EPA-600/2-77-104
June 1977
Environmental Protection Technology Series
OZONE TREATMENT OF CYANIDE-BEARING
PLATING WASTE
I
55
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LLJ
CD
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service. Springfield, Virginia 22161.
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EPA-600/2-77-104
June 1977
OZONE TREATMENT OF CYANIDE-BEARING PLATING WASTE
by
L. Joseph Bollyky
PCI Ozone Corporation
for
Sealectro Corporation
Mamaroneck, New York
Project No. R802335
Project Officer
Herbert S. Skovronek
Industrial Pollution Control Division
Industrial Environmental Research Laboratory
Cincinnati, Ohio 45268
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Industrial Environmental Research
Laboratory-Cincinnati, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily reflect
the views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or re-
commendation for use.
ii
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FOREWORD
When energy and material resources are extracted, processed, converted,
and used, the related pollutional impacts on our environment and even on our
health often require that new and increasingly more efficient pollution con-
trol methods be used. The Industrial Environmental Research Laboratory -
Cincinnati (IERL-CI) assists in developing and demonstrating new and im-
proved methodologies that will meet these needs both efficiently and
economically.
This full scale demonstration of a highly automated ozonation system
for the destruction of cyanide in electroplating wastewaters will help to
establish the technical and economic feasibility of this alternate technol-
ogy. Such information will be of value both to EPA and to the industry
itself. Within EPA's R&D program the information will be used as part of
the continuing program to develop and evaluate improved and less costly
technology to minimize industrial waste discharges. Besides its direct
application to cyanide wastes from electroplating, this technology may find
application in the control of cyanide from other sources as well as for
the destruction of carbonaceous pollutants generated by a host of other
industries.
For further information concerning this subject the Industrial Pollu-
tion Control Division should be contacted.
David G. Stephen
Director
Industrial Environmental Research Laboratory
Cincinnati
iii
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ABSTRACT
A plating waste treatment plant was built to demonstrate the effective-
ness of ozone treatment for the oxidative destruction of cyanides and cya-
nates and for the removal of copper and silver as their oxides on a plant
scale. The plant was designed to treat all the waste from copper, gold, and
silver plating operations.
A 9-month study was carried out to evaluate the effect of process param-
eters, to identify and optimize key parameters, to establish capital cost and
operating costs, and to explore the possibility of producing an effluent of
the highest quality.
The results of the study clearly show that ozone treatment rapidly and
economically destroys copper and sodium cyanides. The reaction first pro-
duces cyanates, which are oxidized further by ozone and simultaneously, but
much more slowly, hydrolyzed. Although the complete removal of cyanates was
demonstrated, it was not practiced under optimum conditions since it is not
required under local or Federal standards. The process precipitates copper
and silver in a readily settleable form. The oxidation of copper cyanide is
more rapid and requires less ozone than that of sodium cyanide.
Cost data have been developed to reflect the optimum operating condi-
tions found experimentally. The plant treats a combined cyanide (alkaline)
and heavy metal (acidic) flow of 185,000 I/day(49,000 gal/day). The costs
of treatment are as follows:
operating cost $ 0.27/1,000 1 ($1.03/1,000 gal)
total cost $ 0.35/1,000 1 ($1.31/1,000 gal)
The costs of ozone treatment of the cyanide waste alone are as follows:
operating cost $ 0.38/1,000 1 ($1.43/1,000 gal)
total cost $ 0.62/1,000 1 ($2.35/1,000 gal)
$10.34/kg CN ($4.70/lb CN)
Capital investment for this optimized system is estimated as $51,200.
This report was submitted in fulfillment of Demonstration Grant #8802335
by Sealectro Corp. under the partial sponsorship of the U.S. Environmental
Protection Agency. Work carried out by PCI Ozone Corp. under contract to
Sealectro Corp. covers the period April 1, 1973 to June 30, 1974 and the
project was completed January 31, 1975.
IV
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CONTENTS
Foreword „.
Abstract '.'.'. i
Figures .....!!..! v
Tables .
• vi
Acknowledgment ..
1. Introduction -i
2. Conclusions * c
3. Recommendations ' /•
4. Design of Treatment Plant '.'.'.'.'.'.'. 1
5. Study Objectives and Approach '.'.'. 13
6. Operation Under Optimum Conditions ! ! ! ! ! 16
7. Study of Process Parameters ] 19
8. Treatment of Sodium Cyanide ' \ 28
9. Discussion ....
10. Cost Evaluation '..'.'.'.'*' 33
11. Analytical Methods ;...!**** 38
References ,,
FIGURES
Number N Page
1 Flow Diagram - Sealectro Plating Waste Treatment Plant . . 8
2 Sealectro Plating Waste Treatment Plant 11
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TABLES
Number Page
1 Plating Waste Effluent Limitations 3
2 Monthly Average Concentrations of Contaminants 4
3 Ozone Treatment of Plating Waste, Typical Operation
Conditions 17
4 Ozone Treatment of Plating Waste (Copper Cyanide Complex)
Under Upset Operating Conditions 20
5 Ozone Treatment of Plating Waste, Less Than Stoichiometric
Ozone Dosage 21
6 Ozone Treatment of Plating Waste (Copper Cyanide Complex)
With Small Excess of Ozone 22
7 Ozone Treatment of Plating Waste (Copper Cyanide Complex)
With Excess Ozone 23
8 The Effect of Ozone Dosage at Low Concentrations of Cyanide 24
9 The Effect of Ozone Dosage on Intermediate Concentrations
of Copper Cyanide 25
10 The Effect of Ozone Dosage on High Concentrations of
Copper Cyanide 25
11 The Effect of Cyanide Concentration at Constant Ozone to
Copper Cyanide Ratios 26
12 Ozone Treatment of Sodium Cyanide on Plant Scale 29
13 Capital Cost of Ozone Treatment 34
14 Weekly Operating Cost for Ozone Treatment 35
15 Treatment Costs 36
16 Cyanide Destruction Costs $ .....,..,, 37
>$
17 Analytical Methods 39
vi
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ACKNOWLEDGMENT
PCI Ozone Corp. is grateful for the support and cooperation extend-
ed by Mr. George E. Mohr, Frederick Baron, and Jesse Fuchs of Sealectro Corp,
This project was carried out with the partial support of the U.S
Environmental Protection Agency. The guidance and assistance of the Project
Officer, Dr. H.S. Skovronek, of the Industrial Environmental Research Labora-
tory- Cincinnati, is acknowledged.
Credit is due to Mr. Charles Ballnt (PCI) for the operation of the
treatment plant during Che study program and to Mr. Barry Siegel (PCI) for
the analysis of the samples.
vii
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SECTION 1
INTRODUCTION
The electroplating industry produces substantial quantities of waste-
™^r ?°nta*nin8 cyani
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some of these studies appear to be contradictory because the experiments were
carried out under different, non-comparable reaction conditions. Neverthe-
less, it is clear from such studies that mass transfer of ozone from air to
water controls the reaction rate in most cases (11,12). In a batch reactor
study, the pH of the solution changes drastically during ozonation, first de-
creasing to an acidic pH, then increasing to a basic pH again as the oxida-
tion of cyanide progresses through cyanate and then to what was believed to
be urea and ammonium nitrate (11). More recent work (lib) projects that the
products are carbon dioxide and nitrogen. Certain metal salts, such as those
of copper, appear to catalyze the oxidation reaction when mass transfer is
not the limiting factor (12). The oxidation of certain hard-to-oxidize com-
plexes of cyanide such as sodium ferricyanide is accelerated by ultraviolet
(uv) irradiation, heating to 83°C (180°F) or both (21).
The stoichiometry of the reaction has been studied under two sets of
different reaction conditions (11,13). From these studies, it appears that
the number of moles of ozone required for the destruction of one mole of cya-
nide is dependent on cyanide concentration, on ozone concentration and on pH.
These findings suggest the presence of competing side reactions. In general,
higher cyanide concentrations, higher ozone concentrations, and higher rates
of ozone mass transfer favor lower ozone dosage for cyanide destruction.
Oxidation-reduction potential measurements (ORP) were found to be a
good indication of the progress of the ozone/cyanide reaction (11).
A laboratory study preceding this demonstration project clearly estab-
lished that the oxidation of cyanides by ozone destroys both cyanides and
cyanates. That is, the reaction does not stop at the cyanate stage. Fur-
thermore, the ozone treatment precipitates copper and silver as a dense,
readily filterable or settleable precipitate which is believed to be com-
posed primarily of the metallic oxides (6).
THE PLATING OPERATION AT SEALECTRO CORPORATION
Sealectro Corp., a manufacturer of connectors and other related com-
ponents for the electronics industry, decided to build a new plating plant
to satisfy its requirements internally in the gold, silver, copper and nick-
el plating area. The plant was designed in-house and installed by Sealec-
tro *s maintenance personnel.
