EPA 600/R-12/572 | December 2012 | www.epa.gov/ord
United States
Environmental Protection
Agency
Rare Earth Elements: A Review of Production,
Processing, Recycling, and Associated
Environmental Issues
Jfflfif-4-n*-'
- -r~'
With Permission of AlanM1/CC-BY-SA-3.
Office of Research and Development
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EPA/600/R-12/572
December 2012 Revised
Rare Earth Elements: A Review of Production,
Processing, Recycling, and Associated
Environmental Issues
Engineering Technical Support Center
Land Remediation and Pollution Control Division
National Risk Management Research Laboratory
Office of Research and Development
Cincinnati, OH
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Foreword
The U.S. Environmental Protection Agency (EPA) is charged by Congress with
protecting the Nation's land, air, and water resources. Under a mandate of national
environmental laws, the Agency strives to formulate and implement actions
leading to a compatible balance between human activities and the ability of natural
systems to support and nurture life. To meet this mandate, EPA's research program
is providing data and technical support for solving environmental problems today
and building a science knowledge base necessary to manage our ecological
resources wisely, understand how pollutants affect our health, and prevent or
reduce environmental risks in the future
The National Risk Management Research Laboratory (NRMRL) is the Agency's
center for investigation of technological and management approaches for
preventing and reducing risks from pollution that threaten human health and the
environment. The focus of the Laboratory's research program is on methods and
their cost-effectiveness for prevention and control of pollution to air, land, water,
and subsurface resources; protection of water quality in public water systems;
remediation of contaminated sites, sediments, and ground water; prevention and
control of indoor air pollution; and restoration of ecosystems. NRMRL collaborates
with both public and private sector partners to foster technologies that reduce the cost
of compliance and to anticipate emerging problems. NRMRL's research provides
solutions to environmental problems by: developing and promoting technologies that
protect and improve the environment; advancing scientific and engineering
information to support regulatory and policy decisions; and providing the technical
support and information transfer to ensure implementation of environmental
regulations and strategies at the national, state, and community levels.
Rare earth elements (REEs) are a group of 15 chemical elements in the periodic
table, specifically the lanthanides. Two other elements, scandium and yttrium, have
a similar physiochemistry to the lanthanides, are commonly found in the same
mineral assemblages, and are often referred to as REEs. Although relatively
abundant in the earth's crust, they rarely occur in concentrated forms, making them
economically challenging to obtain. These elements comprise critical components
of many of our modern-day technological devices and everyday electronics. REE
demand in the United States is projected to increase given global demand for green
and sustainable products in energy, military, and manufacturing uses. China has
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been providing 95% of REEs worldwide but the United States is increasing its
interest in exploring and mining REEs.
Mining in the natural environment comprises the majority of acquisition of REEs
and, like most mining operations, results in a large quantity (greater than 90
percent) of excess and un-used materials. At present, there is no formal EPA or
national strategy existing for managing resource development and mitigation of
impacts during the acquisition, use, and disposal of REEs. The purpose of this
document has been to compile current information to develop a strategy for
managing REE resources and reducing potential environmental impacts. Though
the vast majority of information in this report is current, as noted in this report,
mining and extraction of REEs is dynamic. For example, we recognize global
market prices for REE's have declined since mid-2011 when this report was
completed. Therefore, some details regarding who is producing what and where may
have changed between the time when: (1) data collection as part of the literature
search for this report was completed in July 2011, and (2) the report's contract was
completed in September 2011, and (3) its subsequent publication in 2012.
This document provides a description of the many environmental facets of the rare
earth mining and disposal issues, and explains the need for a national strategy for
the continued supply of required REEs in future technological development
nationally and internationally, and for the reuse of these materials versus disposal
in landfills.
Cynthia Sonich-Mullin, Director
National Risk Management Research Laboratory
IV
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Abstract
Rare earth elements (REEs) are a group of 15 chemical elements in the periodic
table, specifically the lanthanides. Two other elements, scandium and yttrium, have
a similar physiochemistry to the lanthanides, are commonly found in the same
mineral assemblages, and are often referred to as REEs. REEs have not been
mined in the United States for about 20 years, and prior to that time, the amount of
mining was minimal compared to coal and hard rock mining. The increased use of
REEs in magnets, modern electronics and in a variety of commercial products has
led to a shortage of REEs for production purposes. Currently, REEs are being
disposed in large quantities rather than being recovered and reused.
The purpose of this report is to serve as a technical information resource to policy
makers and other stakeholders who are concerned with the potential environmental
and health effects and impacts that can be identified across the REE supply chain.
RTI conducted a search of the technical literature and other Internet sources related
to each segment of the supply chain, including recent initiatives of U.S.
government agencies that document issues associated with REE production,
processing, manufacturing, end uses, recycling, and health/ecological effects.
Information contained in this report also draws upon past domestic and
international experience, as appropriate.
Compared to coal and other hardrock mining, the scope of REE mining has always
been very small, both in the U.S. and globally. No major REE mining operations
have been conducted in the U.S. since 1995. Mining and processing activities have
the potential to create a number of environmental risks to human health and the
environment. The severity of these risks is highly variable between mine and mine
plant operations. The contaminants of concern will vary depending on the REE-
mineral ore, the toxicity of the contaminants from the waste rock, ore stockpiles,
and process waste streams. The mobility of contaminants will be controlled by the
characteristics of the geologic, hydrologic, and hydrogeologic environments where
the mine is located, along with the characteristics of the mining process and waste
handling methods.
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Acknowledgements
David J. Reisman (retired), Director of the Office of Research and Development
(ORD), Engineering Technical Support Center (ETSC) and Robert J. Weber of the
EPA ORD, Office of Science Policy (OSP) served as co-principal investigators on
this project. They would like to acknowledge the exemplary contribution from the
RTI International team led by Coleen Northeim and consisting of Scott Guthrie,
James Cunningham, and Susan Wolf. Without their assistance this document
probably would not have been developed. The draft and final versions of this
document were prepared under the ORD STREAMS contract (EP-C-05-060), Task
35.
Throughout the development of the document, monthly teleconference calls took
place among members of the REE work group and was comprised of the following
individuals who gratefully gave their time and expertise voluntarily. Dr. Michael
McKittrick of ORD National Center for Environmental Research (NCER), Dr.
Robert Seal of the U.S. Geological Survey, Dr. David Drake of EPA Region 7, and
Kathleen Graham of ORD/OSP in EPA Region 8 played a key role in developing
this issue over less than a year. Additionally, special thanks go out to Jim Sims and
Scott Honan of MolyCorp, Inc. for providing input on their current REE mining
and resource recovery processes. We would also like to acknowledge the reviews
and constructive comments provided by Karen Pollard and William Schoenborn of
the Office of Solid Waste and Emergency Response, Dr. Anne Riederer of the
ORD Assistant Administrator's office, Diana Bless (ORD), and Holly El wood of
the Office of Pesticide Programs and Toxic Substances. Finally, we would also like
to thank our current (and former) immediate management, Albert Venosa and
Randy Parker in EPA ORD/NRMRL, Maggie LaVay of EPA ORD/OSP, Nigel
Fields, formerly of EPA ORD/OSP (now with DOI/NPS), and Gene Gunn and Dr.
David Drake in EPA Region 7, for their support of our work.
VI
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Table of Contents
List of Acronyms xi
1. Introduction 1-1
1.1 Background 1-1
1.2 Report Organization 1-1
2. Introduction to Rare Earth Elements 2-1
2.1 Abundance of REEs in Earth's Crust 2-1
2.2 Geologic Environments of REEs 2-3
2.3 Applications of REEs 2-6
2.4 REE Global Economic Supply and Demand 2-7
3. Life-Cycle Stages of Rare Earth Mineral Mines 3-1
3.1 Active REE Mining 3-2
3.2 REE Ores 3-3
3.3 Mining Permitting and Life-Cycle 3-4
3.3.1 Permitting Requirements for New Rare Earth Mines 3-4
3.3.2 Mining Life Cycle 3-5
3.4 Characteristics of Mining Waste Sources 3-19
3.4.1 Soil Storage Piles 3-20
3.4.2 Overburden 3-20
3.4.3 Ore and Subeconomic Ore Storage 3-20
3.4.4 Waste Rock 3-21
4. Resource Processing 4-1
4.1 Bevill Amendment 4-4
4.2 Beneficiation Processes 4-4
4.2.1 Bastnasite Beneficiation 4-5
4.2.2 Monazite/Xenotime Beneficiation 4-5
4.3 Extraction Processes 4-5
4.3.1 Bastnasite Extraction 4-6
4.3.2 Monazite/Xenotime Extraction 4-7
4.3.3 Tailings Extraction 4-7
4.4 Reduction Processes 4-7
4.5 Potential Environmental Impacts 4-7
4.5.1 China Legacy 4-8
4.5.2 United States Legacy 4-8
5. Rare Earth Element Recovery/Alternative Material Use 5-1
5.1 Introduction 5-1
5.2 Recycle Processing Steps 5-3
5.2.1 Collection 5-5
5.2.2 Dismantling/Preprocessing 5-5
5.2.3 Processing 5-7
5.3 Commercial REE-Recycling Applications 5-8
5.4 Environmental Implications of Recycling REEs 5-10
5.5 Research on Alternatives to REEs 5-10
5.6 Emerging Policies/Programs to Support REE Recycling 5-11
vn
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6. Potential Human Health and Ecological Risks of Production, Processing, and Recycling of
REEs 6-1
6.1 Generalized Conceptual Site Model for Environmental Risk from a REE Mine and
Mineral Processing Plant 6-2
6.1.1 Contaminant Release and Transport 6-6
6.1.2 EPA Studies of HardrockMine Environmental Risks 6-10
6.2 Pathway and Exposure Scenarios for REE-Recycling 6-14
6.3 Documented Human Health and Ecological Effects from Exposure to REE 6-15
7. Summary, Key Findings from Literature Review, and Potential Next Steps 7-1
7.1 Summary 7-1
7.2 Key Findings 7-2
7.3 Suggested Next Steps 7-3
8. References 8-1
Appendices
A Selected Chemical Properties of REEs
B Locations of REE-Producing Mines and REE-Containing Mineral Deposits in the U.S.
C Process Flow Diagrams for Extraction and Processing Operations
Of
2-1. Periodic table of the elements showing the division between LREES and HREES
(Schuleretal.,2011) 2-3
2-2. Map showing occurrences of REEs, by rock type (adapted from multiple sources, see
Appendix B) 2-5
2-3. In-use stocks of selected REEs by specific application or industry (in gigagrams) (Du and
Graedel,2011) 2-7
2-4. Global production of rare earth oxides (Du andGraedel, 2011) 2-8
3-1. Molycorp Minerals rare earth mine, Mountain Pass, California 3-3
3-2. Typical time frame for amine project 3-12
3-3. Aerial image of Pea Ridge magnetite mine, Missouri 3-16
3-4. Conventional hardrock deposit mining process and wastes emissions 3-22
3-5. Conventional placer deposit processing and wastes emissions 3-22
4-1. Conventional placer deposit resource processing and potential wastes emissions 4-2
4-2. Conventional hardrock resource processing and potential wastes emissions 4-3
4-3. Anticipated Molycorp Mountain Pass mine water reclamation process and potential
waste emissions 4-10
5-1. Representative rare earth oxide prices from 2007-2010 (The 2007-2010 figures are
fourth-quarter [Q4] average prices. The 2011 numbers represent spot prices on
February 25) 5-2
5-2. REE recycling steps and waste emissions 5-4
5-3. Left: Dismantling table with pneumatic tools used for manual dismantling of hard disks
Right: Components resulting from the process and including REE-containing magnets
(upper right corner) (Schluep etal., 2009) 5-6
6-1. Generic above-ground hardrock mine conceptual site model and exposure pathways (U.S.
EPA, 2009a) 6-5
6-2. Sources of potential human exposures resulting from mining operations (U.S. EPA
ORCR,2010) 6-11
6-3. Sources of potential exposures of current and future ecological receptors resulting from
mining operations (U.S. EPA OCRC, 2010) 6-12
6-4. "Low-tech" gold recycling in Bangalore/India (Schluep etal., 2009) 6-14
Vlll
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of
2-1. Abundance of Elements in the Earth's Crust (Wedepohl, 1995) 2-2
2-2. Rare Earth Elements, Their Applications, and Potential Supply Issues for Clean-Energy
Technologies 2-6
2-3. Distribution of REEs by End Use in 2008 (U.S. DOI/USGS, 2010) 2-7
2-4. Current Activities at Selected, Potential U.S. REE Mines 2-9
3-1. Numbers of Existing Mines by State Where Potential REE Resources Have Been
Reported (see Appendix B for References) 3-18
4-1. Rare earth extraction methods (adapted from Meyer and Bras, 2011) 4-6
4-2. Rare Earth Processing Waste Streams and Their Hazardous Waste Potential (U.S. EPA,
1991) 4-8
5-1. Recycling Operations, Technologies Utilized, Current Status, and Benefits 5-8
6-1. Summary of pollutants, impacted environmental media, emission sources, and activity
associated with REE mining, processing, and recycling 6-2
6-2. Frequency of Various Types of Impacts from CERCLA Sites (U.S. EPA, 1995) 6-13
6-3. REEs and Available RfCs and RfDs 6-17
6-4. Selected Toxicity and Epidemiology Findings for Rare Earth Elements, 6-17
6-5. Selected Biomonitoring Findings for Rare Earth Elements 6-22
6-6. Selected Ecotoxicity Findings for Rare Earth Elements 6-25
IX
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Rare Earth Elements Review
List of Acronyms
List of Acronyms
AMD acidic or alkaline mine drainage
ARD acid rock drainage
BLM Bureau of Land Management
CLERCA Comprehensive Environmental Response, Compensation and Liability Act
CO2 carbon dioxide
CR3 Center for Resource Recovery and Recycling
CREI Colorado Rare Earths Incorporated
CSM Conceptual Site Model
DoD U.S. Department of Defense
DOE U.S. Department of Energy
EPA U.S. Environmental Protection Agency
EIS environmental impact statement
ES environmental study
EU European Union
HC1 hydrochloric acid
ISL in situ leach
HREE heavy rare earth element
LCD liquid crystal display
LREE light rare earth element
MIW mining-influenced water
NaOH sodium hydroxide
NEDO New Energy and Industrial Technology Development Organization
NEPA National Environmental Policy Act
NIMS National Institute for Material Science
NMD neutral mine drainage
NORM naturally occurring radioactive material
ORD Office of Research and Development
PCB polychlorinated biphenyl
PFD neutral mine drainage
RCRA Resource Conservation and Recovery Act
REACT Rare Earth Alternatives in Critical Technologies
REE rare earth element
REM rare earth metal
XI
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Rare Earth Elements Review List of Acronyms
REO rare earth oxide
RESTART Act Rare Earths Supply-Chain Technology and Resources Transformation Act of 2010
RO reverse osmosis
RTI RTI International
TDS total dissolved solids
TENORM technologically enhanced, naturally occurring radioactive material
UN United Nations
UNEP United Nations Environment Programme
USGS U.S. Geological Survey
VOC volatile organic compounds
xn
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Rare Earth Elements Review Section 1 - Introduction
1. Introduction
1.1 Background
Rare earth elements (REEs) are a group of 15 chemical elements in the periodic table, specifically the
lanthanides. Two other elements, scandium and yttrium, have a similar physiochemistry to the
lanthanides, are commonly found in the same mineral assemblages, and are often referred to as REEs.
Although relatively abundant in the earth's crust, REEs rarely occur in concentrated forms, making them
economically challenging to obtain. These elements constitute critical components of many important
technologies and products, such as hybrid vehicles, wind turbines, and cell phones. Given this global
demand for green and sustainable products in energy, military, and manufacturing industries, REE
demand in the United States and throughout the world is projected to increase.
In recent years, China has been providing 95 to 97 percent of REEs worldwide. Because China has
demonstrated its ability to control and limit REE exports, it is crucial that the United States expand its
ability to obtain REE resources. Mining in the natural environment is the primary means of REE
acquisition; however, it results in a large quantity (greater than 90 percent) of excess and unused materials
and other environmental impacts. If the United States is to ensure a continuous supply of REEs,
responsible mining practices will need to be developed and enhanced. Additionally, effective recycling,
recovery, and reuse of spent consumer and industrial products may reduce the need to develop new
mineral resource areas.
To obtain up-to-date information on the environmental aspects and potential impacts of REE mining,
recovery, recycling, and reuse, the U.S. Environmental Protection Agency (EPA) Office of Research and
Development's (ORD's) Engineering Technical Support Center contracted with RTI International (RTI)
to conduct a literature review and to develop this report.
The purpose of this report is to serve as a technical information resource to policy makers and other
stakeholders who are concerned with the potential environmental and health effects and impacts that can
be identified across the REE supply chain. This document is not a life-cycle assessment or a risk
assessment. However, it does, to the extent possible based on anticipated, proposed, or past practices,
attempt to identify environmental compartments (i.e., aquatic environment, terrestrial environment, and
air) that may be at risk and the corresponding environmental loads (e.g., raw material consumption, air
emissions, water discharges, wastes), when that information is available in the literature or an association
can be made with anticipated, current, and past practices.
RTI conducted a search of the technical literature and other Internet sources related to each segment of
the supply chain, including recent initiatives of U.S. government agencies (i.e., U.S. Geological Survey
[USGS], U.S. Department of Energy [DOE], and the EPA) that document issues associated with REE
production, processing, manufacturing, end uses, recycling, and health/ecological effects. Information
contained in this report also draws upon past domestic and international experience (United Nations
Environment Programme [UNEP]), as appropriate.
1.2 Report Organization
This report is organized into eight sections and appendices, as follows:
Section 1 provides the overall background for the project.
Section 2 provides general background information on REEs, including information on their uses,
their reserves in the United States, and their current supplies and demand worldwide.
Section 3 provides information on REE mining operations and potential environmental impacts.
1-1
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Rare Earth Elements Review Section 1 - Introduction
* Section 4 focuses on beneficiation and processing, along with associated environmental impacts,
and includes information related to the Molycorp Minerals mine in Mountain Pass, California,
which is scheduled to resume full-scale production in 2012.
« Section 5 summarizes the steps associated with REE recycling and provides information on the
status of commercial recycling processes. This section also includes information on potential
alternatives to REEs and a summary of new policies and programs that will impact future
recycling.
« Section 6 summarizes information from the literature on health and environmental issues
associated with REEs.
« Section /presents a summary of the report information, a list of key findings, and recommended
next steps.
« Section 8 provides a reference list.
« Appendix A describes selected chemical properties of REEs; Appendix B provides a table with
locations of REE-producing mines and REE-containing mineral deposits in the United States; and
Appendix C presents process flow diagrams of REE extraction and processing operations.
This report is envisioned as a starting point for the ORD to investigate potential environmental and health
issues concerning the production, processing, recycling, recovery, and life cycle of REEs. This report is
an overview intended to set the framework for these issues and should not be viewed as a comprehensive
document on REEs and the mining of those materials.
1-2
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Rare Earth Elements Review Section 2 - Introduction to Rare Earth Elements
2. Introduction to Rare Earth Elements
For the purposes of this report, the series of 15 lanthanide metals, plus scandium and yttrium, have been
designated as REEs; however, it should be noted that other elements also are sometimes referred to as REEs.
Rare earth oxides (REOs), and rare earth metals (REMs). While these elements are widely dispersed and
generally common in nature, minable concentrations of REEs are less common than for most other metal ores.
Rare earths have become important in modern commercial and industrial processing and products. Metallurgical
processing, alloying, and electronics applications (e.g., cell phones, computer components, electric motors,
specialty glass and lenses) represent the most significant uses of REEs. In addition, due to the dependence on
several of these elements for military applications, REEs are considered a national strategic resource. Analysis of
the future supply and demand for each of the REEs indicates that, by 2014, global demand could exceed 200,000
tons per year, which would exceed current production by over 75,000 tons per year. It is reported that if the new
mines under development are able to meet their projected production levels, world-wide demand for REEs will be
met from these new sources.
The International Union of Pure and Applied Chemistry, an organization devoted to maintaining
international consistency for chemical nomenclature, has identified the 15 transition metals from the
periodic table of the elements with atomic numbers 57 (lanthanum) through 71 (lutetium) as lanthanides
or lanthanoids. These 15 elements share common physiochemical properties and are listed below:
Lanthanum (57La) Samarium feSm) Holmium (6?Ho)
Cerium (58Ce) Europium (esEu) Erbium (6sEr)
Praseodymium (59Pr) Gadolinium (64Gd) Thulium (egTm)
Neodymium (eoNd) Terbium (esTb) Ytterbium (?oYb)
Promethium (6iPm) Dysprosium (66Dy) Lutetium (7iLu).
Due to their similar physiochemistry, these lanthanides often occur together as elemental constituents of
their host minerals. Two other metals commonly found in association with lanthanides in the same
mineral assemblages are the following:
Scandium (2iSc)
Yttrium (39Y).
These two metals also have physiochemical characteristics that are very similar to the lanthanides.
2.1 Abundance of REEs in Earth's Crust
Together, the lanthanides, yttrium, and scandium are commonly referred to as REEs or REMs, although
this is a misnomer since most of the REEs are common mineral constituents as compared with other metal
elements. The term "rare" is a carryover from metallurgical chemists from around the 1940s (Gupta and
Krishnamurthy, 2004). The metallurgical processes needed to isolate the individual metal species are
complex, and early technology prevented commodity-level production. As a result, lanthanide metals or
metal oxides (i.e., REOs) were difficult to obtain and thus are considered rare. The abundance of REEs in
the earth's crust relative to other common metals is presented in Table 2-1; these abundances from
Wedephol (1995) are only one of several interpretations, but those presented here are generally
representative. As shown in the comparison, the content of lanthanides relative to other REEs in rock-
forming minerals is not rare at all.
2-1
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Rare Earth Elements Review
Section 2 - Introduction to Rare Earth Elements
Table 2-1. Abundance of Elements in the Earth's Crust (Wedepohl, 1995)
Elements
Nickel (28Ni)
Zinc (soZn)
Copper (29Cu)
Cerium (ssCef
Lanthanum (syLa)
Cobalt (27Co)
Neodymium (soNd)
Yttrium (39Y)
Scandium (2180)
Lead (82Pb)
Praseodymium (ssPr)
Thorium (goTh)
Samarium <62Sm)
Gadolinium (64Gd)
Dysprosium (ssDy)
Tin (soTn)
Erbium (ssEr)
Ytterbium (70Yb)
Europium (ssEu)
Holmium (syHo)
Terbium (ssTb)
Lutetium (71 Lu)
Thulium (ssTm)
Silver (47 Ag)
Gold (7gAu)
Promethium (siPm)
Crustal Abundance
(parts per million)
90
79
68
60.0
30.0
30
27.0
24.0
16.0
10
6.7
6
5.3
4.0
3.8
2.2
2.1
2.0
1.3
0.8
0.7
0.4
0.3
0.08
0.0031
ID'18
Lanthanides (lanthanoids), scandium,
in boldface type.
and yttrium are presented
Following a common pattern within the periodic table, the lanthanides with even atomic numbers are
more common in nature. Additionally, early on, geochemists observed a pattern in the occurrence and
crustal abundance of some lanthanides. Lanthanides with lower atomic numbers were noted to be more
common ionic constituents in REE mineral ores and, in general, occurred in greater abundance than the
lanthanide elements with higher atomic numbers.
These observed trends in crustal abundance among the geochemical models suggest a divide between
light and heavy lanthanide-enriched minerals. Although variation exists, one example of an REE
classification is presented in Figure 2-1 and shows the division between light REEs (LREEs) and heavy
REEs (HREEs) (Schuler et al., 2011). Some investigators classify gadolinium and dysprosium as
medium-weight lanthanides due to their physiochemical properties. Additional information on REE
chemistry and other classifications is provided in Appendix A.
2-2
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Rare Earth Elements Review
Section 2 - Introduction to Rare Earth Elements
Figure 2-1. Periodic table of the elements showing
the division between LREEs and HREEs (Schuleret al., 2011).
The elemental forms of REEs that are extracted from mineral ores, as oxides (i.e., REOs), are iron-gray to
silvery lustrous metals that are typically soft, malleable, ductile, and usually reactive, especially at
elevated temperatures or when finely divided. The REEs' unique properties are used in a wide variety of
applications. For example, magnets made with REEs are much more powerful, weigh less, and can be
made smaller than conventional magnets. Some REEs also have high electrical conductivity, can
withstand extreme heat, and give off intense white light when heated.
In aquatic systems, REEs typically occur in the trivalent state. However, cerium can be present as Ce4+
and europium can occur in both the divalent and trivalent states. The chemical behaviors of all REEs are
very similar, but smooth variations can be attributed to their atomic number and ionic radii, which are
inversely correlated. These attributes make REEs well suited to the study of processes such as
complexation, sorption, precipitation, and the formation of colloids (Merten and Biichel, 2004).
2.2 Geologic Environments of REEs
REEs do not occur as native elemental metals in nature, only as part of the host mineral's chemistry. For
this reason, the recovery of REMs must be accomplished through a complex processing method
(described in Section 4) to chemically break down the minerals containing the REEs.
Despite more than 200 known REE-bearing minerals, only three are considered to be the principal REE
mineral ores most feasible for the extraction of REMs: bastnasite, xenotime, and monazite (Gupta and
Krishnamurthy, 2004), as described below:
Bastnasite, the most abundant among the three REE mineral ores, is a carbonate mineral found
mainly enriched in LREEs (e.g., cerium, lanthanum, and yttrium). Bastnasite is found in vein
deposits, contact metamorphic zones, and pegmatites. It forms in carbonate-silicate rocks
occurring with and related to alkaline intrusions (e.g., Mountain Pass mine).
The two phosphate minerals, xenotime and monazite, can occur together, but crystallize in
different temperature and pressure regimes from a similar igneous environment. While these
2-3
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Rare Earth Elements Review Section 2 - Introduction to Rare Earth Elements
minerals can contain any of the REEs (i.e., HREEs or LREEs), enrichment of specific REEs is
variable and a function of the temperature and pressure regime in which they formed. Monazite
commonly occurs in placer deposits; xenotime can occur along with monazite, but generally
occurs as a more minor constituent of these types of deposits. Deposits of phosphate rare earth
ores provide the opportunity to produce co-products of phosphates and REEs. Thorium and
uranium may also be taken advantage of and produced as a co-product, or may represent a
significant management challenge. A further description of these two minerals follows:
Monazite is generally enriched with the LREEs cerium, lanthanum, and neodymium, but can
also contain HREEs, particularly yttrium (Ni et al., 1995). The predominance of LREEs is
due to the lower crystallization temperature and pressures of this mineral; however, it
typically contains more HREEs than bastnasite ore deposits. It occurs in acidic igneous rocks
(primarily pegmatites), metamorphic rocks, and some vein deposits. Monazite is resistant to
weathering and occurs in many placer deposits as the host rocks are eroded. Thorium may
also be associated with monazite in various amounts.
- Xenotime crystallizes under higher temperatures and pressures than those of monazite;
therefore, its crystalline structure more readily accommodates a higher ratio of HREEs
(terbium through lutetium, and yttrium) than is commonly found in monazite. It is primarily a
yttrium phosphate mineral and occurs as a minor constituent of granitic and gneissic rocks.
Although not always present in significant quantities, uranium and thorium can also occur as
constituents of xenotime.
There are two other important REE-containing minerals in the United States (Long et al., 2010)
including:
- Euxenite which contains yttrium, erbium, and cerium. It is found mostly in placer deposits in
Idaho, and occurs as a tantaloniobates (e.g., minerals where Ta and Nb form the compound)
of titanium, rare earths, thorium, and uranium.
Allanite is an epidote mineral and contains cerium, lanthanum, and yttrium. It occurs in
igneous, metamorphic, and hydrothermal environments and is disseminated in pegmatite or
occurs in vein deposits.
These five minerals are considered to represent the principal occurrences and the potentially more
significant REE reserves in the United States (USGS, 2010). However, many other minerals containing
REEs do occur, and deposits of these minerals could be found in the United States and prove to be viable
for mining. It is also not uncommon for REEs to be produced as a coproduct or byproduct of other
mineral production. A list of minerals that commonly contain REEs is presented in the USGS report by
Long etal. (2010).
The principal future domestic supply of REEs is one carbonatite formation in Mountain Pass, California.
Other common and potentially viable deposit types containing almost exclusively the two phosphate
REE-bearing minerals (monazite and xenotime) are most common as placer ores that originated from the
erosion of pegmatite granites and related gneisses. The general occurrences of rock types that host REE-
containing mineral ores in the United States are shown in Figure 2-2.
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Rare Earth Elements Review
Section 2 - Introduction to Rare Earth Elements
Uok;in Mountain
(Ross- Adams)
l-r
0
REE Deposit Type
Q Placer (Alluvial, Palroplacer, Shoreline, Fluvial)
r. Igneous-Affiliated (Including pegmatites and veins)
O t'arbonatite
rj Phcispliates
4 Alkaline-Igneous
A jVletamnrphic
3 11\ th olIurniLiI Fe-o\ide
« Uranium l)i posits
a Other ISA Federal Lands
F.PA Regions
sea
Miles
1.000
Figure 2-2. Map showing occurrences of REEs, by rock type (adapted from multiple sources, see Appendix B).
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Rare Earth Elements Review
Section 2 - Introduction to Rare Earth Elements
2.3
The REEs and their key applications are identified in Table 2-2. Also included in the table are the (1) key
categories of uses by the U.S. Department of Defense (DoD) and (2) DOE's classification of the elements
determined to be critical or near critical due to projected supply risks and their importance to clean-energy
technologies. Figure 2-3 graphically presents additional information on the specific types and quantities
of REEs that were reported as being in use in various products in 2007. Table 2-3, taken from USGS
data, provides a breakdown by industrial application on the uses of REEs in the United States in 2008.
Table 2-2. Rare Earth Elements, Their Applications, and Potential Supply Issues
for Clean-Energy Technologies
Element
Scandium
Yttrium
Lanthanum
Cerium
Praseodymium
Neodymium
Promethium
Samarium
Europium
Gadolinium
Terbium
Dysprosium
Holmium
Erbium
Thulium
Ytterbium
Lutetium
Applications
Metal alloys for the aerospace industry.
Ceramics; metal alloys; lasers; fuel efficiency; microwave communication for satellite industries;
color televisions; computer monitors; temperature sensors. Used by DoD in targeting and
weapon systems and communication devices. Defined by DOE as critical in the short- and mid-
term based on projected supply risks and importance to clean-energy technologies.
Batteries; catalysts for petroleum refining; electric car batteries; high-tech digital cameras; video
cameras; laptop batteries; X-ray films; lasers. Used by DoD in communication devices. Defined
by DOE as near critical in the short-term based on projected supply risks and importance to
clean-energy technologies.
Catalysts; polishing; metal alloys; lens polishes (for glass, television faceplates, mirrors, optical
glass, silicon microprocessors, and disk drives). Defined by DOE as near critical in the short-
term based on projected supply risks and importance to clean-energy technologies.
Improved magnet corrosion resistance; pigment; searchlights; airport signal lenses;
photographic filters. Used by DoD in guidance and control systems and electric motors.
