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WHAT KINDS OF OPPORTUNITIES ARE THERE FOR
RARE EARTH MATERIALS IN MONGOLIA?
Terry Surles
Abstract
Rare earth elements are of growing importance in our modern world. These elements are required for new renewable energy and energy efficient technologies. They include lighting phosphors for energy-efficient lighting and permanent magnets for electric vehicles and wind turbines. Additionally, rare earth elements find use in industrial lasers, consumer electronics, industrial catalysts, and newer medical diagnostic instrumentation.
The world supply is limited, with a significant majority coming from China. As a result the cost for specific rare earth elements can be significant, for example up to $800/kg for europium and terbium. Some of these mines are close to China’s border with Mongolia. It is conceivable that Mongolia could have similar resources. Mongolia also has substantial coal reserves and development. Work done by the US Geological Survey and US Department of Energy has shown that rare earths are co-located with many coal resources. Thus, it is possible that rare earths can be economically recovered with coal at mines in Mongolia.
I. Introduction
There has been increasing interest in the utilization of rare earths in modern-day
technology. These are the elements that are in the lanthanide series of elements that are
changed only by additions of electrons to their 4f shell. An amusing sidelight as stated
by Dr. Harry Eick, who was an expert in rare earth chemistry, is “They’re not rare and
they’re not earths!”
Rare earths are a series of chemically similar elements. From an atomic structure
standpoint, this is because the changes from one element to another do not occur in the
outermost shell of elections. (These are the electrons that are normally involved in
reactions with other elements. This is called the valence shell.) Instead, the number of
electrons changes in an interior shell of the atom’s electronic structure and, as such, is not
involved in typical chemical reactions. These changes do not substantively influence
changes in their individual chemistries. However, there are substantive differences
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between these elements that modern technology and engineering have made use of and
these have, in turn, substantially increased the value of these elements.
One reason for the recent increased interest in rare earths is that, until very recently,
China produced more than 97% of all rare earths in the world. Their lower prices drove
other producers out of business either temporarily or permanently. Starting in 2004,
China utilized this market power as an economic tool. This motivated a number of
countries to re-examine their existing rare earth resources to determine their economic
viability. For example, in the United States, Molycorp has recently upgraded and re-
opened their rare earths mine in southeastern California.
The concern about critical materials, including rare earths, has led the United States
Department of Energy (USDOE) to set up a five-year, $120M “Hub” for critical materials
research. The Hub is at Iowa State University, a long-time leader in rare earths research,
with substantive contributions from the Colorado School of Mines. While rare earths are
a focus, other elements such as indium, gallium, and tellurium, as well as lanthanide
congeners (yttrium), are included as important to the American security and economy.
Because of these recent events, there may be an opportunity for Mongolia to diversify
their mining activities to incorporate the development of potential rare earth resources. In
doing so it will be important to examine the economic and societal impacts that could be
associated with successful development of new mineral resources.
While there is no development at the current time, Mongolia is close to some of the
most productive rare earth mines in the world, located in China. Thus, this paper focuses
on a review of rare earth chemistry and industrial and commercial applications and why
these elements are important to today’s global economy. It then surveys what activities
are occurring around the globe. Lastly, there is a commentary on the potential
implications for rare earth development in Mongolia.
II. Commercial Use of Rare Earth Materials
II.A. Overview
The ubiquity of uses of rare earth materials is summarized in this section. It is divided
into the aggregated uses of these rare earth elements. Where applicable, unique uses are
highlighted. An additional summary is provided for gallium, tellurium, and indium
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following the discussion of rare earth elements. Much of this review material is from the
report entitled, “Critical Materials Strategy” that was published by the United States
Department of Energy in December 2011. Since much of this document is referenced in
this report, specific citations are shown as CMS, DOE with the page number.
II.B. Lighting
Many rare earth elements have been used as part of lighting technologies for many years.
These include yttrium, cerium, lanthanum, europium, terbium, praseodymium, samarium,
and dysprosium.
Recently, certain rare earth elements have become more important. This is
because new low energy lighting technologies are being developed and/or have come on
the market, which require these elements. Thus, cerium, europium, and terbium have
increased in importance.
In addition, some of these elements have industrial applications for carbon arc
lighting. These elements are dysprosium, samarium, praseodymium, and lanthanum.
