48
Tellurium [Te, 52]
48.1 INTRODUCTION
Tellurium (Te), a silvery-white metalloid of group 16 in the periodic table of elements,
is one of the rarest stable elements in the Earth’s crust, where its mean abundance
is about 1 μg/kg. Its contents in sedimentary rocks, up to 5 μg/kg, are higher than
in magmatic rocks. Due to the ability to be fixed by organic matter (OM), its concentration in coal is high, as well as in fly ash, within the range of 20–2000 μg/kg.
Concentrations of Te in volcanic gases and volcanic deposits are also elevated.
The oxidation states of Te are –2, +2, +4, and +6, with the +4 state being most
common.
There is a great similarity between Se and Te, and thus minerals and compounds
are also similar. The most common Te minerals are tellurite (TeO 2 ), hessite, (Ag 2 Te),
calaverite (AuTe 2 ), sylvanite [(Ag,Au)Te 4 ], and emmonsite [Fe 2 (TeO 3 ) 2 ·2H 2 O].
Today, most Te is obtained as a by-product of mining and refining Cu. Tellurium
minerals are also associated with Fe, Ag, and Au deposits. Production of Te in 2010,
in various countries, was as follows: Canada—20 t, Japan—40 t, Peru—30 t, and
Russia—35 t (USGS 2011). Tellurium is primarily used as an alloying agent, mainly
to make alloys easier to machine and mill, and also to increase their strength and
resistance to sulfuric acid. It is also used as a semiconductor in various electronic
devices and is used in rubber production to increase resistant to heat and abrasion.
Tellurium is applied as a pigment to produce various colors in glass and ceramics.
It is also used in optical glasses, as well as in photographic and pharmaceutical
industries.
48.2 SOILS
The worldwide mean Te levels in soils are given as 0.006 mg/kg (Reimann and de
Caritat 1998) and 0.03 mg/kg (FOREGS 2005). The average Te level in soils of the
United States is estimated to be 0.04 mg/kg (Burt et al. 2003). The general range of
Te in soils, given for various countries, is from 0.02 to 0.5 mg/kg (Kabata-Pendias
2011). The elevated Te contents of soils, up to 6.55 mg/kg, are reported for soils surrounding various smelters, as well as for soils in vicinities of Au mineralization. Soils
of mining districts in the United States (Nevada State) contain Te up to 10 mg/kg
(Cowgill vide Kabata-Pendias 2011). In soils of the remote region in Spitzbergen,
its contents vary within the range of 0.00002–0.0016 mg/kg (Gulińska et al. 2003).
The elevated Te contents of upper soil layers, compared to deeper soil horizons,
suggest its fixation by the OM. Because microbial metabolism of Te is similar to that
of Se, bacteria that methylate Se may also methylate Te, which increases its mobility. Its anionic species, TeO 3
and TeO H
3
, are also mobile. Processes of reduction
of tellurite, TeO 2 , which is relatively common in soils, are stimulated by variety of
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