EPA-600/2-77-038
February 1977
Environmental Protection Technology Series
ZINC SLUDGE RECYCLING AFTER KASTONE®
TREATMENT OF CYANIDE-BEARING
RINSE WATER
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 five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental 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-600/2-77-038
February 1977
ZINC SLUDGE RECYCLING
AFTER KASTONE© TREATMENT OF CYANIDE-
BEARING RINSE WATER
by
Joseph G. Moser
Metal Plating Corporation
Connersville, Indiana 47331
Grant No. S803265-01
Project Officer
Donald L. Wilson
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. U. S. Environmental Protection Agency, and
approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the the
U. S. Environmental Protection Agency, nor does mention of trade
names or commercial products constitute endorsement or recommen-
dation for use.
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FOREWORD
When energy and material resources are extracted, processed,
converted, and used, the pollution to our environment and to our
aesthetic and physical well-being requires corrective approaches
that recognize the complex environmental impact these operations
have.
The Industrial Environmental Research Laboratory - Cincinnati
uses a multidisciplinary approach to develop and demonstrate
technologies that will rectify the pollutionai aspects of these
operations. The Laboratory assesses the environmental and socio-
economic impact of industrial and energy-related activities and
identifies, evaluates and demonstrates control alternatives.
This report is a product of the above efforts. It attempts
to show the feasibility of zinc metal recovery after oxidation
of cyanide by formaldehyde and Kastone®. Included is a critique
of the design of necessary equipment and modifications of the
plating process needed to accommodate the recovery.
It was found that the zinc sludge could be recovered. This
recovery required minimizing volume of the solids, by eliminating
water hardness and then utlizing filtration. There are savings
which result primarily from lowered anode useage as well as the
recovered zinc. Recycling is useful to metal finishers using the
Kastone system where transportation cost to landfill are high.
Transportation costs would be $2,000.00 per year minimum at $40.00
pen drum of sludge. Thus those companies whose transportation
costs are as large as this would benefit from recycling as an
economic alternative.
Further information on the subject could be obtained from
the Industrial Pollution Control Division, Industrial Environ-
mental Research Laboratory, U.S. Environmental Protection Agency,
Cincinnati, Ohio.
D.G. btephan, Ph. D.
Director
Industrial Environmental Research Laboratory
in
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ABSTRACT
The purpose of this project was to demonstrate the feasibility
of reclaiming sludge. The sludge was produced by the destruc-
tion of cyanide by Kastone@in zinc-cyanide dragout rinse water,
The clear supernatant was discharged to the municipal sewer
and the sludge eventually recycled to the plating tank. The
general approach was to transfer cyanide-bearing rinse water to
the treatment tank, treat, settle, decant clear supernatant.
transfer sludge for further concentration, and in one way or
another return dissolved sludge to the plating tanks.
The possibilities of contaminant accumulation were present.
Breakdown products, ferrocyanide. copper and other possible
metallics would be returned to the plating tank. The opera-
tion at Metal Plating Corporation has two plating tanks. This
allowed a control and experimental tank for evaluation. The
major difficulty encountered was a precipitate mostly of
calcium and magnesium hydroxides that was formed in the treat-
ment process and does not redissolve as does the zinc oxide
sludge. The presence of calcium and magnesium is known to be
present in the water used. The hydroxide sludge presented
mechanical problems in handling in the recycling process.
It was also found that methods used to minimize dragout mini-
mized subsequent treatment and had a positive influence on our
recycling efforts.
This report was prepared and submitted by Metal Plating
Corporation under partial sponsorship of the USEPA in fulfill-
ment of Project No. S-803265. This project was completed as
of July 15. 1975.
IV
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CONTENTS
Foreword iii
Abstract iv
List of Figures vi
List of Tables vi
Acknowledgments vii
I Introduction 1
II Conclusions 5
III Process Discussion 8
IV Proposed Method of Recycling and General Procedures 11
V Appendices 14
1. Equipment List and Figures Showing Approxi-
mate Layout of Equipment
2. Critique and Recommendations 17
3. Detailed Procedure tor Treatment and 17
Recycling
4. Types of Recycle Observed 19
5. Analytical Procedures Used for Cyanides 24
6. Addendum 27
v
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LIST OF FIGURES
Number page
1 Schematic layout of equipment - a nonpropor-
tioned view of the general hookup of equipment. 12
2 Schematic showing approximate layout of treat-
ment and recycling equipment. 15
3 Schematic showing an overhead view of the
positioning of all the equipment used and the
area they take up. 16
4 Analytical equipment used for the total distilla-
tion for CN-. 27
LIST OF TABLES
1 Examples of Daily Treatment
2 Examples of Total NaCN in Plant Effluent
vi
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ACKNOWLEDGMENTS
The author acknowledges the efforts of Mr. Matthew
Stringham and Mr. Lee Heck, technicians, who closely assisted
in the recycling project. Without their help much of the
project would not have been accomplished. Also vital to the
project were the technical help, suggestions and attention of
Dr. Bernard Lawes and Mr. John Straub of DuPont Company.
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SECTION I
INTRODUCTION
The conventional method of treating metal finishing wastes is
chemical oxidation of cyanide, reduction of chromate, and pre-
cipitation of the heavy metals. The heavy metal sludge is gen-
erally disposed of by landfill burial, which represents an
economic loss to the plater and an irretrievable material loss
of a non-renewable metal resource. Cyanide zinc plating is a
major portion of all cyanide plating in the country, and much
of the zinc metal value is lost each year by platers because
the zinc metal lost in the rinse water is not recovered and
reused. Large quantities of metals are similarly lost from
cyanide copper, cyanide brass and cyanide cadmium plating oper-
ations. There has been no systematic plant demonstration to
show that sludges produced by current destruction processes for
cyanide plating wastes can be recycled to plating baths. The
second problem is that as platers adopt water conservation
techniques, it is expected that the concentration of typical
rinses will increase from 40-500 mg/1 NaCN up to about 2000 -
3000 mg/1 NaCN. Chlorination of these more concentrated rinses
requires that extreme care be taken to avoid the release
of a chemical intermediate, highly noxious cyanogen chloride
gas. There is thus a need to demonstrate a process that does
not have the potential for producing this intermediate in the
treatment of concentrated cyanide rinses, and which allows
simple recycle of the resultant metal precipitate.
To briefly summarize, a cyanide zinc rinse containing typically
500-5000 mg/1 NaCN is first treated at up to 104'P (40°C) for
about 1 hour using roughly equimolar guanities of formalin (37%
solution of formaldehyde) and Kastone® peroxygen compound (Reg.