II.C. Electric and Hybrid Vehicles
A number of rare earth elements are now needed as part of the development of electric
and hybrid vehicles. As the market share of these vehicles grows, so will the need for
these elements. This need is divided into two categories, although some elements are in
both. Praseodymium, neodymium, and dysprosium are used for the proper utilization of
magnet technology. Neodymium and praseodymium, as well as lanthanum and cerium
are required for the development and operation of hybrid and electric vehicle batteries.
In addition, a lanthanum/nickel alloy has been developed for the storage of hydrogen.
This can have application to the emergence of fuel cell vehicles, such as that recently
highlighted by Honda.
II.D. Magnets
Highly efficient magnets are becoming workhorses in industry. “Super magnets” are
made of an alloy that is comprised of neodymium, iron, and boron, called the NIB super
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magnet. Dysprosium is used in an alloy for neodymium-based magnets for wind turbines
and electric vehicles.
Samarium and praseodymium are two other rare earth elements used for these
industrial magnets. The samarium/cobalt magnet has enabled the miniaturization of a
number of consumer electronic devices, such as headphones.
II.E. Industrial Lasers
Three rare earth elements are used in the development of industrial lasers. Yttrium is
found in two types of lasers. The yttrium/aluminum garnet laser is one of them. The
yttrium/iron garnet laser is utilized in microwave filters and radar applications.
Neodymium is used for a similar laser - the neodymium/aluminum garnet laser.
Ytterbium has also been utilized for the development of tunable lasers.
II.F. Neutron Absorbers
The earlier sections have focused on the development of better renewable energy and
energy efficient technologies. However, rare earths have other energy-related
applications. One of the most important is as neutron absorbers in nuclear power plants.
The rare earth elements most frequently used for this application are samarium,
europium, gadolinium, dysprosium, and holmium.
II.G. Optical Glasses and Ceramics
Rare earth elements have a long history in coloring glasses and ceramics.
However, rare earths have found substantive applications in other industrial operations.
In particular, a number of these elements are now used for various welding operations as
a safety feature for welders’ eyes. These elements include yttrium, lanthanum,
praseodymium, neodymium, and erbium.
In addition to its historic use for glass and ceramic coloring, yttrium is part of a
compound utilized as a high temperature superconducting ceramic material. This is the
yttrium/barium/copper oxide.
II.H. Industrial Catalysts
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Due to their atomic structure, a number of rare earth elements are being used as
industrial catalysts. These elements catalyze reactions without chemically changing their
own structure. Many of these elements are used in oil refineries, primarily associated
with cracking operations. These elements include cerium, lutetium, lanthanum, yttrium,
and ytterbium.
II.I. Utilization of Rare Earths in Metal Alloys
Rare earth elements are used in metal alloys for a number of reasons. Praseodymium is
part of a high-strength alloy with magnesium used in aircraft engines. Gadolinium is
used in iron (ferrous) and chromium alloys to improve the “workability” of the alloy.
Erbium is added to vanadium alloys as well to improve its workability.
II.J. Fiber Optic Technology
Three rare earth elements have applications in fiber optic systems. Erbium is utilized to
amplify broadband signals. Ytterbium and europium are also utilized to improve these
signals as well as the operation and efficiency of the fiber optic systems.
II.K. Applications Unique to One Element
Despite their similar chemical behavior, some of the rare earth elements have uses that
other rare earth elements do not. Cerium helps to enhance the operation of flat screen
TVs. Samarium oxide is joined to indium for touch screen technology. Gadolinium
enhances the operations of magnetic resonance imaging (MRI) systems. Terbium is used
with calcium tungstate and tin molybdate in solid-state devices. Terbium also plays a
role in X-ray technology.
Thulium can be found as part of lasers in surgical operations. Irradiated thulium
helps to make portable X-ray machines. And, perhaps most interestingly, europium is
used in printing Euro banknotes as a method for discouraging counterfeiting!
II.L. Other Strategically Critical Elements: Indium, Gallium, and Tellurium
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Although not rare earths, these elements are included when critical materials are listed
and therefore are also considered here as part of a possible development strategy for
Mongolia.
Tellurium, gallium, and indium all have applications to solar cells. While silicon
is certainly ubiquitous, gallium arsenide (GaAs) cells or cells utilizing tellurium and
indium have been shown to have higher efficiencies. The major issue is cost and their
hazardous nature. In fact, GaAs solar cells are being used on the Mars Rover.