The expected wastewater flows from the plant, based on design, were as
follows:
a) Alkaline cyanide flow: 25.5 1/min (6.75 gpm) with surges to 39.0 1/min
(10.4 gpm) containing contaminants in the following maximum concentra-
tions (mg/1) :
cyanide 60
copper 32
silver 3.4
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b) Acidic wastewater flow: 60 1/min (16 gpm) with surges to 93.0 1/min
containing contaminants in the following maximum concentrations (mg/1):
nickel 14
tin 2
lead 0.08
In order to be discharged, the treated effluent had to meet or exceed
the requirements of Act. No. 27-1968, County Public Works Sewer Ordinance
No. 1, Board of Supervisors of Westchester County, N.Y., effective May 20,
1968, which may be summarized as follows:
1. pH in the range of 5.5 to 9.5
2. temperature not to exceed 65°C (150°F),
3. maximum concentration of toxic substances (mg/1):
copper 3.0
cyanate 10.0
cyanide 1.0
nickel 10.0
silver 0.05
chlorine 100.0
After the construction of the Sealectro Plating Waste Treatment Plant,
the EPA published guidelines and standards on March 28, 1974 (Federal Regis-
ter, Vol. 39, No. 61, covering the waste treatment requirements for the plat-
ing industry). The permissible amounts of pollutants are related to the sur-
face area plated as summarized in Table 1.
TABLE 1. PLATING WASTE EFFLUENT LIMITATIONS
Best Practicable Technology Currently Available, 07/01/77
Parameter Effluent (mg/m2)
1 day max. 30 day avg. max.
Cu 160 80
Ni 160 80
Cr (VI) 16 8
Cr, total 160 80
Zn 160 80
CN A* 16 8
CN! total 160 80
TSS 4800 3200
pH 6.0-9.5 6.0-9.5
*CN, A means chlorine-oxidizable cyanides.
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A monthly average rinse water flow of 80 1/m2 (1.96 gal/ft ) of plated
surface is assumed with a one day maximum of 160 1/m (3.93 gal/ft2). On
the basis of 80 1/m2 (1.96 gal/ft2) the concentrations of contaminants per-
mitted were calculated as shown in Table 2 for BPTA.
TABLE 2. MONTHLY AVERAGE CONCENTRATIONS OF CONTAMINANTS*
BPTCA
Pollutant Effluent Parameters
(mg/1)
Cyanide (Dest. by Cl) 0.1
Total 1.0
Copper 1.0
Iron 2.0
Lead 1.0
Nickel 1.0
Silver 0.1
Tin 2.0
Zinc 1.0
TSS 40.0
pH (avg. Daily Discharge) 6.0-9.5
*Based on 80 1/m2 flow and 30 day average maximum
discharge rates.
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SECTION 2
CONCLUSIONS
The Sealectro demonstration project achieved its major objectives. It
has demonstrated on a plant scale the effectiveness of ozone for cyanide and
cyanide-bearing plating waste treatment. It has confirmed the results of
laboratory work in the laboratories of PCI Ozone Corp. in Stamford, Connecti-
cut* concerning the removal of cyanide, cyanate, copper, and silver by ozone
treatment.
The major results of the study may be summarized as follows:
a) Optimum operating conditions were determined for the Sealectro Plant to
be 1 to 1.5 moles of ozone/mole CN~at a pH of 7 to 9.5 in the ozone
contactor and a final clarifier pH of 9 to 9.5 at ambient temperatures
of 14 to 20°C (57 to 68°F).
b) It was established that the ozone dosage is the most critical operating
parameter, with 1 to 1.5 moles 0,/mole CN**found to be optimum at low
CN~concentrations (<20 mg/1) and 1.8 to 2.8 moles 0_/mole CN'at higher
levels (>40 mg/1).
c) The pH of the cyanide waste in the ozone contact tank was found to have
no significant effect in the range of 7 to 10, thereby eliminating the
need for precise pH control during ozone treatment.
d) Firm cost data were established based on plant experience. ^Treatment
operating cost was $0.38/1000 liters ($1.43/1000 gal) of CN influent
and $0.27/1000 liters ($1.03/1000 gal) total wastewater. The total
capital costs were $66,613.00 for the Sealectro installation but are
estimated at $51,200 for an optimized, non-research installation.
e) The ozone treatment proved to be a safe operation. It did not emit
ozone into the atmosphere.
f) Side benefits of ozone treatment include improved safety by eliminating
the need for the transportation and storage of toxic and hazardous
chlorine or hypochlorite and, in general, a sophisticated and highly
automated operation requiring a minimum of attention and chemical ad-
ditions.
*Now located in West Caldwell, N. J.
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SECTION 3
RECOMMENDATIONS
The Sealectro demonstration project achieved its major objectives and
clearly demonstrated that ozone treatment is an effective, economical and
safe method for cyanide plating waste treatment. We recommend a further
demonstration study covering the following areas.
Recycling of treated effluent into the plating process should be pos-
sible by providing a small increase in ozone dosage, eliminating cyanide from
the acid flow* and improving the operation of the settling tank. The efflu-
ent is suitable as is for the cooling of operating machinery, such as ozone
generators, air conditioners, etc.
Other metal complexes of cyanide should also be responsive to ozone
treatment. These metal complexes include those of cadmium, zinc, and iron.
(The removal of the iron complex, a particularly stable one, may require
simultaneous ultraviolet irradiation or elevated temperatures).
The severity of treatment conditions should be determined for each metal
complex anticipated in a plating plant.
Cyanide was discovered in the acid stream of the Sealectro Plating Plant
and ultimately found to be due to plumbing and maintenance difficulties.
The problem was only partially resolved during the course of the study pro-
gram.
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SECTION 4
DESIGN OF TREATMENT PLANT
The plating wastewater treatment plant was designed and installed by
PCI Ozone Corp. under the direction of Dr. L. J. Bollyky. It was started up
in January 1974, placed into full operation February 25, 1974 and has been
in operation since that date with no design or operation-related downtime.
The Sealectro Plating Waste Treatment Plant is designed to treat the
two wastewater streams produced during the plating operations of the Sealec-
tro Corp. Plating Plant. The expected discharges from the plating plant are
as follows:
Alkaline cyanide wastewater: Flow under normal conditions, 25.5 1/min
(6.75 gpm), with provision to accept surges in flow (spills, bath dis-
charges, etc.) or growth to 39 1/min (10.4 gpm). The wastewater con-
tains cyanide up to 60 mg/1, copper up to 32 mg/1, silver up to 3.4 mg/1,
Acid waste: Flow under normal conditions, 60 1/min (16 gpm), with provi-
sion to accept surges in the flow or growth to 93 1/min (24.6 gpm).
This flow may contain nickel up to 14 mg/1, tin up to 10 mg/1, and lead
up to .08 mg/1 concentrations.
The combined average flow of acid and cyanide waste is 86 1/min (22.75 gpm),
with provisions to accept surges in flow rates up to a total of 132 1/min
(35 gpm) flow. Peaks and surges are to be equalized in separate underground
holding tanks.
The plant is designed to operate continuously around the clock, if
necessary. The flow of both wastewater streams is controlled automatically,
as is the pH of the cyanide stream and of the effluent from the treatment
plant. The ozone dosing rate is also controlled automatically by on-line
monitoring of residual ozone.
Flexibility was engineered into the plant and numerous sampling points
were provided to allow for experimentation and modifications necessary for
the demonstration study. Thus, this plant is over-designed to allow varia-
tion of process parameters over a broad range.
The general design of this wastewater treatment plant is shown in the
flow diagram, Figure 1. The plant has two separate underground storage tanks
to receive and equalize the segregated wastewaters; a 7500 1 (2000 gal) tank
for the alkaline cyanide waste (T-2), and a 15,000 1 (4000 gal) tank for the
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oo
ALKALINE CYANIDE
WASTE
0-
ACIDIC METAL
WASTE
L"
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T-
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t
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-2
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EQUALIZATION
TANK
1 I
T-l
(t)
OZONE
<
1
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T-4
I
DZONE
REACTOR
VENT
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EQUALIZATION
TANK
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1 T-5
NaOH
T-3
CAUSTIC
TANK
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T~ C. ' x^x
FINAL
FLASH MIXER \ / LhhLULNI
\/SETTLING
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LEGEND:
SAMPLE POR'
THE STUDY "
USED FOR
m AND
SOLIDS
FIG, i - FLOW DIAGRAM -SEALECTRO PLATING WASTE TREATMENT PLANT
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acid wastewater (T-l). Tank T-2 is provided with a pH sensor, a flash mixer,
a pump to transfer wastewater into the ozone reaction tank (T-4), and a water
level sensor. The pH of the cyanide wastewater is adjusted automatically in
this tank with 15% caustic from a storage tank (T-3).
