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MNTAP MINNESOTA TECHNICAL ASSISTANCE PROGRAM
The Minnesota Technical Assistance Program is funded through a grant provided by the Waste Management Board. I
1 n 1 1 :1 :1 : I :I n :I I] 3 :I :I 11
Reducing Chromium Losses from a Chromium Plating Bath
1987 Summer Intern Report
By Diane Achman
Project Conducted at New Dimension Plating
Hutchinson, M N
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New Dimension Plating, Inc. of Hutchinson, Minnesota plates a variety of parts including motorcycle accessories, stove parts, exercise equipment parts and also does some custom plating. The company employs about 40 people and operates for 1 or 2 eight hour shifts each day depending on the work load. Reducing the chromium carried out of the plating bath is the focus of this report.
Because New Dimension Plating is a job shop, they plate parts that vary greatly in size and shape. This fact along with the fact that the plating is done manually are the main reasons that a significatnt amount of chromium is carried out from the plating tank on the racks each day. At the beginning of this project, the daily increase in chromium concentration in the stagnant rinse tank was determined to be about 1 oz/gal. As the tank contains 115 gallons, this loss added up t o about 7 lbs of chromium per day. On an average day 300-350 racks of parts are plated with chromium.
Options reviewed to reduce chromium drag-out included using a drip bar, installing an automatic hoist, or utilizing a spray rinsing system. Utilizing a spray rinsing system in a separate tank before the stagnant rinse was evaluated to be the best option.
In addition to reducing chromium dragout, options for returning chromium to the plating tank were investigated. The options reviewed included evaporation, reverse osmosis and use of ion exchange columns. Because of the relatively low volume of processing in this line, reverse osmosis and ion exchange were ruled out in part due to cost. Evaporation was selected as the preferred option although no units on the market were small enough for New Dimension Plating.
Once the preferred options were selected, an appropriately sized spray rinse system and evaporators were built on-site. The spray rinse system fitted with 6 nozzles is rectangular, fitting around the inside of a 115 gallon rinse tank. A drip bar allows the parts to be suspended in the spray rinse tank while they are sprayed with a fine mist of water for 5 seconds. After dripping, parts are rinsed in the stagnant rinse, and the overflow rinse which follow.
Two small evaporators have been installed, each with a 20 gallon capacity. One is used to reduce the volume of the plating tank, and the second one concentrates the stagnant rinse.
After one month of operation, test results show drag-out to the stagnant rinse has been reduced from 7 lb. of chromium per day to just over 1 lb. of chromium per day. The spray rinse volume averaging about 25 gallons per day is added back to the plating tank as is the stagnant rinse after concentration in the second evaporator.
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T a b l e of C o n t e n t s
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I n t r o d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . 1
O b j e c t i v e . . . . . . . . . . . . . . . . . . . . . W a s t e s u r v e y . . . . . . . . . . . . . . . . . . . .
E v a l u a t i o n of Chromium Loss t o S t a g n a n t R i n s e . O t h e r F a c t o r s E v a l u a t e d . . . . . . . . . . . .
Waste R e d u c t i o n O p t i o n s Development . . . . . . . . . R e d u c i n g Chromium D r a g o u t . . . . . . . . . . . R e c o v e r y of Chromium for R e t u r n t o P l a t i n g Tank
C o n t a m i n a n t Removal . . . . . . . . . . . . . . E v a l u a t i o n of O p t i o n s . . . . . . . . . . . . . . .
O p t i o n s f o r R e d u c i n g Chromium D r a g o u t . . . . . R e c o v e r y of Chromium for R e t u r n t o P l a t i n g Tank
C o n t a m i n a n t Removal . . . . . . . . . . . . . . Recommendation . . . . . . . . . . . . . . . .
I m p l e m e n t a t i o n . . . . . . . . . . . . . . . . . . .
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Resu l t s . . . . . . . . . . . . . . . . . . . . . . . . . 21
Servings E v a l u a t i o n . . . . . . . . . . . . . . . . . . . 23
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
A p p e n d i c e s
A p p e n d i x A . . . . . . . . . . . . . . . . . . . . . . . 2 6 A p p e n d i x B . . . . . . . . . . . . . . . . . . . . . . . 27 A p p e n d i x C . . . . . . . . . . . . . . . . . . . . . . . 2 8 A p p e n d i x D . . . . . . . . . . . . . . . . . . . . . . . 29 A p p e n d i x E . . . . . . . . . . . . . . . . . . . . . . . . 30 A p p e n d i x F . . . . . . . . . . . . . . . . . . . . . . . 3 1 A p p e n d i x G . . . . . . . . . . . . . . . . . . . . . . . 32
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New Dimension Plating, Inc. is a small metal plating shop located
in Hutchinson, Minnesota. The company employs about fourty people and
operates for one or two eight hour shifts with an average of 315 racks
of chrome plating per eight hour day. They plate a variety of metals
including copper, nickel, gold, brass and chromium. (See Appendix A,
page 2 6 ) Chromium is the major metal plated and is usually the last
step in plating cycle. Most parts are copper plated and then nickel
plated in preparation for chrome plating. The main difference between
New Dimension Plating and other plating shops is the variety of parts
plated. As New Dimension Plating is a job shop, a wide range of parts
such as motorcycle accessories, stove parts, and custom items are
metal finished. The plating lines are manual, meaning employees dip
the racks into the tanks by hand. This fact along with the fact that
parts vary greatly in size and shape accounts for the significant
drag-out on the chromium plating line.