Gallium and indium, due to their low melting points for metals are used in alloys
where this is an attribute, such for building sprinkler systems. Gallium is used as a
semiconductor in combination with either nitrogen or arsenic. Similarly, indium is a
semiconductor in microchips as part of a compound with nitrogen, phosphorus, or
antimony.
Tellurium is used in copper and iron alloys to improve the “machinability” of
these alloys. It is also used in re-writable CD and DVD technologies. As with some of
the rare earth elements, tellurium is also used as a catalyst in oil refining operations.
II.M. Summary
As this overview shows, these elements have critical uses, particularly in technologies
that are becoming more important to the world today. This includes their role in new
efficient and renewable energy technologies. They are also used for operations in the oil
industry and nuclear power plants.
Outside of energy technology and industrial applications, these elements have a
whole range of emerging applications to consumer electronics, industrial technology,
industrial alloys, and in health care. All of these sectors are important to any nation’s
economy and would be impacted should these elements either be unavailable or if their
costs substantially.
III. Current Global Status of Rare Earth Elements
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This section discusses the current availability of these elements and some of the geo-
political aspects of their availability. As with the previous section, much of the material
is from the USDOE report, “Critical Materials Strategy.” 1
III.A. Key Findings From the DOE Report
The report resulted from efforts that included workshops and reviews. In addition to
DOE and other government experts, academic experts and industrial experts involved in
mining and production were included in the discussions. Here are key findings as
developed by the group of experts. (CRM, DOE, p.2):
• Several clean energy technologies—including wind turbines, EVs, PV thin films and fluorescent lighting—use materials at risk of supply disruptions in the short term. Those risks will generally decrease in the medium and long terms.
• Supply challenges for five rare earth metals (dysprosium, neodymium, terbium, europium and yttrium) may affect clean energy technology deployment in the years ahead.
• In the past year, DOE and other stakeholders have scaled up work to address these challenges. This includes new funding for priority research, development of DOE’s first critical materials research plan, international workshops bringing together leading experts, and substantial new coordination among federal agencies working on these topics.
• Building workforce capabilities through education and training will help address vulnerabilities and realize opportunities related to critical materials.
• Much more work is required in the years ahead.
While some of these findings do not concern the nature of this conference in Hawai`i,
the first two are the focus of the discussion that follows.
III.B. Current State of Supply – Situation in China
1 The USDOE report also cited other timely and cogent reports on the same subject.
These are: Resnick Institute Critical Materials for Sustainable Energy Applications. Hurd et. al. Energy-Critical Elements for Sustainable Development. Parthemore, Elements of Security: Mitigating the Risks of U.S. Dependence on Critical Minerals. Moss et. al. Critical Metals in Strategic Energy Technologies.
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The world is not running out of these minerals. Returning to the quote by Dr. Harry Eick,
these elements are not rare. However, due to the similarity in their chemical behavior, it
is difficult to separate them from one another. 2
At the same time demands on these rare earth elements are growing with the
increasing popularity of new energy and consumer technologies. Thus there is concern
that the current supply in only a small number of mines and countries adds to supply
risks. The fact that rare earths are marketed by a small number of producers means higher
supply risks. In such a highly concentrated market, disasters (natural or manmade) or
labor strikes impacting a major supplier can lead to a global supply shock. A resource-
rich country that is politically unstable also adds significant uncertainty to global supply.
Greater market concentration also implies that a large producer or group of
producers can (and have, as will be discussed below) more readily exercise market
power. For example, a large producer might lower its asking price relative to that of its
competitors to gain market share. The impact of this on consumers could be positive in
the short term. However, the resulting reduction in competition could enable a large
producer or group of producers to later engage in limiting production quotas and/or
export quotas to drive up the price in order to capture higher revenues at the expense of
the consumer.
Prior to 2000, the United States produced a significant amount of rare earth
minerals. Shortly thereafter, South America became center of mining production, with
Chile being a particular focus. However, due to production cost considerations, this
shifted to China where - by 2004 - as much as 97% of all rare earths around the globe
were produced.
China’s stated goals (Global Times, 2011, “October Launch of Rare Earth
Association”) respect to mineral extraction policy include maintaining stable supplies for
the Chinese economy, reducing the environmental impacts of resource extraction and
stopping illegal mining, overproduction, and smuggling. These goals apply to rare earth
elements, of which China is the world’s leading producer, as well as to indium.