U. s. Pat. & tm. off., DuPont Company), a specially formulated
peroxygen product containing about 41% hydrogen peroxide and
special stabilizers and flocculants. During treatment, free
cyanide is converted to a mixture of ammonia, sodium cyanate,
and glycolic acid amide, and concomitantly the zinc ion is
precipitated as zinc oxide. The zinc oxide sludge can be re-
moved by settling without the use of added polyelectrolyte, and
can be filtered to yield a high solids sludge, e.g., containing
up to 20% by weight of zinc (calc. as Zn). The sludge is then
dissolved in a quantity of plating solution, and the resulting
solution, after filtration to remove any insolubles, is fed to
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the original cyanide zinc plating bath.
Metal Plating Corporation obtained provisional permission to
operate the DuPont Kastone® system from the Indiana State Board
of Health in March 1973. The company went on stream in June
1973, obtained the grant for this demonstration project effective
July 1974, and started recycling sludge in November 1974. From
March 1973 to November 1974, some 53-55 gal drums of precipi-
tated zinc plus calcium and magnesium sludges were accumulated;
since the advent of recycling, no more has accumulated. The
operation of the Kastone® system has been successful. About
1100 gal (4164 1) of rinse water is pumped to the treatment
system. Approximately 1000-3000 mg/1 of NaCN was reduced to
1.0 - 7.0 mg/1 NaCN, the latter analyzed by total distillation.
"Hie treated solution contains <^.25 mg/1 free NaCN. Analyses
of total plant effluent indicated <1.0 mg/1 NaCN (by total
distillation). Examples of treatment are indicated in Tables
1 and 2.
Since this is the first project of this sort to attempt zinc
sludge recycling, there were several unknown parameters that
had to be estimated. The first parameter was the size of any
filters used. It became quickly evident that the initial
filter was too small. The second parameter was how well the
sludge would concentrate. The third was how much any insol-
ubles would interfere with the recycling. Fourth, would the
return of any breakdown products from brighteners, cyanides,
and formaldehyde interfere with the plating bath? Other re-
turned (recycled) impurities would be copper and ferrocyanides.
Would these have any accumulative effects?
The one problem area in the process that needed to be overcome
was the labor intensive aspects of the recycling. This in
itself is basically a matter of design and sizing of the filtra-
tion unit for concentrating the zinc slidge. Currently it takes
about 3 hours of direct labor to accumulate the sludge. A
reduction in the amount of chemicals that require treatment
can reduce the volume of sludge to be handles and thereby
reduce the time required to handle the resultant volume of sludge.
A secondary benefit of reduced treatment costs can also be
realized. This has been indicated by experimenting with a
drip station before the first rinse tank after plating.
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TABLE 1. EXAMPLES OF DAILY TREATMENT a.b,C,d
Date NaCN Orig.pH/ Additions Final
(mg/1)
14Nov74
27Nov74
02Dec74
13Dec74
27jan75
19Feb75
27Feb75
10Mar75
27Mar75
15 Apr 7 5
08May75
16Jun75
2511®
1480
2381
1795
2871
3365
775
3665
578
2156
1646
2372
Adj. pH
12
12
12
12
12
12
12
13
12
12
12
12
.4/10/6
.5/10.6
.8/11
.9/10
.9/11
.8/11
.0/11
.2/11
.4/10
.9/10
.4/10
.1/10
.4
.7
.6
.3
.5
.2
.6
.6
.4
.4
NaHCO
db)
40
40
60
40
40
40
20
60
20
40
40
40
HCHO
(gal)
3.0
3.0
5.0
3.0
4.0
5.0
2.0
5.0
1.0
3.0
2.0
4.0
Kas'tone© pH
(gal)
6
5
6
5
6
7
3
7
2
4
4
6
.0
.0
.6
.0
.6
.0
.0
.8
.0
.4
.0
.0
10
10
10
10
10
10
10
10
10
10
10
10
NaCNr
(mg/1 )
.4
.1
.2
.0
.8
.7
.5
.6
.2
.1
.2
.2
2.0e'9
5.8
1.2
5.8
3.2
7.8
3.2
3.4
1.8
.76
1.6
2.0
a Volumes treated ranged from 960 to 1200 gal.
b Temperature change was due to heating ranged from 18
to 25°C initially to a final temperature usually 29-
41" C, and volumes ranged from 960 gal to 1200 gal.
c Reaction time is at least 1 hour. There are bccas-
sions where up to \\ hours were needed to get reac-
tion tetnpeature up to 40 C.
d Settling times are usually 2 hours.
e Samples were taken directly from the treatment tank.
f Free NaCN <.25 mg/1 (Appendix 5).
g NaCN in the last column is total NaCN by distillation.
(Appendix 5).
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TABLE 2. EXAMPLES OF TOTAL NaCN IN THE PLANT EFFLUENT3'b'c»d'e
Date Total NaCNd
by distillation
20Jan75 .45 mg/1
27Jan75 No Analysis6
19Feb75 .35 mg/1
27Feb75 .45 mg/1
10Mar75 .35 mg/1
27Mar75 No Analysis
15Apr75 .32 mg/1
08May75 No Analysis
16Jun75 1.2 mg/1
a These data are generally consistent with the bulk of the
data accumulated.
b The samples are taken from a manhole access situated at
the intersection of 17th and Georgia Streets, southwest
of the plant. Another plant's effluent gets into our
effluent and somewhat affects our analysis by dilution.
This effect can be minimized but not altogether elimina-
ted.
c The samples are taken during time of discharge of treated
supernatant to the sewer.
d Free NaCN is generally <.125 mg/1 (Appendix 5).
e The dates on which there is no analysis are days when it
rained. The storm sewer and sanitary sewer are one, and
massive dilution occurs.
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SECTION II
CONCLUSIONS
After investigating different types of recycling utilizing a
pilot process, it was concluded that recycling of zinc oxide
sludge following treatment of cyanide-zinc-bearing rinse waters
is feasible with the following qualifications:
1. Equipment should be scaled up and designed to minimize
labor.
2. Sludge generated is best handled on a day-to-day basis
versus weekly accumulation.
3. Bag type filtration is the better of the two types of
filtration tested. This is not an endorsement or
criticism of the particular makes employed. The bag
type filter was simply easier to operate.
4. Dragout should be minimized by using dragout stations
where feasible, or use other methods to minimize drag-
out such as air knives..
5. Slightly lowered anode useage was observed in the
reclaiming process. The lowering of the useage was
in the range of 10% - 30% depending on bath formula-
tion and eventual transportation to landfill are
taken into account, the savings become significant
enough to warrant a positive attitude toward re-
cycling.
6. Secondary insolubles create some sludge handling
difficulties. However, treated water (i.e. softening)
eliminates these insolubles. Should the insolubles
enter the plating tanks no apparent plating problems
occur.
The mentioned insolubles result from the formation of calcium
and magnesium hydroxides in the cyanide treatment process.
These precipitates are gelatinous in nature and are inherently
hard to filter out completely. Waters found in Indiana ordi-
narily contain 250 - 350 mg/1 of total calcium and magnesium.
This translates to 3.0 - 3.5 Ib (1.36 - 1.58 kg) of these
hydroxides in the sludge . They also constituted 30% - 40%
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of the volume of the sludge handled. Some insolubles come
from the Kastone® formulation: but these are on the order of
only JLO% of the total insolubles coming from the hardness in
the water itself.
