Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ELECTROPLaTING RECOVERY PROCESS
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Peealization of the in~ury to rivers, lakes and
oceans by reason of the di~charge therein of heavy metal
solutions and other chemicals ha~ caused severe re~tric-
tions, both voluntary and legi61ative, upon the discharge
of such materials into such bodies. ~oreover, the
increasing cost of chemicals a~d metals has increased
the necessity of their economical use
Electroplating solutions have presented
particular problems in di6posa1 and efforts have been
directed to recovering the chemicals utllized therein.
United States Patent No. 3,637,467, for example, described
a process utilizing a reverse osmosis unit in co~nectlon
with the recovery and recycling o~ chemicals in a gold
plating operation. The system therein descrlbed would
not be ~uitable for a bra~s or similar large volume f1Ow
rate plating operation. Other systems utilizing reverse
osmosis units have been suggested, but none, so ~ar a~ is
known, have been capable of continuous plating operatlon
while eliminatlng totally any discharge outside of the
system.
- It is a principal object of the present invention
to provide an improved completely closed system for
recovery of chemicals and water in an electroplating
system.
Another object i~ to provlde a closcd recoYery
system that will permit continuous plating operation.
In accordance with the invention parts to be
plated are~ follo~ing suitabl~ preparation, subjected to
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a "strike" plate in a dual chamber tank, one chamber of which constitutes an
electroplating bath, the other a drag out or pre-Tinse bath although the two
portions are in fluid communication. Following the strike, the parts are
placed in a conventional plating bath. After plating they are dipped in the
pre-rinse portion of the dual chamber tank and ~hereafter passed through a
series of rinse tanks substantially to remove all plating chemicals from
the parts. The solution in the dual chamber tank is one half the concentra-
tion in ~he plating tank thereby reducing by one half the amount of chemicals
carried over into the rinse tanks.
Solution in various of the rinse tanks is treated by reverse
osmosis to remove chemicals, some solution being returned to other of the
rinse tanks. The concentrate from treatment of the solution in the firs~
rinse is placed in a holding tank. This solution is itself passed through
a reverse osmosis unit, the permeate being returned to a rinse tank, the
concentrate to the holding tank. Periodically the contents of the holding
tank are returned to the plating bath.
According to the broadest aspect of the present invention, there is
provided in a plating process wherein articles are plated in a solution
within a plating tank and thereafter rinsed in a series of rinse tanks, the
improvement comprising, providing a dual chamber tank having an electrically
non-conducting divider therein separating the dual chamber tank into two
portions, said divider having an opening therein to permit flow of solution
between said one portion of said dual chamber tank and the other portion
thereof, plating an article in said one portion of said dual chamber tank,
passing the article from said tank one portion to said plating tank and
efecting a plating of said article, passing the article from said plating
tank to the said other portion of said dual chamber tank, and thereafter
passing said article seriatum to said rinse tanks.
The invention will now be described in greater detail with refer-
ence to the accompanying drawings, in which:
Figure 1 is a schematic flow chart showing the path of objects tobe electroplated in accordance with the invention;
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Figure 2 is a semi-schematic cross sectional view of a dual
chamber tank utilized in the system of the invention; and
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Fig. 3 is a schematic flow chart of the process
of the invention indicating thereon the operating conditions
at one perio~ of the process.
The illustrated embodiment of the inventlon is
for plating brass upon articles such as furniture hardware
rom a conventi~nal sodium cyanide process, In accordance
with such process and referring first to F1g. 1, wherein
the path of the article being plated is shown by the
solid line A, the parts to be plated are placed as customary
with~n a perforated barrel or otherwise suitably supported
and dipped in an alkaline cleaning solution contained in
a tank 10~ Prior to this step the parts are suitab~y
sandblasted, tumbled, or glv0n other treatment as desired
to remove burrs, flashings, etc., so as to provide a
desired surface -for plating. From the tank 10 the parts
are passed to a rinse tank 12 where the parts are dipped,
sprayed or otherwise suitably rinsed with water substan-
tially to remove the alkaline cleaning solution which may
be retained on the surface of the parts. Next the parts
are dipped in an acid bath in a tank 14 to effect neutrali-
zation of any residual alkali which may remain on the
parts. From the tank 14 the parts are carried to rinse
tank 16 where the parts are again suitably rinsed ~ith
water.
From the tank 16 the parts are carried to and
immersed in the plating solution retained within one
portion 18 of a dual chamber tank or cell 20 illustrated
in greater detail in Fig. 2. This may be the conventional
sodium cyanide solution. Referring to Fig. 2, the tank
20 is divided by a partition 22 of electrically non-
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conducting material so as to divide the tank into twoportions, the portion 18 which comprises a strikinK bath
and a further portion 24, comprising a drag out or pre-
rinse bath the purpose for which will ~e described in
detail subsequently. The partition ~2 is pro~ided with
an opening 28 near the bottom of the tank so RS to provide
for fluid communication between the portions 18, 24
whereby, as will be seen, the ion concentration of the
solution in the two portions will be substantially the
same. The tan~ portion 18 is provided with a brass anode
or anodes 30 suspended on contact bars 32 connected to
the positive side of a source of direct current elec-
trical energy. The plating barrel 34 within which the
parts to be plated are carried is shown suspended from a
pair of cathode contacts 36 which are connected to the
negative side of the energy source. The striking step is
adapted to deposit a thin film of brass upon the parts.
