Sulfamate Nickel and Aluminum Revisited

In my June column, I answered a question regarding the removal of aluminum from a sulfamate nickel plating bath. A reader offered an additional suggestion. Here’s the original question and answer followed by the additional information. My thanks to Jack Berg for this information.

Q: We have a sulfamate nickel plating bath that has more than 1400 ppm of aluminum present. Will this affect the quality of the sulfamate nickel deposit? How can we remove the aluminum from the bath? S.N.

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A: I remember reading a number of years ago that aluminum in a nickel sulfamate plating bath affects the upper limiting current density. Unfortunately, I’m unable to find the article, but from my days as a practicing chemist I can tell you that the aluminum will precipitate out as aluminum hydroxide once the pH of the bath is higher than 3.5. If aluminum oxide does precipitate out you will notice roughness in your deposit. Removal of the aluminum can be accomplished by raising the pH and filtering the plating solution. This isn’t a “slam dunk” process since the aluminum hydroxide that forms becomes colloidal and rather messy to filter. The aluminum hydroxide is gel-like in structure and tends to plug filters. Sometimes a filter aid can be used to reduce or alleviate this problem.

The most obvious thing here is for you to figure out where the aluminum is coming from. In my experience, I have never seen or heard of a situation prior to yours in which aluminum was present in a nickel sulfamate bath in the concentrations you mention.

Additional Comment:
Many platers have found use of coarse depth wound filter media to be a good way of removing aluminum and other colloidal contaminants from plating solutions.