At the beginning of the recycling project both tanks had 27
anodes (baskets and zinc ball anodes) on 3 anode bars. The
bars split the 1400 gal plating tank into 2 stations. Zinc
content in both baths rose from about 4.0 oz/gal (30 g/1) to
near 5.0 oz/gal (37.4 g/1) and NaCN was raised accordingly
(NaCNrZn ratio was kept near 2.8:1 to 3.0:1). By placing
steel anodes so that each bar had 5 zinc anodes and 4 steel
anodes (15 total and 12 total zinc and steel per tank) the
zinc metal content was reduced to about 4.0 oz/gal (30.0 g/1)
zinc. Currently the following anode composition is being used
- 18 zinc anodes and 15 steel anodes per tank. Each bar
contains 6 steel and 5 zinc anodes equally spaced and placed -
zinc - steel - zinc - steel, etc.
This has resulted in some savings in anodes. The recycling
in the experimental tank appears to have offset some zinc
anode useage also. The "fine tuning" of the plating bath
anode composition resulted in stabilizing the zinc content
near 4.3 - 4.5 oz/gal (32.2 - 33.8 g/1). Zinc ball anode
consumption was reduced by about 30% at most. On the average,
the control tank took 35 Ib/day of zinc ball anodes.
Reduction of the amount of cyanide treated is economically
advantageous. A drip station was used for a limited time.
The initial data, though not conclusive indicates a reduction
of approximately 50% of dragged out cyanide and subsequent
treatment.
The main advantage to recycling of sludge is primarily econ-
omical. Equipment can be amortized, whereas the aforemen-
tioned accumulation storage and transportation are simply
ongoing costs. »s indicated the project was set up as a
pilot project and proper scaling of the equipment becomes
imperative to minimize labor.
A general layout and overview of the equipment utilized to
date is given in figures 2 and 3, Appendix 1.
ECONOMICS OF RECYCLING
1. Daily Treatment Costs (Cyanide converted to Cyanate):
Chemicals
3.0 gal Formaldehyde, 28.8 Ib @ $ .094/lb $ 2.71
5.0 gal Kastone® ,500 Ib @ $ .245/lb 12.25
40.0 Ib Sodium Bicarbonate, 40.0 Ib ® 3.00
17.96
Labor, 2 hours ® $5,00/hr 10.00
TOTAL $27.96
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This cost is ongoing whether or not recycling is accompli-
shed and does not include investment in the equipment re-
quired to treat (treatment tank, console, plumbing, or
pumps). The above chemical cost is based on 1800 ppm NaCN
maximum, which is the current maximum dragout of NaCN.
2. Daily Recycling Costs
Labor, 3 hours <§> $5.00/hr $15.00
To reitterate this labor is directly associated with the
filtration process and is the main reason for wanting to
mechanize it more.
3. Daily Saving of Zinc
Dragout of Zinc (approx 700 mg/1) 7 Ib @ $ .70/lb $ 4.90
Zinc Ball Anodes 10 Ib @ $ .70/lb 7.00
Total $11.90
4. Daily Cost to Store and Transport Zinc Sludge
Labor (to accumulate sludge), 2 hours @ $5.00/hr $10.00
Transportation of Sludge 8.45
Total $18.45
The cost of transportation was based on the year's accumu-
lation (prior to recycling) of 53 drums of sludge and a
Quote from a local firm of $40.00/drum to take to a land-
fill. Using a 250-day year, one obtains $8.45/day for
hauling expenses.
Comparing points 2 and 4 even though the 3 hours of labor can
be minimized, it is still more expensive for Metal Plating to
store and transport sludge. Then added to that is the lost
value of the zinc which would bring the total cost of this way
of handling sludge to $31.05/day. Point 2 is based on the
current filtration practice which is soon to be alleviated via
larger filtering capacity.
To date there has been an outlay of $10,600. in equipment only
for treatment and recycling (treatment - $4,800 and recycling
$5,800). Investment in a larger filter will bring the outlay
to $12,800. Using this last figure and a 5 year amortization
gives $2,540/year or $l0.16/day in investment. This translates
to $4.53/day investment to treat and $5.53/day investment to
recycle.
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SECTION III
PROCESS DISCUSSION
Since this project is rather new and no previous experience
(in this particular area) exists to rely upon, it is necessary
to draw upon information from various resources, and arrive
at some conclusions as to the nature of the dissolution of
zinc oxide. The ions Zn (OH)^ and Zn (CN)^ are considered to
be the predominant species existing in zinc cyanide plating
baths. The tetracyanide ion is believed to predominate over
the zincate ion as cyanide tends to form stronger bonds with
transition metals than does hydroxide. Since the starting
material is ZnO (or possibly Zn(OH)z in the presence of water),
the following mechanism for dissolution was proposed. Sludge
will be mixed with plating solution having the following
approximate composition NaOH-10.0 oz/gal (75.0 g/1 ) . NaCN-13.0
oz/gal (97.5 g/1), and Zn-4.0 oz/gal (30.0 g/1). This re-
presents approximately .45 molar Zn and 1.9 molar NaCN or
CN .
REACTIONS
1. ZnO(s) + H2O^Zn(OH)2 (s)^Zn(OH)2 (aq) in the
presence of excess OH~. Reference: Andrews, H. A.
and Kokes. R. J.: Fundamental Chemistry, 2nd ed.:
Wiley and Sons, 1965: pp 425-426.
2. ZntOH^
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The one conclusion drawn was that a fairly large volume of
plating solution is required to redissolve a relatively small
amount of sludge. The other supposition to be made is that
sodium cyanide should be added to aid dissolution of the sludge.
This will be touched on later. It should also be considered
that some agitation and possible steam heat be admitted to aid
dissolution as well.
These items were taken into consideration in the design of the
secondary settling tank (see Appendix 1). It was scaled to a
300 gal volume, However, the selection of the return cartridge-
type filter was done on a relatively arbitrary basis for this
pilot project. The immediate impact was the fact that it was
too small. The bag type filter which was supplied to Metal
Plating for evaluation is also too small. Both filters had a
tendency to allow slippage of insolubles through to the plating
tank. This was also attributed to each being pilot sized. A
difficulty which arose was the inability to wash out cyanide
from the cartridge-filter completely before stripping it down.
The bag type filter did not present these problems. However,
as stated both were too small for the volume of sludge produced.
The bag type filter had a definite advantage in being able to
clean out accumulated sludge easily thereby minimizing labor.