2 The techniques developed at Iowa State University in the 1930s for separating these lanthanide elements became a critical component of the Manhattan Project in World War II, as the separation requirements for actinide elements such as uranium, thorium, and plutonium were very similar.
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China continues to implement a comprehensive industrial policy of consolidating
production, limiting exports, enacting environmental regulations and restricting certain
foreign investment in the rare earth sector. Industry consolidation has accelerated over
the past year with the closure of hundreds of mines and the acquisition of many smaller
producers by the country’s major mining companies. Production quotas, higher taxes on
domestic producers, and a ban on new separation projects will supplement this
consolidation over the next five years. In July 2011, a new industry body called the
Chinese Association of Rare Earths was created to help oversee the administration of
China’s rare earth industry, including the implementation of production and export
quotas.
China imposed increasingly stringent export quotas on rare earth products.
Between 2004 and 2009, the overall export quota was reduced by more than 20% from
65,609 tonnes of rare earth oxides (REOs) to about 50,000 tonnes of REOs. (CMS, DOE,
p.66) In July 2010 China further reduced its export quota to 30,258 tonnes of REOs, a
significant decrease from the years prior to 2009. For 2011 the nominal quota was set at
30,246 tonnes, which for the first time included rare earth containing ferroalloys, which
effectively further reduced the allowed REO exports.
As a result of these increasingly stringent quotas, prices, as would be expected,
rose considerably. Figures 3 and 4 show the average prices of individual rare earth
metals between April 2001 and early November 2011. The heavy rare earths
(dysprosium, terbium, europium and yttrium) are consistently priced higher than the
lighter rare earths (lanthanum, cerium, neodymium, praseodymium and samarium) due to
scarcer global supply. In general, prices rose modestly from 2003–2008, followed by
steep increases from 2009–2011. Price increases during the earlier period were mostly
due to increasing global demand. The price jumps during 2009– 2010 were due, in part,
to falling Chinese exports. Rare earth prices generally peaked in mid-2011. Some
analysts have suggested that speculation and hoarding of REOs and metals contributed to
both the initial price increases and subsequent decreases in 2011 due to sell-offs by the
speculators. Based on the particular element, prices rose from four to forty-nine times
between 2001 and 2011! (Metal-Pages. 2011. “Rare Earth Price Surge Hits Brazil Ferro-
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Alloys Producer.” October 6. https://www.metal-pages.com/news/story/57438/rare-earth-
price-surge-hits-brazil-ferro-alloys- producer/.)
III.C. Future Technology Demand for Rare Earths
The DOE conference focused on energy technologies and, the following discussion will
be on these systems. However, as already discussed in Section II, many new consumer
products (primarily electronic entertainment systems), health care technologies, and
industrial catalytic operations (outside the energy industry) may be considered more
important from a national perspective. While certain rare earths, such as lanthanum, are
used as catalysts for cracking operations at oil refineries, their critical need is not as great
as what is seen for other emerging renewable energy and energy efficiency technologies.
Manufacturers of wind power and electric vehicle technologies are pursuing strategies
to respond to possible rare earth shortages. As discussed previously, permanent magnets
containing neodymium and dysprosium are used in wind turbine generators and electric
vehicle motors. Manufacturers of both technologies are currently making decisions on
future system design, trading off the performance benefits of neodymium and dysprosium
due to potential vulnerability to supply shortages.
As lighting energy efficiency standards are implemented globally, heavy rare earths
used in lighting phosphors may be in short supply. In the United States, two sets of
lighting energy efficiency standards that came into effect in 2012 will lead to an increase
in demand for fluorescent lamps containing phosphors made with europium, terbium and
yttrium.
Due to the substantively increased need for these rare earth elements, it is important
to look at which elements may be at risk. This analysis is shown in Figures 5 and 6.
These figures illustrate that dysprosium, europium, terbium, yttrium, and neodymium are
in a critical situation now for meeting industrial demand. These are immediate needs. In
the mid-term, with new mining efforts commencing due to these significant price
increases, the availability of some of these elements will not be as much of a risk.
However, from 2015 to 2025, it is projected that neodymium, dysprosium, europium,
yttrium, and terbium will continue to remain in a critical situation for meeting demand.
