Metals subcategory

Each metal subcategory uses different processes and emits different pollutant concentrations and types in the process wastewater. The following paragraphs and tables present information on the wastewater streams for each of the subcategories.2-3... 

Pollutant parameters found in the common metals subcategory raw waste stream from sampled plants are shown in Table 9.4. The major constituents shown are parameters, which originate in process solutions (such as from plating or galvanizing) and enter wastewaters by drag-out to rinses. These metals appear in waste streams in widely varying concentrations. 

Concentrations of Pollutants Found in the Common Metals Subcategory of Raw Wastewater... 

Table 9.5 shows the concentrations of pollutant parameters found in the precious metals subcategory raw waste streams. The major constituents are silver and gold, which are much more commonly used in metal finishing industry operations than palladium and rhodium. Because of their high cost, precious metals are of special interest to metal finishers. 

The concentrations of metals found in complexed metals subcategory raw waste streams are presented in Table 9.6. Complexed metals may occur in a number of unit operations but come primarily from electroless and immersion plating. The most commonly used metals in these operations are copper, nickel, and tin. Wastewaters containing complexing agents must be segregated and treated independently of other wastes in order to prevent further complexing of free metals in the other streams. 

The treatment methods used to treat wastes within the common metals subcategory fall into two groupings ... 

Mixed-Metal Oxide Pig ments. Mixed-metal oxide pigments can be considered a subcategory of complex inorganic color pigments. The name, mixed-metal oxides, does not, however, represent the reaUty as these pigments are not mixtures but rather soHd solutions or compounds consisting... 

There are an estimated 800 plants in the U.S. involved in the primary or secondary recovery of nonferrous metals. These plants represent 61 subcategories. However, many of these subcategories are small, represented by only one or two plants, or do not discharge any wastewater. This chapter focuses on 296 facilities that produce the major nonferrous metals [aluminum, columbium (niobium), tantalum, copper, lead, silver, tungsten, and zinc]. The volume of wastewater discharged in this industry varies from 0 to 540 m3/T (0 to 160,000 gal/t) of metal produced.13 The global size of the industry is reflected in Table 3.1 (reported in 1000 USD) for the top 20 export countries for nonferrous base metal waste and scrap.4 Here T = metric ton = 1000 kg = 2204.6 lb, t = 2000 lb. 

Table 3.2 presents an industry summary for the nonferrous metals industry indicating the number of subcategories and the number and type of dischargers. Table 3.3 presents best practicable technology (BPT) limitations that have been promulgated and reported in the Federal Register.3-5... 

The nonferrous metals industry is divided into 61 subcategories by the type and source of the metal to be smelted and/or refined and by similar wastewater sources. Twenty-six of these subcategories... 

Many toxic pollutants were detected in the process wastewaters from metal molding and casting processes. The toxic pollutants detected most frequently in concentrations at or above 0.1 mg/L were phenolic compounds and heavy metals. The pollutants include 2,4,6-trichlorophenol, 2,4-dimethyl-phenol, phenol, 2-ethylhexyl, cadmium, chromium, copper, lead, nickel, and zinc. Each type of operation in the foundry industry can produce different types of pollutants in the wastewater stream. Also, because each subcategory operation often involves different processes, pollutant concentrations per casting metals may vary. 

Drawing is the process of pulling metal through a die or succession of dies to reduce the metal s diameter or alter its shape. There are two aluminum forming subcategories based... 

Porcelain enameling on copper represents a very small part of the porcelain enameling category. It is not practiced by many firms and the ones involved do it on a small scale. Enameled copper is used mostly for ornamental purposes, such as jewelry, decorative ware, and metal sculpture. The average yearly production of a plant in this subcategory is 1.4 x 104 m2 (1.5 x 104 ft2). 

In addition to the above subcategories, porcelain enameling on continuous strip is a subdivision within this industry. However, because there are only two plants in the U.S. producing this product, a separate subcategory is not necessary. These plants start with coils of steel, aluminum, or aluminized steel, porcelain enamel them and either recoil them for sale to metal fabricators or shear them into pieces for use as architectural panels or chalkboards. The estimated production was 2.0 x 106 m2 (22 x 106 ft2). This figure represents the area of enamel applied. For multiple coats, the area for each coat is considered. 

There shall be no discharge of process wastewater pollutants from any metal preparation operations in the cast iron basis material subcategory. The discharge of process wastewater pollutants... 

Table 9.1 presents an industry summary for the metal finishing industry including the total number of subcategories, number of subcategories studied, and the type and number of dischargers. 

Table 9.2 lists the unit operations associated with each of the seven industry subcategories (raw waste characteristics). Common metals are found in the raw waste of all 44 unit operations. Precious metals are found in only seven unit operations complexed metals are found in three unit operations hexavalent chromium is found in seven unit operations and cyanide is found in eight unit operations. Within the organics, oils are found in 22 unit operations and solvents are found in nine unit operations. A unit operation will often be found in more than one subcategory. 

Pollutant parameters and their concentrations found in the oily waste subcategory streams are shown in Table 9.9. The oily waste subcategory for the metal finishing industry is characterized by both concentrated and dilute oily waste streams that consist of a mixture of free oils, emulsified oils, greases, and other assorted organics. Applicable treatment of oily waste streams is dependent on the concentration levels of the wastes, but oily wastes normally receive specific treatment for oil removal prior to solids removal waste treatment. 

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