The primary intent of this investigation was to accumulate
sludge on the filter, and then redissolve it by recirculating
plating solution through the filter. The filter would retain
insolubles. Since the filters were too small, the next most
probable approach was to use the filters to concentrate the
sludge. The sludge would be transferred back to the secondary
settling tank. NaCN, plating solution, heat and air would be
applied, and the resulting solution would be filtered back to
the plating tank. However, the insolubles became a significant
factor. The are primarily calcium and magnesium hydroxides
(Ca(OH)j. and Mg (OH^ ). Most of the Ca and Mg come from using
hard water in the rinse system. Kastone® simply adds a little
more solids. The total effect is the equivalent of 2Jb to 2.5
Ib of Ca and Mg. CaCOHj^ and Mg(OH)z are not redissolved by
NaCN. Also some Ca and Mg may be in the form of CaCOs and
MgCOj as NaHCO^ is used in the destruction of CN~. These pre-
cipitates are gelatinous and plug the filter. Some of the
precipitates pass through the filter as previously mentioned.
In practice this "secondary sludge" has to be handled. Admiss-
ion of this material to the plating tank does not seem to ad-
versely effect the plating quality. The loose flocculent
material is readily resuspended, but does not appear to cause
shelf roughness and, as such, can be tolerated in the plating
bath. However, in the overall picture, it is not advisable to
operate a plating bath with foreign material present. More
frequent desludging of the plating bath may also be necessary,
and downtime, labor and disposing of the extra sludge that re-
sults are extra expenses that are basically undesirable.
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Elimination of Ca aid Mg by softening is currently being em-
ployed. Some reduction of the volume of sludge handled is the
first benefit noted, and there has been no build up of insol-
ubles. Handling of the resultant zinc sludge has not been
minimized. However, keeping in mind the pilot nature of the
process, simple scaling up of the filtration will eliminate
all unnecessary handling.
10
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SECTION IV
PROPOSED METHOD OF RECYCLING AND GENERAL PROCEDURE
From the information and experience gained by operating some
types of recycling (Appendix 3), the following method has been
abstracted, and is considered to be the most promising and
least labor intensive (and therefore desireable) method of
recycling. Once treatment and primary and secondary settling
have taken place, the sludge is further concentrated and col-
lected on a battery of pressure filters. Excess supernatant
is discharged to the sewer. Plating solution is then recir-
culated through the filters dissolving the zinc sludge. Once
dissolution is completed the filtering system is blown clean
again to eliminate cyanides from this portion of the system.
The water used is sent to treatment. This completes the
process and the system is ready for the next treatment.
The equipment proposed is described in figure 1 and is
scaled up per Appendix 2. The sludge from the secondary
settling tank is concentrated on filters a, b, c. and d,
shown in figure 1, and eventual recirculation of plating
solution then dissolves the sludge.
COLLECTION OF SLUDGE:
Valves 1, 5, 6-13, 17 and 18 are open. All others are
closed. The sludge is then filtered and recirculated to and
from the secondary settling tank, and once a clear super-
natant is observed, valves 17 and 18 are closed and valve 19
is opened. This then eliminates the final volume of treated
supernatant and delivers it to the holding tank for discharge
to the sewer.
AIR PURGE:
Sludge is concentrated on the filters. Valve 5 is closed
and compressed air is admitted to the filter chambers through
the air ports, and filter chambers are purged of any final
volume of supernatant.
RECIRCULATION:
The line from the plating tank is primed by admitting water
(either city or softened) through valves 2 and 13 then closing
2. Valve 5 is opened and 19 is closed. Valve 15 is then opened
and the pump started. Plating solution then circulates to and
from the plating tank through the filter. This is continued for
about one hour or until visual inspection of a given filter
11
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clear treated ^
liquid to sewers
air
heat
chemicals
sludge pump
city or soft water in
from plating
Air Port
Pressure
Filters
to plating **"
to sewer
TREATMENT TANK
1200 gal
econdar
settli
tank
SOOgal
m* m* 357 JKJ
000©
y. Sci y. y.
Figure 1 Proposed Treatment and Recycling System.
12
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indicated dissolution is complete.
AIR PURGE
At this point valves 3, 5, 6 -13, and 15 are open. All
others are closed. Valve 15 is closed and air is admitted as
before through the ports on the filter chambers. Plating sol-
ution is blown back to the tank clearing the inlet line and
pump. Valves 3 and 5 are closed. Valve 15 is opened and the
air is applied through the chambers and the outlet line from
the filtering system. Valve 15 is then closed.
WATER-AIR PURGE
Valves 6-13 are opened. All others are closed. Valves 2, 3,
5, 18 and 16 are opened and the system filled with softened
water. Valves 2, 10-13 are closed and valves 4 and 14 are
opened. Air is admitted as before clearing the inlet side of
the filters, and pushing the cyanide contaminated water to
treatment. Valves 4, 5. and 14 are closed, and valves 10 -
13 are cleared of cyanide contaminated water sending it to
treatment. All opened valves are now closed and the system
is ready for new sludge.
The main reasons for clearing the lines to and from the plating
tanks are (l)standing air in the lines prevents possible
siphoning of solution from the tanks (in case of a leak) and
(2) solution standing in pipes has a tendency to "creep out"
through joints and unions even though tightening appears to
be sufficient. PVC could be used and all joints glued to pre-
vent creepage. However, PVC also presents a problem of its
own fragility. All of the foregoing then is a representative
of a relatively full scale system for the recycling of zinc
sludges and the volumes and sizes recommended should be
considered tninimums. Items not shown in Figure 1 are catch
pans under the pump and filters (to catch any small spillage
of contaminated water), and the console unit which meters
formaldehyde and Kastohe® . These were deleted for the sake
of simplicity. The overall system treatment and filtering can
be set in an area approximately 16' x 9'. Softened water
be preferably used to flush out the system (water purge) but
municipal water could be used. The basic idea is to keep
calcium and magnesium from hard water to an absolute minimum
so as to minimize their influence. The foregoing, then, would
be considered as a complete recycling system for a 1100 gal
rinse system which would have a total of 1000-3000 ppm of NaCN
dragout with the corresponding 370-1110 ppm Zn.
-------
SECTION V
APPENDICIES
APPENDIX 1. EQUIPMENT LIST AND FIGURES SHOWING APPROXIMATE
LAYOUT OF EQUIPMENT
1. March magnetic pump, centrifugal. Mod. No. TE-7R-MD
2. Treatment tank, 6' dia x 6' with 1' deep conical bottom,
1200 gallon
3. Platecoil. steam coil, 2' x l^1 (in treatment tank)
4. Airsparger (in treatment tank 4' x V pipe with holes on
6 " centers )
5. Sludge pump, Texstream, TD 390
6. Control Console, Lenape Engineering, with 2-0.4 gpm
metering pumps
7. Industrial filter 1800 gph, 6 - 29" cartridges
8. Transfer pump, centrifugal TENV motor. Industrial
Plastics 1800 gph
9. Secondary Settling Tank 3*7" dia x 4* with 6' deep
conical bottom - approximately 300 gal capacity
10. Serpentine steam coil (4 loops - 2' lengths of V1 pipe)
Ch Secondary Settling Tank)
11. Airsparger (in Secondary Settling Tank 3 x V pipe air
filters on 6" centers)
12. Sethco SS-1200 cartridge filter
13. Gaflo, Pressure filter. Mod. RB-1A (This is currently
Mod RB4A which has four times the filter capacity)
14. Fittings and pipe. 1" black iron
15. Valves, 1" PVC (for recycle portion)
16. Holding tank 100 gal
14
-------
Air Steam
Air 'Heat'
Secondary
Settling
00
Sludge Pump
Ta
Filter
Tanl
ter - TJ
Pump
i
sewer
«-|—
I
i
#7 Plating
Tank 1400 gal
(control)
#2 Plati
Tank
1400 gal
experimental
I
1st Stagnant
Rinse 550 gal
2nd Stagnant
Rinse 550 gal
Figure 2. General layout of treatment and recycling equipment.