The acid wastewater is received in Tank T-l. The tank is provided with
a water level sensor and a pump (P-i) for the transfer of this wastewater
into the flash mixing tank (T-5) where it is combined with ozone-treated al-
kaline wastewater from the reaction tank (T-4) to gain all possible neutral-
ization benefit.
The PCI Model G-20-M Ozone Generator has an ozone generating capacity
of up to 9.1 kg/day (20 Ib/day) of ozone from air under normal operations
and up to 12 kg/day (26 Ib/day) of ozone using the auxiliary blower. The
auxiliary blower is part of the PCI Model PRE-23-M Air Preparation Unit.
The air preparation unit provides the clean, oil free, particle free, dry
air needed for the generation of ozone. Oxygen could also be used and the
output of the same unit would increase twofold.
The ozone reaction tank (T-4) is a fiberglass tank of 2250 1 (600 gal)
capacity. This tank consists of two major compartments:
The lower, large compartment where the wastewater is treated by ozone.
The ozone is introduced through porous diffusers at the bottom of the
tank, which is filled with cyanide-containing wastewater.
In the upper, smaller compartment the spent ozone off-gas is reintro-
duced and either passed through a packed column, sprayed with the in-
coming cyanide waste or diffused into the incoming cyanide waste. In
either mode of operation, this upper compartment serves to remove un-
reacted ozone from the off-gases to assure complete utilization of the
ozone and to prevent ozone from escaping to the outside atmosphere
through the vent.
The fiberglass flash mixer tank (T-5) receives treated alkaline waste
from Reaction Tank T-4 and acidic waste from Tank T-l. The combined waste-
waters are mixed with the flash mixer and a final pH adjustment then made
with caustic or sulfuric acid based on the signal from the pH detector in
Tank T-5. The tank is covered to prevent splashing of the wastewater.
The settling tank (T-6) receives the neutralized combined wastewater
from the flash mixer tank (T-5). The metal oxides and/or hydroxides settle
out in this quiescent tank and the clear, treated water is discharged
through the overflow to the sewer. The solid waste is removed manually, as
necessary, through a bottom outlet, as a sludge. The calculated retention
time in the settling tank is a minimum of 50 minutes.
pH CONTROL SYSTEM
The pH control system consists of the pH detectors mentioned earlier,
controllers, and tranducers. All are products of Foxboro Corp. This pH con-
trol system adjusts the pH in Tank T-2 and in Tank T-5 by using a 15% caustic
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solution held under approximately 52 mm Hg (10 psig) pressure in a pressure
rated fiberglass tank (T-3). Compressed air from the PRE-23-M Air Prepara-
tion Unit or instrument air from the plant is used to maintain the pressure
on the caustic solution in Tank T-3. The caustic solution is fed into Tank
T-2 and Tank T-5 as needed through pneumatically controlled metering valves
activated by the pH detectors and their automatic controllers. The caustic
solution is prepared from caustic flakes in a separate tank (T-3A) and
pumped into Tank T-3.
PROCESS CONTROLS
The process controls wired into the central process control unit allow
either an automatic mode of operation or manual operation. All major com-
ponents of this system are fused separately and are wired to permit their
operation independently from the total system in the manual mode of opera-
tion. The automatic mode of operation makes use of signals from level sen-
sors, located in Tanks T-l and T-2. Signals from these two level control-
lers will operate the pumps to transfer cyanide waste into Reaction Tank T-4
or acidic waste into Tank T-5. The wastewaters flow by gravity from these
tanks through the rest of the system. The ozone output of the ozone gener-
ator is controlled by an ozone detector which assures sufficient ozone for
the complete destruction of cyanide in Tank T-4. If there is a wastewater
flow through the system, both the ozone generator and the pH control system
will operate automatically. A failure of any component, such as a pump or
controlling instruments, is indicated by a visual-audio alarm.
The waste treatment plant is separated from the plating facilities and
located ina5.8mx5.8m (19 ft x 19 ft) area with a ceiling height of
4.3 m (14 ft). A removable cover is provided for the portion of the roof
directly over the ozone contact tank to permit inside inspection of this
tank. The holding tanks (T-l and T-2) are located underground next to the
treatment plant and are accessible through manholes.
LIST OF MAJOR COMPONENTS
Model G-20-M Ozone Generator (PCI Ozone Corp.), with ozone generating
capacity of 12 kg/day (26 Ib/day) from air (See Figure 2).
Model PRE-23-M Air Preparation Unit (PCI Ozone Corp.), with an output
of 0.678 m /min (24 scfm), oil free, particle free air with a dew
point of -40 C (-40°F) or lower.
Ozone Detector Automatic Controller (PCI Ozone Corp.), one set point
unit to maintain an ozone residual of 0.1 to 2.0 mg/1 in the effluent
from the ozone reaction tank, T-4.
Ozone Reaction Tank (PCI Ozone Corp.) 5.6 m (18.5 ft) tall, 0.8m (30 in)
diameter, two compartment fiberglass tank, volume: 2250 1 (600 gal),
T-4.
Flash Mixer Tank (PCI Ozone Corp.), 1.5 m (5 ft) tall, 0.8 m (30 in)
10
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Figure 2. Sealectro Plating Waste Treatment Plant
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diameter, fiberglass covered tank, volume: 700 1 (180 gal), T-5.
Settling Tank (PCI Ozone Corp.), 2.3 m (7.5 ft) tall, 1.8 m (6 ft) di-
ameter, fiberglass tank with conical bottom, volume: 6500 1 (1730 gal),
T-6.
pH Detector and Controllers (Foxboro Corp.)
Central Control Panel (PCI Ozone Corp.).
12
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SECTION 5
STUDY OBJECTIVES AND APPROACH
This study was carried out to evaluate the operation of the plating
waste treatment plant and to confirm laboratory findings that ozone effec-
tively destroys both cyanide and cyanate and precipitates copper and silver
ions as readily settleable solids (6).
Further objectives were to study the effects of changes in major pro-
cess parameters such as ozone dosage, ozone concentration, pH, and temper-
ature and to find the optimum values for those effects.
Another objective was to establish the cost of this plant and of a new
plant based on optimum operating parameters. Both capital cost and operat-
ing cost were to be considered.
APPROACH
The study was carried out in three phases as described below. A major
constraint placed on the study was that it had to be carried out while the
plating plant was in full operation, requiring treatment of plating waste as
generated. The plating operation could not be interrupted for extended
periods for obvious economic reasons.
In the first phase of the study, the major objective was to learn about
the operating characteristics of the plant and to resolve any possible prob-
lems, that is, to conduct a plant shakedown operation.
Two problems were encountered during this phase of operation. The
first was excessive wastewater flow from the plating plant due both to im-
proper piping that channeled cooling water from air conditioners into the
system and due to the simultaneous shakedown operation of the new plating
plant and the inexperience of the new crew. The second problem was the
presence of significant amounts of cyanide in the acid wastewater line, due
again to faulty piping in the plating plant.
During the second phase of the study, the major objectives were to
evaluate the effect of process parameters and to determine optimum condi-
tions, while still providing uninterrupted waste treatment for the plating
plant.
To accomplish these objectives, the treatment process parameters were
varied by upsetting the waste treatment plant's operation temporarily and
their effects evaluated as follows:
13
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a) Cyanide concentrations were adjusted by adding concentrated plating
solution to the cyanide waste holding tank. The plating plant tended
to produce wastewater with a high flow but with low cyanide concentra-
tion because of the earlier noted problems. In order to evaluate
treatment in the higher (20 to 100 mg/1) cyanide concentration range,
plating solution had to be added.
b) Ozone dosage was adjusted upward by increasing the output of ozone or
downward by adding concentrated plating solution to the underground
cyanide waste holding tank, thereby changing both cyanide concentra-
tions and ozone/cyanide ratio.
c) pH was adjusted in the cyanide holding tank or in the flash mixer and
thereby, in the settling tank, independently.
d) The temperature changed naturally as the study progressed through
spring, summer, fall, and winter. It did not produce a noticeable ef-
fect over the observed range of 14 to 20 C (57 to 68 F).
e) Experimental treatment of sodium cyanide was carried out during a sum-
mer plant shut-down of the plating plant to obtain background data.
The temporary large upset of certain process parameters such as cyanide
concentration and ozone dosage could only be maintained for about three
hours without affecting plating plant operation. Nevertheless, this time was
sufficient to obtain useful data from the ozone contact tank; however, equi-
(J.ibrium conditions were not always established in the settling tank. There-
fore, metal concentration values obtained for the final effluent under these
conditions should be treated with caution. They probably reflect maximum
values.