High-power magnets for laptops, lasers, fluid-fracking catalysts. Used by DoD in guidance and
control systems, electric motors, and communication devices. Defined by DOE as critical in the
short- and mid-term based on projected supply risks and importance to clean-energy
technologies.
Beta radiation source, fluid-fracking catalysts.
High-temperature magnets, reactor control rods. Used by DoD in guidance and control systems
and electric motors.
Liquid crystal displays (LCDs), fluorescent lighting, glass additives. Used by DoD in targeting
and weapon systems and communication devices. Defined by DOE as critical in the short- and
mid-term based on projected supply risks and importance to clean-energy technologies.
Magnetic resonance imaging contrast agent, glass additives.
Phosphors for lighting and display. Used by DoD in guidance and control systems, targeting and
weapon systems, and electric motors. Defined by DOE as critical in the short- and mid-term
based on projected supply risks and importance to clean-energy technologies.
High-power magnets, lasers. Used by DoD in guidance and control systems and electric motors.
Defined by DOE as critical in the short- and mid-term based on projected supply risks and
importance to clean-energy technologies.
Highest power magnets known.
Lasers, glass colorant.
High-power magnets.
Fiber-optic technology, solar panels, alloys (stainless steel), lasers, radiation source for portable
X-ray units.
X-ray phosphors.
Source: U.S. DOE, 2011.
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Rare Earth Elements Review
Section 2 - Introduction to Rare Earth Elements
90.0
o 70.0
_.£ 60.0
2 50-°
50 40.0
JU
3 30.0
_c 20.0
10.0
H
! .
J^ 0^ ^
Y
Dy
Tb
Gd
Eu
Sm
- Nd
Pr
-Ce
- La
Figure 2-3. In-use stocks of selected REEs by specific application or industry (in gigagrams)
(Du and Graedel, 2011).
Table 2-3. Distribution of REEs by End Use in 2008 (U.S. DOI/USGS, 2010)
End Use
Metallurgical applications and alloys
Electronics
Chemical catalysts
Rare earth phosphors for computer monitors, lighting, radar, televisions, and X-ray-
intensifying film
Automotive catalytic converters
Glass polishing and ceramics
Permanent magnets
Petroleum refining catalysts
Other
Percentage
29%
18%
14%
12%
9%
6%
5%
4%
3%
2.4 REE Global Economic Supply and Demand
From the 1960s until the 1980s, the United States was the world leader in REO production. In fact, in
1984, the Mountain Pass Mine in California supplied 100 percent of U.S. demand and 33 percent of the
world's demand for rare earths. In the late 1970s, China started increasing production of REEs, and as
illustrated in Figure 2-4, rapidly became the world's dominant producer. Active mining operations at
Mountain Pass Mine were suspended in 2002. Since 2007, separation of REE from stockpiles at the site
has continued. As REE production in the U.S. has declined, China has become the world's leading
producer of REEs and is currently responsible for more than 95 percent of global production.
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Rare Earth Elements Review
Section 2 - Introduction to Rare Earth Elements
160
140
120
$ 100
o
'B 80
I «
40
20
Global Production of Rare Earth Oxides, 1950-2007
China
1950
1960
1970
1980
1990
2000
Figure 2-4. Global production of rare earth oxides (Du and Graedel, 2011).
Annual global production of REEs totaled about 124,000 tons in 2008, according to a recent report by the
U.S. Congressional Research Service (Humphries, 2010). According to this same report, analysis of the
future supply and demand for each of the REEs indicates that, by 2014, global demand could exceed
200,000 tons per year, which would exceed current production by over 75,000 tons per year. Additional
analysis by others indicates the high likelihood of shortages of neodymium, dysprosium, terbium, and
praseodymium and the potential for shortages of lanthanum, yttrium, and, europium by 2014 (Schuler et
al., 2011). This information, combined with the data shown in Figure 2-3, indicates that the uses most
likely to be impacted by future shortages are magnets for use in computers, audio systems, wind turbines,
and automobiles; motors/generators; batteries; metallurgy; and catalysts. The critical nature of these uses
is driving the push for increased mining, expanded recycling and research into alternatives, and changes
in U.S. and international policy.
In 2008, the United States consumed 7,410 metric tons of REEs (U.S. DOI/USGS, 2010). Currently, this
demand is met mainly through imports from China, industry inventories, and stockpiles. However, as
early as 2012, U.S. production may be resumed at the Mountain Pass Mine, which is projecting
production of 18,000 tons in 2012 and up to 40,000 tons per year in following years. The status and
critical issues facing this mine, as well as other potential U.S. mines, are presented in Table 2-4. It is
reported that if the new mines under development are able to meet their projected production levels,
world-wide demand for REEs will be met from these new sources (Long, 2011).
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Rare Earth Elements Review
Section 2 - Introduction to Rare Earth Elements
Table 2-4. Current Activities at Selected, Potential U.S. REE Mines
Factor
Status
Resources
Potential
Production
Critical
Issues
Mountain Pass
(California),
RCF, Goldman
Sachs, and Traxys
Recommissioned
separation plant.
Feasibility study of
recommencing mining
and processing under
way.
20 Mt @ 9.2% rare
earth
oxides (REO);
1.8 Mt REO contained
(a proven reserve).
Target: 18,000 tons
per year REO;
start-up in 2012.
New owners.
Completing
Definitive
Feasibility Study
(DFS).
Restarting an "old"
plant.
Bear Lodge
(Wyoming),
Rare Element
Resources Ltd.
Resource engineering
study underway.
Process development
commenced.
9Mt@4.1%REO
0.4 Mt REO (inferred).
Unknown.
Define "ore reserve."
Develop process.
Complete DFS.
Approvals.
Customer support.
Pea Ridge
(Missouri),
Upland Wings/Wings
Enterprises and
Glencore International
Commercial and
technical studies
ongoing. Property
ownership has changed
to Pea Ridge
Resources, Inc..
4 Mt iron ore; $3 billion
of REE; small HREE
deposit, but potentially
higher concentrations
than in any deposit
worldwide.
Output of REE from
tailing unknown;
underground mine
production unknown.
Define "ore reserve."
Develop process.
Complete DFS.
Approvals.
Customer support.
Round Top Mountain
Project (Texas),
Texas Rare Earth
Company
Exploration potential
open pit mine. 82,000
feet of drill core
available for evaluation.
Preparing for
aeromagnetic survey
and additional drilling.
67% of REOs are
HREEs.
Information not
available.
Information not
available.
Sources: http://phx.corporat.e-ir. net/phoenix.zhtml?c=236277&p=irol-news&nvo=0:
http://www.rareelementresources.eom/s/Home.asp: http://www.winqsironore.com/: http://texasrareearth.com/:
http://pearidqeresources.com/
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Rare Earth Elements Review
Section 3 - Life-Cycle Stages of Rare Earth Elements Mines
3. Life-Cycle Stages of Rare Earth Mineral Mines
The increasing importance of REMs for the manufacture of modern devices upon which society has become
reliant, along with uncertain supplies (see Section 2), is encouraging exploration and development of new mining
sites. While REMs are an important resource needed to sustain our modern technologies, the waste footprint and
environmental impact from REM mining operations is expected to be as significant as current mining practices for
metals and minerals. The requirements, regulations, and financial obligations and assurances fora new mine are
usually complex and take years of planning. The economic feasibility of discovered deposits must be proved, and
environmental effects to the local communities and habitat also must be evaluated to determine feasibility. The
process of exploration, development, and construction typically required before mining can begin may exceed 10
years. Except for a few locations, known rare earth deposits in the United States are generally considered small
to medium reserves. This section presents a discussion of the typical process steps used in developing a new
rare earth deposit and the associated mining wastes that typically would result. It is not expected that the mining
stages of a rare earth mine would be different than other hardrock or metal mining operations. Except for the
radioactivity of uranium and thorium, the potential REM waste emissions would be generally comparable to a
typical hardrock mine.
Mining operations produce a variety of solid materials that have the potential to cause environmental
contamination and require long-term remedial actions and operation and maintenance. The largest mines
may generate more than a billion tons of solid wastes that may cover areas exceeding a thousand acres,
and smaller operations still must handle and dispose of
quantities of materials that can affect large areas (U.S.
EPA, 2003). Most deposits of REE ores in the United
States would be expected to require mining operations
that likely would produce far less quantities of solid
wastes than the largest operating mines. An example
of an existing REE mine in the United States that
would be considered a large mining operation, is the
Molycorp Minerals rare earth mine in Mountain Pass,
California (see sidebar). It would be expected that rare
earth mineral mining operations developed in the
United States would be similar to other large hardrock
and placer mines that recover minerals containing
primary metals (e.g., gold, silver, copper, zinc, lead).
As examples, the mass of selected types of individual
REE-containing ore deposits occurring in the United
States is estimated by the USGS to be the following:
0.2 million tons (approximate average) for
thorium-rare earth vein deposits
(Armbrustmacher et al., 1995)
3.5 to 450 million tons for low titanium iron
oxide deposits containing REE, with a median
quantity of 40 million tons (Foose, 1995)
6.6 to 331 million tons for minable carbonatite
ore deposits (Modreski et al., 1995).
These rough quantity estimates are based on known
deposits, as characterized in geochemical deposit
models prepared by the USGS; other deposit models
may also exist other than those found and reviewed
and that provide additional estimates. Averages for the
The Scale of an Existing REE Mine
in the United States
The largest rare earth minerals mine in the
United States is Molycorp Mineral's Mountain
Pass rare earth mine and site, which occupies
2,222 acres of land in San Bernardino County,
California. The mine started operation in 1952,
operating as an open pit lanthanide mining,
beneficiation, and processing facility. The period
of greatest ore production was from 1965 to 1995.
Mining activities ceased in 2002, but minor milling
activity continued to process stockpiled ore; and
full-scale ore production may resume in 2012.
When mining activities ceased, the open pit was
1,500-feet wide by 400-feet deep. Overburden
materials were held on site, and numerous
process water, tailings, and product storage ponds
were also operated.
Remaining REE reserves (relative to a 5
percent cutoff grade) at the Mountain Pass mine
are estimated to exceed 20 million tons. The
average REE content in the bastnasite mineral ore
is approximately 9 percent. The remaining gangue
minerals (calcite, barite, and dolomite) in the
carbonatite igneous rock body make up
approximately 91 percent of the ore-containing
rock. The expected overburden produced is
estimated to be 104 million tons, which will be
stored at two existing storage piles. These storage
piles will together cover approximately 315 acres
within 30 years of the proposed period of
operation through 2042 and represent
approximately a 120 percent change over current
stockpiles accumulated between 1950 and 2002.
California Regional Water Quality Control
Board, Lahontan Region (2010)
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Rare Earth Elements Review Section 3 - Life-Cycle Stages of Rare Earth Elements Mines
mass of overburden and waste rock that might be removed from aboveground mining operations are not
provided in these models. The amount of overburden and waste rock depends on many factors, including
the type of deposit, the geometry of the ore body, and the mining method. In general, overburden includes
the sediments or rock materials below the soil horizon that must be removed from above and possibly
around a subsurface deposit and that does not contain concentrations of the commodity mined.
Overburden does not include the mass of waste rock removed from around the economically viable ore.
Waste rock may represent a subeconomic ore material, removed from around or within specific regions of
the ore body, that does not contain appreciable quantities or concentrations of the mined commodity
relative to the target ore. Waste rock is removed to reach the more economically viable regions of the ore-
containing rock. Subeconomic ore specifically refers to conventionally mined ore with a grade that is not
rich enough to meet the current market condition for viable production. Mines classify their subeconomic
to uneconomic material based on potential for future processing, given appropriate market conditions and
environmental risks. Active mining can encounter all variations in the concentration of the commodity in
the rock or sediments being extracted, depending upon the complexity of the ore body. The waste rock
material is generally managed separately from the overburden piles since the waste rock can contain
higher concentrations of metals that, if released, may have environmental consequences. Clearly, the
efforts and resources required for management of overburden, waste rock, and ore materials alone are
generally significant. Management of the soil and rock material removed from the mine is necessary since
these materials may contain concentrations of metals, acid-producing sulfides, and radioactive elements.
Freshly exposed rock surfaces enhance the effects of weathering and can allow release of metals as
environmental contaminants, which may represent a potential human and ecological health risk to site
workers, nearby residents, nearby recreational users, and aquatic and terrestrial species and habitat.
However, REE ores generally contain few acid-producing sulfide minerals, so the risk of producing acids
to leach metals and producing mine drainage (AMD) is considered low. Because REE deposits are
associated with igneous rocks, the greatest AMD risk would probably come from these igneous bodies
intruding sediments or other rocks containing sulfide minerals.
3.1 Active REE Mining
As of this writing, ongoing active mining operations for extraction of REE ores are not widespread in the
United States. Aboveground mining of REEs last occurred in the United States in 2002 (Long et al.,
2010) at the Molycorp Minerals rare earth mine in Mountain Pass, California (Figure 3-1). Currently, the
Molycorp mine is preparing to resume ore production, but initial start-up plans are for operations to begin
with processing of stockpiled ore (Jim Sims, Molycorp; personal communication).
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Section 3 - Life-Cycle Stages of Rare Earth Elements Mines
With Permission of GoogleEarth (© 2012 Google) and USDA Farm Service Agency and © 2012 GeoEye
Figure 3-1. Molycorp Minerals rare earth mine, Mountain Pass, California.
Other mine sites around the conterminous United States and Alaska have produced REE-containing
minerals in the past; however, the status of those sites is currently undetermined. A listing of known
mines that have produced REE-mineral ores or REOs and locations where REE-containing mineral
deposits have been discovered was compiled from Gupta and Krishnamurthy (2004), Orris and Grauch
(2002), and Schuler et al. (2011) and is provided in Appendix B. The only other significant REE mining
operations are located in the Sichuan, Jiangxi, Shandong, and the Inner Mongolia provinces in China
(Schuler et al., 2011); however, the Chinese REE mining operations and environmental practices are not
considered applicable for comparative purposes in this report and are not discussed in any detail. In the
absence of modern examples of mining activities for the extraction of REE ores in the United States, and
considering the variability in the mineralogy and geology of known REE reserves, the following sections
present a general discussion that introduces the life cycle of typical mining operations. The wastes
generated during each mining stage that have the potential to cause environmental effects are also
discussed, as applicable.
3.2 REE Ores
The REE metal is an elemental constituent of mineral REO ores. Concentrations of REE minerals
typically occur in igneous and metamorphic rocks and also in sedimentary placer deposits. As discussed
in Section 3.3.2.1, concentrations of the target REO in the ore have implications for selection of the
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mining method needed to obtain adequate quantities of the ore; the processing steps required (see
Section 4), and the volumes of wastes that must be managed.
The location of both hardrock and placer deposits in the conterminous United States and Alaska was
discussed in Section 2, along with the more common REE-minerals (i.e., bastnasite and monazite). The
REE-containing minerals in a hardrock or placer deposit may or may not be viable for mining due to
various reasons, including economic, technical, and environmental reasons, stemming from the
concentration of the REE-bearing minerals in the host rock. The definition of an "ore" for the purposes of
this document is as follows:
"... a mineral source from which a valuable commodity (e.g., metal) is recovered. The
term ore implies economic viability, given the concentration of metal in the host rock, the
costs of extraction, processing and refinement, waste management, site restoration, and
the market value of the metal" (U.S. EPA, 2008).
As the definition implies, the potential environmental impacts from all stages of a mine must be
considered in evaluating the feasibility of the mine start-upincluding the costs of mine restorationto
determine if a REE deposit represents an ore from which REOs and then REMs can be recovered
economically.
3.3 Mine Permitting and Life-Cycle
Four life-cycle stages of a mine are generally recognized. These life-cycle stages include exploration,
mine development, ore extraction and processing, and mine closure. Additional steps or phases are also
incorporated within each stage. The activities associated with each stage can be considered as generally
linear, but overlap is common. The time needed to complete each of the steps for mine startup depends on
many factors and can potentially require many years before the mine is in full production.
3.3.1 Permitting Requirements for New Rare Earth Mines
A discussion of applicable mining regulatory policy and permitting requirements developed to manage
the environmental impacts from mining operations is beyond the scope of this document. A detailed
summary of applicable federal regulations can be found in the agency document EPA and Hardrock
Mining: A Source Book for Industry in the Northwest and Alaska (January 2003:
http://vosemite.epa.gov/R10AVATER.NSF/840a5de5dOa8dl418825650f00715a27/e4bal5715e97ef21882
56d2c00783a8e/$FILE/Maintext.pdf). In general, projects with potential to have significant
environmental impact are regulated under federal or state permitting programs. Mines developed near
tribal lands require consultation with tribal leadership, especially if the mining activity or associated
operations could impact the community or subsistence resources. As mentioned, mining operations on the
scale that would be expected for recovery of REE minerals would potentially require large areas to
accommodate an individual mine and its associated support facilities (e.g., waste material management
areas and tailings ponds). This need for large areas of land often means that the land occupied by a mine
is of mixed ownership and includes a combination of federal and private lands (National Academy of
Sciences, 1999).
If a mining project is located on, adjacent to, or requires access and egress through federally managed
lands, or has planned discharges to surface waters, then the permitting process is implemented under
Section 102 of the National Environmental Policy Act (NEPA) [42 U.S.C. 4321 et seq.]. The life-cycle
paradigm is typically used in the development of environmental impact statements (EIS) under NEPA for
assessing the environmental impacts of a proposed mining activity on federal lands and this perspective
will generally serve to frame the following discussion, which describes the mining life-cycle. The NEPA
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process is not described in detail within this document, but can be found in EPA 's Hardrock Mining
Source Book (2003).
For general reference, known REE deposits that are located on or near federally managed lands are
presented in Figure 2-2 and are tabulated in Appendix B. States may also apply a NEPA-type process for
permitting mining operations located within their boundaries, regardless of whether the mine property is
located on federally managed lands.
3.3.2 Mining Life Cycle
Whether the environmental impact evaluation is performed under NEPA, state agencies, or through due
diligence by the mining company, four life-cycle stages of the mine are generally recognized. These life-
cycle stages are exploration, development (includes development planning, permitting, and construction),
ore extraction and processing, and mine closure (includes shutdown, reclamation, and long-term
monitoring). There are a number of steps that can be included within each of these mining stages that are
briefly described below. However, the remainder of this section generally discusses the mining life-cycle
stages, focusing on exploration and development phases and then ore extraction (i.e., mining) activities to
remove rock or unconsolidated or semi-consolidated sediments (i.e., placers) containing the REE-mineral
ores. Processing of REE-mineral ores and associated wastes is discussed in Section 4.
It is important to recognize that there are not specific starting or ending points, or limitations, for these
associated activities. Mining stages at a particular site can be cyclic and recur as mining operations
progress. Exploration activities, for example, initially occur to evaluate the economic feasibility of the
deposit, but then in-mine exploration generally continues once mining commences. Exploration activities
may continue for less than a year, or may extend over a several years at a site until the economic viability
of the deposit is determined. Once mining is underway, exploration work may progress beyond the mine,
or in a near-mine area, to trace the extension and continuity of the ore deposit as the ore body is exposed
during the mine advance. Reclamation activities are another example of how some mining operations are
recurring during the life of the mine. These activities are also very site-specific and occur at various scales
at the same site. Although areas of impact and the mass of earth materials resulting from exploration
activities that require management are small in comparison to subsequent mine stages, some reclamation
is often needed. Reclamation activities may be completed at the end of the exploration activity; occur
intermittently as long-term exploration or mine advance continues; may not occur until mining is
completed; or be initiated only after mining activities have ceased.
While the mining life-cycle is commonly discussed as definitive stages of activities inferring a linear
temporal scale encompassing the life span of the mine, the previous examples illustrate how activities
may occur and recur as phases or be on-going operations during the life of a mine. It is also important to
understand that activities to prove a deposit or develop a mine may respond to external drivers, and that
an active mine may stop operations for short or extended periods. Intermittent operations may be in
response to seasonal conditions when the mine site is inaccessible due to weather extremes, or mine
production may exceed the capacity of the processors to accept ore feed stock. Temporary stops in work
(long and short term) may occur due to economic fluctuation in the price of the commodity, engineering
failures associated with the mine or equipment, or technological issues (e.g., difficulty in controlling
ground water infiltration; encountering complex geologic structure such as faults; and excessive depth of
deposit). If mining activities are suspended, the permits and leases are often maintained in anticipation of
resuming activities and operations at a later time. Mine sites generally close and are reclaimed only if
pressured by the local community (e.g., due to poor safety or environmental record), the ore body has
been exhausted, or if, due to technological issues, mining is no longer possible.
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3.3.2.1 Exploration
Mineral exploration includes any activity performed to discover a potential ore reserve and determine the
location, size, shape, position, and current economic value of the deposit. Prospecting, staking, sampling,
assessment of mineral potential and economic feasibility, development plan, and permitting are all steps
and activities that can be considered as part of the exploration stage. Prospecting employs non-invasive
methods to evaluate the presence and characteristics of a potential deposit. Staking establishes mineral
rights to develop the mine. An exploration step, using more sophisticated methods to delineate the deposit
(e.g., geophysics), is followed by an intermediate stage of exploration that uses invasive methods (e.g.,
trenching, core or rotary drilling, bulk sampling) to sample the deposit. Samples are analyzed for metal
content, and the data collected from the previous steps are used to create mineral potential maps showing
the geologic favorability of the deposit; definition drilling is generally performed during this advanced
stage of exploration. If the deposit is proven economically viable, then a mining development plan is
drafted and applicable permits are obtained. These steps can also be considered as independent stages
with exploration (i.e., use of invasive assessment methods) as one of these steps. As previously
mentioned, the resource evaluation and scoping of the deposit can also be performed during the mine
design stage. Baseline environmental studies may be conducted, if required, prior to exploration to
determine the presence of sensitive species and habitat that might be impacted during these activities.
Permitting and regulation of these activities results from the interplay of state and federal agencies
responding to their respective authorities and responsibilities. EPA's authority is invoked on matters of
site assessment, financial responsibility, and future CERCLA related concerns. Examples of documents
that can be requested or required in the permitting process include but may not be limited to: 1)
documentation to address the requirements of the National Environmental Policy Act (NEPA), 2)
National Pollutant Discharge Elimination System (NPDES wastewater discharge) permits for mining
operations, 3) Underground injection control (UIC) permits for mining operations and 4) CERCLA
financial responsibility documentation.
Exploration Methods
The approach and methodology used for exploration depend upon various factors, such as terrain, nature,
and size of the target, and expected depth of the ore body; regulatory and permitting requirements and
restrictions; available information and technology; and available capital resources. The intent of the
exploration company (e.g., prove the deposit for sale, develop the mine) will also influence the scope of
the initial exploration project and the approach and methods used to prove the deposit. The methods used
may be very simple and low cost, or technically sophisticated.
The location of a proposed mine will also influence the extent and type of exploration activities that can
occur. If the deposit is located in an existing mining district and/or on privately owned lands, then drilling
permits may be more easily obtained by the exploration or mining company, and more aggressive
exploration (e.g., exploratory drilling) may occur. If the site of the deposit is located near, for example,
national forest lands, then exploration activities requiring land disturbance may not be allowed until a
preliminary environmental information document (EID) is completed and undergoes EPA/NEPA review.
Upon approval by the EPA or state agencies, drilling data can be collected and analyzed. The exploration
data would then be used to inform additional environmental assessment that may be needed in the mine
development-construction stage. The environmental impacts of exploration activities are sometimes
overlooked; however, in many states, permits are required. An example (U.S. EPA, 201 Ib) is in the state
of Alaska, where permits required for exploration activities include a Clean Water Act 404 permit for
wetlands disturbance; camp permits; a temporary water use permit; an overland travel permit; land-use
permits for off-claim camps or staging areas; bonds for staging fuel; hardrock exploration land-use
permit; and a state bond pool requirement for reclamation. Drilling and trenching can be extensive, long-
term operations using multiple types of heavy equipment with associated waste (e.g., used vehicle fluids,
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lubricants and greases, solvents, other traditional industrial materials). Additionally, mining-type wastes
(e.g., waste rock) can be produced during exploration activities and will need to be managed.
Passive Mine Exploration Methods
Examples of passive exploration methods applicable to rare earth deposits include common prospecting
approaches (e.g., water, rock, soil, and sediment sampling; shallow pits) and geologic mapping and
general field investigations. More sophisticated techniques employ geophysics, aerial and satellite remote
sensing, mineral deposit models, and potentially other geochemical testing methods. The exploration team
will generally attempt to identify geochemical and geophysical signatures that suggest the presence of the
target REE-containing minerals; however, the response of geophysical techniques (such as magnetometer,
radiometric, gamma-ray spectrometry, and remote spectral surveys) depends upon the mineral
associations in the rock that accompany the REE-containing mineral deposits. Detailed spectral data from
remote-sensing surveys can identify carbonate, ferrous iron, and REEs associated with thorium-rare earth
element deposits (Armbrustmacher et al., 1995).
The commonly identified passive exploration steps do not generate many wastes and have little if any
environmental impact. The one exception is ground-based geophysical exploration, which may require
clearing through forested or other heavy-growth areas to accommodate larger truck-mounted equipment,
resulting in an alteration of the terrain. Occasionally, earth-moving equipment may be used to remove
soils and overburden or remove boulders that may be in the way of ground-survey activities. Soil and rock
removed during exploration activities may be stockpiled onsite and used for onsite purposes or
reclamation activities, as needed. As the exploration activity progresses, from more general information
collection to more detailed data acquisition, ground surface disturbances generally are required.
Additional access roads and drill sites are constructed to begin subsurface testing to sample from the
mapped mineralized zone to further delineate and prove the resource.
Exploratory Drilling and Trenching
Data resulting from prospecting activities, geophysical surveys, geochemical surveys, and geological
modeling are used to guide an exploratory drilling program to further substantiate and quantify the
attributes of the ore body or target deposit, including its size, shape, and composition. These subsequent
drilling programs can incorporate various types of tests. The drilling program seeks to determine the
lateral and vertical extent of the REE deposit. Generally, rock cores are collected for further analysis to
evaluate continuity of mineralization, grade, mineralogical relationships, rock types, and local
hydrogeologic data. Rock strength testing and borehole geophysics may also be performed, and trenching
may be used to collect bulk samples (i.e., several tons of material) across mineralized zones for
metallurgical testing used to develop and evaluate processing methods that will be incorporated into the
processing plant design. Large vertical shafts may be advanced to recover bulk samples or large tunnels
or shafts that will accommodate large earth-moving equipment.
Exploratory drilling can be ongoing for long periods (i.e., weeks, months, or even years). The footprint of
a single drill site may be a few hundred square feet in size, and there can be numerous drill locations.
These operations can potentially disturb several acres of land to accommodate the drill sites, staging
areas, and the onsite support facilities for the drilling operation. The spacing of drill sites is variable and
dependent upon the continuity of the deposit. Exploratory borings may be drilled very closely spaced (i.e.,
100 feet or less) or at larger intervals, depending on the characteristics of the site (National Academy of
Sciences, 1999). Drilling boreholes to probe the REE deposit produces both waste solids and fluids. Rock
flour or cuttings are removed as the borehole is advanced to greater depth. The nature and volume of
cuttings produced at the ground surface depends upon the characteristics of the rock being drilled, the
depth and diameter of the borehole, the presence of potable aquifers, and the drilling method. Rotary
drills can require the use of a mixture of water and bentonite clays (i.e., a mixture often referred to as
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drilling mud) as a drilling fluid to entrain and carry the cuttings to the surface while cooling the drill bit.
Often, only water is used as a drilling fluid during exploration since clay drilling muds have the potential
to complicate the petrologic and geochemical analyses; however, formation characteristics and the local
hydrogeology may make drilling with muds or other additives necessary. Other rotary drills use
compressed air to force the cuttings to the surface and keep the drill bit cool. Polymers, oils, or other
synthetics are added to water or air flows to enhance the operational properties of the drilling mud or air,
if needed. Prior to use, the drilling muds do not generally represent an environmental hazard and are
either inert or break down quickly.
When the borehole intersects groundwater, the water can entrain materials from the borehold and
transport those materials to the surface. The potential toxicity of these materials depend on the
composition of any drilling fluids used and materials swept from the subsurface. These formation fluids
can be highly mineralized, and the cuttings and drilling muds can entrain toxic levels of metals and other
chemicals. Drill cuttings and drilling fluids are typically collected once the borehole is completed and
abandoned; however, regulations in some states allow return of cuttings to the borehole. Excess materials
may be stored in drums, contained in mud pits, or managed and disposed of as a waste.
Locations in the United States with Recent Exploration Activity and a Summary of Potential REE
Resource Areas
Potential sites of REE resources have been under evaluation in recent years to prove the reserves and
determine the mining potential at these locations. Sites receiving current or recent attention are located in
Utah, Colorado, Wyoming, Alaska, California, Nevada, and Nebraska.
During 2008, the Great Western Minerals Group, Ltd. completed an extensive drilling and
sampling program at the Deep Sands deposit located in the Snake Valley and adjacent to the Deep
Creek Mountains of west-central Utah. After a feasibility study to consider the low-grade
monazite mineral ore containing rare earth concentrations, the company announced that it did not
currently plan to undertake additional exploration at the site (Great Western Minerals Group,
2011).
A recently formed company, Colorado Rare Earths Incorporated (CREI), announced in March of
2011 that it was soliciting funding to begin exploration near the Powderhorn mine site in
Colorado (Colorado Rare Earths, Inc, 2011). CREI also has acquired properties at Iron Hill and
Wet Mountains Colorado, where potential REE resources have been identified. CREI is currently
organized as a mineral claims acquisition company, but plans to expand to an exploration and
development company in the future.
In Alaska, exploration is underway at the Bokan Mountain site that is located at the southern-
most end of the Alaskan panhandle on Prince of Wales Island. This is a site that was mined in the
past for uranium ore, but also has known HREE and LREE resources.
Molycorp Minerals, as described earlier, is a past producer of REEs and is currently preparing to
re-open its mine at Mountain Pass, California.
In Nevada, about 16 miles east of the Mountain Pass mine, Elissa Resources is exploring multiple
locations called the Thor REE Project Area, where HREEs and LREEs have been discovered; at
least one of these locations is geologically similar to the Mountain Pass deposit (Elissa
Resources, 2011). To date, Elissa Resources' exploration activities have included surface
mapping, a district-scale detailed high-resolution airborne magnetic geophysical survey,
extensive ground radiometric surveys, satellite imagery studies, petrographic studies, and
sampling programs, including channel sampling and the sampling of historical surface workings
that are remnants of a 1950s uranium-thorium prospecting rush.
Quantum Rare Earth Developments Corporation recently has begun exploratory drilling at the Elk
Creek Project in southeastern Nebraska. The focus of these drilling efforts is to perform a
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resource assessment of niobium and associated REEs contained in a carbonatite deposit. These
efforts are in the early stages, and no final determination about the resource has been made at this
time (Quantum Rare Earth Developments Corporation, 2010).