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N I Dimension’s prim
OBJECTIVE
ry concern is to reduce chromium o ste and
still maintain a high level of quality in plating. The company is
currently meeting EPA and city requirements for wastewater discharges
but at a great expense. The objective of this project has three main
parts. The first was to quantify the amount of chromium lost as drag-
out from the plating tank. The second was to identify the particulars
of the process to pinpoint where the major losses of chromium occur and
explore alternative processes for these areas. Finally it became
necessary to identify options to reduce the amount of chromium that is
inevitably carried out of the plating tank. At this stage research
was conducted on different technologies available for recovering and
reusing the chromium in their plating process tank as opposed t o
recovering the metal to ship off-site for use elsewhere. With
information about different options, New Dimension Plating could decide
what management system best suits the company’s needs.
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HASTE S_U_R_VE_Y The chromium plating line at New Dimension Plating consists of a
470 gallon chromium tank, a 115 gallon stagnant rinse tank, and three
counterflow rinse tanks followed by a hot still rinse. (See Appendix
B, page 2 7 ) The plating tank contains chromium at a concentration of
32 ounces per gallon and a temperature of 115'F.
tank serves to "catch" a large portion of the chromium rinsed off the
parts with the idea that it can be added directly back to the plating
tank to replace water lost to evaporation. The countercurrent rinsed
have a continuous water flow which averaged 1.2 gallons per minute.
The last rinse in the countercurrent series, the rinse directly after
the stagnant rinse tank, drains to the plant's waste treatment system
which removes chromium from the wastewater. The current waste
treatment operation for removing chromium in the waste water begins by
reducing the hexavalent chromium to trivalent chromium with sodium
metabisulphite. This waste stream is then mixed with the waste
streams from other processes and the pH is adjusted to between 7 and 9
with sodium hydroxide. Sludge is generated in a filter press and then
dried in a sludge drier. An average of 5 barrels of dried sludge from
total wastewater treatment are produced each month.
The stagnant rinse
To evaluate the loss of chromium from the plating tank, the
stagnant rinse and flowing rinse tanks were emptied and replaced with
clean water at the beginning of this project. Due to the wide
variability of the shape of the parts which influences the amount of
chromic acid solution they drag-out, it is difficult to establish a
close correlation between surface area plated and increase in
concentration in the stagnant rinse tank. Although the parts plated
vary from small screws to large tubular parts, the number of racks
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processed each day is fairly constant, the average being 315.
Evaluation of the stagnant rinsewater to determine chromium
losses was a primary emphasis of the waste survey. At the time of the
survey, the evaluation of the countercurrent rinses was limited to
flow rate considerations. The countercurrent rinses are continually
diluted s o they are maintained at low enough chromium concentrations
to provide good rinsing. Low chromium concentrations in the
counterflow rinses were difficult to measure by the titrimetric method
used at New Dimension Plating therefore it was decided to concentrate
first on reducing the drag-out to the stagnant rinse tank and evaluate
the rinses later if necessary. Lowering the concentration in the
stagnant rinse tank would reduce the amount of chromium dragged into
the countercurrent rinses.
EVALUATION OF CHROMIUM LOSS TO THE STATIC RINSE
The stagnant rinse concentration was monitored for two days and
the hourly increases were recorded. The results for the total daily
increases are graphed 'for one week in Figure 1 along with the result
of an additional sample tested about two weeks later. The data shows
that the daily increases of chromium in the stagnant rinse tank is
quite steady for the first few days, then it begins to level off.
As the concentration increase levels off, a significant amount of
chromium is no longer being saved in the stagnant rinse tank.
(Appendix C, page 28 provides the data used to construct Figure 1.)
The daily increase in a stagnant rinse concentration was calculated
to be approximately 1 oz/gal per day. This adds up to nearly 7 lbs. of
chromium (about 4 gallons of plating solution) that is being removed
from the plating tank by drag-out each day. Previous to emptying the
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Figure 1.
Equilibration o f Drag Out
0 1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 17 18 19 20 21 22 23 24
Date o f June -- 2:45 p.m.
stagnant rinse tank it had not been changed for five months yet the
concentration of chromic acid was only 8 .4 ounces per gallon. This
revealed that an equilibrium had been reached and the amount of chromic
acid solution dragged out of the stagnant rinse tank equalled the volume
dragged-in.
Once the chromium increase of about 1 ounce per gallon per day in
the stagnant rinse was known, the volume of drag-out per rack could be
calculated. This was done by dividing the total number of racks
processed by the total number of gallons of solution dragged out that
day. The total volume dragged out was determined by calculating how
much of the 32 oz/gal chromium plating solution was dragged out t o give
the stagnant rinse concentration increased by 1 oz/yal and it holds 115
gallons of water, this means that 115 ounces of chromium or 3 . 6 gallons
5
of plating solution were dragged into the stagnant rinse that day. As
the average number of racks plated per day was 315, the average drag-out
volume was calculated to be .012 gal/rack. This value compares well
with the experimental value of .013 gal/rack obtained by allowing a
plated rack to drip into an empty container for 2 minutes and then
measuring the volume that dripped off. The figure of .013 gal/rack is
the average of repeating this test three times.
