41
Scandium [Sc, 21]
41.1 INTRODUCTION
Scandium (Sc) is a silvery-white transition metal of group 3 in the periodic
table of elements, with properties similar to Al and Y. Its mean concentration in the
Earth’s crust is estimated to be 11 mg/kg, but also the range of 16–30 mg/kg is given.
In higher amounts, it may be accumulated in mafic igneous rocks and argillaceous
sediments. Its lowest contents, <5 mg/kg, are in calcareous rocks. Some organic raw
materials, such as coal, peat, and crude oil, may accumulate elevated Sc amounts, up
to 100 mg/kg ash weight (AW). Its mean content in the U.S. coal is 4.2 mg/kg, but
may be elevated up to 100 mg/kg (Finkelman 1999). Its level in fly ash is up to about
5 mg/kg, mainly after burning lignite coal.
Scandium oxidation state is +3, and it may easily substitute for Al 3+ , Fe 3+ , and
Ti 3+ . Thus, it is likely to be associated with ferromagnesian minerals, biotite, and
some phosphates, up to about 40 mg/kg. Its minerals, which are its primary sources,
are thorveitite, Sc 2 (Si 2 O 7 ), and kolbeckite, ScPO 4 ·2H 2 O.
The worldwide Sc mining is about 2 t/yr of Sc 2 O 3 , mainly in three mines: China,
Ukraine, and Russia (USGS 2011). Some other sources gave Sc production at
10–50  kg/yr of Sc. The mineral thortveitite, Sc 2 (Si 2 O 7 ), contains 35%–40% Sc 2 O 3
and is used, as well as kolbeckite, ScPO 4 ·2H 2 O, for the Sc production. Its another
important source (at about 2.5  t/yr) is a by-product from U ore processing, even
though it only contains 0.02% Sc. Scandium is also associated with several rare earth
element minerals.
Scandium is applied for light Al–Sc alloys used mainly in the aerospace industries. It is also used for the production of various lamps, lasers, and fluorescent materials, and as a catalyst in organic chemistry.
41.2 SOILS
The worldwide mean Sc content in soils is estimated to be 12 mg/kg, within the range of
0.8–28 mg/kg. Higher amounts are in heavy loamy soils, especially those that are derived
from granitic and volcanic rocks. It may also be accumulated in some organic soils
(Table 41.1). Scandium contents of soils of different countries are given as follows (in mg/kg):
China, 5–28; Japan, 13–28; Poland, 0.5–7.9; Sweden, 3.5–16; the United States, 5–18; and
Russia, 5 (mean value for loess deposits). Soils in remote regions of Spitsbergen, Norway,
contain Sc within the range of 0.02–0.14 mg/kg (Gulińska et al. 2003).
Scandium in soils may occur as oxide, Se 2 O 3 , and hydroxide, Se(OH) 3 , and is
likely to form complexes such as Sc(H 2 O) 6
3+  and Sc(H 2 O) 6
2+
. It shows an affinity for
the association with PO 4 , SO 4 , and CO 3 , as well as with some organic compounds.
Elevated Sc amounts in P fertilizers, up to about 40 mg/kg, may be its source in
agricultural soils.
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