Bear Lodge Rare-Earth Project is located approximately 6 miles north of Sundance, Wyoming,
and is comprised of 90 unpatented federal lode claims and one state lease, for a total of about
2400 acres. It is owned by Rare Element Resources through its Wyoming-incorporated Paso Rico
(USA) Company, Inc. Twenty-three of the mining claims were obtained from Phelps Dodge
Corporation and are subject to 2-percent net smelter return production royalty. The site has been
prospected at various times since 1949. Several areas of mineralization have been identified,
including high-grade copper, molybdenum, gold, and REMs within an altered carbonatite-
alkaline-intrusive complex. Exploration efforts to date estimate that the rare earth resources at
Bear Lodge could match or exceed the size and grade of deposits at Mountain Pass, California.
The company web page reports that Rare Element Resources is currently exploring for rare earths
and gold, and results have been very good to date.
Pea Ridge mine (formerly owned by Upland Wings / Wings Enterprises, and currently owned by
Pea Ridge Resources, Inc.) is a iron mine that has been in operation for about 40 years. The site
is located in Missouri. The mine, under former ownership, had planned to produce HREEs as a
byproduct from the iron ore body; however, mining of an adjacent ore body containing primarily
REEs had also been planned (Wings Enterprises, 2011).. A mine feasibility study is underway
(Pea Ridge Resources, 2012), but no information is readily available to determine whether or not
REE will be produced.
The above locations are only examples of sites where some level of exploration activities have occurred,
but others may exist. A general list of potential rare earth resource locations that have been documented in
the United States is summarized in Appendix B, which was compiled from a combination of sources.
Other deposits likely exist or are being explored that were not identified or included in Appendix B.
3.3.2.2 Mine Development
The term "mine development" is applied differently, depending on the region and entities involved. It is
most often understood to be primarily a planning stage; however, it is also sometimes used to denote the
construction phase, considering that planning has been accomplished during the exploration stage.
Feasibility Study
A financial analysis and corresponding feasibility study are important parts of this stage, as defined here,
and are conducted considering the market value of the metal commodity, cost of production,
characteristics of the deposit, and anticipated closure costs. The results are then used to determine if the
deposit should be abandoned (i.e., not likely to ever be an economically viable deposit), should remain
idle (i.e., could become economically viable in the future), or if development of the deposit is
economically feasible and should proceed. Typically, a feasibility study for a medium-size mine requires
3 to 4 months and, for larger projects, 6 to 9 months (De la Vergne, 2003). Concerns for the
environmental effects of the proposed mining activity, and associated mine areas must be considered
relative to long-term costs. The potential impacts to the immediate property, adjacent lands, and
surrounding community are identified, and additional baseline environmental studies may be performed
or continued during this stage. Investors may be sought using the results of the feasibility study.
Mine Plan
The layout and design of the mine is performed to locate stockpile areas and waste areas where these can
be best managed to prevent or minimize environmental damage. Engineering design and environmental
assessment should be conducted in tandem so that collected and measured data can mutually benefit both
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purposes and allow for collaboration of engineers and environmental scientists; however, while this is
best practice, the approach is sometimes not used due to inadequate planning or logistical difficulties.
Mitigation measures can then be addressed more efficiently through management plans and compensation
measures that are integrated into the feasibility models to evaluate costs.
REEs commonly occur in ores that also contain uranium and thorium. Ores containing the REE-bearing
mineral monazite are particularly high in concentrations of thorium (Long et al., 2010). Uranium also
occurs in or with ore deposits that contain REE-bearing minerals. The amounts of radioactive elements in
the ore is not dependent upon the mineral type specifically, but more on the petrogenesis of the deposit
containing the ore. In general, nearly all rocks, soils, and water contain small amounts of radioactive
materials, such as uranium, thorium, radium, radioisotopes of potassium, lead, polonium, and their decay
products. When naturally occurring radioactive materials (NORM), in their undisturbed natural state,
become purposefully or inadvertently concentrated, either in waste by-products or in a product, they
become technologically enhanced naturally occurring radioactive materials (TENORM) (U.S. EPA,
1999).
Waste areas containing high concentrations of uranium and thorium require complex management.
Management begins at the mine design stage, where the mining methods and milling plant processes are
planned to optimize a waste reduction-minimization strategy. The treatment of tailings is a significant
safety concern, as well as an environmental issue. The EPA reports (U.S. EPA, 1999) that the radiation
levels from waste rock and sludges associated with the production of REOs range from 5.7 to 3,224
pCi/g. Additional treatment circuits are generally required to precipitate radium from tailings, and
additional controls are needed to manage radon. Production and management of radioactive mining and
milling wastes is tightly controlled by national (including the Safe Drinking Water Act, Clean Water Act,
Comprehensive Environmental Response, Compensation and Liability Act [CERCLA], and Clean Air
Act) and state regulations, and if REE is produced with commercial uranium or thorium, then
international protocols and agreements also may apply. Information pertaining to laws and regulations
that apply to TENORM can be found at EPA's Radiation Protection website
(http://www.epa.gov/radiation/tenorm/regs.html). The challenge is generally balancing the human health
and environmental risks with production costs. The issues associated with these materials can affect the
feasibility and viability of a proposed mining project, especially when addressing plans to reopen older
mining sites. Tighter regulation on the use of radioactive minerals has been identified as the primary
factor that pressured many sources of monazite out of the REEs market during the 1980s (Long et al.,
2010).
Processing these ores containing radionuclides subsequently increases the concentration of naturally
occurring radioactive materials, and the levels of radioactivity can become higher than background levels
near waste management areas. However, it should be noted that radioactive wastes from mining and
milling operations are not the same as waste containing special nuclear materials that are associated with
the production of enriched (i.e., increased concentrations of highly radioactive isotopes) radioactive
materials generated by nuclear fuel cycle facilities or disposed of by nuclear power plants. The principal
issue at mining and milling sites is the volume of wastes containing natural radioactive elements that are
produced and managed.
Environmental Studies
This section is presented for general background and to provide some perspective of the complexity of
mine siting studies under NEPA; however, the information presented here should not be considered as
guidance, nor should it be taken as a comprehensive discussion of the types of environmental assessment
activities that may be required.
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In general, if mines are located on or adjacent to federally managed lands or will have discharges to
surface water then an Environmental Information Document (BID), also known as an Environmental
Study or Environmental Report under some programs, is required under NEPA. Preparation of this report
is generally performed by the proponent during early mine stage activities as the viability of the mining
operations is being assessed. The EID describes the project, characterizes the environment that potentially
may be impacted by the mining activities (including cumulative impacts), assesses the potential severity
of any impact, identifies mitigation measures to avoid or lessen the impacts, and discusses alternatives for
methods and operations, that may include an evaluation of the critical need of the commodity (e.g.,
availability of the commodity from other markets, substitute materials, or recycling). Information from
the proponent's EID is used by the managing agency for the project to prepare an Environmental
Assessment (EA) report describing the potential for environmental impact and the preferred alternative.
If the mine project is considered a major federal action that has the potential to significantly affect the
quality of the human environment, then the EID and/or EA is used by the lead government agency to
develop an Environmental Impact Statement (EIS); however, additional environmental baseline and
engineering studies may be needed. The EIS is then reviewed by EPA and other agencies, if applicable, as
part of the NEPA process to determine if unavoidable adverse impacts will occur, and if irreversible and
irretrievable commitments of resources are likely, considering connected actions, cumulative actions, and
similar actions. A period of public review and the issuance of a Record of Decision (ROD) follows. If an
EIS is implemented, monitoring is required for any mitigation steps required and implemented.
Common baseline studies performed to support the EID might include an evaluation of aquatic resources
(including wetlands), terrestrial habitat, ground water quality and supply, air quality, and human
population and demographics. Each of these studies focus on characterizing the environment that
potentially may be affected by the operations and activities at the site. The information from baseline
studies is then used in the EID to assess the potential impact that the operations and activities may have
on the site and surrounding environment, relative to the potential impacts identified and anticipated for
the mining method used and the associated operations and processes. Impact may include degradation of
habitat or habitat alteration or loss; however, in some special cases, habitat may actually be enhanced or
created. Water use for mining operations may also cause flow alterations that have adverse impacts to
aquatic habitat, or in-stream structures used for water control may obstruct fish movement, migration, and
spawning patterns. An aquatic resource study generally evaluates the distribution, abundance, and
condition offish species, benthic macroinvertebrates, and amphibians, along with the distribution and
extent of the habitat and riparian zones. To assess existing stress on the aquatic environment, water
quality criteria are evaluated against the actual condition of the water body, and toxicity studies and
metric analysis of macroinvertebrates may also be performed. Aquatic impacts from mining and mine
processors are often considered to be the most significant.
Milling and processing operations are sometimes shared by multiple mines, and ore must be conveyed to
the mill or processor site. The impacts to health and safety from the method used for ore conveyance,
often by heavy truck or railway, through in-route communities and sensitive areas must be considered in
relation to existing traffic patterns, spillage of loads along routes, and the degradation of air quality. This
generally includes the release of windblown air particulates and vehicle exhausts. However, in addition to
air particulates, other studies may be necessary to evaluate the potential impacts from stationary and
mobile sources of air emissions that could emit any of the hazardous air pollutants (HAPs) that are
regulated under the Clean Air Act.
In order to determine the severity of potential impacts to nearby human receptors, a population study is
usually performed. Land-use mapping is also a common analysis performed to aid with population studies
and to help identify farming areas, parks, schools, hospitals, and other potentially sensitive areas (both
human and ecological habitat) adjacent to the proposed mine site. Evaluation of local demographics is
generally performed to insure fair treatment of racial, ethnic, and socioeconomic groups.
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NEPA stipulates that 3 months may be needed for review of an BID, but that a longer period may be
required. NEPA also describes the preparation of the EIS and the intra-agency review process as
potentially requiring 12 months or longer. Therefore, there could be a period of several years between
initial exploration steps and startup of a REE mine that is located on federally managed lands. If needed,
land, mineral leases, and all regulatory permits would be acquired pending acceptance of the EIS. Any
environmental audits required would also be performed.
The USGS (2011) evaluated the time it took to develop metal mines that opened in the United States
since 2000. It was found that even if expedited permitting occurs, the period to obtain a permit could take
7 years. It was also found that periods of 1 month to 17 years may be required before commercial
production. Ramp-up times for new mines might take from 2 to 12 months.
The typical time frame for a mine project from prospecting (i.e., initial exploration) through construction
of the mine was generalized by EPA Region 10 and is presented in Figure 3-2, below (U.S. EPA, 201 Ib).
Initial
Typical Time Frame
for a Mine Project
Advanced
, Exoloration
Prefeasibility
Feasibility
Financinc
.Construction.
6
YEARS
Figure 3-2. Typical time frame for a mine project.
There are numerous factors that affect the time required for mine development. Some examples might
include the location of the mine (e.g., federal lands, state lands, or private lands and greenfields versus
brownfields); geologic complexity of the site; metallurgical complexity of ore; level of stakeholder
involvement; availability of required infrastructure; and experience of regulatory authorities with mine
type and area where deposit is located.
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Financial Assurance Requirements
Mining companies must also provide for financial assurance that the mine site will be restored to a
condition that does not represent a risk to the environment or human health. The federal Superfund law,
also known as the CERCLA, contains a provision that requires EPA to establish financial assurance
requirements for facilities that produce, treat, store, or dispose of hazardous substances. Under CERCLA,
a wide range of elements, compounds, and waste streams are specifically designated as "hazardous
substances" in Title 40 of the Code of Federal Regulations, Section 302.4. Many states have established
financial assurance requirements that are in place; however, the CERCLA 108(b) financial assurance
regulation for hardrock mining currently implements section 108(b) of CERCLA (42 U.S.C. 9608(b)(l)),
which directs the President to promulgate requirements that
"...classes of facilities establish and maintain evidence of financial responsibility
consistent with the degree and duration of risk associated with the production...
treatment, storage, or disposal of hazardous substances."
As of the issuance of this report, the EPA is currently working on a methodology that will be used to
determine the level of financial responsibility requirements that will be imposed on the mine or mine
facility owner under Section 108(b) of CERCLA.
EPA's responsibilities in this area are defined by the federal Superfund law also known as CERCLA.
CERCLA contains provisions that give EPA the authority to require that classes of facilities maintain
financial responsibility consistent with the degree and duration of risk associated with the production,
transportation, treatment, storage, or disposal of hazardous substances.
Current and Prospective Mine Development Activity
Rare earths are often a constituent in ores processed to recover other metal or mineral commodities. The
demand for rare earths may create opportunity for these mines to consider expanding their operations to
produce rare earths in addition to their primary commodity. Expansion of mining operations and changes
to milling and processing operations may require environmental review and additional permitting for
these active mining operations.
In addition to rare earth production from current mining sites, it could become profitable for operations to
resume at former mine locations. These may be mines with active permits that are currently not in
operation due to the current market value of the principal commodity mined, or closed mines where ore
remains but no mining is occurring, equipment has been removed, and possibly some level of reclamation
has been started or completed. Stockpiles of subeconomic ore, or potentially the waste tailings, may now
represent a rich source of ore for REEs that can help the mine transition back into production as the mine
site is re-developed. Most of the prospective REE mines in the United States include those that produced
REE ores in the past (e.g., Molycorp Mineral's mine in Mountain Pass, California) or produced another
commodity from an ore containing REEs (e.g., Pea Ridge iron ore mine). Some exploration may be
required, or enough existing data may be available to begin planning the re-opening of the mine. Most of
the activities required for the mine development stage will be needed to reopen the mine. In some cases,
the environmental impacts from past mining activities and practices will need to be considered in
development of the new mining operation.
Development activity is currently occurring at two locations in the conterminous United States to reopen
idle mines. These include the Molycorp mine in California (as previously discussed) and the Pea Ridge
mine in Washington County, Missouri. Pea Ridge is a $1 billion dollar project that is underway in
Missouri to reopen the existing Pea Ridge mine and to begin construction of a processing plant for
magnetite iron ores (Baranyai, 2011). The iron ore processing plant will be located 1 mile from the mine,
and ore will be pumped through a pipeline to the plant. A St. Louis-based company (Wings Enterprises,
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Inc.), with support from Glencore International AG of Baar, Switzerland, was developing plans around
the opening of the Pea Ridge Mine, and, in early 2012, had expected to start producing rare-earth minerals
from holding ponds left by previous mining activity and also from newly mined ores (Wings Enterprises,
2011). Wings Enterprises had estimated that underground mining may extract as much as 5,000 tons of
rare earths in 3 years. In addition to construction activities, planning and feasibility studies were under
way for the joint iron ore and REE mining operations in Missouri. However, Pea Ridge Resources, Inc.
recently purchased the mine from Upland Wings/Wings Enterprises. No additional information was
provided on the company's website to determine when or if REE resource planning and/or production
will resume or continue (Pea Ridge Resources, 2012).
3.3.2.3 Construction and Mining (Mineral Extraction)
Once regulatory approvals have been acquired, construction can begin on waste management and
processing areas, followed by the commencement of mining activities. The mining methods that might be
used to recover REE ores are not different from hardrock or placer mining operations used for extracting
other metal ores. The EPA defines a hardrock mine in accordance to the BLM definition:
"(as extracting) Locatable minerals that are neither leasable minerals (oil, gas, coal, oil
shale, phosphate, sodium, potassium, sulfur, asphalt, or gilsonite) nor saleable mineral
materials (e.g., common variety sand and gravel). Hardrock minerals include, but are not
limited to, copper, lead, zinc, magnesium, nickel, tungsten, gold, silver, bentonite, barite,
feldspar, fluorspar, and uranium (BLM, 1999b). Usually refers to rock types or mining
environments where the rocks are hard and strong and where blasting is needed to break
them for effective mining."
Placer mining and placer deposits are generally defined (U.S. EPA, 201 Id) as
"The extraction of a mineral deposit that has achieved its present distribution through the
prior action of moving water or wind. Placers are usually in poorly consolidated materials
and are the sources of much, but not all, tin, titanium, rare earths, diamonds, and
zirconium, and some gold."
Hardrock mines are typically either aboveground or underground operations. Solution mining techniques
could also be used to extract REM oxides from the subsurface; however, the use of solution mining is
unlikely in the United States due to the potential for environment impacts and the absence of suitable
deposits. Solution mining is one of the principal mining methods currently used in China to recover REEs
from clay deposits. Placer deposits are typically near-surface deposits that extend over greater areas rather
than to great depths.
The method of extraction is dependent on the grade of the ore; size of the deposit; ore body position (i.e.,
the size, shape, dip, continuity, and depth); geology of the deposit; topography; tonnage, ore reserves; and
geographic location and is based on maximizing ore recovery within economic constraints. A low-grade
cutoff point is established on a site-specific basis and depends on recovery costs at the site, the market
price of the ore, and feed requirements at the mill. It is not uncommon for open-pit and underground
mining to occur at the same site. Mine pits at aboveground mines are generally conical in shape, with the
diameter decreasing with increasing depth; however, a conical pit is not always developed, and the
advance of some aboveground mines are controlled by topographic and/or geologic features. Eventually,
there may no longer be adequate room for equipment to work safely in the pit, and it may not be feasible
or practical to remove additional waste rock to widen the pit. After that point, an underground mine may
be developed inside the lower reaches of the mine pit to reach deeper parts of the deposit. The economics
of widening the pit may also make mining of deeper sections of the ore body using underground methods
more advantageous. The more common mining methods are described below.
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In Situ Leach Mining
It is unlikely that in situ leach (ISL) mining methods would be used in the United States to recover REEs.
Limited geologic conditions suitable for ISL, environmental concerns associated with the strong acids that
would likely be needed, and the low solubility of REEs likely preclude ISL from being considered as a
viable method for recovering REEs from deep ore deposits. However, this method is presented here
because ISL has been used in China and in the United States for other metals.
Very simply, ISL mining injects a fluid (i.e., water, acids, or other chemicals) into a circuit of drilled
boreholes intersecting the mineralized zone, and then an enriched or saturated solution is pumped from
the ore containing the target metals. The enriched or saturated solution is then processed, typically with a
solvent extraction method, to recover the metals. This method has been used for mining copper and
uranium in the United States on a limited scale. Copper ore dumps around formally active underground
copper mines have also been mined using similar techniques, and REEs are known to occur along with
some copper deposits (e.g., Bear Lodge, Wyoming). Although it is thought to be unlikely, use of ISL
might be considered as an alternative to recover REEs from abandoned shafts backfilled with
subeconomic ore, dredge wastes of former mines, or from the waste of active mines producing other
commodities from ores containing REE. The hydrogeologic conditions must be suitable for in situ mining
to be successful and also environmentally safe. Because in situ mining does not cause the level of ground
disturbance that either aboveground or underground mining does, due to the lack of waste piles and ore
stockpiles, it is sometimes initially considered as an alternative mining method in the NEPA process
during the mine development stage.
In situ mining is typically used where the mineral or metal deposit is very deep underground and also
where there are lower grade ores. The success of the method depends of the solubility of the target metals,
geochemistry, and hydrologic characteristics of the ore. Solution mining of shallow deposits (e.g., placer
deposits) is also possible, but using this approach risks contaminating an aquifer suitable as a drinking
water source or that is in direct hydraulic connection with and recharging a surface water body or the
marine environment. Chemicals used for leach solutions and leachate solutions containing concentrated
metals and other salts must also be managed and stored. Strong chemical reagents would likely have to be
used to recover the REEs from the rock or waste materials so the environmental risk is likely too high for
this to be a viable method. Due to environmental concerns associated with this mining method, solution
mining would likely have limited application for the recovery of REMs in the United States.
Surface and Underground Mining
Underground and open-pit mining are the more conventional methods used in the hardrock mining
industry. Both of these more familiar mining methods produce common wastes; however, the
environmental impact from underground mining is generally considered to be potentially less due to
minimized land disturbance, targeted mining producing less waste rock, and differences in handling
practices for the rock waste, although there are likely exceptions to this generalization. Underground
mining is generally more expensive, primarily due to the lower production rates possible at higher cost
compared to aboveground methods. Additional safety measures are also usually required for underground
methods that increase operational costs.
An example of an open-pit mine is the Molycorp Minerals rare earth mine in Mountain Pass, California
(see Figure 3-1, above). The mining operations at Pea Ridge, Missouri, are extensive and deep
underground mining works. An aerial view of the Pea Ridge mine is provided in Figure 3-3.
3-15
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Rare Earth Elements Review
Section 3 - Life-Cycle Stages of Rare Earth Elements Mines
Attribute Google (© 2011 Google) and USDA Farm Service Agency
Figure 3-3. Aerial image of Pea Ridge magnetite mine, Missouri.
Open-pit mines use a variety of drilling, earth-moving equipment, and explosives to terrace into the
subsurface to extract overburden, waste rock, and ore. Underground mine operations are more targeted,
but also use drilling, excavation equipment, and explosives to construct a series of shafts that advance to
and then remove ore to the surface. Because of their typically elongated nature, geochemical deposit
models suggest that both thorium-rare earth element veins and carbonatite dikes could be developed by
underground mining techniques (Armbrustmacher et al., 1995). The depth and extent to which open-pit or
underground works are advanced depends upon the ore grade, nature of the overburden (e.g., thickness
and hardness, or difficulty of removal), and the stripping ratio. Stripping ratios of overburden to ore can
be large (e.g., 80:1) for aboveground mines and much smaller for underground mines (e.g., 1:1 to 1:20).
Stripping rations for open pit uranium mines range from 10:1 to 80:1 with an average of around 30:1
(USEPA, 1983b, Vol. 2). The stripping ratios also illustrate that the potential of environmental impact
from rock waste is generally much less from underground mining operations.
Both methods produce overburden piles, piles of waste rock, ore and subgrade-ore stockpiles, and
sediment. Overburden piles that contain soil and non-ore-bearing (or non-mineralized) rock, removed to
expose the mineralized ore body, are produced during aboveground and underground mining operations.
Overburden is typically stored separately from other stockpiles and wastes because it can contain less of
the deeper mineralized rock of the ore body. Overburden may also be stored from the development of
underground mines or used to backfill mine shafts as mining progresses; however, the volume of
overburden and waste rock is typically less from underground mines. Waste rock piles store more
mineralized rock that was removed from around the ore body. The differentiation between waste rock and
ore can be relative and dependent upon economic variables.
3-16
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Rare Earth Elements Review Section 3 - Life-Cycle Stages of Rare Earth Elements Mines
Placer Mining
Placer deposits are accumulations of mineral or metal-bearing alluvial sediments that have accumulated in
depressions or stream beds. Placer mines are not considered hardrock mining because the REE ore is
recovered from unconsolidated alluvial or colluvial deposits; however, these mines are often grouped with
hardrock mines for regulatory purposes because the REE host minerals can present the same processing
challenges as those mined directly from a rock ore body.
Placer mining includes the classic image of a gold miner using a pan or a sluice box. Larger and more
modern operations may excavate an open-pit or tunnel into ancient riverbed sediments. Excavation might
be achieved using water pressure (hydraulic mining), excavation or tunneling equipment, or dredging
equipment that is used to mine ore-bearing sediments from stream beds or depressions. Native gold
deposits, uranium, thorium, zirconium, and mineral ores for REMs are examples of placer ore deposits
that occur in the United States. More REE mineral ores have been discovered associated with placer
deposits in the United States than any other deposit type (see Table 3-1 and Appendix B). The Vero
Beach mine in Florida and the Old Hickory mine in Virginia are examples of placer mines that had
produced REEs as a by-product of zirconium mining in the past. The Old Hickory mine continues to
operate, but currently is not producing REE-containing minerals (ILUKA Resources, Ltd, 2007). Placer
deposits containing monazite REE-mineral ores are typically associated with higher concentrations of
minerals containing radioactive elements, which has deterred production from these deposits in the United
States.
Prospective Mine Types by State
A general summary indicating the number of potential rare earth mining sites (i.e., potential resources)
that have been documented in the United States is summarized in Table 3-1. Data were summarized from
the table in Appendix B, which was compiled from a combination of sources, but is principally from
information available from the U.S. Geological Survey. The table is presented not to suggest that every
known deposit will be exploited, or that there is potential viability for the rare earth resources that occur
at these locations. It is provided simply to assist stakeholders in these states gain an awareness of the level
of known occurrences of REE resources. Other deposits and mine sites likely exist or are being explored
that were not identified or included in Appendix B, however, the following table gives a general idea of
types of mines that might be found or developed in each state. It should be noted that this information is
very general; no aspects of the mine sites have been verified, and the current condition of the mines listed
is largely unknown. Actual data were available for some existing mines, but the mine type for a few of the
mines listed was inferred from the deposit types or information found on the Internet; approximate counts
are shown in parentheses.
In large part, the table illustrates that the majority of discovered REE deposits, documented in the
information sources found, would be mined as placer deposits or from aboveground open pit mine types.
Neither the Molycorp or Pea Ridge mines, previously discussed, that are being developed and are near
production stage are the more common placer deposit (i.e., dredge type mining) operations, but rather the
Molycorp mine is an aboveground mine and the Pea Ridge mine is an underground mine. As previously
discussed, the feasibility and viability of a deposit depend on a number of complex variables.
3-17
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Rare Earth Elements Review
Section 3 - Life-Cycle Stages of Rare Earth Elements Mines
Table 3-1. Numbers of Existing Mines by State Where Potential REE Resources Have Been
Reported (see Appendix B for References)
State
Alaska
Arizona
Arkansas
California
Colorado
Florida0
Georgia0
Idaho
Illinois
Missouri
Montana
Nebraska
Nevada
New Jersey
New Mexico
New York
North Carolina
Oregon
South Carolina
Tennessee
Texas
Utah
Virginia
Wyoming
Totals:
Placer Mine
or
Sedimentary
Deposit3
(9)
0
0
(1)
0
2, (4)
1,(4)
7,(15)
0
0
0
0
0
0
0
0
1,(1)
0
1,(2)
1,(5)
0
(1)
1
(5)
61
Open Pit or
Underground -
Unspecified3'13
(5)
(2)
1
2
(3)
0
0
(2)
(1)
0
1,(3)
(1)
1
0
(6)
0
0
(1)
0
0
1
0
1,(1)
(5)
37
Existing
Open Pit
1
0
0
1
1
0
0
4
0
0
0
0
0
0
4
0
0
0
0
0
0
0
0
0
11
Existing
Open Pit with
Underground
Works
0
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
2
Existing
Underground
Mine
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
1
0
0
0
0
0
0
0
0
3
Total Mines/
Deposits by
State
15
2
1
4
4
6
5
29
1
1
4
1
1
1
11
1
2
1
3
6
1
1
3
10
113
a Numbers in parentheses indicate that a record of an existing mine was found, but that the type of mine was not
specified; numbers in parentheses are known occurrences.
b Mines assigned to this category are for igneous or metamorphic deposits and not placer or sedimentary deposits.
c A few mines extend across state boundaries between Florida and Georgia.
3.3.2.4 Mine Closure
The closure of a mine refers to cessation of mining at that site. It involves completing a reclamation plan
and ensures the safety of areas affected by the operation; for instance, by sealing the entrance to an
abandoned mine. EPA requires that planning for closure is ongoing for mines located on federal lands and
not left to be addressed at the end of operations. The Surface Mining and Control Act of 1977 states that
reclamation must
"restore the land affected to a condition capable of supporting the uses which it was
capable of supporting prior to any mining, or higher or better uses."
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Rare Earth Elements Review Section 3 - Life-Cycle Stages of Rare Earth Elements Mines
In some cases, reclamation may not be possible to a level that would support past uses, and long-term
monitoring and management may be required.
Mines close for a variety of reasons, including economic factors due to a decline in the market value of
the metal; geological factors such as a decrease in grade or size of the ore body; technical issues
associated with geotechnical conditions, such as mine stability or in-rush of ground water at rates too high
to manage; equipment failure; environmental impacts; and community pressures (Laurence, 2003).
Often, mines will not close but rather become idle, with plans for reopening when the market will support
the venture. Idle mines can continue to cause a variety of health-related hazards and threats to the
environment if not properly managed. While the mine is idle, the waste piles, the tailings ponds that are
associated with the processing plant, and other mine areas must be stabilized and managed, potentially
over many years.
Mines can be adequately managed to avoid log-term problems; however, the pollution and contamination
issues that generally require environmental management over the life of the mine can remain after mine
closure, such as the following:
Sedimentation of surface waters
Effluent and drainage (e.g., due to heavy precipitation during the rainy season and snow melt)
from the mine, storage piles, or tailings management areas that can impact downstream drinking
water sources and aquatic habitat
Acid mine drainage (AMD) and enhanced acid rock drainage (ARD) that also effect aquatic
habitat
Continued pumping of mine water and contaminant plume migration control pumping that causes
drawdown of nearby aquifers
Contaminated dusts
Subsidence or collapse of tunnels and subsurface structures, which also represents a safety hazard
Hazardous materials remaining on-site (e.g., fuels, lubricants, other chemicals).
These management activities must be planned for long after operations cease and the mine is closed. The
risks associated with these impacts are discussed in Section 6.
In the case of public lands the state or a land management agency has the final authority for concerting
various regulatory authorities and overseeing mine closures. For example, EPA's responsibilities may
include but not be limited to; NPDES wastewater discharge permits for post-closure mining operations,
Clean Water Act (CWA) and Resource Conservation and Recovery Act (RCRA) related permits required
for wastewater or contaminant treatment options (if necessary), and CERCLA financial responsibility
documentation.
3.4 Characteristics of Mining Waste Sources
Mining wastes could be referred to as (managed) materials of concern and, in general, some materials are
not considered wastes until a particular time in their life cycle. However, that is not to imply an absence
of environmental risk from stockpiled or stored materials. Mined materials that are generated may only
occasionally or periodically be managed as wastes. Often, these materials are used for various onsite or
offsite purposes instead of being stored as wastes, although the volume of waste material can often exceed
the demand for reuse alternatives.
EPA evaluates the risks to human health and the environment from reuse of various types of industrial
sector wastes, including mining; however, many of these studies are ongoing, and this report does not
3-19
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Rare Earth Elements Review Section 3 - Life-Cycle Stages of Rare Earth Elements Mines
specifically address reuses or reuse issues as they relate to mining wastes from hardrock mining
operations (e.g., REE mines). Reuse of mine wastewater is a common practice. The wastewater is
removed from underground workings or open pits and then re-circulated for onsite use (e.g., processing
areas) or even offsite use if the water is of adequate quality. However, these waters must meet discharge
limits for concentrations of metals or other constituents and also be permitted for discharge to surface
waters. Unless it represents a problematic waste, rock waste materials may be used as aggregate for a
variety of onsite and offsite construction purposes. These might include uses such as base material for
building foundations, road beds, retaining structures, or other purposes. Many of these reuse strategies
encapsulate waste-rock material, effectively separating it from atmospheric influence that would cause a
release of toxic metals, acids, or alkaline waters to the environment.
3.4.1 Soil Storage Piles
The soils removed during the construction-mining stage of an aboveground mine site are typically placed
in a storage pile and may be used during restoration at the end of the mine's life. Soils are typically not
considered wastes but can be a potential source of pollution if not properly managed, especially for
providing a source of sediment in runoff. Humus-rich soils may be acidic, and fines that run off to streams
could affect surface water quality. Acidic soils used as cover for metal-bearing rock-waste areas could
encourage metal leaching from the rock.
