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SOURCES OF
SELENIUM AND TELLURIUM
Se and Te are rare elements almost never found in the
native state. Tellurium was discovered in 1782 by an
Austrian chemist, Von Reichenstein, while examining gold
ore from Transylvania. Selenium was discovered in 1817 by
a Swedish chemistry professor, Berzelius. They are widely
dispersed in the earth's crust at average levels less
abundant than silver. They rank 69th and 75th,
respectively, in order of abundance. There are no ores
from which Se can be mined as a primary product. It is
found principally in sulfide minerals of copper iron, and
lead and is most common in chalcopyrite, bornite and
pyrite. It occurs most abundantly in the North American
porphyry copper deposits of the western U.S., and in the
copper-nickel and copper-zinc ores of central and eastern
Canada. Se values also occur in copper ores in Africa,
Asia, Europe, South America, Oceania and Australia.
Occasionally it is found in conjunction with native sulfur
and in the form of selenites of other metals. Te rarely
occurs in the native state, usually being associated with
gold, silver, copper, lead, mercury and bismuth ores. One
of the most common tellurium minerals is sylvanite, a
complex gold-silver telluride. Extraction of Se and Te
from ore is a complex process involving numerous hydro-
and pyro-metallurgical treatments. Flotation concentrates
are smelted to remove sulfur, iron and other impurities.
Treatment of 200 tons of copper ore typically yields one
pound of Se. Treatment of 500 tons of copper ore typically
yields one pound of Te. Se and Te are undesirable
impurities in copper. Separation takes place in the
electrolytic copper refinery where impure Cu anodes are
dissolved by electrolysis and redeposited as high purity
copper cathodes. The impurities dissolve in the
electrolyte or settle as slimes to the bottom of the
cells. Present in the slimes as selenides and tellurides
of copper, gold, and silver, Se and Te are separated by
various processes, and are further refined into commercial
product forms and compounds. Both Se and Te are ecomically
recoverable from industrial scrap and chemical process
residues. For example, worn out and damaged photoreceptor
drums are returned to manufacturers for recycling, where
the Se-Te alloy is stripped off and shipped to refineries
for separation and purification. An estimated 15% of
refined selenium production comes from secondary sources.
APPLICATIONS FOR
SELENIUM
The first commercial application for Se was found during
World War 1, as a substitute for critically short
manganese, a decolorizer in glass making. A wide variety
of industrial applications have since been developed.
Average annual usage is currently estimated at 1850 metric
tons.
Electrical: 30%
of demand. High purity selenium and selenium alloys are
used in photoreceptors for
plain paper copiers and laser printers; rectifiers and
voltage surge protection devices; CO 2 laser windows,
infrared detectors, photovoltaic cells, x-ray receptors
for medical imaging.
Pigments:10% of
demand, Cd sulfoselenide compounds are highly stable
pigments used in plastics, ceramics, glazes and paints,
for products which during manufacturing or use are
subjected to moisture, high temperature, ultraviolet or
chemical exposure. Se in pigments can produce a wide
variety of colors as diverse as red, orange and maroon.
Glass: 35% of
demand. Selenium decolorizes the green tint caused by iron
impurities in glass bottles; produces the ruby red color
in art glass; reduces solar heat transmission through
architectural glass.
Metallurgy: 10%
of demand. Selenium addition improves mach inability of
carbon steel, stainless steel, copper, and acts as a grain
refiner in the grids of low-maintenance lead-acid
batteries.
Agricultural/Biological:
5% of total demand. An essential element to life, Se is
added in trace amounts to animal feeds, veterinary
preparations, and boluses to prevent certain diseases in
animals and increase growth. Soil deficiencies are
corrected by adding selenium to chemical fertilizers. In
medicine, Se compounds act as a fungicide to control
dandruff and dermatitis, and as a human diet supplement
for control of certain diseases.
Other Applications:
10% of total demand. Used as a component in catalysts for
selective oxidation; in plating solutions to improve
appearance, antiquing effects, and durability; blasting
caps; gun bluing; to increase yields in electrolytic
manganese production, etc.
FORMS &
COMPOUNDS COMMERCIALLY AVAILABLE
Selenium
Metal, Alloys & Compounds
Selenium metal,
commercial grade (99.5% min. Se)
Selenium metal, high purity (99.999% Se) Selenium-Antimony
Alloys, Selenium-Arsenic Alloys
Selenium-Tellurium Alloys, Selenium Dioxide, Selenious
Acid, Barium Selenate, Barium Selenite
Bismuth Selenide, Calcium Selenite, Copper Selenide, Ferro
Selenium, Potassium Selenate
Sodium Biselenate, Sodium Selenate, Sodium Selenite, Zinc
Selenide, Zinc Selenite
Tellurium Metal, Alloys & Compounds
Tellurium
metal, commercial grade (99.5% min. Te)
Tellurium metal, high purity (99.99%-99.9999% Te)
Tellurium-Manganese Alloys, Bismuth-Tellurium Alloys
Copper-Tellurium Alloys, Ferro Tellurium
Tellurium Dioxide, Telluric Acid
This list does not presume to be complete. Other
compounds may be available from time to time and
inquiries concerning non-listed compounds or prod-ucts
may be made to the STDA Information Office.
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