.
Scrubber Water
Throughout this industry, water scrubbers are used to remove process
vapors and/or dusts from tail gases or from gaseous process streams.
The used scrubber water is regarded as process water since direct and
intimate contact has occurred; the resultant solution or suspension may
contain impurities or may be too dilute a solution to reuse or recover
and thus is discharged.
Auxiliary Process Water
This water is used in medium quantities by the typical plant for
auxiliary operations such as ion exchange regenerants, makeup water to
boilers with a resultant boiler blowdown, equipment washing, storage and
shipping tank washing, and spill and leak washdown. The volume of waste
water from these operations is generally low in quantity but highly
concentrated in effluents.
Miscellaneous Water Uses
These water uses vary widely among the plants with general usage for
floor washing and cleanup, safety showers and eye wash stations,
sanitary uses, and storm run-off. The resultant streams are either non-
contaminated or slightly contaminated with wastes. The general practice
is to discharge such streams without treatment except for sanitary
waste.
47
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PROCESS WASTE CHARACTERIZATION
The descriptions of the manufacturing processes in Section III, and the
flow diagrams included in that Section, qualitatively discussed the
sources of wastes. The following discussion is intended to quantify
these waste streams both in quantity and in composition. These waste
streams are the "raw" wastes prior to control or treatment (which is
separately discussed in Section VII).
Aqueous wastes emanating from air pollution abatement equipment are
considered as process wastes in this study.
The following sections quantify the raw process wastes in each segment
of the industry. A discussion of the source, nature, and amount of
these wastes for each segment is followed by a table summarizing the
standard raw waste load.
Various plants in the industry differ significantly in the deqree of
process and coolinq water recirculation. Hence, the waste water
quantities and constituent concentrations quoted may be qrossly
different from piant-to-piant. However, the raw loads in kq per kkg of
product (Ib/ton) are dependent primarily upon the manufacturing
processes and are therefore much more representative of the entire
industry.
The Phosphorus Production Subcategory
The discussion of phosphorus manufacturing technology in Section III and
the flow diagram of Figure 2, qualitatively pointed out the following
streams emanating from the process (in addition, of course, to the
phosphorus product stream):
By-products: Slag, Ferrophosphorus, and carbon Monoxide
Non-contact Cooling Water
Electrostatic Precipitator Dust
Calciner Precipitator Dust
Calciner and Furnace Fume Scrubber Liquor
Phosphorus Condenser Liquor (Aqueous phase)
Phosphorus Sludge (or mud)
Slag Quench Liquor
The following sections discuss each of the above in quantitative detail,
and identify which are typically returned to the process and which are
classified as raw waste streams from the manufacturinq operation.
By-product Streams
The by-products of the phosphorus manufacturinq operation are:
48
-------
Ferrophosphorus 300 600
Slag (CaSiO3) 8,900 17,800
CO qas 2,800 5,600
Both ferrophosphorus and slaq are sold, and the carbon monoxide is
either used to generate heat in the process or is otherwise burned on
site. Hence, none of the above three materials is considered a waste.
The quench water used for the by-product slaq is separately discussed as
a waste stream.
The by-product ferrophosphorus is cast as it is tapped from the furnace
and air-cooled. The solids are then broken up and shipped. No water is
used specifically for ferrophosphorus, and there are no wastes
accountable for ferrophosphorus manufacture.
Non-Contact Cooling Water
Phosphorus production facilities generate huge quantities of heat. The
electrical power consumption is approximately 15,500 kwh/kkq (48 million
Btu/ton). An additional 8,100 kwh/kkq (25 million Btu/ton) are generated
by combustion of the by-product carbon monoxide. Some of this energy,
6,100 kwh/kkg (19 million Btu/ton), is absorbed in the endothermic
furnace reaction, and some is absorbed by the endothermic calcining
operation. Other portions of this energy are released to the atmosphere
by burninq of waste carbon monoxide (that not used for calcining) and by
convection, radiation and evaporative losses from the eguipment and
process materials. Still other portions are absorbed by contact waters
in the calcining and furnace from scrubbers, in the phosphorus
condenser, and in the slag quenching operation.
After accounting for the above energy demands, a significant quantity of
heat is absorbed by non-contact cooling water for the furnace shell, the
crucible bottom, the fume hood, the tap holes, the electrode fixtures,
the electrical transformer, and for any indirect phosphorus
condensation. The quantity of this water is hiqhly variable from plant-
to-plant, and depends upon the furnace design, the furnace size and the
degree of recirculation (through heat exchangers with other water
streams or through cooling towers), whether or not cooling water is used
in series for different requirements, the inlet temperature of the
available cooling water, and the ambient air temperature. Plant 181
uses 325,000 liters/ kkg of product (78,000 gal/ton); Plant 159 uses
38,000 liters/ kkg (9,000 gal/ton); and TVA at Muscle Shoals,
Alabama, (5) uses 130,000 1/kkg (31,000 qal/ton).
Electrostatic Precipitator Dust
49
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The high-temperature electrostatic precipitator removes dusts from the
furnace gases before these gases are condensed for recovery of
phosphorus. These dusts may contain up to 50 percent P2O5, and
therefore finds value either as a fertilizer for sale or for return to
the process. In the latter case, it is transported to the ore blending
head end of the plant. One TVA scheme slurries the dust for transport;
the slurry is pumped to a settling pond, the settled solids are fed to
the ore - blending unit, and the pond overflow is reused in the
slurrying operation.
The guantity of precipitator dust is approximately 125 kg/kkg of product
(250 Ib/ton). Regardless of the method of sale or reuse, the
precipitator dust is not a waste material to be disposed of from the
plant.
Calciner Precipitator Dust
Dry dust collectors are used in the calcining operation, upstream of wet
scrubbing systems. The dry fine dusts collected are recycled directly
to the sizing and calcining operations. The collected and recycled
fines may amount to as much as 30 percent of the net production from the
nodulizing process.
There is no plant discharge of dry calciner precipitator dusts;
therefore this is not a component of the plant's raw waste load.
Calciner and Furnace Fume Scrubber Liquor
Water scrubbers are used for air pollution abatement for the calciner
exhaust stream (downstream of dry dust collection), for furnace fumes,
for ore sizing dusts, for coke handling dusts, for raw material feeding
operation dusts, and for furnace taphole (slag and ferrophosphorus)
fumes. The scrubber liguor contains suspended solids (which are mainly
Si02_ and Fe^O3_) , some phosphates and sulfates as dissolved solids, and a
large guantity of fluorides. To explain the presence of these fluorides
in the scrubber liguor, Table 6 lists the guantities of materials in
commercial phosphate rock. presented as pounds per ton of phosphorus
ultimately produced after normalizing of 26 percent P£O5 content. From
Table 6, the average guantity of F in ore is 275 kg/kkg of P4 (550
Ib/ton). Approximately 8 percent of this guantity of F, or 22 kg (44
Ibs), is volatilized in the ore calcining operation, and is subsequently
a constituent of the scrubber liquor.
50
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TABLE_6
of Commercial Phosphate Rocks (12)
Expressed as kg per kkq (Ib/ton) of Phosphorus Produced
Constituent
Florida Land
Pebble
_Furnace,Grade
kg/kkq Ib/ton"
Tennessee
Brown Rock
Furnace Grade
Western
Phosphoric Acid
Low Grade
kg/kkg _lb/ton kq/kkq Ib/ton
P205 2,600 5,200
CaO 3,800 7,600
MgO 35 70
A1203 125 250
Fe203 155 310
Si02 725 1,450
S03 215 430
F 305 610
C02 330 660
Organic Carbon 40 80
Na20 10 20
K20 10 20
2,600
3,550
75
1,230
760
3,150
50
270
150
35
35
50
5,200
7,100
150
2,460
1,520
6,300
100
540
300
70
70
100
2,600
3,150
190
810
550
3,750
260
24-5
550
685
205
135
5,200
6,300
380
1,620
1,100
7,500
520
490
1,100
1,370
410
270
51
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This scrubber liquor is highly acidic for three reasons: the
sulfur (as SOD forms sulfuric acid: the P.2O5 forms phosphoric
acid; and the fluorine, which is released in the form of sili-
con tetrafluoride, forms fluosilicic acid and silicic acid
upon hydrolysis.
The quantity of scrubber liquor wasted depends upon the degree
of recirculation of this liquor from a sump back to the scrub-
bers. TVA at Muscle Shoals circulates approximately 21,000
1/kkg of product (5,000 Ib/ton) with a portion bled off to
control the composition. This scrubber liquor is of the foll-
owing composition:
Constituent Concentration. %
F 3.1
Si02 1.1
P205 0.2
F6203 0.1
S 1.7
52
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If the fluoride concentration of 3.1 percent is equated to a
standard raw waste load (as previously discussed) of 22 kg/kkq
(44 Ib/ton), the quantities of other scrubber liquor components
may be calculated:
Constituent Raw Waste Load
kg/kkq Ib/ton
F 22 44
Si02 8 16
P205 1.5 3
Fe203 0.5 1
S 12 24
The total CaCO3 acidity of the scrubber liquor, calculated from the
above constituent quantities, is 60 kg/kkq (120 Ib/ton).
Other plants do not recirculate scrubber liquor; the volume wasted is
much greater and the constituent concentrations are much smaller, but
the raw waste loads (in kq/kkq of product) should be comparable. Plant
181 does not directly recirculate the liquor, and uses 300,000 1/kkq
(71,000 gal/ton) for scrubbing.
Phosphorus Condenser Liquor
The furnace gases pass from the electrostatic dust precipitator to the
phosphorus condenser, where a recirculating water spray condenses the
product. The condenser liquor is maintained at approximately 60°C
(140°F), hiqh enough to prevent solidification of the phosphorus
(freezing point 44°C (112°F)). This condenser liquor is "phossy water",
essentially a colloidal dispersion of phosphorus in water, since the
solubility at 20°C (68°F) is only 3.0 mg/1. Depending upon how intimate
the water/phosphorus contact was, the phosphorus content of phossy water
may be as high as several weight per cent.
The condenser liguor also contains constituents other than elemental
phosphorus: fluoride, phosphate, and silica. Using the average F
content of ore (from Table 6) of 275 kg/kkg, plus the estimate that 12
percent of the F in the ore volatilizes in the furance and is therefore
equivalent to 33 kg/kkg (66 Ib/ton), and by accounting for 6 kg of F per
kkg (12 Ibs/ ton) which is collected in the precipitator dust and in the
phosphorus sludge ash; a raw waste load of F is derived of 27 kg/kkg (54
Ib/ton) in the condenser liquor. This condenser liquor is not acidic
despite the hydrolysis of P2O5 and SiF4 to H3PO4, H2SiF6, and H2Si03
because aqueous ammonia or caustic is added to prevent undue corrosion
in the condenser.
53
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There are other sources of phossy water within the plant. Storage tanks
for phosphorus have a water blanket, which is discharged upon phosphorus
transfer. Railroad cars are cleaned by washing with water. Phosphorus
may be purified by washing with water. Together, all sources of phossy
water wastes amount to abcut 5,400 1/kkg (1,300 gal/ton), and at a
concentration of 1,700 mg/1, the guantity of phosphorus wastes amount to
about 9 kg/kkg produced (18 Ib/ton), as reported by TVA.
At TVA, the condenser liguor is recirculated at the rate of 33,000 1/kkg
(8,000 gal/ton). Other plants may differ significantly in the quantity
of phossy water circulated, but the raw wastes (in kg/kkg of product)
should be fairly uniform. For example, Plant 181, which does not
directly recirculate its condenser water, uses 84,000 1/kkg (20,000
gal/ton), with an additional 17,000 1/kkg (4,000 gal/ton) for phosphorus
handling and storage.
To calculate the raw waste loads of phosphate and silica in the
condenser liguor, the following TVA recirculated-liguor composition was
used:
Constituent Concentration, %
F 8.3
P205 5.0
Si02 4.2
Equating 8.3 per cent F with the previously-derived 27 kg/kkg of F, the
raw waste loads of P2O5 and SiO2 become (respectively) 16.5 kg/kkg (33
Ib/ton) and 13.5 kg/kkg (27 Ib/ton).
Phosphorus Sludge
In addition to phossy water, the phosphorus condenser sump also collects
phosphorus sludge, which is a colloidal suspension typically 10 per cent
dust, 30 per cent water and 60 per cent phosphorus. The quantity of
sludge formed is directly dependent upon the quantity of dust that
escapes electrostatic precipitation; hence the very large investment
made for highly efficient precipitators.
Using 125 kg of dust (per kkg of product) collected by the electrostatic
precipitator, and assuming a 98 per cent collection efficiency, the dust
reaching the condenser amounts to 2.5 kg/kkg (5 Ib/ton). If all of this
dust became part of the sludge, the sludge guantity would be 25 kg/kkg
(50 Ib/ton) of product, and it would contain 15 kg/kkg (30 Ib/ton) of
elementa1 phosphorus.
This sludge is then universally processed for recovery of phosphorus,
typically by centrifugation. A 96 percent recovery has been reported,
with the product (subsequently returned to the process) averaging 92 to
54
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96 percent phosphorus. The remaining 4 per cent of the phosphorus in the
sludge is burned in a phosphoric acid unit, so that no wastes emanate
from the plant.
Other methods for processing the sludge which also result in no plant
effluent include heating in a slowly rotating drum in an inert
atmosphere to drive off phosphorus vapor, which is then condensed with a
water spray into a sump. The solid residue obtained is completely free
of elemental phosphorus and can be safely landfilled or recycled to the
feed preparation section of the plant.
Slag Quenching Liquor
Slags from phosphorus furnaces are mainly SiO2 and CaO, and would also
contain A12O3, K2O, Na2O, and MgO in amounts consistent with the initial
ore composition. In addition to these oxides, phosphate rock may
contain 0.1-0.2 kg/kkg (0.2-0.4 Ib/ton) of uranium in the ore, and the
radiation levels of both the slag and the guench waters must be appro-
priately noted. Other constituents of the slag presenting problems for
quench water pollution control are fluoride and phosphate.
Approximately 80 per cent of the original F in the phosphate rock, 220
kg/kkg of P4 (440 Ib/ton), referring to Table 6, winds up in the slag.
About 2.7 per cent of the original P2O5 in the phosphate rock, 70 kg/kkg
(140 Ibs/ ton) , wind up in the slag.
At Plant 181, approximately 24,600 1/kkg (5,900 gal/ton) may be used for
quenching the slag, with the slag quench liquor having the following
composition and raw waste loads:
Cons.;titue.nt Concentration, mg/1 Raw Waste Load
kg/kkg P4 Ib/ton P4
Total Suspended 800 20 40
Solids
Total Dissolved 1,700 42 85
Solids
Phosphates (as P) 12 0.3 0.6
Sulfate (as S) 1,000 25 50
Fe 14 0.35 0.7
F 170 4.5 9
Total Alkalinity 230 5.5 11
55
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TABLE 7
Summary of Raw Wastes from Phosphorus Manufacture
Note: Waste water Quantities and Constituent Concen-
trations are highly variable, depending upon
degree of recirculation, but the raw waste
loads should be representative.
Calciner
Scrubber
Liquor
Phosphorus
Condenser
Plus Other
Phossy Water
Waste water Quantity,
1/kkg 300,000
gal/ton 72,000
Raw Waste Load,
kg/kkg
TSS
P4
PO4
SOU
F
Total Acidity
Total Alkalinity
Raw Waste Load,
Ib/ton
TSS
P4
PO4
SO4
F
Total Acidity
Total Alkalinity
Concentrations, mg/1
TSS
P4
PO4
S04
F
Total Acidity
Total Alkalinity
8.5
2
36
22
60
17
4
72
44
120
28
7
120
73
200
100,000
24,000
13.5
9
22
27
27
18
44
54
135
90
220
270
Slag
Quenching
Water
25,000
6,000
20.5
—
1
75
4.5
—
5.5
41
-
2
150
9
_
11
820
—
40
3,000
180
—
Composite
Waste
425,000
102,000
42.5
9
25
111
53.5
54.5
85
18
50
222
107
109
~
100
21
59
260
126
128
220
56
-------
The Phosphorus Consuming Subcategory
No direct process aqueous wastes are generated in this segment of the
industry. The raw wastes arise from phosphorus storage and transfer,
from wet scrubbing of tail gases, from vessel cleaning, and from leaks
and spills.
Phossy Water Wastes
Because phosphorus is transported and stored under a water blanket,
phossy water is a raw waste material at phosphorus using plants as well
as at phosphorus producing plants. The standard procedure when liquid
phosphorus is transferred from a rail car to the using plant's storage
tank is to pump the displaced phossy water from the storage tank back
into the emptying rail car as practiced at Plants 037 and 192. Instead
of being wasted at the phosphorus-using plant, the phossy water is
shipped back to the phosphorus-producing facility for treatment and/or
reuse. Therefore, standard raw phossy water wastes at the phosphorus-
using plants are due to surges or to anomalies in the storage tank water
level control system rather than to the direct wasting of all displaced
water.
A more insidious source of phossy water may arise at phosphorus
consuming plants. Should reactor contents containing phosphorus ever be
dumped into a sewer as a result of operator error, emergency conditions
or inadvertent leaks or spills, the phosphorus would remain at the low
points in the sewer line generally as a solid (melting point UU°C
(111°F)) and would contact all water flowing in that sewer from that
time on. Since phosphorus burns when exposed to air (autoignition
temperature 93°C), there is general reluctance to clean it out; the
common practice is to ensure a continuous water flow to prevent fire.