3.4.2 Overburden
Overburden storage piles of sediments and rock materials that do not contain the commodity can include
other metals and constituents that may also be a source of pollution and contamination. While relatively
small in comparison to quantities of other mining waste, overburden, which is the material removed to
expose the ore during mining, may include unconsolidated materials such as alluvium, colluviums, glacial
deposits, or residuum and be a source of sediment or acid-generating minerals; however, the acidity of
these materials is usually low and they generally do not contain significant concentrations of metals.
Overburden usually does not include rock that contains the mineral ore, but it may include the very low
mineralized rock removed from around the ore from hardrock mines. These materials can contain greater
metal concentrations than typically associated with unconsolidated deposits. Without proper management,
erosion of the overburden storage piles resulting in sediment loading to streams and surface water can
occur. Ground water may be entrained with the overburden material, which can then leach through to the
base of the pile, carrying with it high concentrations of metals and other potentially harmful constituents.
Overburden piles can cover hundreds of acres and be a prominent feature in the general landscape as they
reach heights extending hundreds of feet. Large mines may have multiple overburden storage piles. Large
mine trucks and other vehicles deliver materials to the top of the pile and shape the slopes. Fugitive dusts
are a concern from overburden storage piles.
3.4.3 Ore and Subeconomic Ore Storage
Ores may be stockpiled to provide a supply, lasting 6 months or more, of ore stock feed for beneficiation
and processing plants. Subeconomic ore is often stockpiled at the mine site for future exploitation under
the appropriate economic or market demand conditions. These ore stockpiles and Subeconomic ore
storage piles can include large areas. Mines may stage ores at multiple sites. Ore stockpiles can represent
a significant source of toxic metals. Runoff, flooding, or infiltration of rainwater, if not captured and
managed, can have significant effects on aquatic habitat. Ground water may be entrained with the ore
material, which can then leach out to the base of the pile, carrying with it high concentrations of metals
and other potentially harmful constituents. Large mine trucks and other vehicles deliver materials to the
top of the pile and shape the slopes. Fugitive dusts containing metals or other harmful constituents from
the ore and Subeconomic ore stockpiles, even though not as much of a concern as tailings wastes or
conveyances, may still be of potential concern depending upon the material stored.
3-20
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Rare Earth Elements Review Section 3 - Life-Cycle Stages of Rare Earth Elements Mines
As previously discussed, AMD is uncommon in most REE deposits; however, some potential exists for
low levels of acid generation from accessory minor sulfide minerals, especially in low-Ti iron oxide Cu-
U-Au-REE deposits like Pea Ridge (Foose et al., 1995). Carbonatite ores, such as those at the Mountain
Pass mine, may cause elevated pH in streams, depending on the concentration of other acid-producing
accessory minerals in the ore-bearing rock and surrounding country rock that can serve to neutralize any
runoff. Thorium-rare earth element veins have moderately high sulfur content, but the sulfur is present
chiefly as sulfate in barite. Sulfide mineral content of these vein deposits is very low, thus potential for
AMD generation is low (Armbrustmacher et al., 1995). Carbonatites are important REE ores, and these
igneous rocks contain greater than 50 percent carbonate minerals. Waste rock from REE deposits could
potentially present a problem with neutral mine drainage (NMD), with pH in the range of 6 to 10. Mine
drainage in the NMD pH range can have various elevated metal (e.g., zinc, cadmium, manganese,
antimony, arsenic, selenium) concentrations (INAP, 2010). In the case of REE deposits, there is generally
a lack of a mineralogical source for metals that are mobile under such conditions; however, elements like
uranium and vanadium could be mobile under NMD conditions, and these elements are constituents of
some REE ores. Special engineering designs, waste handling and disposal procedures, or closure and
reclamation plans may be required for those materials whose characteristics may pose significant risks.
The impact of AMD depends upon the ability of receiving waters (ground water and surface water) to
neutralize and dilute the drainage.
3.4.4
The following description of waste rock is adapted from EPA and Hardrock Mining: A Source Book for
Industry in the Northwest and Alaska (U.S. EPA, 2003). Waste rock is removed from above or within the
ore during mining activities. It includes granular, broken rock, and soils ranging in size from fine sand to
large boulders, with the fines' content dependent upon the nature of the geologic formation and methods
employed during mining. Waste rock consists of non-mineralized and low-grade mineralized rock.
Materials may be designated as waste because they contain the target minerals in concentrations that are
too low to process, because they contain additional minerals that interfere with processing and metals
recovery, or because they contain the target metal in a form that cannot be processed with the existing
technology. These materials are stored as waste at one point in a mine's life, but may become ore at
another stage, depending on commodity prices, changes in and costs of technology, and other factors.
Waste rock and subeconomic ores may be stockpiled together or separated in grades of material.
Similar to ore/subeconomic ore stockpiles, waste rock storage piles are typically large, covering acres of
land and extending to a height of many feet. Waste rock piles can represent a significant source of toxic
metals. Runoff, flooding, or infiltration of rainwater, if not captured and managed, can have significant
effects on aquatic habitat. Ground water may be entrained with the waste rock if the rock units being
mined occur below the water table, which can then leach out to the base of the pile, carrying with it
concentrations of metals and other potentially harmful constituents. Large mine trucks and other vehicles
deliver materials to the top of the pile and shape the slopes. Fugitive dusts containing metals common to
the ore material are also a concern from waste rock storage piles. Figures 3-4 and 3-5 present block flow
diagrams of conventional hardrock and placer deposit mining, materials management, and potential
pollutants.
3-21
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Rare Earth Elements Review
Section 3 - Life-Cycle Stages of Rare Earth Elements Mines
I I
Radiologicals
V J Turbidity
@V ' V
X N \ \
V X ^ Stockpile /' '
( Sub-ore ]
L-\ Stockpile/..- / Air: /
C Ore ^ Dust*
*V )
Water:
Stockpile / Metals
\ AMD \
\ Turbid ty \
| | Process \ / Product management \ / Waste management unit
C ) Product C ) Waste ( ( Emissions
* In addition to airborne-particulate hazards (e.g., respiratory impacts), a fraction of the dust may include
radiological and metals contamination.
Figure 3-4. Conventional hardrock deposit mining process and wastes emissions.
/ /
Dredaina C Dredge ^ / Water: /
Dred9ln9 V Wastewater J Radiologicals
f Air: I : AMD
1 Dusfl*' \ Turbidity \
- \ \
f Waste Rock ) ^. Stockpile /
{ Sub-ore | ^ Stockpile /
I ^ /
C Ore ^ Dust* /
^V Ore )
Water:
\ Stockpile / Meta|s
\ AMD
\ Turbidity \
| | Process \ / Product management \ / Waste management unit
( ) Product ( ) Waste ( ( Emissions
* In addition to airborne-particulate hazards (e.g., respiratory impacts), a fraction of the dust may include
radiological and metals contamination.
Figure 3-5. Conventional placer deposit processing and wastes emissions.
3-22
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Rare Earth Elements Review Section 4 - Resource Processing
4. Resource Processing
Rare earth milling and processing is a complex, ore-specific operation that has potential for environmental
contamination when not controlled and managed appropriately. Waste streams from REE processing have been
identified, and their hazardous waste potential assessed. Although potentially significant, based on case studies
and chemical composition, the waste streams with the greatest pollution potential are the tailings and their
associated treatment and storage. Heavy metals and radionuclides associated with REE tailings pose the
greatest threat to human health and the environment when not controlled. However, adoption of new technologies
and management processes show potential to reduce the risk of environmental contamination.
The two major mineral sources of REEs are bastnasite and monazite and will be the focus of this section.
However, it is important to note that production can come from a variety of minerals, such as xenotime,
apatite, yttrofluorite, cerite, and gadolinite. Due to their strong affinity for oxygen, REEs are primarily
present as oxidic compounds, and resources are often expressed as REOs. Processing REOs into usable
products is a very complex process and often varies significantly between deposits. The major factors
affecting the selection of treatment processes are listed below (Perron et al., 1991):
Type and nature of the deposit (e.g., beach sand, vein type, igneous and complex ores) and its
complexity
Type and nature of other valuable minerals present with REOs
Type and nature of gangue minerals present in the deposit (e.g., slimes, clay, soluble gangue)
Type and composition of the individual REO minerals
The social and environmental acceptability of the process.
The primary steps involved in processing REOs are separation and concentration from the host material in
acidic or alkaline solutions, separation of the REOs using solvent extraction or ion exchange, and
reduction of the individual REOs into pure metals (Tran, 1991; Gupta and Krishnamurthy, 2004). The
first step typically includes crushing the ore and separating the REO by flotation, magnetic, or gravimetric
separation. This separation process dramatically increases the percentage of REOs in the working
material. For example, the Mountain Pass mine separates and concentrates REOs in bastnasite from
7 percent to 60 percent. A tremendous amount of discarded waste rock (tailings) is generated in this
process and is typically managed onsite or used as backfill material. Chemical changes typically do not
occur during the first step, and this process is usually situated near the mine site to reduce transport costs.
Subsequent steps in the process aim to change the concentrated mineral into more valuable chemical
forms through various thermal and chemical reactions. Typically utilizing hydrometallurgy techniques
(e.g., leaching, extraction, precipitation), the mineral concentrates are separated into usable oxides.
Further processing by techniques such as metallothermic reduction can refine the oxides or metal
mixtures into high-purity REMs.
Figures 4-1 and 4-2 present block flow diagrams of typical extraction and processing steps involved in
hardrock and placer mining operations that highlight potential environmental emissions.
4-1
-------
Rare Earth Elements Review
Section 4 - Resource Processing
: Dred
I Air: L-'.
I Dust* P
jT Ore
gmg ^v Wast
^t Qnh nrn 1
f ore ]
(/ Grinding
Air: [ ;
Dust* P
\ >
Mag
Sepa
Ac
Dige
Filtr;
Precip
r
ietic /
ration \
t
stion \
\
r
/
c
itation
r
Caustic
Digestion
r
Rare Earth
Separations
r
C RE Oxides ^
1
dge \ /
swater )" _.W_ate '/__._
* Metals
Turbidity
X Stockpile /
+ immediate
^. Stockpile / mine
/
/ Air:
/ Dust* J
f Water: I
1 Radiologicals 1
1 Metals \
\ AMD \
\ Turbidity
/
/ Air:
Dust*
Tailings /
Impoundment / "'....> Water:
Radiologicals
Metals
:^ v Organics
Liquid Waste J \ Turbidity
| | Process
( ) Product
\ / Product management
( ) Waste
\
rial may be
ly returned
-eviously
d area
/
\
\
\ / Waste management unit
( ( Emissions
* In addition to airborne-particulate hazards (e.g.,
respiratory impacts), a fraction of the dust may
include radiological and metals contamination.
Figure 4-1. Conventional placer deposit resource processing and potential wastes emissions.
4-2
-------
Rare Earth Elements Review
Section 4 - Resource Processing
C~o
^_
/ A" L
\ Dusp v MJ;
^f
V_
verburden j 1
~"\
Sub-ore } 1
1 \ Stockpile /
^\ r
i i
\
Grinding
4
Acid Digestion
iiiibneiimy
1
Rare Earth
Separations
(/
DAusi* V Dr*n*
\
(REO Concentrate!
/
-I 1
Water: /
Radiologicals
Metals
AMD
Turbidity
/ Air /
f Dust* /
Water: I
Radiologicals
Metals I
1 AMD \
\ Turbidity \
^^^C Tamngs j
\ Tailings /
\ Impoundment/
/ A,,: /
Dust* /
VOCs /
Water:
Radiologicals
Metals 1
Organics I
\ AMD \
\ Turbidity \
| | Process
( 3 Product
\ / Product management
C j Waste
\ / Waste management unit
( ( Emissions
1
,
* In addition to airborne-particulate hazards (e.g.,
respiratory impacts), a fraction of the dust may
include radiological and metals contamination.
Figure 4-2. Conventional hardrock resource processing and potential wastes emissions.
4-3
-------
Rare Earth Elements Review Section 4 - Resource Processing
4.1 Bevill Amendment
The 1980 amendment to the Resource Conservation and Recovery Act (RCRA), known as the Bevill
exclusion, was enacted to exclude specific solid wastes from the extraction, beneficiation, and processing
of ores and minerals. The EPA established criteria for determining beneficiation and process waste for
each mineral production sector and reported this information in the final rule (54 Fed. Reg. 36592, 36616
codified at 261.4(b)(7)).
The EPA determined the line between beneficiation and processing of rare earths for one particular rare
earth operation is when the ore is digested with concentrated acids or caustics (U.S. EPA, 1991).
However, several factors are involved in making Bevill determinations, and official assistance should be
sought from the RCRA authorized state or the EPA Regional office. The basic steps in making Bevill
determinations are the following:
1. Determine whether the material is considered a solid waste under RCRA.
2. Determine whether the facility is using a primary ore or mineral to produce a final or intermediate
product, and also whether less than 50 percent of the feedstock on an annual basis are from
secondary sources.
3. Establish whether the material and the operation that generates it are uniquely associated with
mineral production.
4. Determine where in the sequence of operations beneficiation ends and mineral processing begins.
5. If the material is a mineral processing waste, determine whether it is one of the 20 special wastes
from mineral processing.
This process of determination will result in one of the three outcomes:
The material is not a solid waste and therefore not subject to RCRA;
The material is a solid waste, but is exempt from RCRA Subtitle C because of the Mining Waste
Exclusion; or
The material is a solid waste that is not exempt from RCRA Subtitle C and is subject to regulation
as a hazardous waste if it is listed or characteristic hazardous waste.
The EPA offers online compliance assistance on the Bevill Amendment at the following Internet address:
http://www.epa.gov/oecaerth/assistance/sectors/minerals/processing/bevillquestions.html.
4.2 Beneficiation Processes
As previously described in Section 4.1, the beneficiation process does not alter the chemical composition
of the ore; rather, these processes are intended to liberate the mineral ore from the host material. The
crushing and grinding steps enable the exploitation of differences in physical properties such as
gravimetric, magnetizability, and surface ionization potential to aid in separation (Apian, 1988). The
separation processes typically employed are (1) gravity separators, (2) electrical/magnetic separators, and
(3) flotation separators.
Gravity concentration methods separate minerals of different specific gravity by exploiting the variance in
their gravity-driven movement through a viscous fluid. For successful separation using this technique,
there must exist a marked density difference between the mineral and the gangue. Examples of gravity
separators include (1) jigs; (2) pinched sluices and cones; (3) spirals; (4) shaking tables; (5) pneumatic
tables; (6) duplex concentrators; (7) Mozley laboratory separator; and (8) centrifugal concentrators.
4-4
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Rare Earth Elements Review Section 4 - Resource Processing
Electrical and magnetic separation methods are considered similar because they exploit some of the same
properties of the mineral and thus their application can overlap. Magnetic separators utilize the
differences in magnetic properties between the mineral of interest and gangue. There are two primary
classifications of materials when applying magnetic separation: (1) diamagnetic and (2) paramagnetic.
Diamagnetic materials are repelled along the lines of magnetic force, while paramagnetic materials are
attracted along the lines of magnetic force. There are two primary classes of magnetic separators: low-
and high-intensity process units. Highly paramagnetic materials (e.g., ferro-magnetic) are typically
separated using low-intensity separators, such as drum separators. Specifically for rare earths, roll
separators that utilize alternate magnetic and non-magnetic laminations are commonly used. High-
intensity separators are employed to separate very weak paramagnetic minerals and include common
configurations such as induced roll magnetic separators and Jones separators. Electrical separation
exploits electrical conductivity differences among various minerals in the ore. For optimum results, the
ore feed needs to completely dry and only one particle deep. This restriction has limited the application
primarily to beach and stream placers, such as those where REEs are found. Examples of electrical
separators include plate and screen electrostatic separators.
In applications where the ore particle size is too small for efficient gravity separation, flotation is typically
employed. Flotation exploits the hydrophobicity of the mineral of interest and the hydrophilicity of the
gangue. Accordingly, the hydrophobic mineral particles tend to "stick" to the air bubbles that are
delivered into the process unit and rise to the surface where they are separated. To aid in this process, a
variety of chemicals are added to the ore slurry and include collectors, frothers, and modifiers.
4.2.1 Bastnasite Beneficiation
Although there are variations in the beneficiation of bastnasite, the general process involves
crushing/grinding and separation by flotation. To provide a relevant example, details of the Molycorp
Mountain Pass mine are presented. The ore containing bastnasite (7 percent REO) is crushed, ground, and
classified in the milling process to achieve 100 percent passing a 150 mesh sieve prior to separation by
hot froth flotation (Gupta and Krishnamurthy, 2004). Prior to flotation, the ore passes through six
different conditioning treatments in which steam, soda ash, sodium fluosilicate, sodium lignosulfonate,
and steam-distilled tall oil are added to aid the separation of the unwanted materials (often referred to as
gangue). This process produces a 60 percent REO bastnasite concentrate. A detailed process flow diagram
(PFD) of this process is presented in Figure C-l in Appendix C.
4.2.2 Monazite/Xenotime Beneficiation
Typically associated with dredged mineral sands, the monazite or xenotime ore is separated and
concentrated after course grinding via gravimetric, flotation, or magnetic processes. As expected, the
complexity of this process is dependent on the specific reserve. A detailed PFD of a conventional
monazite extraction and processing operation is presented in Figure C-2 in Appendix C.
4.3 Extraction Processes
Hydrometallurgy is the most common chemical extraction method of separating individual REOs from
the mineral concentrate. Basicity differences between the various rare earths influence the solubility of
their salts, the hydrolysis of ions, and the formation of complex species (Gupta and Krishnamurthy,
2004). The differences in these properties are exploited by fractional crystallization, fractional
precipitation, ion exchange, and solvent extraction to separate the individual REOs. Although some of the
individual REOs and rare earth chlorides resulting from these processes have market value, further
processing and refining are required to produce high-quality pure metal end products to maximize value.
These processes are also utilized to recover REEs from recycled materials. Table 4-1 presents a list of
rare earth extraction methods and a brief description of each.
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Section 4 - Resource Processing
Table 4-1. Rare earth extraction methods (adapted from Meyer and Bras, 2011)
Method
Liquid-Liquid
Extraction
Solid-Liquid
Extraction
Solid Phase
Ion Exchange
Supercritical
Extraction
Electrowinning
Electrorefining
Electro Slag
Refining
Type
Hydrometallurgy
Hydrometallurgy
Hydrometallurgy
Hydrometallurgy
Hydrometallurgy
Electrometallurgy
Electrometallurgy
Pyrometallurgy
Extraction Trait
Solubility
Solubility
Solubility
Chemical Affinity
Variety
Electronegativity
Electronegativity
Density
Process
The liquid containing the desired element is mixed with
an immiscible solvent, which preferentially dissolves the
desired element. When the liquids separate, the
desired element separates with the solvent.
The solid is placed into a solvent, which dissolves the
desired soluble component.
The fluid containing the desired element is poured
through a sorbent bed, which forms equilibrium by the
liquid adsorption to the solid surface or penetration of
the outer layer of molecules on that source. Either
undesired components can be washed-out or elutriants
can be used to selectively extract the desired elements.
The fluid containing the desired elements are mixed
with an elutriant and poured through a resin. The
molecules are separated based on their affinity split
between the elutriant and the resin.
The fluid containing the desired element undergoes a
reaction with CC>2 at or over the critical temperature of
31 °C and critical pressure of 72.9 atm. This amplifies
minute differences between elements to allow
separation.
A current is passed from an inert anode through a liquid
leach solution containing the metal. The metal is
extracted by an electroplating process, which deposits
the rare earths onto the cathode.
The anode is composed of the recycled material. When
the current passes from the anode to the cathode
through the acidic electrolyte, the anode corrodes,
releasing the rare earth solution into the solution, then
electrowinning occurs.
Electricity melts the metal. The molten metal is
combined with a reactive flux, which causes the
impurities to float off the molten metal into the slag.
4,3,1
The desired end product(s) dictates the subsequent processing steps of the bastnasite concentrate. Typical
processes include leaching, washing, filtering, and drying or calcining to increase the percent REO from
approximately 60% up to as much as 90%. In previous operation, the Mountain Pass Mine produced three
commercial grades of bastnasite, with end uses such as glass polishing powders and master alloys for iron
and steel production. To produce individual lanthanides, the concentrate was first calcined to convert the
contained cerium to plus four valency while leaving the other lanthanides in the plus 3 valency. Acid
digestion followed and resulted in the dissolution of most of the non-cerium lanthanides. The resulting
solution was then processed using multistage solvent extraction to produce high-purity rare earth
compounds, such as (1) neodymium-praseodymium carbonate, (2) lanthanum hydrate, (3) cerium
concentrate, (4) samarium oxide, (5) gadolinium oxide, (6) terbium oxide, and (7) europium oxide. A
detailed PFD of this process in presented in Figure C-l in Appendix C.
It is important to note that the Mountain Pass Mine (Molycorp Metals and Alloys) extraction processes
and associated equipment are currently being upgraded and the previously described process may not
accurately reflect planned or current practice.
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Rare Earth Elements Review Section 4 - Resource Processing
4.3.2 Monazite/Xenotime Extraction
In one common method of processing monazite/xenotimes, the ore concentrate from the beneficiation
process is first digested with 70 percent sodium hydroxide (NaOH), producing rare earth hydroxides. The
rare earth hydroxides are then leached with HC1 to recover the soluble rare earth chlorides. The rare earth
chloride solution is then processed using multistage solvent extraction to produce individual, high-purity
REOs (95-99.995 percent). A detailed PFD of this process is presented in Figure C-3 in Appendix C.
4.3.3 Tailings Extraction
Another potential source of REO is the tailings waste from other mineral processing operations. For
example, the apatite tailings from the Pea Ridge iron ore mine and processing operation contain 0.5%
REO. The two primary methods for extracting REO from apatite are selective acid extraction and physical
separation techniques. Through gravimetric processes, the U.S. Bureau of Mines was able to recover 90%
of the REO and produce a 70% lanthanide concentrate (US DOI, 1993). Specifically, the pulped apatite
was mixed with oleic acid to collect the phosphate when pine oil was used as the frother. Three
successive flotation steps yielded the desired lanthanides. The tailings impoundment currently contains 20
million tons that is over 7% apatite.
4.4 Reduction Processes
The liberation of REMs from compounds such as oxides or chlorides can be a very difficult process due
to their extreme stability. Several methods have been developed to accomplish this task. However, the
three primary methods of producing REMs are (1) reduction of anhydrous chlorides or fluorides, (2)
reduction of REOs, and (3) fused salt electrolysis of rare earth chlorides or oxide-fluoride mixtures
(Gupta and Krishnamurthy, 2004). Currently, only one facility is producing high-purity rare earth alloys
and metals in the United Statesthe recent Molycorp acquisition, Santoku America, Inc., in Phoenix,
AZ.
Metallothermic reduction (smelting) is the most widely used method for REM preparation. Reductants
react in the furnace with oxidants (e.g., oxygen, sulfide, carbonate) to separate and free the metal.
Less common processes that can be employed in the reduction of rare earth compounds are
Electrolysis
Gaseous reduction
Vacuum distillation
Mercury amalgamate oxidation and reduction
High-performance centrifugal partition chromatography
Si-octyl phenyloxy acetic acid treatment.
4.5 Potential Environmental Impacts
The EPA (1991) previously identified specific waste streams in rare earth processing and assessed their
hazardous waste potential (Table 4-2). The review identified four waste streams that would likely be
classified hazardous: (1) waste solvent due to ignitability, (2) spent lead filter cake due to toxicity,
(3) waste zinc contaminated with mercury due to toxicity, and (4) solvent extraction crud due to
ignitability. However, the major environmental risk in mining and processing rare earths is associated
with the treatment and disposal of the tailings (Oko-Institut e.V., 2011). The tailings typically contain
high-surface-area particles, wastewater, and process chemicals. The impoundment areas are exposed to
weathering conditions and have the potential to contaminate the air, soil, surface, and groundwater if not
properly controlled and managed. Typical pollutants that have been associated with rare earth tailings
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Section 4 - Resource Processing
impoundments are solids; ore-associated metals (e.g., aluminum, arsenic, barium, beryllium, cadmium,
copper, lead, manganese, zinc); radionuclides; radon; fluorides; sulfates; and trace organics. Fugitive dust
from the tailings impoundment can contaminate the air and surrounding soil. Surface water runoff from
precipitation events or dam overtopping can transport pollutants from the impoundment to surrounding
soil and surface waterbodies. Additionally, if adequate groundwater protection measures are not utilized
(e.g., impoundment liner), the potential exists to contaminate surrounding groundwater resources. A
worst-case scenario is dam failure due to poor construction or from a catastrophic event, resulting in
serious long-term environmental damage. However, proper design, operation, and management of a mine
and its associated pollution control systems can greatly reduce the risk of environmental contamination
from REE mining and processing activities.
Table 4-2. Rare Earth Processing Waste Streams and Their Hazardous
Waste Potential (U.S. EPA, 1991)
Process Waste Stream
Off-gases from dehydration
Spent hydroxide cake
Spent monazite solids
Spent off-gases from electrolytic reduction
Spent sodium fluoride
Waste filtrate
Waste solvent
Spent lead filter cake
Lead backwash sludge
Waste zinc contaminated with mercury
Solvent extraction crud
Hazardous Waste Potential
None
None
None
None (after
appropriate treatment)
None
None
Ignitability
Toxicity
None
Toxicity
Ignitability
The process that generates waste zinc contaminated with mercury was generally abandoned in
the 1990s.
4.5.1 China Legacy
China's high REE production, combined with limited environmental regulations, has resulted in
significant environmental damage to the areas surrounding mining and processing operations. Operations
range from large government-operated minTes and processing facilities to small illegal endeavors. Often,
smaller operations have little or no environmental controls, and larger operations have only recently
begun adopting such measures. For example, after 40 years of operation, the Bayan-Obo mine has an
11-km2 tailings impoundment that has radioactively contaminated the soil, groundwater, and vegetation of
the surrounding area (Oko-Institute e.V., 2011). As reported by Hurst (2010), The Chinese Society of
Rare Earths stated that every ton of rare earth produced generates approximately 8.5 kg of fluorine and 13
kg of dust. Also, they reported the use of concentrated sulfuric acid during high-temperature calcinations
produces 9,600 to 12,000 m3 of waste gas containing dust concentrate, hydrofluoric acid, and sulfur
dioxide, and approximately 75 m3 of acidic wastewater, as well as 1 ton of radioactive waste residue
(Hurst, 2010). Additionally, the REE separation and refining process known as saponification had been
used extensively in China until recently, generating harmful wastewater. It was estimated that, in 2005,
the process generated 20,000 to 25,000 tons of wastewater, with total ammonia nitrogen concentrations
ranging between 300 mg/L and 5,000 mg/L (Oko-Institut e.V., 2011).
4.5.2 United States Legacy
The primary source of environmental contamination at the Molycorp Mountain Pass site was process
wastewaters and tailings impoundments. Prior to 1980, the facility utilized onsite percolation-type surface
impoundments to dispose of wastewater, while conventional dam impoundments were utilized to dispose
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Rare Earth Elements Review Section 4 - Resource Processing
of tailings. These past operations have impacted groundwater at the site. The greatest impact has been an
increase in total dissolved solids (TDS), primarily as a result of neutralizing HC1 in the wastewater with
sodium hydroxide (NaOH). Groundwater TDS concentrations impacted by unlined impoundments have
been reported by the current operator in the range of 10,000 mg/L. Background concentrations of TDS
have been documented by the current operator from 360 to 800 mg/L TDS, with low but detectable
concentrations of barium, boron, strontium, and radiological constituents. Additional constituents such as
metals, nutrients, and radiological constituents in the wastewater and tailings have potentially had a
negative impact on groundwater quality. In 1980 and 1987, two additional off-site evaporation ponds
were constructed to dispose of wastewater. During the time of operation of these units, multiple instances
of mechanical failure of the pipeline connecting the Mountain Pass site to the evaporation ponds resulted
in surface soil contamination. Specifically, two wastewater spills were documented at the site (U.S. EPA,
1994). The first spill, as reported by EPA, occurred in 1989 and involved the surface discharge of 3,375
gallons of tailings and process wastewater from a failed pipeline. The second spill occurred in 1990 and
involved the surface discharge of 45,000 gallons of process wastewater from a failed pipeline. Both spills
were contained onsite and deemed insignificant due to the low risk to human health and the environment.
Contaminated groundwater is actively being remediated. Groundwater interceptor wells and the mine pit
have resulted in a cone of depression that is allowing capture and treatment of the contaminated plumes
(CA RWQB, 2010). Additionally, the pipeline involved in the wastewater spills is currently being
removed by the former mine owner.
The newly proposed facility will utilize multiple technologies and management strategies to minimize
environmental impacts. The primary improvement involves the management of water and tailings.
Dewatered tailings result in a "paste"' that is pumped to an onsite location and layered into a stable
containment mound. The process will result in the elimination of 120 acres of evaporation ponds. Reverse
osmosis (RO) will be used to treat and reuse 90 percent of the wastewater, while the RO reject will be
further treated to produce value-added products that can be reused in the process or sold. An onsite chlor-
alkali facility will use the treated RO reject from the previous step as feed to produce NaOH, HC1, and
sodium hypochlorite (NaCIO) for reuse or for sale (RTI International, 2011). However, as with any reuse
technology, the result is often a concentrated wastewater stream that will require disposal. In the
Molycorp-proposed process, pollutants such as heavy metals concentrated in the RO reject are destined
for precipitation and removal via nanofiltration. The brine from this process will be dried in on-site
evaporation ponds prior to final disposal. Based on available information, Figure 4-3 presents a
simplified block flow diagram of the proposed wastewater and tailings treatment process that highlights
potential environmental emission points and potential contaminants of concern. It is reported that this
approach would also result in less chemical use, less water consumption, and reduced reagent trucking
volume (RTI International, 2011).
Additional improvements and management strategies include (1) improved milling to improve resource
recovery and lessen tailings volume per unit of REO produced, and (2) utilization of a new natural gas
pipeline to supply a combined heat and power system to provide electricity and heat that is 20 percent
more efficient than the previous methods (RTI International, 2011).
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Section 4 - Resource Processing
f NaOH, NaOCI,
\ HCI for Reuse
1
Metal
Recovery or
Off-site
Disposal
Air:
DusP
Water:
Radiologicals
, Metals
\ Turbidity
Air:
DusP
Water:
Radiologicals
Metals
Organics
Turbidity
| | Process
C "') Product
\ / Product management
( ) Waste
V 7 Waste management unit
( Emissions
* In addition to airborne-particulate hazards (e.g.,
respiratory impacts), a fraction of the dust may
include radiological and metals contamination.
Figure 4-3. Anticipated Molycorp Mountain Pass mine water
reclamation process and potential waste emissions.
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Rare Earth Elements Review Section 5 - Rare Earth Element Recovery/Alternative Material Use
5. Rare Earth Element Recovery/Alternative Material Use
Increased demand and reduced supply of REEs, along with the knowledge of the quantities available in waste
products, has resulted in expanded research and development efforts focused on the recycling of rare earths.
