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How to neutralize the waste sludge from cleaning chrome plating tank

Q. Dear Sir/Madam

We undertake hard chrome electroplating and have made a practice to clean the electroplating tanks after 5-6 months. The sludge/waste (waste of chromic acid) obtained from the tank that settles down is removed and tank is completely cleaned.

We would like to know the process of neutralising the sludge of hard chrome plating.

Please help!

Mohsin Siddiqui
- Karachi, Pakistan
March 13, 2008

April 14, 2008

A. Dear Mohsin,
You can neutralize chromic acid solution with sodium bisulphate, then with sodium hydroxide.

Hani Dgaimat
Amman, Jordan

A. I think the previous poster meant sodium bisulfITE. Sodium bisulphate has no reducing power.

My own approach to this waste: add plenty of ferrous sulphate ferrous sulphate [affil links], dry. Mix very, very well. Take a sample, periodically, and spot test with acid/1,5 diphenylcarbohydrazide [affil links] reagent to make sure the chrome is all reduced. Then, add lime till the pH of a water suspension is between 10 and 12.

The result will be a fairly nontoxic, reasonably stable mud. Allow it to dry, and you can go ahead and landfill it in my backyard.

Dave Wichern
Consultant - The Bronx, New York
April 15, 2008

A. You can use sodium bisulphate at pH 2,5 - 3 then you adjust pH with NaOH to 7 -8.

Ali Gomaa
- Cairo, Egypt
May 10, 2008

What is the content of Chrome Plating Sludge

Q. What is in Chrome plating sludge? Are we correct this will be Chromic acid and then the rest Barium Sulphate from the breakdown of sulfuric acid after Barium additions?

Rebecca Belt
- Kent, UK
January 10, 2018

Hi Rebecca. I assume you are talking about the bottom sludges from a chrome plating tank which your company is operating? If so, and if you know that your shop adds barium to precipitate the sulphate, then it's probably a Sergeant's bath and your assumptions are probably correct.

If, however, you were trying to guess from the literature what might be in chrome plating bottom sludges in general, you should be aware of the possibility of fluoride being in the sludge; some self-regulating high speed plating baths rely on bottom sludges of sparingly soluble fluoride salts as the plating catalyst. Good luck.

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
March 2018

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