Clarification Regarding Anodizing

In the May 2014 issue of The Construction Specifier, Ben Mitchell, CSI, wrote a piece, “VOCs… and Beyond: Powder and Liquid Coatings Reviewed.” We recently received a letter from Roger Thomas and Rand A. Baldwin, respectively, the chair and president of the Aluminum Anodizers Council (AAC).

Mr. Mitchell did a decent job comparing powder and liquid coatings, but he gave an unfair and false impression of anodizing.

He writes, “aluminum hydroxide sludge and water must be properly disposed of to avoid contaminating the environment.” We agree with this statement—any sludge should be properly disposed. However, Mr. Mitchell uses a footnote to characterize aluminum hydroxide as a hazardous waste under CFR 40 Section 261.31, F019. This is incorrect. The table in the referenced regulation provides a list of hazardous wastes from non-specific sources. The description of F019 is “Wastewater treatment sludges from the chemical conversion coating of aluminum[.]”

For the adherence of paint, either applied as a wet or powder coating, a conversion coating must be applied to the aluminum. Sulfuric acid anodizing is not a conversion coating. In fact, such a coating would inhibit the anodizing process. Aluminum also is mentioned in the discussion of F019 as a specific exemption in aluminum can washing. Therefore, sulfuric acid anodizing is not a listed hazardous waste under the definition of F019.

Perhaps Mr. Mitchell confused F019 with F006, where “sulfuric acid anodizing of aluminum” is found in the text. F006 is defined as “Wastewater treatment sludges from electroplating operations except from the following process: (1) Sulfuric acid anodizing of aluminum…” Therefore, aluminum hydroxide sludge is not a listed F006 waste.

The only other way aluminum hydroxide sludge would be a hazardous waste is if analytical analysis demonstrated it failed one of the tests required by 40 CFR 261.20. To be in compliance with 40 CFR 262.11, which requires all waste streams to have a determination of whether the waste is hazardous, members of Aluminum Anodizers Council (AAC) have had independent laboratories analyze aluminum hydroxide sludge. Aluminum hydroxide sludge is not ignitable, reactive, or corrosive as defined in 40 CFR 261.21 through 261.23. Additionally, aluminum hydroxide sludge does not fail any of the Toxicity Characteristic Leaching Procedure tests specified in 40 CFR 262.34. Therefore, aluminum hydroxide sludge is not a characteristically hazardous waste.

It should also be pointed out aluminum hydroxide sludge has beneficial uses. Members of AAC sell aluminum hydroxide to companies that recycle this non-hazardous byproduct of the sulfuric acid anodizing of aluminum process. Other members dispose of aluminum hydroxide sludge in landfills that cannot receive hazardous waste, where it is considered an excellent daily cover for other wastes.

We would appreciate your printing this correction to Mr. Mitchell’s comments.

Mr. Mitchell acknowledged the AAC members were correct, and apologized for his error.

Leave a Comment


Your email address will not be published. Required fields are marked *