-------
16ft-
•j^r n
f J Formal dehy
Console
Feed
Treatment
Tank
1200 gal
Polish filter to sewer
ludgej
Pump
Secondary-*
Settling
Tank
GAP HOLDIf 3
ilter Tank
From Plating
To Plating
9 ft
|
Figure 3. Approximate positions of current equipment
and over all area. No attempt has been made to exact
scale each item. This figure merely shows the juxta-
positioning of the various elements and the plumbing
to each.
16
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APPENDIX 2. CRITIQUE AND RECOMMENDATIONS
Refer to the succeeding appendix for the particular details
of the procedure used and the time element involved for
carrying out this procedure. The major areas of improvement
involve scaling up some of the process equipment.
1. Use of soft water for treatment.
2. Larger pump and lines going to treatment.
3. Larger heating area in treatment tank.
4. Larger ports and discharge lines on treatment tank.
5. Larger filtering surface 8.4 sq ft (.78 sq M).
There are only 3.0 sq ft (.28 sq M) now.
The main reason for scaling up is to speed up certain steps of
the operation in order to minimize the time element. This will
make time less of a factor in the operation and will be less
critical to be sure that all steps are carried out promptly.
This is not to say that the operation requires one persons full
attention for 8 to 9 hours; however, a reduction of 3 to 4 hours
is possible and desirable.
APPENDIX 3. DETAILED PROCEDURE FOR TREATMENT AND RECYCLING
1. Pump rinses to treatment
This involves the pumping out of 2 - 550 gallon rinse tanks
and hosing out of any precipitated zinc cyanide (Zn (CN)a ).
The actual pumpout involves 1 hour, and the hosing involves
Jj to *s hour. The lines and fittings from rinses to treat-
ment are 1" I.D. The pump fittings are 1" (see Appendix 1).
The improvement here would be to either gang a similar pump
to the original or go to a larger pump to get about 2000
gph and utilize at least IV lines and fittings from rinse
to treatment.
2. Analyze, add chemicals and treat
It takes H hour to analyze and add the chemicals necessary
and at least 1 hour after adding them to get the solution
to 104°F (40°C). Here a larger heating coil is necessary
on the order of 2 to 3 times as large as the current coil.
This coil (Appendix 1.3) has 7.0 sq ft (.65 sq M) of sur-
face. Steam heat is applied as soon as the coil is
covered with rinse waters and the actual total heating time
is Ih hours to 2 hours, leaving about 1 hour of heating
to be done after addition of chemicals.
17
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3. Settling
This does take 2 hours to accomplish for this installation
and there appears to be no other means of speeding this up.
The main problem was the sludge became more gelationous,
and harder to handle in the final filtering prior to re-
dissolving when a polyelectrolyte was added to increase^
settling rate
4. Decant
Using the polishing filter reduces the discharge time to 1
hour versus 2 hours of gravity flow discharge. However,
larger ports and lines from the treatment tank would speed
up both. At the time of this writing the polished filter
is used as needed when the supernatant is not clear to a
depth of 6 (see Appendix 1 dimensions of treatment tank).
5. Pump Sludge to Recycle
This is only 10 to 15 minutes at the very most since only
70 to 90 gallons of "boot" is left after decanting about
1100 to 1200 gallons of supernatant.
6. Settle and Decant
Once the sludge in the "boot" has been pumped to the
secondary settling tank it is allowed to resettle and
usually 50 to 60 glllons of clear liquid are decanted
again. This reduces the total amount of sludge to 30 to 40
gallons. This last volume is dependent on the total
amount of dragout initially treated.
7. Filter and Concentrate Sludge
Metal Plating purchased a Sethco filter. As it turns out
this filter is too small to adequately handle all the
sludge involved. A GAP bag filter was obtained and evalu-
ated. Its use resulted in reduced handling and operator
time. It, however, is also too small and should be 3 to
4 time larger, as should be the Sethco unit. The sizing
up of the filter will make a simple single pass filtration
possible and eliminate the need for changing filter bags
or inserts. This will allow simple accumulation of
sludge on the filter and subsequent recirculation of
plating solution through the filter.
8. Redissolve Sludge and Return to Plating Tank
Since the zinc baths are operated at room temperature and
since dragin of water from prior rinses about equals drag-
out of plating solution, there is little loss of volume
from the plating tanks. This makes reduction of volume of
returned sludge quite critical. To be explicit, the return
volume for this specific situation is 15 gallons (57 1) max-
imum per day. The accumulated sludge is placed in a 30
gallon barrel: plating solution added; this is slurried:
and then added back to the plating bath. If the filter
noted in the previous step were large enough the sludge
could be accumulated thereon and redissolved by simply
18
-------
recirculating plating solution through the filter and
returning it to the plating tank.
These last steps require more close personal attention. To
summarize, operator time is the most important element in-
volved and these last steps are the most labor intensive.
The single item of most importance to recycling is the
filter which should be 8.4 sq ft (.78 Sq M) for 1000 to
2000 mg/1 of NaCN or 330 to 670 mg/1 of zincprecipated as
zinc oxide sludge.
APPENDIX 4. TYPES OF RECYCLE OBSERVED
The first but not necessarily desireable approach taken would
be considered the quick and dirty method. This worked fairly
well with the exception that there was extra liquid volume
which needed to be handled.
PROCEDURE
1st day 1. Treat rinses and settle sludge; decant super-
natant.
2. Pump sludge to secondary settling tank and let
settle overnight. (approx 90 gal or 340 1)
2nd day 1. Decant supernatant.
2. Pump sludge (20 - 40 gal or approx 76 - 150 1)
directly to plater without any treatment.
This method at first looked somewhat attractive, and in a few
respects remains so. The method is direct, simple and requires
an absolute minimum of attendance and handling. The main
problem is that with a room temperature plating bath dragin of
water just about equals or excedes dragout of plating solution.