The typical phosphorus loss for phosphorus-consuming plants is 1 kg lost
to phossy water per kkg consumed (2 Ib/ton). Whenever phosphorus is
tranferred by displacement, 580 liters of water are displaced per kkg of
phosphorus (140 gal/ton). These values are equivalent to a phosphorus
concentration of 1700 mg/1. For comparison, a typical phosphorus
content in phossy water at a phosphorus-producing plant has also been
reported at 1700 mq/1.
Phosphoric Acid Manufacture
The production of phosphoric acid by the "dry" process from elemental
phosphorus consumes a total of about 380 liters of water per kkg of
product (92 gal/ton) for both the hydration and the acid dilution steps.
The cooling water requirements are typically 92,000 liters per kkg of
product (22,000 gal/ton); but with recycle of cooling water, the makeup
cooling water requirement is approximately 4,600 liters per kkg of
product (1,100 gal/ton). There is no aqueous process waste from notable
57
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phosphoric acid Plants 003, 006, 042, and 075. However, despite good
housekeeping at an notable plant, leaks or spills of phosphoric acid may
account to an average of 1 kg/kkg (2 Ib/ton), with a range of 0 to 2.5
kg/kkg (0 to 5 Ib/ton).
Where food-grade phosphoric acid is produced, a standard raw waste of
0.1 kg/kkg (0.2 Ib/ton) of arsenic sulfide is precipitated by addition
of a soluble sulfide (H2S, Na2S, NaHS), and filtered out of the acid. An
additional 0.75 kg/kkg (1.5 Ib/ton) of filter-aid material may accompany
the sulfide as a solid waste.
Phosphorus Pentoxide Manufacture
The waste water from the tail seals on the condensing towers typically
contain 0.25 kg/kkg (0.5 Ib/ton) of H3P04 (100 per cent basis).
Approximately 500 1/kkg (120 gal/ton) of water may be used, resulting in
a concentration of 470 mg/1 for the effluent bleed.
The inlet air dryer silica gel is regenerated often, but is renewed very
infrequently (perhaps every ten years). The wasted material is
typically landfilled.
Approximately 29,000 1/kkg (7,000 gal/ton) of non-contact cooling water
is used.
Phosphorus Pentasulfide Manufacture
The water seals on the batch reactor vent lines accumulate a mixture of
phosphorus mud and lower phosphorus sulfides. These seals are cleaned
once a week, and the residue amount to 0.15 kg/kkg (0.3 Ib/ton). This
residue is hazardous and flammable, and is typically buried.
Should any batch be aborted (a rare occurrence) because of agitator
failure, cast-iron pot failure or other reason, the material is disposed
of by incineration.
The dust collected by a cyclone from the P2S.5 crushing operation amounts
to 1 kg/kkg (2 Ib/ton).
The still pot for the vacuum distillation step accumulates impurities,
which include carbon and iron sulfur compounds and glassy phosphates.
Most important, the residues contain arsenic pentasulfide, which is
higher-boiling than the corresponding phosphorus pentasulfide. Arsenic
occurs naturally with phosphorus (they are both Group V-A elements) at a
level of about 0.075 kg/kkg (0.15 Ib/ton), of arsenic which is
equivalent to 0.05 kg of As2S5 per kkg of product P2S5 (0.1 Ib/ton).
The entire still pot residue is about 0.5 kg/kkg (1 Ib/ton), Per-
iodically, these residues are removed and the solids are broken up and
58
-------
buried. Approximately 17,000 1/kkq (4,000 gal/ton) of non-contact
cooling water is used.
In the casting of liguid P2S5, the fumes from burning liguid (molten
PJ2S5 auto-ignited) are scrubbed. Typically, the scrubber water contains
1.25 kg of combined P2O5 and SO2 per kkg of product P2S5 (2.5 Ib/ton).
Because both P2OJ5 and SO2 are absorbed by a water scrubber only with
difficulty, the water flow rate is high, 30,000 1/kkg (7,200 gal/ton).
These values reduce the concentrations of PO233 and so.3~2 in the
scrubber effluent of 17 and 34 mg/1 (respectively). Much lower scrubber
flow rates could be used should weak caustic or lime be used instead of
water.
Phosphorus Trichloride Manufacture
The batch or semicontinuous reactor/stills accumulate residues which are
periodically but infrequently removed. These residues contain arsenic
trichloride, which is higher-boiling than the corresponding phosphorus
trichloride. Arsenic occurs naturally with phosphorus (they are both
Group V-A elements) at a level of about 0.075 kg/kkg (0.15 Ib/ton) of
arsenic, which is equivalent to 0.05 kg of AsCl.3 per kkg of product PC13
(0.1 Ib/ton). This is about half the quantity of total residue in the
stills (exclusive of residual PC13 from the last batch or run before
shutdown) .
The average non-contact cooling water reguirement is 54,000 1/kkg
(13,000 gal/ton) .
Water scrubbers collect PC13_ vapors from the reaction, the product
distillation, the product storage, and the product transfer operations,
and hydrolyze these vapors to HC1 and to H3P0.3 (which may subsequently
be oxidized to H.3PO4) . The quantity of PCl.3 collected is highly
dependent upon the efficiency of the upstream condensers, since PC13 is
highly volatile:
Temp, °C Temp, °F PC13 Vapor Pressuret mm_Hg_(27)
20 68 99
40 104 235
60 140 690
76 169 760
At Plant 037, sufficient heat transfer area was provided in the
condensers to limit the raw waste load to 3 kg of HCl plus 2.5 kg of
H3PO3 per kkg of product PC13 (6 Ibs and 5 Ib/ton). Approximately 5,000
1/kkg (1,200 gal/ton) of scrubber water were used to collect these
wastes. Other smaller waste quantities of HCl and H3PO3_ generated from
tank car and returnable container cleaning operations have been included
in these quantities.
59
-------
These quantities are based upon the most reliable data available at
Plant 037; overall material balances of product PC13 shipped vs.
elemental phosphorus received. These data, validated over long periods
of time for profitability purposes, show a total loss of phosphorus
trichloride of 5 kg/kkg (10 Ib/ton). An estimated breakdown of this loss
is:
Transfer and Storage of Phosphorus,
Reactor/Still Residues,
Scrubber for Distillation Tail Gases,
Transfer of PC13,
1.0 kg/kkg (2 Ib/ton)
0.1 kg/kkg (0.2 Ib/ton)
2.5 kg/kkg (5 Ib/ton)
1.0 kg/kkg (2 Ib/ton)
Other than the estimated loss of elemental phosphorus and the
reactor/still residues, the losses which become water-borne
raw wastes amount to 3.5 kg/kkg (7 Ib/ton). Upon hydrolysis,
this stoichiometrically becomes 3 kg/kkg (6 Ib/ton) of HCl
plus 2.5 kg/kkg (5 Ib/ton) of H3PO3_. These material-balance
data have been used because of their long-term confirmation.
Direct measurements of waste water flow rates and of waste water
constituent analysis were not relied upon in this case since
accurate flow rate measurements were not possible in the exist-
ing plant configuration and since no statistically-meaningful
analytical data had been collected.
The acid wastes from washing tank cars and tank trucks, and from
washing used POC13 filter elements, are very small at present.
Water use data taken from Plant 037, supplemented by independent
analyses of the waste water, yielded the results in Table 8.
Total raw waste generated in truck-loading, in tank-car cleaning,
and in filter-element washing is 0.014 kg/kkg (0.028 Ib/ton)
of HCl plus 0.003 kg/kkg (0.007 Ib/ton) of total phosphates.
60
-------
TABLE 8
Minor Wastes from Plant 037 (PC13 and POC131
Water Use: 1/kkq
qal/ton
Constituent Analysis, mq/1:
Chloride
Total P04
Total Acidity
Raw Waste Load, kq/kkq:
Chloride
Total PO4
Total Acidity
Raw Waste Load, Ib/ton:
Chloride
Total PO4
Total Acidity
Truck-Loadinq
Vent
Scrubber
8.8
2.1
340
260
660
0.0030
0.0023
0.0058
0.006
0.005
0.012
Tank Car
Cleanout
-Water
10.5
2.5
715
26
0.0075
0.0003
0.015
0.001
Filter Element
Wa shout
____Drum
0.46
0.11
6,480
590
18,200
0.0030
0.0003
0.0083
0.006
0.001
0.017
61
-------
Phosphorus Oxychloride Manufacture
The water scrubber for the distillation operation in the standard
process (using P2O5 and C12) typically collects 1.5 kg of HCl (anhydrous
basis) and 0.25 kg of H3PCW (100 per cent basis) per kkg of product
POC13 (3 Ibs and 0.5 Ib/ton), and the scrubber for POC13 transferring
collects about 0.2 kg of HCl and 0.15 kg of H3PCJ* per kkg of product
(0.4 Ib and 0.3 Ib/ton). Allowing for small wastes from returnable
container cleaning operations, the standard raw waste load is 2 kg of
HCl and 0.5 kg of H3PO4 per kkg of product (4 Ibs and 1 Ib/ton). Ap-
proximately 2,500 1/kkg (600 gal/ton) of water are used, so that the raw
waste concentrations are 800 mg/1 HCl and 200 mg/1 H3PO4.
The source of the above data on raw waste loads was Plant 147 records
and plant personnel analysis of these records. An independent
verification of these results was not judged valid since at this plant
neither an accurate determination of wastewater flowrate nor the
collection of a distinct waste water sample from each unit operation
contributing to the waste load was practical; and since statistically-
valid background data was not at hand.
These waste guantities for POC13 manufacture are somewhat smaller than
for PCljJ manufacture since POC13 is less volatile (boiling point 107°C) .
In the batch process, the refluxing liguid is all PC13 at the start, but
becomes increasingly richer in POC13.
The air-oxidation process presents a much more difficult task for the
reflux condenser, since the vapors are highly diluted with non-
condensibles. However, with the use of refrigerated condensers, the
measured raw waste load is no different for this process. At Plant 037,
data collected over three months from the reactor/still scrubber for
POC13 manufacture, which had an estimated flowrate of 1,800 1/kkg (430
gal/ ton), had average net values of:
Chloride 669 mg/1
CaC03 acidity 1,213 mg/1
These data reduce to a raw waste of 1.2 kg/kkg (2.4 Ib/ton) of HCl plus
0.35 kg/kkg (0.7 Ib/ton) of H3PO4; which are extremely close to the
corresponding values for Plant 147.
Where product POC13 is filtered, the used filter elements are first
washed to hydrolyze the residual POC13. Disposable elements are then
landfilled. The guantity of filtered solids retained on the elements is
only a very small fraction of the weight of the used element. The
elements are washed in a 55-gallon drum, so that a very small guantity
of waste water (and of acid wastes) is involved compared to the scrubber
waste load. Although there is no continuous withdrawal of residues from
62
-------
POCL3 distillations, very little residue accumulates. Twice a year,
this residue (mostly glassy phosphates) is washed out with hot water.
The non-contact coolinq water requirement for POC13 manufacture by
either the standard or the alternate method is approximately 50,000
1/kkq (12,000 qal/ton).
Variability of Raw Wastes from the Production of Phosphorus Trioxide and
Phosphorus Oxychloride
The data below indicates the variability of concentrations in the raw
waste load at Plant 037.
Date (1973) CaCO3 Acidity, mq/1 Chloride, mq/1
2/27
2/28
3/1
4/19
a/23
4/24
4/25
4/26
4/27
4/30
5/1
5/2
5/3
5/4
5/7
5/8
5/9
1170
1220
1720
850
480
950
1430
1250
1300
1120
1470
1690
280
1340
1810
1220
1290
560
603
822
447
305
532
851
589
1035
518
1040
716
773
603
1000
574
716
Mean
Std. Deviation
Std. Deviation
95X Conf. Int.
(Sinqle Day)
1217
384
384
+ 814
687
208
208
441
In this case, there was no dampinq capacity; the acidity and chloride
concentrations were closely coupled to the manufacturinq process. The
comparison of the 95% confidence intervals with the daily data show only
one point of 17 (for acidity) and no points outside (for chloride).
Eased on these very limited samples of data, it appears that the
classical statistics may be applied, but with extreme caution.
For the above sets of data from Plant 037, a value of (X + 3<5) / X miqht
represent a maximum allowable daily readinq as a multiple of the mean:
63
-------
Parameter (X + 3dY/ X
Acidity Concentration 1.95
Chloride Concentration 1.91
This maximum allowable value would be extremely liberal, since a
Students "t" value of 3 is equivalent to less than one reading in 100
being unduly rejected. To be even more liberal (since the data base for
this analysis is extremely skimpy), the maximum value from the above
table will be assumed, so that the effluent limitation guideline for the
manufacture of PC13_ and POC13 should be a maximum daily value no greater
than twice the mean (as represented by consecutive 30 day averages).
pH can be controlled much more closely than other parameters. Hence, it
is recommended that the pH limitation be met at all times.
64
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TABLE 9
Summary of Raw Waste from Phosphorus-Concuming Plants
Phossy Water: Pq cone, ppm
1/kkg ?4 consumed
kcip/s./kka ?4 consumed
g si /ton P/J. consumed
Ib /ton ?4 consumed
Process Water Wasted: 1/kka Pdt
gal /.ton Pdt
Raw Waste Load, kg/kkg Pdt:
HC1
H2S03
H3P03 + H3P04
Raw Waste Load, Ib /ton Pdt:
HC1
H2S03
H3P03 + H3P04
Concentrations, mg/L: HC1
HoS03
H3P03 + H3P&4
Process Water Consumed-
1/kkg Pdt.
gal /ton Pdt
Cooling Water Used: 1/kkg 'Pdt
gal /ton Pdt
Solid Wastes, kg/kkg Pdt:
As Compounds
Total Residues ..'..'.
Solid Wastes, Ib /ton Pdt:
As Compounds
Total Residues
H3P04
(75%)
1,700
580
1
140
2
—
—
1
2
High
380
92
91 ,000
22,000
0.1
0.2
" —
P2°5
1,700
580
1
140
2
500
120
0.25
0.5
470
M. —
29,000
7,000
—
"~ —
.P2S5
1,700
580
1
140
2
30,000
7,200
1
0.5
2
•i
i
34
17
—
16,600
4,000
0.05
0.7
0.1
1.4
PCI,
- - o
1,700
580
1
140
2
5,000
1:200
->
_>
2.5
6
5
600
500
_ _
54,000
13,000
0.05
0.05
0.1
0,1
poci3
--
__
2,500
500
2
0.5
4
1
800
200
--
50,000
12,000
<0.05
<0.1
65
-------
The Phosphate Subcategory
The aqueous wastes from this segment of the industry arise from the use
of wet dust scrubbing equipment for the finely divided solid products,
and from processes which use excess process water which may become a
waste stream.
Sodium Tripolyphosphate Manufacture
Exemplary Plants 006, 042, and 119 have no process wastes. The dust
collected from the spray dryer gaseous effluent stream is added to the
spray dryer solid product stream. The water used for subsequent
scrubbing of this gas stream from the spray dryer is then recycled to
the mix area and is used as process water in the neutralization step.
The cooling air used for the product tempering is vented into the spray
dryer vent line upstream of the scrubbing operation.
The neutralization step requires a total of 1,040 I/ kkg (250 gal/ton),
of which 290 1/kkg (70 gal/ton) are recycled from the scrubber. Make-up
water, 750 1/kkg (180 gal/ton) , are added since water is evaporated in
the product drying step. The makeup water is softened, and regeneration
of the softener combined with boiler and cooling tower blowdowns amounts
to 210 1/kkg (50 gal/ton); 70 per cent of which is from water treatment
regeneration and 30 per cent from blowdowns. These blowdown wastes
typically contain 1,500 mg/1 of dissolved chlorides.
Calcium Phosphates
The raw aqueous wastes from the manufacture of food-grade calcium
phosphates are from two primary and approximately equal sources: the
centrate or filtrate from dewatering of the dicalcium phosphate slurry,
and the effluent from wet scrubbers which collect airborne solids from
product drying operations.
Both of these sources contain suspended, finely-divided calcium
phosphate solids. It is normal practice in an integrated plant to
partially recycle the scrubber water and to partially utilize the DCP
centrate or filtrate as makeup scrubber water, as at Plant 003.The total
raw wastes from this system are typically 4,200 1/kkg (1,000 gal/ton)
containing 100 kg/kkg (200 Ib/ton) of solids (a concentration of 2.4 per
cent). An additional 36 kg/kkg (60 Ib/ton) of dissolved solids (0.7 per
cent of this waste stream) originates from phosphoric acid mists in the
scrubbers and from excess phosphoric acid in the reaction liquid.
For non-food grade dicalcium phosphate plants, the water scrubbers which
collect airborne solids normally operate at partial recycle. Since there
is no waste from a dewatering operation, and since dry dust collection
typically precedes wet scrubbing, the raw wastes are considerably
66
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smaller than for the food-grade operation. Dry dust collection is
typical since only one or two products are made, so that the collected
solids may be added directly to the product stream without extensive
segregation. Moreover, since purity reguirements are considerably less
severe, the product stream can tolerate such additions. With the above
measures, the wet scrubber wastes are typically 420 1/kkg (100 gal/ton)
containing 22.5 kg/kkg (45 Ib/ton) of suspended solids (a concentration
of 5 per cent) plus 4 kg/kkg (8 Ib/ton) of dissolved phosphates from
acid mists (0.7 per cent). At the notable Plant 182, this bleed stream
from the wet scrubber recalculation system is charged directly to the
neutralization reactor; hence, this plant had no discharge whatever. As
an added feature, this notable plant used cooling water blowdown as
makeup to the airborne-solids scrubbing system, thereby eliminating all
agueous discharges (except for the effluent frcm regeneration of the
water softener).
