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Aluminum-Brightening Waste

2002

Please help me understand the aluminum-brightening process, from a waste standpoint: 1) Does nitric-phosphoric dipping produce any waste (e.g., can you just keep adding new acid to a drum or tank without ever changing the solution or cleaning out sludge)? and 2) Does all "iridite" contain chromium or is there a suitable substitute?

Thank you!

Martha Worland
- Orlando, Florida

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The bath will eventually be consumed to the point that it will make sense to start fresh in order to keep moving. The solution will be a corrosive waste that will need to be neutralized before discharge to your POTW. It will also likely contain metals such as copper that will exceed your wastewater permit limit and will need to be removed prior to discharge. The removed metal will then be a solid waste that will need to be disposed of properly. The bottom line is that you really can't do chemical processing in today's world without having to deal with and properly dispose of chemical wastes.

Iridite is a brand name for a whole family of conversion coatings. Most conversion coatings contain hexavalent chrome. Certainly the ones that work the best do, but there are a few substitutions that your chemical supplier can recommend that may give a satisfactory result for your application.

Jon Barrows, MSF, EHSSC
GOAD Company

Independence, Missouri

2002