Currently, commercial recycling of rare earths is very limited; however, it is reported in the literature that, within
the next year, several new commercial recycling operations will begin operation, with the focus being on
magnets, batteries, lighting and luminescence, and catalysts. Recycling of postconsumer, end-of-life products,
typically involves four key steps: (1) collection; (2) dismantling; (3) separation (preprocessing); and (4)
processing. A general description of each step is provided, along with the potential waste streams and
environmental impacts. While environmental impacts can occur, when compared with primary processing, it is
reported that controlled recycling of REEs will provide significant benefits with respect to air emissions,
groundwater protection, acidification, eutrophication, and climate protection.
5.1 Introduction
While research on methods for recycling and recovering REEs from as early as 1984 was identified
during our literature review, it is not until recently that more attention within industry and the literature
has been given to the topic of REE recycling. The primary drivers for this renewed focus include the
increased demand for REEs, concern about REE supplies, increasing cost of REEs, and new policies
implemented by some countries mandating REE recycling for selected items. For example,
Annual global production of REEs totals about 124,000 tons, according to a July 2010 report by
the U.S. Congressional Research Service. By 2014, global demand could exceed 200,000 tons per
year, which would exceed current production by over 75,000 tons per year, according to the
report (Humphries, 2010);
Currently, China produces over 95 percent of all REEs used in the world. This monopoly has
resulted in concerns with respect to supplies and prices of REEs; and
Prices are increasing rapidly for REEs and REOs. Dysprosium, which sold for $300/kg in 2010, is
selling for $3,600/kg in 2011 (Gordon, 2011). Figure 5-1 illustrates price trends for selected
REOs over the past few years.
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Section 5 - Rare Earth Element Recovery/Alternative Material Use
150
2007 2008
Ssurce: MeW Pages onme.
2009
2010
2011
Figure 5-1. Representative rare earth oxide prices from 2007-2010 (The 2007-2010 figures are
fourth-quarter [Q4] average prices. The 2011 numbers represent spot prices on February 25).
(from: http://www.osa-opn.orq/OpenContent/Features/Rare-Earth-Elements-Hiqh-Demand-Uncertain-Supplv-3.aspx)
Information from the literature indicates that large amounts of REEs are currently in use or available in
waste products and would be able to support recycling operations. Specifically, a recent study by the
Japanese government-affiliated research group National Institute for Material Science (NIMS) estimated
that Japan has 300,000 tons of REEs and 6,800 tons of gold currently sitting in e-wastes (Tabuki, 2010).
A recent study by Yale University estimated that 485,000 tons of REEs were in use globally in 2007 (Du
and Graedel, 2011). The study further states that four REEs (cerium, lanthanum, neodymium, and
yttrium) constituted more than 85 percent of the global production, and that recycling the in-use stock for
each of these is possible, but remains a challenge. The research concludes that for the other rare earths
that are generally used in much lower quantities, recycling would be difficult primarily due to technical
challenges associated with separating the rare earths from the product. On an individual basis, cerium is
mostly concentrated in catalytic converters and metal alloys; neodymium is used in permanent magnets,
computers, audio systems, cars, and wind turbines; lanthanum is used in catalysts, metal alloys, and
batteries; and yttrium is used in lasers and superconductors. A newly published report by the USGS
provides additional information on the end uses of REEs and the potential for recyclability by end use
(Goonan, 2011).
To put use quantities in perspective, a Toyota Prius uses 2.2 pounds of neodymium (Wheeland, 2010) and
over 10 pounds of lanthanum (Koerth-Baker, 2010); atypical air conditioner unit includes 4 magnets that
contain about 30 grams of rare earths (Montgomery, 2011); and a new-generation windmill requires 1,500
pounds of neodymium (REVE, 2011).
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A recent United Nations (UN) report on recycling rates of metals estimates that the end-of-life functional
recycling (i.e., recycling in which the physical and chemical properties that made the material desirable in
the first place are retained for subsequent use) for rare earths is less than 1 percent (UNEP, 2011).
Another study estimates that world-wide, only 10 percent to 15 percent of personal electronics are being
properly recycled (Billow, 2011). Of the items that are sent
for recycling, the European Union (EU) estimates that 50
percent of the total is illegally exported, potentially ending
up in unregulated recycling operations in Africa or Asia.
These recycling operations frequently result in
environmental damage and worker exposure, as documented
in a separate UNEP report (Schluep et al., 2009) and
discussed further in Section 6.
"If the United States committed itself to
meeting its critical materials needs in large
part through recycling, there is no nation
on earth that could match American
resources. The United States has the
largest "above-ground" mines of critical
materials in the world, in the sense that
this country's supply of industrial scrap and
end-of-life automobiles, electronics, and
electronic appliances - whether they are in
wreckers'yards, land-fills, or Americans'
basements and attics - can't be matched
by any other nation. In essence, these
"above-ground mines" make the United
States the Saudi Arabia of critical
materials. A well-developed recycling
system could tap these mines for U.S.
critical materials security without limit."
Waste Management World, 2011
The increasing prices of REEs (as well as other recyclable
metals), along with the knowledge of the quantities available
in discards and the increased worldwide demand, have led to
the concept of "urban mining." Urban mining is defined as
the recovery of elements and compounds from waste
materials and products. Consumer electronics are
increasingly becoming subject to urban mining practices
and with over 6.5 million metric tons of personal computers,
computer monitors and peripherals, televisions, and mobile
devices being generated in 2007 in the United States, Europe, China, and Indiathe supply available for
"mining," or recycling, is large and increasing (ICF International, 2011). A short introductory video on
urban mining, with a focus on efforts in Japan, is available on the Internet
(http://english.ntdtv.com/ntdtv en/ns offbeat/2010-10-19/822469802087.html).
Some small electronics such as cell phones reach their end of life after a few years, while many of the
products that contain larger amounts of REEs have useful lives of well over one decade. The recycling of
the REEs contained within products will occur many years in the future and is not a short-term solution to
the current demand. Another factor that will impact one of the recycling drivers is that as additional REE
mines begin operation outside of China, global production will increase, costs may decrease, and the
urgency behind the push to recycle may be reduced.
5.2 Recycle Processing Steps
The recycling process for post-consumer, end-of-life products typically involves four key steps, as
illustrated by Figure 5-1: (1) collection; (2) dismantling; (3) separation (preprocessing); and
(4) processing.
As previously noted, a 2011 status report (UNEP, 2011) states that the end-of-life recycling rates, defined
as the "percentage of a metal in discards that is actually recycled," for REEs is less than 1 percent. As
cited by Meyer and Bras (2011), the consumer products with the most rare earth recycling potential are
the ones that contain high levels of rare earths and an established collection or recycling infrastructure,
such as fluorescent lamps, magnets, car batteries, and catalytic converters. Three factors noted as
contributing to the effectives of recycling efforts are the following (UNEP, 2011):
1. Economics - The value of the materials to be recycled must be greater than the cost of recycling.
In situations where this is not the case, laws and incentives can be effective in increasing
recycling rates.
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Section 5 - Rare Earth Element Recovery/Alternative Material Use
2. Technology - Products that are designed with recycling in mind will be easier to disassemble and
re-process.
3. Societal - Programs will be more effective when the public is aware of the benefits of recycling
and the collection and recycling infrastructure is accessible and well publicized.
Recycling can be conducted on either pre-consumer or post-consumer items. While most of the literature
identified pertains to post-consumer recycling initiatives, it has been reported that 20 to 30 percent of rare
earth magnets are scrapped during the manufacturing process and that research is ongoing to develop
ways for recycling this "waste stream" (Schuler et al., 2011). Similar information was not identified for
other pre-consumer items, but may prove to be an opportunity in the future for manufacturing processes
with high scrap rates.
I
Air:
Dust*
VOCs
Air:
Dust*
Collection
Dismantling
Air:
Transportation
Pollutants
Scrap Waste
j
\Waste 7
Management /
(Landfill) /
c
Air:
Dust*
VOCs
Water/soil:
Metals
Organics
Air:
Dust*
VOCs
Dioxins
Water/soil:
Metals
Organics
Recycled REE Metals
)
| | Process
( ) Product
\ / Product management
( ) Waste
\ / Waste management unit
( ( Emissions
* In addition to airborne-particulate hazards (e.g.,
respiratory mpacts), a fraction of the dust may
nclude rad o ogical and metals contamination.
Figure 5-2. REE recycling steps and waste emissions.
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5.2.1 Collection
The first step, defined as collection, is discussed in the recent report by UNEP (Schluep et al., 2009) and
can be accomplished through a variety of means, but it is generally more efficient when a collection
infrastructure is already established. In the past, state regulations have been effective at establishing the
collection and recycling infrastructure required to increase recycling rates for consumer goods in the
United States. For example, in the 1980s, the recycling of lead-acid car batteries became required by
many states and resulted in a 95 percent recycling rate by 1990. The EPA data show that, nationally, 19%
of consumer electronics were recycled in 2009 (Bomgardner, 2011). As of May 2011, 25 states have laws
requiring e-waste recycling, and 5 additional states have pending laws. In most cases, manufactures are
required to cover the costs associated with the collection and recycling. A summary of these state laws
and information on collection volumes to date is available on the Internet (Electronic Take Back
Coalition, 2011). In further support of electronics recycling, the Responsible Electronics Recycling Act
was introduced into the U.S. House of Representatives in June 2011(H.R. 2284) and includes as one of
three main focus areas: support for collection, logistics, and supply chain optimization to support REE
recycling.
The EPA's Plug-In To eCycling Partners website provides links to take-back programs and drop-off
locations for mobile devices, computers, printers, and televisions. The partners include retail stores,
equipment manufacturers, and mobile device service providers. Together, they collected and recycled 68
million pounds of used consumer electronics in 2008 (U.S. EPA, 2008b). Collection methods include
direct mail of products to locations established by equipment manufactures and drop off of used products
at designated locations, such as retail stores or locations specifically setup as part of collection day events.
Environmental impacts from the collection step are most predominantly due to transportation/shipping of
materials to the collection point and from the point of collection to the location of the processing facility.
5.2.2 Dismantling/Preprocessing
Dismantling and preprocessing steps are critical for separating the high-value components from less
valuable materials. Frequently, high-value materials such as REEs and other metals, like gold, make up a
small percentage of the item being recycled, and separation steps will make it more efficient to recover
them. However, even when metals are separated from other nonmetal components, mixed metal scrap is
more challenging to recycle than segregated metals.
Typical dismantling and preprocessing steps include manual or mechanical separations, manual or
mechanical disassembly, mechanical shredding, and screening. The specific details of each step are
reported in the literature and are dependent on the item being recycled and the material being recovered
(Schluep et al., 2009). Figure 5-2 provides photos of a facility where computer hard disk drives are
manually disassembled, and of the resulting separated components, including magnets containing REEs.
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Section 5 - Rare Earth Element Recovery/Alternative Material Use
Figure 5-3. Left: Dismantling table with pneumatic tools used for manual dismantling of hard
disks. Right: Components resulting from the process and including REE-containing
magnets (upper right corner) (Schluep et al., 2009).
Advances to manual separation methods are being investigated as a way to reduce costs, increase speed,
and reduce potential worker exposures. Two examples of successes in this area are the following:
A process developed by Hitachi for disassembling hard disk drives that involves placing the
drives in a rotating drum where forces such as shock and vibration are employed. This process is
reported to be eight times faster than manual separation and, therefore, more cost-effective
(Clengfield et al., 2010).
A process developed by NIMS that includes a small-scale electronic crushing device that, in a
few seconds, is able to reduce cell phones and small home appliances to small pieces. This step is
followed by placing the pieces in a three-dimensional ball mill that degrades the parts recovered
from the crushing device to a powdered form. Because of the short treatment time in the ball mill,
the remaining pieces of plastics and other materials remain intact and therefore can be recovered
in a condition that allows for plastic recycling. The powder can then be further processed to
recover metals of concern (NIMS, 2009).
During the dismantling and preprocessing steps, hazardous or other unwanted substances have to be
removed and then either stored or treated safely while valuable materials are removed for reuse or
recycling. For devices containing ozone-depleting substances, such as refrigerators and air-conditioners,
the degassing step is crucial in the preprocessing stage because the refrigerants used (e.g.
chlorofluorocarbon or hydrochlorofluorocarbon, in older models) need to be removed carefully to avoid
air emissions of ozone-depleting substances, which have a large global warming potential. LCD monitors
containing mercury or other toxic metals need to be dismantled with care to ensure worker and
environmental protection. Circuit boards present in electronic equipment can contain lead in solder and
flame retardants containing resins (Schluep et al., 2009). After removal of the hazardous and other special
components, the remainder of the item being recycled can be further separated by manual dismantling or
mechanical shredding and (automated) sorting techniques. Some shredding technologies have the
potential to generate dust or other particulate matter that can impact worker health. Additionally, all
mechanical processing equipment requires energy inputs that have additional associated environmental
impacts.
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Rare Earth Elements Review Section 5 - Rare Earth Element Recovery/Alternative Material Use
5.2.3 Processing
After completion of the preprocessing steps, the components of interest are ready for the processing step.
Processing technologies that are currently used, or are in the research stage, for the recovery of REEs are
discussed in several references (Schuler et al, 2011; Ellis et al., 1994; Schluep et al., 2009; ICF
International, 2011; Meyer and Bras, 2011) and can be grouped into the following general categories:
Pyrometallurgy processes are energy intensive, using high temperatures to chemically convert
feed materials and separate them so that the valuable metals can be recovered. It should be noted
that rare earths can oxidize easily in these types of processes, making recovery difficult. While
one recycling facility in Japan reportedly is recovering REEs using this type of process (Tabuki,
2010), others companies such as Umicore and Alcoa are conducting research that will enable
wider use of this type of technology for REE recycling. During smelting, volatile organic
compounds (VOCs) and dioxins could be generated and would need to be managed.
Hydrometallurgy processes use strong acidic or basic solutions to selectively dissolve and then
precipitate metals of interest from a preprocessed powder form. The specific process used will
vary depending on the metal to be recovered, but options could include solvent extraction,
leaching, and selective precipitation, among others. Variations of this type of technology are
frequently reported in the literature, and a recent summary is provided by Schuler et al. (2011).
The fundamental processes used for recycling REEs are the same as those utilized for raw ore.
Accordingly, the waste streams and pollutants of concern are the same as those presented in
Section 4. In short, chemical and particulate air emissions, as well as slag material from the
smelting process are all potential pollutant sources.
Electrometallurgy processes such as electrowinning (where a current is passed from an inert
anode through a liquid leach solution containing the metal; the metal is extracted by an
electroplating process, which deposits the rare earths onto the cathode), and electrorefming
(where the anode is composed of the recycled materialwhen the current passes from the anode
to the cathode through the acidic electrolyte, the anode corrodes, releasing the rare earth ions into
the solution, then electrowinning occurs). No specific information was located on environmental
impacts from these processes when they are used to recycle REEs; however, they are expected to
be similar to those identified in Section 4 for primary processing operations.
Dry processes (research stage) use hydrogen gas at atmospheric pressure to turn neodymium-
containing magnets to a powder that can then be re-formed into new magnets under heat and
pressure. This research is being conducted at the University of Birmingham in the United
Kingdom, and while the newly produced magnets are not of the same quality as the originals,
they are suitable for use in motors (Davies, 2011).
Tailings recycling involves reprocessing of existing tailings to recover the remaining amounts of
REEs they contain. Recycling of tailings generally will occur at the same location as the mining
operation using existing processes and equipment and resulting in the same contaminants as when
processing the original ore. As reported by Xiaozhi (2011), the economic benefit, energy savings,
and environmental benefits can be significant.
Microbe-filled capsule technology (research stage) has been recently reported in the literature as
being developed jointly by Morishita Jintan Co. and Osaka Prefecture University. With this
technology, capsules are reportedly placed in a medium containing rare metals, and the microbes
then absorb the metals. While the research to date has focused on rare metals (not specifically
rare earths), it is thought to be transferable. If this is in fact proven to be true, an official at the
Japan Society of Newer Metals has indicated that it could help to make REE recycling more cost-
effective (Alibaba.com, 2010).
Titanium dioxide process (research stage): While evaluating a process to develop methods for
extracting higher yields of titanium dioxide, researchers from the University of Leeds, Faculty of
5-7
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Rare Earth Elements Review
Section 5 - Rare Earth Element Recovery/Alternative Material Use
Engineering discovered how to recover significant quantities of REOs present in titanium dioxide
mineral. While the original benefits of this technology were thought to be that it could improve
purity, eliminate hazardous wastes, and cut costs and CO2 emissions, the team also discovered
that they could extract significant quantities of REM oxides as co-products of the refining
process. Current recovery rates of oxides of neodymium, cerium, and lanthanum vary between 60
percent and 80 percent and are thought to be able to be increased in the future (University of
Leeds, 2009).
5.3 Commercial REE-Recycling Applications
Review of the literature indicates that the number of commercial REE-recycling operations is limited, but
that is likely to change in the near future due to the number of operations under development and the
amount of research that is ongoing. Table 5-1 provides a summary of commercial, or soon-to-be-
commercial, operations by selected companies and includes the information that is known on the target
item to be recycled, the materials being recovered, the technology to be used, the anticipated time frame
until commercial application; notes with respect to cost or environmental benefits; and the source of
information. Consistent with the information reported here, the literature indicates that the focus of REE-
recycling research and commercialization efforts has been on magnets, batteries, lighting and
luminescence, and catalysts (Schuler et al., 2011). It should be noted that in many cases, the companies
that are in the process of developing or deploying recycling technologies have not published reports or
papers with the details of their individual processes, as these are generally a competitive advantage and
considered proprietary.
Table 5-1. Recycling Operations, Technologies Utilized, Current Status, and Benefits
Company
Hitachi
Toyota
Japan's
Shin-Etsu
Chemical
Showa
Denko KK
Target
Feedstock/
Element
Rare earth
magnets from
air conditioner
compressors
and hard disk
drives
Hybrid car
batteries
Air conditioners
Dysprosium and
didymium (a
mixture of
praseodymium
and
neodymium)
Technology
to Be Used
Automated
separation
process and
dry extraction
process
Unknown
Plans to
recycle
recovered
REEs into
magnets
No
information
readily
available.
Anticipated Time to
Commercialization
Anticipates recycling
will meet 10% of its
need by 2013 when
facility goes online
Ongoing
2011
Estimated output of
800 tons from
recycling facility
Benefits (Cost and
Environmental)
Dry extraction
method that allows
processing without
acids; resulting waste
water problem.
Automated
separation process is
faster than manual.
Cost savings
anticipated.
Main driver is supply
concerns
No information
readily available.
No information
readily available.
Source
http://www.hit.achi.
com/New/cnews/1
01206.pdf
http://shanqhaiscr
ap.com/?p=5654
http://www. matter
network.com/2011
/3/new-push-
recvcle-rare-
earth.cfm
http://www.bloomb
erq.com/news/201
0-12-08/hitachi-
recvcles-rare-
earth-as-china-
crimps-
supplv.html
5-8
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Rare Earth Elements Review
Section 5 - Rare Earth Element Recovery/Alternative Material Use
Company
Mitsubishi
(with
Panasonic
and Sharp)
Kosaka,
Dowa
Holdings
Raptor
Technology
Group
Creative
Recycling
Systems/
GreenRock
Rare Earth
Recovery
Corporation
Wings
Enterprises
Inc.
Umicore and
Rhodia
Target
Feedstock/
Element
Neodymium and
dysposium,
washing
machines and
air conditioners
Existing
electronics
recycling
plant future
processing of
neodymium.
Mine tailings
(from hardrock
ore deposits
from Washoe
mine).
Electronics
Tailings from
previous mining
at Pea Ridge,
Missouri
Nickel Metal
Hydride (NiMH)
rechargeable
batteries
Technology
to Be Used
No
information
readily
available.
Smelter 300
tons of
material per
day are
processed,
resulting in
150 grams of
rare metals
"Advanced
chromatog-
raphy and
innovative
separation
technologies"
"Closed loop"
process.
Details not
available
No
information
readily
available.
Umicore's
proprietary
Ultra High
Temperature
(UHT) battery
recycling
process in
combination
with Rhodia's
rare earth
refining
processes
Anticipated Time to
Commercialization
Currently in research
stage. Anticipated
production stage by
2014
Research being
conducted to develop
technologies for REE
recovery
2,000 tons of ore per
year, currently. New
facility being built with
capacity of over
10,000 tons of ore
per year.
By end of 2011,
estimated to have
four processing
facilities with a
capacity to process
500 million pounds of
electronics per year.
Within 12 months.
First production
expected by end of
2011.
Benefits (Cost and
Environmental)
No information
readily available.
Factory is making
money. Process for
neodymium
extraction is
estimated to be
costly.
Cost savings;
reclaimed mine
wastes' chemical
recycling and water
savings
No information
readily available.
No information
readily available.
This is the first known
technology for
recycling rare earths
from NiMH batteries.
"Atypical NiMH
battery will contain
some 7% of rare
earth elements
including cerium,
lanthanum,
neodymium and
praseodymium. This
equates to 1 gram of
rare earth for a AAA
battery, 60 gram for a
household power tool
and 2 kilograms for a
hybrid electric vehicle
battery."
Source
http://www.bloomb
era.com/news/201
0-12-08/hitachi-
recvcles-rare-
earth-as-china-
crimps-
supplv.html
http : //www. n vti me
s.com/2010/10/05/
business/qlobal/0
5recvcle.html?em
c=eta1
http : //www. ra pto rt
echnoloqvqroup.c
om/qeneral.php c
ateqorv=Raptor+T
echnoloqies=meta
l.php
http: //www. sustain
ablebusiness.com
/i n d ex. cf m/a o/n ew
s.displav/id/21900
http://www.rareme
talbloq.com/2011/
01/rare-earths-
producer-
molvcorp-rivals-
seek-us-aid-as-
china-chops-
exports.html
http://www.eu rone
xt.com/fic/000/064
/994/649944.pdf
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Rare Earth Elements Review Section 5 - Rare Earth Element Recovery/Alternative Material Use
5.4 Environmental Implications of Recycling REEs
As recently reported by UNEP (Schluep et al., 2009), uncontrolled recycling of e-wastes has the potential
to generate significant hazardous emissions. While this report is focused on e-wastes, the emission
categories presented below pertain to the recycling of other types of wastes as well:
1. Primary emissions - Hazardous substances contained in e-waste (e.g., lead, mercury, arsenic,
polychlorinated biphenyls [PCBs], ozone-depleting substances).
2. Secondary emissions - Hazardous reaction products that result from improper treatment (e.g.,
dioxins or furans formed by incineration/inappropriate smelting of plastics with halogenated
flame retardants).
3. Tertiary emissions - Hazardous substances or reagents that are used during recycling (e.g.,
cyanide or other leaching agents) and are released because of inappropriate handling and
treatment. Again, as reported by UNEP (Schluep et al., 2009), this is the biggest challenge in
developing countries engaged in small-scale and uncontrolled recycling operations.
For recycling operations using pyrometallurgy, facilities need to have regulated gas treatment
technologies installed and properly operating to control VOCs, dioxins, and other emissions that can form
during processing.
In hydrometallurgical plants, special treatment requirements are necessary for the liquid and solid effluent
streams to ensure environmentally sound operations and to prevent tertiary emissions of hazardous
substances.
Recovering metals from state-of-the art recycling processes is reported as being 2 to 10 times more
energy efficient than smelting metals from ores. Recycling also generates only a fraction of the CO2
emissions and has significant benefits compared to mining in terms of land use and hazardous emissions.
While examples are not provided in the literature specifically for REEs, production of 1 kg aluminum by
recycling uses only one-tenth or less of the energy required for primary production and prevents the
creation of 1.3 kg of bauxite residue, 2 kg of CO2 emissions, and 0.011 kg of SO2 emissions. For precious
metals, the specific emissions saved by state-of-the-art recycling are reported as being even higher
(Schluep et al., 2009).
Schuler et al. (2011) report that when compared with primary processing, recycling of REEs will provide
significant benefits with respect to air emissions, groundwater protection, acidification, eutrophication,
and climate protection. This report also states that the recycling of REEs will not involve radioactive
impurities, as is the case with primary production.
Additional benefits of recycling that are not directly linked with the environment include improved supply
of REEs, and therefore less dependence on foreign sources; the potential for reduction in REE costs due
to supply increases and reduction of the current "monopoly" from foreign suppliers; and the potential for
job creation from an expanded recycling industry.
5.5 Research on Alternatives to REEs
Research into alternative materials is another strategy that is being explored in response to the REE
supply issues. Generally, this can fall into two main categories: research into alternatives to REEs, or
research into alternative product designs that require fewer or no REEs. Schuler et al. (2011) provides an
analysis and summary of the substitutes. This reference, along with many others, stresses the need for
additional research in this area. As reported in March 2010 by Science magazine (Service, 2010),
examples of selected research efforts under way include the following:
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Rare Earth Elements Review Section 5 - Rare Earth Element Recovery/Alternative Material Use
IBM researchers have developed alternatives to the indium-containing films used in solar cells.
The alternatives have included elements such as copper, zinc, tin, and sulfurall of which are
currently plentiful and relatively inexpensive. While performance is still lacking, it is getting
close to that required for commercialization.
University of California, Los Angeles, researchers are working on replacements for indium used
in transparent conductors in electronic displays. The alternatives that they have developed include
single-atom-thick sheets of carbon and carbon nanotubes.
Researchers at the University of Delaware, Newark, have received funding to develop high-
strength magnetic material from neodymium, iron, and boron nanoparticles. While still requiring
some neodymium, their process is thought to be able to yield as much magnetization using
smaller amounts of rare earths.
Japanese researchers have been studying iron nitride as a candidate magnet material that does not
use any REEs as part of the Rare Metal Substitute Materials Development Project, led by Japan's
New Energy and Industrial Technology Development Organization (NEDO)
(http://techon.nikkeibp.co.jp/english/NEWS_EN/20110307/190128/).
NEDO is in the process of developing a motor for hybrid vehicles that uses ferrite magnets rather
than REE-containing magnets (Tabuki, 2010). According to a report by the Associated Press
Toyota is also working on a new type of motor which does not use any REMs. This could
dramatically reduce production costs and, therefore, the cost of electric vehicles (Gordon-
Bloomfield,2011).
Researchers at Ames Laboratory (a U.S. DOE laboratory) are evaluating methods for making
neodymium-iron-boron magnets less expensively and without generating the hazardous by-
products formed by today's standard manufacturing methods. Other researchers at Ames
Laboratory are searching for substitutes to permanent magnets that will not require REEs. Focus
areas include the Alnico iron-alloy family, iron-cobalt-based alloys, and nanostructured
compounds made from combinations of REEs and transition metals (Jacoby and Jiang, 2010).
Also, in June 2011, Ames Laboratory announced a new partnership with the Korean Institute of
Industrial Technology. The objectives of this partnership are to: improve processing techniques
for rare earths, transfer rare earth discoveries to industrial applications, and educate scientists and
engineers on rare earths (U.S. DOE, 201 la).
GE Global Research, in Niskayuna, New York, has recently received a $2.25 million grant from
DOE for a project titled "Transformational Nanostructured Permanent Magnets." The objective of
this grant is to "develop next-generation permanent magnets that include lower content of critical
rare-earth materials." The focus of the effort will be to develop bulk nanostructured magnetic
materials, resulting in a "dramatic increase in performance over state-of-the-art magnets" (Terra-
Magnetica, 2010).
5.6 Emerging Policies/Programs to Support REE Recycling
REE recycling and research are dynamic fields, with new information becoming available almost daily. In
conjunction with that, there are rapidly developing government policies and research initiatives aimed at
ensuring continuing supply of REEs. At the time of this report for example in the United States, the Rare
Earths Supply-Chain Technology and Resources Transformation Act of 2010 (H.R. 4866, or RESTART
Act) had recently been introduced to Congress. The objective of this bill is to re-establish a competitive
domestic rare earth minerals production industry; a domestic rare earth processing, refining, purification,
and metals production industry; a domestic REMs alloying industry; and a domestic rare earth-based
magnet production industry and supply chain in the United States. Selected other U.S. and international
activities follow:
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Rare Earth Elements Review Section 5 - Rare Earth Element Recovery/Alternative Material Use
In April 2011, DOE announced that through the ARPA-E program it would be providing up to
$30 million in funding for a new research area called Rare Earth Alternatives in Critical
Technologies (REACT). The goal will be to fund early-stage technology alternatives that reduce
or eliminate the dependence on rare earth materials by developing substitutes for REEs used in
electric vehicle motors and wind generators.
The Responsible Electronics Recycling Act was introduced into the U.S. House of
Representatives in June 2011(H.R. 2284) and would add a section to the 1976 Resource
Conservation and Recovery Act (RCRA). The purpose of this Act would be to prohibit U.S.
companies from exporting certain electronic wastes to developing countries. Associated with this
Act will be the establishment of a Rare Earth Materials Recycling Research Initiative that will
fund projects in three main areas: (1) removal, separation, and recycling of rare earth metals from
electronics; (2) new electronics design that promotes ease of separation and recycling; and
(3) collection, logistics and supply chain optimization to support REE recycling.
The Critical Minerals Policy Act (S. 1113) was introduced to the U.S. Senate in May 2011 and is
intended to modernize U.S. policies related to production, processing, manufacturing, recycling
and environmental protection. The Act is focused on minerals identified as being most critical to
military security and a strong economy (Lasley, 2011).
The proposed Critical Minerals and Materials Promotion Act of 2011 (S. 383) directs the U.S.
Department of Interior to conduct research related to ensuring the supply of critical minerals
throughout the supply chain.
The Center for Resource Recovery and Recycling (CR3), funded by the National Science
Foundation and industry partners, was established in 2010 and is located at the Colorado School
of Mines, Worchester Polytechnic Institute, and the Katholieke Universiteit Leuven in Belgium
(Worcester Polytechnic Institute, 2011). As part of its mission, the Center plans to develop
technologies to identify and separate scrap materials from waste streams and build strategies and
technologies to enable greater scrap utilization within materials processes. Current research
activities include efforts focused on REE recycling.
With a possible $2.5 M in funding from the EPA, the UN has initiated a new project that will
track discarded mobile phones and other electronic wastes generated in the United States in order
to develop solutions aimed at recovering REMs (and other materials) from the equipment through
proper recycling. In addition to the United States, the project includes international partners
(Dillow, 2011).
The government of Japan has instituted subsidies and facilitated inter-industry cooperation, both
with the goal of encouraging REE recycling. Japan's Ministry of Economy, Trade and Industry
has published a list of five main focus areas designed to ensure a stable supply of REEs. These
focus areas include: (1) accelerating the development of alternatives to REEs; (2) positioning
Japan as a global hub for REE recycling; (3) working with manufacturers to install equipment
that would result in reduced REE consumption; (4) providing support to companies trying to
acquire rights to REE mines outside of China; and (5) investigating the feasibility of stockpiling
REEs (Hosaka, 2010). In support of these initiatives, the Ministry of Trade has provided a third of
a billion dollars in subsidies, which has been used as seed money for 160 projects. Future funding
will increase as the Japanese government is offering another 110 million dollars in subsidies in
the next fiscal year. The Japanese have set a goal of reducing the amount of rear earths imported
by its domestic industry by one-third (Kidela Capital Group, 2011) In addition, another source
reports that Japan has made recycling of rare earth minerals mandatory (Baudzus, 2011).
