How to remove Zinc from Nickel Sulfamate plating bath
Q. Hi. I am trying to remove zinc from a nickel sulfamate bath.
I've tried dummy plating but I can't seem to lower the level. It is at about 300-350 ppm. Any ideas on how to remove it or about what I might be doing wrong with my dummy plating attempts? I'm running the dummy plate at ~5ASF. I have tried dummy plating as is, with 3ml/liter H2O2, and at low pH's (2.5).
Any help would be appreciated.JD Kronicz
- Hanover, Pennsylvania
A. Dear Mr Knonicz ,
I trust that you are using a corrugated cathode? Try the following: Get the pH up into the 3 -->4 range, reduce the current density to approx. 2 ASF and plate for at least 12 hours (preferably 24) which must be continuous. The longer you plate the better. Regards,
- Victoria Australia
A. Dear Mr Kronicz,
Follow John's advice regarding use of corrugated sheet, and get the average CD down to 2 ASF, etc. -- these are very important for effective removal. The level of zinc contamination is abnormally high (from my experience) Have you identified the source? If not, the source of contamination may still be in contact with the solution, and thus as fast as you dummy zinc out, it is being re-introduced.
Some suggestions based on experiences: Once saw a situation where a foreign anode material got into a basket. Don't know how it got there, but it was the problem. If you are plating a substrate which is high in zinc, have you removed any parts from the bottom of the tank? A few parts dissolving on the bottom of the tank can produce high levels of contamination. Once had a situation where a customer had received an off-spec grade of activated carbon... it was high in zinc. Use of this carbon on the filters produced an abnormally high level of zinc contamination in the nickel plating solution. If your source of zinc contamination has not been identified and eliminated, the source may not be readily obvious, as in our case of the carbon. This took a few days of investigation before we decided to check the carbon (actually we were running out of things to check). Trust the above gives you some ideas. Regards,
Burlington, Ontario, Canada
A. Kronicz, I agree with both John and Ken. You added 3 ml/L H2O2 and used 5 ASF to remove zinc from nickel solution while the pH value of your bath was as low as 2.5. This method is efficient only when pH is higher than 4.0. In most efficient cases, pH is in the range of 4.5 to 5.5. It is recommended to raise pH using nickel carbonate. Then you have to investigate the source of zinc contamination so that you can eliminate the contamination.
- Grand Rapids, Michigan
A. I agree with the 2 ASF. Would increase the agitation and dummy every night and weekend until you got it down.James Watts
- Navarre, Florida
A. I agree with Ken that 350 ppm of zinc is quite unusual but I do remember such a high figure in a nickel plating solution that was dedicated to zinc die casting. It took more than a week to reduce the zinc level . The source of this high concentration of contamination were zinc parts at the bottom of the tank. As the concentration of the zinc is high, you can begin the plating out at quite high current density like 1 amp/dc2. In case you perform a Hull Cell test you will observe that even at 1.5 amp/dc2 the deposit is still black. After one day of dummying you can reduce the current to 0.2. You can observe the colour of the corrugated cathodes -- when it starts to get bright, reduce the current. Avoid parts from the corrugated cathodes from falling back into the plating tank. It is a good practice to finish the dummying process by plating for 30 minutes at 2-3 amp/dc2.
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