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Electroplating Cr / Sludge evaporation / Cr emissions?

April 29, 2008

I'm giving a close look to our process of electroplating, and essentially to our disposal of sludge and acid rinse.
We're currently thinking on using an evaporator, but somehow it makes me feel uncomfortable (meaning, I don't know) about whether or not we will be having Cr emissions (just like the ones we prevent from the tanks using fume suppressants). Initial investigation provided positive results, in the sense that the process is widely used and no emissions are identified.

Do any of you evaporate your wastes? What restrictions apply? Where can I find reliable information on what emissions to expect?

Anthony Caulker
Engineer - Edmonton, AB, Canada

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May 5, 2008

Anthony

In a past life, I used an atmospheric evaporator to minimize and recycle rinse water from a traditional chemical film process (hex chrome)in California. They too were concerned about what we put into the air. The manufacturer had run tests on their products and the amount of hex chrome emitted was minimal with a ambient system.

Check with manufacturer(s) to see if they have available data to share.

Willie Alexander
- Colorado Springs, Colorado

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June 7, 2008

I not really sure how viable it is to evaporate the waste. evaporators make more sense to concentrate say rinse water so that it can be reused in the plating bath.
also I don't think there will be any Cr in the evaporate. But you should test it and make sure because chromium poses some pretty serious health hazards.
you might want to consider sulfide precipitation to get rid of chromium.

Ravi Patel
- Anand, Gujarat, India

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June 11, 2008

Whether the hex chrome will pass to the atmosphere depends a lot on whether the waste is boiling, or is evolving gas. Under those conditions, a mist will be thrown up that will contain hexchrome. If the evaporation is taking place from the surface of a tank, or a falling film, the hex should not volatilize.

I must respectfully disagree with Mr. Patel. To the best of my knowledge, Cr, either in tri or hexavalent form, is one of the few metals that will not be precipitated by sulfides. If a low limit for discharge must be met, the best way to accomplish this is to reduce with metabisulfite, polish with ferrous sulfate ⇦this on eBay or Amazon [affil links] , raise the pH to 9 - 10 with sodium hydroxide and a dab of lime, then drop solids with a suitable flocculant.

Dave Wichern
Consultant - The Bronx, New York