South Korea has plans to spend $15 million by 2016 as part of a long-term policy for securing
rare earths. The policy, titled "Plans for Stable Procurement of Rare Metals," was scheduled to be
finalized in 2010 and to include strategies related to developing mines, investing in alternative
materials, and recycling technologies (Hosaka, 2010).
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Rare Earth Elements Review Section 5 - Rare Earth Element Recovery/Alternative Material Use
In the European Union, there is a new law that requires car and electronic manufacturers to start
recycling rare earth minerals (Baudzus, 2011). The European Commission also has adopted a new
strategy targeted at better utilization of supplies in the EU, partnership with new sources (with
Africa as the key focus), and increased recycling. In addition, Germany has passed its own
strategy specifically designed to ensure that it is able to secure enough rare earths to support
manufacturing operations. The strategy includes developing partnerships with countries that
produce rare earths and is also designed to encourage recycling (Bloomberg BusinessWeek,
2010).
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5-14
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Rare Earth Elements Review Section 6 - Human Health and Environmental Risks
6. Potential Human Health and Ecological Risks of Production,
Processing, and Recycling of REEs
Since the early 1990s, EPA has performed a number of studies to evaluate the environmental risks to human
health and the environment from hardrock mining and metal ore processing activities. The most significant
environmental impact from contaminant sources associated with hard rock mining is to surface water and ground
water quality. However, documented impacts have also occurred to sediments, soils, and air. Comparisons can
generally be made for mining of rare earth mineral ores and processing those ores into the final products with
other hard rock metal mining and processing operations. These comparisons are suggested at a high level
relative to the typical waste streams that are produced by a hardrock mine. Although process waste streams and
sources are explored from past practice, direct comparisons are not attempted at an operational level since every
deposit is geochemically unique and every mine and processor must conform to the characteristics of the ore
deposit. These environmental and human health impacts are largely associated with the release of mine waters
that typically contain elevated concentrations of metals, industrial chemicals used to maintain the mine site and
equipment, and processing chemicals needed for milling and final processing steps. However, the specific health
effects of elevated concentrations of REEs in the environment are not well understood. There is also potential for
impacts to human health and the environment from recycling activities to recover REMs. This section presents a
general conceptual site model (CSM) for a generic, aboveground hardrock mine site.
Mining and processing activities have the potential to create a number of environmental risks to human
health and the environment. The severity of these risks is highly variable between mine and mine plant
operations. The contaminants of concern will vary depending on the REE-mineral ore, the toxicity of the
contaminants from the waste rock, ore stockpiles, and process waste streams. The mobility of
contaminants will be controlled by the characteristics of the geologic, hydrologic, and hydrogeologic
environments where the mine is located, along with the characteristics of the mining process and waste
handling methods. The environmental impact from urban mining or REM recycling operations is similar
to mineral processing, since recovery and refining methodologies can be identical.
A summary of the potential emission points and pollutants of concern associated with mining, processing,
and recycling REEs are presented in Table 6-1.
6-1
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Rare Earth Elements Review
Section 6 - Human Health and Environmental Risks
Table 6-1. Summary table of pollutants, impacted environmental media, emission sources, and
activity associated with REE mining, processing, and recycling.
Activity
Mining (aboveground and
underground methods)
Processing
Recycling
Emission Source (s)
Overburden
Waste Rock
Sub-ore Stockpile
Ore Stockpile
Grinding /Crushing
Tailings
Tailings Impoundment
Liquid Waste from Processing
Collection
Dismantling and Separation
Scrap Waste
Landfill
Processing
Primary Pollutants of Concern
Radiologicals
Metals
Mine Influenced Waters/Acid Mine
Drainage/Alkaline or neutral mine drainage
Dust and Associated Pollutants
Dust
Radiologicals
Metals
Turbidity
Organics
Dust and Associated Pollutants
Transportation Pollutants
Dust and Associated Pollutants
VOCs
Metals
Organics
Dust and Associated Pollutants
VOCs
Dioxins
Metals
Organics
In general, limited toxicological or epidemiological data are available to assess the potential human health
effects of REEs. A preliminary literature search was conducted to identify human health, epidemiology,
and toxicity studies on REEs. The identified literature was briefly reviewed and summarized in tables
provided later in this section.
6.1 Generalized Conceptual Site Model for Environmental Risk from a REE
Mine and Mineral Processing Plant
This section provides a generic Conceptual Site Model (CSM) to illustrate and provide general
perspective for common sources of contamination along with typical contaminant release, transport, and
fate scenarios that could be associated with a larger hardrock mine site. It attempts to describe the sources
of contaminants, the mechanisms of their release, the pathways for contaminant transport, and the
potential for human and ecological exposure to chemicals in the environment
As in other parts of this document, the discussion presented here is general and cannot specifically
address every circumstance or condition. However, to reiterate a previous point: while the geochemistry
of the ore, and therefore the characteristic of pollutants, is likely quite different, a REE mine is similar to
many other hardrock mining operations and the methods used to beneficiate and mill REE-mineral ores
are also similar. While the basic metallurgical processes used to extract a metal from hardrock mineral
ores are similar, the actual mineral ore processing steps used to recover a metal or metal oxide are varied.
Metallurgical processing is generally unique to the deposit's geochemistry, and therefore the actual
methods and chemicals used are often proprietary. Environmental impact occurs at every stage of the
mines life-cycle.
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Rare Earth Elements Review Section 6 - Human Health and Environmental Risks
The CSM presented in the discussion assumes that within the property boundaries of a single mine there
can be a variety of support process areas and facilities. Waste materials are associated with each step of
mining and the subsequent ore processing steps used in extraction metallurgy for the target metal. In
general, the waste streams from mining and mineral processors can include sediment, particulates, vapors,
gases, wastewater, various chemical solvents, and sludge from chemical extraction and filtration steps.
Most mining and processing operations will produce these and/or other wastes that require management
and have the potential to create environmental risks to human health and sensitive habitat.
The CSM provided in Figure 6-1 shows a mining and processing site of nonspecific location, climate,
and physical setting. Mine conditions, ore geochemistry, and geologic, physiographic, and hydrogeologic
settings where the mine is located will define many of the factors that influence the likelihood and
potential severity of environmental risks associated with a specific mine site. This CSM is provided for
general perspective and to orient the reader who is unfamiliar with the site features and conditions
generally found at a commercial hardrock mine site. The features illustrated in the CSM include mine
pits, leach piles, other processing areas, tailings, and waste piles.
As previously discussed in this document, mining is the removal of ore from the ground on a large scale
by one or more of four principal methods: surface mining, underground mining, placer mining, and in situ
mining (extraction of ore from a deposit using chemical solutions). After the ore is removed from the
ground, it is crushed so that the valuable mineral in the ore can be separated from the waste material and
concentrated by flotation (a process that separates finely ground minerals from one another by causing
some to float in a froth and others to sink), gravity, magnetism, or other methods, usually at the mine site,
to prepare it for further stages of processing. The production of large amounts of waste material (often
very acidic) and particulate emission have led to major environmental and health concerns with ore
extraction and concentration. Additional processing separates the desired metal from the mineral
concentrate.
The CSM shown in Figure 6-1 illustrates that there are various receptor types around the mine site at
different times during the life cycle of the mine:
Construction worker - May be exposed for short or extended periods depending on role and
responsibilities; levels of exposure differ depending on mine's life-cycle stage when work is
performed and location of work relative to source.
Outdoor worker - Experiences potential exposure from dust, radiologicals, and hazardous
materials.
« Indoor worker - Experiences either less exposure if in office spaces or potentially more
exposure if inside process areas.
Off-site tribal practitioner - Assumed that tribal peoples may use traditional hunting and
fishing areas for some level of subsistence.
Recreational user - May use lakes, streams, or trails near the mine site or recycling facility and
may also boat, swim/wade, bike, hike, camp, hunt, fish or subsist temporarily in the area.
Agricultural worker - May experience more exposure from dusts, noise, or impacted water
supply.
Trespasser - Exposure dependent upon mine site life-cycle stage and activity while on-site.
« Off-site resident - Exposure would depend upon mine site life-cycle stage and distance from
potentially multiple source areas; routes could be air, ingestion of dust or native or gardened plant
or animal, ingestion of contaminated water, and dermal contact with soil or water.
On-site resident - Exposure would occur after mine land is reclaimed and re-developed for
residential use. Routes of exposure could be air, ingestion of dust or native or garden plant or
native animal, ingestion of contaminated water, and dermal contact with soil or water depending
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Rare Earth Elements Review Section 6 - Human Health and Environmental Risks
on residual concentrations remaining in un-reclaimed source areas or in yard soil if mine wastes
were mixed with clean soil and used as fill.
« Ecological receptors - Aquatic and terrestrial.
Direct exposure can occur as a result of direct contact with solid phase mine or process wastes. General
protections at mine sites are typically required, especially those located on federal lands. For example,
fencing is generally required for isolating mine site areas where certain leaching chemicals are used to
protect and prevent the direct exposure of the public, wildlife (including migratory birds), and livestock.
Indirect expose to humans can occur through the food chain by, for example, the consumption of meat
from exposed fish, shellfish, wild game, grazing farm animals, or by consuming vegetables grown in
contaminated soils.
The EPA stipulates in its risk guidance (1989) that a completed exposure pathway must contain the
following elements:
« Source and mechanism for release of chemicals
« Transport or retention medium
Point of potential human contact (exposure point) with affected medium
« Exposure route (e.g., dermal contact, inhalation, or ingestion) at the exposure point
If any one of these elements is missing, then no human health or ecological risk exists. The CSM
presented in Figure 6-1 shows a simplified model of the chemical transport pathways for the site. The ten
receptor types (listed above) are shown in the CSM along with likely exposure routes.
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Rare Earth Elements Review
Section 6 - Human Health and Environmental Risks
FUTURE CONSTRUCTION WORKER
CURRENT AND FUTURE OUTDOOR
WORKER
TRADITIONAL TRIBAL LIFEWAYS
ON-SITE RESIDENT"
OFF-SITE RESIDENT
C4MMCTHDH NAT NT KAN P.;
WCLUDWG INJCSTIQN.CULTURAL
USLiJ,«DI»IALA.T«H
" Includes exposure to associated surface soil
" Tor on-site residents, oxposure routes are low probabiity artd potentially incomplete
Figure 6-1. Generic above-ground hardrock mine conceptual site model and exposure pathways (U.S. EPA, 2009a).
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6.1.1 Contaminant Release and Transport
The environmental behavior of mine/ore materials, REE-containing minerals, and the mineralogy of
overburden and waste rock can vary significantly. Some of the potential effects include alteration of
wildlife habitats, erosion, sedimentation, generation of windblown particulates, pollutant loading to
groundwater and surface water, losses of chemical solutions from process areas, and surface subsidence.
Generally, the specific areas of concern arise from sediment loading, metals contamination, toxic chemical
release, and acidification.
6.1.1.1 Surface Water and Ground Water Pathways
Surface Water
In addition to mining and processing activities, exploration activities can initially impact surface water
and groundwater resources at the site. The potential impacts that could occur during this phase of a mine's
life are variable and are influenced by location; impacts in densely forested areas will be different than the
impacts to sparsely forested and arid regions. Ore bodies located in more remote locations may require an
extensive network of access roads to drilling sites that result in the removal of habitat and alteration of
terrain by removing soil and rock to create a stable road bed. Where water bodies exist along these
constructed unpaved access roadways, or the drilling sites, pollution to streams and other water bodies
can potentially become problematic. Additional runoff from clearing or other land alterations can increase
normal stream flow during rainfall events, which increases the potential for downstream impacts from
flooding. These types of impacts are more pronounced the closer the access roadways are constructed to
the water body and the greater the area cleared.
Drilling fluids from exploration activities can have significant impacts to aquatic environments or shallow
groundwater if discharged or accidentally released to the environment. Suspended and dissolved solids
concentrations would potentially overwhelm a small stream. The drilling fluids are managed at the
borehole, either in a constructed mud box or in a pit. After the borehole is completed, the drilling fluids
may be contained in drums for disposal, moved to an on-site waste management area (e.g., a landfill),
dispersed at a land application unit (i.e., landfarming or landspreading), or stabilized in the mud pit and
buried in place. Recycling of the drill cuttings is a common practice (i.e., road spreading and on-site
construction base material), but additional uses are being tried in some sectors, such as the use of drilling
mud and cuttings for use as substrate for wetland revitalization (Argonne National Laboratory, 2011).
During any phase of mining operations, water bodies may receive increased sediment loads from erosion
of freshly exposed soils that can cause decreases in available oxygen content of waters and decrease light
penetration for photosynthesis to occur for aquatic plants.
Erosion of rock surfaces, especially where sulfide minerals are present, can cause a natural acidification
of runoff water (i.e., acid rock drainage or ARD) that can affect surface water bodies. Acid mine drainage
(AMD) and neutral mine drainage (NMD) exacerbates the problem of releasing metals from mined
materials and surfaces in addition to naturally occurring ARD. AMD occurs when oxide ore minerals
(metalliferous minerals) are altered by weathering, rainwater, and surface water into oxides or sulfides.
AMD usually is not a significant issue for REE deposits; however, the rock that surrounds or is overlying
an ore body may contain the sulfide minerals that could create AMD. REEs often occur in ores rich in
carbonate minerals, which can help buffer any effects of AMD that might occur; however, aquatic
systems are very sensitive to changes in pH and increases in alkalinity can also be problematic. While
AMD can result in metal toxicity problems, divalent metals are generally less toxic at higher pH and in
more mineralized waters associated with NMD. AMD and NMD are collectively referred to as mining-
influenced water (MIW). Because the surface area of mined materials is greatly increased, the rate of
chemical reactions that generate AMD, or increase alkalinity is also greatly increased. MIW can occur
from stockpiles, storage piles, and mined or cut faces that can potentially impact local soil, groundwater,
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and surface water quality. Typically, drainage from these management areas is controlled, but releases
can potentially happen due to overflows during storm events, liner failure, and other breaches of
engineered controls.
Aquatic organisms will generally only tolerate a narrow fluctuation in the acidity or alkalinity of the
natural system until reproductive capacity is diminished or mortally occurs. Erosion of exposed rocks can
cause an increase (more acidic) or decrease (more basic) in the hydrogen ion concentration (pH) of the
aquatic environment. Prior to mining, oxidation is a function of natural weathering, and any acid
generation (i.e., acid rock drainage), or increases in alkalinity, occurs very slowly. Soils and riparian areas
help to mitigate AMD and MIW, but these buffer zones are usually missing from the mining site unless
maintained or constructed. However, as previously noted, acid mine drainage is not a significant issue that
is typically associated with REE-deposits.
Potential impacts to surface waters from mining operations can be mitigated. Maintaining buffer zones
between stream areas and areas of exploration and mining activity can help to control runoff to streams.
Capturing and containerizing drilling fluids also can mitigate impacts to streams, groundwater, and
nearby habitat. Excavated soils, rock, and dry cuttings, either from mine areas or drilling activities, can
also be controlled to prevent release of sediments and contaminated runoff.
Groundwater
Groundwater and surface water interactions are common in the hydrogeologic cycle. At mining sites,
those interactions are often enhanced. Groundwater can migrate to existing mine pit lakes or evaporation
ponds, or be recharged from surface mine units. Mine pit water is generally removed to evaporation ponds
or treated and discharged to surface waters or injected into the aquifer. It also is often used in the milling
processes. Water may flow out of and transport chemicals from mine pit lakes into alluvial and bedrock
groundwater flow systems, particularly during periods of high precipitation. Groundwater inflow to pit
lakes, streams, buried trenches, or surface ditches may also result in the transport of chemicals from
subsurface environments to surface waters, including the transfer of chemicals in suspended sediments.
Pumpback well systems are sometimes used to extract a portion of mineralized groundwater or pit
seepage water that could migrate off-site and impact neighboring or nearby human or ecological
receptors. The effluent is then pumped and released to lined evaporation ponds, resulting in an
accumulation of potentially contaminated sediment. Chemical precipitate accumulations can also occur in
active pumpback water systems and evaporation ponds. Losses of dewatering effluent from pipelines
carrying water from mine pits, holding ponds, or from pumpback water systems can be a potential source
of soil and groundwater contamination.
Examples of Environmental Damages to the Aquatic Environment
There is one CERCLA site within the Blackfoot River sub basin where REE-containing mineral deposits
were mined (U.S. Forest Services, 2011). An Administrative Order of Consent for South Maybe Canyon
Mine Site was entered into by the U.S. Forest Service and Nu-West Mining, Inc., in June 1998. The
primary reason for the order was the release of hazardous substances, including selenium, from the site
into groundwater and surface waters above Idaho state water quality standards. It should be noted that
rare earth metals were not identified as hazardous substances that had been released from the site. The
South Maybe Canyon Mine was developed for the production of phosphate, and REEs were recovered as
a byproduct (Long et al., 2010). This mine has been identified as a possible source of REEs for future
development.
In March 2010, the EPA imposed administrative penalties against Upland Wings, Inc. for Clean Water
Act violations at the former Pea Ridge Mining Operation in Washington County, Missouri. Violations
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were associated with the discharge of metals and other constituents (i.e., oil and grease, copper,
chromium, cadmium, iron, lead, and total suspended solids) in concentrations that exceeded permitted
levels. Earth-moving equipment was also used to dredge iron ore tailings from settling ponds and to
dispose of the materials in a nearby creek without a permit that affected nearby wetlands.
6.1.1.2 Air Pathway
Fugitive Dust
Direct exposure of humans can occur from inhalation of fine dusts (i.e., particulates) or by ingestion or
dermal contact of contaminated dusts. Particulates or fugitive dust from storage piles, conveyor systems,
site roads, or other areas can be transported by wind and may be deposited and accumulated in downwind
areas, including surface soils and surface water bodies (e.g., ponds, pit lake), or be inhaled by site workers
and nearby residents. Dust can be an irritant, a toxicant, or a carcinogen, depending on the particles'
physicochemistry, and can be composed of inorganic and organic chemicals. However, the presence of
physical barriers, such as vegetation or structural foundations, may dampen or reduce the transport of
particles as wind-blown dust. Accumulated mine sediments or dust may become secondary sources of
chemicals transported to groundwater via leaching and percolation.
Aerosols and Chemical Vapors
Mine workers can be exposed to aerosols from numerous processes, including comminution (i.e., the
process in which solid materials are reduced in size by crushing, grinding, and other techniques), re-
entrainment (i.e., air being exhausted is immediately brought back into the system through the air intake
and/or other openings), and combustion sources. Aerosols are dispersed mixtures of dust and/or chemical-
containing water vapor. Cutting, drilling, and blasting of the parent rock, especially in underground
mines, creates aerosols with a composition similar to the parent rock. As previously discussed,
comminuting the ore underground is sometime practiced for efficient transport out of the mine area, and
aerosols can accumulate in these areas. The dusts from ore mineral liberation and separation steps settle to
other areas such as ventilation systems, roadways, work areas, and nearby surrounding areas. Aeration
ponds are sometimes used to treat waste waters on a mine site, and the aerators used to disturb the surface
of the water can create aerosols; the problem can become worse if surfactants are used and not managed
properly. Aerosols can potentially accumulate along perimeter areas of ponds and lagoons and
contaminate soils, sediments, surface water, and shallow groundwater through deposition and transport.
Radioactivity
Lanthanides and yttrium are recovered primarily from ores and minerals that naturally contain uranium
and thorium; however, some level of radioactive materials is found in association with many REE
deposits. As a result, the waste rock and sludges from the extraction of rare earths also contain these
radionuclides and are considered Technologically-Enhanced, Naturally-Occurring Radioactive Materials
(TENORM). TENORM wastes contain radionuclides in concentrations that could give rise to
unacceptable radiation levels. The EPA has estimated that levels of naturally occurring radioactivity
contained in common rare earth (e.g., monazite, xenotime, bastnasite) deposits in the United States range
from 5.7 to 3,224 picoCuries per gram (pCi/g). The USGS has estimated uranium and thorium content of
minerals found in REE deposits. Additional information can be found in Long et al., 2010. Radioactive
elements, such as thorium and uranium, can concentrate in mining dusts and sediments that must be
managed. Radon gas can also be emitted from these sources. Transport of particulates containing uranium
and thorium may occur by any of the transport pathways described above. Acidic groundwater and
surface water and low concentrations of organic material in soils can contribute to the mobility and
transport of radioactive materials. Accumulations of sediments deposited by runoff and dusts also can
concentrate radioactive materials. External exposure to naturally occurring radiation and radon gas is
often limited to soil or waste materials that are within several inches of the ground or pile surface;
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Rare Earth Elements Review Section 6 - Human Health and Environmental Risks
radioactive materials found deeper in the soil column or accumulated sediments are generally shielded by
the top layer of soil. Geometric attenuation generally limits the external radiation from naturally
radioactive materials with no interposed shielding materials to within a few meters (i.e., less than 5 meters
and often less than 1 to 2 meters from the source). Radioactivity can become concentrated in mineral
scales that develop in groundwater recovery wells, holding tanks, aeration ponds, and milling processes
areas. Inhalation of contaminated dusts is generally of greatest concern for naturally occurring radioactive
materials.
Tailings storage facilities typically receive the bulk of processing water, which is normally recycled, but
some of it could be released into the environment through seepage or overflows due to unusually high
rainfall. The tailings storage facilities (TSF), when dry, usually represent the main source of
radon/thorium and dust emissions to the environment. Special containment arrangements are required for
the disposal of tailings generated during chemical and/or thermal processing of uranium and thorium-
bearing minerals to ensure that environmentally mobile radionuclides are not released into the
surrounding environment. The disposal of contaminated equipment and materials also needs to be
controlled. In addition, the possibility of off-site contamination from trucks and equipment moving off-
site needs to be considered.
After milling and concentrating, the mineral is sometimes stockpiled at the mine site prior to transport to
the processing sites, and these stockpiles may contain radioactive minerals in concentrations sufficient to
produce elevated radiation levels and radon. The stockpiles, therefore, need to be protected against
unauthorized access and also against the possibility of the material spreading through wind saltation.
Ideally, stockpiles containing radionuclides in concentrations that require signposting of areas as
"supervised" and/or "controlled" should be located on a concrete slab to simplify the management and
clean-up operations.
The tailings from the separation and downstream processing of minerals may contain radionuclides in
concentrations that could give rise to unacceptable levels of radiation and radon. Appropriate
management is typically required, and the disposal of the waste will depend on the method used to
process the mineral and on the respective levels of radiation and the concentration of radon gas emitted.
The possibility of ground water contamination increases if chemical and/or thermal treatment of the
mineral occurs (e.g., in the case of separating the heavy mineral sands). Otherwise, the radionuclides in
the tailings could be considered as remaining bound in the individual mineral grains; therefore, the
possibility of the contamination of groundwater by radionuclides from tailings is not considered to be less
significant. Radium may be present in the tailings water, which would require removal before being
disposed.
Where any grinding, chemical, and/or thermal treatment of minerals containing radionuclides takes place,
additional safeguards must be implemented due to the fact that secular equilibrium in both uranium and
thorium decay chains may be disrupted. This could result in an increased environmental mobility of
radionuclides, such as radium and radon. Cleaning of certain minerals prior to processing (such as, for
example, the cleaning of the heavy mineral sand grains) may produce finely powdered waste (slimes).
Slime wastes may have significant uranium or thorium content, and the disposal as radioactive waste may
be required.
The equipment used in downstream processing of minerals often becomes contaminated by NORM or
TENORM. Contaminated equipment must either be disposed of properly, or thoroughly decontaminated
prior to any re-use. Scales and sludge build on the inside surfaces of pipes and vessels used in chemical
and thermal processing, and these materials often have elevated levels of radionuclides.
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Regulation and guidance vary among federal agencies and organizations for the handling of TENORM
waste and the associated environmental and health risks. The EPA (2000) began to address this issue in
its work with the National Academy of Sciences in 1999. However, work is on-going to streamline policy
and guidance related to TENORM.
Example of Environmental Damage from Radioactivity
An example of issues associated with radionuclides from the production of rare earths is occurring in
Malaysia. According to a Physorg.com news article (Zappei, 2011), international experts are currently
investigating whether a refinery being built by an Australian mining company, Lynas Corp. Ltd., to
process rare earth minerals in Malaysia presents any threat of radioactive pollution. Malaysia's last rare
earth refinery in northern Perak state was closed in 1992 following protests and claims that it was the
source of radionuclides that were identified as the cause of birth defects and leukemia among nearby
residents. The refinery is one of Asia's largest radioactive waste cleanup sites. The Pahang plant is meant
to refine slightly radioactive ore from the Mount Weld mine in Western Australia, which will be trucked
to Fremantle and transported to Malaysia by container ship. Lynas plans to begin operations at the
refinery late in 2011 and could meet nearly a third of world-wide demand for rare earths, excluding
China.
Similar issues are being addressed for proposed rare earth production in the United States. Thorium waste
will be produced along with rare earths mined from the proposed operations at Pea Ridge, Missouri. The
owners of the mine have proposed to construct a rare earth refinery and regional thorium stockpile along
the Mississippi River near St. Louis (Lambrecht, 2011). It is believed by the proponent that the thorium
storage facility will help address environmental liability concerns in the production of rare earths. The
thorium would be stockpiled in anticipation of using it for nuclear power production. Currently, the
United States does not have a thorium fuel cycle, but China is reported to have thorium reactors in
operation. Public concerns raise the issue of site clean-up that has occurred at former thorium production
facilities once operated by the DOE.
6.1.2 EPA Studies of Hardrock Mine Environmental Risks
Generalized risk information is presented below from past studies of hardrock mines. The geologic
environments where other types of metal mines are developed are often similar to geologic settings where
REEs are found. In addition, mining and processing operations are similar to other hardrock mines.
Therefore, past information gather by EPA to characterize the risks from hardrock mines is likely relevant
to the risks from the mining of REEs.
6.1.2.1 Environmental Impacts from CERCLA Sites
Collected human and ecological risk information (U.S. EPA, 201 Id) was summarized from a subset of 25
National Priority List hardrock mining and mineral processing sites by EPA and is presented here in
relation to risks that could also be typical from a hardrock mining operation for REEs. The summary of
the contaminant sources, primary transport media or pathway, routes, and the receptors is provided in
Figures 6-2 (human receptor) and 6-3 (ecological receptor). The sample set of NPL sites represents those
listed on the NPL post-1980, and it is thought that these sites likely represent the conditions that could be
found at modern mine sites. It could then be expected that similar source, fate, and transport scenarios
could be related to REE mining and processing facilities.
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Rare Earth Elements Review
Section 6 - Human Health and Environmental Risks
CONTAMINANT RELEASE
CONTAMINANT TRANS
,PflRT
^> CONTAMINANT FATE
N PL Sites
SOURCES
Acid Mine/Rock Potliners
Drainage Pressing Ponds
Asbestos Fibers Process Fluids
Process Stacks Emissions
Demolition Dumps Quartzite Dust Slurry
Deposition Radioactive Waste Piles
Dredged Sediments Run-off
Flue Dust Sewage Sludge
Fugitive Dust
Housekeeping Debris
Incinerator Ash Storage Tanks
Iron-rich Liquid Acid Sulfate Residuals
Metal Ore Waste Tailings
Non-Contacting Cool Transformers
Water Effluent Treater Dust Stock Piles
Ore Slimes Underflow Solids Piles
Ore/Nodule Stockpiles Unlined Pits
Overburden Waste Drums
Overburden Waste Piles
Waste Rock
PATHWAYS
Groundwater
Sediment
Soil
Surface Water
Vadose Zone
ROUTE
Dermal Contact
External Radiation
Ingestion of
Food-Plants
Food-Birds
Food-Mammals
Food-Terrestrial
Food-Benthic
Food-Fish
Food-Aquatic Plants
Food-Aquatic
Inhalation
Combined Routes
RECEPTORS
Occupational (Agricultural)
Occupational (Construction)-Current
Occupational (Construction)-Future
Occupational (Dredging)-Future
Occupational (Industrial)-Current
Occupational (Industrial)-Future
Occupational(Not Specified)-Current
Occupational(Not Specified)-Future
Recreational-Current
Recreational-Hiker
Residential-Current
Residential-Future
Site Visitor
Trespasser-Current
Trespasser-Future
Removal Sites
SOURCES
Adit Drainage Overburden
Adits Raffinate Leachate
Tailings
Vat Leachate Tailings
Condenser Waste Waste Drums
Manual/Aerial Waste Rock Piles
Deposition Water Drainage
Mill Foundation
Mill Tailings
Mine Waste
PATHWAYS
Air
Groundwater
Soil
Surface Water
ROUTE
Dermal Contact
Inhalation
Ingestion
RECEPTORS
Occupational
Recreational-Current
Residential-Current
Trespasser-Current
Figure 6-2. Sources of potential human exposures resulting from mining operations (U.S. EPA OCRC, 2010).
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Rare Earth Elements Review
Section 6 - Human Health and Environmental Risks
CONTAMINANT RFI FASF > CONTAMINANT TRANSPORT > CONTAMINANT FATF
r r
SOURCES
Adit Drainage Ore Stockpiles
Adits Overburden
Airborne Emissions Phossy Water
ARD Potliners
Process Residues
Process Stacks Air Emissions
Ouartzite Dust Slurry
Run-off
Condenser Waste
Debris Sludge
Exposed Mineralized Spent Mineral
Bedrock Waste
Fuel/Oil Spent Ore
Fugitive Dust Tailings
Leachate Treater Dust
Manual/ Aerial Stock Piles
Deposition Underflow Solids
Mine Waste Piles
Municipal Waste Vat Leachate
Nodule Stockpiles Tailings
Non-Contacting Cool Waste Drums
Water Effluent Waste Piles
Waste Rock
Wastewater
Water Drainage
PATHWAYS
Food-Aquatic Invertebrates
Food-Aquatic Plants
Food-Benthic Invertebrates
Food-Birds
Food-Fish
Food-Mammals
Food-Plants
Food-Terrestrial Invertebrates
Food-Terrestrial Plants
Groundwater
Plants
Sediment
Soil
Soil Invertebrates
Subsurface Soil
Surface Soil
Surface water
Water
ROUTE
Dermal Contact
Ingestion
Inhalation
Combined Routes
RECEPTORS
Birds
American Dipper Migratory Birds
American Kestrel Mountain Chickadee
American Robbin Northern Harrier
Barn Owl Omnivorous Birds
Belted Kingfisher Pine Grosbeak
Bobwhite Quail Red-tailed Hawk
Carnivorous Birds Red-tailed Hawk
Cliff Swallow Sage Grouse
Great blue heron song sparrow
Horned Lark spotted sandpiper
King Fisher Waterfowl
Mallard Woodcock
Mammals
Carnivorous Mammals Mink
Coyote Montane Vole
Deer Omnivorous Mammals
Deer Mouse Piscivorous Mammals
Deer Mouse Rabbits
Field Mice Raccoon
Herbivorous Mammals Red Fox
Long-tailed Weasel Small mammals
Masked Shrew Soil Invertebrate-
Meadow Vole feeding Mammals
White-tailed Deer
Other
Amphibians Plants
Benthic Invertebrates Predatory Fish
Benthic Rainbow Trout
macroinvertebrates Sagebrush
Benthic Organisms Soil invertebrates
Deepwater Habitats Terrestrial Invertebrates
Fish Terrestrial Organisms
Future-Aquatic Organisms Terrestrial Plant
Future-Wetland Invertebrates Community
Future-Wildlife Terrestrial Soil
Herbivores Community
Macroinvertebrates Thickspike Wheatgrass
Periphyton Community Transient Organisms
Pets Vegetation
Figure 6-3. Sources of potential exposures of current and future ecological receptors resulting from mining operations
(U.S. EPA ORCR, 2010).