Once the drag-out per rack was known, it became possible to
experiment on the amount of time needed for racks to stop dripping
plating solution. This would give insight as to whether drip bars would
be advantageous. Ten seconds was sufficient time for dripping to end,
and five seconds of dripping removed as much as 7 5 % of the carried out
solution (drag-out). This value was estimated by comparing the volume
that dripped off in 5 seconds as opposed to letting the rack drip for 5
minutes. But it was observed that a film of chromic acid coated the
parts even after extended draining periods. By rinsing the film off and
then measuring the concentration of the resulting solution, a value for
the ounces of chromic acid on the part was obtained. From this value it
was estimated that up to 50% of the chromic acid solution carried out
clings to the parts and does not drip off. This was important
information to be considered when procedural changes were studied.
OTHER FACTORS EVALUATED
Other areas included in the process of evaluating for the waste
survey were; flow rates of overflow rinses, the evaporation rate from
the plating tank, and possible contaminants. The flow rate of the
countercurrent rinses was determined by allowing the stream to fill a
container for one minute, then measuring the amount collected. The flow
6
rate varies greatly when an additional source of water is pumped into
the last rinse tank in the countercurrent series. This additional water
is pumped in once every ten minutes for a one minute interval. The
water flow is nearly tripled during this time. The flow rate was
calculated by incorporating both values proportionately and was
determined to be an average of 1.2 gal/min.
Rate of evaporation is one factor that limits the amount of drag-
out that can be added back to the plating tank. The evaporation rate is
relatively low because the plating bath is kept at only 115OF. Another
factor is the wetting agent that is added to the bath which creates a
foam blanket to control fumes thus inhibiting evaporation. An average
of 11 gallons evaporates each day from the plating tank which is 470
gallons and has a surface area of' 15 square feet.
Another factor that limits the quantity of drag-out that can be
added back to the plating tank is the effect of returning unwanted
contaminants to the plating bath. The contaminants are carried into the
plating bath from baths through which parts pass prior to the chromium
plating tank. The contaminant concentration in the plating tank has
remained low and relatively constant because as impurities are carried
into the bath, the impurities are also being dragged out with the
chromic acid solution. The impurities include metals such as nickel,
copper, zinc and iron and the chloride ion. Trivalent chromium, which
is produced as a secondary reaction in the plating tank, is also a
contaminant of concern. The monthly increases as determined by M&T
Chemicals, Inc. are listed in Appendix D. Controlling contaminant build
up will be an important limiting factor when considering methods f o r
returning the chromium to the plating tank.
7
WASTE RE_DUC_TION OllTIONS DEVELOPMENT
New Dimension Plating, Inc. was interested in first reducing the
chromium drag-out from the plating tank and then recovering the
chromium that had been carried out for return to the plating tank.
Non-return methods were not studied because New Dimension’s aim was to
return a concentrated solution back to the originating process rather
than recover metals or chemicals for use elsewhere. Information
gathered is described in three sections; options which would reduce
chromium drag-out, options which could be used to recover chromium
from drag-out solution and a third section is used to discuss options
for removing contaminants.
REDUCING CHROMIUM DRAG-OUT
Reducing the amount of plating solution carried out could be
accomplished at a low cost by simply increasing the time allowed for
the solution to drip off the parts. The racks used are made of solid
copper so they are quite heavy and difficult to hold up for even short
periods of time. For this reason the racks are usually not allowed to
drip thoroughly and large amounts of chromic acid solution are carried
out into the rinse baths. The three options that were evaluated to
reduce drag-out are installing a drip bar, using an automatic hoist,
or spray rinsing the parts before they are placed in the drag out
tank.
Drip bars could be used either above the plating tank or the
stagnant rinse tank. The two problems that must be considered are
possible staining of parts and loss of efficiency in production. If
the racks were hung on the drip bar and then accidently forgotten, the I1
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chromic acid could stain the parts. Sometimes the stains can be wiped
off with a cloth, but other times only grinding out the stain will
remove it. The added step of hanging the racks on the drip bars and
waiting for them to drip thoroughly could be inconvenient and time
consuming.
An automatic hoist could help decrease drag-out by allowing the
parts to drip thoroughly, but may reduce production also. It may
actually be more work to use a hoist than to plate manually due to the
variability of the size of the parts. The layout of the shop would
also make it quite difficult for a hoist to be used efficiently.
Rapid Plating located in Sauk Rapids, Minnesota was visited to view
their use of automatic hoists on their plating lines. They plate
mainly zinc on industrial type parts and plate many parts of the same
type at one time. Because of the shapes of the parts and the set up
of their tanks, the hoists aided in their production.
