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Tungsten [W, 74]
52.1 INTRODUCTION
Tungsten (W), known also as wolfram, is a rare metal of group 6 in the periodic table
of elements. In the Earth’s crust it occurs only as chemical compounds, at an average
content of about 1.5 mg/kg. Its contents of acidic magmatic rocks, <2.5 mg/kg, is a
bit higher than in alkaline rocks. Coal may contain W at >1 mg/kg, some oil shales
may have up to 2.5 mg/kg, and in fly ash it may be accumulated to about 4.5 mg/kg.
The oxidation states of W are from +2 to +6, and most commonly are at the
highest value. Geochemical properties of W are similar to those of Mo, thus in several minerals the substitution of W for Mo takes place. Most minerals contain the
anionic species of W, namely, (WO 4 ) 2− . Common minerals of tungsten are wolframite [(Fe,Mn)(WO 4 )], scheelite (CaWO 4 ), and sanmartine [(Zn,Fe)(WO 4 )], of which the
first two minerals are its important ores. Under most geochemical conditions, minerals and compounds of W are slightly soluble, but some complex compounds, especially those associated with Mo are likely to be mobilized, under specific conditions.
Global W production (rounded), excluding the United States, in 2010 was 61,000 t, of
which 52,000 t was produced in China; 2,500 t in Russia; 1,100 t in Bolivia; and 1,000 t
in Austria (USGS 2011). The main use of W is in cemented carbide parts for cutting
and wear-resistant materials, primarily in the construction, metalworking, mining, and
oil- and gas-drilling industries. It is also consumed to make heavy alloys for applications requiring in high-density electrodes, filaments, wires, and several other electronic
components. This metal reveals very high robustness, and in carbide (WC) form has a
hardness of that of a diamond. Tungsten is also used for catalysts in automobile exhaust
systems, and as pigments in dyes and inks. It is used in bullets, as a replacement for Pb,
and in some tools, as a substitute for depleted U.
52.2 SOILS
Tungsten’s average content in the worldwide soils is estimated to be 1.7 mg/kg, within
the range of <0.17–5.0 mg/kg. The highest mean W contents, about 5.0 mg/kg, is in
soils of Europe (FOREGS 2005). However, W concentration, up to 85.5  mg/kg is
reported for soils in China (Govindaraju 1994). Presumably, it might be contamination effects. Range of W contents in soils of some countries are given as follows
(in mg/kg): 0.6–3.4 in Brazil, 1.0–85.5 in China, 0.9–1.8 in Japan, 0.7–2.7 in Scotland,
<1–51 in Slovak Republic, 0.4–2.4 in Sweden, and 0.5–5.0 in the United States. Soils
surrounding the W ore-processing plant in Russia contain W within the range of
100–200 mg/kg (Kabata-Pendias 2011).
Tungsten sources in soils are from fly ash and some sludge used for soil amendments.
Mean V content of sludge is given as about 8 mg/kg, whereas in slurry from dairy cows
its mean amount is 0.082 mg/kg (Eriksson 2001a). Some type of ammunition may also
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