Elements that rule the world: Impending REE metal crisis
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Summary of the lecture to be delivered at the monthly meeting of the Geological Society of India on 29 August 2012
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The rare earth elements (REEs) or
lanthanides include 15 elements of the
periodic table from lanthanum to lutetium.
They are all metallic elements closely
related to each other in their chemical
properties, geochemical behaviour and
distribution in the earths crust. REEs are
high-tech metals with endless uses in
Smartphones, LCD screens, computer hard
disks, CFL, LED, MRI, positron emission
tomography (PET), portable X-ray units,
fibre optics, lasers, petroleum refining, glass
colouring, permanent magnets, hybrid cars,
wind turbines, atomic reactors and defence
hardware. Potential uses include magnetic
refrigeration, medical diagnostics and
treatment and hetero-metallic hydrides for
hydrogen fuel storage. Many applications
of REE metals in defence weapons system
such as smart bombs, guidance missiles and
lasers are kept under strict governmental
control.
REEs are large-ion-lithophile elements
incompatible in the structure of upper
mantle minerals and are thus fractionated
into the earths crust. Because of the
property of lanthanide contraction, the
LREEs easily get into the melt phase and
eventually are concentrated in crustal rocks,
while the HREEs are left in mantle minerals
during partial melting of the upper mantle.
The REEs are not that rare and are more
abundant compared to metals like Cr, Ni,
Cu, Zn, Mo, Sn, W or Pb in the earths crust
but have no tendency to concentrate and
form economic mineral deposits like the
base metals or iron ores.
The process of mining and beneficiation
of REEs is environmentally hazardous as it
produces enormous mine waste, toxic and
reactive effluents and radioactive tailings.
The associated radioactive U and Th pose
problems of beneficiation and safe handling.
Isolation of the individual REEs from the
beneficiated ore is again a cumbersome
process owing to their similar chemical
properties.
There are more than 200 minerals
containing essential or significant REEs.
But bastnaesite, xenotime and monazite are
the three most economically significant REE
minerals while eudialyte, loparite and
allanite are less important REE minerals.
REE carbonates and phosphates are better
amenable to beneficiation than REE silicates.
Besides, small amounts of Th and U are
always associated with the REE minerals.
REE minerals are distributed in diverse
types of igneous, sedimentary and
metamorphic rocks. Often many REE
minerals occur in complex associations in
these rocks. The chief geological
environments where they are known are: (i)
Carbonatites and related rocks such as
syenites, nepheline syenites and nephelinites
(ii) Beach placers containing detrital REE
minerals associated with other heavy
minerals (iii) Peralkaline granitic and
syenitic igneous rocks, (iv) Iron-REE
deposits of hematite-granite-breccia-style,
(v) Pegmatites, hydrothermal quartz and
fluorite veins (vi) Skarn deposits and
(viii) Ion-adsorption clays, where the
REEs occur as ions adsorbed onto residual
clay minerals. In addition phosphorites
contain the LREEs, La, Ce and Nd in the
mineral francolite.
Almost 97% of the world production of
REEs today comes from China which
produced 1,30,000 tonnes of REEs in 2010,
while the share of the rest of the world was
a mere 3600 tonnes of which India
accounted for 2700 tonnes. In 2010 China
also produced 97% of the worlds rare earth
oxide, 89% of the worlds rare earth alloys,
75% of the worlds NdFeB magnets and
60% of SmCo magnets. China thus holds
the monopoly in the production and export
of these critical metals today. Many REE
mines in the West had to be closed when
cheap REEs from China flooded the market
in the 1990s. The known world reserves of
REEs are 110 million tonnes, nearly half of
which is in China. Following a maritime
dispute with Japan, which buys roughly
50% of Chinese REE exports, China has
considerably reduced export of REE since
2010 seriously affecting electronic
industries in Japan and the industrialized
western countries. If China stops export of
REEs completely as is feared, Japan and the
western world will face shortage, crippling
their electronic industry.
As a consequence of these
developments, many countries are vigorously
exploring for REEs and many mines long
closed are being reopened. There are several
new discoveries, the most promising one
being in Afghanistan, where a million tonnes
of REE ore has been identified within the
Khanneshin carbonatite complex, Helmand
Province. But any new mine would require
5-10 years to reach the production stage,
which means Chinas preeminence in REE
production and supply would continue for
decades.
Over the past few decades, China has
mastered the entire gamut of REE
technology: mining, processing and
isolation of REEs, and their application in
electronic industries. China is also the major
producer of REE magnets, the demand for
which is likely to leapfrog with the world
poised for greener (...truncated)