A spray rinse tank could be used before the stagnant rinse tank
to keep the concentration of the stagnant rinse low. If a drip bar
were used above a spray rinse tank, the majority of drag-out could be
confined to one tank. The water would dilute the concentrated
solution clinging to the parts and the drip bar would allow the parts
to drip more completely. Also , the fine mist from the spray rinsing
would create a very humid atmosphere which would prevent the parts
from being stained because the solution would not dry on them. The
process could be very efficient if a timer were installed s o the
spraying would occur for a given number of seconds each time a button
was pushed. An automatic timer would allow the employees t o simply
hang the rack in the spray rinsing tank, push the button, and attend
to other duties while the parts are rinsed and allowed to drip off.
9
The length of time for spraying and number of spray nozzles needed to
provide adequate rinsing would have to be determined. The amount of
solution resulting from spray rinsing could be added directly back to
the plating tank each day if the amount produced did not exceed the
amount of evaporation from the tank.
RECOVERY OF CHROMIUM FOR RETURN TO THE PLATING TANK
Methods of recovering chromic acid solution can be divided into
two basic categories; those processes that deal with the diluted
rinse waters and those that work with concentrated solutions such as
the drag-out solution.
Reverse osmosis and ion exchange are the two options that were
considered for removing chromium from dilute rinse waters. In reverse
osmosis, water is forced out of solution through a selective membrane
thus concentrating the solution. It is called reverse osmosis because
a pressure greater than the osmotic pressure must be applied to a dilute
solution to force water through the membrane. The process yields a
moderately concentrated solution that can he added back to the plating
tank. However, it does not remove impurities so they must be removed
by another method. Water Technologies Inc. located in Mineapolis,
Minnesota offered a unit for New Dimension to use on a trial basis but
because the cost of the systems was out of the company's range, it was
decided that our time would better be spent pursuing other options.
Ion exchange uses specific resins to remove either cations or
anions or can have both incorporated on one unit. This method is
effective in collecting essentially all traces of cations and/or anions
from dilute rinse streams. Resins must be regenerated chemically when
they become ''loaded". This method was studied rather extensively
10
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because it can remove impurities as well as chromium from rinse water
with the use of different resins. Douglas America Inc. of Eden
Prairie, Minnesota was visited and the Douglas recycling system
evaluated to see if it would suit New Dimension’s needs. Their system
used two resins: a cation resin to remove the metals and an anion
resin to remove the non-metals, including the chromic acid anion from
the water. Indian Head Plating of Chippewa Falls, Wisconsin was also
visited to evaluate their ion exchange system, They plated hard
chromium as opposed to New Dimension’s decorative plating s o the system
differed slightly from what New Dimension would need. The system was
manufactured by Eco-Tec Limited located in Ontario, Canada. This
system used the same basic principles of ion exchange but differed in
design from the Douglas system.
Evaporation is the primary method used to recover chromium from
concentrated solutions. This method was studied extensively due to
its relatively low cost and ease of operation. It is a very
straightforward and reliable method. An evaporating unit can be
constructed with a few calculations to determine evaporation rate once
surface area, temperature, and power available are known. By adjusting
these three variables the efficiency of the evaporator can be
maximized.
The Surface Finishing Convention held in Chicago was attended and
representatives from Industrial Filter and Pump Manufacturing Company
were consulted on their Max-Evap evaporator. The design of the
evaporator enables it to evaporate approximately 8 to 10 gallons of
water from the chromium tank per hour when the tank is maintained at
llO°F to 115’F.
11
CONTAMINANT REMOVAL
When concentrated drag-out solution is returned to the plating
tank, impurities concentrated in the drag-out are also returned to the
tank. Therefore, procedures which could be used to remove impuritiies
had to be considered in evaluating reverse osmosis and evaporation as
options for the recovery of chromium. Two methods that could be used
to remove impurities were studied.
The first method is the use of electrolytic purification cells
manufactured by Cosmos Mineral Corporation of Camarillo, California.
The system is set up as a separate tank that is connected to the
plating tank. The unit incorporates the use of ceramic cells in
compartments with sets of anodes and cathodes to remove contaminating
metal cations from the plating solution. The size of tank and number
of cells required is based on the level of contaminants in the
solution and the size of the process tank. The chromic acid solution
is circulated from the process tank through the purification cell and
returned to the process tank. This system is capable of removing large
amounts of impurities.
The second method studied was removal of cation impurities by the
use of a mini CatNapper manufactured by Innova Technology, Inc. of
Clearwater, Florida. The mini CatNapper uses a specially designed
membrane in conjunction with electromigration principles to remove the
cations. It is actually just one cell from the larger CatNapper unit
which is commonly sold. The mini CatNapper modules are installed
directly into the existing plating bath. It is convenient f o r New
Dimension Plating that Innova offers a small unit to handle a low
contaminant level.
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In addition t o the metal impurities, the chloride ion is also a
contaminant, however it can be more easily removed. Chemical
suppliers for New Dimension Plating suggest dummying the tank with the
smallest cathode area possible and highest attainable voltage when the
chloride concentration becomes too high. Flew Dimension uses an old
rack with 3" wires connected radially from the center of the rack as a
dummy rack. Plating this dummy rack at a high voltage removes the
chloride ion as an impurity plated in the chromium metal.
