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topic 3213

Waste Cyanide Treatment by Hexavalent Chromium


For cyanide waste water treatment, waste chromic acid (or hexavalent chromium) could be used to oxidize the cyanide (this is an idea). Now the question is how complete this reaction will be. By other words, how much of cyanide will be left after reaction. Does any body have idea and like to share? Yong Liao

Yong Liao
aerospace metal finishing - Schomberg, Ontario, Canada


You may know something I don't know, and your question may suggest a good laboratory scale research project, but plating shops used to mix all their waste together and discharge it. And if the approach had worked the plating industry wouldn't be under the environmental pressure that it is.smiley

The first problem is that it is a terrible safety risk to mix an acid like chromic acid with cyanide. Such mixes release HCN and many people have died from inhaling it--some in plating shops, some in California's gas chambers.

The second problem I foresee, although it may not be as large an impediment as I think, is that cyanide oxidation and chromium reduction proceed very rapidly at the right pH and very slowly at the wrong pH, and the right pH for cyanide is in the area of 11, the right pH for chromium in the area of 3.

Finally, many reactions are driven very rapidly by excess of reagent, and the speed dwindles to near zero when there is no excess reagent. I can't see getting to completion on the cyanide without adding a lot of excess chromium, which would then have to be reduced.

Have fun and play safely under a lab hood but don't consider this approach in a production scenario unless armed to the teeth with successful experience.

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


I want to know Waste Cyanide Treatment of Hexavalent Chromium.

Kantapon Somsakul
- Nonthaburi, Thailand

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