37
Rhenium [Re, 75]
37.1 INTRODUCTION
Rhenium (Re) is a silvery metal of group 7 in the periodic table of elements. It may
be readily oxidized and become black. Its content in the Earth’s crust is within the
range of 0.4–0.6 μg/kg. Sometimes, it is accumulated in carbon shales and some
coal, up to about 100 μg/kg.
Rhenium oxidation states vary from −1 to +7, and the most common is +7. It does
not occur as free metal, and its mineral, dzhekazganite (CuReS 4 ), is very rare. It reveals
geochemical similarity to Mo and may be associated with some minerals: molibdenite,
zircon, and gadoline. Higher concentrations of Re are also found in some minerals
of LAs.
The global Re production (rounded) in 2010 was estimated to be 48 t, of which
25 t was produced in Chile, 6 t in the United States, 5 t in Peru, and 4.5 t in Poland
(USGS 2011). Rhenium is very hard and resistant to corrosion. Its main use is in
superalloys for blades in turbine engines. It is an ideal metal for use at very high
temperatures, which makes it suitable for rocket motors. In alloy forms with Mo, Pt,
and W, it is used in various thermocouples, X-ray tube, and electrical and catalytic
devices. Occasionally, it has been used for plating jewelry. Some Re compounds have
recently been used in the treatment of cancer patients (Collery et al. vide KabataPendias and Mukherjee 2007).
37.2 ENVIRONMENT
Rhenium is readily soluble, mainly as the anion, ReO
−
4 , during weathering processes,
especially in oxidizing and acidic media. It is precipitated and/or sorbed by various
sediments, especially by shales and some coals, where it may be accumulated up
to 10 mg/kg. Arable soils of Sweden contain Re at an average value of <40 μg/kg
(Eriksson 2001a), whereas in soils along motorways in Australia, its content is up to
9.8 μg/kg (Frische and Meisel vide Kabata-Pendias 2011).
Mobile Re species are relatively easily available to plants. Some plants, mainly
from U ore regions, may accumulate high amounts of Re. Its highest concentrations,
up to 31 mg/kg ash weight, were found in some plants from vicinities of U mines
(Bushkov et al. vide Kabata-Pendias 2011). Cereal grains from Sweden contain Re at
an average value of <0.1 μg/kg (Eriksson 2001a).
37.3 HUMANS
Rhenium is not an essential element, and the toxic effect occurs only at its high concentrations. Because its uptake by plants is limited, the animal and human tissues
contain it in very small amounts. Therefore, negative consequences because of Re
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