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

by Larry Zitko, ChromeTech, Inc.
July, 2002

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.



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