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topic 4204

Treatment of Black Dye


Q. I just started waste treatment at a big company. I have no experience. I want to learn as much as possible. I am trying to treat Black Dye. I mixed 300 gallons of black dye with about 27.5 gallons of chlorine after I raised the pH to 8.5. I then mixed for about two hours. I lowered the pH to 3.0 with Sulfuric acid. Then I added metabisulfate to the ORP reading of 2.7. I brought the pH up to 9.0. I then added a flocculant. After mixing for about 4 hours, I brought a sample to the lab. The results came back with about 161 ppm of chrome. The lab suggested to use Hydrogen Peroxide. Will this drop the chrome out? Do you have any suggestions for future treatment of black dye?

Randy Mattson
- Sumner, Washington


A. Hi, Randy. Since you claim no experience, I do have an important lesson for you. Do your experiments on a small beaker of under a lab hood, rather than with a 300-gallon batch :-)

After you've proven the feasibility of your treatment sequence with a small beaker of the waste, only then should you scale it up.

But I think I would address the chrome first, and the black color secondarily. In other words, I would keep the pH low (about 2.5-3.0) and add the metabisulphite. Then I would raise the pH to 8.0-9.0 to precipitate the chrome. Then I would filter or allow settling time and decant. (You're not doing alchemy or nuclear science, you can only precipitate the Chrome and remove it, you can't destroy it).

Then I would deal with the colored, chrome-free water by oxidizing the black dye. Peroxide is worth a shot, but you may find that bleach is more effective in removing the color. Best of luck.


Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


A. I had this problem, once. Here's how I solved it.

First I lowered the pH to about 4.5. Then, some ferrous sulfate, added as a solution and mixed in well. Then, 35% hydrogen peroxide. You'll have to do some bench experiments to find out exactly how much. It will take about 12 hours till you see significant bleaching of the color. This chemical treatment is called "Fenton's Reaction".

Now bring the pH up with caustic soda to about 9. If you see a lot of foaming, wait till it subsides. Then add an anionic flocculant to settle the solids.

I have heard of chlorination being recommended for organic wastes. My humble opinion is: this is a terrible idea. It could result in the formation of all kinds of chlorinated organic byproducts, some of which may be regulated and many of which are impossible to remove.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

Hi, Dave. Thanks for the warning to be thoughtful before using chlorination on organic wastes. You certainly may be right that it could prove problematic, and that 27.5 gallons of it is a lot!

But many metal finishing wastewater treatment systems already use chlorine anyway for cyanide treatment, and the residual chlorine probably does bleach out the anodizing dyes the shops use; and every housewife uses Clorox to remove dyes from fabrics. So while it sometimes can be a problem, other times it may be de minimus.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

April 5, 2012 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Bk Excel dye Disposal: Is there a chemical treatment to remove the color in a dye for neutralization and disposal?

Robert Galligan
- Melbourne, Florida

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