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-----Closing the loop on Nickel Plating rinses
Q. I run a large job shop that has (9) 2200 gallon nickel tanks. Six of them are semi-bright and three of them are bright. I periodically have to decant the nickel solution due to metal growth within the baths.
One of my associates has told me that this is a needless waste of nickel and by simply reducing the anode area we will reduce the amount of nickel build up in the baths. He feels that we could close the loop on our bright nickel tanks with evaporators and feed all of the filtered, carbon treated rinse water back into the bright nickel tanks. Since we don't rinse between semi-bright and bright nickel that is the only option we have obviously.
I know nickel is 97% efficient and Faraday's Law is pretty straight forward. I've heard varying opinions about this and people have warned me about anode polarization among other ills. My problem is that I can't afford to have anode polarization occur and have chrome plated bumpers peeling by the hundreds. I suspect that I wouldn't know about it until it was too late.
I don't have much drag out and even if I did, with a closed loop system I would recover all of the nickel anyway. The idea of not treating nickel rinses anymore is very intriguing but something just doesn't add up here. Am I missing something obvious? If he's wrong, it could cost me thousands. If he's right, I'm wasting thousands now. Anybody out there have some answers? Thanks for the advice!
Daryl Spindler, CEF
decorative nickel-chrome plating - Greenbrier, Tennessee
1999
A. Daryl,
although your tanks are relatively large compared to most shops it is possible to cut the nickel to almost zero. The first thing I would do is a mass balance to see what the drag out content is. This will tell how much water is needed to maintain a reasonable nickel level in the rinses. Second, do an evaporation study to see how many gallons per hour are being evaporated by the bright tanks. Once you have the evaporation rate and the gallons per hour needed to keep the rinses clean it's just a matter of choosing the right technology to achieve a balance. Certainly carbon treating the drag out rinse is a good idea. You may want to step up your dummying schedule due to an increase of contaminants from the drag out being added back. We've been doing this for years on several bright nickel processes without any problem.
I would recommend reading the chapter on rinsing in the Metal Finishing Guidebook. It was written by Ted Mooney and it tells you all you need to know to get started. It may even be worth paying him for a few days of his time to evaluate your process since this is his specialty (no...I don't get any commission!)
Jim Conner
Mabank, Texas USA
1999
1999
A. Following Jim's reply, Ted also has a software named Perfect Rinsing that can make all the calculations for you regarding the evaporation, # of rinses, etc. We use it a lot and it is great. (and just like Jim, I also get no commission). Closed loop systems for nickel plating is popular for years. Of course, you have to use two different loops for the semi-bright ( I assume sulfur free) and the bright line.
Why is you nickel concentration growing? What kind of anodes are you using? I hope that you use R and not S nickel. Or maybe that your chloride concentration is too high and that is causing a high anode corrosion.
Sara Michaeli
Tel-Aviv-Yafo, Israel
February 28, 2009
! Thanks for the kind words Jim and Sara.
Regards,
Ted Mooney, P.E.
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