When the desired strike plate has been made
the parts are moved to a plating tank 40 provided with
suitable brass anodes and conventional means for applying
plating current between the anodes and the parts in the
plating barrel 34.
After suitable plate is applied to the parts,
the barrel 34 is lifted out of tank 40 and immersed in the
portion 24 of the tank 20. This substantially removes the
concentrated plating solution from the plated parts. The
barrel is then successively transferred through rinse
tanks 42, 44~ 46 and 48 so as to effect rinsing of the
parts and by the time they are removed from tank 48,
substantial~y complete removal of the plating solution
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From the surface of the parts is obtained. In each of
these tanks the parts may be sprayed, tumbled or otherwise
agitated to effect rinsing of the surface thereof.
Attention is now directed to Fig, 3 constituting
a flow chart o~ the recovery system of the invention.
Since the so~ids recovery system is involv~d only with
the plating tank 40 and subsequent rinses, the initial
wash and cleanin~ tanks 10 to 16~ inclusive, are omitted
from Fig, 3. Indicated in Fig~ 3 are the volumetric flow
rates of a typical system and the dissolved solids
concentrations at one point in the cycle o~ operation,
As the parts are moved from tank to tank they will carry
with them solution or so-called drag out. In the illus-
trated embodiment this amounts in volume to 0.75 liters
per minute. ~n accordance with the invention, solution
is continuously withdrawn -Erom the thir~ rinse tank 46 at
a rate of 11.1 liters per minute and passed through a reverse
osmosis cell 50, a suitable pump 52 being provided t-o main-
tain sufficient pressure on the incoming fluid side of the
cell to secure reverse osmosis flow across the cell membrane
which may be a polyamide type or other suitable type. The
concentrate from cell 50 is passed to the second rinse
tank 44 at a rate of 3.7 liters per minute, the permeate
to the fourth rinse tank 48 at a rate of 7,4 liters per
minute. Tanks 46, 48 are interconnected to permit free
flow between them so that an unrestricted counterflow of
7,4 liters per minute occurs from tank ~8 to tank 46,
Solution from the first rinse tank 42 is also
continuously withdrawn at a rate of 11.1 liters per minute
~0 and passed through a pump 54 to second reverse osmosis
cell 5fi. The concentrate in this instance is passed to
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a holding tan~ 60 at a rate of 3.7 liters per minute, the
permeate being passed at 7.~ liters per minute to the
second rinse tank 44, Tanks 42, 44 are interconnected
so that an unrestricted counter flow of 11.1 liters per
min~te occurs from tank 44 to tank 42.
To effect concentration of the solution in the
holding tank 60 it is withdrawn by a pump 62 at the rate
of 11.1 liters per minute and passed to a third reverse
osmosis cell 64. The permeate is passed to the third rinse
tank 46 at 3.7 liters per minute, the concentrate being
returned at 7.~ liters per minute to the holding tank 60.
For reasons to be made clear the cell 64 is operated
only fifty per cent of the time, all other operations
running continuously. Provision is also made for adding
make up water to the fourth rinse tank as indicated
at 66.
Fig. 3 shows system conditions at start up of
a cycle. During the following twelve hour period there
will be no return of solution from the holding tank 60
to the plating tank 40. Instead, following start up
solution will be retained within the holding tank 60,
gradually increasing in concentration as solution is
cycled through the reverse osmosis cell 64. The approx-
imate solids concentration in each tank at the start of
this cycle of operation is also shown ln Fig. 3, The
solids concentration is the total concentration of copper,
zinc and sodium cyanides and sodium carbonate.
The material balance in flow per minute in each
tank at start up is as follows:
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_IRST RINSE TANK 42
In
From tanl~ 24, 0.75 l/min. x 100,000 ppm = 75,000 mg/min,
From tank 44, 11.1 l/min. x 2150 ppm = 23,86S "
Total 98,865
Out
To tank 44,0.75 l/min. x 9000ppm = 6,750 mg/mln.
To cell 56,11.10 l/min. x 9000ppm =5 99,900
Total 106,650 "
lQ SECONI) ~INSE TANK 44
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From tank 42, 0.75 l/min. x 9000 ppm = 6,750 mg/min.
From cell 56,7.4 l/min. x 900ppm = 6,600
From cell 50,3.7 l/min. x 3220ppm ~ 15
Total 25,265
Out
To tànk 46,0,75 l/min. x 2150 ppm = 1,612 mg/min.
To tank ~2,11.10 l/mln. x 2150 ppm = 23,865 "
Total 25,477 "
20 TIIIRD RINSE TANK 46
In
From tank 44,0.75 l/min. x 2150ppm = 1,612 mg/min.