For the operation at Metal Plating this results in a volume
loss of about 15 gal (57 1). Typically, there were about 30
gal (114 1) of sludge. This sludge was usually 4-5% by weight
solids and it resulted from treatment of rinse waters bearing
2000-2500 mg/1 NaCN. This translates to about 750-850 mg/1 of
zinc metal. Based on volume of rinse water and concentration
we get:
1. 750 mg/1 Zn = .75 g/1 = .1 oz/gal
2. 1200 gal x 1 oz = 120 oz Zn =7.5 bl
1. 850 mg/1 Zn = .85 g/1 = .113 oz/gal
2. 1200 gal x .113 oz/gal = 136 oz Zn = 8.47 Ib Zn
This gives rise to an almost direct simple relation that every
100 mg/1 approximately equals 1.0 Ib Zn or NaCN in 1200 gal.
This will help to simplify future calculations, (i.e. 2500 mg/1)
NaCN = 25 Ib NaCN also).
19
-------
Also, since Zn is in the form ZnO (reference: "A Peroxygen
System for Destroying Cyanide in Zinc and Cadmium Rinse
Waters", Lawes, B.C.Fournier, L.B. and Mathre, O.B. (Paper
presented at 48th Annual Technical Conference, American Elec-
troplaters Society, Buffalo, New York, June 15, 1971.), there
is 1.25 Ib ZnO for every 1.0 Ib Zn. Thus 7.5 Ib Zn becomes
8.4 Ib ZnO and 8.5 Ib Zn becomes 10.1 Ib ZnO. Since, the
sludge is in 30 gallon (approx 250 Ibs) water, the ratio of
ZnO to water approximates 3.4-4.0% by weight solids. Add to
this the other insolubles and 4-5% by weight solids results.
This appears to be a maximum value obtainable by settling
alone. Thus, other means (i.e. filtration) are needed to
effectively concentrate the sludge further and reduce overall
volume of the sludge. Since this simplistic approach gave too
much volume to handle, other approaches were evaluated. There
was at least 15 gal (57 1) per day extra volume that was de-
canted from the experimental plating tank to the nearby
b a rrel line plating system in order not to have a few drums
of solution standing around. Operation of this method
occurred in January 1975. There were a few tentative trials
in December 1974 once all equipment was hooked up.
Possible solutions to the problem encountered while trying
this method could be:
1. Warm plating baths to get evaporation and volume loss.
2. Reduce dragin of water from previous rinse so that
(dragin< dragout) volume loss occurs in plating
baths.
3. Evaporate excess volume of sludge.
4. Filter off excess volume.
The first possible solution gives some changes in the plating
baths which are undesireable to Metal Plating. As such this
solution was abandoned. The second solution was deemed un-
feasible but was not tried. The third solution was tried with
some success. However, ammonia fumes are given off rather
profusely (refer to above reference by Lawes. Pournier & Mathre)
at 40-50°C while heating at that temperature for several hours
to get about 15 gal (57 1) volume loss in the sludge. Vent-
ing of ammonia was not available and this approach was aband-
oned. Thus the most favorable approach at the moment appears
to be filtration after settling. Combinations of the fore-
going solutions were not tried. The basic format to this
particular type of recycling would be to (a) force a volume
loss in the plating bath and (b) concentrate sludge as simply
as possible, then recycle to the plater.
This type of recycling does give rise to some other problems.
1. Organics are returned. This gave rise to a cathodic
film on the parts (from the experimental tank) which
was hard to remove in the nitric rinse. Subsequent
20
-------
permanganate treatment of the plating bath elimated
this problem.
NOTE: The direct relation of organics recycled and
the film were not completely ascertained. However,
since the same film did not occur in the control
tank by inference the problem occurred as a result
of recycling. Hull Cell tests run on both baths
(control and experimental) by DuPont did not
indicate organic contamination.
2. Bath dilution occurs by returning 30 gal of sludge
per day and additions of NaCN become larger.
To summarize, this method of recycling is appealing because
of apparent simplicity. However, the simplest method may or
may not be the best. Application of volume control at the
plating tank could still make this a possible method of
recycling.
The second approach to recycling was a result of the con-
clusion to limit sludge volume. In setting up the recycling
equipment a Sethco SS1200 cartridge filter was obtained.
It utilized 10 micron filter cartridges. This second method
would be to (a) collect sludge on the filter, then (b) re-
circulate plating bath through the filter to redissolve ZnO.
Immediately it was found that the filter was undersized.
The sludge plugged the whole filter chamber leaving more
sludge in the Evaporator-Dissolver to be concentrated.
Subsequently it was almost impossible to consider alternate
collection and recirculation as planned. The recirculation
of plating bath was tried. This met with only limited
success. Apparently one of two things occurred: (a) by-pass-
ing of the filter elements or (b) the insoluble particulate
matter was too small to be held by the 10 micron filter or
(c) a combination of (a) + (b) occurred. This method was
operated one week in February 1975 and abandoned.
Possible solutions to the problem would be:
1. Increase size of filter possible 3 to 4 times.
Information for this will come later.)
2. Use a different type of filter.
To summarize this portion, a larger filter might work better
to collect sludge but still may admit insolubles to the plating
bath due to the nature of the insolubles.
The third method evaluated was the accumulation of sludge in
the treatment tank over the period of a week. The sludge was
then fed into the plating bath a portion at a time by redissol-
ving in the secondary settling tank and filtering to the
plating bath. The procedure was:
21
-------
1. Leave sludge in treatment tank, and decant clear
supernatant daily.
2. At the end of the week transfer accumulated sludge
to Secondary Settling Tank, and decant any super-
natant .
3. The following week while more sludge is accumulating
in treatment tank, return the dissolved sludge in the
Secondary Settling Tank to the plating tank.
4. Return of the sludge to the plater is done by:
a. Pumping some plating solution 100 gal (379 1)
to the Secondary Settling Tank.
b. Heat and air agitate to redissolve zinc.
c. Return through filter.
The main positive feature of this method is that it minimized
labor. However, once keyed into this process it is almost
impossible to switch to another process because of the volume
of the accumulated sludge 120 gal (456 1). This method was
operated relatively successfully from February 1975 through
April 1975. The "organic problem" which occurred in the
first part of recycling had not re-occurred. However, another
problem had come about. This was a darkening of plating in
certain parts which had areas of extreme low current density.
This darkening occurred in both plating baths and as such was
not attributed to the recycling efforts. Permanganate treat-
ment alleviated this problem somewhat and tended to prove
the problem was organic in nature.
In March a GAF bag type filter was acquired for evaluation.
This was hooked up to the system. The new filter was used to
try to concentrate the sludge further. The new procedure
was:
1. Leave sludge in treatment tank; decant clear super-
natant daily.
2. At end of week, transfer accumulated sludge to the
Secondary Settling Tank and decant any supernatant.
3. The following week use the new GAF filter to concen-
trate sludge and transfer sludge to drums.
4. Place the sludge back into the Secondary Settling
Tank.
a. Pump plating solution 150 gal (568 1) to Secon-
dary Settling Tank.
b. Add NaCN to aid redissolving, with air and heat.
c. Return to plater through new GAF filter.
