Geology Reference
In-Depth Information
B.2.50 Rare Earth Elements: Praseodymium, Samarium,
Europium, Gadolinium, Terbium, Dysprosium, Holmium,
Erbium, Thulium and Lutetium
All fourteen members of the lanthanide series have very similar geochemical pro-
perties. There are over 100 minerals known to contain lanthanides but the only
two of commercial importance are monazite, a mixed La, Th, Ln phosphate and
bastnaesite, a La, Ln fluorocarbonate. Samarium, terbium and erbium are also
found in xenotime and euxenite, while gadolinite is also an important source for
holmium, terbium and thulium.
Many applications of REE are characterised by high specificity and high unit
value. For example, europium is used for colour cathode-ray tubes and liquid crys-
tal displays used in monitors and televisions. A major use of praseodymium is in
the mischmetal, which is employed in cigarette lighter manufacture. Samarium is
used as a catalyst in certain organic reactions. Erbium finds extensive use in laser
repeaters for fiber-optic telecommunication cables. Permanent magnet technology,
meanwhile, has been revolutionised by alloys containing gadolinium, dysprosium
and other REE. Terbium, gadolinium or europium are used in new energy-e
cient
fluorescent lamps. Lutetium can be used as a catalyst in petroleum cracking in re-
fineries and in alkylation, hydrogenation and polymerisation applications. Holmium
and thulium can be found in lasers for medical applications.
B.2.51 Rhenium
The concentration of rhenium in the Earth's crust is extremely low. It is also very
diffuse. Being chemically akin to molybdenum it is in the molybdenites that its
highest concentrations (0.2%) are found.
Rhenium was the last naturally-occurring element to be discovered. Its main
applications in industry are found in the manufacture of tungsten-rhenium and
molybdenum-rhenium alloys. Other important uses of rhenium are in platinum-
rhenium catalysts, used primarily in producing lead-free, high octane gasoline and
in high-temperature superalloys used for jet engine components.
B.2.52 Rhodium
Rhodium is one of the platinum group metals. It occurs as rare deposits of the native
element and in rare minerals associated with the other metals of the platinum group.
That said, usually, the commercially available metal derives from a byproduct of
the refining of copper and nickel ores which can contain up to 0.1% rhodium.
Most of its production is directly related to catalytic converters in cars and
in some industrial processes. It is used in alloys together with platinum and irid-
ium, giving improved high-temperature strength and oxidation resistance to furnace
windings, high-temperature thermocouple and resistance wires, spark plugs, bear-
ings, electrical contacts, amongst others.
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