13
rtYAliUATIQN BE OPTIQNS The process of evaluating options for reducing chromium waste
occurred in three steps. The first step was to review options which
would decrease the amount of chromium carried out from the plating
tank. After reducing the amount carried out as much as possible,
options to recover the chromium that does get carried out were
evaluated. Finally if chromium is recovered and added back to the
plating tank, the impurities will also be added back so options to
remove them were reviewed.
OPTIONS FOR REDUCING CHROMIUM DRAG-OUT
The installation of a drip bar is a very low cost way to help
decrease the amount of chromic acid solution carried out of the
plating tank. The major concern with this is the possibility of
staining if the racks are left to drip too long. One way to solve the
problem would be to install a drip bar in a spray rinse tank. By
using the spray rinse the volume of concentrated drag-out could be
greatly reduced. The size of nozzles and length of spraying time are
two variables that could be adjusted to control the amount of solution
produced so that it could be returned to the plating tank each day.
It was calculated that six fine nozzles in an empty tank the size of
the current stagnant rinse tank would produce approximately 20 gallons
of solution each 8 hour day if the spraying was pulsed for 5 seconds.
Each nozzle was experimentally determined to release 75 ml of water
when pulsed for 5 seconds. The expected concentration of the solution
was calculated to be 5 ounces per gallon by knowing an approximate
value of the amount of chromium drag-out per rack was and the amount
of water released during a 5 second pulse of spraying. If the
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evaporation from the chromium tank was increased by 10 gallons per
day, all of this solution could be returned to the plating tank each
day.
The estimated cost for making a spray rinsing systems is about
$200 since the current stagnant rinse tank would be used. The drip
bar can be made from a sturdy piece of pipe. The combination of spray
rinsing with the use of a drip bar was in fact pursued as discussed in
the implementation section.
The use of an automatic hoist was ruled out because it would be
inefficient with the way the tanks are arranged. A hoist would work
best when process tanks are large and arranged in a line in plating
order and when parts are very similar in type.
RECOVERY OF CHROMIUM FOR RETURN TO THE PLATING TANK
When using reverse osmosis to achieve a concentrated stream for
return to the plating bath the solution must be circulated through
the unit several times because there is insufficient loss through
natural evaporation from the plating tank to accomodate the direct
return of a large amount of solution. Another problem is the fact
that undesirable impurities are not removed through reverse osmosis s o
an additional method would be needed to purify the solution. The cost
of the reverse osmosis system manufactured by Water Technologies, Inc.
is approximately $30,000. Since the solution would probably need to
be purified and further concentrated following reverse osmosis, this
system would not be economical for New Dimension Plating, Inc.
The Douglas Recycling System sold by Douglas America, Inc.
utilized a series of ion exchange columns consisting of four
cartridges. The cartridges contain resins through which rinse water
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is pumped upward from a reservoir at the base of the column.
Maintenance of the system is relatively simple. The bottom cartridge
11
ii fills up first and is removed for regeneration. The top cartridge
takes its place and a regenerated cartridge is added. Regeneration is
accomplished by running an acid through the cartridge to dissolve the
metal. The cation resin collects metal impurities and the anion resin 11
/ I collected the chromic acid anion. Options for the handling of
solution obtained when the resins are regenerated would need to be
considered.
The advantage of this system is that both functions are performed ll II l l II II
within the same unit, only in different cartridges, making it very
convenient. The estimated cost of the system is $30,000. The cost of
the ion exchange system manufactured b y Eco-Tech Limited is about
$60,000. The payback period would be a few years so it was decided
that perhaps the purchase of an ion exchange system could be a long ' I term goal. Because of the high cost for this system, it was not seen
as an option to pursue currently.
Evaporation as a method of recovery is very widely applicable and l l
the materials of construction are readily available. Two offsetting
/ I factors are relatively high energy consumption and the fact that
evaporation will not remove undesirable impurities. If a high
percentage of chromium drag-out is returned to the plating tank an
additional technique will be needed to remove accumulated metal
1 1
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Evaporation can produce a highly concentrated solution which can I1
be added directly to the plating tank or can be used to evaporate
water from the plating tank so additional solution can be returned to
the tank. The costs of the Mac-Evap evaporation built b y Industrial l l
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Filter and Pump Manufacturing Company is $4,000. It will evaporate up
to 10 gallons of water from the chromium plating tank per hour. This
would create extra space in the tank so more drag-out solution or spray
rinsing solution could be added back to it each day. The estimated
cost to build an evaporator, depending on size and design, is under
$500. The cost can be even lower if existing equipment, such as a
used tank, is used in its construction. The payback would be within 6
months to two years depending on the size of the evaporator and its
initial cost. This is quite reasonable for a company the size of New
Dimension Plating, and was selected as the option to pursue.