For the non-food grade plants, however, acid defluorination is an
additional source of raw wastes (unless already-defluorinated acid is
delivered to the plant) . Wet-process phosphoric acid (54 per cent P.2O5)
contains approximately one per cent fluorine. Upon silica treatment,
13.5 kg per kkg of acid (27 Ibs/ ton), or 10.5 kg of silicon
tetrafluoride product dicalcium phosphate dihydrate (21 Ib/ton), are
liberated. When hydrolyzed in the acid scrubber, the raw waste contains
12 kg/kkg product (24 Ib/ton) of combined fluosilicic acid (H2SiF6),
hydrofluoric acid (HF) and silicic acid (H2SiO3). These raw wastes are
contained in a scrubber water flow of 6,300 liters/ kkg (1,500 gal/ton),
so that the combined concentration of fluosilicic acid, hydrofluoric
acid and silicic acid is 1,900 mg/1. For any plant manufacturing
calcium phosphates of any grade, non-contact cooling water is used in
reactors and/or in dried product coolers.
Other possible sources of aqueous wastes are from regeneration of water
softeners and from storm water runoff (all exterior surfaces of calcium
phosphate plants become coated with fine lime and/or phosphate dusts).
In dry-product plants, a significant housecleaning effort must be
continually maintained. In non-food grade calcium phosphate plants, the
dry product sweepings (from dust, spills, etc) are added to the process
stream, in food-grade plants, however, the sweepings (consisting of
lime, lime grit, and calcium phosphates) are wasted. Typically, this
solid waste amounts to 10 kg/kkg (20 Ib/ton).
67
-------
TABLE 10
Summary of Raw Wastes from Phosphate Plants
Food Grade Animal Feed
Sodium Calcium Phosphates Calcium Phosphates
Tripoly- Solids Acid Deflu- Solids"
Phosphate Dewaterina Scrubbing orination
Process Water Wasted:
1/kkg Pdt
qaI/ton Pdt
Raw Waste Load,
kg/kkg Pdt:
TSS
Dissolved PO4
HF, H2SiF6, H2SiO3
Raw Waste Load,
Ib/ton Pdt:
TSS
Dissolved P4
HF, H2SiF6, H2Si03
Concentrations, mg/1:
TSS
Dissolved PO4
HF, H2SiF6, H2SiO3
TDS, mg/1
Solid Wastes:
kg/kkg Pdt
Ib/ton Pdt
0
0
2,100
500
50
15
100
30
24,000
7,000
7,000
2,100
500
50
15
100
30
24,000
7,000
7-, 000
6,300
1,500
12
1,900
1,900
420
100
22.5
4
45
8
54,000
7,000
7,000
10
20
68
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SECTION VI
SELECTION OF POLLUTION PARAMETERS
INTRODUCTION
Section V of this report quantitatively discussed the raw wastes
generated in the phosphate manufacturing industry. The following were
identified as being constituents of the industry's process waste waters:
Suspended Inorganic Solids
Dissolved Phosphates or Phosphites
Dissolved Sulfates or Sulfites
Dissolved Fluorides or Fluorosilicates
Dissolved Chlorides
Total Dissolved Solids
Acidity or low pH
Heat (High Temperature)
Elemental Phosphorus
Arsenic Compounds
Vanadium, cadmium, radium and uranium
The following discussion examines each of the above constituents and
their impact upon receiving waterways from a chemical, a physical and a
biological viewpoint. Additional, constituents such as hexavalent
chromium, iron, alkalinity, and hardness, which are of typical concern
whenever blowdowns from cooling towers, boilers and water treatment
facilities are involved, are noted here but are not discussed in detail
in this study (which deals more specifically with the process wastes of
the phosphate industry).
SUSPENDED INORGANIC SOLIDS
Suspended solids discharged into receiving waters adversely impair
navigation, recreation, water supply and fish propagation water uses.
Navigation may be impaired as a result of sedimentation in guiescent
regions in the stream bed. Recreational and water supply uses would be
impaired as a result of turbidity of the water. The fish population
suffers from loss of suitable breeding areas, loss of food chain
organisms because of change in benthic characteristics, fish kills from
excessive turbidity, and reduction of light penetration into the
streams.
Suspended solids affect fisheries directly by covering the bottom of a
stream with a blanket of material which kills out the bottom fauna,
directly depriving the fish of a considerable part of their food (which
lies at the bottom), or indirectly by eliminating species in the food
chain. In addition, portions of the bottom, usually in the shallower
69
-------
parts of the stream, provide nesting sites and spawning grounds for
certain species.
The suspended solids directly affect fish through mechanical and
abrasive action which clogs or otherwise injures the gills and
respiratory structures. Although normal healthy fish secrete mucus to
wash away suspended solids as they lodge on gills and other exposed
parts, the synergistic action of other pollutants such as small amounts
of acid wastes greatly augments the abrasion by solids by inhibiting the
normal flow of mucus.
Indirectly, suspended solids affect fisheries by effectively screening
out the light necessary to species of flora which may be important parts
of the food chain. Also indirectly, but none the less effectively,
solids which settle at the bottom trap organic wastes which might
otherwise be dispersed, thereby increasing the oxygen demand at the
bottom of the stream with disastrous results to the bottom fauna.
Of special concern in the phosphate industry is that much of the
suspended solids in the raw wastes are calcium phosphates. It has
recently been shown that calcium phosphates deposited in bottom muds of
lakes are not inert solids, but are indeed available for uptake by the
lake waters, and are a prime source of nutrients for algae blooms and a
prime cause for lake eutrophication.
DISSOLVED PHOSPHATES AND PHOSPHITES
Phosphites are oxidized to phosphates in streams, exerting a chemical
oxygen demand upon the streams.
The controversy over the nutrient and eutrophication effects of
phosphates has received much attention in recent years, resulting from
the phosphate constituent in domestic wastewater. The average
concentration in domestic waste water is 30 mg/1 (as PO4) ; and the
domestic waste guantities are about 1.6 kg (3.5 Ibs) per capita per
year, one-third of which are from human excretions and two-thirds from
synthetic detergents. Runoff of synthetic fertilizers also contribute
heavily to phosphate pollution of surface waters. For the purpose of
this study, it appears sufficient to rely for guidance upon the massive
effort and expenditure to remove phosphates from domestic waste water to
come to the conclusion that dissolved phosphates from the industry under
study are indeed a pollution parameter.
The natural concentration of phosphates in sea water is 0.7 to 1.4 mg/1.
DISSOLVED SULFATES OR SULFITES
Sulfites are oxidized to sulfates in streams, exerting a chemical oxygen
demand upon the streams.
70
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Sulfates are not particularly harmful, but are a major constituent of
the total dissolved solids in waste waters from this industry (and are
discussed separately as such).
DISSOLVED FLUORIDES AND FLUOROSILICATES
Fluosilicic acid and its salts are highly deleterious materials. They
also decompose to form fluorides. Hydrolysis causes fluosilicates to
form gelatinous precipitates which are difficult to settle and dewater
in treatment operations.
Fluorides are present in natural waters in concentrations less than 1
mg/1, and are widely used as drinking water additives in concentrations
of a few mg/1 for beneficial dental effects. However, at higher
concentrations than 7 or 8 mg/1, fluorides have caused severe damage to
bone structures. Fluorosis from airborne fluorides has been documented
in cattle and in humans in the proximity of phosphate-rock mining
operations.
Fluorides and fluorosilicates are definitely harmful materials, and can
be identified as pollution parameters for the purposes of this study.
DISSOLVED CHLORIDES
Dissolved chlorides are a major constituent of the total dissolved
solids in waste waters from this industry (and are discussed separately
as such) .
Sodium and calcium chlorides are found naturally in unpolluted waters,
but are harmful to fish in high concentrations.
The natural salinity of river water in the Chesapeake Estuary is 9.5 to
11.0 mg/1 of chloride; and the natural salinity of ocean water is 7,000
to 10,300 mg/1 of chloride.
TOTAL DISSOLVED SOLIDS
Unpolluted natural waters contain small quantities of dissolved
carbonates, chlorides, phosphates, sulfates and nitrates. All of the
substances in solution in river water exert osmotic pressure on the
aguatic organisms, and many of these substances are physiologically
active, so that the organisms have become adapted to this salt complex.
Most aquatic species will tolerate changes of considerable magnitude in
the relative amounts of these salts provided the total dissolved solids
remains constant.
The specific conductance, a direct measure of dissolved inorganic
solids, lies between 150 and 500 umhos/cm in inland streams and rivers
which support good, mixed fish faunas. In the Western plains and desert
71
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areas, natural quantities of dissolved solids are higher, with specific
conductance ranqing to 2,000 umhos/cm. The blood of fresh-water fish
contains approximately 7,000 mq/1 of dissolved salts (mainly NaCl). If
the total dissolved solids in the external medium exceed this 7,000 mq/1
by much, water will be withdrawn by osmosis from the qills of fish and
from other delicate external organs of various species of aquatic life
with lethal effects.
ACIDITY OR LOW pH
Acidity, or low pH, kills fish through the precipitation and coagulation
of the mucus on the gills and by the coagulation of the gill membranes
themselves (specifically the proteins in the membranes). This
precipitation and coagulation proceeds rapidly below a pH of 4.5; but
species unprotected by mucus (such as Daphnia magna) are killed below a
pH of 5. 5
A typical State water quality standard (that of Maryland) specifies a pH
of 6.0 to 8.5 reqardless of water use.
HEAT (HIGH TEMPERATURE)
The impact of hiqh water temperatures takes several forms which may also
act synergistically:
(a) Alteration of the physical properties of water.
(b) Decrease in the solubility of oxygen upon which most aquatic
organisms depend.
(c) Increase in the rate of chemical and biochemical reactions,
particularly in the oxidation of organic wastes (thereby decreasing the
level of dissolved oxygen).
(d) At sufficiently high temperatures, organisms are killed directly.
(e) Physiological processes such as reproduction, development and
metabolism are temperature-dependent.
(f) Temperature anomalies can block the passage of anadromous fish,
greatly reducing future populations.
Most fish are poikilothermal animals whose body temperature follows
changes in environmental temperatures rapidly and precisely. The
tolerance of fish to high temperatures is dependent upon the normal
temperature to which the fish are acclimated and to the abruptness of
temperature changes (both temporally and spatially). In general,
however, the upper temperature limits for fish survival are in the range
of 25 to 35<>C (75 to 95°F) .
A typical State water quality standard (that of Maryland) specifies the
following with respect to heat rise regardless of water use:
72
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Natural Max. Temp .. Maximum
Rise, °F Temp,0F
Tidal 50 20 60
50 10 90
Non-Tidal 50 20 60
50 10 93
ELEMENTAL PHOSPHORUS
Elemental phosphorus has been identified as an extremely harmful
material in very small amounts. The lethal dose for humans is 100 mg and
the chronic dose is 1 mq/day. Ingestion of elemental phosphorus by the
human body causes bone and liver damage.
ARSENIC COMPOUNDS
The dangerous properties of arsenic compounds in very small amounts is
well known. The Federal Water Quality Administration presented a
summary of the hazards of arsenic. The U.S. Public Health Service
Drinking Water Standards set a maximum concentration of 0.05 mg/1, with
a recommended limit of 0.01 mg/1. There is a continuing controversy
over the health hazards of minute guantities of arsenic either naturally
entering the ground or surface waters; and particularly over the arsenic
that occurs naturally in phosphates (at a level of As:P of 75 mg/1) and
is subsequently discharged into municipal waste water.
VANADIUM, CADMIUM, RADIUM AND URANIUM
Phosphate rock ore does contain trace amounts of one or more of these
elements. These elements are chemically and/or radioactively harmful as
detailed in Reference 72, but are not in such concentrations as to cause
a serious health problem.
CONCLUSION
In view of the data presented above, it is judged that all of the
mentioned waste constituents generated in the phosphate industry be
identified as pollution parameters as defined in the Federal Water
Pollution Control Act Amendments of 1972.
In the paragraphs above, the harmful characteristics are given of all
the parameters that are encountered in the phosphate manufacturing point
source category. Table 1 1 summarizes the parameters found for each
chemical. The chemicals PC1.3 and POCl.3 require further consideration.
73
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Chemical
TABLE 11
WASTE WATER CONSTITUENTS OF PHOSPHATE CATEGORY
Parameter
TSS P04
P03
?4 & Fe2P
H3P04
P2°5
P2S5
PC13
POC13
Na5P3010
CaHP04 (feed grade)
CaHP04 (food grade)
0
X
X
0
0
0
0
0
0
0
0
0
0
0
SO^ F Cl TDS
S03 SiFfc
0
0
0
0
0
0
0
0
0
0
X
X
0
0
0
low Heat P, As V, Cd,
pH Ra, U
0
0
0
0
X
X
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
-------
Although many parameters appear in the waste streams from these plants
only those primary parameters signified by "x" need be used to set
effluent standards.
The remaining parameters for PC1.3 and POC1.3 signified by zeros are
adeguately treated if the primary parameters are so treated. Special
consideration for these two chemicals is necessary since they are the
only exceptions to the proposed guidelines (no discharge of process
waste water pollutants) for this category.
75
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-------
SECTION VII
CONTROL AND TREATMENT TECHNOLOGY
INTRODUCTION
Section V of this report quantitatively discussed the specific water
uses in the phosphate industry and the raw wastes from this industry
prior to control and/or treatment of these wastes. Section VI
identified the constituents of the raw wastes which are classified as
pollutants. Table 11 summarizes the pollutant constituents found as raw
wastes in each of the three segments of the industry:
Two major observations may be made from table 11:
1. Classical sanitary engineering practices that treat effluents
containing organic material or that are aimed at reducing biological
oxygen demand are inapplicable to the phosphate manufacturing industry,
where such pollutant constituents are usually very low and not a
significant factor. Hence, control and treatment of the wastes in this
industry are of the chemical and chemical engineering variety, and
include neutralization, pH control, precipitation, ionic reactions,
filtration, centrifugation, ion exchange, demineralization, evaporation
and drying.
2. A limited number of pollutant constituents characterizes the entire
industry, crossing the lines between segments of the industry. Hence,
the control and treatment techniques should be similar throughout the
industry.
In this section of the report, the control and treatment technology is
discussed in considerable detail. Much of this discussion is based upon
observed actual abatement practice in the industry; the accomplishments
of independently-verified sampling data of plant effluents.
IN-PROCESS CONTROLS
Control of the wastes includes in-process abatement measures, monitoring
techniques, safety practices, housekeeping, containment provisions and
segregation practices.
Segregation of Water Streams
Probably the most important waste control technique, particularly for
subsequent treatment feasibility and economics, is seqregation.
77
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Incoming pure water picks up contaminants from various uses and sources
including:
1. non-contact cooling water
2. contact cooling water
3. process water
4. washings, leaks and spills
5. incoming water treatments
6. cooling tower blowdowns
7. boiler blowdowns
If wastes from these sources are segregated logically, their treatment
and disposal may sometimes be eliminated entirely through use in other
processes or recycle. In many instances, the treatment costs,
complexity and energy reguirements may be significantly reduced.
Unfortunately, it is a common practice today to blend small, heavily
contaminated streams with large non-contaminated streams such as cooling
water effluents. Once this has been allowed to happen, treatment costs,
energy reguirements for these treatments, and the efficient use of water
resources have all been compromised.
In general, plant effluents can be segregated into:
1. Non-contaminated Cooling Water. Except for leaks, non
contact water has no waste pickup. It is usually high volume.
2. Process Water. Usually contaminated but often small
volume.
3. Auxiliary Streams. Ion exchange regenerants, cooling
tower blowdowns, boiler blowdowns, leaks, washings -
low volume but often highly contaminated.
Although situations vary, the basic segregation principle is don't mix
large uncontaminated cooling water streams with a smaller contaminated
process and auxiliary streams prior to full treatment and/or disposal.
It is almost always easier and more economical to treat and dispose of
the small volumes of waste effluents - capital costs, energy
reguirements, and operating costs are all lower.
In the phosphorus chemicals industry, many plants have accomplished the
desired segregation of water streams, often by a painstaking rerouting
of sewer lines which have existed for many years. Among these plants
which are notable in this respect are Plants 003, 037, 042, 075, and
182.
Recycle of Scrubber Water
78
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The widespread use of water for scrubbing of tail gases in this industry
has unfortunately led to many examples where once-through scrubber water
is the mode of operation. However, there are several plants notable in
this respect which recycle scrubber water from a sump, thus satisfying
the scrubber water flowrate demands (based upon mass transfer
considerations) while retaining control of water usage. These notable
plants are TVA (Muscle Shoals, Alabama), and Plants 003 and 182.
Recycle of scrubber water permits the subseguent treatment of much
smaller guantities of waste water with much higher concentrations of
polluting constituents. Both of these attributes make waste water
treatment more economical, and in some cases, more efficient, from a
removal viewpoint.
