US3578469A - Removal of ferrous sulfate from nickel baths - Google Patents

Abstract

PROCESS FOR THE REMOVAL OF FERROUS SULFATE FROM NICKEL PLATING SOLUTIONS WHICH INVOLVES ADDING HYDROGEN PEROXIDE TO THE SOLUTION AND ADJUSTING THE PH TO A VALUE OF ABOUT 3.1 TO 3.3 TO THEREBY PRECIPITATE FERRIC SULFATE IN A FORM WHICH CAN BE READILY REMOVED FROM THE REMAINDER OF THE SOLUTION BY FILTRATION.

Description

United States Patent 3,578,469 REMOVAL OF FERROUS SULFATE FROM NICKEL BATHS Richard N. Hudd, Wheaten, and Heinz Seller, Cicero,

Ill., assignors to Eagle-Picher Industries, Inc., Cincinnati, Ohio No Drawing. Filed Mar. 24, 1969, Ser. No. 810,012

Int. Cl. C23c 3/02 U.S. Cl. 106-1 8 Claims ABSTRACT OF THE DISCLOSURE Process for the removal of ferrous sulfate from nickel plating solutions which involves adding hydrogen peroxide to the solution and adjusting the pH to a value of about 3.1 to 3.3 to thereby precipitate ferric sulfate in a form which can be readily removed from the remainder of the solution by filtration.

BACKGROUND OF THE INVENTION Field of the invention This invention is in the field of treating nickel plating solutions which become contaminated with ferrous sulfate as nickel plating proceeds, the treatment consisting of adding hydrogen peroxide to the solution at a controlled pH to thereby oxidize the ferrous sulfate toferric sulfate and provide a precipitate which can be easily removed from the nickel plating bath by means of filtration.

Description of the prior art In Zander U.S. Pat No. 2,837,443 issued June 3, 1958 and assigned to the same assignee as the present application, there is described a method of porcelain enameling which permits the direct on or single coat application of titania opacified porcelain enamels over ferrous substrates of various descriptions. This type of process involves first cleaning the piece one or more times with an aqueous alkaline cleaner containing sodium phosphate, sodium carbonate, sodium hydroxide, soaps, wetting agents and detergents. The cleaning takes place at the boiling temperature of the cleaner, and the article remains immersed in the cleaner for ten to fifteen minutes in each stage. Then, the cleaned article is rinsed with first warm and then cold water, after which it is pickled with a nitric acid solution containing about 8 to nitric acid. After rinsing with running water, the article is then subjected to treatment with aqueous sulphuric acid and iron sulfide, the treating solution containing about 6.5 to 8.0% sulphuric acid, and 4 to 8 grams of iron sulfide per gallon of acid solution. The temperature is maintained at about 180 F., and the article remains immersed in the solution for four to five minutes.

After a succession of rinses with running water, the article is immersed in a bath of sodium cyanide having a concentration of about 1 ounce per gallon or so, and at a temperature of about 120 F. The immersion time is normally two to three minutes in this stage. After another running water rinse, the article is immersed in an aqueous bath of nickel sulfate from which it receives a flash coating of nickel. The usual concentration of nickel sulfate in this bath is about 1.5 ounces per gallon at a temperature of about 165 to 175 F. The pH is usually on the order of 3 to 3.5. The article remains immersed in the bath for four to five minutes or so, whereupon it receives a nickel flash deposit ranging from about 0.05 to 0.12 gram per square foot.

The nickel deposition proceeds according to the ollowing equation:

3,578,469 Patented May 11, 1971 'ice Continued operation of the nickel plating bath increases the concentration of ferrous sulfate in the tank, whereupon the operation has to be stopped and the contents of the nickel tank dumped. As the ferrous sulfate concentration builds up, the efficiency of the nickel plating operation decreases. In addition, the presence of ferrous sulfate results in building up iron scale in the tank, in spray nozzles, headers and other portions of the pickling machine.

SUMMARY OF THE INVENTION The present invention provides a means of removing the detrimental effect of ferrous compounds in the nickel plating bath by oxidizing the same with hydrogen peroxide either continuously or on an intermittent basis. The oxidation takes place when the pH of the nickel plating bath is maintained at a range of about 3.1 to 3.3 through the addition of any of a variety of alkaline acting agents. The ferric sulfate which is formed precipitates cleanly from the nickel plating bath and can be removed without significant loss of nickel values.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The ferrous sulfate in the nickel plating bath is oxidized to ferric sulfate according to the following equation:

As the above reaction proceeds, the pH becomes more acid and approaches 1.5. In order to bring the pH back to the desired range of 3.1 to 3.3, various alkaline acting materials can be used. For example, nickel carbonate may be used in its anhydrous or hydrated form. In addition, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide may be used. An alkali metal carbonate including sodium carbonate and potassium carbonate may similarly be employed. The hydroxides or carbonates of alkaline earth metal such as barium and calcium are also useful for this purpose. Still another class of materials which can be used for securing the proper pH control are the alkali metal and alkaline earth metal peroxides, such as the peroxides of sodium, potassium, barium and calcium.

As mentioned previously, the hydrogen peroxide can be added continuously or intermittently as the nickel plating reaction proceeds. It is merely necessary to maintain the proper molar concentrations for the reaction to proceed, namely, one molecular proportion of hydrogen peroxide for every two molecular proportions of ferrous sulfate formed. The hydrogen peroxide can be added either as a dilute or as a concentrated solution.

The ferric sulfate which results from this reaction is a precipitate which is easily removed from the remaining solution by filtration. It has been found that the process of the present invention significantly improves the life of the nickel plating solution so that fairly concentrated nickel containing solutions need not be disposed of and create a pollution problem. Furthermore, the plating reaction occurs at maximum efiiciency, without interference from the ferrous ions. The removal of iron in insoluble form reduces the possibility of building up iron scale in the equipment and reduces the maintenance problems associated with the pickling machine. It has also been found that with the process of the present invention, a given thickness of nickel deposit can be achieved at a reduced solution contact time. The normal nickel plating temperature of to F. can be employed for this reaction, so that there is no interference with the normal plating reaction by virtue of the addition of hydrogen peroxide.

It should be evident that various modifications can be made to the described embodiments without departing from the scope of the present invention.

We claim as our invention:

1. The method of treating a nickel plating solution containing nickel sulfate and sulphuric acid in amounts and under conditions conducive to the continued formation of ferrous sulfate produced by immersing ferrous articles in said solution for the oxidation and removal of ferrous sulfate which comprises adding hydrogen peroxide to said solution in an amount sufficient to oxidize the ferrous sulfate to ferric sulfate, and adjusting the pH to a value in the range from about 3.1 to about 3.3 with an alkaline acting agent to thereby cause precipitation of readily filterable ferric sulfate therein.

2. The method of claim 1 in which the pH is adjusted by the addition of nickel carbonate to said solution.

3. The method of claim 1 in which the pH is adjusted by the addition of an alkali metal hydroxide to said solution.

4. The method of claim 1 in which the pH is adjusted by the addition of an alkali metal carbonate to said solution.

5. The method of claim 1 in which the pH is adjusted by the addition of an alkaline earth hydroxide to said solution.

6. The method of claim 1 in which the pH is adjusted by the addition of an alkaline earth carbonate to said solution.

7. The method of claim 1 in which the pH is adjusted by the addition of an alkali metal peroxide to said solution.

8. The method of claim 1 in which the pH is adjusted by the addition of an alkaline earth peroxide to said solution.

References Cited UNITED STATES PATENTS 3,265,511 8/1966 Sall 106-1 LORENZO B. HAYES, Primary Examiner US. Cl. X.R. 117-130