CONTAMINANT REMOVAL
The electropurification system manufactured by Cosmos Mineral
Corporation is capable of removing a much higher level of contaminants
than is necessary for New Dimension Plating. For this reason the mini
CatNapper suits their needs more efficiently. The fact that the mini
CatNapper module is installed directly into the plating bath makes it
very convenient t o use. Another positive feature is that the
maintenance of the mini CatNapper is minimal. The cost of one module
is $900. New Dimension would need one or two cells to purify their
plating bath. This is much lower in costs than any other purification
method researched. Once implementation of recovery options begins,
New Dimension Plating plans to conduct further testing on the rate of
increase of impurity concentration in the plating bath before making
any final decision on the purchase of a purification system.
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17
RECOMMENDATION
In summary, the most economical and efficient way to reduce New
Dimension’s chromium loss seems to be a combination of three different
options. Incorporating the use of spray rinsing in conjunction with a
drip bar before the stagnant rinse is the first step. The rinse tank
directly following the spray rinse could be converted to a stagnant
rinse. An evaporator used to evaporate water from the plating tank
would allow all of the spray rinse solution and some of the stagnant
rinse water to be added back to it each day. An additional evaporator
may be needed to concentrate the stagnant rinse. A mini CatNapper
installed in the plating tank would continually purify the plating
bath.
l l
18 ll
-------------- IMPLEMENTATION
New Dimension Plating, Inc. has made the following changes to
incorporate the recommendations made. The stagnant rinse tank was
converted into a spray rinse tank with a drip bar and the next tank in
line was changed to a stagnant rinse tank. This set up provided
adequate rinsing so that the next two smaller rinses could be combined
into one larger rinse tank. Figure 2 shows the new layout for the
rinse system. The flow rate was decreased from 1.2 gal/min to 1
gal/min. Two evaporators were installed, one above the plating tank
to evaporate directly from it and one behind the stagnant rinse tank
to concentrate its solution.
Evaporator Overflow to drain
Figure 2. Layout of Chromium Plating Line before and after Implementation of the Spray Rinse Tank
. Evaporator
Hot S t i l l 0 Overflow to drain
Stagnant Rinse
AFTER -
Hot Still c) 19
The spray rinse ring and evaporators were
Plating. The spray rinse ring was constructed
built by New Dimension
to fit inside the tank
previously used as a stagnant rinse tank. It was constructed from
1/2" PVC piping and is secured 4" from the top of the tank. Three
nozzles were evenly spaced along each of the two long sides of the
ring. The nozzles were purchased at a farm implement store and are
usually used on equipment to apply fertilizer. Their spray angle is
120 which is very effective in covering all parts of a rack.
Testing had to be done to determine flow rate because they were rated
in gal/acre. Other sources of nozzles would be from companies that
sell fluid handling equipment. These would generally be rated in
gal/min. Appendix E, page 30 shows a picture of possible nozzles.
The main feature of these nozzles is that they are installed
vertically but spray horizontally. This is important so that the spray
rinsing apparatus is parallel with the tank so that the racks will not
catch on protruding objects when they are placed in the tank. A
solenoid valve and timer were connected to the spray rinse ring so
that when a button is pushed, spraying occurs for 5 seconds. A drip
bar rests on the top of the tank. It can be easily slid back so racks
can be placed in the tank, then slid to the middle so the racks can
hang on it while they are sprayed and allowed to drip. Using the drip
bar allows the parts to hang above the surface of the water.
The evaporators were constructed from used 45 gallon rinse tanks.
Their dimensions are approximately 24" x 18" x 12". They are sealed
but have access ports on the top in case problems occur. Each
evaporator is divided into 4 equal sections. An air blower is mounted
on the top of the first section to push air into the first chamber.
The second chamber is filled with 3/4" polyethylene balls and has a
solution inlet at the top where the solution is pumped in and allowed to
run down through the balls. The air flows through the balls covered
with solution and goes into chamber 3 . There is a drain at the bottom
of this chamber to allow unevaporated solution to drain back into the
tank. The air must pass through baffles before it goes into chamber 4
where it is exhausted to the ventilation system. (See Appendix F, page
31 for diagram.) One evaporator is connected to the plating tank s o
n 1 1 1
the solution is already heated. The second evaporator evaporates 1 rinse water from the 45 gallon tank filled with stagnant rinse water.
The rinse water is heated llO°F using a water heater and pump to
circulate hot water through PVC coils immersed in the solution.
. J
._ I 1
RESULTS
n The spray rinse tank was experimentally determined to collect
approximately 2 . 8 gallons of solution per hour. This adds up to about
22 gallons per 8 hour day with an average of 315 racks plated. The
evaporator over the plating tank evaporates approximately 1 gal/hour.
Combined with the natural evaporation from the plating tank of .5
gal/hr, this adds up to about 36 gallons per day which allows all of
-1 3
the spray rinse solution and some stagnant rinse solution t o be
returned to the plating tank. 3 The drag-out solution from the stagnant rinse is concentrated in
the second evaporator before it is added t o the plating tank.
Once the spray rinse tank was functioning properly and
employees were comfortably using it, chromium analyses were conducted
to evaluate improvements. At the beginning of the project, the level
1
of chromium in the stagnant rinse increased at a rate of approximately J II 21
concentration in the stagnant rinse increases at only . 02 oz/gal per
hour. These values were averages calculated for an 8 hour day. In
both cases the number of racks processes per day was close to 315.