During the third phase of the study, the treatment plant was operated
under optimum (or close to optimum) conditions for extended periods to ob-
tain data for process and cost evaluation. These results are compiled and
discussed later. Although the plating plant operates within the limits of
local and EPA standards for a small plating operation, it produces a large
flow of wastewater, far in excess of what would be permitted by the EPA from
a large plating operation. In addition, the acid waste flow, which should
have contained no cyanide, carried a cyanide concentration of 0.3 to 1.0
mg/1. Sealectro Corp. made repeated attempts to eliminate cyanide from the
acid flow by checking piping and floor cracks in the plating plant and by
tightening housekeeping operations. As a result, the cyanide concentrations
in the acid stream were lowered slightly to 0.2 to 0.8 mg/1. No further
improvements were made during the course of the study because of pressing
need for production and other economic reasons. Because of the time limita-
tions of this EPA study, the third or final phase of this project was com-
pleted under these conditions. The data presented in Section 6 show the re-
sults on that basis, as well as residual cyanide analyses of the effluent
from the ozone contact tank (T-4). The cyanide concentration in the efflu-
ent from the ozone contact tank could consistently be reduced to 0.8 mg/1.
-------
The analyses of the samples were carried out in the laboratories of PCI
Ozone Corp. in Stamford, Connecticut* using standard analytical methods de-
scribed in Table 17. The modified Liebig method was used for all cyanide
determinations.
*Presently located in West Caldwell, New Jersey
15
-------
SECTION 6
OPERATION UNDER OPTIMUM CONDITIONS
Optimum operating conditions were determined by studying the effect of
process parameters, as described in Sections 5 and 7.
The optimum process parameters for the Sealectro Plating Waste Treat-
ment Plant were found to be as follows:
a) Ozone dosage: 1 to 1.5 mole 0 /mole CN~ or 1.85 to 2.8 mg/1 0_ per mg/1
QT. •* 3
b) pH of cyanide waste: 7.0 to 9.5 before ozone treatment.
c) pH of treated final effluent: 9.0 to 9.5 in the settling tank.
d) Ambient temperature any time during the year (14 to 20°C).
The plant was operated under these optimum conditions for approximately
two weeks, 16 hours per day, at combined waste flows approximately 1.5 times
that of design capacity. Typical data obtained at the extremes of the opti-
mum operating range are shown in Table 3.
The data in Table 4 indicate that an ozone dosage of only one mole of
ozone per mole of cyanide ion suffices to reduce the cyanide concentration to
0.08 mg/1 in the effluent from the ozone contact tank (Effluent III). How-
ever, contamination by CN"in the acid waste stream caused the final discharge
(Effluent IV) to contain 0.64 mg/1 cyanide. Metal ion concentrations in the
final treated effluent (Effluent IV) were as follows (mg/1):
Copper 1.7
Silver <0.1 (the limit of detection for the analytical
method used.)
Nickel 0.4
The cyanate concentration was 6.0 mg/1. More complete removal of cya-
nate can be achieved with a higher dosage of ozone, but cyanate control is
not necessary to meet local or Federal standards.
These results are remarkably good considering the fact that the acid
waste contained 0.2 to 0.8 mg/1 cyanide when it was not supposed to contain
any. During the treatment sequence the acid wastewater is combined with the
ozone treated cyanide waste, the pH adjusted and the combined wastewater fed
into the settling tank and then discharged as final treated effluent (IV).
16
-------
TABLE 3
OZONE TREATMENT OF PLATING WASTE2
TYPICAL OPERATING CONDITIONS
Experiment
CN~ @ Port I
Ozone
(0.*)/(CN ) "**",
(03-Cu)/(CN~r
Cyanide Waste
(mg/1)
>, Cmg/1)
Wr
1
Input
15.2s. o,
29. 7/ '-' "
1.05
1.03
12. 9 > °
35.2
1.48
1.47
pH at Sample Ports0
CN Tank (I)
Reactor (III)
Clarifier (IV)
Cu
Ag
Ni
CN-
CN Removal
CN
CNO~
Cu
Ag
Ni
Metal Input in Combined
(mg/1)
(mg/1)
(mg/1)
7.0-8.0
7.0
9.5
Inflow (I + II)
4.24.
NFd
0.84
9.5
7.0-8.0
9.0
7.50
0.71
NF
Effluent from Ozone Treatment Tank fill)6
(mg/1)
Final Effluent
(mg/1)
(mg/1)
(mg/1)
(mg/1)
(mg/1)
0.08
99.5
(IV)f
0.64
6.0
1.7
g
0.4
0.08
99.4
0.85
4.2
2.2
g
0.7
d
e
f
g
Plating Waste: Na3Cu(CN)4 at 34 1/min (9 gpm) flow, 1.33X design
flow of 25.5 1/min (6.75 gpm). Acidic waste flow: 94.5 1/min
(25 gpm) or 1.5 X design flow of 60 1/min (16 gpm).
(°3'Cu.^/(CN ) is the mole ratio after accounting for oxidation of Cu"1
to Cu
Roman numerals refer to sampling ports indicated on Figure 1.
NF - None found.
Ozone treated cyanide waste before mixing with acid waste.
Metal values = total; includes soluble plus suspended.
Detected at limit of detection of procedure used, 0.1 mg/1 for Ag.
17
-------
Cyanide in the acid waste stream has two undesirable effects. It
increases the cyanide concentration in the effluent. That is the reason
why Effluent III contains only 0.08 mg/1 cyanide while Effluent IV con-
tains 0.64 mg/1. The second undesirable effect is that the cyanide pre-
sent in the settling tank may increase the solubility of metal ions by
complexing. The system is so designed that the acid waste cannot be ozo-
nated. Correction lies in improved maintenance and housekeeping. Never-
theless, even with this minor problem, the Sealectro Plating Waste Treat-
ment Plant meets all local and EPA code requirements, as discussed in
Section 1. Cyanide concentration was consistently reduced to 0.08 mg/1
in the ozone reactor effluent.
Another key point worth mentioning is that repeated measurements,
using a Mast ozone meter, showed no significant ozone emission in the vent
gases from the ozone contact tank. All measurements showed an ozone con-
centration of 0.05 ppm or less.
The sludge from the settling tank was collected during the two weeks
of optimum conditions operation. A very small amount of sludge formed
during that time (approximately 1 to 2 kg on a dry basis). It was readily
settleable and filterable. A sample was dried at 130°C and analyzed for
metal content, using atomic absorption spectroscopy. The results are as
follows: copper 18%, silver 0.1%, nickel 18%, iron 0.6%, lead 0.8%,
tin 24%, all by weight.
18
-------
SECTION 7
STUDY OF PROCESS PARAMETERS
The effect of various process parameters on the plating waste treatment
was studied to establish optimum operating conditions. The study was carried
out by temporarily upsetting the various parameters and recording their ef-
fect without interrupting the operation of the treatment plant or of the
plating facility. This approach permitted the normal production schedule for
the plating plant to be maintained.
*
The study could not be made as detailed and thorough as would have been
preferred due to time and budget limitations. An added limitation was the
initial operating difficulties with the new plating plant and the inexper-
ience of the operating personnel with the new equipment.
The approach used for the study was discussed in detail in Section 5.
The quality of the final treated effluent was somewhat affected by low cya^
nide and metal concentrations in the acid waste as noted in Section 5 and 6.
The results of the process parameter study are compiled in Tables 4, 5,
6 and 7. The data in these tables include most of the information obtained
when the treatment plant was operated under upset operating conditions, with
less than stoichiometric amounts of ozone and with both a small excess and
with a large excess of ozone. For ease in understanding, these data are also
presented in a summarized form in Tables 8, 9, 10 and 11 later in the report,
together with the following discussion of the various process parameters.
The effect of ozone dosage or the ozone/cyanide mole ratio was studied
at several concentration levels of cyanide. These studies showed that ozone
dosage is the most important process parameter. The results are as follows:
a) At a low cyanide concentration (to 20 mg/1) an 03/CN~mole ratio of 1:1
is sufficient to reduce cyanide concentrations to below 0.1 mg/1, as
indicated by the data in Table 8;
b) At intermediate cyanide concentrations (20 to 40 mg/1) a mole ratio of
2.0 ozone/cyanide is needed to reduce the cyanide concentration to
<1 mg/1 and 3.6 to achieve <0.1 mg/1, as indicated by the data in
Table 9. The relationship for cyanate is less clear, but suggests that
high 0,/CN~ratios (3.6) are also necessary for effective destruction;
c) At higher concentrations (>50 mg/1) a mole ratio of 1.33 ozone/cyanide
reduces the cyanide concentration to 0.52 mg/1, as indicated by the
data in Table 10. This ratio is inadequate for effective CNO"removal.
19
-------
T«bl« 4
OZOm TMATMEHT OT P1ATCTC VAST! TOPER PTSCT OPE1ATOTC COHPITIOIIS*
FaraMUr DpMt
Acidic pi In Clarlflu
rum* DOM** V«rl«d
n
•lib Coaantntlon (2X)
OmoM CM,"**"
It
Input
OT (I) Oion. Mole Utlo
(»«/l) (»t/l) (Qa/a-)
2.1 43.6 11.4
IS. 7 «.« 1.5
1.2 23.8 12.2
10.3 50.1 2.7
17.5 50.1 1.6
27.0 217.2 4.4
31.5 254.3 4.4
3».0 243.7 3.5
pR >t Sovl* rort«k
(Or) luctor Cl.rlfUt
(I) (III) (TO
8.0 7.0 2.0-3.0
S.O 7.0 2.0-3.0
7.5 7.1 ll.»
