Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)
by Larry Zitko, ChromeTech, Inc.
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