Recycling/Purification for Plating/Cleaning Baths

PACIFIC NW POLLUTION PREVENTION RESOURCE CENTER
POLLUTION PREVENTION RESEARCH PROJECTS DATABASE

Project Title: Recycling/Purification for Plating/Cleaning Baths

Date Last Updated: 11/96

Project Summary: Department of Defense electroplating shops use process solutions containing hazardous materials for plating, metal stripping, acid etching, alkaline cleaning, anodizing, and other metal finishing operations. The effective life of these solutions is limited by the increasing levels of contaminants that are dragged in from the parts being plated or cleaned. These contaminants reduce plating and cleaning efficiency and will eventually adversely affect the quality of the metal finishing operation. As a result of this contamination, the "spent" bath must be periodically dumped and it consists of large volumes of concentrated hazardous wastes. The goal of this effort is to develop innovative techniques for prolonging process bath life and for recycling hazardous materials from spent process baths to reduce the generation of hazardous wastes.

In 1990, the Navy's spent process baths in decreasing order included sodium hydroxide, chromic acid/sodium dichromate, hydrochloric acid, cyanide, sulfuric acid, nitric acid, electroless nickel and nickel sulfamate. While ongoing efforts to develop new technologies for eliminating chromium and cadmium (cyanide) plating operations will reduce the use of these particular process baths, many of the alternative processes will require purification (i.e. replacement of chromic acid anodizing with sulfuric-boric acid anodizing, replacement of cadmium plating with zinc-nickel plating, use of electroless nickel coatings in place of hard chromium plating). Development of alternative application techniques such as spray casting which eliminate the use of chemical process solutions are in the developmental stages and not currently available. Cleaning and stripping operations will continue to be used. In addition, many new aqueous cleaning solutions are being used to eliminate solvent cleaning with CFCs. These cleaning solutions will require purification to maximize the solution life.

This effort will address a variety of process solutions and removal of different contaminants that buildup. Separation technologies such as ultrafiltration, ion exchange, electrolysis, membrane electrolysis, electrodialysis, and diffusion dialysis will be investigated for use in removing contaminants from plating/metal cleaning process baths. The process baths requiring purificaiton will be prioritized based on Department of Defense volumes of solution waste generated, disposal costs, toxicity, and continued use. The impact of ongoing efforts to eliminate chromium and cadmium plating also will be considered. Several technologies will be developed for specific applications as required. Test and evaluation of purification technologes with applicability to a variety of process baths will be given the most emphasis. Purification of alternative plating solutions will be considered in the test program.

Field testing of selected technologies will be performed to determine the effectiveness and to optimize design and operational parameters for each purification system developed for specific process baths. Appropriate planning, design, operation, and maintenance criteria will be developed for technology transfer of each system and will be coordinated with the American Electroplating and Surface Finishing society for transfer to private industry.

Based on the survey of DoD plating shops, and a technology assessment, the four process solutions types most commonly discarded due to contaminant buildup and the most feasible associated bath purification technologies are: 1) mineral acid etches - resin adsorption, diffusion dialysis, and electrodialysis; 2) alkaline cleaning solutions - crossflow ultrafiltration; 3) electroless nickel (EN) plating baths - electrodialysis, and chemical precipitation; and 4) chromic acid solutions - electrodialysis. Laboratory scale feasibility studies with a crossflow filtration process for removal of oil and grease from alkaline cleaners, and the use of electrodialysis to rejuvenate spent EN plating baths have been completed, and have transitioned to field demonstration projects. Field demonstration of a crossflow filtration system is ongoing. System installation, startup, and 140 hours of operation during first test run completed. Three additional test runs are planned. Startup of field projects with an electrodialytic process for EN rejuvenation project utilizing electrodialysis is pending results of a site selection study. Laboratory scale feasibility studies are underway with resin adsorption, and diffusion dialysis for purification of mineral acid solutions. Field demonstration of a preferred technology will commence pending results of the feasibility studies. Processes based on electrochemical reactions were considered most feasible for purification of chromic acid solutions based on their capability to both remove dissolved metal contaminants and oxidize trivalent chrome back to its desired hexavalent state. Field test projects with four alternative configurations were planned. To date, two have been completed, and the remaining two test efforts are underway.

Project Keywords: metal finishing, electroplating, metals removal, membrane separations, purification

Organizing Performing Research: Naval Facilities Engineering Service Center, Air Force Wright Laboratory, Manufacturing Technology Division, EPA Risk Reduction Engineering Laboratory

Primary research Contact:
Mr. Nick Stencel, Code 421
Naval Facilities Engineering Service Center
560 Center Drive
Port Hueneme, CA 93043-5003
PHONE: (805) 982-1674
FAX: (805) 982-1409
E-MAIL: NSTENCE@NCEL.NAVY.mil

Date research Started/Completed: 1/94 - 12/96

Publications Based on Research: none available

Approximate Project Budget: $2,200,000

Primary Project Funder: Strategic Environmental Research & Development Project (SERDP)

Funder Contact:
Dr. Robert Holst
Program Manager for Compliance and Pollution Prevention
SERDP Program Office
901 North Stuart Street, Suite 303
Arlington, VA 22203
phone: (703) 696-2125
fax: (703) 696-2114
e-mail: holstrw@acq.osd.mil