Filtering of spent chrome stripping bath
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We have a small tank plating system for the gold plating of chrome plated objects. We first remove the chrome with NaOH, activate with HCl acid and plate with cyanide gold. Is there a way to filter out the chrome stripping bath so that it would not have to be totally replaced? Someone told us to use some sort of rosin bag but we have not heard of that.
Rob Henry - tech manager
There are two generally accepted ways to strip chrome, Rob, depending on circumstance and substrate: a dip in HCl, or electrolytically in a caustic tank. I have seen these electrolytic tanks still functional even when lemon yellow from hex chrome, so maybe you don't have to dump it quite yet.
Hexavalent chrome is anionic (CrO4-2) rather than cationic like most other metals so it is theoretically possible to remove the chrome with a simple anion exchange resin. But whether you will have attack, or gumming up of the resin, or chemical imbalances, and so on in the real world is something you will either have to test or rely on the experience of the vendor. Good luck.
Ted Mooney, P.E.
Pine Beach, New Jersey
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