Chemical Engineering October 2010 - 23

CritiCal metals
go well beyond
rare earths
R
are-earth metals are far from the
only group of elements with clear
technological importance and concern
over future supplies. In 2008, the
National Research Council (NRC), the
research arm of the National Academies
(www.nationalacademies.org),
explored the relationship between
metal minerals and the U.S. economy.
The research group, led by industry
consultant Stephen Freiman, devised
a Metals Criticality Matrix that assessed
the impact of supply restrictions
of various metals on the economy. The
analysis depends heavily on the ease
or difficulty of substituting away from
the mineral in question. Along with the
rare earths, the NRC mentioned indium,
niobium and the platinum group
metals (including rhodium and palladium)
as ranking high on the Metals
Criticality Matrix. Others have pointed
to metals such as germanium, gallium
and the tungsten-group metals as also
having high criticality.
❏
Rare-earth metals in post-consumer
waste may be too diffuse and too difficult
to extract economically, but industrial
recycling may be a more achievable
goal, says consultant Lifton.
TNO's Diederen points out that
rare-earth recycling, as well as other
metal recycling, should be viewed from
more of a product lifecycle perspective.
Specifically, R&D projects aimed at extending
product lifetimes would be important,
as would conducting upfront
product design to make future recycling
of the material more amenable.
Although substitutes for the rareearth
metals are difficult to find without
sacrificing performance in many
cases, Morley points out that it may
end up being more fruitful to look
for substitutes not for the rare-earth
materials themselves, but for alternatives
to the products and applications
for which they are required.
Another strategy for extending REE
supplies involves finding ways to reduce
rare-earth metal content in products as
a way of lessening overall demand. An
example comes from Ames Laboratory,
where researcher Bill McCallum is investigating
how to lower the rare-earth
content in the permanent magnets
that are used in the traction motors of
hybrid electric vehicles.
A final approach would be to find alternative
sources of REEs. An example
of this approach began as an offshoot
of a project originally conceived for
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another purpose. University of Leeds
(Leeds, U.K.; www.leeds.ac.uk) materials
scientist Animesh Jha discovered
that rare-earth metal oxides are produced
as co-products in a process he and
colleagues were working on for refining
titanium dioxide from the mineral ilmenite.
Depending on the titanium minerals
they use, the rare-earth content can
be up to several percent. In the titanium
dioxide process, a colloidal layer is generated
that was found to contain lanthanum,
cerium, praseodymium and other
rare-earth metals. The researchers are
working on improving the recovery rate
of the rare earths beyond the 50-80%
presently achievable.
■
Scott Jenkins
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Chemical Engineering October 2010

Table of Contents for the Digital Edition of Chemical Engineering October 2010