S.O 7.0 9.0
8.0-9.0 7.0-8.0 9.0-10.0
13.5 12.9 13.1
9.5 7.8 S.5
1.6 7.0-8.0 6.5
Total Burr M>t*l Input
la Combined Inflow I «nd II
Cu A* Pb Rl r«
(n«/0
4. 54 0.10 XT 0.63 O.S1
5.27 0.11 IT ICT HT
3.42 0.42 W 1.33 0.56
S.01 0.10 IT MT XT
9.25 0.69 XT 4.69 W
,-m m n mm
10.36 0.12 XT 0.21 XT
15.99 0.03 »T »6.8 0.62
Oson* Kaactor
Sffluent (III)
U«/l)
0.08 3.5
4.1 14.0
0.2 ID
0.21 11.0
0.43 21.0
0.23 44.1
0.16 26.0
0.15 16.0
naal Effli»nt (IV)C
C^/l)
0.60 0.0 0.7 0.17 IT 0.4 1.7
0.71 0.0 4.6 0.23 XT 0.4 1.1
0.72 m 3.0 0.23 1.3 0.6 0.5
0.53 4.2 7.0 0.12 XT 2.1 IT
1.4 6.0 6.4 0.64 IT 3.6 CT
0.6* 7.2 «D ID m> TO XO
0.54 S.O 12.4 0.12 IT 0.3 HT
0.13 7.2 ID ID ID ID IT
•tUttns MM OU}Ca«a4) at 9 CFM flov. 1.3 tliaa dealfn flow of 6.75 CTM. Ih« acid mitt flow vai 25 GPM, 1.5 tlmei de«ljn flow of 16 CW. Th« otooc conemtratloB In Mlutloa nprunt* th.
aMBt of OIOIM f«d lato thtt T**ctor.
NJ
O
••OMB mania npraaaat aanpla porta, aa par Wgara I.
Tha a»tal anljala doaa not rapraaant aqalllbrlim opaTatlng condltlona. Sufficient tlna probably
not «llov»d for th* cl«rlfl«r to raach equlllbrlim condition!.
•T -mol
ID-not
-------
TABLE 5
OZONE TREATMENT OF PLATING WASTE
LESS THAN STOICHIOMETRIC OZONE DOSAGE3
Experiment No.
CN- @ Port I
Ozone
Mole Ratio (0,/CN)
CN- (I)
Reactor (III)
Clarifier (IV)
Cyanide Waste Input
(mg/1) 71.0
(rag/1) 46.0
0.35
pH At Sample Ports
8.5
8.1
8.5
Metals in Combined Inflow (I) +
Cu
Ag
Pb
Ni
Sn
CN-
CNO"
CN"
CNO"
Cu
Ag
Pb
Ni
Sn
CNT (¥)
CNO" (%)
20.7
0.71
NFC
1.4
NF
Ozone Reactor Effluent (III)
12.1
48.0
78.0
50.5
0.35
8.6
8.1
9.5
(II) (mg/1)
21.0
0.43
1.1
NF
NF
(mg/1)
5.4
65.0
75.0
48.0
0.35
8.1
8.0
7.1
28.2
0.24
NF
NF
NF
12.8
25.0
75.0
48.0
0.35
9.4
9.1
6.6
26.6
NF
0.6
NF
NF
11.5
47.0
Final Effluent (IV! fme/11d
3.2' '
3.5
8.1
1.03
NF
1.41
NF
Percent Removal at (IV)
95.5
94.8
1.8
4.8
10.3
0.46
NF
NF
NF
97.6
93.7
4.2
0.0
22.4
0.11
NF
0.89
NF
94.4
100.0
4.6
0.0
11.9
0.17
NF
0.62
NF
93.9
100.0
Cyanide Complex, Na3Cu(CN)4 plating work at 34 1/min (9 gpm) flow, 1.33X
design flow of 25.5 1/min (6.75 gpm). The acidic waste flow was 94.5
mg/1 (25 gpm), 1.5 X design flow of 60 1/min (16 gpm). The ozone con-
centration represents the amount of ozone fed into the reactor.
Roman numerals represent sample ports as per Figure 1.
NF - None found.
The metal analyses at IV should be considered only as an indication be-
cause sufficient time probably was not allowed for the clarifier to
reach equilibrium.
21
-------
Table 6
OZONE TREATMENT OF PLATING WASTE WITH SMALL EXCESS OF OZONE3
Input
CN- @ I Ozone Mole Ratio
(mg/1) (mg/1) (03/CN~)
15.2 29.7 1.05
63.0 173.1 1.33
38.0 129.8 1.84
37.5 194.8 2.81
36.3 194.8 2.91
29.0 194.8 3.64
pH at Sample Portsb
(CN~) (Reactor) Clarifier
(I) (III) (IV)
7.1-8.0 7.0 12.0
11.0 10.0 6.8
10.2 8.9 8.5
10.9 9.8 8.5
11.2 9.8 9.0
10.8 8.7 6.9
Reactor Effluent (III-)
CN~ CNO~ CN~
(mg/1) % Removal
0.52 42.5 99.2
0.23 10.6 99.1
0.35 8.9 99.1
0.21 7.2 99.4
0.08 0.0 99.7
Final Effluent (IV)
CN~ CNO~ CN~ CNO~
(mg/1) % Removal
0.64 6.0 96.6 60.5
0.90 8.4 98.6 86.7
0.60 6.3 98.4 83.4
0.9 4.4 97.6 88.3
0.75 0.5 97.9 98.6
0.31 0.0 98.9 100.0
to
aCyanide Comolex
Roman numerals represent sample ports as per Figure I.
-------
TaM« 7
PIQUE TKEAlrlPIT OF PUTIKS WASTI WITH EXCISS OZJIIEa
to
u>
zntn
a5rT.yy Vffa TpJWT^
3«-4 141.1 2.0
M-* 141.J -3
31.0 141.1 .3
32.8 143.3 .4
32.S 143.3 .4
32-1 143.1 .4
12.0 14J.1 .4
31.5 143.3 .5
10.2 141.] .6
29. S 141.1 .6
11.0 6*. 4 .7
21.5 14X1 .7
6.5 64.4 .4
S.« 64.4 .1
3.3 64.4 .6
5-3 64.4 .6
.B .t s.,01. Port,"
fCB-1 (11 mactor [HI) Clirifler ID ID
11.95 0.06 C.35 3.43 ft
31.99 0.35 IF IF IT
BD ID HO HO ID
BD ID BO 1C H>
8.86 0.13 BD 3.24 ID
BD ID BD BD ID
2.25 0.06 BF BF IT
7.30 0.37 ttr 0.37 ID
BD ID ^0 BD ID
12.60 0.39 ff jj 0.42 IF
9.07 0.21 HT 0.22 ID
39.70 0.31 1..47 0.49 IF
14.74 0.03 HF 0.56 BF
Ozon« leftctor
EffliMnt III (ma/11
0.82-0.66 ID ID ID ID ID BD
0. 22 12.0
0. (2 5.0 l.E IF IF 3.81 BF 1 0.34 BD
0.62-0.86 ID 1.5 0. 16 IF IF BF I 0. GO NO
0.64 ID 1.8 0.11 IF 0.57 BF
0.38 13.0
0.71 ID 6.9 IF BF SF F? | 0. 40 10.0
0.75 0.0 8.4 IF IF 4.86 BF 0.55 10.0
O.42 7.0 ID ID BD ID BD
0.72 0.0 1.5 0.16 BF IT BF
O.75 ID 1.1 0.11 BF IF BF
C.75 ID ID ID BD ID BD
0.04 ID 8.7 0.81 IF 0.29 BF
0.75 6.0 7.8 0.37 IF 0.68 BF
0.3 ID 2.7 0.11 IF 0.44 BF
0.3 KD 13.5 0. 37 BF IF BF
7.27 0.18 SI 0.42 IF j 0.5 ID 6.9 0.11 IF 0.73 BF
7.87 0.36 Nf 0.84 IF | 0.7 ID 7.3 0.26 BF 1.75 BF
0.54 16.0
0.52 16.0
0.60 ID
0.62 BD
0.02 BD
0.62 BD
0.08 BD
0.12 ID
0.3 ID
0.04 BD
co.pl.,
nu»«r*ls r*pr*nnt
HI * not d.tirmined
BF • not found
ports u p«r
-------
TABLE 8
THE EFFECT OF OZONE DOSAGE AT LOW CONCENTRATIONS
OF CYANIDE*
to
Influent
Cyanide Ion
(mg/1)
2.1
5.3
6.5
12.9
13.0
15.2
Mole Ratio
(03/CN-)
11.37
6.62
5.39
1.48
2.69
1.05
pH at CD
8.0
12.6
10.1
7.5
7.7
9.5
Ozone Reactor
Effluent (III)
(CN- rag/1)
0.08
0.04
0.08
0.08
0.02
0.08
Cyanide is present as Naj:u(CN)
•J *
-------
in
TABLE 9
THE EFFECT OF OZONE DOSAGE ON INTERMEDIATE CONCENTRATIONS
OF COPPER CYANIDE3
Ozone Reactor Effluent (III)
Cyanide Ion Mole Ratio
a
b
(mg/1)
29.0
37.5
32.0
34.2
38.4
Cyanide
*m XT^~
pH at
(I)
(03/CN-)
3
2
2
2
2
is present as
» — . JA4..A.A^.A.J
.64
.81
.42
.26
.01
Na3Cu(CN)4
10
10
11
9
9
.8
.9
.9
.6
.5
Cone.