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From a previous study (U.S. EPA, 1995) of risks to human health and the environment from hardrock
mines, it was concluded that the 66 hardrock mining cases illustrated that significant human health and
environmental damages were caused by the management of wastes from mining and mineral processing,
particularly placement in land-based units. Molycorp Minerals rare earth mine in Mountain Pass, CA, was
one of the sites included in the study. Wastes subject to the RCRA Bevill Amendment were found to be
the cause of the damages. These damages occurred in all hardrock mining sectors and across all
geographic regions of the United States. Table 6-2 excerpted from the report summarizes the type of
impacts.
Table 6-2. Frequency of Various Types of Impacts from CERCLA Sites (U.S. EPA, 1995)
Type of Impacts
Surface water contamination
Ground water contamination
Soil contamination
Human health impacts
Flora and fauna damage
Air dispersion or fugitive emissions
Portion of Damage Cases
(Total NPL Sites = 66)
70 percent of cases
65 percent
50 percent
35 percent
25 percent
20 percent
6.1.2.2 Acid Mine Drainage at CERCLA Sites
In another review by EPA of 156 hardrock mine sites, the results showed that approximately 30 percent
(or about 45) of the sites had problems with acid mine drainage (U.S. EPA, 2004). The report also
suggested that acid mine drainage occurred most often in EPA Regions 8, 9, and 10. The EPA OIG
(2004) also reiterated the concern from the National Wildlife Federation that sites where AMD is present
should be carefully monitored as "the presence of acid mine drainage is either underestimated or ignored
until it becomes evident, at which time the costs often exceed the operator's financial resources, leading
to bankruptcy or abandonment of the site in many cases." As previously stated, it is not anticipated that
the mining of REE will typically produce AMD given the typical geochemistry of these deposits.
6.1.2.3 Prospective REE Mining Sites and CERCLA Review
A comparison of USGS (Orris et al., 2002) data and EPA CERCLA documents revealed four mines that
have been damage case sites. While these sites are not yet being mined for REEs, they have been
identified as potential future sources:
Maybe Canyon Phosphate Mine (Superfund site);
Mountain Pass REE Mine (when owned by Union Oil Company of California (Unocal); not to be
confused with current owner, Molycorp Minerals, LLC);
Smoky Canyon Phosphate Mine (Superfund site); and
Bokan Mountain Uranium Mine (not on NPL but Federal Facilities review site).
Releases of radionuclides were the environmental impacts that were investigated for both Mountain Pass
and Bokan Mountain mines. Maybe Canyon Mine was in operation between 1977 and 1984.
Approximately 120 acres of waste rock (29 million cubic yards) was present from which selenium and
other hazardous substances were reported to have contaminated ground water and surface water (U.S.
Department of Agriculture, 2011). Selenium contamination is a common problem at phosphate mines and
it was also found to be an environmental contaminant of concern at the Smoky Canyon Mine.
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6.2 Pathway and Exposure Scenarios for REE-Recycling
During collection of items to be recycled, exposure to hazardous materials is likely to be minimal and, if
occurring, will likely result from either dermal or inhalation exposures to materials released from
damaged items. Similarly, when done properly, manual dismantling is likely to have a low potential for
worker risks resulting from exposure to hazardous materials. Mechanical dismantling and shredding can
generate dust containing hazardous components. If not properly controlled, the dust can result in
inhalation or dermal exposures to workers. Dust control is particularly important when the items being
shredded contain brominated flame retardants, because high temperatures during shredding could result in
the formation of dioxins (Schluep et al., 2009).
Leaching processes using liquids such as nitric acid or aqua regia can cause release of nitrogen oxide or
chlorine gases and therefore must be controlled to prevent human and environmental impacts. In other
processes that use strong acids or bases, safe handling of chemicals and disposal of resulting waste
streams is important to protect workers and the environment. Thermal processes used for recycling can
result in air emissions, liquid wastes, and solid waste streams. As for mineral processing, TENORM is a
safety and environmental concern related to the recycling of metals. Again, proper controls and handling
are necessary to prevent human exposures and environmental impacts.
As reported by Schuler et al. (2011), when compared with primary processing, recycling of REEs will
provide significant environmental benefits with respect to air emissions, groundwater protection,
acidification, eutrophication, and climate protection. This report also states that the recycling of REEs
will not involve the majority of the impacts from mining operations and the impacts that can result from
radioactive impurities, as is the case with primary production of metals. As previously noted in Section 5,
a large percentage of REE-containing materials are shipped to developing countries where they are
recycled using informal processes. These informal operations can include manual dismantling, open
burning to recover metals, de-soldering of printed wiring boards over coal fires, and acid leaching in open
vessels, as illustrated in Figure 6-4. In almost all cases, these operations are uncontrolled and can lead to
human exposure and extensive environmental damage. In addition, the processes used are generally less
efficient and result in lower materials recovery than from more formal or established methods.
Environmental regulations would prevent these types of uncontrolled REE recycling and metal recovery
operations from establishing in the United States.
Figure 6-4. "Low-tech" gold recycling in Bangalore/India
(Schluep et al., 2009).
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Rare Earth Elements Review Section 6 - Human Health and Environmental Risks
6.3 Documented Human Health and Ecological Effects from Exposure to REE
In general, limited toxicological or epidemiological data are available to assess the potential human health
effects of REEs. A literature search was conducted to identify human health, epidemiology, and toxicity
studies on REEs. The identified literature was briefly reviewed and summarized in tables provided later in
this section. Many studies examined mixtures of REEs, rather than individual elements. Respiratory,
neurological, genotoxicity, and mechanism of action studies were identified. As evidenced by additional
literature cited in secondary sources, an additional literature search should be conducted and the literature
review summaries presented here should not be considered comprehensive. Many studies were conducted
by Chinese investigators and are not available in English (only the abstracts were available in English).
REEs are broadly grouped into "light" (La, Ce, Pr, Nd, Sm, Eu, and Gd) and "heavy" (Y, Tb, Dy, Ho, Er,
Tm, Yb, and Lu) classes (Wells and Wells, 2001, as cited by U.S. EPA, 2009b, 2009c, 2009d). For any
given lanthanide, soluble forms include chlorides, nitrates, and sulfates, while insoluble forms include
carbonates, phosphates, and hydroxides. The larger, lighter (smaller atomic number), and less soluble ions
have been observed to deposit primarily in the liver, while the smaller, heavier (larger atomic number),
and more soluble ions are similar in ionic radius to divalent calcium and distribute primarily to bone
(Wells and Wells, 2001, as cited by U.S. EPA, 2009a, 2009b, 2009c). Because distinguishing individual
lanthanides is analytically challenging, it is has been difficult to discern the effects of the individual
lanthanidesboth in human cases and animal studies. In addition, the co-occurrence of radioactive
lanthanides, thorium isotopes, and silica dust has complicated the interpretation of toxicityespecially
with regard to human exposures (Palmer et al., 1987, as cited by U.S. EPA, 2009b, 2009c, 2009d).
The pulmonary toxicity of inhaled REEs has been the subject of debate, especially with regard to the
relative contributions of radioactive contaminants versus stable elements in the development of
progressive pulmonary interstitial fibrosis (Haley, 1991; U.S. EPA, 2007b). In particular, although it is
understood that stable REE compounds can produce a static, foreign-body-type lesion consistent with
benign pneumoconiosis; it is uncertain whether they can also induce interstitial fibrosis that progresses
after the termination of exposure. Human inhalation toxicity data on stable REEs mainly consist of case
reports on workers exposed to multiple lanthanides (U.S. EPA, 2007b).
EPA has reviewed the human health toxicity for a few REEs in its Integrated Risk Information System
(IRIS) and Provisional Peer-Reviewed Toxicity Values (PPRTV) programs. Human health benchmark
values (where derived) and background toxicity information are summarized below (presented
alphabetically by REE); the reader is referred to these health benchmark technical background documents
for additional detailed information. EPA has not reviewed the toxicity of dysprosium, erbium, europium,
holmium, lanthanum, scandium, terbium, thulium, ytterbium, or yttrium.
Cerium - In a 2009 IRIS assessment on cerium oxide and cerium compounds, available human
and animal studies demonstrated that ingested cerium may have an effect on cardiac tissue
(endomyocardial fibrosis) and hemoglobin oxygen affinity; however, data were insufficient to
derive an oral Reference Dose (RfD). An inhalation Reference Concentration (RfC) of 9E-4
mg/m3 was derived based on increased incidence of alveolar epithelial hyperplasia in the lungs of
rats. The lung and lymphoreticular system effects reported in the principal study are consistent
with effects observed in humans, which were characterized by the accumulation of cerium
particles in the lungs and lymphoreticular system and histologic effects throughout the lung. Data
are unavailable regarding the carcinogenicity of cerium compounds in humans or experimental
animals (U.S. EPA, 201 Id).
Gadolinium - In a 2007 PPRTV document, minimal effects on body weight gain and liver
histology were reported following ingestion of gadolinium in rats. Pulmonary histopathological
changes with manifestations that included decreased lung compliance and pneumonia leading to
mortality were observed in mice and guinea pigs subchronically exposed to gadolinium oxide via
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Rare Earth Elements Review Section 6 - Human Health and Environmental Risks
inhalation. Data were insufficient to derive any quantitative health benchmarks. Gadolinium was
assigned a weight-of-evidence description of "inadequate information to assess carcinogenic
potential" (U.S. EPA, 2007a).
« Lutetium - In a 2007 PPRTV document, a subchronic oral provisional RfD (p-RfD) of 9E-4
mg/kg/day was derived based on a stand-alone no observed adverse effect level (NOAEL) in
mice; there are no data to indicate the toxicological endpoint(s) or target organ(s) of oral exposure
to lutetium. A comprehensive assessment of human and animal data by Haley (1991) concluded
that the evidence suggests that inhalation exposure to high concentrations of stable REEs can
produce lesions compatible with pneumoconiosis and progressive pulmonary fibrosis, and that the
potential for inducing these lesions is related to chemical type, physiochemical form, and dose
and duration of exposure. Data were insufficient to derive an inhalation RfC. Lutetium was
assigned a weight-of-evidence description of "inadequate information to assess carcinogenic
potential" (U.S. EPA, 2007b).
« Neodvmium -A subchronic oral p-RfD of 5E-1 mg/kg/day was derived for neodymium based on
a freestanding NOAEL in rats (no effects on body weight, hematology, and histopathology) in a
2009 PPRTV document (subchronic p-RfD = 8E-1 mg NdCl3/kg/day). Data were insufficient to
derive an inhalation RfC. Neodymium was assigned a weight-of-evidence description of
"inadequate information to assess carcinogenic potential" (U.S. EPA, 2009b).
« Praseodymium - In a 2009 PPRTV document, a subchronic oral p-RfD of 5E-1 mg/kg/day was
derived for praseodymium based on a freestanding NOAEL in rats (no effects on body weight,
hematology, and histopathology) (subchronic p-RfD = 8E-1 mg PrCl3/kg/day). Data were
insufficient to derive an inhalation RfC. Praseodymium was assigned a weight-of-evidence
description of "inadequate information to assess carcinogenic potential" (U.S. EPA, 2009b).
« Promethium - Although a 2007 PPRTV document was prepared for promethium, no human
health benchmarks were derived due to lack of data. Promethium was assigned a weight-of-
evidence description of "inadequate information to assess carcinogenic potential" (U.S. EPA,
2007c).
« Samarium - In a 2009 PPRTV document, a subchronic oral p-RfD of 5E-1 mg/kg/day was
derived for samarium chloride based on a freestanding NOAEL in rats (no effects on body
weight, hematology, and histopathology) (subchronic p-RfD = 9E-1 mg SmCl3/kg/day). A lowest
observed adverse effect level (LOAEL) was reported for increased relative pancreas and lung
weights and increased malondialdehyde concentrations in liver tissues of rats exposed to
samarium nitrate in drinking water. Data suggest that different chemical forms of samarium have
different toxic potencies. A subchronic study in samarium nitrate suggests a LOAEL point of
departure more than 2000 times lower than the NOAEL point of departure for samarium chloride.
In the absence of evidence explaining the large differences in apparent toxicity between the
chloride and nitrate salts, the p-RfD for samarium chloride should be used with caution. The large
differences in acute and subchronic toxicity preclude generalization of the p-RfD for samarium
chloride to other samarium compounds. A screening subchronic oral p-RfD of 2E-5 mg/kg/day
was also derived for samarium nitrate based on a freestanding NOAEL in rats (no effects on body
weight, hematology, and histopathology) (screening subchronic p-RfD = 4E-5 mg
(SmNO3)3/kg/day). Data were insufficient to derive an inhalation RfC. Samarium was assigned a
weight-of-evidence description of "inadequate information to assess carcinogenic potential" (U.S.
EPA, 2009d).
In addition to the EPA documents discussed above, Toxicology Excellence for Risk Assessment (TERA)
(1999) conducted a literature review for the Bureau of Land Management (BLM) examining the health
effects of lanthanides and developed non-radiological, non-cancer risk assessment values for the oral
and/or inhalation routes of exposure. Human health benchmark values are summarized in Table 6-3,
below.
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Section 6 - Human Health and Environmental Risks
Table 6-3. REEs and Available RfCs and RfDs
REE
Ceric oxide as Ce
Cerium oxide as Ce
Europium chloride as Eu
Europium oxide as Eu
Gadolinium oxide as Gd
Lanthanum carbonate as La
Lanthanum chloride as La
Lanthanum oxide as La
Lutetium chloride as Lu
Neodymium chloride as Nd
Praseodymium chloride as Pr
Samarium chloride as Sm
Samarium nitrate as Sm
Scandium oxide as Sc
Yttrium chloride as Yt
Benchmark
RfC
RfC
RfD
RfD
RfC
RfD
RfD
RfD
s-RfD
s-RfD
s-RfD
s-RfD
s-RfD
RfD
RfD
Value
3E-4 mg/cu.m
9E-4 mg/cu.m
3E-2 mg/kg-day
2E-3 mg/kg-day
2E-3 mg/cu.m
5E-1 mg/kg-day
5E-3 mg/kg-day
2E-2 mg/kg-day
9E-4 mg/kg-day
5E-1 mg/kg-day
5E-1 mg/kg-day
5E-1 mg/kg-day
2E-5 mg/kg-day
5E-3 mg/kg-day
4E-3 mg/kg-day
Source
TERA, 1999
U.S. EPA, 201 1d
TERA, 1999
TERA, 1999
TERA, 1999
NSF International, 2010
TERA, 1999
TERA, 1999
U.S. EPA, 2007b
U.S. EPA, 2009a
U.S. EPA, 2009b
U.S. EPA, 2009c
U.S. EPA, 2009c
TERA, 1999
TERA, 1999
Additional primary toxicity studies were identified through the literature search and the objectives and
key findings are briefly summarized in Table 6-4, below; the information is organized by REE.
Table 6-4. Selected Toxicity and Epidemiology Findings for Rare Earth Elements,
REE(s)
Cerium
Cerium
Cerium,
lanthanum,
neodymium
Citation
Gomez-Aracena et al.,
2006. Toenail cerium levels
and risk of a first acute
myocardial infarction: The
EURAMIC and heavy
metals study. Chemosphere
64:112-120
McDonald et al., 1995. Rare
earth (cerium oxide)
pneumoconiosis: analytical
scanning electron
microscopy and literature
review. Mod Pathol 8:859-
865
Palmer et al., 1987.
Cytotoxicity of the rare earth
metals cerium, lanthanum,
and neodymium in vitro:
comparisons with cadmium
in a pulmonary macrophage
primary culture system.
Environ Res 43:142-56.
Objective/Purpose
Examine the association
between cerium exposure
and risk of first acute
myocardial infarction (AMI)
in a case-control study in
Europe and Israel.
Describe a male patient's
respiratory effects; patient
had a chronic history of
optical lens grinding, an
occupation associated with
exposure to cerium oxide.
Evaluate cerium, lanthanum,
and neodymium in an in
vitro cytotoxicity assay
system using rat pulmonary
alveolar macrophages. Both
the soluble chloride form
and their insoluble metal
oxides were studied.
Key Findings
Cases had significantly higher levels
of cerium than controls after various
adjustments. Results suggest that
cerium may possibly be associated
with an increased risk of AMI.
Patient presented with progressive
dyspnea and an interstitial pattern
on chest X-ray; open lung biopsy
showed interstitial fibrosis, while
scanning electron microscopy
demonstrated numerous particulate
deposits in the lung (most containing
cerium). This is one of the first cases
to describe RE pneumoconiosis
associated with pulmonary fibrosis in
the occupational setting of optical
lens manufacture.
The results suggest that rare earth
metal fumes should be considered
as cytotoxic to lung tissue and
potentially fibrogenic.
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Section 6 - Human Health and Environmental Risks
REE(s)
Gadolinium
Gadolinium
Gadolinium
Gadolinium,
lanthanum
Gadolinium,
samarium
Holmium
Citation
Bussi et al., 2007.
Toxicological assessment of
gadolinium release from
contrast media. Exp Toxicol
Pathol 58:323-330
Perazella, 2009. Current
status of gadolinium toxicity
in patients with kidney
disease. Clin J Am Soc
Nephrol 4: 461-469.
Sharma, 2010. Gadolinium
toxicity: epidermis thickness
measurement by magnetic
resonance imaging at 500
MHz. Skin Res Technol 16:
339-353.
Yongxing et al., 2000.
Genotoxicity of Lanthanum
(III) and Gadolinium (III) in
Human Peripheral Blood
Lymphocytes. Bull Environ
Contain Toxicol 64: 61 1-
611.
Haley etal., 1961.
Toxicological and
pharmacological effects of
gadolinium and samarium
chlorides. Brit J Pharmacol
17:526-532.
Qiu etal., 2008. Current
Research in Toxicology and
Application of Rare-earth
Element Holmium. Huanjing
yu Zhiye Yixue 25:207-208
Objective/Purpose
In vivo gadolinium release
was evaluated for 3
magnetic resonance
imaging (MRI) contrast
agents estimating
gadolinium content in liver,
kidneys, spleen, femur and
brain after single or
repeated intravenous
administrations to rats.
Gadolinium acetate (GdAc)
was used as a positive
control.
Examine the possibility of
nephrotoxicity from
gadolinium-based contrast
(GBC) in humans.
Assess the contrast agent
gadolinium toxicity on mice
skin by measuring regional
epidermal thickening and
hair follicle width resulting
from delayed gadolinium
contrast MRI.
Examine the genotoxicity of
trivalent lanthanum and
trivalent gadolinium in
human peripheral blood.
Examine the effects of
SmCb or GdCI3 in food of
rats for 12 weeks. Body
weight, hematology, and
histology were assessed.
Review the potential
cytotoxicity, genotoxicity,
and biochemical toxicity of
holmium.
Key Findings
No blood chemistry, hematology, or
histopathology changes were seen
with the tested contrast media,
whereas increased white blood cell
count and serum cholesterol were
found after GdAc.
Reports of a rare systemic fibrosing
condition called nephrogenic
systemic fibrosis (NSF) were linked
to exposure of patients with
advanced kidney disease to certain
GBC agents. Only patients with
advanced acute or chronic kidney
disease were found to be at risk for
developing NSF.
Gadolinium treatment showed skin
toxicity as epidermis thickening due
to the use of high concentrations of
gadolinium in microimaging.
Micronuclei frequency increased in a
dose-dependent manner upon
exposure to both rare-earth
elements. Significant differences in
single-stranded DNA breaks and
unscheduled DNA synthesis.
Among Sm-treated animals, no
exposure-related histopathological
or other changes were observed.
Minimally decreased body weight
gain and liver histological alterations
were reported in male, but not
female, Gd-treated rats.
NA
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Section 6 - Human Health and Environmental Risks
REE(s)
Lanthanum
Lanthanum
Lutetium
Monazite
Multiple
Multiple
Multiple
Citation
Damment et al., 2005.
Evaluation of the potential
genotoxicity of the
phosphate binder
lanthanum carbonate.
Mutagenesis 20:29-37
Feng et al., 2006.
Neurotoxicological
consequence of long-term
exposure to lanthanum.
Toxicol Lett 765:112-120
Haley etal., 1964a.
Pharmacology and
toxicology of lutetium
chloride. J Pharm Sci
53:1186-1188.
Katsnelson etal., 2009.
Toxicity of monazite
particulates and its
attenuation with a complex
of bio-protectors. Med Lav
100:455-470
Bryan-Lluka and Bonisch
1997. Lanthanides inhibit
the human noradrenaline,
5-hydroxytryptamine and
dopamine transporters.
Naunyn Schmiedebergs
Arch Pharmacol 355:699-
706
Fan etal., 2004. [Study on
the effects of exposure to
REEs and health-responses
in children aged 7-10 years].
Wei Sheng Yan Jiu 33: 23-
28
Haley. 1991. Pulmonary
toxicity of stable and
radioactive lanthanides.
Health Phys 61:809-820
Objective/Purpose
Lanthanum was evaluated
for potential genotoxicity
using a range of in vitro
assays (as the carbonate) in
the presence and absence
of post-mitochondrial
fraction (S9) and in vivo in
tests for mutagenicity and
clastogenicity (as the
carbonate and chloride).
Study whether subchronic
lanthanum [chloride]
exposure affects nervous
system function in rats.
Examine the effects of LuCb
in food of rats for 90 days.
Body weight, hematology,
and histology were
assessed.
Study the health effects of
monazite particles in rats.
Determine the effects of
lanthanides on the activities
of the human noradrenaline,
5-hydroxytryptamine (5-HT),
and dopamine transporters.
Study effects of
environmental exposure to
REEs on children's health.
Examine whether lanthanide
dusts that are devoid of
radioactive contaminants
are capable of producing
progressive pulmonary
disease, or are lanthanide-
induced lesions more
appropriately termed
"benign pneumoconiosis".
Key Findings
The drug was devoid of mutagenic
activity in bacterial assays
(Salmonella typhimurium TA1535,
TA1537, TA1538, TA98, TA100 and
TA102 and Escherichia coli WP2
uvrA and WP2 uvrA pkml 01 ). No
effects were seen in the hgprt gene
mutation assay in Chinese hamster
ovary cells in the presence of S9.
Authors concluded that lanthanum is
not genotoxic.
Neurobehaviorial effects (as
observed by Morris water maze test)
were reported, as well as inhibited
Ca(2+)-ATPase activity, disturbed
central cholinergic system function,
and decreased monoamines
neurotransmitters. Chronic exposure
to lanthanum may impair learning
ability, possibly due to the
disturbance of the homeostasis of
trace elements, enzymes, and
neurotransmitter systems in brain.
No exposure-related
histopathological or other changes
were observed.
Intratracheal injection of monazite
resulted in cytotoxicity, fibrogenicity,
systemic toxicity, and genotoxicity.
Lanthanides 1) cannot substitute for
Na+ in the transport of substrates by
monoamine neurotransmitter
transporters and 2) inhibit the latter
transporters by interacting with sites
of the transporters involved in amine
and Na+ binding.
Reported effects included significant
differences in immunological
parameters (IgM, CDS, CD4,
CD4/CD8) , lower IQ scores,
decreased percentage of high IQ,
and increased percentage of low IQ.
Author reviews available
epidemiological and animal data and
concludes that the pulmonary
syndrome induced by stable rare
earths includes progressive
pulmonary fibrosis and should not
be referred to as "benign
pneumoconiosis."
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Rare Earth Elements Review
Section 6 - Human Health and Environmental Risks
REE(s)
Citation
Objective/Purpose
Key Findings
Multiple
Hirano and Suzuki. 1996.
Exposure, metabolism, and
toxicity of rare earths and
related compounds. Environ
Health Perspect 104 Suppl
1: 85-95
Provide an overview of the
metabolism and health
hazards of REEs.
NA
Multiple
Ji and Cui 1988.
Toxicological studies on
safety of rare earths used in
agriculture. Biomed Environ
Sci 1:270-276.
Studied the toxicity of a
mixture of rare earth metal
nitrates (Ce, La, Nd, Pr, and
Sm) used in agricultural
operations.
In mice, rats, and guinea pigs, the
oral LD50 ranged from 1397 to 1876
mg/kg; absorption in the
gastrointestinal tract was low. Mild
skin and eye irritation were reported
in dermally exposed rabbits. No
biochemical and histopathological
effects were reported in monkeys or
rats following subchronic exposure.
No teratogenic effects were
observed in rats. Ames mutagenicity
tests were negative. The authors
conclude that 60 mg/kg should be
considered a NOAELforthe RE
nitrate mixture, with an acceptable
daily intake (ADI) of 0.6 mg/kg/day
resulting.
Multiple
Palasz and Czekaj. 2000.
Toxicological and
cytophysiological aspects of
lanthanides action. Acta
Biochim Pol 47:1107-1114
Review the toxicological
effects of several
lanthanides.
Gadolinium selectively inhibits
secretion by Kupffer cells and
decreases cytochrome P450 activity
in hepatocytes. Praseodymium ion
produces the same effect in liver
tissue cultures. Lanthanides'
cytophysiological effects may result
from the similarity of their cationic
radii to the size of Ca2+ ions.
Trivalent lanthanide ions, especially
La3+ and Gd3+, block different
calcium channels in human and
animal cells. Lanthanides (Dy3+,
La3+, Mg2+, Eu3+, Tb3+) can affect
numerous enzymes. Lanthanide
ions regulate the transport and
release of synaptic transmitters and
block some membrane receptors of
neurons.
Multiple
Sabbioni et al., 1982. Long-
term occupational risk of
rare-earth pneumoconiosis.
A case report as
investigated by neutron
activation analysis. Sci Total
Environ 26: 19-32.
A case of rare-earth (RE)
pneumoconiosis in a
photoengraver is discussed.
Authors suggest that a relationship
exists between pneumoconiosis and
occupational exposure to RE dusts
(La, Ce, Nd, Sm, Eu, Tb, Yb, and
Lu).
Multiple
Sarkanderand Brade. 1976.
On the mechanism of
lanthanide-induced liver
toxicity. Arch Toxicol 36: 1-
17.
Examine the effects of
Pr(lll), Nd(lll), Sm(lll),
Gd(lll), Dy(lll), andEr(lll)on
rat liver nuclear in vitro RNA
synthesis catalyzed by RNA
polymerase B.
The results indicate a primary ionic
size-correlated interference of
lanthanides with the nuclear control
mechanisms of RNA synthesis.
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REE(s)
Multiple
Multiple
Multiple
Multiple
Multiple
Multiple
Neodymium
Neodymium,
praseodymium
Citation
Vocaturo etal., 1983.
Human exposure to heavy
metals. Rare earth
pneumoconiosis in
occupational workers. Chest
83: 780-783.
Wuetal., 2003. [A case-
control study on the risk
factors of leukemia in
mining areas of rare-earth in
South Jiangxi]. Zhonghua
Liu Xing Bing Xue Za Zhi
24: 879-882.
Yu etal., 2007. Effects of
REEs on telomerase activity
and apoptosis of human
peripheral blood
mononuclear cells. Biol
Trace Bern Res 116: 53-59.
Yu etal., 2004. [Effects of
rare earth compounds on
human peripheral
mononuclear cell
telomerase and apoptosis].
Zhonghua Yu Fang Yi Xue
Za Zhi 38: 248-251 .
Zhang et al., 2000. Chronic
toxicity of rare-earth
elements on human beings:
implications of blood
biochemical indices in REE-
high regions, South Jiangxi.
Biol Trace Bern Res 73: 1 -
17.
Zhu etal., 2005.
Investigation on liver
function among population
in high background of rare
earth area in South China.
Biol Trace Bern Res 104: 1-
8.
Haley etal., 1964b.
Pharmacology and
toxicology of neodymium
and neodymium chlorides.
Toxicol Appl Pharmacol
6:614-620.
Haley etal., 1964c.
Pharmacology and
toxicology of praseodymium
and neodymium chlorides.
Toxicol Appl Pharmacol
6:614-620
Objective/Purpose
A case in a photoengraver is
investigated with regard to
potential RE
pneumoconiosis.
Examine causes of leukemia
in mining areas of REEs.
Study effects of REEs on
human telomerase and
apoptosis of mononuclear
cells from human peripheral
blood (PBMNCs).
Study effects of REEs on
human telomerase and
apoptosis of human
peripheral mononuclear
cells (PBMNs).
Examine hematological
parameters in humans with
elevated REE exposures.
Investigate health effects of
long-term ingestion of REEs
on Chinese villagers living in
high-REE-background
areas.
Examine the effects of
NdCI3 in food of rats for 90
days. Body weight,
hematology, and histology
were assessed.
Investigate pharmacology
and toxicology of
praseodymium and
neodymium chlorides in
animals.
Key Findings
Chest x-ray films showed a severe
pulmonary fibrosis; high RE
concentrations were reported in the
pulmonary and lymph node biopsy
specimens. Results suggest that
long-term accumulation of RE in the
lungs played a role in the
pathogenesis of the observed
pulmonary fibrosis of the worker.
Leukemia was associated with
environmental pollution with REEs
and organophosphorus pesticides.
Increased telomerase activity and
percentages of cells in the S-phase
and the G2/M phase in PBMNCs,
but no effect on the apoptotic rate of
PBMNCs.
The telomerase activity of PBMNs
was higher than controls, and there
is no effect on apoptotic rate of
PBMNs, but may promote the diploid
DNA replication, and increase the
percentage of G2/M and S phase
cells.
Decreased total serum protein
(TSP), albumin, beta-globulin,
glutamic pyruvic transitanase,
serium triglycerides, and
immunoglobulin, and increased
cholesterol were reported.
Decreased serum total protein and
globulin and albumin, and elevated
IgM compared to controls.
No exposure-related
histopathological or other changes
were observed.
Ingestion of PrCIs for 12 weeks
produced no hematological or
histopathological changes.
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REE(s)
Samarium
Thulium
Citation
Weilinetal., 2006. Effects
of samarium on liver and
kidney of rats. J Rare Earths
24:415-418.
Fan etal.,2005. Effects of
Thulium Exposure on IQ of
Children. J Environment and
Health 22:256-256-257
Objective/Purpose
Study rats exposed to
Sm(NOs)3 in drinking water
for five months and examine
for pathological changes.
Study effects of
environmental exposure to
REEs on children's
intelligence.
Key Findings
Increased relative pancreas and
lung weights and increased liver
MDA concentrations were reported
at the lowest dose.
Significantly lower IQ score,
decreased percentage of high IQ,
and increased percentage of low IQ.