Dry Dust Collection
A drastic reduction in the agueous waste load may be made by replacing
wet scrubbing systems with baghouses, or alternately, by placing cyclone
dust collectors upstream of wet scrubbers. This approach is feasible
because baghouses have recently been improved in design to the point
where operation and maintenance costs are not excessive, where solids
collection efficiences exceed those of wet scrubbers, and where
operating temperature ranges have been extended with high-temperature
media development. Dry collected solids may be returned to the product
stream, provided that a separate collector is installed for each
product. This is a change in approach for the typical multi-product
phosphate plant, since conventional practice has been to centralize the
collection and treatment functions across product lines. With dry
separate collection, the product recovered may significantly contribute
towards the operating cost of the collectors.
Plants in this industry which are notable in this respect by having at
least some dry dust collection include Plants 003, 006, 042, 119, and
182.
Housekeeping and Containment
Containment and disposal reguirements may be divided into several
categories:
1. minor product spills and leaks
2. major product spills and leaks
3. upsets and disposal failures
U. storm water runoff
5. pond failures
6. vessel and container cleanout
79
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Minor Spills and Leaks
There are minor spills and leaks in all industrial chemical
manufacturing operations. Pumps seals leak, hoses drip, washdowns of
equipment, pipes and equipment leak, valves drip, tank leaks occur,
solids spill and so on. These are not goinq to be eliminated. They can
be minimized and contained. In some cases the products are valuable; in
other cases, personnel safety and prevention of corrosion may become
paramount.
Reduction techniques are mainly good housekeeping and attention to sound
engineering and maintenance practices. Pump seals or types of pumps are
changed. Valves are selected for minimizing drips. Pipe and equipment
leaks are minimized by selection of corrosion-resistant materials.
Containment techniques include drip pans under pumps, valves, critical
small tanks or equipment, and known leak and drip areas such as loading
or unloading stations. Solids can be cleaned up or washed down. All of
these minor leaks and spills should then go to a containment system,
catch basin, sump pump or other area that collects and isolates all of
them from other water systems. They should go from this system to
suitable treatment facilities.
Of special importance in the phosphorus-consuming subcategory of the
industry is the containment of phossy water from phosphorus transfer and
storage operations. While displaced phossy water is nominally shipped
back to the phosphorus-producing facility, current practice in
phosphorus storage tanks is to maintain a water blanket for safety
reasons by makeup water addition and by subsequent overflow over a weir
or excess water.
This method of level control is unacceptable since it results in the
discharqe of phossy water. One way to ensure zero discharge is to
install an auxiliary tank to collect phossy water overflows from the
phosphorus storage tank; this system can be closed-loop by reusing this
phossy water from the auxiliary tank as makeup for the main phosphorus
tank. This scheme preserves the positive safety features of the
existing level control practice and also safeguards against inadvertent
large discharges resulting from leaky or maladjusted water makeup
valves.
Major Product Spills and Leaks
These are catastrophic occurrences with major loss of product, tank and
pipe ruptures, open valves, explosions, fires, and earthquakes.
No one can predict, plan for or totally avoid these happenings, but they
are extremely rare. Probably the most common of these rare occurrences
is tank or valve failures. These can be handled by adequate dikes able
80
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to contain the tank volume. All acid, caustic or toxic material tanks
should be diked to provide this protection. Other special precautions
may be needed for flammable or explosive substances. Plant 037 is a
prime example where product tanks and trsnsfer pumps have been
systematically diked for containment or spills.
Upsets and Disposal Failures
In many processes there are short term upsets. These may occur during
startup, shutdown or during normal operation. The phosphorus-consuming
subcategory and the phosphate subcategory of this industry may be more
vulnerable to this type of upset since so many of the processes are
batch-type operations with much more direct operator control then the
typical large-scale automated continuous processes in the chemical
industry.
These upsets represent a small portion of overall production but they
nevertheless contribute to waste loads. Hopefully, the upset products
may be treated, separated, and largely recycled. In the event that this
can not be done, they must be disposed of.
One very special problem in the phosphorus-consuming subcategory is the
inadvertent spill of elemental phosphorus into a plant sewer line. Past
practice has been to let it remain in the sewer and to ensure a
continuous water flow to prevent fire. There has been general
reluctance to clean it out since phosphorus burns when exposed to air.
With this practice, of course, all water flowing^ in that sewer from that
time on contains phosphorus and ostensibly becomes contaminated.
Provisions can be made for collecting, segregating and bypassing such
phosphorus spills. One method is the installation of a trap of
sufficient volume just downstream of reaction vessels, with appropriate
installations and valving to enable the bypass of that trap after a
spill has occurred and the offline removal and cleaning of the trap
(with safe disposal of the phosphorus).
Stormwater Runoff
The phosphates segment of this industry is characterized by the
handling, storing, conveying, sizing, packaging and shipping of finely-
divided solid products. Typically, a phosphates plant has all exterior
surface of buildings, equipment and grounds covered with dusts. An area
of concern is the pickup of these solids by stormwater either as
suspended solids or as dissolved solids. Of course, washing down of
these dusts is not acceptable; the dry solids must be collected. Where
possible, the solids may be returned to appropriate process streams.
Where purity requirements prohibit this return, adequate means for safe
disposal of solid wastes must be provided.
81
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Plants 003, 042 and 182 are examples of plants which have positive
continual cleanup proqrams for solids, which minimize stormwater runoff.
Most plants (with considerable credit to air pollution abatement
practices) have also minimized the quality of airborne dusts.
The very practice of process water segregation discussed previously has
led to the direct discharge of stormwater without treatment. Little is
known from a quantitative standpoint about the severity of this problem
in the phosphates segment of the industry, or to what extent containment
and treatment of stormwater is required. In the phosphorus manu-
facturing segment of the industry, where large quantities of dusts are
handled, Plant 159 collects approximately 10 kg/kkg (20 Ib/ton) in a
settling pond for stormwater and non-contact cooling water.
Pond Failures
Unlined ponds are the most common treatment facility used by the
industry. Failures of such ponds occur because they are unlined and
because they are improperly constructed for containment in times of
heavy rainfall.
Unlined ponds may give good effluent control if dug in impervious clay
areas or poor control if in porous, sandy soil. The porous ponds will
allow effluent to diffuse into the surrounding earth and water streams.
This may or may not be detrimental to the area, but it is certainly poor
waste control. Lined ponds are the only answer in these circumstances.
Many ponds used today are large low-diked basins. In times of heavy
rainfall, much of the pond content is released into either the
surrounding countryside, or, more likely, into the nearest body of
water. Again, whether this discharge is harmful or not depends on the
effluent and the surrounding area, but it does represent poor effluent
control.
Good effluent control may be gained by a number of methods, including:
1. Pond and diking should be designed to take the antici-
pated rainfall - smaller and deeper ponds should be used
where feasible.
2. Control ponds should be constructed so that drainage
from the surrounding area does not innundate the pond
and overwhelm it.
3. Substitution of smaller volume (and surfaced) treatment
tanks, coagulators or clarifiers can reduce rainfall
influx and leakage problems.
82
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Vessel and Container Cleanout
One common characteristic of the phosphorus-consuming subcateqory of the
industry is the planned accumulation of residues in reaction vessels and
stills, with infrequent shutdowns to clean and remove these residues.
In many cases, the residues are washed down with firehoses and the
wastes discharged. This practice is clearly unacceptable. One
alternative is the diking of the area (as described previously), with
collection and treatment of the aqueous wastes, in conjunction with an
effort to minimize the quantities of washwater.
A similar situation exists with regard to the cleaning of returnable
containers (drums, tank trucks and tank cars) prior to reuse. Since
these are routine operations, procedures and facilities must be made
available for minimizing the quantities of waste water and for the
collection and treatment of these waste waters.
Monitoring Techniques
Since the chemical process industry is among the leaders in
instrumentation practices and application of analytical techniques to
process monitoring and control, there is rarely any problem in finding
technology applicable to waste water analysis. Acidity and alkalinity
are detected by pH meters, often installed in-line for continuous
monitoring and control.
Dissolved solids may be estimated by conductivity measurements,
suspended solids and turbidity, and specific ions by wet chemistry and
colorimetric measurements. Flow meters of numerous varieties are
available for measuring flow rates.
The pH meter is the most universal of the in-line monitoring
instruments. Spills, washdowns and other contributions become quickly
evident. Alarms set off by sudden pH chanqes alert the operators and
often lead to immediate plant shutdowns or switching effluent to
emergency ponds for neutralization and disposal. Use of in-line pH
meters will be given additional coverage in the control and treatment
sections for specific chemicals.
Monitorinq and control of harmful materials such as phosphorus and
arsenic is often so critical that batch techniques may be used. Each
batch can be analyzed before discharginq. This approach provides
absolute control of all wastes passinq throuqh the system. Unless the
process is unusually critical, dissolved solids are not monitored
continuously. This follows from the fact that most dissolved solids are
rather inert. Chemical analyses on grab or composite effluent samples
are commonly used to establish total dissolved solids, chlorides,
sulfates, and other low ion concentrations.
83
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Summary
The preceding narrative described general treatment practices and in-
plant controls. The following discusses specific abatement measures
recommended for each subcategory.
8U
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TREATMENT OF WASTE WATERS IN THE PHOSPHORUS SUBCATEGORY
Neutralization of Acidic Waste waters
Virtually every manufacturing process in the phosphate industry results
in a raw waste load of significant acidity. In some cases, advantage is
taken of the availability of alkaline waste to at least partially
neutralize the acid waste streams.
At phosphorus-producing plants, some neutralization of acidic calciner
scrubber liquor is achieved by the alkaline slag or by the slightly
alkaline slag guench liguor (see Table 7). At TVA, the slag is
granulated by quenching with a high-velocity jet of calciner scrubber
liquor plus process cooling water; the granulated slag (with its large
surface area) effectively neutralizes the acidic liquors. At plants not
granulating slag, the slightly-alkaline slag quench liquors are mixed
with the highly-acidic scrubber liquors for partial neutralization.
This is practiced at Plants 028 and 181.
Except for this one case where granulated slag is available, lime or
limestone neutralization cf acid waste streams is standard practice in
this industry, as observed at Plants 003, 006, 028, 159, 181, and 182.
The relative chemical costs reported by Downing, Kunin and Polliot(28),
listed in Table 12, show that limestone or lime are far and away more
economical than other neutralizing materials. Limestone is the lower
cost material (approximately $ll/kkg ($10/ton)) but suffers the
disadvantages of slower reaction and lower obtainable pH than with lime.
Lime costs are approximately $22/kkg ($20/ton).
With the exception of hydrochloric acid from PCI3 and POC13
manufacturing facilities, every acid waste in the phosphorus chemicls
industry forms insoluble or slightly-soluble calcium salts when treated
with lime:
Acid Calcium Salt Solubility*, rng/1
H3P04 Ca(H2P04) 2.H2O, MCP 18,000
" CaHP04.2H20, DCP 200
11 Ca3(P04)2, TCP 25
HF, H2SiF6 CaF2 16
H2Si03 CaSi03 95
H2S04 CaS04.2H20 2,410
H2SO3. CaSO3.2H2O 43
H3P03 2 CaHP03.3H20 (Slightly Soluble)
*Between 17°C and 30°c.
It is readily apparent that lime treatment (with excess lime) not only
performs neutralization of acidic waste waters from the phosphate
85
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TABLE 12 Relative Chemical Costs for Neutralizing Acid Wastes
(28}
Source: Downing, Kunin and PoTliotv '
NI-III'RAI.IZING MATERIAL
Lump limestone, high Ca
Lump limestone, dolomitic
Pulv. limestone, high Ca
Pulv. limestone, dolomitic
Hydrated lime, high Ca
Hydrated lime, dolomitic
Pebble lime, high Ca
Pebble lime, dolomitic
Pulv. quicklime, high Ca
Pulv. quicklime, dolomitic
Sodium bicarbonate
Soda ash
Caustic soda (50%)
Ammonia (anhyd.)
Magnesium oxide
Relative
Cost per
Pound
Alkali*
1.16
1.00
1 .59
1 .37
3.06
2.50
Relative Weight Alkali
Required Per Pound Acid
H2S04
no
94
no
94
79
65
2.07 ' 60
1.87
2.18
1.97
20.65
13.08
9.96
5.90
3.90
54
60
54
173
119
164
35
42
HC1
148
127
148
127
107
87
80
73
80
73
233
160
220
47
56
H3P04
165
141
165
141
119
98
90
81
90
81
260
179
246
53
63
Relative Cost
Per Pound Acid
H2S04
128
94
175
129
242
162
124
101
131
106
3570
1560
1630
207
164
HC1
172
127
235
174
327
217
166
136
174
144
4810
2090
2190
277
218
H3P04
191
141
262
193
364
245
186
151
196
159
5360
2340
2450
313
246
Delivered cost including freight.
86
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manufacturing industry, but also demineralizes most waste waters by
precipitating calcium salts. This then produces a solid waste which may
be disposed of by landfilling.
The effectiveness of the control specified in the preceding paragraphs
is summarized in table 13 for four plants (TVA, 181, 028 and 159). Data
for plants 028 and 159 were taken from tables 1U and 15 which include a
complete analysis on the intake and effluent waters.
Removal of Anions (Except Chlorides) From Acidic Wastes
Neutralization of acid waste waters with lime also precipitates the
calcium salts of all acid wastes in this industry (with the exception of
hydrochloric acid from PC13 and POC13_ manufacture) . This treatment is
widespread throughout the phosphate manufacturing industry, and
represents a class of treatment technology which has widespread
validation and demonstration on plant-scale installations.
Other technologies for removing dissolved solids (except chlorides) are
also presented in this section, with a somewhat lesser degree of full-
scale validation than lime treatment.
Treatment of Acidic Fluoride Wastes
Acidic fluoride wastes are generated by the phosphorus production
segment of the industry and by the defluorination of wetprocess acid in
the manufacture of animal-feed grade calcium phosphates. These waste
waters containing large guantities of hydrofluoric, fluosilicic and
silicic acids are neutralized with lime (which breaks down H2SiF6 at
high pH) to precipitate calcium fluoride and gelatinous hydrated silica.
Lime treatment is standard operating technology at Plants 128, 159, 181
and 182.
Like lime treatment of phosphoric acid, lime treatment of acidic
fluoride wastes is enhanced by the decreased solubility of CaF2 at high
pH:
2H2O
CaF2(s) >Ca + 2F >Ca + 20H + 2HF
The eguilibrium is driven to the far left by the addition of excess
lime. The theoretical solubility of CaF2 may be calcined in much the
same manner as outlined for Ca3(PO4)2» using the ionization constant of
HF and the pure water solubility data for CaFJ2.
There has been recent commercial interest in recovering the fluoride
values in acidic waste waters. Two commercial processes have been
87
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TABLE
13
Summary of Control & Treatment Techniques at Phosphorus-
Producing Plants
(For Process Waters Other Than Phossy Water)
Raw Waste Loads (from
Sec. V)
Kg/Kkg
Ih /ton
Waste Discharged, Kg/Kkg:
TVA
Plant 181
Plant 028 (Net)
Plant 159 (Gross)
Waste Discharged, Ib /ton:
TVA
Plant 181
Plant 028 (Net)
Plant 159 (Gross)
Control & Treatment Effi-
ciency, Per Cent:
TVA
Plant 181
Plant 028
Plant 159
TSS
42.5
85
0
0
0.5
0.5
0
0
1
1
100
100
99
99
Total
Acidity
(Alkal-
inity)
54.5
109
0
0
1
(12)
0
0
3
(24)
100
100
-
-
TDS
-
-
0
0
4
22
0
0
9
45
100
100
-
.
Fluoride
53.5
107
0
0
0.1
0.04
0
0
0.2
0.07
100
100
99+
99+
Sulfate
111
222
0
0
2
3
0
0
4
7
100
100
98
97
Total
Phosphate
25
50
0
0
0.2
0.8
0
0
0.4
1.6
100
100
99
97
88
-------
TABLE 14 - Effluent from Riant 028 (Discharge No. 001)
Effluent Flowrate = 103-200 1/kkg (24,700 gal/ton)
Notes; 1. This Discharge is from Cooling Water and Dust Collector Water.
2. There is Zero Discharge of Phossy Water and Calciner Scrubber
Water
Constituent
pH
Turbidity
Conductivity
TSS
TDS
Alkalinity
CaC03
Acidity
Chloride
Fluoride
Sulfate
COD
Total
Hardness
Total
Phosphate
Ortho
Phosphate
Water & Wastewater Analysis
Units
-
FTU
ymhos
cm
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
S04
mg/1
mg/1
mg/1
P04
mg/1
P04
Intake
-
26
359
15
160
116
-
<0.1
0.19
6.4
2.0
116.7
1.2
1.2
Effluent
Plant
Data
7.3-9.5
32
408
15
202
110
-
4.1
1.14
13.8
53.5
129.7
2.4
2.4
Effluent
Ind.
