Environmental Engineering Reference
In-Depth Information
emissions due to natural sources have ranged from as low as 10% to as high
as 50% [26]. Some of these natural emission sources include weathering and
erosion of parent rocks, volcanic activity, and forest i res. Anthropogenic
sources of cadmium releases include products and materials to which cad-
mium has deliberately been added to impart a specii c chemical, mechani-
cal or physical property and products or materials in which cadmium is
naturally present as a residual or impurity element. Because of its unique
chemical, mechanical and physical properties, cadmium is utilized delib-
erately in a number of important industrial and consumer applications.
h ese include nickel-cadmium (NiCd) batteries for both industrial and
consumer uses; cadmium corrosion-resistant coatings on iron, steel, alu-
minum and titanium; cadmium pigments in plastics, glasses, ceramics,
enamels and artists' colors; weathering and ultraviolet light stabilizers
for polyvinyl chloride (PVC); as an alloying element in soldering, braz-
ing, electrical contact, high electrical conductivity and high thermal con-
ductivity alloys; and in electronic compounds such as cadmium telluride
and cadmium suli de employed in solar cells, detectors, electronic gates,
switches, sensors and relays.
Chromium is a naturally-occurring element found in rocks, animals,
plants, and soil, where it exists in combination with other elements to form
various compounds. h e three main forms of chromium are Cr(0), Cr(III),
and Cr(VI). Small amounts of Cr(III) are needed for human metabolism.
Chromium is released into the environment from natural and anthropo-
genic sources, with the largest release occurring from industrial releases.
Chromium is widely used in manufacturing processes to make various
metal alloys such as stainless steel. Chromium can be found in air, soil,
and water at er release from industries that use chromium, such as indus-
tries involved in electroplating, leather tanning, textile production, and the
manufacture of chromium-based products [27]. Chromium can also be
released into the environment from the burning of natural gas, oil, or coal.
Lead is a heavy, low melting, bluish-gray metal that occurs naturally
in the Earth's crust. However, lead rarely occurs in its elemental state, but
rather in its +2 oxidation state in various ores throughout the earth. h e
most important lead-containing ores are galena (PbS), anglesite (PbSO
4
)
and cerussite (PbCO
3
). It is usually found combined with two or more
other elements to form lead compounds. Lead and lead alloys are com-
monly found in pipes, storage batteries, weights, shot and ammunition,
cable covers, and sheets used to shield from radiation. h e largest use for
lead is in storage batteries in cars and other vehicles [28]. Lead compounds
are used as a pigment in paints, dyes, and ceramic glazes. Tetraethyl lead
may still be used in gasoline for of -road vehicles and airplanes. It is also
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