(CN-)
0.08
0.35
0.38
0.60
0.62
(mg/1)
(CNO-)
0.0
8.9
13.0
ND
ND
% Removal
(CN-)
99
99
98
98
98
.7
.1
.8
.2
.4
(CNO-)
100.
76.
59.
ND
ND
0
3
4
TABLE 10
THE EFFECT OF OZONE DOSAGE ON HIGH CONCENTRATIONS
OF COPPER CYANIDE3
Ozone Reactor Effluent (III)
Cyanide Ion
(mg/1)
63.0
75.0
Mole Ratio
(03/CN-)
1.33
0.35
pH at (I)
11.0
9.4
Cone.
(CN-)
0.52
11.5
(mg/1) % Removal
(CNO-)
42.5
47.0
(CN-)
99.2
84.6
(CNO~)
32.5
37.3
Cyanide is present as Na_Cu(CN)^
-------
ISJ
TABLE 11
THE EFFECT OF CYANIDE CONCENTRATION
AT CONSTANT OZONE TO COPPER CYANIDE RATIOS
a
Ozone Reactor Effluent (HI)
Cyanide Ion Mole Ratio pH at (I) Conc.(mg/l) % Removal
(mg/1)
37.5
75.0
12.9
63.0
13.0
32.0
34.2
(03/CN-)
0.35-0.5
0.35-0.5
1.3 -1.6
1.3 -1.6
2.3 -2.7
2.3 -2.7
2.3 -2.7
10.9
9.4
9.5
11.0
7.7
11.9
9.6
(CN-)
0.35
11.5
0.08
0.52
0.02
0.38
0.6
CCNO- )
8.9
47.0
4.2
42.5
ND
13.0
ND
CCN-)
99.1
84.6
99.4
99.2
98.8
98.2
(CNO-)
76.3
37.3
59.4
ND
b Cyanide is present as Na,Cu(CN)4
None detected
-------
Insufficient experimentation was done at this level, which is well be-
yond that encountered by Sealectro, to arrive at more specific conclu-
sions such as the ozone dosage needed for complete CN~ removal
«0.1 mg/1).
d) The effect of cyanide concentration at three ozone/cyanide ratios is
shown in Table 11. These data again suggest that a larger dosage of
ozone is needed to reach the same residual cyanide concentration
(<1 mg/1) at higher influent cyanide concentrations.
The pH of the cyanide waste prior to ozone treatment (Sample Port I)
was found not to be a critical variable in the range of 7.0.to 13.0,
as shown by data in Table 7. It was observed that ozone treatment lowers
the pH by approximately one pH unit, as indicated by comparing the data in
Tables 4, 6 and 7, for Sample Ports I and III, i.e., before and after ozo-
nation.
The pH of the treated effluent in the clarifier also is not critical,
as far as the cyanide and cyanate concentrations are concerned. Acidic pH
in the settling tank leads to lower cyanate and cyanide concentrations
probably by accelerating decomposition of them as indicated by the data in
Table 4. Surprisingly, the acidic pH did not seem to increase the total
copper and silver concentrations in the effluent (IV). The explanation may
be that these metals are present as relatively insoluble oxides or the
times of these experimental runs were insufficient to establish equilibrium
in the settling tank (See Section 5). Analyses are, however, total values
and it should be noted that the metal values presented in Tables 4 to 7
reflect both soluble and suspended (non-settled) metal in the effluent.
An increase of ozone concentration from 1% to 2% in the ozone feed did
not produce a significant reduction in cyanide or cyanate concentration under
the test conditions, as indicated by the data in Tables 4 and 7. This result
suggests that mass transfer of ozone is not the limiting parameter under the
conditions of this study.
The reaction temperature was carefully recorded for all experiments but
variations did not produce an observable effect. No effort was made to con-
trol the temperature. The ambient wastewater temperature varied in the range
of 14 to 20 C during the test program.
27
-------
SECTION 8
TREATMENT OF SODIUM CYANIDE
The ozone treatment of sodium cyanide was studied during a summer plant
shut-down. The approach taken was as outlined in Section 5. The results
summarized in Table 12 indicate that ozone treatment effectively destroys
sodium cyanide as well as the cyanate generated as an intermediate. Complete
removal of cyanide and cyanate is possible if a sufficiently large ozone
dosage is used. A mole ratio of 2.65 ozone/cyanide or higher removed at
least 97.6% of the cyanide. However, a mole ratio of 4.3 ozone/cyanide was
needed to remove 44.8% of the cyanate generated and an 0 /CN"ratio of 14.0
was needed for 97% CNO~ removal. The pH was again not critical based on re-
actions carried out at several pH's in the range of 7.7 to 10.5. Thus, it
appears that ozonation of cyanide is more rapid than the ozonation and, pos-
sibly, the hydrolysis of cyanate.
The main process parameters, cyanide concentration, ozone/cyanide mole
ratios, and pH were varied through a very broad range to cover all areas of
interest. Additional experiments are still needed to refine the results.
28
-------
TABLE 12
OZONE TREATMENT OF SODIUM CYANIDE ON PLANT SCALE*
to
VD
Input
Cyanide Ion Mole Ratio
pH at Sample Ports
I III
Ozone Reactor Effluent (III)
Conc.fmg/1) % Removal
(mg/1)
3.6
19.2
18.0
34.0
55.0
140.0
250.0
to
43
1.4
8
4
2
1
0
3/CN-)
.0
.0
.11
.30
.65
.04
.58
8
7
8
9
10
10
10
.2
.7
.2
.6
.1
.5
.4
5.
5.
5.
7.
8.
9.
9.
4
7
4
3
9
6
2
(CN-)
0.0
0.23
0.23
0.38
1.30
40.0
71.0
CCNO-)
0.0
0.6
5.3
30.0
56.0
71.0
209.0
(CN
100
98
98
98
97
71
71
~)
.0
.8
.7
.9
.6
.4
.6
(CNO-)
100.0
96.9
70.6
44.8
36.3
37.5
28.2
Sodium Cyanide (NaCN)
Roman numerals represent sample ports as per Figure 1
-------
SECTION 9
DISCUSSION
This demonstration study program reconfirmed on a plant scale our ear-
lier laboratory findings (6) that ozone treatment of copper cyanide plating
waste is effective, economical, safe and reliable. The treatment of sodium
cyanide is also effective. It was studied briefly in order to establish
relative ease of treatment on a plant scale. The data in Tables 3 and 11 in-
dicate that copper cyanide reacts faster and requires less ozone than does
sodium cyanide. This is consistent with earlier evidence that copper is a
catalyst for cyanide ozonation.
The Sealectro Plating Plant is a small plating facility. It plates ap-
proximately 2.6m /hr surface area and has an installed DC amperage capacity
of 1200 amps. The wastewater discharge from this plant is subject to the
Westchester County Sewer Code and the EPA standards for small plating instal-
lations, as discussed in detail in Section 3. The Sealectro Plant operates
well within those standards when following the standard operating procedures
with the PCI ozone system.
The new Sealectro Plating Plant produces an average flow of 130 1/min
(34 gpm) wastewater consisting of 34 1/min (9 gpm) alkaline cyanide flow and
95 1/min (25 gpm) acid waste flow. This is an unusually high flow for such
a small operation. The management believes that the high rinse water flow as-
sures the all important high quality plating at minimum cost. Furthermore,
the acid flow should contain no cyanide, but it does contain cyanide in the
range of 0.2 to 0.8 mg/1 from leaks and unidentified sources.
The above two problems, namely excessive wastewater flow and cyanide in
the acid line, placed a limitation on this study. Efforts were made by
Sealectro Corp. to resolve them. Definite improvements were made, but the
problems were not completely resolved during this study. We expect that with
further experience in the plating shop these problems will be minimized and
resolved.