The labor intensive aspects of this type of procedure can be
readily appreciated. The process of filtering the settled
sludge from the secondary settling tank to a more concentrated
form took 4 to 5 hours of concerted effort. A larger filter
could have possibly alleviated this.
22
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Examples of concentrating sludge.
1. Volume of one weeks sludge pumped to Secondary
Settling Tank - 234 gal. (886 1)
2. Volume of one weeks sludge after settling in
Secondary Settling Tank - 144 gal. (545 1)
3. Volume of one weeks difference (1 +2) clear
supernatant - 90 gal. (148 1)
4. Volume of one weeks sludge after concentrating
in drums - 39 gal.
It can be seen that the effect of using the filter gives
about a six to one concentration (234/39 = 6.0) and starting
with 8-10% by weight solids a final value of 48-60% solids
could be expected. All of this required 40-50 separate filtra-
tions and 4 to 5 hours of labor.
A summary of this aspect of recycling would be that while the
concentrating aspects were good the same insolubles problem
was evident. This type of recycling was abandoned by the end
of May 1975, because this method is quite labor intensive.
The fourth method of recycling was simply returning to a daily
basis and applying filtration using the GAP bag type filter.
The procedure was:
1. Treat rinses, and allow sludge to settle, and decant
supernatant.
2. Pump sludge to Secondary Settling Tank and allow
sludge to settle overnight.
3. Decant supernatant.
4. Concentrate sludge through filtration.
5. Redissolve sludge.
An example of this method would be:
Volume of boot 90 gal (341 1)
Volume of settled sludge 35 gal (132 1)
Volume of decanted supernatant 55 gal(208 1)
Volume of filtered sludge 8 gal (30 1)
As such there is a concentrating effect and this keeps the
level of sludge volume less than the 15 gal dragout of volume
stated in the first approach to recycling. Since the insolubles
still pass through the GAP filter as seen in the third method
evaluated it was decided that other methods to relieve in-
solubles be investigated. As such the concentrated sludge is
taken to the plater in a 30 gallon drum. Plating solution is
then mixed with the sludge, slurried up and poured back into
the plating bath. This type of recycling has been practiced
through June 1975 to the date of this writing. This method is
still somewhat labor intensive as the final concentration re-
quires 4 to 5 separate filterings and 1 to lh hours to accomp-
lish those filterings. Also slurrying of the sludge and re-
turn to the plating bath requires ^ to h hour of labor.
23
-------
To summarize this method, it appears daily recycling of sludge
is most desirable simple by keeping the total volume generated
at an acceptable level (<15 gal).
The main thrust of this portion of the recycling is that at
least effective concentrating of sludge is available. Labor
is minimized to an extent. The method is more direct and
less involved than the second approach' and the third method
used. Despite the insolubles problem recycling is taking
place. The main point is then how to remove the insolubles
effectively.
APPENDIX 5. ANALYTICAL PROCEDURES USED FOR CYANIDES
The basic procedures used are volumetric and can be found in
literature such as "Standard Methods". DuPont has developed
a quick test for obtaining a target concentration of sodium
cyanide to be treated. This test is not to be construed as
total cyanide.
Initial Cyanide (Quick Test)
1. Pipette 100 ml of cyanide bearing rinse water into
a 250 ml Erlenmeyer flask. Use precautions (safety
bulb) for drawing cyanide into the pipette.
2. Add 1 ml of .25% w/v p-dimethylaminobensalrhodanine
in acetone-.
3. Titrate with O.lN AgNO^ to a salmon pink endpoint.
4. Calculate NaCN as:
mg/1 NaCN = mis of O.lN AgNO3 x 98
5. Discussion of error: As with any experiment error
begins with initial pipetting of the sample. The
pipette should be 100 ml + .1 ml at 25 c, and
made from borosilicate glass.- The ± .1 ml is
predicated on a given size opening at the tip.
Since cyanide solutions are caustic in nature,
the tip tends to erode and widen allowing slightly
fester delivery of sample. Subsequently, slightly
less sample is delivered favoring lower titration
and final results.
The next source of error comes from reading the
burette. A 50 ml burette can be read with ± .05 ml
accuracy. Since two reading are needing the cumula-
tive error is ± .1 ml. For a titration on the order
of 20.0 mis, the + .1 ml is the ± .05% error or
i 20 ppm NaCN (approx) in the final calculation.
This writer has found that the reproduceable error is
24
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on the order of ± .2 ml or ±1.0% (approx) for the
same 20 ml titration. This translates to 40 ppm
NaCN in the final calculation. In all reproducible
error overwhelms the error of pipetting though
erosion could lower the final results. It can be
concluded that error in this test is no better than
i 1.0% depending on the total titration.
Free NaCN (after reaction and/or in plant effluent
1. Pour 400 ml of reacted rinse water (or plant effluent
into a 500 ml ± 5% Erlenmeyer flask, and add 1 ml of
rhodanine (previous analysis).
2. Titrate with either .OlN or .02N AgNO5 to a salmon
pink endpoint.
3. Calculate NaCN as :
mg/1 free NaCN = mis of .02N AgNOj x 2.5
or = mis of .OlN AgNO3 x 1.25
4. Discussion of error: At this point a straight for-
ward discussion of error is. not possible due to the
fact that the free cyanide is generally nondectable.
That is the titration is generally .1 ml of .OlN or
.02N AgNOj which translates to either 0.125 mg/1 or
0.25 mg/1 respectively. At this point other influ-
ences come into play. NH3 from hydrolysis of CNO~
and S~ which are present can use up some Ag+ and
add to the results. As such one can only report
<0.25 or <0.13 mg/1 NaCN. ALso since the plant
effluent sample is drawn from the sanitary sewer
one can expect influences from possible dissolved
organics.
Total Cyanide by distillation (after reaction and/or in
plant effluent.
1. Assembly equipment as shown in figure 4. Adjust
air flow through thegas absorber to about one
bubble per second. The gas absorber has 50 ml of
l.ON NaOH in it.
2. Remove air inlet tube and add 250 ml of sample from
a 250 ml graduated cylinder designed to deliver. Re-
place air inlet tube.
3. Through the air inlet tube add 1 ml of 68 g/1 HgClz
and 4 ml of 510 g/1 MgCl» • 6Ha O and mix for 5 min-
utes with the air agitation.
25
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4. Through the air inlet tube add 15 ml of concentrated
H2SO/,. The treated sample has carbonates and CO£
will outgas upon admission of acid. Pressure can
then build up rapidly forcing the solution back up
and out of the air inlet tube.
5. Once the additions are mixed apply heat and reflux
for 2 hours. Then remove heat allowing air to flow
for another 15 minutes.
6. Remove the gas absorber from the installed equipment
and wash down the connecting tube with distilled
water delivering this to the absorber tube. Pour
the contents of the absorber into a 250 ml Erlenmeyer
flask and wash the absorber with 10 ml portions of
distilled water adding the washings into the Erlen-
meyer flask.
