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Complete electroplating of Zn?

I was wondering whether typical electroplating processes (hardware, for example) involve plating all of the Zn in solution, or if some Zn is left in the bath at the end of the process? Also, what is done with the Zn still in solution at the end of the process?

I am a graduate student studying Zn isotopes in common materials and have found that electroplated hardware consistently has a high ratio of light Zn isotopes. This implies to me that light isotope are preferentially electroplated first, and that not all of the Zn in solution is plated...but I don't know much about the industrial processes.

Also, I have a hot-dip galvanized sample that is isotopically HEAVY. Is it possible that this sample was hot-dip galvanized in metal that was recovered from an electroplating bath?

Seth John
MIT

Seth G. John
Graduate Student, MIT - Cambridge, Massachusetts
2007

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2007

There are a number of ways of applying a zinc coating to an object, Seth; electroplating and hot dip galvanizing are two of them.

Omitting a discussion of the pretreatment or post treatment, and keeping it simple--

Hot dip galvanizing involves dipping the part into a vat of molten zinc, like chocolate on strawberries.

Zinc electroplating consists of dipping the part into an aqueous solution that contains a dissolved zinc salt, and applying electricity to reduce the dissolved zinc as a metal onto the substrate.

No, all of the zinc is not plated out. Quite the opposite: the zinc content is maintained consistent via dissolving a matching amount of zinc into the solution from zinc anode metal. The zinc plating solution is not dumped; rather, it is maintained as an equilibrium solution -- sometimes for decades.

I'd say there is something wrong with your theory. Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

During the electroplating process, surely some Zn must be lost into the waste stream. But how much? 10% ? ...or 1/100th% ?

Seth G. John
Mass. Inst. of Technology - Cambridge, Massachusetts
2007

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Yes, some of the zinc is lost to the waste stream, Seth.

Some of the loss may go to periodic washdown of filtration equipment and entrainment of solution into the fume extraction system, but the biggest loss will be dragout into the rinsing steps. It is difficult to put a number on this because it depends on the type of plating, and is very dependent on the shape of the parts and how they are transported into and out of the plating bath. However, I don't think it ever approaches 10 percent. I think 1 percent might be a good guess. Techniques are employed to get the zinc values of this rinsewater back into the plating bath if the dragout is high. I doubt that it would ever be as low as 1/100 of one percent . . . 1/10 of one percent would sound very good to me.

Perhaps a plating shop which buys zinc anodes and disposes of zinc-bearing sludges from their water treatment would offer their numbers of what percentage of the zinc they buy ends up on the parts, but I'd guess at 98 - 99 percent pending some feedback.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007