Silver

There are four primary silver production facilities in the U.S. Of these, two discharge wastewaters. Wastes containing silver include materials from photography, the arts, electrical components, industry, and miscellaneous sources. These wastes are processed by a wide variety of techniques to recover the silver.2 Because the process is highly specific for the type of waste, no attempt to discuss the various processes will be made in this chapter.

3.2.7 Tungsten

There are several variations in the processes of this industry depending on the ore. In each process, one of the intermediate products is tungstic acid. The tungstic acid is converted to ammonium tungstate, which is dried and heated to form ammonium paratungstate. This intermediate is converted to oxides in a nitrogen-hydrogen atmosphere. Finally, the oxides are reduced to tungsten metal powder at high temperature in a hydrogen atmosphere.2

3.2.8 Beryllium

Primary beryllium production occurs at two plants within the U.S. One of these plants discharges its wastewater to the environment. Because of the limited number of facilities, beryllium production will not be discussed in this chapter.

3.2.9 Selenium

Primary selenium recovery occurs at a single site that does not discharge to the environment. Consequently, this subcategory is not discussed further in this chapter.

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