Data
7.55
30
300
20
176
130
-
8
0.87
26
25
160
2.9
Net Effluent
Qty Kg/Kkg
Plant
Data
-
-
-
-
4 '
(-D
-
0.4
0.10
0.8
5.3
1
0.12
0.12
Inde-
pendent
Data
-
-
-
0.5
2
1
-
0.8
0.07
2.1
2.4
4
0.18
Net Effluent
Qty Lb /ton
Plant
Data
-
-
-
0
9
(-1)
-
0.9
0.20
1.5
10.6
3
0.25
0.25
Inde-
pendent
Data
-
-
-
1
3
3
-
1.6
0.14
4.1
4.8
8
0.35
89
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TABLE 15
Effluent from Plant 159
Notes: 1. There is Zero Discharge of Phossy Water
2. These data are Plant Data, Not Independently Verified
Effluent Flowrate = 36,100 1/kkg (8,640 gal/tori)
Constituent
PH
Turbidity
Conductivity
TSS
TDS
CaOh
Alkalinity
CaC03
Acidity
Chloride
Fluoride
Sulfate
COD
Total
Hardness
Total
Phosphate
Ortho
Phosphate
Water & Waste-
water Analysis
Units
_
FTU
ynihos
cm
mg/1
mg/1
mg/1
•mg/1
mg/1
mg/1
mg/1
S04
mg/1
mg/1
mg/1
P04
mg/1
P04
Treated
Intake
7.5
<1
966
11
617
358
-
50
0.84
91.5
-
465
18.0
15.9
Effluent
8.0-8.5
11
898
15
620
323
-
53
1.01
90.0
6
468
22.4
19.3
Gross Effluent
Quantity
Kg/kkg
_
-
-
0.54
22.4
11.7
-
1.9
0.04
3.2
-
16.9
0.8
0.7
Ib /ton
-
-
-
1.08
44.8
23.4
-
3.8
0.07
6.5
0.2
33.8
1.6
1.4
Net Effluent
Quantity
Kg/kkg
~
-
-
0.14
0.11
(-1.3)
-
0.11
0.0061
(-0.054)
0.22
0.11
0.16
0.12
Ib /ton
_
-
-
0.29
0.22
(-2.6)
-
0.22
0.0122
(-0.108)
0.43
0.22
0.32
0.24
90
-------
developed to manufacture hydrofluoric acid, and one to manufacture
synthetic cryolite for the aluminum industry.
Removal of Suspended Solids
The raw waste streams from the phosphorus-producing segment and from the
phosphate subcategory of the industry contain considerable quantities of
suspended solids. Moreover, the chemical treatment of acidic wastes
described in the previous section produced in many instances, additional
suspended solids.
To facilitate settling of suspended solids, large quiet settling ponds
and vessels are needed. Settling ponds are the foremost industrial
treatment for removing suspended solids. They are in use at Plants 006,
028, 119, 159, 181 and 182. Removal of suspended solids generates a
solid waste effluent which must be disposed of by landfilling.
The size and number of settling ponds differ widely depending on the
settling functions required. Waste streams with small suspended solids
loads and fast settling characteristics can be cleared up in one or two
small ponds; others with heavier suspended solids loads and/or slower
settling rate may require 5 to 10 large ponds. Most settling ponds are
unlined, but the technology exists for lined ponds.
Although not as widely used as settling ponds, tanks and vessels are
also employed for removal of suspended solids in the phosphate
manufacturing industry. They are in use at TVA (Muscle Shoals, Alabama)
and at Plants 003, 006, 028 and 159.
Commercially these units are listed as clarifiers or thickeners
depending on whether they are light or heavy duty. They also have
internal baffles, compartments, sweeps and other directing and
segregating mechanisms to provide more efficient performance. This
feature plus the positive containment and control and reduced rainfall
influence (smaller area compared to ponds) should lead to increasing use
of vessels and tanks in the future, especially where a plant is short of
available land for settling ponds.
Filtration eguipment, such as plate-and-frame pressure filters, pressure
or vacuum leaf filters, rotary vacuum filters, and pressure tubular
filters, has been widely used in the chemical and waste treatment field
for many years. The batch-type filters find most use in polishing
applications, to completely remove small quantities of suspended solids,
since the labor-intensive blowdown operation is dependent upon cake
volume. These filtrations are common for collection of undesirable
solid wastes, such as arsenic sulfide from food-grade phosphoric acid.
Continuous rotary vacuum filters find general applicability in
dewatering sludges with high concentrations of solids. Sand-bed
filtration also finds increasingly-widespread use.
91
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Filtration is in use at Plants 006, 075 and 119 in this industry. In
general, filtration is not economically attractive for huge quantities
of waste water (except for sand-bed filtration). It is usually preceded
by a gravity thickening operation so that it treats the thickened sludge
which is only a small volumetric percentage of the total waste water
flow.
Centrifugation, in use at Plant 003 and at the TVA installation, is an
alternate means for mechnical dewatering of relatively low flow rate
sludges, and has made major recent inroads into the domestic waste water
treatment field. The continuous solid-bowl centrifuge, as its name
implies, provides for continuous removal of the cake, and its design
reaches a compromise between solids recovery and cake dryness. The
basket solid-bowl centrifuge, on the other hand, discharges cake
intermittently, and the dewatering and cake-drying portions of the cycle
may be separately controlled. Perforated-bowl centrifuges are really
centrifugal filters. The solid-bowl machines offer the significant
advantage over filters that blinding of a medium is removed as a problem
area.
Dewatering of Lime-Precipitated Phosphates
Although (as previously discussed) lime can be used to effectively
precipitate phosphates from solution to reduce the concentration to 0.3
mg/1 or less (as PO.4) , the lime-precipitated phosphates do not dewater
readily, but form a water-trapping gel structure. After 24 hours of
settling, clarified effluents still may have 15 to 50 mg/1 of suspended
solids. This can be significantly improved by increasing the detention
time to 7 days, but the suspended solids content may still be 5 mg/1 or
greater. In the phosphate manufacturing industry, settling ponds with 7
days or longer detention times (equivalent to an overflow rate of 420
lpd/m2 (10 gpd/ft2) at a nominal depth of 3m (10 ft) are used. It has
been reported that the settling characteristics are strongly dependent
upon the initial concentration of phosphate ion. An initial
concentration of 75,000 mg/1 resulted in a compacted settled slurry
density 3 to 5 times higher than if the initial concentration was 1,500
mg/1.
Where sufficient land area for large settling ponds is not available,
average removal efficiencies of 80 to 95 per cent have been obtained
with mechanically raked gravity thickeners. A typical thickener design
has a 2-hour detention time and an overflow rate of 42,000 lpd/m« (1,000
gpd/ft2) .
Synthetic organic, water-soluble, high molecular weight polyelectrolytes
have achieved great success in flocculation and clarification and in
sludge conditioning prior to centrifugation or filtration. A polymer
dosage of 0.05 kg per kkg of dry sludge solids (0.1 Ib/ton), or about 1
mg/1 of a 2 per cent slurry, may achieve 85 per cent removal of
92
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suspended solids at a detention time of 2 hours, with a 12 per cent
solids content in the thickened sludqe. If this thickened sludge were
then vacuum-filtered, a cake of 30 per cent solids could be obtained
with a solids content in the filtrate of 0.5 mg/1 of less.
The following may be a typical performance chart for an influent sludge
containing 100 liters of water:
Influent Thickener Thickener Filter Filtrate
Qyerflow_ Underflow Cake
Water, Liters 100 84 16 5.1 10.9
Suspended Solids,Kg 2.56 0.38 2.18 2.18 5 x 10-6
Suspended Solids 2.5% 0.45% 12% 30% 0.5
Concentration
The dewatered cake, containing 85 per cent of the original solids, may
be landfilled. The filtrate, when combined with the thickener overflow,
would consist of 95 per cent of the original water quantity and would
have a suspended solids concentration of 4,000 mg/1.
A much clearer effluent could be obtained, of course, if all of the
influent waste water were directly filtered. Such is the practice at
Plant 006, which achieves an average phosphate removal efficiency of 95
per cent.
Mechanical dewatering of lime-precipitated phosphates by centrifugation
was attempted, but it proved unsuccessful because the highly thixotropic
cake plugged the solids-removal screw.
Because an excess of lime is used in the precipitation of the
phosphates, the effluent from the ponds or from mechanical thickening
and dewatering would have a high pHr typically 10 to 11. This effluent
could be partially carbonated (with CO2) to reduce the pH to 8.0 to 8.5
prior to discharge, with another filtration step to remove the calcium
carbonate precipitate. Alternately, it has been shown that subsequent
activated sludge treatment of high-pH waste water at municipal treatment
plants lower the pH due to biologically-released CO2 from the oxidation
of organic material.
Treatment Alternatives
There were two treatment alternatives considered for this subcategory.
The first alternative is the treatment currently employed by 90 percent
of the industry. This includes complete recycle of phossy water,
evaporation of some process water, lime treatment, and sedimentation of
the remaining water prior to discharge. The second alternative
practiced by 10 percent of the industry involved 100 percent recycle of
all process water.
93
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TREATMENT OF WASTE WATERS IN THE PHOSPHORUS CONSUMING SUBCATEGORY
Control and Treatment of Phossy water at Phosphorus Producinq Plants
Because of harmful effects of elemental phosphorus in small
concentrations in waste water, and because complete removal of the
phosphorus from the water is not practical,, it is univeral practice at
phosphorus-producinq plants to reuse the phossy water after treatment
(which is required to removed other constituents in the waste water
which would otherwise build up to concentration).
Barber(5) discusses several methods tried experimentally to remove
elemental phosphorus from phossy water. Amonq these methods were
chlorination, which was tried more than 20 years aqo and which was
discarded at that time because "accurate chlorinator control was found
to be impractical". With the development of chlorine analyzer-
controllers for municipal waste water treatment, however, it appears
that chlorination deserves another trial. Air-oxidation was attempted,
but the reaction was far from complete, leavinq 14 to 37 per cent of the
original colloidal phosphorus unoxidized. Filtration of the colloidal
phosphorus was investigated but found impractical. As a result of these
discouraqinq results, the industry has adopted the route of containment
and reuse rather than treatment and discharge.
At the TVA Muscle Shoals plant, a commercial flocculant, at a
concentration of 40 mg/1, is employed to settle both the phosphorus and
the suspended solids. Using a clarifier, the system removes 92 to 93
per cent of both the phosphorus and the suspended solids as the
phosphorus sludge underflow (which is only 2 per cent of the waste water
volume). The presence of suspended solids is necessary for efficient
removal by this method.
The underflow from the clarifier may be treated as other phosphorus muds
or sludges are treated. The sludqe may be qravity thickened and/or
dewatered by centrifugation or filtration. The sludge, thickened
sludge, or sludge cake (with respectively lower moisture contents) may
then be heat-dried in an inert atmosphere using the process byproduct
carbon monoxide as fuel. Elemental phosphorus (nominally 40 to 65 per
cent of the "solids" in the sludge) are recovered. The remaining non-
volatile solids contain no elemental phosphorus and can be safely
disposed of or recycled to the feed preparation section of the
phosphorus manufacturing plant.
The clarifier overflow, containing only 7 or 8 per cent of the original
phosphorus and suspended solids, may then be recirculated to the
phosphorus condenser sump and to other areas where water contacts
phosphorus. However, because the phossy water accumulates dissolved
salts (mainly fluorides and phosphates, see Table 7), about 6 per cent
of the clarified water must be bled off and discharged. In addition to
-------
suspended solids and dissolved solids, this bleed contains 120 mg/1 of
elemental phosphorus, equivalent to 0.4 kg/kkg, or 0.08 pound per ton,
of product.
At Plant 181, a different approach is taken towards phossy water wastes.
Very large lagoons not only reduce the concentration of suspended solids
in the phossy water, but also serve to slowly oxidize much of the
elemental phosphorus to phosphates. Subsequent lime treatment of the
lagoon overflow (after combining with other waste water streams)
precipitates not only the phosphates but also the fluorides in the
water, thereby reducing the quantity of dissolved salts so that the
water may be reused without a bleed. At this plant, the waste streams
may be combined since all wastes are recycled without discharge.
A slightly different approach is taken at Plant 128. The phossy water
is combined in a closed treatment and recycle system with calciner
scrubber liquor. After settling of suspended solids and partial
oxidation of phosphorus in a pond, lime treatment is used to precipitate
dissolved phosphates and fluorides. Upon subsequent settling, the
clarified (but still phossy) water is reused as calciner scrubbing
water. Fresh makeup is used for the phosphorus condenser. The key to
this scheme, which results in zero discharge of phossy water, is that
the quantity of water vaporized in the calciner scrubber (in cooling the
calciner tail gases) exceeds the quantity of phossy water in the raw
waste load, so that fresh water may be continuously added to the loop
without discharging any contaminated water.
Plant 159 achieves zero discharge of phossy water in a rather unique
system. The completely segregated raw waste phossy water is sent to a
clarifier in a manner similar to the TVA technique described above. The
clarifier underflow of phosphorus sludge is treated in conventional
ways, with complete return of the material to the process. The overflow
from the clarifier is not recycled (as is the TVA practice, which
requires a bleed discharge); but is sent to an evaporation pond.
In the approaches used by Plants 028 and 159, some or all of the phossy
water is evaporated. This presents no hazard of elemental phosphorus,
since it is very rapidly oxidized to phosphate as soon as the protective
water is removed.
In summary, this study found three different ways that existing plants
are achieving zero discharge of phossy water.
Treatment of Arsenic-Rich Residues
Arsenic-rich solid residues accumulate from the purification of
phosphoric acid and of phosphorus pentasulfide. The common disposal
method is burial in a controlled area, as practiced at Plants 075, 119,
147 and 192.
95
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The arsenic-rich liquid residue from the PC13 distillation is more
difficult to dispose of. At Plant 037, this residue is first treated
with trichloroethylene, in which PC13 is miscible but AsCl3_ is not. The
trichloroethylene is then water-washed to remove the arsenic-free PCI3
and the trichloroethylene is reused. The Asd3-rich residue is then
segregated and stored in drums for final disposal in an environmentally
safe manner.
Treatment of Phosphoric Acid Wastes
The standard treatment of these wastes is by neutralization and/ or
precipitation with lime as discussed for the phosphorus production
subcategory. the final product of neutralization in an excess of lime
and in a considerable excess of water, is formed:
6 H3P04 + 10 Ca(OH)2->9 CaO. 3 P205.Ca(OH)2 + 18 H2O
Although this material is very insoluble, the reaction does not proceed
to completion in practice unless a Ca/P mole ratio of at least 1.9 is
reached. Moreover, the reactivity of the lime in precipitating the
dissolved phosphate is strongly dependent upon the lime source and the
slaking conditions. It has been found that freshly-slaked pebble
quicklime can precipitate in excess of 97 per cent of the phosphate,
whereas commercial hydrated lime (calcium hydroxide) or freshly-slaked
ground quicklime only succeeded in a 73 to 80 per cent precipitation
efficiency under the same conditions.
A large body of literature has been developed in the lime treatment of
domestic waste waters for phosphate removal. The study performed by
Black & Veatch for EPA (31) summarizes the efforts that have been
sufficiently demonstrated to be applied to current municipal waste water
treatment projects. It is pointed out that the average concentration in
domestic raw waste water is about 10 mg/1 (expressed as elemental
phosphorus). The domestic sources are about 1.6 kg (3.5 Ibs) per capita
per year, one-third of which are from human excretions and two-thirds
from synthetic detergents.
The existing practice achieves better than 90 per cent removal of the
phosphates from domestic waste water, reducing the concentration
(expressed as PO.4) from 30 mg/1 to as low as 0.3 mg/1. At first glance,
this seems to conflict ,with the fact that tricalcium phosphate (or
hydroxylapatite) has a solubility of 25 mg/1 (equivalent to 15 mg/1 as
PO.4) . However, in a large excess of lime, the pH is sufficiently high
(10 to 11) to reduce the solubility of this salt of a strong base and
weak acid. The equilibrium -
2H20
Ca+3 (P04)2 (s) >3Ca+2 + po4~3 >3Ca*2 + 20H~ + 2HPO4-2
96
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is driven to the far left (reducing phosphate solubility) by the
addition of excess lime. The solubility of tricalcium phosphate may be
theoretically calculated as a function of pH (or of Ca:P ratio) using
the ionization constants for H3PCW, H2PO.41, and HPO.42 in conjunction
with a solubility product for tricalcium phosphate (which may be
calculated from solubility data in pure water).
This phenomenon, substantiated by full-scale operating data as reported
by Black & Veatch(31), is summarized below:
Phosphate Concentration of
pH Filtered Effluent, mg/1
9.0 5.7
9.5 l.ii
10.0 0.6
10.5 0.3
11.0 0.2
The literature is replete with details of technology to achieve high
removal efficiencies.(31-42) For example, thickened sludge recirculation
to the neutralization tank has been found to seed the precipitation of
calcium phosphate, resulting not only in better removal of dissolved
phosphates but also in the growth of larger crystals for easier
dewatering.
Although lime treatment of phosphates has been the predominant route,
ferric chloride and alum have also been extensively used. Ferric salts
are most effective in the 4 to 5 pH range and aluminum salts are most
effective in the 5 to 6 pH range, as opposed to the 10 to 11 range for
lime. The mole ratio of Fe/P or Al/P should be around 2.0, the same as
the Ca/P ratio with lime treatment.
The use of lanthanum salts has recently been demonstrated to more
effectively precipitate phosphates over a much wider pH range than
calcium, ferric, or aluminum. The drawback is cost; the treatment
system must recover and reuse the lanthanum.
Another process for phosphate removal is adsorption by activated alumina
with subsequent stripping with caustic acid then regeneration of
phosphate-free caustic by lime precipitation. Ion exchange has also
been investigated.