Comparison of the data once the spray rinse was implemented
indicates that the dragout to the stagnant rinse tank is about one
sixth of the chromium previously lost to the stagnant rinse. At the
beginnning of the project about 7 lbs of chromium was carried into the
stagnant rinse daily. With the spray rinse operating, just over 1 lb
is carried out into the stagnant rinse. Appendix 0 , page 32 shows
increases in chromium concentration in the stagnant rinse tank after
the spray rinse was implemented.
At the time of this report, both evaporators had been operating
for four weeks. Evaporation rates from the plating tank have been as
predicted allowing about 25 gallons of spray rinse to be returned to
the plating tank every day. In additign to this, 10 gallons of
concentrated stagnant rinse is returned. Each day about 30 gallons of
stagnant rinse is added to the 45 gallon tank evaporator used for the
stagnant rinse. It is hoped that by removing this amount on a daily
basis, the stagnant rinse concentration can be kept below 2 oz/gal.
The additional solution needed to fill the plating tank is taken from
this evaporator. Since the evaporator for the stagnant rinse
evaporates about 1 gallon/hour, about 20 gallons will evaporate in a
day, leaving 10 gallons that can be returned to the plating tank.
Figure 3 provides a visual image of the process just described.
Both evaporators are exhausted through a common vent. There is
concern about the l o s s of chromium to the atmosphere, although it is
not a problem mentioned by manufacturers of evaporators. I1
22
n n 1
n :I 1
1
3 3 ,1
J
Q
Figure 3 . Chromium Return and Evaporating Process
25 gallons transferred daily 30 gallons transferred daily 10 gallons transferred daily Approximately 35 gallons evaporated daily
PLATING YANK
I I
SAVINGS EVALUATION
Attempts were made to determine the savings achieved by the
implementations of the spray rinse system and the evaporators. The
reduction in chromium drag-out has resulted both in a decrease in
chromic acid use and in the use of chemicals needed to treat the
chromium in the wastewater.
An evaluation of savings has been difficult to formulate because
the volume of work increased, therefore shifts were lengthened and
production increased. An attempt was made to come up with a value
with these variables factored in.
I] 23
M o n t h l y S a v i n g s :
c h g n ~ i y g u s e :
c o s t ( p r e v i o u s u s e ) - c o s t ( c u r r e n t u s e ) = $ s a v i n g s / m o n t h 2 .96 /1b (100 l b ) - $2 .96 /1b ( 2 0 l b ) = $238/month
gqgjyg M&lEligy&Eh&gg gs_e igsggcgingll
3.16 l b / l b C r = l b s used /mon th $ . 4 2 / l b ( 3 1 6 l b ) - $ . 4 2 / l b ( 6 3 . 2 l b ) = $ l l O / m o n t h
T o t a l m o n t h l y s a v i n g s : $348.00
I n a d d i t i o n t o t h e s e s a v i n g s , t h e r e w i l l b e a r e d u c t i o n i n t h e u s e of
s u l f u r i c a c i d n e e d e d t o l o w e r t h e p H o f h e x a v a l e n t chromium b e f o r e
r e d u c i n g i t a n d i n t h e u s e of sodium h y d r o x i d e used t o r a i s e t h e pH a t
t h e t i m e of p r e t r e a t m e n t b e f o r e f i n a l release t o t h e sewer. The
volume of s l u d g e w i l l a l s o b e r e d u c e d , b u t s i n c e t h e volume p r o d u c e d
by t h e chromium d r a g o u t w a s c a l c u l a t e d t o b e o n l y be tween 1 / 2 a n d 1
b a r r e l p e r month b e f o r e t h e p r o j e c t s t a r t e d , t h e s a v i n g s w i l l n o t b e
as s i g n i f i c a n t as s a v i n g s i n c h e m i c a l c o s t s f o r chromium a n d sod ium
m e t a b i s u l p h i t e .
A cost e v a l u a t i o n i n terms o f payback w a s n o t c o n d u c t e d b e c a u s e
b o t h t h e s p r a y r i n s i n g s y s t e m a n d t h e e v a p o r a t o r s were f a b r i c a t e d a t
New Dimens ion p l a t i n g . An e v a p o r a t o r c o m p a r a b l e i n s i z e and d e s i g n t o
t h e o n e b u i l t b y N e w Dimens ion P l a t i n g was n o t f o u n d on t h e m a r k e t .
A l s o no s p r a y r i n s i n g s y s t e m o f a n y k i n d w a s f o u n d .
ll I1 II ii ll ii I1 I/ I1 I1 /I ll II l l l l I1
24
3 n
:1 1
1 3
11
SUMMARY
The changes made at New Dimension Plating, Inc. were possible
because of the involvement and cooperation of management and
employees. Because of the fact that New Dimension is a job shop,
there were always many variables to keep in mind when testing was
conducted. With the help of the employees, these variables were
controlled ae, much as possible t o collect consistent, reliable data.
From the data collected at the beginning of the project and then after
the implementations were made, it can be shown that a significant
amount of chromium is now being recovered and returned to the plating
t a n k . However, the project does not end here, as there will a lways be
room for further improvements.