The demonstration study produced valuable information concerning the
process parameters for plating waste treatment and the safety of ozone treat-
ment, as discussed below. It should be recognized that the data obtained in
this study are strictly true for the ozone contactors used and for ozone con-
tactors of very similar design. Other type of contactors such as multistage
diffusion systems, positive pressure injectors, etc., may lead to somewhat
different results. Key considerations should be the mass transfer rate of
ozone and the concentration of cyanide being treated.
30
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OZONE DOSAGE
The ozone dosage, that is, the mole ratio of ozone to cyanide, is the
most important process parameter. However, the ozone dosage required for
the complete destruction of cyanide is also-dependent on the cyanide concen-
tration. A mole ratio of 1 to 1.5 mole ozone per mole of cyanide was found
to be sufficient for the complete destruction (CN~<0.1 mg/1) of copper cya-
nide when cyanide concentration was 20 mg/1 or less. This requirement grad-
ually increases to 3.0 moles of ozone per mole of cyanide at cyanide concen-
trations of 75 mg/1.
There are several possible explanations for the dependence of the mole
ratio on cyanide concentration, as follows:
a) The mass transfer of ozone from gas to water is the rate controlling
step in the initial stages of the reaction. The destruction of the
last 4 to 5% cyanide is reaction rate controlled (10). To achieve com-
plete cyanide destruction (0.1 mg/1 CN~ or less) at high initial cya-
nide concentrations, ozone must be fed into the system for a longer
period of time under slow, reaction rate controlled conditions. How-
ever, under these conditions more ozone may be consumed by competing
side reactions such as oxidative destruction of cyanates to carbon di-
oxide.
b) The cyanide waste may also contain hard-to-decompose cyanide complexes
such as iron complexes or slower reacting sodium cyanide. These re-
quire a higher mole ratio of ozone to lower the final level of cyanide
to 0.1 mg/1 or below. Although we have occasionally detected iron in
the Sealectro plating waste, in most cases it was not present in sig-
nificant amounts. The waste was not analyzed for other cyanide salts
or complexes.
c) The final, reaction rate controlled part of the reaction may be slow
because all the copper is removed by oxidation and precipitation as in-
soluble copper oxide; thus, no copper catalysis occurs.
Most likely all three cases occur. However, the Sealectro Plant nor-
mally treats a relatively low concentration of cyanide where these problems
are not very important. At higher cyanide concentration, the ozone dosage
might be minimized by using a multistage ozone contact tank with possible
uv irradiation in the final stage, if necessary.
pH OF CYANIDE WASTE
The pH of cyanide waste before the ozone treatment is relatively unim-
portant in the range of 7 to 10. Since the cyanide waste is normally dis-
charged from the plating plant in this pH range, no pH adjustment is neces-
sary prior to ozone treatment. This finding represents a significant saving
in capital cost since it eliminates one complete pH control system and one
agitator.
31
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REACTION TEMPERATURE
Reaction temperature did not have a significant effect in the normal
ambient temperature range of 14 to 20°C, which is in agreement with previous
observations (12).
SLUDGE FROM THE REACTION
The sludge from the reaction was collected at the bottom of the clari-
fier. The sludge that settled during the process parameter study was discar-
ded, since there was no way to assure equilibrium conditions in the settling
tank.
During the optimum conditions experiments the sludge was collected. How-
ever, only a small amount formed during the two weeks of operation. The
sludge was heavy, readily settleable, and filterable. The analysis of its
metal content is noted in Section 6. The operation of the settling tanks was
not studied in depth due to the shortness of the study time. The use of co-
agulants and settling tubes could be expected to improve the settling sub-
stantially and could result in further improvements in the effluent quality.
RECYCLING OF TREATED EFFLUENT
Recycling of treated effluent was outside the scope of the project and
was not investigated due to a lack of time. However, it is clear that the ef-
fluent could be used as cooling water for the ozone generator and for other
equipment, such as air conditioning and other machinery.
The recycling of the effluent into the plating process is a real pos-
sibility in the Sealectro Plant under the following conditions:
a) If cyanide is kept out of the acid waste flow.
b) If a slightly larger ozone dosage is used, approximately 2 moles of ozone
per mole of cyanide, to assure essentially complete removal of all cya-
nate and copper and, possibly, more of the other trace metals.
c) If a coagulant is added or settling tubes are used in the settling tank
to further improve metal removal.
Naturally, prior to embarking on a recycling program it should be ascer-
tained that there is no adverse effect on plating quality.
In conclusion, the Sealectro demonstration project is believed to have
achieved its major objectives and is presently discharging an environmentally
acceptable effluent.
32
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SECTION 10
COST EVALUATION
The Sealectro Plating Waste Treatment Plant was designed with the re-
quirements of a plant demonstration study in mind. Consequently, the design
exceeds the normal requirements for an operating plant in several respects,
especially in ozone generating capacity, instrumentation and flexibility built
into the plant. Naturally, these extras carry a price tag. Therefore, the
cost data given here should be considered with the above in mind.
To present the most accurate and useful cost evaluation, data are com-
piled for the Sealectro Plant as it was built, as well as for a new hypothe-
tical plant as it would be built as an optimized operating plant based on the
Sealectro experience. The Sealectro data were based on 1973 prices while the
new plant data are based on 1975 prices.
The Sealectro Plant proved by weeks of continuous (16 hr/day) operation
that it can treat the following plating waste, well above original design
values:
a) Cyanide Waste: 34 1/min average, 57 1/min peak (9 gpm average, 15 gpm
peak) for short periods, cyanide (CN~) concentration
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TABLE 13
CAPITAL COST OF OZONE TREATMENT
1975 1973
Optimum Actual
Ozone Generator, PCI, G-20 with auxilliary Air
Prep Unit PRE-23 20 Ib/day 0 $25,000 $ -
26 Ib/day 0^ - 26,000a
Ozone Detector - Auto Control - PCI 2,700 2,500
Tanks 3,000 3,900
pH Control System - Foxboro/PCI 3,000 2,800
Installation 5,000 10,000
Central Control Panel - 800
Building 300 sq ft @ $25/ft^ 7,500
360 sq ft § $22/ft - 7,922C
Holding Tanks, pumps, auxilliaries (above ground) 5,000 - d
(underground) - 12,691
TOTAL CAPITAL COST $51,200 $66,613
a The ozone generating capacity of this ozone generator is 30% higher
than necessary to provide flexibility for the EPA study.
b Although only one pH control loop is necessary, two loops were in-
stalled to provide flexibility for the EPA study.
c The cost of the building may vary depending on location and type of
construction.
The holding tanks at Sealectro were exceptionally expensive. Due to
space limitations they were installed underground in a high water
table, flood area. Normally, above ground tanks would suffice.
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TABLE 14
WEEKLY OPERATING COST FOR OZONE TREATMENT
1975
Optimum
Labor: caustic make-up, operate 5 hr/wk 8 $10/hr $ 50.00
3 hr/wk 8 $16.67/hr
Maintenance: maintenance, repair, housekeeping
5 hr/wk 8 $7/hr
7 hr/wk 8 $5.52/hr
Power 20 Ib 0 /day 8 11.5 kwh/lb 0 8 Sf/kwh
10 Ib 03/day 8 11.5 kwh/lb 0^ 8 7*/kwh
Chemicals 420 Ib NaOH/wk § 26
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TABLE 15
TREATMENT COSTS
1975 Optimum 1973 Actual
24 hr/day 16 hr/day
Capital Cost $ 51,200.00, 66,613.00,
$/1000 gal 1,045.70? 2,040.86°
$/1000 1 276.76 539.91
Total Operating Cost $/day 50.34 55.50
$71000 gal 1.03 1.70
$/1000 1 0.27 0.45
Total Treatment Cost $/dayC 63.99 73.26
$/1000 gal 1.31 2.24
$71000 1 0.35 0.59
Due to the 16 hr/day operation at Sealectro, these costs are ap-
proximately 1.5X higher than they would be for a 24 hr/day operation.
These costs are capital cost/daily volume and not depreciated.
These costs include capital equipment depreciated over 15 years (at
250 day/yr) and operating costs.
36
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TABLE 16
CYANIDE DESTRUCTION COSTS
Capital Cost
1975 Optimum 1973 Actual
24 hr/day 16 hr/daya
45,000.00, 55,468.00V
1 918.58° 1,698.41?
$71000 gal 3,472.22° 6,420.00?.
15,254.23^ 28,182.55?
6,933.74b 12,810.25b
Operating Cost
$/day 18.50 15.09
$71000 1 0.38 0.46
$/1000 gal 1.43 1.75
$/kg CN 6.27 7.66
$/lb CN 2.85 3.48
c
Total CN Removal Costs
$/daX 30.50 29.88
$/1000 1 0.62 0.91
$71000 gal 2.35 3.45
$/kg CN 10.34 15.18
$/lb CN 4.70 6.90
Due to the 16 hr/day operation at Sealectro, these costs are ap-
proximately 1.5X higher than they would be for a 24 hr/day operation,
These costs are not depreciated.
