US3928146A

US3928146A - Electroplating recovery process

Info

Publication number: US3928146A
Application number: US503631A
Authority: US
Inventors: James P Russell
Original assignee: Winter Products Co
Current assignee: Winter Products Co
Priority date: 1974-09-06
Filing date: 1974-09-06
Publication date: 1975-12-23
Anticipated expiration: 1992-12-23
Also published as: AU8431075A; CA1058550A; GB1515926A

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

United States Patent Russell Dec. 23, 1975 [54] ELECTROPLATING RECOVERY PROCESS 3,658,470 4/1972 Zievers et a1. 204/232 Inventor: James P. Russell, Oregon y, 3,681,210 8/1972 Zlevers et al. 204/232 Oreg' Primary Examiner-T. M. Tufariello [73] Assignee: Winter Products (30., Portland, Attorney, Agent, or Firm-Klarquist, Sparkman,

Oreg. Campbell, Leigh, Hall & Whinston 22 F1 d: Se t. 6 19 1 p 74 57 ABSTRACT [21] Appl' N03 503631 Plating line passes parts from plating tank to insulated portion of dual chamber strike tank so as to cut drag [52] US. Cl 204/14 R; 204/232; 204/237 out concentration by one half to further rinse tanks. [51] Int. Cl. C07B 5/00; A44B 9/12 Solution in certain rin tanks p d hrough reverse [58] Field of Search 204/14 R, 232, 237-241, osmosis cells and recycled to y Most concen- 204/267 269 trated product of reverse osmosis cells placed in holding tank and concentrated therein by cycling through [56] References Cit d another reverse osmosis cell before periodic return to UNlTED STATES PATENTS Platmg bath- $637,467 1/1972 Spatz 204/14 R 8 Claim 3 Drawing Figures U.S. Patent Dec. 23, 1975 Sheet 2 of2 3,928,146

PDOU EO ELECTROPLATING RECOVERY PROCESS BACKGROUND OF THE INVENTION Realization of the injury to rivers, lakes and oceans by reason of the discharge therein of heavy metal solutions and other chemicals has caused severe restric tions, both voluntary and legislative, upon the discharge of such materials into such bodies. Moreover, the increasing cost of chemicals and metals has increased the necessity of their economical use. i

Electroplating solutions have presented particular problems in disposaland efforts have been directed to recovering the chemicals utilized therein. US. Pat. No. 3,637,467, for example, described a process utilizing a reverse osmosis unit in connection with the recovery and recycling of chemicals in a gold plating operation. The system, therein described would not be suitable for a brass or similar large volume flow rate plating operation. Other systems utilizing reverse osmosis units have been suggested, but none, so far as is known, have been capable of continuous plating operation while eliminating totally any discharge outside of the system.

SUMMARY OF THE INVENTION 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 is to provide a closed recovery system that will permit continuous plating operation.

In accordance with the invention parts to be plated are, following suitable preparation, subjected to a strike plate in a dual chamber tank, one chamber of which constitutes an electroplating bath, the other a drag out or pre-rinse 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 thereafter passed through a series of rinsetahks substantially ro remove all plating chemicals from the parts. The solution in the dual chamber tank is one half the concentration in the 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 first 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.

Other objects and advantages of the invention will become apparent hereinafter.

- DRAWINGS 8 FIG. 1 is a schematic flow chart showing the path of objects to be electroplated in accordance with the invention';

FIG. 2 is a semi-schematic cross sectional view of a dual chamber tank utilized in the system of the invention; and j FIG. 3 is a schematic flow chart of the process of the invention indicating thereon the operating conditions at one period of the process.

DETAILED DESCRIPTION OF THE INVENTION The illustrated embodiment of the invention. is for plating brass upon articles such as furniture hardware from a conventional sodium cyanide-process. Inaccordance with such process and referring first to FIG. 1, wherein the path of the article being plated is shownby the solid line A, the parts to be plated are placed as customary within a perforated barrel or otherwise suit ably supported and dipped in an alkaline cleaning solution contained in a tank 10. Prior to this step the parts are suitably sandblasted, tumbled, or given 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 substantially 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 neutralization 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 with 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-conducting material so as to divide the tank into two portions, the portion 18 which comprises a striking bath and a further portion 24, comprising a drag out or pre-rinse bath the purpose for which will be described in detail subsequently. The partition 22 is provided with an opening 28 near the bottom of the tank so as to provide for fluid communication between the

portions

18, 24 whereby, as will be ssen, the ion concentration of the solution in the two portions will be substantially the same. The tank portion 18 is provided wtih a brass anode or anodes 30 suspended on contact bars 32 con nected to the positive side of a source of direct current electrical 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, substantially complete removal of the plating solution 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 of the recovery system of the invention. Since the solids recovery system is involved only with the plating tank 40 and subsequent rinses, the initial wash and cleaning tanks 10 to 16, inclusive, are omit- 3 ted 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 of operation. As the parts are moved from tank to tank they will carry with them solution or so-called drag out. In the illustrated embodiment this amounts in volume to 0.75 liters per minute. In accordance with the invention, solution is continuously withdrawn from the third 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 to maintain 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 15 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 unstricted counterflow of 7.4 liters per minute occurs from tank 48 to tank 46.