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III.D. Summary
There will be an ongoing and growing need for rare earth elements and related critical
materials in the near term. The requirements to have them in emerging energy efficiency
(lighting phosphors), renewable energy (“super-magnets”), consumer electronic products
(such as flat screen TVs, headphones, etc.), and advanced health care technologies
(Magnetic Resonance Imaging), as well as for other industrial applications (catalysts,
phosphors, tunable lasers, fiber optics, improved alloys) will only grow. Thus, there will
be continued efforts to develop these mineral resources in other parts of the world. This
leads to the implications for the development of rare earth mineral resources that could be
advantageous to Mongolia.
III.E. Late Breaking News
In January, China announced that it will do away with the previously discussed quota
system and replace it with a “resource tax,” the nature of which remains to be
determined. This is because only 25,000 metric tons of rare earths were exported in
2014. This reflects the fact that, while over 90% of these minerals still come from China,
it only has about one-third of the global resource.
IV. Commentary of Issues Related to Rare Earth Production in Mongolia
There currently are no rare earth mines under development in Mongolia. However, the
recent significant increases of rare earth prices have caused exploration for these
elements to increase significantly around the world. Further, one of the larger mines in
the world, Bayan Odo, is in Inner Mongolia not too far from the border with Mongolia.
For these reasons, it is worth examining the possible impacts and potential development
of these resources.
IV.A. Current State of Affairs
This section reviews some recent highlights related to the Mongolian mining industry.
(Others papers in this volume discuss this in greater depth.) One important reason for the
focus on mining is that a very high proportion of all Mongolian exports are minerals-
related.
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Issues related to the change in government leadership and the price of minerals
has caused the Mongolian economy to slow down. A few years ago Mongolia had one of
the highest GDP growth rates in the world. Recently, as is well known, this has dropped
substantially, accompanied by decreases in foreign investment.
Oyu Tolgo is a very large copper/gold development in the Gobi Desert that is not
too far from the border with China. As a consortium led by Rio Tinto (and subsidiaries)
and the Mongolian government, it is anticipated to significantly impact the overall export
of minerals form Mongolia. Recently, because of governmental change, talks about how
to move forward on the development of the underground resources have stalled. The
current open pit operations are projected to produce approximately 175,000 tons of
copper and 600,000 ounces of gold in 2015. This reduction in production is mainly due
to the drop in these resource prices on the world market.
Another mining related initiative that the Mongolia government has taken is to
allow the construction of a rail line that will allow 100 million tons/year of coal to be
shipped from the Ovoot Coking Coal Project. This project is the second largest
agreement that the Mongolian government has with China. In addition, in northern
Mongolia, the biggest coal project in the country, Tavar Tolgoi, continues its
development. It should be noted that on-going development of coal resources at new
locations, such as Berkh Uul, now require more stringent environmental reviews.
While there has been no development of possible rare earth resources, it should be
noted that in addition to the Big Three (coal, gold, copper), there are other resource
developments in Mongolia. The Chinese are developing the Selenge iron ore project. A
Chinese company has also struck oil at Khanbogd. There has also been development of
molybdenum and uranium resources by Japanese companies. These recent events
demonstrate that, if rare earth resources are economically recoverable, consortia will
want to do so in Mongolia.
IV.B. Implications to Mongolia’s Economy and Society
As there are numerous of stories related to improper use of funds in resource-rich nations,
this is a cautionary tale. The Mongolian government will need to develop policies that
address two economic issues. First, with future resource development, there will always
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be global boom/bust cycles. The government must develop policies that will shield the
country from the worst economic impacts of these events. Second, all minerals are
depletable resources. Thus, policies must be developed that should include a severance
tax, as is the case in many states in the United States for resources such as oil and coal.
Or, as China has recently proposed, a resource tax may be more appropriate.
Proactive policies, such as these can further bolster organizations such as Erdenes
Tavan Tolgoi (ETT). As part of governmental policy to give each citizen some funds as
a result of resource development, ETT will give each citizen 536 shares in mining stock.
Therefore, the government must examine which of these policies will be best for its
citizens and which will go the farthest in ameliorating the downsides of the overall
development of resources. In doing this correctly, Mongolia can emulate other small
population countries, such as Qatar in terms, of wealth distribution.
There are downsides associated with the development of mineral resources. First,
one must take into account the overall aspects of the country. Poorly structured policies
will simply result in a significant bifurcation of wealth. This could leave the poverty-
stricken at a 40%, while allowing a few citizens to amass large amounts of wealth. All of
this while there has been a significant rise in inflation.
