Iron Buildup in Chrome Tank

Question:

We are plagued by the buildup of iron in our hard chromium plating baths. We use the classical method for reducing the iron concentration by removing half the bath and then reconstituting the remaining half. The problem with this approach is that we end up with chromium plating solution that has to be disposed of. Is there a better way of handling this? S.O.

Answer:

This is a problem that seems to crop up often based on the e-mails I receive. The classic method that you describe is not the best way to handle this problem. Not only does this approach generate waste hexavalent chromium solutions but also it is environmentally unfriendly and costly. There are better ways.

Two better methods of handling this problem is to use ion exchange equipment or electrodialysis equipment to remove the iron. Both of these methods are environmentally friendlier and while the initial cost of the equipment is more than a Starbucks Double Grande, the payback period is relatively short. You can find names of vendors in the Products Finishing Directory and Guidebook, 2004 edition, www.pfonline.com/suppliers.html.

You should also address a more fundamental question. Where is the iron coming from? Have you investigated the quality of the water you are using? City water normally is not high enough quality. It may contain iron, which will build up in the tanks. If you are using city water or well water, get an analysis of the water. A major source of iron in a chromium plating tank is reverse etching of the parts in the plating tank. I recommend a separate chromic acid tank for the reverse etching step.