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Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)

by Larry Zitko, ChromeTech, Inc.
November, 2002

Chromium Emissions From Chromium Stripping

Q. Is emission of chromium possible from chromium stripping? The chromium stripping process uses sodium hydroxide and current.

A. When an alkaline electrostrip bath like yours is new, there will be an alkaline mist released from the surface of the liquid during the stripping process. This alkaline mist poses a health risk of its own, and should be captured by a good exhaust air system which contains an effective air pollution control device.

As the alkaline electrostrip bath ages, the metallic chromium that has been stripped from parts builds up in the solution in the form of soluble chromium compounds. For example, most chemists I have talked to suggest that (hexavalent) sodium chromate compounds are formed. It has been my experience that most facilities use the strip bath for as long as possible before replacing the bath, which has the effect of increasing the chromium concentration in the bath to high levels. As the chromium concentration in the bath increases, the chromium component of the mist that is released to air (above the surface of the liquid) during electrostripping will also increase. Now the mist has both alkaline and chromium components.

To summarize, chromium air emissions are expected from an alkaline electrostrip tank. The uncontrolled air emission, from the surface of the tank, increases as the dissolved chromium in the bath increases over time (from stripping parts). It is important to exhaust all process fumes to protect the health of persons inside the plating room environment, and to include an effective air pollution control device to extract entrained chromium from the exhaust air stream before discharging the air from the exhaust stack.



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