One interesting process for phosphate removal is borrowed from a
commercial process for HCl acidulation of phosphate rock. Phosphoric
acid is recovered by solvent extraction, using C4 and C5 primary
alcohols such as n-butanol and isoamyl alcohol. The chloride-free
phosphoric acid is then extracted from the organic phase by water
97
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washing, the solvent is recycled, and the pure phosphoric acid may be
concentrated by evaporation of water. This treatment method appears
attractive for application to the food-qrade calcium phosphate waste
streams. The suspended solids may be dissolved by HCl addition, and
solvent extraction may be used to regenerate phosphoric acid for return
to the process.
Treatment of Acidic Sulfite, Sulfate, and Phosphate Wastes
These acids are components of the waste streams from the phosphorus-
consuming subcategory of the industry; and sulfuric acid is also a
constituent of the wastes from the phosphorus-production segment. The
sulfurous and phosphorus acids may be partially oxidized prior to
treatment to sulfuric and phosphoric acids.
The neutralization and precipitation of the slightly soluble calcium
salts is exactly comparable to the treatment of acidic phosphate and
fluoride wastes. The solubilities of calcium sulfite and of calcium
phosphite are repressed by excess lime as in the previously-discussed
cases, but the solubility of calcium sulfate (a salt of a strong base
and a strong acid) is not affected by pH.
Removal of Chlorides
Ion Exchange and Demineralization
Ion exchange and demineralizations are usually restricted in both
practice and costs to total dissolved solids levels of 1000 to UOOO mg/1
or less.
An ion exchange may be simply defined as an insoluble solid electrolyte
which undergoes exchange reactions with the ions in solution. An
exchanger is composed of three components: an inert matrix, a polar
group carrying a charge and an exchangeable ion carrying an opposite
charge. The inert matrix is usually cross-linked polymeric resin
containing the needed polar groups.
There are two types of ion exchangers: cation and anion. Cation
exchangers contain a group such as sulfonic or carboxylic acid. These
can react with salts to give products such as the following:
RSO3H + NaCl £ RSO3Na * HCl
RCO2H + NaCl £ RCO2Na + HCl
The above reactions are reversible and can be regenerated with acid.
Anion exchangers use basic group such as the amino family.
98
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RNa30H + NaCl £ RNa3Cl + NaOH
This is also a reversible reaction and can be regenerated with alkalies.
The combination of water treatment with both cation and anion exchangers
removes the dissolved solids and is known as demineralization (or
deionization). The quality of demineralized water is excellent. Table
16 gives the level of total dissolved solids that is achieved. Special
ion exchange systems have been developed for treating high dissolved
solids content(more than 1000 mg/liter total dissolved solids),
minimizing regenerant chemicals costs.
Reverse Osmosis
The phenomenon of osmosis has its explanation in thermodynamic
equilibrium and free energy concepts. Essentially, when a semipermeable
membrane separates a pure liquid and solution of dissolved material in
the same liquid there is a net migration of the pure liquid to the
solution, driven by the free energy difference between the two sides of
the membrane. Equilibrium is reached only when the liquids on each side
of the membrane are of the same composition or sufficient additional
pressure is applied on the solution side of the membrane to
counterbalance the osmotic driving force. Application of additional
pressure on the solution side reverses the direction of osmotic flow
through the membrane and results in concentration of the solution and
migration of additional pure liquid to the pure liquid side. This is
reverse osmosis. It may be looked at as pressure filtration through a
molecular pore-sized filter.
The small pore size of the reverse osmosis membrane is both its strength
and its weakness. Its strength comes from the molecular separations
that it can achieve. Its weakness comes from the criticalness it has to
blinding, plugging, and chemical attack. Acidity, suspended solids,
precipitations, coatings, dirt, organics and other substances can make
it inoperative. Membrane life is critical and unknown in many mediums.
99
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TABLE 16 Water Quality Produced by
Various Ion Exchanqe Systems
Exchancjer_ Setup.
Strong acid cation
+ weak-base anion
Stronq-acid cation
* weak-base anion
«• strong-base anion
Stronq-acid cation
+ weak-base anion
+ strong-acid
cation + strong-
base anion
Mixed bed (stronq-
acid cation +
strong-base anion)
Mixed bed + first
or second setup
above
Similar setup as
immediately above
+ continuous re-
circulation
Residual
Silica,
mg/1
No silica
removal
0.01-0.1
0.01-0.1
0.01-0.1
0.05
0.01
Specific
Residual Resistance
Electrolytes, ohm-cm
mg/1 B 25 C
3 500,000
3 100,000
0.15-1.5 1,000,000
0.5
1-2,000,000
0.1 3-12,000,000
0.5
18,000,000
100
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With these restrictions there is little wonder that its industrial
applications are few. Fortunately, the phosphorus chemicals in-
dustry water purification needs are similar to those of the areas
where reverse osmosis has been shown to be applicable — treat-
ment of brackish water and low (500 mq/1 to 20,000 mq/1) dissolved
solids removal. Organics are usually absent, suspended solids
are low and can be made low rather easily, acidity is easily
adjusted, and the dissolved solids are similar to those in brack-
ish water — sodium chlorides, sulfates and their calcium counter-
parts.
Evaporation Ponds
Plant 159 utilizes an evaporation pond for disposal of phossy
water from phosphorus manufacturing. They may also be reason-
ably used for other waste water disposal where the waste water
quantities are not overwhelming.
The size of an evaporation pond depends upon the climatic diff-
erential between evaporation and rainfall:
Evaporation-Rainfall
Differential Pond Area
0.6 m/yr (2 ft/yr) 0.060 ha/cu m/day (560 acres/MGD)
1.2 m/yr (4 ft/yr) 0.030 ha/cu m/day (280 acres/MGD)
1.8 m/yr (6 ft/yr) 0.020 ha/cu m/day (190 acres/MGD)
Evaporation ponds may be either unlined or lined, and should be diked.
Use is often made of natural pits, valleys or ponds.
Conventional evaporation ponds are not, of course, among the useful
treatments in areas where the rainfall exceeds the evaporation.
However, surface aerators (commonly used for aerated lagoons in
secondary treatment of organic wastes) can significantly increase the
evaporation from a pond by increasing the water/air surface area.
Single-Effect and Multiple-Effect Evaporators
For the treatment of small waste streams, single-effect evaporators are
characterized by low equipment costs and by inherent reliability, at the
expense of high steam requirements. Conventional multiple-effect
evaporators, with 2 to 6 effects, have somewhat hiqher capital costs,
but require much less steam.
Evaporation is a technology, of course, that is aptly demonstrated
throughout the chemicals process industry (although not extensively for
101
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the sole purpose of waste treatment), and as such meets the requirements
of beinq currently available.
Refriqerated Condensers for PC 13 and POC13
In the standard processes for manufacturinq PC13 and POC13, the present
industry practice is to use water-cooled condensers to reflux the
reaction vapors and to collect the product. Because the vapor pressure
of PC13 is siqnificantly hiqh (boilinq point 76°C (169°F)) at normal
condensinq temperatures, the raw waste load in the tail-qas water
scrubbers contain rather larqe quantities of the hydrolysis products of
PC 13.. The use of refriqerated condensers in place of the water-cooled
condensers; or alternately, the use of cold traps downstream of the
water-cooled condensers; would drastically reduce the amount of PC13_ in
the tail qas which subsequently becomes acid aqueous wastes:
PC13 Vapor Pressure,
Temperature, °C Temperature^ °F nJ2J_Hc[.J£7)
-40 -40 3
-20 - 4 13
0 32 38
+20 68 99
+40 104 235
It is apparent that a condensinq temperature below -20°C (-4°F) would
lower the PC13 vapor pressure by an order of maqnitude over normal
condensinq temperatures, and would virtually double the temperature
drivinq force for heat transfer.
Refriqerated condensers are in current use (for POC13 manufacture usinq
air oxidation) at Plant 037.
Inert-Atmosphere Castinq of P2S.5
The present industry practice is to cast molten P2SJ5 product into
shippinq containers or into conical forms. When molten P2S5 is exposed
to the atmosphere, it spontaneously iqnites, forminq P2O5 and SO2 which
are subsequently water-scrubbed.
There are various state-of-the-art techniques available for castinq
either in an inert atmosphere or in vacuum, to eliminate this source of
raw aqueous waste.
Treatment Alternatives
The treatment alternatives considered for the manufacture of phosphoric
acid are first no addition treatment (the only discharqes are from leaks
and spills) and no discharqe of any process waste water pollutants to
102
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navigable water?. The latter alternative involves tightened
housekeeping and maintenance construction of dikes and dams around
pumps, valves, and tanks; construction of sumps and sump pumps; lime
treatment of leaks and spills; and landfill of the sludge. This is
currently practiced by 10 percent of the industry.
There were two treatment alternatives considered for the manufacture of
phosphorus pentoxide: no additional treatment and no process waste water
discharge.
Three treatment alternatives were considered for the manufacture of
phosphorus pentasulfide. The first involves no additional treatment.
The second includes reduction of the volume of waste water discharge by
the recycle of scrubber water. The third alternative includes no waste
water discharge, lime treatment, settling tanks, recycle of tank
overflow back to the process, and landfill of sludge.
Several treatment alternatives were considered for the manufacture of
phosphorus trichloride and phosphorus oxychloride. The first
alternative is no treatment. The second involves reduction of waste
water volume by recycle of scrubber water. The third alternative
includes lime treatment, settling tanks, and landfilling of sludge. The
fourth alternative involves no discharge of process waste water
pollutants to navigable waters.
103
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TREATMENT OF WASTE WATERS IN THE PHOSPHATE SUECATEGORY
Treatment of Specific Wastes
Sodium Tripolyphosphate Manufacture
As stated in section V, three notable plants (006, 042 and 119) achieve
no discharge of porcess waste waters. Airborne solids collected in dust
collectors from the spray dryer gaseous effluent stream are added to the
product. Scrubber water is used to form a slurry with caustic in the
initial process neutralization step.
The manufacture of sodium tripolyphosphate is therefore a water
consuming process, requiring no waste water treatment.
Calcium Phosphates Manufacture
The amount of airborne solid wastes removed by wet scrubbers can be
minimized by preceding wet scrubbers with dry dust collection equipment.
Treatment of phosphoric acid, suspended solids and sludges resulting
from wet scrubbing has been previously described for the phosphorus
production subcategory.
Wet phosphoric acid is frequently used for animal feed grade phosphates.
Fluosilicic, hydrofluoric and silicic acid wastes will subsequently
result from acid defluorination. Treatment of these parameters has also
been discussed previously for the phosphorus production subcategory.
Treatment Alternatives
The only treatment alternative considered for the manufacture of sodium
tripolyphosphate is no discharge of process waste water pollutants.
This is essentially accomplished by all of this industry through dry
dust collection and return of scrubber water to the system.
Two treatment alternatives were considered for the manufacture of feed
grade dicalcium phosphate. The first, employed by at least 50 percent
of the industry, involves in-process controls for phosphate and lime
dusts and phosphoric acid mists. The second alternative inlcudes the
above plus lime treatment settling, and recycle of clarified water to
the acid scrubbers and landfill of the sludge.
Three treatment alternatives were considered for the manufacture food
grade dicalcium phosphate. No treatment is the first alternative. In
the second alternative baghouses replace wet scrubbers with product
recovery. Approximately 30 percent of the industry is practicing this
technology. In the third alternative waste water is treated with lime,
filtered, and recycled in the process. The filter cake is landfilled.
104
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Approximately 10 percent of the industry is achieving no discharge of
process water pollutants by this technology.
105
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-------
SECTION VIII
COSTS, ENERGY AND NON-WATER QUALITY ASPECTS
INTRODUCTION
The control and treatment technologies applicable to the raw wastes of
the phosphate manufacturing industry were discussed in Section VII of
this report. In this Section, each of these technologies is reviewed
from the following standpoints:
* The cost of applying the technology.
* The energy demands of the technology.
* The impact of the technology upon air guality, solid
waste management, noise and radiation.
* The recovery and subseguent use of process materials
from raw waste streams, as a result of applying the
technology.
A representative hypothetical plant for each chemical produced in the
industry is synthesized. Cost-effectiveness data for the plant for the
various treatment alternatives (see table 17) appear as table 18. The
cost is in terms of both investment cost and eguivalent annual cost, and
the effectiveness in terms of pollutant guantities is compared to the
raw waste load. The discussion of costs and benefits in this Section,
however, is formulated to be more generally useful in evaluating the
economics for any particular plant within the industry. Costs for a
specific plant may be significantly influenced by the following factors
which cannot all be incorporated into a single hypothetical plant:
The degree of freedom, which personnel of each plant must
retain, to choose among the alternative control and treat-
ment technologies presented in Section VII, to choose
from technologies not presented in this report, and to
choose any combination or permutation of these technologies.
The cost tradeoffs, which are unigue for each plant, be-
tween in-process controls and end-of-process treatments;
with material recovery being an important parameter.
The real raw waste load for each plant, which may be app-
reciably different (in either direction) from the standard
raw waste loads as presented in Section V. In particular,
much greater plant-to-plant variability was observed
with respect to production-normalized raw waste water
guantities than with respect to production-ion-normal-
ized raw quantities of polluting constituents.
107
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TABLE 17
TREATMENT ALTERNATIVES
Subcategory
Phosphorus
Producing
Phosphorus
Consuming
Phosphate
Producing
Chemical
PA (Fe2p)
H3POA
• P2°5
P2S5
PCI 3
POC13
*sW>zo
CaHPOA
CaHP04
Feed grade
Alternative
A
B
A
B
A
B
A
B
C
A
B
C
D
A
B
C
D
A
A
B
A
B
Description
Existing control complete recycle of phossy water. Evaporation of some other process water.
Lime treatment and sedimentation of remaining process water prior to discharge.
Piping, pumping, and controls for 100% recycle of process wastewaters.
No treatment. (Only wastewaters orginate from leaks, spills, etc.)
Tighten housekeeping and maintenance. Dike and dam around pumps, valves,, tanks, etc.
Provide sumps and sump pumps. Treat with lime and landfill the sludge.
No treatment.
Lime treatment, settling tank, recycle of tank overflow back to process, and landfill sludge.
No treatment.
Recycle scrubber water.
Lime treatment, settling tank, recycle tank overflow back to process, landfill sludge + B.
No treatment.
Recycle scrubber water.
Lime treatment, settling tank and landfill sludge + B.
Evaporation + B + C.
No treatment.
Recycle scrubber water.
Lime treatment, settling tank, and landfill sludge + B.
Evaporation + B + C.
Dry dust collection already in exi stance at exemplary plant. M.ay be economically
justified on the basis of product recovery.
In-process controls for phosphate and lime dusts and for phosphoric acid mists, including
dry dust collection and scrubber water recycle to process.
Lime treatment, settling pond, recycle of clarified water to acid scrubbers, and landfill
sludge. + A.
Replace wet scrubbers with baghouses.
Lime treatment, filtration of slurry, recycle of filtrate, and landfill of filter cake + A.
o
00
-------
TABLE 18
TREATMENT ALTERNATIVES
COST - EFFLUENT QUALITY COMPARISON
Chemical Treatment * Industry Investment Annual Cost Wastewater TSS TDS Acidity F SO;, P04
Alternative Using $1,000 Operating Per Units 1/Kkg Kg/Kkg Kg/Kkg Kg/Kkg Kg/Kkg Kg/Kkg Kg/KKg H3P04S, H3POA H2S03 HC1 HF,H2SiF6 pH
Alternative Costs $/Kkg H3P03 H,Si03
$1,000 Kg/Kkg Kg/Kkg Kg/Kkg Kg/kkg Kg/Kkg
p
p/,
4
P
H3P04
P205
P2s5
PC13
POC13
p
Na5P3Olo
CaHP04
(Feed Grade)
CaHP04
(Food Grade)
Subcategory
Raw Waste
A
B
.
90
10
.
-
500
_
-
228.2
_
-
5.07
426,000 42 - 54 54
104,000 0.5 4 1.5 0.1
00 0 0 0
111 25
2 0.2
0 0
Consuming Subcategory
Raw Waste (A)
B
Raw Waste (A)
B
Raw Waste (A)
B
C
Raw Waste (A)
B
C
D
Raw Waste (A)
B
C
D
Subcategory
Raw Waste
A
Raw Waste
A
B
Raw Waste
A
B
90
10
100
0
100
0
0
100
0
0
0
100
0
0
0
_
100
_
50
50
60
30
10
95
_
20
_
12.5
49.5
_
4.2
16.5
20.5
2.2
14.2
15.9
_
A
_
A
186
-
A
33
42.9
-
9.1
_
5.6
22.8
_
1.8
8.8
18.3
1.0
6.9
10.1
_
A
_
A
91.6
-
A
97.2
0.67
-
1.54
_
0.44
1.87
_
.17
.77
1.54
.16
.94
1.38
_
A
_
A
1.54
-
A
1.65
8
0
500
0
30,000
3,000
0
5,000
500
420 0.7 5
00 0
2,500
250
210 0.2 3.5
00 0
0
0
6.700 22
6,300 22
0 0
4,200 100
2,100 50
0 0
0.2
0
0.5 1
0.5 1
0 0
2.5 3 2
2.5 3 1.5
0 0 6-10.5
00
0.5 2 2
0.5 2 1.5
0 0 6-1-.5
0 o -
4 J|
0
30
15
* Use of dry dust collection and product recovery will cover cost of this alternative, hence, no costs were listed.
