40
Ruthenium [Ru, 44]
40.1 INTRODUCTION
Ruthenium (Ru) is a hard, white metal of group 8 in the periodic table of elements
and is a member of the platinum group metals (PGMs). It is resistant to acids, but
reacts with alkalis, especially under oxidizing conditions. Its mean concentration in
the Earth’s crust is about 1 μg/kg, whereas its contents in rocks vary from 0.01 to
60 μg/kg. It usually occurs as a minor component of Pt ores. The PGMs mined in
South Africa contain, on average, 11% Ru, whereas the PGMs mined in the former
USSR contain only 2% Ru. It may also be associated with ores of some base metals,
such as Fe, Ni, and Cu. Fission products of 235 U contain significant amounts of Ru,
and therefore, used nuclear fuel might be its possible source.
The annual Ru production is 12–20 t, as given by various sources (USGS 2001).
Most Ru is used for wear-resistant electrical contacts and the production of thickfilm resistors. Its minor use is in Pt and Pd alloys, which are applied in jewelry and
stomatology. It is also used for some catalytic processes and in medicine, mainly as
antimalaria and immunosuppressive drugs.
Ruthenium oxidation states range from −2 to +8, and the most common are +2,
+3, and +4. Chemically, it is similar to Os. Its known compounds are dipotassium
ruthenate, K 2 RuO 4 , and potassium perruthenate, KRuO 4 .
40.2 ENVIRONMENT
There are not many data on Ru in soils. Its average content in soils of Sweden is
about 40 μg/kg, and its deposition was calculated as <11 mg/ha/yr (Eriksson 2001a).
In soils along motorways, Ru amounts vary from 0.01 to 5.77 μg/kg (Fritsche and
Meisel vide Kabata-Pendias 2011).
Ruthenium concentrations in water vary from 0.7 to 20  ng/L, in seawaters
and lakes, respectively. Its highest content, about 0.1  μg/L, is in stream waters
of India (Reimann and de Caritat 1998). Its relatively high accumulations are
in pelagic sediments, within the range of <0.2–7 μg/kg, and in ferromanganese
nodules, up to 46 μg/kg (Bertine et al. 1993). Elevated 106 Ru contents were found
in bottom sediments of the Danube River, below the nuclear reactor (Pavlotskaya
vide Kabata-Pendias 2011). Rainwater in Sweden contains Ru <1 ng/L (Eriksson
2001a).
Plants uptake Ru relatively easily, and its elevated contents, within the range of
0.3–0.9 μg/kg, are in plants grown along motorways (Djingova et al. vide KabataPendias 2011). The average Ru concentration in plants is estimated to be 5 μg/kg.
However, it may highly vary in various environments. In tropical forest region of
Central America, its contents in plants may be up to about 2000 μg/kg (Duke vide
Kabata-Pendias 2011).
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