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Iron contaminated Cobalt Hardened Gold Plating Bath
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I am trying to remove Iron from a potassium cyanide gold citrate based plating solution. The bath has a gold content of 4 g/l with a pH of 4.2 - 4.6 and a cobalt content of 300 - 500 mg/L. The bath has a Iron content of 200 mg/L and it is causing a problem as to meeting a purity of deposit spec. The Iron is being plating out in a matter of 0.298% in deposit. I have tried a variety of resins but to no success.
The Iron has to be possibly lowered to 25 - 35 mg/L to pass our purity of deposit spec.
Is there a chemical treatment process which will not remove all of the Gold and most of the iron. Dummy plating is not an option.
Doug Duda- Southington, Connecticut
March 8, 2011
I know with the case of Rhodium plating, you can utilize Potassium Ferrocyanide to precipitate out Iron impurities. We have utilized this method very efficiently, however, the affect on Gold and/or Cobalt concentration is unknown to me.
I would take a small sample size ~ 100 mL of solution and try to add Potassium Ferrocyanide to this. I would try a 1:1 stoichiometry ratio. The solution may need to sit for a couple of days and try to be very careful with siphoning out the solution, as these complexes are very fluffy and will go back into solution easily.
Try to run the analysis on the solution, following the precipitation method and see how much of the iron has been depleted.
- Temecula, California