Rare Earths and the Balance Problem
J. Sustain. Metall.
Rare Earths and the Balance Problem
Koen Binnemans 0 1
Peter Tom Jones 0 1
0 P. T. Jones Department of Materials Engineering, KU Leuven , Kasteelpark Arenberg 44, P.O. Box 2450, 3001 Heverlee , Belgium
1 K. Binnemans (&) Department of Chemistry, KU Leuven , Celestijnenlaan 200F, P.O. Box 2404, 3001 Heverlee , Belgium
Maintaining the balance between the demand by the economic markets and the natural abundance of the rare-earth elements (REEs) in ores constitutes a major challenge for manufacturers of these elements. This is the so-called balance problem (or balancing problem). The ideal situation is a perfect match between the demand and (production) supply of REEs, so that there are no surpluses of any of the REEs. The balance problem implicates that the rare-earth industry has to either find new applications for REEs that are available in excess, or needs to search for substitutions for REEs that have limited availability and that are high in demand. Different solutions are proposed to solve the balance problem: diversification of REE resources, recycling and urban/landfill mining, substitution, reduced use and new high-volume applications. No single solution can solve the balance problem, but a combination of different strategies can. It is illustrated that the issue of thorium in REE ores is also directly related to the balance problem: presently, thorium is considered as radioactive waste, but this waste could be turned into a valuable resource by using thorium in a thorium-based nuclear fuel cycle.
Lanthanides; Permanent magnets; Rare earths; Recycling; Substitution; Thorium
Introduction
The global annual production of rare earths or rare-earth
elements (REEs) is typically expressed in tonnes of
rareearth oxides (REOs). At present, the estimated yearly total
production of REOs is about 125,000 tonnes, although
accurate production numbers are very difficult, if not
impossible, to obtain. However, these total production
numbers give no indication about the availability of the
individual REEs. First of all, not the total amount of REE
ores mined is of importance, but rather the total amount of
REE concentrate separated in the different individual REEs.
For some applications, such as mischmetal, no separated
REEs are required. Secondly, the REEs are not present in
equal amounts in the REE ores, due to differences in the
natural abundances of these elements. The general trend in
the natural abundance of the rare earths is that the elements
become scarcer with increasing atomic number Z; as the
abundances decrease over the lanthanide series, the heavy
rare-earth elements (HREEs) are much less abundant than
the light rare-earth elements (LREEs) [
1
]. Additionally,
elements with an even atomic number Z are more abundant
than elements with an odd atomic number (Oddo-Harkins
rule). For example, cerium (Z = 58) is more abundant with
respect to its neighbours lanthanum (Z = 57) and
praseodymium (Z = 59). Cerium is the dominating rare-earth
element in LREE-rich ores (bastna¨site and monazite), while
yttrium is the main rare-earth element in HREE-rich ores
(xenotime and ion-adsorption ores).
The availability of the individual REEs is of concern for
applications that require the use of pure REEs, such as
phosphors and permanent magnets. If the REEs that are
required for high-volume applications have a low natural
abundance, the minimum quantity of REE concentrate that
needs to be processed and separated is that quantity that
will produce at least the amount of REEs required for these
critical applications. As a consequence, some REEs will be
produced in larger quantities than required by the REE
market and, subsequently, these elements need to be
stockpiled, which comes at a cost. The balance between the
demand by the economic markets and the natural
abundances of the REEs in ores is a major problem for
manufacturers of these elements [
2
]. This is the so-called
balance problem (or balancing problem) [
3, 4
]. The ideal
situation is a perfect match between the demand and
(production) supply of REEs, so that there are no surpluses
of any of the individual REEs. This would result in the
lowest market price for any of the REEs, because the
production costs are shared by all rare-earth elements.
Unfortunately, a market in balance is very difficult to
achieve, because of changes in demand due to
technological evolutions in applications. The result is a sometimes
very high demand of a REE that is a minor constituent in
the ore (such as dysprosium), while the demand of the
major constituent (such as yttrium) is much lower. The size
of the REE market is different in terms of value and
volume. For instance, phosphors are a very important
application of REEs in terms of value (1/3 of the REE market),
but they are a rather modest application in terms of volume
(about 7 %). The balance problem is related to the volumes
of the individual REEs consumed.
For the REE industry the balance problem i (...truncated)