These costs include capital equipment depreciated over 15 years (at
250 day/yr) and operating costs.
37
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SECTION 11
ANALYTICAL METHODS
Table 17 presents the references for the analytical procedures used
during the course of this project. These are the methods commonly used in
the electroplating industry, although it must be recognized that only the
larger companies can be expected to have the equipment and trained personnel
necessary to carry out the analyses. (It should also be noted that analy-
tical services., either in-house or purchased, were not included as a line
item in the cost assessment.)
38
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CNO"
Cu
Ag
Ni
Pb
Sn
TABLE 17
ANALYTICAL METHODS
Compound to
Be Analyzed
NaCN as CN~
Na Cu(CN)
as CN" 4
Method Used
Modified Liebig
Titration
Modified Liebig
Titration
Range of
Application
Cmg/1)
1-20
1-20
Limit of
Detection
(ing/l)
0.1
0.1
Source
a
a
p-dimethylben-
zalrhodanine as
indicator
Pyridine- 0.07-5
Pyrazolone
Colormetric
Selective Ion
Electrode 1.0 -10.0
Modified Nessler
Method 1.0 -10.0
Atomic Absorption
Spectroscopy
(A.A.S.)
Sources
0.05
0.5
0.5
c, d
0.2
0.1
0.3
0.5
20
0.2
0.1
0.3
0.5
20
f
f
f
f
f
Dodge, Zabban § Serfass, Analytical Methods for the Determination of Cya-
nides in Plating Wastes and in Effluents from Treatment Processes, Plating,
39: pp 267-273, 1952.
Standard Methods for the Examination of Water and Wastewater, APHA: AWWA:
WPCF, 1965, pp. 448-457.
Riseman, John, Electrode Techniques for Measuring Cyanide in Wastewaters,
American Laboratory,. Dec. 1972.
39
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TABLE 17 (Continued)
Sources
Frant, M. S., J. Ross, J. Riseman, Electrode Indicator Technique for
Measuring Low Levels of Cyanide, Orion Research, Inc., Cambridge, MA.
Dodge, B. F., and W. Zabban, Analytical Methods for the Determination of Cya-
nates in Plating Wastes and in Effluents from Treatment Processes, Plating,
39: pp 381-384, 1952.
Elwell, W. T. and J. A. F. Gidley, Atomic Absorption Spectrophotometry,
2nd Edition, Bergman Press, N.Y., 1966.
° Instruments used for analysis: 1. Beckman Spectrograph Model DB-GT.
2. A.A.S. - Atomic Absorption Spectrophotometer made by Aztec, Inc.
3. Selective Ion Electrode, Model 407A, Orion Corp. (CN~) electrode 94-06A;
Ref electrode 91-0100.
40
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REFERENCES
1. Battelle Memorial Institute for U.S. Dept. of Interior, Federal Water
Quality Administration: A State-of-the-Art Review of Metal Finishing
Waste Treatment, Water Pollution Control Research Series 12010 EIE,
Nov, 1968.
2. Lancy, L. E., Economic Study of Metal Finishing Waste Treatment, at
53rd Annual Convention, American Electroplaters Society, East Orange,
NJ, June, 1966.
3. Mulcahy, E. W., Pollution by Metallurgical Trade Wastes. A Study of
Causes and Suggested Cures, Metal Finishing, I: 289, July, 1955.
4. Pinner, W. L., Progress Report of American Electroplaters Society Re-
search Projects on Plating Room Waste, In: Proced. 7th Industrial
Waste Conference, Purdue Univ. Eng. Ser. No. 79, 1952. pp 518-540.
5. Bollyky, L. J., Removing Specific Contaminants from Water: Cyanide,
Environmental Engineers' Handbook, Liptak, B. G. (ed.), Chilton Book Co.
Radnor, PA, 1974. Vol. I, pp 1587-9.
6. Bollyky, L. J., Ozone Treatment of Cyanide and Plating Waste. In:
Proc. of the First Symposium of the International Ozone Institute,
Washington, DC, International Ozone Institute, Syracuse, NY, Dec, 1973.
7. Ozone Counters Waste Cyanides Lethal Punch, Chem. Eng. (Mar, 1958).
8. Guillerd, J. and C. Valin, Traitment par 1'Ozone, L'Eau, May, 1961.
9. Diaper, E. W. J., Ozone Moves to the Fore, Water and Wastes Eng., pp 65-
69, May, 1972.
10. Sondak, N. E. and B, F. Dodge, The Oxidation of Cyanide-Bearing Plating
Wastes by Ozone, Plating, 48: 173-180, Fed, 1961; pp 280-284, Mar,
•i- y o A •
11. Selm, R. P., Ozone Oxidation of Aqueous Cyanide Waste Solutions in
Stirred Batch Reactors and Packed Towers, Amer. Chem. Soc. Ozone Chem-
istry and Technology, Advances in Chemistry Series, #21, 1959. pp 66-
/ / •
lib. Mathieu, G. I., In: Proc. of the First Symposium of the International
Ozone Institute, Washington, DC; International Ozone Institute, Syra-
cuse, NY, Dec, 1973. pp 533-550 (See also Ref. 10, 21).
41
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12. Khandelwal, K. K., A. J. Barduhn and C. S. Grove, Kinetics of Ozonation
of Cyanides, Amer. Chem. Soc. Ozone Chemistry and Technology. Advances
in Chemistry Series, #21, 1959. pp 78-86.
13. Walker, C. A. and W. Zabban, Plating, 40: 777-780, 1953.
14. Niegowski, S., Ind. Eng. Chem., 45: 632, 1953.
15. Tyler, R. G., W. Maske, M. J. Westing, and W. Mathews, Sewage and Ind.
Wastes, 23: 1150-1153, 1951.
16. Neuwirth, F., Berg-u Huttenman, Jahrb., 81: 126-131, 1933.
17. Serota, L., Cyanide Waste Treatment Ozonation and Electrolysis, Metal
Finishing, 56: 71-74, 1958.
18. Kandzus, P. F., and A. A. Mokina, Use of Ozone for Purifying Industrial
Waste Waters, Tr., Vses. Nauch. -Issled. Inst. Vodosnabzh, Kanaliz.,
Gidrotekh. S-oruzhenii Imzh. Gidrogol., 20: 40-5, 1967 (Russ.); C.A.,
71: 6388v, 1969.
.19. Bischoff, Ch., Fine Purification of Waste Water by Ozone with Low Pol-
lution Load, Fortschr. Wasserchem. Ihrer Grenzgeb., 9: 121-30, 1968
(Ger.); C.A., 70: 14237q, 1969.
20. Bahenski, V. and Zika, Treating Cyanide Wastes by Oxidation with Ozone,
Koroze Ochrana Mater., 10 (1): 19-21, 1966; C.A., 65: 6907c, 1966.
21. Garrison, R. G., C. E. Mauk, and H. W. Prengle, Cyanide Disposal System,
In: Proc. of the First Symposium of the International Ozone Institute,
Washington, DC, International Ozone Institute, Syracuse, NY, Dec, 1973.
42
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-77-104
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Ozone Treatment of Cyanide-Bearing Plating Waste
5. REPORT DATE
June 1977 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
L. Joseph Bollyky, PCI Ozone.,
8. PERFORMING ORGANIZATION REPORT NO.
9. PERF
WING ORGANIZATION NAME AND ADDRESS
Sealectro Corporation
225 Hoyt St.
Mamaroneck, New York 10543
10. PROGRAM ELEMENT NO.
1BB610
11. CONTRACT/GRANT NO.
R 802335
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Lab,
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, 0-hio 45268
- Cin., OH
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/12
15. SUPPLEMENTARY NOTES
The use of ozone for CN destruction in the metal finishing -industry has long
been recognized as a technically attractive alternative to chlorine oxidation. High
capital cost has, in earlier years, prevented its implementation.
This report documents a full scale installation in which it was demonstrated
that alkaline cyanide waste could be effectively destroyed to levels well below
1 ppm and with CN~ removal?? of 99% at the levels normally encountered, thus satis-
fying BATEA requirements. Design features, problems and capital and operating cost
data are presented and discussed.
Selected aspects of the cyanide-ozone reaction were also studied, such as the
effect of CN~/03 ratios, cyanide source and concentration and the effectiveness of
ozone for cyanate elimination.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Water pollution; Abatement; Metal
finishing; Electroplating; Waste treat-
ment; Waste water; Oxidation; Cyanides;
Ozone
b.lDENTIFIERS/OPEN ENDED TERMS
uzonatlon; metal
oxides; Cyanide removal
c. COS AT I Field/Group
Unclassified
CLASS (This Report)
iihl
EPA Form 2220-1 (9-73)
ITY CLASS (Thispage)
Unclaaalfj
21. NO. OF PAGES
51
22. PRICE
43
U.S. GOVERNMENT PRINTING OFFICE: 1977-757-056M28 Region No. 5-ll
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