From cell 64, 3.70 l/rnin. x 1260 ppm = 4,662
From tank 48, 7.40 l/min. x 212 ppm = 1, 568
Total 7, 842 "
Out
To tank 48,0.75 l/min. x 1150 ppm = 862 mg/min.
To cell 50,11.10 lfmin, x 1150 ppm = 12,765
Total 13,627
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FOURTH RINSE TANK 48
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In
From tank 46, 0O75 l/min. x 1150 ppm = 862 mg/min.
From cell 50, 7.4 l~min. x 115 ppm - 851
Total1~713
Otlt
~ith parts, 0.75 l/min. x 212 ppm - 159 mg/min.
To tank 46 t 7.40 l/min. x 212 ppm = 1,568
Total 1,727 "
It will be observed that at this point in time
the system is not balanced. All of the tanks are being
depleted, the thîrd rinse tank 46 undergoing the ~reatest
rate of change. However, as the third reverse osmosis
cell continues to operate concentrating the solution in
the holding tank 60, it will ~eed a continuously enriching
permeate to the third rinse tank 4G eventually effecting
a return sufficient to make up the excess solids withdrawn
during the initial period of the cycle. The other tanks
will likewise receive a balancing flow.
It will be appreciated that the concentrations
in the various tanks will vary from time to time. For
example, the plating solution of tank 40 may vary from
150,000 ppm to 250,000 ppm over a complete cycle and the
solution ln the other tanks will also vary although to
a lesser degree.
At the end of the twelve hour period of operat~on
of the reverse osmosis cell 64, its operation is termin-
ated. Make up water is then started into rinse tank 48
at 3,7 liters per minute. At the same time the solution
in tlle holding tank 60 is returned to the plating tank 40
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since in the preceding period it has lost fluid by drag-
out loss and evaporation, Also since the elcctroplating
operation is not one hundred per cent efficient, it will
be necessary to add make up copper cyanide, zinc cyanide
and sodium cyanide to the plating tank 40 in amount suf-
ficient to maintain the desired cOncentratiQns therein,
Some of the solution from the holdin~ tank will also be
returned to the tank 20 to make up or solution lost by
evaporat iOII .
As the reverse osmosis cells S0, 56, 64 lose
efficiency, adjustments will have to be made in the flow
rates through the various cells so as to maintain the
system balance. For this purpose suitable flow control
valves and flow rate meters (not shown) may be placed in
the various lines.
It will be observed that the concentration of
the solution in tank 20 is only one-half that in the
plating tank 40. Thus, while serv~ng as a convenient
strike tank it serves the equally important function o~
reducing the concentration of dragout carried into the
rinse tank 42 by fifty per cent. This reduces the metal
ion and cyanide content in the rinse solution of tank 42
by like amount and likewise reduces the concentration in
the subsequent tanks reducing by one-half the total amount
of chemicals to be treated in the reverse osmosis cells 50
and 56. This reduction in ion concentration in the
solution in first rinse tank 42 and third rinse tank 46
results in increased efficiency in operation of the reverse
osmosis cells 50, 56, since the osmotic pressure which
has to be overcome will be reduced. Substantial savings
in powe,r are thus realized.
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The reverse osmosis cell 64 maintains an ion
balance in third rinse tan~ ~6. As indicated above,
without the feed back of product from cell ~4, tank 46
would suffer a depletion in ion content and the entire
system would become unbalanced i~ it were attempted to
operate it continuously. Without the cell 64 the system
may be operated or sixteeD hours out of twenty four, but
plating operations must be discontinued for eight hours
out of a t~enty ~our hour period in order to permit
sufficient evaporation from the plating tank 40 to
permit return from the holding tank of all of the permeate
collected from reverse osmosis cel~ 56. The reverse
osmosis cell 64 reduces the volume of the holding tank
by about one-third enabling plating operations to be
carried out continuously.
The illustrated system utilizes four rinse
tanks. I~owever, if a higher dissolved content could be
tolerated in the final rinse the fourth rinse tank 48
could be eliminated in which case the product from reverse
osmosis cell 50 would be returned directly to tank 46
and make up water also added directly to such tank.
~lternatively additional rinse tanks could be added and
the product of cell 50 simply passed to the final ri~se
tank.
As will be observed, the system illustrated is
completely closed. No chemicals are removed from the
system except for the very minor amount carried out on
the parts from the fourth rinse tank 48. Thus, besides
eliminating costly cyanide destruction and costly metal
ion recovery processes that otherwise would have to be
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employed, the system permits maximum utilization o~ plat-
ing metal and electrolytic bath chemicals. The system
also conserves water, the only loss being evaporative
loss and that carried out with the parts from the final
rinse tank.
The syst~m described would also be adaptable
in any type o-f hot plating process wherein an evapor~tive
loss occurs in the plating tank, for example, copper,
nickel or chromium plating In a cold system, such as is
used in zinc plating, an evapora*in~ arrangement would
have to be employed with the plating bath to remove
sufficient water to enable receipt of the holding tank
solution. ~loreovert while the invention has been
described in connection with an electroplating process,
it will be apparent it has usefulness in other types of
plating processes.