7. Titrate as before in the "free NaCN" procedure using
.02N AgNO3 and rhodanine.
8. Calculate total NaCN as:
mg/1 total NaCN = mis of .02N AgNO5 x 2
9. Discussion of error: Here again a relatively straight
forward discussion of error is not possible. This is
because HZS and HCHO are boiled over with the HCN and
are captured also in the gas absorber. Both of these
items directly interfer leading to higher results of
NaCN.
The flow of air through the system can cause much error
generally low results from either too much or too
little flow, ibo much flow does not allow enough time
for absorption and too little flow results in not
enough HCN being pulled over to the absorber. One
bubble per second has been the accepted flow rate.
Taking the foregoing into account and noting the cum-
ulative effects of sampling and reading the burette.
it is then safe to say that the total error lies
between ± 5% and +10%. Generally, the amounts of
NaCN reported in the treated sample lie between 1.0
and 3.0 mg/1 and in the plant effluent between .3 and
.6 mg/1.
It is to be noted here that CN"~ is reported as NaCN
when +the species to be found in the effluent is Fe
(CN)j (ferrocyanide) . Cyanide plating solutions
and rinses will have ferrocyanide. The Kastone® pro-
cess destroys virtually all the free NaCN and the
remaining ferrocyanide is precipitated into the sludge
and returned to the plating bath via recycling. Some
26
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Connecting tube
Graham
T Condenser
to suction
Gas Absorption Tube
(100ml Nessler Tube)
500 ml
Modified Claissen
Flask
Heat
Figure 4. Total distillation apparatus
27
-------
ferrocyanide remains in solution. This then is re-
ported as NaCN.
The total cyanide procedure is that procedure curr-
ently in use by the Indiana Stream Pollution Control
Board Waste Treatment Division.
APPENDIX 6. ADDENDUM
As of this writing the following modifications to the overall
recycling process have been made. In reference to Appendix 2
several items have been scaled up to facilitate a more rapid
treatment and recycle process.
The heating surface has been increased to an approximate
4' x 2V plate coil ( the previous onewas 21 x IV) increasing
the surface area by about 3 times. This has resulted in low-
ering the total heating time from 3 hours to l*s hours, allow-
ing the solution to heat to 45 -50°C instead of just 40°C.
Soft water has been provided to eliminate calcium and magnesium
in the rinse waters. This has resulted in no observable in-
crease in insolubles in the plating bath. This has eliminated
a precipitate build up in the rinse tanks which was calcium
and magnesium carbonates and hydroxides.
Larger porting on the side of the treatment tank allows faster
draining of the treated supernatant once the sludge has settled.
This was taking about 2 hours and now takes 45 minutes to drain
the treatment tank completely.
Filtration was being done on the GAP RB-1A pressure filter,and
is now being done on the RB-4A which has 4 times the filtration
surface. There was too much sludge for this 3 sq ft of filter-
ing for the RB-1A surface to handle at one time. Generally
speaking the zinc sludge follows the approximate volume reduct-
ion.
80-90 gal Treatment boot
40 gal After secondary settling
6-8 gal After filtration (40-50% solids)
The filtration process still required 4-5 separate filtrations
before the RB-4A indicating 4-5 times the filter surface will
be required to entrap all solids. The current filter has 3.0
sq ft (.28 SqM) of surface. This then would indicate 12 - 15
sq ft (1.11 - 1.39 Sq M) of surface is needed. It was hoped
that elimination of calcium and magnesium would drop the
amount of surface needed. It is anticipated that a Gaflo RB-
4A will handle all solids at this time.
What is happening is this. The micron size of the sludge is
well below 25 microns, generally between 5 and 1 microns.
28
-------
Initially there is a passage of sludge through the filter
while the 25+ microns sized particles are being filtered.
When plugging of the filter finally occurs only a small
portion of the sludge has been trapped. Refiltering is done
in order to entrap solids as much as possible. Finer micron
sizing will be employed to efficiently trap more solids.
None the less a larger filtering surface will be necessary
to hold the total volume of solids. Experimentation is un-
derway to increase the particle size while treating. There
are no conclusive results as yet.
Semi-automation of the pumping process from the rinse tanks to
the treatment tank has been accomplished. This allows the
technician on the second shift to initiate this process at the
end of that shift and allow the pumping to go on unattended.
Since the treatment tank is emptied out daily and can hold
1200 gal (453 1) and since the volume of rinse water is 1100
gal (4146 1) there is no chance for overflow. The pump is
plugged into a timer, turned on, and left on. This was orig-
inally the initial hour of the treatment process (Appendix 3,
step 1).
Note: This addendum has been added after the expiration
date of the grant period. It was felt that an updating of
some of the information was necessary and justified in light
of Metal Plating's ongoing efforts to recycle zinc sludge.
29-
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-77-038
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
ZINC SLUDGE RECYCLING AFTER KASTONE TREATMENT OF
CYANIDE-BEARING RINSE WATER
5. REPORT DATE
February 1977 issuing date
6. PERFORMING ORGANIZATION CODE
'. AUTHOR(S)
Joseph G. Moser
8. PERFORMING ORGANIZATION REPORT NO.
I. PERFORMING ORGANIZATION NAME AND ADDRESS
Metal Plating Corporation
1740 Georgia Avenue
Connersville, Indiana 47331
10. PROGRAM ELEMENT NO.
1BB610; 01-01-07A
11. CONTRACT/GRANT NO.
S803265-01
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Laboratory-Cin., OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/12
5. SUPPLEMENTARY NOTES
The purpose of this project was to demonstrate the feasibility of reclaiming
sludge. The sludge was produced by the destruction of cyanide by Kastdne®in zinc-
cyanide dragout rinse water. The clear supernatant was discharged to the municipal
sewer and the sludge eventually recycled to the plating tank. The general approach
was to transfer cyanide-bearing rinse water to the treatment tank, treat, settle,
decant clear supernatant, transfer sludge for further concentration, and in one way
or another return dissolved sludge to the plating tanks.
The possibilities of contaminant accumulation were present. Breakdown
products, ferrocyanide, copper and other possible metal!ics would be returned to the
plating tank. The operation at Metal Plating Corporation has two plating tanks. This
allowed a control and experimental tank for evaluation. The major difficulty
encountered was a precipitate mostly of calcium and magnesium hydroxides that was
formed in the treatment process and does not redissolve as does the zinc oxide sludge.
The presence of calcium and magnesium is known to be present in the water used The
hydroxide sludge presented mechanical problems in handling in the recycling process
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
*Metal finishing
Plating
Cyanides
Zinc Coatings
Industrial Waste Treatment
Sludge disgestion
Chemical treatment
Wastewater treatment
Pollution control
Cyanide oxidation
Kastone
13B
8. DISTRIBUTION STATEMENT
RELEASED TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
38
20. SECURITY CLASS (TMspage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
30
60VEMWNT PRINTING OFFICE 1977-757-056/558't Region No. 5-11
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