Chloride in Chromium Plating Bath

Question:

How can I remove a large amount of chloride ion from my chromium plating bath? The chromium plating bath is the classic chromic acid/sulfuric acid bath. S.D.

Answer:

A classic way to reduce the amount of chloride ion in the bath is to remove part of the plating bath and then rebuild the remaining portion of the bath by adding good quality water, chromic acid and sulfuric acid. The problem with this approach is you now have chromium plating solution that must be disposed of.

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A better approach is to use silver oxide to remove the chloride from the bath. One suggested method is to fill a couple of polypropylene anode bags with silver oxide and suspend them in the plating bath. The silver oxide will react with the chloride and form a precipitate that can be filtered from the solution. This is not necessarily a “fun” task.

A very important question to ask yourself is this: How did the excessive amounts of chloride get into your plating bath? As you apparently have found out, chloride in concentrations above 0.003 oz/gal can cause problems. You should not be using city water for make-up in your plating bath. It usually contains a small amount of chloride that can build up over time! Use of good quality water should always be used when making up chromium as well as all other types of plating baths.