logo Pollution Prevention in Metal Finishing: Plating
A Northwest Industry Roundtable Report

Appendix C: Primary Chemicals Used in Metal Plating Processes and Waste Quantities

Primary Chemicals
Metal plating shops use a number of chemicals in their operations, and some facilities may use several hundred different chemicals. The following includes an overview of some of the more common types of chemicals used that are of environmental concern. Basic information about the chemicals, their use in the industry, and the reasons they are of concern to public health and the environment are provided. Health and environmental effect information was obtained in part from the EPA report The Product Side of Pollution Prevention: Evaluating the Potential for Safe Substitutes, and from the Hazardous Substances Databank (HSDB). The HSDB is a data file of more than 4,300 chemicals from the TOXNET system of the National Library of Medicine.

Acids and bases are used in the metal plating industry in oxiding, plating, and stripping baths and in the waste treatment process. Acids and bases are used to adjust the pH of a solution into operational limits or to provide oxidizing power to "clean" a surface. Acids used in the industry include sulfuric, nitric, phosphoric, boric, and hydroflouric. One of the main bases used is sodium hydroxide. Exposure pathways for these chemicals are inhalation, absorption, or ingestion. Their high corrosivity make them extreme hazards, with exposure leading to chemical burns and, in severe cases, death. Some acids, such as nitric acid, have chronic exposure risks, and are linked to anemia, leukopenia, and esteoscherosis.

Cyanide Compounds
Cyanide compounds are used in plating baths because they accomodate a wide range of electrical current, remove tarnish or other undesirable films from surfaces to be plated, and cause an even metal deposit to form that has lower sensitivity to impurities present in the the bath. Metals coatings of cadmium, iron, gold, and zinc often use cyanide compounds. Cyanide is typically found complexed with plating metals, or as sodium cyanide or potassium cyanide, which is added to the bath. Cyanide exposure pathways include inhalation, ingestion, or absorption through skin or mucous membranes. Most cyanides are acutely poisonous. Overexposure interferes with the operation of the metabolic system and can cause rapid death. Cyanide is not bioaccumulated or stored in humans or animals.

Metal Compounds
Metals are coated onto parts in metal plating shops to increase wear resistance, corrosion resistance, or for enhanced appearance. Metals are supplied to plating baths either in their metallic form or complexed with another compound, such as cyanides, oxides, sufides, or chlorides. Some primary metals used that are of significant environmental or health concern and their applications include:

Other metals that are fairly common in the industry include copper, zinc, and precious metals such as silver and gold.

The primary function of solvents in the metal plating industry is for the cleaning of parts. Traditional industry solvents such as trichloroethylene (TCE) and 1,1,1 trichloroethane (TCA) have the advantage of rapidly disolving oils and greases on parts, and of rapidly evaporating thereby minimizing drying time. TCA is in the process of being phased out of production as an ozone-depleting substance. TCA is not considered a human carcinogen by EPA and is a mild eye and skin irritant. TCE is classified by EPA as a possible to probably human carcinogen and is an irritant to the eyes, nose, and throat. Exposure to either chemical in acute concentrations can be lethal.

Waste Quantities
Waste streams from metal plating shops include air, water, hazardous, and solid waste. To provide a general idea of some of the more significant chemicals that are released by metal platers, toxics release inventory data from 1993 is presented in the tables on the following page. In the Northwest, 14 companies met the criteria to be Toxic Release Inventory reporters in the SIC code 3471, which is the code for electroplating shops. The data is in no way representative of the entire industry in the Northwest, since only a small fraction of the shops are represented, but it does provide a benchmark of the releases of the larger waste generators in the industry as a group.

The pounds of releases of the five most-released chemicals from the 14 companies are shown in Table 1. The total pounds of releases of all chemicals for the 14 companies are shown in Table 2. It is interesting to note that two of the most-released chemicals, methyl ethyl ketone and toluene, are not used in metal plating but in the coating (painting) part of the metal finishing process. This indicates that many metal finishing facilities include both metal plating and metal coating.


Table 1. Region 10 Toxics Release Inventory Releases for SIC 3471 in Pounds: Top Five Most-Common Chemicals Used*
Chemical AIR (stack) AIR (fugititve) POTW OFF-SITE
111 Trichlorethane -- 29,707 5 19,646
Methyl Ethyl Ketone 29,235 67,758 15 54,627
Strong Acids 3,530 9,788 255 16,600
Toluene 20,300 1,276 5 4,522
Trichloroethylene -- 75,246 -- 9,086
TOTAL 53,070 183,775 280 104,481


Table 2. Region 10 Toxics Release Inventory Releases for SIC 3471 in Pounds: Total Pounds of all Chemicals Used*
Chemical AIR (stack) AIR (fugititve) POTW OFF-SITE
TOTAL 64,011 191,135 1,140 104,900

* Table includes 14 reporters in Oregon and Washington, and excludes aerospace SIC.


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This report was developed with grant funding from the U.S. Environmental Protection Agency, and was a joint project of the Business Assistance Programs in Alaska, Idaho, Oregon and Washington.

© 1999, Pacific Northwest Pollution Prevention Resource Center
phone: 206-352-2050, e-mail: office@pprc.org, web: www.pprc.org