Two other downsides must be considered. Traditional industries in Mongolia are
important, not only for export, but for a continuation of Mongolian culture. One of these
industries is the production of cashmere garments. The cost of labor has increased over
the past few years due to the competition for workers vis-a-vis the mining industry. In
addition, the costs of raw cashmere have tripled over the recent years, in part due to
inflation. Downsizing the cashmere industry would impact the country’s way of life.
Finally, the development of mines throughout the country has both a direct and an
indirect impact on the environment. Indirectly, due to the increased concentration of
people and wealth in Ulaan Baator, air pollution has grown to almost unmanageable
levels. The capital city is now considered one of the more polluted cities in the world.
Mining development and operations require large amounts of water. There are
efforts to develop “fossil water” resources. These are deep aquifers that are not used by
the population, since they are saline. The produced water must be treated for use in the
mines. Otherwise, water resources for Mongolian citizens will become depleted. This
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will be particularly problematic for herders living in arid zones close to where many of
these mines are either under development or in operation.
V. Co-Production of Rare Earths with Coal Mining
Published work suggests that it might be possible to economically obtain rare earths as
part of co-production with coalmines. (Triplehorn and Bohor; Long et. al.) While their
analysis is specific to the United States, it is possible that similar opportunities exist in
Mongolian coalmines.
It is known that volcanic eruptions contribute distinctive features to coal mines.
This was first observed in western United States coalmines, but is also shown to be true
for eastern United States coalmines. This is based upon a review that Triplehorn and
Bohor did of the US Geological Survey Coal Quality Data Base. Figure 7 shows there are
a number of areas in the eastern United States that have concentrations of rare earth
elements (plus yttrium) greater than 1000 ppm. Typically, rare earth extraction is
economically appropriate when concentrations are at least 1.5% of the mineral location.
Analysis for co-production with coal shows that rare earth extraction may be
economically feasible at concentrations as low as 0.3%.
V. Summary
This paper was developed with the idea that there may be rare earth mineral resources in
Mongolia. It is reasonable to consider these resources being located in Mongolia as
similar resources are being developed just across the country’s border by China. This
development would allow for diversity of resources rather than being dependent on only
a few as is presently the case. The importance of these resources will be increasing over
the coming years. However, the government must remain vigilant as there are clear
downsides with continued development of depletable resources and their potential
impacts on Mongolian society, economy, and environmental resources.
References
Hurd, Alan, Kelley Ronald, Eggert, Roderick and Lee, Min Ha Energy-Critical Elements for Sustainable Development MRS Bulletin 37 (04) April 2012 405-410.
15
Long, K.R., Van Gosen, B.S., Foley, N.K., and Cordier, Daniel, (2010) The principal rare earth elements deposits of the United States—A summary of domestic deposits and a global perspective. U.S. Geological Survey Scientific Investigations Report 2010–5220, 96 p. Available at http://pubs.usgs.gov/sir/2010/5220/. Posted November 2010.
Moss, R.L. Tsimas, E. Kara H. Willis P. and Kooroshy, J. Critical Metals in Strategic Energy Technologies (2011) Report. The European Commission Joint Research Centre Institute for Energy and Transport.
Parthemore, Christine Elements of Security: Mitigating the risks of U.S. dependence on critical minerals. Report. Center for a New American Security May 2011.
Resnick Institute Report, Critical materials for sustainable energy applications. California Institute of Technology September 2011.
Triplehorn, Don and Bohor, Bruce (undated) Volcanic ash layers in coal: origin, distribution, composition, and significance. University of Alaska- Fairbanks and United States Geological Service
United States Department of Energy “Critical Materials Strategy” December 2011.
Figures
Figure 1. Heavy Rare Earth Metal Prices, 2001 to 2011 (CMS, DOE, p.46)
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Figure 2. Light Rare Earth Metal Prices, 2001 to 2011 (CMS, DOE, p.46)
Figure 3. Rare Earth Supplies at Risk – Current (CMS, DOE, p.4)
Figure 4. Rare Earth Supplies at Risk – to 2025 CMS, DOE, p.4)
17
Figure 5: Locations of Coal Mines in the United States Where Rare Earth Concentrations Exceed 1000 ppm (USGS Coal Database)
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