CA1058550A

CA1058550A - Electroplating recovery process

Info

Publication number: CA1058550A
Application number: CA232,282A
Authority: CA
Inventors: James P. Russell
Original assignee: Winter Products Co
Current assignee: Winter Products Co
Priority date: 1974-09-06
Filing date: 1975-07-25
Publication date: 1979-07-17
Also published as: AU8431075A; GB1515926A; US3928146A

Abstract

ELECTROPLATING RECOVERY PROCESS

ABSTRACT

Plating line passes parts from plating tank to insulated portion of dual chamber strike tank so as to cut drag out concentration by one half to further rinse tanks. Solution in certain rinse tanks passed through reverse osmosis cells and recycled to system.
Most concentrated product of reverse osmosis cells placed in holding tank and concentrated therein by cycling through another reverse osmosis cell before periodic return to plating bath.

Description

1805~ Foreign Sf~55(~

ELECTROPLaTING RECOVERY PROCESS
_ 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 .

5S(~
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;

~ -2-` ~5~355~

Figure 2 is a semi-schematic cross sectional view of a dual chamber tank utilized in the system of the invention; and -2a-1~056 Foreign 358~50 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-l~056 Fori3i~

~C~5~355~

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 18056 rOrei~ll 9 ~5!3SS(~

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 ; O I` C ~

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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:

1~3056 Forei~ll ~0~855~

_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 -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 "

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 18U5~; Fol~ei~n ~58~5~3 -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 1~3()5~ Forei~ll ~OS85S0 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.

_g_ 1~05G Forei~ll 16~51~55~

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 _ln_ 1~05~ F~ll ~58S50 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.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a plating process wherein articles are plated in a solution within a plating tank and thereafter rinsed in a series of at least three 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 including a plating portion and a rinse portion, said divider having an opening therein to permit flow of solution between said one portion of said dial 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 effecting a plating on said article, passing the article from said plating tank to the said other portion of said dual chamber tank, thereafter passing said article seriatum to said rinse tanks, continuously withdrawing solution from the first of said rinse tanks and subjecting it to a first reverse osmosis while continuously passing the concentrate from said first reverse osmosis to a holding tank and the permeate from said first reverse osmosis to the second of said rinse tanks, passing solution from said second rinse tank to said first rinse tank, continuously withdrawing solution from the third of said rinse tanks and subjecting it to a second reverse osmosis while continuously passing the concentrate from said second reverse osmosis to said second rinse tank and the permeate from said second reverse osmosis to the final one of said rinse tanks, adding make-up solution to said third rinse tank and return-ing solution from said holding tank to said plating tank.

2. The process of claim 1 wherein said solution is accumulated in said holding tank for predetermined periods of time and periodically returned to said plating.
tank.

3. The process of claim 2 including periodi-cally terminating said plating and evaporating solvent from the plating solution prior to the return of solution from said holding tank.

4. The process of claim 1 comprising with-drawing the solution from said holding tank and subjecting it to a third reverse osmosis whlle passing the permeate to said third rinse tank and returning the concentrate to said holding tank.

5. The process of claim 3 wherein said solution in said holding tank periodically is subjected to said third revsrse osmosis and at the terminatioll of said third reverss osmosis cycle the solution in said holding tank is returned to said plating tank.

6. The process of claim 5 comprising addlng make up solvent to said final rinse tank as said solution is returned to said plating tank.

7. The process of claim 6 wherein said solu-tion is brass cyanide plating solution and said solvent is water.

8. 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 effecting 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.