- - - - - - - Diane Achman is a senior chemistry major at St. Cloud State University, St. Cloud, Minnesota.
J 25
C h r o m i u m P Z a L i n g Process
I
I I I 1
m I
t 1 4 0 n
A l l racks cleaning line. D) Nickel plating Copper plating of steel and zinc die cast parts, Aluminum cleaning and precoat. 2) steel parts Zincate and copper strike. 3) steel parts
1) zinc and aluminum parts
E) Chrome plating (after nickel) Note: Blowup for (E) on following page
lu U
r + Cr ,
Rinse l inse 45 ga1.45 gal.
6 0 Hot S t i l l 0
I
0 Rinse 115 gal. @
Stagnant Rinse 115 gal.
chrome 470 gal. 0
Tank Set Up
%munterflow rinsing i n tanks 3,4,5 Wmmiun plating tank 110-115 F :"xnium plating tank approximately 32 oz/gal
Appendix C
Drag Out R e s u l t s
J u n e 1
7 : 00 . o o 8 : 1 0 .20 9: 30 . 3 8 10: 30 .54 11: 30 . 6 5 2 : 4 5 ( e n d of d a y ) 1 . 0 1 T o t a l # of r a c k s : 334
J u n e 2
7: 00 1 . 0 1 8 : 00 1 .34
10: 00 1.69 1 1 : o o 1 .87 12: 00 1 .94 1: 00 2 . 0 0 2:oo 2 .03
T o t a l # of r a c k s : 372
.........................................
9: 00 1 . 4 8
2:45 ( e n d of d a y ) 2 . 1 8
' I
J u n e 4
' 2 : 4 5 ( e n d o f d a y ) 3 . 6 8 T o t a l # of r a c k s : 257
ll
28
n n I 1 1 n :-I 3 n 111
Appendix D
Contaminant Concentration
Dates
-- Imparity ---- Eel?: ss Des: sG AEEL 82 J w e 82
trace Trivalent -18 . 06 -
Iron .04 - . 0 7 . 0 5
.03 .05 Copper .08 -
e 007 Chloride . 009 a 003 -
a 13 e 19 Nickel .26 -
.01 . 0 2 Zinc -
* Concentration units: ounces/gallon
* Analysis done b y M&T Chemicals Inc. of New Jersey. Their midwest representatives are Industrial Chemical and Equipment Company of Minneapolis.
I
2 9
Appendix E
b d u d No.
Spray Nozzles
THREAD CONNECTION 5PSIG 20PSlG
,145 ,168
,239 ,274
.32 .37
.083 ,095
278 ,314
,120 .135
,252. ,285
25PSlG
,192
,307 .41
,108
,360
.I51
,321
- EFLEC TlON ,NGLE - 650
68O
680
710
215-1 118"male NPT
215-2 1/8"male NPT
215.12 118"male NPT
215.14 114" 28 straight
215-15 1/4"28 straight
215.16 114" 28 straight
215.28 1/8"male NPT
215.29 118 male NPT
215.30 1/8"male NPT
215.65 118'' male NPT
with O-ring groovl
with O-ring groovc
with O-ring groow
Suitable for - Liquid Spray Characteristic - Flat Material - PFA
I s* CAPACITY
% 39 1
146
19
05
163
075
153
.19
,092
,050 - Model No. A
215.2 .59" 215-14 97" 215-15 .55" 215-16 9 7 "
,215.28 59'' 215-65 59''
DIMENSIONS
"O-ring Groove
- ID. 0 2 Gland Depth .400" 598 ' ' ,020''
(Use AS-012 0-Ring where required.)
0 PSlG
,125
.195
.2 7
,068
,233
,099
,208
-
.27
,122
,067 - 0
.28"
.70"
.28"
.70"
.28"
.28"
.32 1 .l1 1 .41
,145 ,168 ,193
.078 ,102
OPSIG 35PSlG
,208 .225
,333 .349 .45 .48
,118 .125
,383 ,417
,167 ,179
,349 372
.45 .48
,208 .225
.114 . .120
Hex Model No. A
60PSlG 10PSlG
.242 1140
.380 250 .51 150°
.133 210
.463 goo
,192 460
,400 34O
.51 1500
,242 1160
.128
0 Hex
518" 215-1 .88" .27" 518" 511 6" 215-12 .97" .27" 518" 5/16" ~ 2 1 5 - 2 9 .9i'#* .27" 518" 5/16" *215-30 .88,# .27" 518" 518" 518"
t- A---l
Y e
'(when applicable)
rY ANGLE at PSlG OPSlG 30PSlG
1230 1350
350 410 1730 173O
410 490
990 1020
670 740
500 560
1730 1730
1330 1420
go' 120
LO P S l C
1400
430 177O
550
1040
79Q
610
-
1770
1450
1 60 -
I
j/
l l /I /I II 11 ll I1 li
ll
11 11
II '(when applicabli
I1 I 1
li Deflection
Angle lJ I
Hex
1' 1986 Galtek Corporation 30
A f :
31
Appendix G
ii /I II ij I; ! ! I1