-------
There is a wide variation in -the existing application of
of effluent control technology, (i.e.some plants have more
equipment to install than others in order to meet the
effluent limitations guidelines).
In addition physical characteristics of each particular
plant will affect treatment costs such as:
* Plant age, size, and degree of automation.
* Plant layout (i.e., can in-process controls
be physically installed between existing
units?).
* Plant distances and topography (i.e., what
are the installation and operating costs of
recycle technologies?).
* Climatic factors (temperature and evaporation/
rainfall).
* Esthetic factors (i.e., is a settling pond
locally acceptable?).
* Land availability (primarily a factor in
applying settling pond and evaporation pond
technologies).
The degree to which a plant is integrated with other pro-
duction departments would significantly affect the cost
of applying control and treatment technologies. Can waste
materials from one department be used in an adjoining
department (i.e., mutual neutralization of acid and alka-
line wastes)? Can common treatment facilities be built
(tradeoff between economies of scale vs. reversing the
principle of segregation of wastes)? Are the waste water
sewers from adjoining departments readily separable?
The feasibility and attractiveness of joint municipal/
industrial waste water treatment, which is a highly
local evaluation to be made. Increasingly more examples
of such dual treatment are being reported.
The local solid waste management situation. The sludges
from applying waste water treatment technologies may be
landfilled at highly different costs, depending upon
the local availability of disposal sites and the dis-
tances involved.
110
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In appreciation of all of the above factors, the discussion of costs in
this Section is formulated to be qenerally useful in evaluating the
economics for any particular plant within the industry.
Definition of Representative Plants
The sizes of the representative plants were chosen so that their
capacities were approximately the averages of the data presented in
Table 2. Although in many cases (especially in the phosphorus-consuming
segment of the industry) more than one product is made at a given
location, each product was addressed separately in this supplement.
Cost savings due to combined treatment facilities are a distinct
probability; the effect in practice would be to achieve the benefits at
costs lower than those presented in this analysis.
The particular assumptions in choosing representative plants were:
1. Phosphorus Manuf acture--The representative plant has already no
discharge of phossy water (as much of the industry has). It has, in
addition, achieved a level of effluent reduction commeasurate with that
of plant 028 (see Tables 13 and 1U, but still discharges 25,000 gallons
of treated process water per ton into a receiving stream. Technology
"A" of Table 17, therefore, represents effluent reduction, with respect
to the raw waste load, already achieved by the representative plant,
with no additional costs required. The effluent from technology "A" is
suitable for process reuse, and technology "B" is the implementation of
this recycle. For the representative plant, it was assumed that the
return water system traversed 1,000 yards back to the head end of the
plant and had a difference in elevation of 60 feet to make up. It was
also assumed that the representative plant had no severe freezing
problems.
2. Phosphoric Acid Manufacture--The representative plant had no process
water discharge (including phossy water), but had not yet performed a
systematic and thorough program for minimizing, collecting, and treating
minor phosphoric acid leaks and spills.
3. Manufacture of P2O.5/ P.2S5, PC13, and POC13—The representative
plants for these chemicals had not yet instituted any control or
treatment of acid waste waters, but have already achieved zero discharge
of phossy water. As a conservative approach for PC13 and POC13
manufacture, it was assumed that solar evaporation for technology "C" in
Table 17 was not feasible for climatic reasons so that mechanical
evaporators were necessa'ry. It was also assumed that refrigerated
condensers proved less economical than larger evaporators.
The representative plants for P.205, P2S.5, PC 13, and POC13 are assumed
not to have sufficient land for settling ponds, so that mechanically-
raked clarifiers are used.
Ill
-------
4. Sodium Tripolyphosphate Manufacture—The representative plant has
either of two situations: (a) Dry dust collection with return of solids
to the process, plus return of wet scrubber liquors to the process, has
already been installed resultinq in zero discharqe of process waste
waters. (b) The above controls have not been installed, but can be
economically justified on the basis of product recovery.
For either of these two situations (which cover much of the industry),
no additional costs (attributable to effluent reduction benefits) are
required.
5. Feed-Grade Dicalcium Phosphate Manufacture--For control of phosphate
and lime dusts and phosphoric acid mists, the representative plant has
no additional required costs (attributable to effluent reduction
benefits), for the same reasons as listed above for sodium
tripolyphosphate manufacture.
However, it is assumed that the representative plant uses wet-process
phosphoric acid and that it performs defluorination of all acid used (in
practice, a qood fraction of received acid may already be
defluorinated). It is further assumed that the representative plants
have sufficient land area for on-site settling ponds.
6. Food-Grade Calcium Phosphate Manufacture--The representative plant
is assumed to have wet scrubbers for dust-laden vent streams.
Technology "A" of Table 17 is the replacement of wet scrubbers with
baqhouses, but that the cost is justified by product recovery. It is
assumed that at this representative plant the elimination of wet
scrubbers reduces the waste load by 50 percent.
Current Selling Prices
Table 3 shows the current list prices of the chemicals within this
industry. These data are useful as a yardstick for measuring the
economic impact of achieving pollution control.
Capital Cost Basis
For these analyses, the capital investment costs have been adjusted to
1971 dollars using the Chemical Engineering Plant Cost Index (1957-59 =
100; 1971 = 132.2). The capital recovery segment of the annual costs
are based upon a 5-year amortization schedule, consistent with IRS
regulations concerning pollution-abatement equipment and facilities; and
upon an 8 percent interest rate. The resulting annual capital recovery
factor (principal and interest) is 0.25046.
"Taxes and Insurance" annual cost is estimated at 5 percent of the
investment cost. "Operating and Maintenance" annual cost includes
labor, supervision, lab support, etc., and is estimated at 15 percent of
112
-------
the investment cost, exclusive of chemicals, energy and power costs
(which are calculated directly for each appropriate case). Chemical
costs are included in "Operating and Maintenance", but power is listed
separately. The cost of lime for neutralization has been assumed at $20
per ton, and the cost of steam for evaporation has been assumed as $0.70
per thousand pounds (or $0.70 per million BTU).
In-Process Controls
The cost of these controls are perhaps the most difficult to generalize,
since they are almost wholly dependent upon the existing equipment
configuration in any particular plant.
Segregation of Waste Streams
First, a plant must be surveyed to pinpoint the sources of both process
water and non-contact cooling water. At one plant, there were a great
many points where process water entered a common sewer, but there were
relatively few cooling water sources. It was much more economical to
divert the cooling water to a new and separate collection system than to
adopt the reverse strategy. The project costs for such a retrofit would
be highly labor-intensive, especially since the construction must
proceed without unduly disrupting production schedules. Other than
capital recovery and associated annual costs, the annual costs would
consist of a small maintenance cost and no costs for operating labor,
materials or power.
There would be no effect of this project on energy demands, since plant
sewers are normally gravity-flow. There would be no adverse non-water
guality impacts of this project.
Recycle of Scrubber Water
The capital costs would be to provide a surge tank, a recycle pump, and
associated piping. The surge tank need not be large; a 15-minute
residence time should suffice. The power costs and energy use of the
pump would not greatly exceed the corresponding values presently
utilized to provide fresh scrubber water at comparable flow rates; in
any event they are small since scrubber flow rates are small.
Dry Dust Collection
Based upon data furnished by the personnel of Plant 007, the capital
cost of high-temperature baghouses for this 91 kkg/day (100 tons/day)
plant was $350,000. The annual operating and maintenance costs, other
than capital recovery, taxes and insurance, is estimated at 6 per cent
of the capital cost. A credit to the annual cost is the value of
recovered material; the quantity might be estimated as 2 to 5 per cent
of the production rate, since baghouses recover virtually all dusts.
113
-------
The power requirements for the fans and shakers are small, and are
usually comparable to the pump power requirements for the liquid
scrubbing systems they replace. Since the recovered dusts are almost
always utilized in the process, there is no adverse impact upon solid
waste management.
Refrigerated Condensers
The condensers are standard items, and in practice the existing
condensers may be used. The refrigeration supply is standard equipment,
and rather expensive in terms of capital costs. An added cost would be
the insulation of existing coolant line and of the condenser. The power
requirement for the refrigeration compressor could be moderately high.
There would be not impact upon non-water quality aspects.
Inert-Atmosphere Casting for P2S5
This is a relatively expensive control technique, requirinq major
revisions not only of the casting equipment but also of the basic
casting procedures. There would be some small power requirement either
for inert-qas blowers or for vacuum pumps. The annual cost of the inert
gas (assuming it is not recycled) must be estimated.
Housekeeping and Containment
Like the previously-discussed project of water segregation, housekeeping
and containment capital costs are labor-intensive and depend to a very
large extent upon the existing plant configuration. A point of
reference might be taken from the experience of one 360 kkg/day (UOO
tons/day) plant which expended $160,000 for isolation and containment
(trenches, sewers, pipelines, sumps, catch basins, tanks, pumps, dikes
and curbs). The need to attend to many small sources of leaks and
spills reduces the economies of scale. The power requirements are
minimal, limited to small sump pumps. No adverse non-water quality
impacts arise from this control technique.
114
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TREATMENT OF SPECIFIC WASTE CONSTITUENTS
Neutralization of Acidic Waste waters and Precipitation of
Calcium Salts
A general cost factor for neutralization is 1.3 to 5.3 cents per cu m (5
to 20 cents/1,000 gallons). However, the cost for lime is directly
dependent not upon the waste water quantity but upon the total acidity.
The data of Table 8, with a lime cost of $22/kkg ($20/ton), can be used
to calculate this cost.
Neutralization tanks are usually small, with residence time varying from
30 seconds to 30 minutes. The installed cost of these tanks may be
approximated by:
Capital Cost = $15,000 _GPD 0.2
10,000
(Note: I/day = 3.785 x GPD)
The power requirements for mixing are rather nominal. Assuming
subsequent sedimentation or other dewatering operations, the
neutralization step alone does not have any adverse non-water quality
impacts.
Treatment of Arsenic-Rich Residues
The cost of this solvent is rather nominal because the quantities of
waste involved are only a very small fraction of the production volume,
and because the solvent (trichloroethylene) is reused; despite the hiqh
unit costs which is more than 10 cents/cu m (40 cents/1,000 qal). There
is virtually no power requirement. There is,however, a very substantial
impact upon solid waste management, since the residues are extremely
objectionable and must be disposed of in special ways. The quantity
involved is 0.05 kg of AsC13 per kkg of product PC13 (0.1 Ib/ton).
Control and Treatment of Phossy Water
Control and treatment of phossy water is a universal practice at
phosphorus-producing plants. Although several different methods were
observed, every plant prevents the discharge of virtually all elemental
phosphorus. This technology is therefore so universally applied that
costs need not be estimated -the price has already been paid.
Similarly, a discussion of energy and of non-water guality aspects would
be academic.
115
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Removal of Suspended Solids
Settling Ponds
Using a detention time of 7 days and a depth of 3 m (10 ft), the
calculated overflow rate is 0.42 cu m/day/m2 (10 gpd/ft2). This is
eguivalent to 4,200 cu m/day/hectare (435,600 gpd/acre).
The capital costs for small unlined ponds, with areas from 0.4 to 2
hectares (1 to 5 acres) can be estimated as:
Capital Cost = $50,000 x Acres - $8,000 x (Acres)2
(Note: Hectares = 0.405 x Acres)
Because diking is a large portion of pond costs, and because the dike
length increases much more slowly than pond area, larger ponds are
considerably cheaper per unit area. For large unlined ponds of 40 to
1,000 hectares (100 to 2,400 acres), the capital cost is $2,500 to
$12,500 per hectare ($1,000 to $5,000 per acre).
For lined ponds, the additional installed capital cost for a 30-mil PVC
liner is $21,500 per hectare ($8,700 per acre). By using the above
overflow rate and the above pond costs per unit area, a pond cost based
on waste water flow may be calculated.
settling ponds utilize no energy. The solids, do, however, collect on
the bottom and must either be periodically removed (creating a solid
waste disposal problem); or the filled pond may be abandoned and
replaced with a new one (creating a land use problem).
Mechanically-Raked Clarifiers and Thickeners
A general cost for gravity thickening is 0 to 2.6 cents per cubic meter
(0 to 5 cents per 1,000 gallons).
The installed cost of mechanically-raked clarifiers and thickeners with
capacities of 38 to 38,000 cu m/day (0.01 to 10 MGD) can be estimated as
Capital Cost = $95,000 (MGD)0.4
(Note: Cu m/day = 3,785 x MGD)
Where polymeric flocculants are used, the additional cost amounts to $4
per kg of flocculant ($1.80/lb). The dosage rate is nominally 0.05
kg/kkg of dry sludge solids (0.1 Ib/ton).
116
-------
The power requirements are nominal, since the rake has a very lonq
period of revolution. Additional nominal power requirements arise from
sludqe pumpinq and clarifier overflow pumpinq.
This treatment has (by definition) a solid waste impact, since its
function is the removal of suspended solids. The sludqe from thickeners
may be 85 to 92 per cent moisture. If the quantities are small, this
sludqe may be directly transported to landfills. Alternately, it may be
dewatered on sand dryinq beds or mechanically (filters or centrifuqes)
to 60-70 per cent moisture before landfillinq. The quantity to be
landfilled is therefore a very stronq function of the deqree of
dewaterinq after thickeninq.
Vacuum Filtration and Centrifuqation
The costs of these two mechanical dewaterinq techniques are competitive.
A qeneral cost for either is 0 to 2.6 cents per cubic meter (0 to 5
cents per 1,000 qallons) .
The installed capital costs for either vacuum filters or centrifuqes are
as follows:
cu m/Dav Installed Cost
0.01 38 $25,000
0.1 378 25,000
1 3785 200,000
10 37850 750,000
Polymeric flocculants are often used to condition the sludqe prior to
dewaterinq. These costs were discussed in the previous paraqraph.
The power requirements for vacuum filtration are moderate; they include
the sludqe pump, the flocculant pump, the rotatinq conditioninq tank,
the vacuum filter drum drive, the sludqe aqitator below the filter drum,
the vacuum pump, the filtrate pump and the cake conveyor belt.
Centrifuqes have much larqer power requirements, since the sludqe must
be accelerated to hundreds or several thousands of Gfs. At hiqh speeds,
the windaqe losses (air friction) of centrifuqes are considerable.
Larqe centrifuqes may require 40 to 75 Kw (50 to 100 HP) of power.
Auxiliary power is also required for sludqe pumpinq, flocculant pumpinq,
centrate pumpinq, the cake scraper, and the cake conveyor belt.
Vacuum filters and centrifuqes have a beneficial impact upon solid waste
manaqement. Rather than landfillinq 12 per cent sludqe, these devices
drastically reduce the solid waste quantity by producinq a 30 to HO per
cent cake.
117
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Centrifuges have, a moderately adverse impact with regard to noise
pollution, since they run with a characteristic high speed whine that is
annoying to the human ear. Vacuum filtration is also a noise
contributor since vacuum pumps are noisy machines.
Landfilling of SQlid_Wastes
The disposal costs for solid wastes are highly dependent upon the
hauling distance. The landfill operations alone may cost $6 or more per
kkg (or per ton) for small operations and $2 to 4 per kkg (or per ton)
for larger operations.
Several pertinent papers have recently been published on the subject of
solid waste management in the chemical industry.(63,64)
Solid waste hauling and the material handling operations at landfills
are energy-consuming operations. Landfilling of containerized soluble
solids in plastic drums or sealed envelopes is practicable but
expensive. Blow-molded plastic drums, made from scrap plastic (which is
one of the present major problems in solid waste disposal) could be
produced for $ll-22/kkg ($1020/ton) capacity at 227 kg (500 pounds)
solids/drum and a rough estimate of $2.50-$5.00 cost/drum. A more
economical method, particularly for large volumes, would be sealed
plastic envelopes, 750 microns (30 mils) thick.
At $1.10/kg (500/lb) of film, low density polyethylene costs about 10«:
per 0.0929 sguare meter (1 sguare foot). Using the film as trench liner
in a 1.8 meters (6-foot) deep trench, 1.8 meters (6-foot) wide, the
perimeter (allowing for overlap) would be approximately 7.5 meters (25
feet). At a density of 1.6 grams/cc (100 pounds/cubic foot) for the
solid, costs of plastic sheet per metric ton would be $2.00 ($1.75/ton).
With sealing, the plastic envelope cost would be approximately $2.20/kkg
($2/ton). With landfill costs of $2.20/kkg ($2/ton) additional, the
total landfill disposal costs would be about $4.40/kkg ($4/ton) .
The above figures for solubles disposal using plastic containers, bags
or envelopes are only rough estimates. Also, the technology would not
be suitable for harmful solids or in situations where leaching
contamination is critical.
Removal of Chlorides
Demineralization and Reverse Osmosis
These treatments are costly, over 10 cents per cubic meter (40 cents per
1, 000 gallons) .
The installed capital costs can be calculated from:
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a. Demineralization, Cap. Cost = $280,000 (MGD)0.75
b. Reverse Osmosis, Cap. Cost = $480,000 (MGD) 0.75
Hence, the capital costs for reverse osmosis are nearly double
those for demineralization.
