Info

* Reference I

11 Total Cyanide c Complexed Cyanide " Chromium as Cr (VI)

* free Cyanide Chromium as Cr (III)

metal coating through electrode deposition. Metal coatings provide protection against corrosion, increase erosion resistance, or can be used for decoration. Facilities in this industry segment are located throughout the United States and vary in size and plating capacity. Captive shops, which plate products made in the shop, make up 75 percent of the metal-plating industry; the remaining 25 percent are independent shops."1

The major metal-bearing waste categories generated in the metal coatings industry segment are rinse waters, bath drag-outs, residues from work pieces, and spent plating baths. This Industry generated 5244 Bg (5768 megatons) of spent plating baths (F007) alone in 1985. Most of the spent plating baths are treated by generators in their own wastewater treatment or pretreatment systems, which contributes significantly to the generation of sludge (F006). Wastewater treatment sludges (FQ06) represent the largest volume of hazardous waste generated in this industry. Two other hazardous waste categories (F007 and F0D8) are generated as wastewaters and listed for cyanide. Predominant metals found in the sludges are nickel, copper, zinc, chromium, lead, cadmium, and silver. Table 6 presents metal concentration ranges for the different metal-coating operations. The sludge metal concentrations will vary with the different processing sequences. Normally, the metallic elements in sludges occur as hydroxides, and chromium is usually found in the trivalent form. Approximately 20 percent of the facilities treat their wastes on-site by use of recovery techniques utilizing evaporation, ion exchange, and reverse osmosis (See Table 7); 80 percent practice offsite disposal mainly through landfills, stockpiles, or surface impoundments . Table 8 presents estimated losses of metals in wastes from the electroplating industry. The present-day value of metals in these wastes is estimated to be $61 million.

TABLE 6. HETAL CONCENTRATION RANGES FOR WASTE STREAMS GENERATED IN THE HETAL-COATINGS INDUSTRY* 0*9/1 Iter)

Metal

Common metals plating

Precious metals plating

Electroless

Anodizing

Coating

Milling and etching

Cadmium

7-21,600

NAb

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