Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)
by Larry Zitko, ChromeTech, Inc.
Chromium Emissions From Electroplating
Q. Can you tell me if chromium is released into the air from metal plating
operations? This question has come up because an environmental consultant
has proposed sampling the homes adjacent to a small plating shop for
chromium-containing dust. However, there is no dust on the site because it
is all paved. Is there another way, besides via dust, for chromium to be
released into the neighborhood air?
A. Yes, chromium mist can be released to the atmosphere from the surface of
hard (industrial or functional) chromium electroplating, bright (decorative)
chromium electroplating and some related processes, such as chromium
stripping operations. These are electrolytic processes which generate
significant amounts of hydrogen and oxygen gasses. As the gasses rise and
break free of the liquid, some of the process solution escapes to the
atmosphere above the surface of the liquid. The escaping process solution is
in the form of a mist with small droplets of varying size.
Typically, hard chromium plating tanks are fitted with exhaust ventilation
and air pollution control systems to capture the process fumes at the source
tank, then remove as much as possible of the entrained chromium from the
exhaust air stream before it is discharged to atmosphere at the stack tip.
Capture efficiency (by the exhaust hood) can be as high as 100%, and removal
efficiency by the scrubber can be 99.9% or higher.
Metal finishers can also use chemical fume suppressants to effectively
reduce the amount of chromium mist that exits the process tanks. These
suppressants usually alter the surface tension of the bath, or create a foam
blanket on the liquid surface.
On January 25, 1995, U.S. EPA published the Final Rule for its "National
Emission Standards for Hard and Decorative Chromium Electroplating and
Chromium Anodizing Tanks" (40 CFR Parts 9 and 63). Prior to the standards,
EPA considered chromium electroplating and anodizing tanks to be the largest
sources of chromium emissions in the United States, and predicted a
reduction of about 173 tons annually as a result of the new federal
standards. The standards include emission limits, an initial performance
(stack) test, work practice standards, ongoing compliance monitoring and
various recordkeeping and reporting requirements.
It is important to understand that prior to the chromium NESHAP, chromium
emissions from electroplating sources were regulated on a state, county or
municipal basis, with varying requirements and effectiveness. Also, older
generation scrubbers did not generally have the high removal efficiencies
found with modern control devices. Chromium discharged from the plumes of
these exhaust stacks typically settled back to earth at concentrations that
varied with distance, atmospheric conditions, etc.
Hexavalent chromium can also be released to the environment by means other
than air emissions. For example, leaks, spills or dumping can contaminate
soil or groundwater. Your inquiry mentioned "dust". It is possible to
generate significant amounts of metallic chromium if parts are polished
after plating using a dry belt. For example, hydraulic repair shops
sometimes polish rods or cylinders after plating to achieve the desired
appearance, profile or dimensional tolerances. If the exhaust and filter
system for the polisher is ineffective, a lot of metallic chromium will
accumulate in the workplace or may blow out an exhaust stack if present.