The operating costs (not including capital recovery costs) are:
a. Demineralization, 20 cents/1,000 gal 8 1,000 mg/1 TDS
40 cents/1,000 gal 5) 2,000 mg/1 TDS
b. Reverse Osmosis, 38 cents/1,000 gal 3 0.01 MGD
20 cents/1,000 gal 3) 0.1 MGD
14 cents/1,000 gal S 1 MGD
Neither demineralization nor reverse osmosis require a great deal of
power, and neither has significant non-water guality impact.
Solar Evaporation Ponds
The installed costs of solar evaporation ponds (on the basis of pond
area) are essentially the same as the costs for settling ponds presented
earlier. The pond area depends in this case upon the climatic
differential between evaporation and rainfall:
Evaporation-Rainfall
Differential Pond Area
0.6 m/yr (2 ft/yr) 0.060 ha/cu m/day (560 acres/MGD)
1.2 m/yr (4 ft/yr) 0.030 ha/cu m/day (280 acres/MGD)
1.8 m/yr (6 ft/yr) 0.020 ha/cu m/day (190 acres/MGD)
The power requirements and non-water quality aspects of solar
evaporation ponds are the same as for settling ponds. However, since
the residue in this case is soluble, extra disposal precautions must be
taken to prevent leaching into groundwaters.
Single-Effect and Multiple-Effect Evaporators
The installed capital and operating costs for single-effect evaporators
and for a 6-effect evaporator (all stainless-steel construction) are as
follows:
>
Installed Capital^Costs O & M Costs, $/l,QOQ gal
Pp 1 Effect 6_Eff ects I_Eff ect 6_Effects
10,000 8,000 5.64
50,000 28,000 5.51
100,000 45,000 177,000 5.45 1.30
250,000 80,000 373,000 5.39 1.22
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500,000 1U6,000 665,000 5.36 1.18
1,000,000 267,000 1,225,000 5.33 1.14
(Note: Liters = 3.785 x Gallons)
The energy requirements for single-effect evaporators are 555 kg-cal per
kilogram of water evaporated (1,000 Btu/lb); while the 6-effect
evaporator requires 100 kg-cal per kilogram of water evaporated (180
Btu/lb). The non-water quality aspects are the same as for solar
evaporation ponds.
NON-WATER QUALITY IMPACT
Air Pollution
The proposed guidelines are not expected to increase air emissions. In
fact, the cited technologies should decrease air emissions in some cases
where dry air pollution equipment is suggested to precede wet scrubbers.
Volatilization of hazardous substances, such as fluorine, from ponds is
not expected to present a problem since addition of lime will
precipitate most fluorides.
Solid Waste
Solid waste disposal will be the chief non-water quality area impacted
by the proposed guidelines. Neutralization of acidic waste streams with
lime or limestone will increase the amounts of sludge, especially when
soluble phosphates and sulfates are precipitated. Installation of dry
air pollution control equipment will reduce the water content of wasted
solids. In addition return of collected solids to the process may be
feasible. As stated in section VII, arsenic rich solid residues
accumulate from the purification of phosphoric acid and of phosphorus
pentasulfide. Burial in a controlled area is the standard disposal
method. Special disposal methods as mentioned previously in this
section may be necessary to prevent leachate from reaching surface or
ground waters. Solid waste quantities and constituents are listed in
Tables 9 and 10.
Energy Requirements
The energy requirements for the proposed treatment technologies are
listed in table 19. For the best practicable control technology
currently available the added energy requirements are insignificant when
compared to the process energy requirements. Except for the production
of phosphorus, energy does not significantly enter into the product
cost. For best available technology economically available, the
additional energy requirements for PC13 and POC13 are substantial. This
is due to the assumption that solar evaporation ponds
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TABLE 19
ENERGY REQUIREMENTS
FOR RECOMMENDED GUIDELINES
Chemical
Process Energy
Requirement
KWH/Kkg
Treatment Energy
Requirement
KWH/Kkg
Percentage Energy
Increase
H3P04
P2°5
PS
3 (BPCTCA)
PC1
PC13 (BATEA'
POC1 (BPCTC
j. \-» J_Q vurxj-i*,rv
POC13 (BPCTCA-)
POC13 (BATEA)
Calcium Phosphates
animal feed grade
Calcium Phosphates
food grade
15,400
48
94
9
27
27
28
28
43
7.06
0.000025
0.0126
0.75
0.13
293
0.063
146
0
0.16
0.053
0.05
0.01
0.01
8.3
0.48
1000
0.22
520
0
BPCTCA - best practicable control technology currently available
BATEA - best available technology economically achievable
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may not be possible in a given locale and evaporators may be necessary.
Ground Water
Since settling pond evaporation ponds are extensively used for waste
water treatment in the phosphate industry, it is highly recommended that
all such ponds be sealed or lined so as to prevent any leakage of
contaminated process waters to ground waters.
Noise
No overall adverse affect on the level of noise is expected, although
individual eguipment may have excessive noise levels (e.g. pumps and
centrifuges).
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SECTION IX
EFFLUENT REDUCTION ATTAINABLE THROUGH THE APPLICATION OF THE
BEST PRACTICABLE CONTROL TECHNOLOGY CURRENTLY AVAILABLE,
EFFLUENT GUIDELINES AND LIMITATIONS
INTRODUCTION
The effluent limitations which must be achieved by July 1, 1977 are
based on the degree of effluent reduction attainable through the
application of the best practicable control technology currently
available. For the phosphate industry, this level of technology is
based on the best existing performance by notable plants of various
sizes, ages and chemical processes within each of the industry^
categories. In some cases where no truly notable plants were surveyed,
this level of technology is based upon state-of-the-art unit operations
commonly employed in the chemical industry.
Best practicable control technology currently available emphasizes
treatment facilities at the end of a manufacturing process but also
includes the control technology within the process itself. Examples of
in-process control techniques which are used within the industry are:
* manufacturing process controls
* recycle and alternative uses of water
* recovery and/or reuse of waste water constituents
* dry collection of airborne solids instead of (or
prior to) wet scrubbing.
Consideration was also given to:
a. The total cost of application of technology in relation
to the effluent reduction benefits to be achieved from
such application;
b. The size and age of equipment and facilities involved;
c. The process employed;
d. The engineering aspects of the application of various
types of control techniques;
e. Process changes;
f. Non-water quality environmental impact (including energy
requirements).
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PROCESS WASTE WATER GUIDELINES
Process water is defined as any water coming into contact with raw
materials, intermediates, products, by-products, or qas or liquid that
has accumulated such constituents. All values of guidelines and limit-
ations for total dissolved solids (TDS), total suspended solids (TSS),
metals and harmful pollutants and and other parameters are expressed as
consecutive 30 day averages in units of pounds of parameter per ton and
kilograms of parameter per metric ton of product produced except where
expressed as a concentration.
Based upon the information contained in Sections III through VIII of
this report, the following determinations were made on the degree of
effluent reduction attainable with the application of the best
practicable control technology currently available in the phosphate
manufacturing industry.
The Phosphorus Production Subcategory
Phossy Water
Because of the extremely harmful nature of elemental phosphorus, it is
standard practice within the industry to maintain tight control over the
discharge of phossy water, as discussed in Section VII.
TVA at Muscle Shoals, Alabama segregates phossy water from all other
process and cooling waters, treats the phossy water, and then recycles
the treated water back to the process. The clarifier underflow is
recycled back to the process, but because of the buildup of dissolved
solids, about 6 per cent of this clarified water is bled off.
It is apparent from the discussion in section VII that existing
practicable technology can eliminate the requirements for any discharge
at this TVA plant. Lime treatment of the blowdown followed by
sedimentation of the precipitated phosphates and fluorides would remove
the materials necessitating a blowdown, so that this treated blowdown
could be recombined with the remainder of the clarified phossy water for
return to the process.
There are three examples of plants which have achieved zero discharge of
phossy water: Plants 159, 028, and 181.
Hence, three plants h^ave recognized the undesirability of elemental
phosphorus in any discharge and have also recognized that no practicable
treatment system can remove a sufficient amount of elemental phosphorus
to permit effluent discharge of phossy water wastes. They have all
solved this dilema by evaporating sufficient phossy water rather than by
discharge. One plant uses an evaporation pond, while two others exploit
other process heat loads for in-process water evaporation.
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In view of this clear-cut demonstration within the industry, it is
recommended that the best practicable control technology currently
available for phossy water wastes be no discharge of pollutants to
navigable waters.
Process Waters Other Than Phossy Water
The standard techniques for treating the waste waters from calciner
scrubbers and from slag quenching are lime treatment and settling ponds,
which perform the following functions:
* Neutralization of acid waste waters
* Sedimentation of much of the original suspended
solids in the waste waters (silica, iron oxide,
and others)
* Precipitation and sedimentation of much of the
phosphates, fluorides and sulfates which were
dissolved in the original waste waters.
* Dissipation of the process heat to the atmosphere
during the extended residence in the settling
ponds.
* Reduction in the waste water quantity as a result
of net evaporation during the extended residence
in the settling ponds.
* Where phossy water is combined with these other
process waters, some oxidation of the elemental
phosphorus to phosphates is accomplished.
At Plant 181, the lime-treated water from all sources is clarified in
settling ponds, and the clarified water is held in reuse water supply
ponds. There is total recycle of all water at this plant, with zero
discharge. Because phosphates and fluorides are removed by lime
treatment and sedimentation, there is no requirement to bleed off water
for the control of dissolved solids.
Under conditions of very abnormally-high rainfall which would exceed the
capacity of the pond system, the only overflow would be from the final
reuse water supply ponds, thereby minimizing the quantities of
pollutants even occasionally discharged. The recirculating water system
runs at a water deficit, due to evaporation in the process and to net
evaporation in the pond system. Hence, fresh makeup water is supplied,
and can be controlled to compensate for temporary swings in the pond
evaporation/rainfall balance.
The TVA plant at Muscle Shoals, Alabama granulates the slag by guenching
with a high-velocity jet of water which is recirculated from a sump in
the slag pit. In this TVA operation, the cooling water and the scrubber
liquors are used for makeup in slag guenchinq. The granulated slag
effectively neutralizes these waters and also acts to filter out the
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scrubbed solids, which become part of the slaq pile to be sold. Nearly
all of the soluble phosphate and 95 per cent of the fluoride is removed
by the slaq, and the fluoride concentration is reduced to 30 mq/1.
Hence, TVA utilizes slaq treatment instead of lime treatment, made
possible because the slaq is finely-divided. Sufficient waste water
treatment is obtained by TVA to enable the plant to completely reuse
this water without any discharqe.
Two other phosphorus plants which utilize lime treatment and
sedimentation for process water treatment are Plants 028 and 159.
Tables 14 and 15 list (respectively) the effluent concentrations and
quantities discharqed from these plants, neither of which recycle
treated waste water. There are three siqnificant differences between
these two plants:
* Plant 028 discharqes into the same waterway as the
plant intake so that its discharqe responsibility is
the net increase in constituent quantities. Plant
159 intakes qround water and discharqes into surface
water so that its responsibility is the qross amount
of constituent quantities.
* It is apparent from the "Intake" columns of Tables
14 and 15 that the intake of Plant 159 contains
much more dissolved solids (and specifically F,
POU and SO4) than the intake of Plant 028.
* The waste water quantity per cent of production
for Plant 028 is three times that of Plant 159.
The above three differences are interrelated and affect the quantities
of fluoride, phosphate and sulfate discharqed by Plant 159 because the
effluent concentrations are of the same maqnitude of the solubilities of
the correspondinq calcium salts. Hence, the effluent quantities are
siqnificantly influenced by factors other than the treatment of the
process waters.
The effectiveness of control and treatment techniques used by the four
phosphorus plants cited are summarized in Table 13. Plants 028 and 159
achieve very hiqh (97 to 99+%) control and treatment efficiencies and
correspondinqly low quantities (althouqh not absolutely zero) of
discharqed constituents.
In areas of the country where very severe and extended cold weather
prevails, total recycle of process water become difficult for two
reasons:
1. The return water pipinq and pumpinq must be protected
aqainst freezinq. However, technoloqy such as buried
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water mains and enclosed, heated pumpinq stations has
been aptly demonstrated in the chemical industry and in
water supply operations.
2. The settling ponds may freeze. In a total recycle
system, this circumstance would prevent the required
water from being supplied back to the process. If
auxiliary fresh water supply were provided to uncouple
the process from frequent climatic perturbations, the
pond system would have to consist of sufficient holding
capacity to prevent temporary overflow and would have
to contain sufficient evaporative capacity to prevent
long-term accumulation of water.
Both of the above difficulties are formidable but not unyielding to
practicable, currently available technology. All aspects of
manufacturing including waste management assume different stances when
the chosen environment is far more severe than the norm; however,
currently-available technology can cope with environmental challenges of
this sort including the special challenges in waste management.
Recommended Effluent Limitations Guidelines Based Upon Best Practicable
Control Technology Currently Available
In view of the existence of three plants (028, 159, and 181) which have
already achieved zero discharge of elemental phosphorus; in view of the
existence of two plants (TVA and 181) which have already achieved zero
discharge of other process waters; in view of the conclusion that "Best
Practicable Control Technology Currently Available" is sufficient to
achieve zero discharge in other plants (such as Plants 028 and 159); and
in full view of the statutory national goal of eliminating the discharge
of all pollutants; it is recommended that the best practicable control
technology currently available be no discharge of process waste water
pollutants to navigable waters.
Waste water from Ore Washing the Beneficiation
The best practicable control technology currently available recommended
in the previous paragraphs do not include wastes from the beneficiation
or washing of phosphate rock. This beneficiation is commonly but not
exclusively conducted at a separate off-site location. The huge raw
waste load from benefication, 7.5 kkg of gangue per kkg of phosphorus
eventually produced, warrants a separate study and separate effluent
guidelines.
The Phosphorus Consuming Subcategory
Phossy Water
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Gross discharges of phossy water are presently avoided by pumping
displaced phossy water form the plant's phosphorus storage tank back
into the emptying rail car which brought the phosphorus, and by
transporting this displaced phossy water to the phosphorus producing
plant for treatment and/or reuse. Such is the practice at Plants 037
and 192.
Smaller quantities of phossy water discharge may also be eliminated
through the use of standard engineering techniques. The phosphorus
storage tank level control system may be altered to provide an auxiliary
water overflow tank with return of the water to the main tank. The
avoidance of elemental phosphorus in plant sewer lines can be
implemented by more stringent process and operator controls and
procedures and by providing traps downstream of reaction vessels.
In view of the harmful qualities of elemental phosphorus and in view of
the available choices from state-of-the-art control techniques, the
recommended best practicable control technology currently available for
phossy water is no discharge of pollutants.
Phosphoric Acid Manufacture
Exemplary Plant 075 operates without the discharge of any process water.
There is no fundamental or practical reason why process water should be
discharged at all from any dry-process phosphoric acid plant. Minor
leaks and spills may be minimized, collected and treated using control
techniques generally available and demonstrated-in the industry.
The recommended effluent guideline of no discharge of process waste
water pollutants applies generally and with special emphasis upon
elemental phosphorus (i.e., phossy water) and upon arsenic residues from
the purification of phosphoric acid.
Phosphorus Pentoxide Manufacture
The single raw waste constituent is phosphoric acid from water tail-gas
seals. Application of two standard techniques would enable total
recycle of this waste water:
1. Reduction in waste water quantites by using dilute
caustic or lime slurry as tail gas liquor instead
of pure water, increasing the absorptive capacity
for P205.
2. Lime treatment and sedimentation to neutralize and
to remove the phosphate, permitting total recycle.
In view of the straightforward application of these two techniques, the
recommended best practicable control technoloqy currently available
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effluent guideline is no discharge of process waste water pollutants.
Since total recycle is practicable technology, this recommended
guideline is not affected by modest inaccuracies in the standard raw
waste as estimated in Section V.
Phosphorus Pentasulfide Manufacture
The sole source of process waste water is the scrubber liquor for fumes
from casting liguid P2S5. One control technique would be the use of
inert-atmosphere casting or vacuum casting to completely eliminate the
need for scrubbing. As an alternate to this approach, the application
of three standard techniques would permit total recycle of scrubber
water:
1. Use of dilute caustic or lime slurry instead of pure
water would reduce the waste water quantities by in-
creasing the adsorptive capacity for P205 and SO2.
2. Partial recycle of scrubber liquor from a sump would
reduce the waste water quantity by decoupling the
buildup of absorbed acids from the mass-transfer
requirements for high scrubber flowrates.
3. Lime treatment and sedimentation to neutralize and
to remove phosphate, sulfite and sulfate would per-
mit total recycle.
In view of these different practicable alternates, the recommended best
practicable control technology currently available is no discharge of
process waste water pollutants to navigable waters. Since total recycle
is practicable technology, this recommended guideline is not affected by
modest inaccuracies in the standard raw waste load as estimated in
Section V.
This guideline also applies to any arsenic-rich residues from the
purification of P2S5; these solid residues may be disposed of by burial
as in Plants 147 and 192.
Phosphorus Trichloride Manufacture
The acid wastes from phosphorus trichloride manufacture arise from the
hydrolysis of PC13 in scrubber water from the reactor/ still, from
product storage tanks, from product transferring operations and from
container cleaning. The scrubber water may be collected in a sump and
recycled to decrease the wasted quantity of scrubber water (while still
maintaining sufficient scrubber flow rates for effective mass transfer)
and to increase the concentration of waste constituents.
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