46 at 3.7 liters per minute, the concentrate being returned at 7.4 liters per minute to the holding tank 60. For reasons to be made clear the cell 64 is operated only 50 percent 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 12 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 approximate solids concentration in each tank at the start of this cycle of operation is also shown in 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:

First Rinse Tank 42 From tank 24, 0.75 1/min. X 100,000 ppm 75,000 mg/min.

Out

To tank 46, 0.75 llmin. X 2150 ppm To tank 42,11.101/min. X 2150 ppm 1,612 mg/min. 23,865 mg/min.

Total 25,447 mg/min. Third Rinse Tank 46 From tank 44, 0.75 1/min. X 2150 ppm 1,612 mg/min. From cell 64, 3.70 I/min. X 1260 ppm 4,662 mg/min. From tank 48, 7.40 l/min. X 212 ppm 1,568 mg/min. Total 7,842 mg/min. Out

To tank 48, 0.75 l/min. X 1150 ppm 862 mg/min. To cell 50, 11.10 l/min. X 1150 ppm 12,765 mg/min. Total 13,627 mg/min. Fourth Rinse Tank 48 From tank 46, 0.75 l/min. X 1150 ppm 862 mg/min. From cell 50, 7.4 l/rnin. X 115 ppm 851 mg/min. Total 1,713 mg/min. Out

With parts, 0.75 l/min. X 212 ppm 159 mg/min. To tank 46, 7.40 llmin. X 212 ppm 1,568 mg/min. Total 1,727 mg/min.

Solution from the first rinse tank 42 is also continuously withdrawn at a rate of 1 1.1 liters per minute and passed through a pump 54 to second reverse osmosis cell 56. The concentrate in this instance is passed to a holding tank 60 at a rate of 3.7 liters per minute, the permeate being passed at 7.4 liters per minute to the second rinse tank 44.

Tanks

42, 44 are interconnected so that an unrestricted counter flow of 1 1.1 liters per minute 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 l 1.1 liters per minute and passed to a third reverse osmosis cell 64. The permeate is passed to the third rinse tank It will be observed that at this point in time the system is not balanced. All of the tanks are being depleted, the third rinse tank 46 undergoing the greatest rate of change. However, as the third reverse osmosis cell continues to operate concentrating the solution in the holding tank 60, it will feed a continuously enriching permeate to the third rinse tank 46 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 z'sopoo' pni over a 'corriplete' cycle and'the solution in the other tanks will also vary' although to a lesser degree. 7 i I At theend of the 12' hour period of operation of the reverse osmosis cell 64, its operation-is terminated. Makeup water is then started-into rinse tank 4.8 at 3.7 liters'per minute. At the same timethe solution in the holding tank 60 is returned to the plating tank 40 since in the preceding period it has lost fluid by dragout loss andevaporation. Also since the electroplating operation is not one hundred percent efficient, it will be necessary to add make up copper cyanide, zinc cyanide and sodium cyanide to the plating tank 40 in amount sufficient to maintain the desired concentrations therein. Some of the solution from the holding tank will also be returned to the tank to make up for solution lost by evaporation.

As the

reverse osmosis cells

50, 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 serving as a convenient strike tank it serves the equally important function of reducing the concentration of dragout carried into the rinse tank 42 by 50 percent. 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 power are thus realized.

The reverse osmosis cell 64 maintains an ion balance in third rinse tank 46. As indicated above, without the feedback of product from cell 64, tank 46 would suffer a depletion in ion content and the entire system would become unbalanced if it were attempted to operate it continuously. Without the cell 64 the system may be operated for 16 hours out of 24, but plating operations must be discontinued for 8 hours out of a 24 hour period in order to permit sufficient evaporation from the plating tank to permit return from the holding tank of all of the permeate collected from reverse osmosis cell 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. However, 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. Alternatively additional rinse tanks could be added and the product of cell 50 simply passed to the final rinse 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 employed, the system permits maximum utilization of 6 plating'metal and electrolytic bath chemicals. The system also conserves water, the only loss being evaporative loss-and thatcarried out with the parts from the final rinse-tank.

The system described would also be adaptable inyany type of hot'p'lating process-wherein an evaporative 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 evaporating arrangement would have to be employed with the plating bath to remove sufficient water to enable receipt of the holding tank solution.'Moreover, 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.

Having illustrated and described a preferred embodiment of the invention, modifications in arrangement and detail will be apparent to those of ordinary skill in the art.

I claim:

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 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 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 to the second of said rinse tanks,

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 to the final one of said rinse tanks,

and returning 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. I

3. The process of claim 2 including periodically 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 withdrawing the solution from said holding tank and subjecting it to a third reverse osmosis while 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 periodicallyjs subjected to said third reverse osmosis and at the termination of said third 7 reverse osmosis cycle the solution in said holding tank is returned to said plating tank.

6. The process of claim comprising adding 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 solution is a 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,

8 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 anarticle 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.

Claims

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 NONCONDUCTING 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 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 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 TO THE SECOND OF SAID RINSE TANKS, 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 TO THE FINAL ONE OF SAID RINSE TANKS, AND RETURNING 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.

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

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

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.