II. R&D NEEDS AND POTENTIAL PROJECTS

C. Hexavalent Chromium

1. Background

Chromium, both hexavalent and trivalent forms, is an industrial material that has been used throughout the metal finishing industry for many years. The hexavalent form has been particularly useful in hard and decorative chromium plating, anodizing aluminum, and producing conversion coating on light metals. There are no viable alternatives for many parts using one or more of these coatings.

There are many other metal processing solutions containing hexavalent chromium. It is commonly used for etching metals prior to bonding, for passivating steel to prevent corrosion, and for stripping of some organic materials from metal surfaces. Additionally, hexavalent chromium is produced in solutions when chromium is stripped from steel using anodic treatment in alkali solutions.

Chromium, especially hexavalent chromium, has come under increasing regulatory scrutiny because of its listing as a human carcinogen with an inhalation exposure pathway. There has not been sufficient documentation of the risk factors associated with the chemicals used in the metal finishing industry for that industry to feel the increased regulatory scrutiny is warranted.

2. Federal Survey

By far, hexavalent chromium has received the most attention and resources. Many projects have recently been and are being supported by the Federal sector. The Federal survey identified contributors from DOD, DOE, and EPA. In addition, the Pacific Northwest database showed that a few State programs are funding chromium pollution prevention research, at a total level of $200K for the States. In all, these two sources showed $21.9M in funding from State and Federal sources directed at this area.

Most of the resources have been used to develop and demonstrate alternatives such as nickel alloys for hard chromium, silane and polymer-based chemistries for chromate conversion coatings, and dry deposition processes for both hard chrome and conversion coatings. In general EPA supports work in chromium alternatives at universities and nonprofit research institutes; DOD supports work at its own facilities using in-house staff and consultants and in the private sector; DOE funds work at its national labs and in the private sector; and the State efforts have been conducted by the private sector. AESF is supporting a university project in Zn/Ni/SiO2 as a chromate conversion coating alternative.

Within the studies identified by these two sources, EPA and AESF are the only groups supporting work to improve efficiency and recover chromium from existing chromium operations; the support level by EPA for these projects has been about $150K over the last several years.

3. Projects

There are several R&D priorities associated with the use of hexavalent chromium processing solutions:

a. Develop simplified risk assessment methodologies to determine the risks associated with the use of chromium in surface finishing processes, as indicated below.


i. Assess the risks to workers in different job classifications from exposures due to working in various plating processes that use hexavalent chromium.


ii. Assess the risks before and consequent to application of technologies to meet the new CAAA chromium emissions MACT standard.


b. Develop a life cycle analysis model to determine when, and when not, to change from processes that use hexavalent chromium.


c. Develop innovative closed-loop processes for chromium processing solutions.

i. Evaluate methods to control discharges to air and water and to recycle chemicals back into the processing tanks in existing shops.


ii. Evaluate methods to control discharges to air and water and to recycle chemicals back into the processing tanks in new installations--concentrating on the best installations extant.


iii. Demonstrate the electrodialytic membrane based "I3" technology for chromium recovery.


d. Develop reduced chromium processes.


i. Modified trivalent chrome conversion coatings.


ii. Modified low chromate conversion coatings.


iii. No-rinse chromate conversion coatings.


iv. Modified (low chromium) anodizing baths and etching solutions.


v. Trivalent hard chromium electroplating baths.


vi. Trivalent chromium brush plating solutions.


vii. Non-chromate corrosion inhibitors.


e. Develop alternative materials and processes. Any work in this area must consider the new waste products (quantities and dangers). Many alternatives create more by-products than the original processes (e.g., hard chrome alternatives). When comparing existing chromium processes to non-chromium processes, state-of-the-art chromium processes should be used, not the 1940's versions.


i. Alternatives for chromium plating processes.


ii. Alternatives for chromic acid anodizing.


iii. Chromium-free conversion coatings for steels, aluminum, and zinc.


iv. Stripping of chromium coatings without generating hexavalent chromium.


v. Chromium-free corrosion inhibitors.