Grantee Research Project Results
Final Report: Development of Zero Emission Hexavalent Chromium Plating Process
EPA Grant Number: R827201Title: Development of Zero Emission Hexavalent Chromium Plating Process
Investigators: Melarkode, Ramesh , Grieszmer, Dan , Govind, Rakesh
Institution: PRD Tech, Inc. , University of Cincinnati
EPA Project Officer: Hahn, Intaek
Project Period: April 26, 1999 through March 31, 2001 (Extended to March 31, 2002)
Project Amount: $50,000
RFA: Exploratory Research - Environmental Engineering (1998) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Sustainable and Healthy Communities , Land and Waste Management
Objective:
The specific objectives of this project were to: (1) evaluate the proposed zero air discharge process at a local commercial plating shop; (2) compare the air emissions and risk reduction with composite mesh pads and use chemical fume suppressants; (3) evaluate the proposed technology for plating typical parts obtained from commercial electroplating operations; and (4) develop a commercialization plan for implementing the technology.
Summary/Accomplishments (Outputs/Outcomes):
The purpose of this project was to design a new process that will prevent the release of chromic-acid mist into the workplace and ambient atmosphere; hence reducing the exposure risk to humans. Regulating bath temperature and mixing the plating solution are essential for successful electroplating. Reject rate of parts increases due to non-uniformity of temperature in the plating bath, and this increases waste generation. Traditionally, temperature control and mixing were achieved by bubbling air at the bottom of the plating bath using a sparger. When these air bubbles, together with the hydrogen and the oxygen evolved at the electrodes, break at the surface of the plating solution, they produce aerosols that are responsible for the chromium emissions. The proposed process uses a fluid layer, immiscible with the plating solution, at the top of the plating solution to control the emissions. Mixing and heat transfer are achieved by sparging this fluid at the bottom of the plating bath. Mathematical models were developed to predict the hexavalent chromium emissions in conventional plating baths, and the optimum thickness of the fluid layer for the proposed plating process.
The quality of finish using the proposed process was evaluated against the conventional plating process using two different criteria: scratch adhesion and pit counts. There was no difference in the critical load of the parts using either plating process during the scratch adhesion tests. The pit count tests that used pictures of the surface scan showed no signs of pit formation on the surface.
Additional tests were conducted outside of the grant funding through a no-cost extension of the project. The testing used parts obtained from commercial entities. The proposed process was compared to the conventional system in terms of chromium emissions to the environment. The quality of plating and hydrogen embrittlement issues were also reviewed during the additional testing. Visual inspection of the plated parts showed that the proposed process delivered a high quality of plating. Some imperfections were noted on the inside surface, which were later attributed to inadequate cleaning prior to plating. Further testing that would use a more systematic protocol of sampling, analysis, and test run procedures was recommended.
The National Risk Management Research Laboratory (NRMRL) of the U.S. Environmental Protection Agency, Cincinnati, OH, performed subsequent testing at a large commercial electroplating shop. This test was undertaken as part of NRMRL's mission to support the Agency effort towards the Common Sense Initiative. The main focus of this study was to determine the practicality of the technology at large shops, where plating is typically performed at 3,000-10,000 amperes (and hence greater emissions of chrome and electrolysis gases). The emission data indicated the PRD-EL1 liquid was successful in reducing the concentration of chromium emissions generated by about 94 percent to 98 percent for plating currents up to 5,000 amperes. However, part of the analysis was flawed, especially for emission data above 5,000 amperes when the data was compared with background emission data from other conventional electroplating tanks. These tanks operated in the vicinity of the test tank, in compliance with the Maximum Achievable Control Technology (MACT) standard. The background emissions from other tanks skewed the analysis of the test data.
The fact that the proposed technology is a source reduction and not a background air "treatment" method appeared to have been misunderstood during the analysis of data. The emission data clearly indicated the background air itself above the MACT standard for some of the test conditions. Therefore, the data was re-analyzed to characterize "true" emissions from the one tank retrofitted with PRD Tech's Zero Emission System. The re-analysis showed that when the background chrome concentration was below the MACT standard, emissions from the retrofitted test tank were suppressed by the blanket liquid ("source reduction") to levels much lower than the MACT standard. In other words, when the test tank was isolated from the influence of other conventional electroplating tanks in the vicinity, the emission data analysis yielded more meaningful results.
Journal Articles:
No journal articles submitted with this report: View all 2 publications for this projectSupplemental Keywords:
exposure, risk, innovative technology, zero emission technology, zero air discharge plating process., Sustainable Industry/Business, cleaner production/pollution prevention, hexavalent chromium, cleaner production, clean technology, zero discharge cycles, environmentally benign coatings, perfluormembranes, chromium plating, alternative coatingsRelevant Websites:
http://www.prdtechinc.com/ Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.