The literature review also identified biomonitoring studies in humans and plants, and are briefly
summarized in Table 6-5. Information on REE concentrations in human hair and bone in regions of
Chinese ore mining, as well as in tumors, was of particular interest. There is also a growing concern about
the environmental impact of REE-enriched fertilizers, as they have been commonly used in agricultural
settings in China since the 1980s. In spite of their increasing use, evidence of the effects of REE-enriched
fertilizers on plant growth and crop yield is conflicting (positive, negative, and no effects have all been
reported). A robust evaluation is not possible because access to the journal sources is difficult and most of
the available research is only available in Chinese.
Table 6-5. Selected Biomonitoring Findings for Rare Earth Elements
REE(s)
Cerium
Cerium
Dysprosium
Multiple
Citation
Chua et al., 1998.
Accumulation of
Environmental Residues of
Rare Earth Elements in
Sugarcane. Environ Int 24:
287-287.
Hollriegletal., 2010.
Measurement of cerium in
human breast milk and
blood samples. J Trace
Elements Med and Biol
24:193-199.
Knaus and EI-Fawaris.
1 981 . A biomonitor of trace
heavy metals: indium and
dysprosium in red alder
roots (Alnus rubra Bong.).
Environmental and
Experimental Botany 21:
217-223.
Koeberl and Bayer. 1992.
Concentrations of REEs in
human brain tissue and
kidney stones determined
by neutron activation
analysis. J Alloys and
Compounds 180: 63-70.
Objective/Purpose
Leaves and roots of
sugarcane and soil were
exposed to radiolabeled
Ce, and bioaccumulation in
sugarcane was assessed.
The relationship between
Ce content in human breast
milk and blood plasma or
serum was evaluated.
Bioaccumulation of Dy by
the roots of red alder
(Alnus rubra Bong.) was
tested in a small free-
flowing stream in Oregon.
Measured REE
concentrations in freeze-
dried human brain tissue
and in kidney stones.
Key Findings
Cerium was adsorbed in leaves via the
stoma and cuticle and then rapidly
distributed to various parts of the plant
(roots, stems, leaves). Exposure to
contaminated soil resulted in
accumulation in the roots, bagasse,
leaves, and sugarcane juice.
Cerium concentration in the breastmilk
samples from Munich and Madrid
showed low values. All (except 2) Ce
concentrations in the German plasma
samples were at the quantification limit,
while the serum samples of the Spanish
mothers showed cerium values ranging
between 21.6 and 70.3 ng/L. The Ce
content in plasma/serum (but not
breastmilk) could possibly be an indicator
for environmental Ce.
Non-chelated Dy was sorbed by roots up
to a concentration of 29 ug Dy/g of root
(dry wt), while the sorption of Dy-DTPA
was less by a factor of 8.
Concentrations for 9 REEs (La, Ce, Nd,
Sm, Eu, Gd, Tb, Dy, Yb, Lu)were
reported. A difference between the REE
patterns for apatite and oxalate kidney
stones was observed.
6-22
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Rare Earth Elements Review
Section 6 - Human Health and Environmental Risks
REE(s)
Citation
Objective/Purpose
Key Findings
Multiple
Liang et al., 2005.
Environmental
biogeochemical behaviors of
REEs in soil-plant systems.
Environmental
Geochemistry and Health
27: 301-311.
REEs' content in soil and
various parts of wheat
under different conditions in
soil-plant systems were
measured by INAA and
ICP-MS.
The mean value of total REEs in soil of
China was 176.8 mg/kg. The mean ratio
of SigmaLREE/SigmaHREE in soils was
8.0 and cerium accounts for 42% of the
total REEs. The content of REEs in
wheat seed ranged between 10E-11 and
10E-8 g/g, 3-4 orders of magnitude lower
than that in soil. The REEs contents in
ryegrass, especially in roots, were
significantly related to that of soil. The
bioavailability of REEs in soil mainly
depended on the exchangeable fraction
of REEs, which was strongly affected by
the physico-chemical properties of the
soil. At the maturing stage of spring
wheat, the REEs content was in the
order of root > leaf >stem and crust.
Multiple
Lihong et al., 1999. The
effect of EDTA on REEs
bioavailability in soil
ecosystem. Chemosphere
38: 2825-33.
The effects of EDTA on the
bioaccumulation of REEs
by wheat seedlings growing
in two types of soils were
studied.
The bioaccumulation values of REEs in
wheat roots were much higher than
those in the tops (stems and leaves) for
both types of soils. EDTA promoted
REEs bioavailability of wheat by
increasing the REEs desorption from
soils.
Multiple
Linsalata etal., 1985.
"Determination of the
Human Intake of Thorium
and the Light Rare Earth
Elements from High and
Typical Natural Radiation
Environments." Univof
Missouri/et al Trace Subst in
Environ Health 19th Conf,
Columbia: 257-257.
Measure the human
ingestion of thorium and
light REEs in Minas Gerais,
Brazil, at a location near an
ore body containing >
100,000 metric tons of
REE.
Based on measurement in feces of
residents located near the ore body, the
annual ingestion intakes of Ce, La, Th,
and Sm calculated from median
concentrations are 24, 10, 5, and 0.6
mg/yr, respectively, for residents of one
farm, and 42, 15, 3, and 1 mg/yr,
respectively, for residents of the second
farm. Comparable ingestion rates for
residents of NY are 2.9, 1, 0.2, and 0.1
mg/yr, respectively.
Multiple
Peng etal., 2003.
[Relationship of the hair
content of REEs in young
children aged 0 to 3 years to
that in their mothers living in
a rare earth mining area of
Jiangxi]. Zhonghua Yu Fang
YiXueZaZhi 37: 20-22.
To study the relationship of
hair content of REEs (La,
Ce, Pr, Nd, Sm) in young
children (aged 0-3 years)
to that in their mothers
living in a rare earth mining
area of Jiangxi Province.
The mean hair content of REEs (e.g., La)
was the highest (2,202.9 ng/g) in the
young children living in the place nearest
to the REE mining area, next was in
those near the low-exposure area, and
the lowest was in those in the control
area. Pair-comparison analysis for the
means showed that the average hair
level of five kinds of REEs in the young
children was two times high as their
mothers'. The hair level of REEs can be
used as a biomarkerto reflect body's
level of exposure to REEs. The hair level
of REEs in young children and their
mothers decreased with the increase of
the distance from their home to rare
earth mining area. Young children living
in the area with REEs mining may be the
high-exposure population.
6-23
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Rare Earth Elements Review
Section 6 - Human Health and Environmental Risks
REE(s)
Citation
Objective/Purpose
Key Findings
Multiple
long et al., 2004.
Distribution characteristics
of REEs in children's scalp
hair from a rare earths
mining area in southern
China. J Environ Sci Health
A Tox Hazard Subst Environ
Eng 39(9): 2517-2532.
Validate the use of REE
scalp hair content (La, Ce,
Pr, Nd, Sm) as a biomarker
of exposure. Hair content
data were collected on 16
REEs from children aged
11-15 years old and living
in an LREEs mining and
surrounding areas in
southern China.
REEs hair content from the mining area
(e.g., range: La: 0.14-6.93 ug/g; Nd:
0.09-5.27 ug/g; Gd: 12.2-645.6 ng/g; Lu:
0.2-13.3 ng/g; Y: 0.03-1.27 ug/g; Sc:
0.05-0.30 ug/g) were significantly higher
than those from the reference area and
higher than those previously published.
Multiple
Zaichicket al., 2011.
Accumulation of REEs in
human bone within the
lifespan. Metallomics 3: 186-
194.
The concentrations of
REEs (Ce, Dy, Er, Gd, La,
Nd, Pr, Sm, Tb, Yb, Ho, Lu,
Tm, Y) in the rib bone
tissue of healthy humans
(38 females and 42 males,
age 15 to 55 years old)
were determined using
ICP-MS.
Age-related accumulation of REEs were
found in the bone tissue of healthy
individuals who lived in a non-industrial
region.
Multiple
Zhang et al., 2003. [Levels
and distribution of 15 REEs
in tumor and normal lung
tissue from the patients with
lung cancer]. Wei Sheng
Yan Jiu 32: 423-426.
Tumor tissue and normal
tissue around tumors were
collected from patients with
lung cancer and 15 REEs
were measured by ICP-MS.
Levels of 15 REEs in normal tissues
around the tumor was as 2.07-2.51 times
high as those in the tumor tissue.
Contents of light REE in lung tissue of
health human were higher while the
contents of media and heavy REE were
lower.
Multiple
Zhuang et al., 1996.
Concentration of REEs, As,
and Th in human brain and
brain tumors, determined by
neutron activation analysis.
Biol Trace Bern Res 53: 45-
49.
6 REE concentrations of
brain tumor tissues from 16
patients with astrocytomas
(grade l-lll) and normal
human brain tissues of 18
male, age-matched
autopsies serving as
controls were measured.
Concentrations of Th, La, Ce, Gd, and Lu
were significantly higher in tumor tissues.
The literature review also identified ecological studies, which are summarized in Table 6-6, below.
Information on ecological effects of REE on marine organisms, soil fauna, and plants were of particular
interest. Many studies were conducted by Chinese researchers. It should be noted that this literature
search was limited to the ecological effects of REEs, rather than the broader environmental contamination
impacts resulting from REE extraction, processing, waste management, and industrial practices.
6-24
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Rare Earth Elements Review
Section 6 - Human Health and Environmental Risks
Table 6-6. Selected Ecotoxicity Findings for Rare Earth Elements
REE(s)
Citation
Objective/Purpose
Key Findings
Cerium,
lanthanum
Oraletal., 2010.
Cytogenetic and
developmental toxicity of
cerium and lanthanum to
sea urchin embryos.
Chemosphere 81: 194-198.
Evaluate the toxicity of Ce
and La on sea urchin
(Paracentrotus lividus)
embryos and sperm.
Embryos reared in 10(-5)M Ce resulted
in 100% embryonic mortality, whereas
10(-5)M La induced 100% developmental
defects, without causing any embryonic
mortality. A significant concentration-
related mitotoxic effect and induction of
mitotic aberrations were observed in Ce-
exposed, but not in La-exposed
embryos, at concentrations ranging from
10(-7)M to 3 x 10(-6)M. Following sperm
exposure, both Ce and La induced a
decrease in sperm fertilization success at
the highest tested concentration (10E-5
M). The offspring of Ce-exposed, but not
of La-exposed sperm displayed a
significant concentration-related increase
in developmental defects.
Gadolinium
Saitoh etal., 2010.
Asymmetric inhibition of
spicule formation in sea
urchin embryos with low
concentrations of
gadolinium ion. Dev Growth
Differ 52(9): 735-746.
Study the effects of
gadolinium ion, a Ca(2+)
channel blocker, on spicule
formation in sea urchins.
Gd(3+) exerts an inhibitory effect on
spicule formation through a mechanism
that does not involve inhibition of Ca(2+)
channels.
Holmium
Qu et al., 2004. [Research
on the cytotoxic and
genotoxic effects of rare-
earth element holmium to
Vicia faba]. Yi chuan =
Hereditas / Zhongguo yi
chuan xue hui bianji 26(2):
195-201.
The root tips of Vicia faba
were soaked in a holmium
solution for 6hr and then
cultivated for 22-24 hr. The
frequency of micronucleus
(FMN), the frequency of
chromosomal aberrations
(CAP), and mitosis index
(Ml) were calculated.
Holmium demonstrated certain cytotoxic
and genotoxic effects.
Lanthanum
Barry and Meehan. 2000.
The acute and chronic
toxicity of lanthanum to
Daphnia carinata.
Chemosphere 41: 1669-
1674.
Acute and chronic toxicity
of lanthanum to Daphnia
carinata.
La was most toxic to Daphnia in soft tap
water (acute 48-h EC50 = 43 ug/l)
compared to ASTM hard water (ASTM)
(EC50 = 1180 ug/l). In the third growth
medium, diluted sea water (DW)
(EC50=49 ug/l), there was significant
precipitation of La. There was 100%
mortality at concentrations > 80 ug/l by
day six using DW media, but no effect on
survival growth or reproduction at lower
concentrations. In the ASTM media, La
caused significant mortality to Daphnia at
concentrations > 39 ug/l, however, at
least one animal survived to the end of
the study at each of the tested
concentrations. There was no effect of
La on growth of surviving daphnids at
concentrations < 57 ug/l, however,
second brood clutch sizes were
significantly increased. La also caused
delayed maturation.
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Rare Earth Elements Review
Section 6 - Human Health and Environmental Risks
REE(s)
Citation
Objective/Purpose
Key Findings
Lanthanum
Chu et al., 2003. Availability
and toxicity of exogenous
lanthanum in a haplic
acrisols. Geoderma 115(1-
2): 121-128.
Study the availability and
toxicity of exogenous La in
Chinese soil. The toxicity of
La was determined by the
evaluation of relative
luminosity of
Photobacterium
phosphoreum T3.
The exogenous La was highly available
in soil, and the average available La
accounted for 56.6% of exogenous La
after 1 week of incubation. La was
biologically toxic in aqueous solution and
soil. Results indicate that the excessive
exogenous La in soil may harm soil
microbial community.
Lanthanum
Zhang et al., 2010.
Ecotoxicological
assessment of lanthanum
with Caenorhabditis elegans
in liquid medium.
Metallomics 2: 806-810.
Caenorhabditis elegans
was used as a test
organism to evaluate the
aquatic toxicity of La.
La(3)+ had significant adverse effects on
the growth and reproduction of worms
above a concentration of 10 umol/L. La
treatment disturbed the metals
distribution in the whole body of a single
tiny nematode at lower levels.
Lanthanum
Zhao et al., 2005. The effect
of the rare earth La2O3 on
growth and reproduction of
Tenebrio molitor. Chinese
Bulletin of Entomology 42:
444-449.
The effects of the rare
earth La2Os on growth and
reproduction of Tenebrio
molitor L. were studied.
Newly eclosion larvae and
adults were continuously
reared in the La2Os food
(contaminated wheat bran)
with different dosages.
After 79 d the larvae reared on the food
with 40 mg La/kg gained 43% more
weight and the female lay 59% more
eggs daily in peak oviposition period than
the control group. The larvae fed on the
food with the dosage of 40 mg La/kg for
50 d resulted in 0.4% La accumulated in
the larval body.
Multiple
Chen et al., 2000. Effects of
Rare Earth Metal Ions and
Their EDTA Complexes on
Antioxidant Enzymes of Fish
Liver. Bulletin of
Environmental
Contamination and
Toxicology 65(3): 357-365.
Study toxicological effects
of different species of REE
to goldfish and validate the
potential use of antioxidant
enzymes as early
biomarkers of REEs in
aquatic ecosystem.
The exposure tests were performed to
observe the changes of SOD CAT
activities of goldfish with the control at
selected times. The toxicological effects
on goldfish were estimated with contrast
and analysis of the test data.
Multiple
He andXue. 2005.
[Biological effects of REEs
and their action
mechanisms]. Ying Yong
Sheng TaiXue Bao 16:
1983-1989.
Review the effects of REEs
on plant root development,
biomass, quality, and
resistance against stress.
REEs can enhance chlorophyll content,
improve photosynthetic rate, increase
plant biomass, promote uptake and
utilization of nutrients by plant when
appropriate amount of REEs was
applied.
Multiple
Ippolito et al., 2010.
Responses of antioxidant
systems after exposition to
rare earths and their role in
chilling stress in common
duckweed (Lemna minor L.):
a defensive weapon or a
boomerang? Arch Environ
Contam Toxicol 58: 42-52.
Study the effects of a mix
of different REE nitrate and
lanthanum nitrate on
catalase and antioxidant
systems involved in the
ascorbate-glutathione cycle
in common duckweed
Lemna minor L.
L. minor shows an overall good tolerance
to the presence of REEs in the media.
Treatments (up to 5 mM REE and 5 mM
La) did not cause either visible
symptoms on plants or significant effects
on reactive oxygen species production,
chlorophyll content, and lipid
peroxidation. Toxic effects were
observed after 5 days of exposure to 10
mM REE and 10 mM La.
Multiple
Lietal.,2006. [Effects of
REEs on soil fauna
community structure and
their ecotoxicity to
Holotrichia parallela]. Ying
Yong Sheng Tai Xue Bao
17: 159-162.
Study the effects of applied
REEs on soil fauna
community structure and
their ecological toxicity to
Holotrichia parallela in
bean field.
No significant differences between the
treatments and the control were
observed in soil fauna species, quantity
of main species, and diversity index.
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Rare Earth Elements Review
Section 6 - Human Health and Environmental Risks
REE(s)
Citation
Objective/Purpose
Key Findings
Multiple
Tai et al., 2010. Biological
toxicity of lanthanide
elements on algae.
Chemosphere 80: 1031-
1035.
Study the biological toxicity
of REEs on marine
monocellular algae
(Skeletonema costatum).
All single lanthanides had similar toxic
effects on Skeletonema costatum. High
concentrations of lanthanides (29.04
umol/L) resulted in 50% reduction in
growth of algae compared to controls (96
hr-EC50). A mixed solution that
contained equivalent concentrations of
each lanthanide element had the same
inhibition effect on algae cells as each
individual lanthanide element at the
same total concentration. The authors
conclude that the monocellular
organisms might not be able to
sufficiently differentiate between the
almost chemically identical lanthanide
elements.
Multiple
Tang et al., 2004.
[Ecological effects of low
dosage mixed REEs
accumulation on major soil
microbial groups in a yellow
cinnamon soil]. Ying Yong
Sheng TaiXue Bao 75(11):
2137-2141.
The ecological effects of
low dosage of mixed REE
accumulation on major soil
microbial groups in a yellow
cinnamon soil was studied.
The continuous accumulation of REE
had the alternative effects of stimulation,
inhibition, and re-stimulation on soil
bacteria and actinomycetes, and a
continuous stimulation on soil fungi. At
the accumulation of 150 mg/kg of REE,
the population structure of three groups
changed remarkably. The number of
REE-tolerant microbes increased, with
gram negative bacteria, white spore
group and penicillium being predominant
in bacteria, actinomycetes and fungi
population, respectively. The authors
propose an EC50 value of 30 mg/kg for
the critical value of mixed REE in yellow
cinnamon soil.
Multiple
Xie. 2007. Detection of
Genotoxicity of 6 Kinds of
Rare Earth Nitrates Using
Orthogonal Experimental
Design. J Agro-Environment
Science 26: 150-155.
The genotoxicity of 6 kinds
of RE nitrates (Ce(NO3)3,
Er(NO3)3, Sm(NO3)3,
La(N03)3, Y(N03)3,
Eu(NO3)3) to root tip cells of
maize was detected using
micronucleus test.
5 RE nitrates played a role in the
formation of micronuclei in root-tip cells
of maize, while La nitrate had no
significant influences. With the
concentration increasing, the FMN in
root-tip cells of maize treated by RE
compounds increased significantly
compared with the control group.
Combined toxic effect was also
observed. The 6 RE nitrates had
genotoxicity to root tip cells of maize and
showed no interaction with each other.
Terbium
Liu and Zhou. 2007.
Response of Terbium
Ecotoxicity Effect on
Cochlearia armoracia L.
Peroxidase (HRP) to Light. J
Agro-Environment Science
26: 977-979.
Study the ecotoxicity
effects of terbium on
Cochlearia armoracia L.
peroxidase (HRP) at
different lights.
The results indicate the toxic effect of
Tb(lll) on HRP was increased with strong
light.
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Rare Earth Elements Review
Section 6 - Human Health and Environmental Risks
REE(s)
Terbium
Ytterbium
Citation
Peng et al., 2007.
Ecotoxicity of Terbium to
Peroxidase Activity of
Cochlearia armoracia L.
Under Different Light and
Temperature. J Agro-
Environment Science 26:
974-976.
Hongyan et al., 2002.
Physiological Responses of
Carassius auratus to
Ytterbium exposure.
Ecotoxicology and
Environmental Safety 53:
312-316.
Objective/Purpose
Study the ecotoxicity
effects of terbium on
Cochlearia armoracia L.
peroxidase (HRP) at
different temperatures.
Physiological and
biochemical effects to the
liver of Carassius auratus
were investigated in vivo
following 40 days of
exposure to ytterbium.
Key Findings
The results indicate the toxic effect of
Tb(lll) on HRP was increased with high
temperature.
Glutamate-pyruvate transaminase
(GPT), superoxide dismutase (SOD),
catalase (CAT), glutathione S-
transferase (GST), and glutathione
peroxidase (GSH-Px) activities were
affected in goldfish liver. CAT was most
sensitive to Yb3+, indicating that CAT
might be a potential tool in the
biomonitoring of exposure to Yb3+ in an
aquatic ecosystem.
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Rare Earth Elements Review Section 7 - Summary, Key Findings, and Next Steps
7. Summary, Key Findings from Literature Review, and Potential
Next Steps
The purpose of this report is to serve as a technical information resource to policy makers and other
stakeholders who are concerned with the potential environmental and health effects and impacts that can
be identified across the REE supply chain. RTI conducted a search of the technical literature and other
Internet sources related to each segment of the supply chain, including recent initiatives of U.S.
government agencies that document issues associated with REE production, processing, manufacturing,
end uses, recycling, and health/ecological effects. Information contained in this report also draws upon
past domestic and international experience, as appropriate. The vast majority of information in this report
is current. But, as noted in this report, mining and extraction of REEs is dynamic. Therefore, some
details regarding who is producing what and where may have changed between the time when: (1) data
collection as part of the literature search for this report was complete in July 2011, (2) the report's
contract was completed in September 2011, and (3) its subsequent publication in 2012.
Although the current literature provides limited information specifically relating to REE mining,
processing, recycling, and environmental or health impacts, it is expected that more information will be
produced in the future as a result of the increased level of interest in REEs in the past few years.
7.1 Summary
REEs include the series of 15 lanthanide metals, plus scandium and yttrium. REEs have become
increasingly important in recent years because their unique chemical and physical properties have
contributed to technological advances in many areas, such as wind turbines, hybrid electric vehicles,
energy-efficient lighting, computers and electronics, and defense applications such as lasers.
In 1984, the Molycorp Minerals, Inc. mine in Mountain Pass, CA, supplied 100 percent of U.S. demand
and 33 percent of the world's demand for rare earths. The mine was shut down in 2002 for a variety of
reasons, and since that time, China has become the world's leading producer of REEs, handling
approximately 95 percent of worldwide production. Due to the increase in demand and the reduction in
supply of REEs, the cost of REEs has increased dramatically in recent years. Given the strategic
importance, supply concerns, and increasing cost of REEs, REE mines outside China are currently being
evaluated or are in development, including multiple sites in the United States. Past producers of rare
earths are re-opening idle or closed mines, and active mines that produce other metals that usually send
rare earths as waste are now considering recovery of rare earth oxides.
Molycorp Minerals, Inc. is at the forefront as one of the first companies to reinitiate mining operations at
their existing Mountain Pass mine. Molycorp also is attempting to find better mineral processing methods
that allow recovery of more rare earth oxides from the ore at a lower cost and with less environmental
impact.
Outside of direct mining operations, other sources of rare earths are being explored, such as recovery
from recycling or urban mining. Currently, commercial recycling of rare earths is very limited; however,
it is reported in the literature that, within the next year, several new commercial recycling operations will
begin operation, with the focus being on magnets, batteries, lighting and luminescence, and catalysts.
Mining and processing activities have the potential to create a number of environmental risks to human
health and the environment. The severity of these risks is highly variable between mine and mine plant
operations. The contaminants of concern will vary depending on the REE-mineral ore, the toxicity of the
contaminants from the waste rock, ore stockpiles, and process waste streams. The mobility of
contaminants will be controlled by the characteristics of the geologic, hydrologic, and hydrogeologic
7-1
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Rare Earth Elements Review Section 7 - Summary, Key Findings, and Next Steps
environments where the mine is located, along with the characteristics of the mining process and waste
handling methods.
The results from the preliminary literature search related to human health, epidemiology, toxicity,
biomonitoring, and ecological studies on REEs resulted in limited data. Most of the studies identified in
the literature review examined mixtures of REEs, rather than individual elements. In addition, many
studies were conducted in regions of Chinese ore mining by Chinese investigators and were not available
in English (only the abstracts were available in English).
7.2 Key Findings
As mentioned previously, this report summarizes the information available during this report's production
and review and should be considered a starting point for future investigations related to the potential
environmental and health issues concerning the production, processing, recycling, recovery, and life
cycles of REEs. Key findings from this literature review include the following:
Analysis of the future supply and demand for each of the REEs indicates that, by 2014, global
demand could exceed 200,000 tons per year, which would exceed current production by over
75,000 tons per year. It is reported that if the new mines under development are able to meet their
projected production levels, world-wide demand for REEs will be met from these new sources.
The waste footprint and environmental impacts from mining operations to extract rare earth
mineral ores are expected to be as significant as current metals/minerals mining practices. The
environmental effects on local communities and habitats must be determined so that mitigation
measures can be considered when determining the feasibility of a proposed rare earth mining
project. Planning the mine in advance and planning for waste management associated with long-
term projects is important to the successful future restoration of a mine site.
The most significant environmental impact from contaminant sources associated with hardrock
mining is to surface water and ground water quality. However, documented impacts also have
occurred to sediments, soils, and air. Mining for rare earth mineral ores and processing those ores
into the final products can be compared to other hardrock metal mining and processing
operations, and similar environmental impacts and risks would be expected.
AMD usually is not a significant issue for REE deposits; however, the rock that surrounds or is
overlying an ore body may contain the sulfide minerals that could create AMD. REEs often occur
in ores rich in carbonate minerals, which generally have high acid-neutralizing potential and
therefore, can help buffer any effects of acidic mine drainage that might occur.
Rare earth milling and processing is a complex, ore-specific operation that has potential for
environmental contamination when not controlled and managed appropriately. Waste streams
with the greatest pollution potential are the tailings and their associated treatment and storage.
Heavy metals and radionuclides associated with REE tailings pose the greatest threat to human
health and the environment when not controlled. However, adoption of new technologies and
management processes has the potential to reduce the risk of environmental contamination.
Increased demand and reduced supply of REEs, along with the knowledge of the quantities
available in waste products, has resulted in expanded research and development efforts focused
on the recycling of, and identification of alternatives to, rare earths. Currently, commercial
recycling of rare earths is very limited; however, it was reported in the literature that within the
next year several new commercial REE recycling operations will begin operation.
Another potential source of REO is the tailings waste from other mineral processing operations.
For example, the apatite tailings from the Pea Ridge iron ore mine and processing operation
contain 0.5% REO. The tailings impoundment currently contains 20 million tons.
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Rare Earth Elements Review Section 7 - Summary, Key Findings, and Next Steps
While environmental impacts can occur, when compared with primary processing of metals, it is
reported that controlled recycling of REEs will provide significant benefits with respect to air
emissions, groundwater protection, acidification, eutrophication, and climate protection.
Frequently, recycling of electronics is taking place outside of the United States in developing
countries using informal processes. These informal operations can include manual dismantling,
open burning to recover metals, de-soldering of printed wiring boards over coal fires, and acid
leaching in open vesselsall with the potential for significant, adverse environmental and human
health impacts.
The specific health effects of elevated concentrations of REEs in the environment from mining
and processing REE-containing ores are not well understood. From the limited literature review,
it appears that most available epidemiological data are for mixtures of REEs rather than
individual elements. These data indicate that pulmonary toxicity of REEs in humans may be a
concern. Additionally, as referenced in Section 6, the larger, lighter (i.e., smaller atomic number),
and less soluble ions have been observed to deposit primarily in the liver, while the smaller,
heavier (i.e., larger atomic number), and more soluble ions are similar in ionic radius to divalent
calcium and distribute primarily to bone.
7.3 Suggested Next Steps
Suggested next steps that could provide the additional information necessary to fill current knowledge
gaps and support future decision-making efforts include the following:
1. Conduct technology review(s) of wastewater treatment (including an evaluation of the
environmental impacts) for REE mining and processing operations. Following the technology
review, efforts could focus on technology development to address gaps identified in the review.
2. Conduct sustainability studies focused on urban mining in the United States to include
information on REEs (and other high-value materials) contained in products, the value of those
materials, methods for reclaiming or recycling the materials, and the environmental impacts from
all steps. Such studies could take a life-cycle approach and include topics such as design of
products to make recycling easier.
3. Support research focused on determining the technical and economic barriers to recycling of
certain rare earths. Following determination of the barriers, explore options for
reducing/eliminating the barriers, including technology research, development, and
environmental impact studies.
4. Expand upon the information provided in this report and develop a system understanding for all
elements associated with REE mining, processing, and recycling that have the potential for
environmental or health impacts. Use this information to perform regional environmental
evaluations of locations where REE mines, processing facilities, and recyclers are likely to be
developed to determine the potential for environmental and health impacts that could occur. Use
the results to plan and prioritize research, regional technical support, and regulatory efforts.
5. Conduct a more complete review of the health, biomonitoring, and ecological impacts literature
to include a comparison of the references cited in health background documents to the
preliminary literature search results presented in this documentto ensure all available studies
are included.
6. Support additional human health toxicity and ecological impact studies on specific REEs and then
use this information to conduct risk assessments related to REE mining, processing, and
recycling.
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Rare Earth Elements Review Section 7 - Summary, Key Findings, and Next Steps
7. Convene EPA/federal agencies/industry workshops and information exchanges on topics related
to REE technology development, recycling, and impacts.
8. Engage other federal agencies, such as DOE, DOD, DOI, USGS, and the BLM, in the
coordination of research, technical support, outreach, policy, and regulatory efforts in the REE
arena.
9. Develop outreach and decision support tools, such as guidance documents, decision trees, and
websites, to provide technical support and information exchange to EPA Regions, states, and
other interested parties.
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Rare Earth Elements Review Section 8 - References
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Rare Earth Elements Review Section 8 - References
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Rare Earth Elements Review Section 8 - References
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Rare Earth Elements Review Section 8 - References
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Rare Earth Elements Review Section 8 - References
8-13
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Rare Earth Elements Review Appendix A - Selected Chemical Properties
Appendix A
Selected Chemical Properties of REEs
It was once thought that rare earth elements (REEs) naturally occur as oxides, referred to as "earths," but
it is now understood that these elements do not naturally occur in the form of an oxide in natural deposits.
Commonly, modern geochemists refer to REEs as the "lanthanide group elements," or "lanthanides,"
since lanthanide is positioned first in a series of elements that all share similar chemical properties. The
elements scandium and yttrium have almost identical physical and chemical properties to that of the
lanthanide group elements; therefore, these are also included in the lanthanide group. All the rare earths
except promethium (Pm) are available in nature. Promethium occurs by thermal neutron fission of
uranium (U235) or by bombarding neodymium with neutrons produced from uranium fission in a nuclear
reactor.
The natural geochemistry and physico-chemical properties of REES that control background
concentrations of these metals in the environment are not well understood, nor are the factors influencing
bioavailability. Studies in the literature appear limited at the present time. Measurement of rare earth
metals (REMs) in environmental media is also problematic due to the physico-chemical properties that
make them unique. Predicting the environmental human and ecological health risks associated with
anthropogenic activities that have the potential to release REMs to the environment is difficult and not
straightforward. Some of the physico-chemical characteristics of lanthanides are presented below that
likely affect the occurrence and bioavailability of these metals. Although not included here, an extensive
tabulation of the properties for the lanthanide group metals is provide by Gupta and Krishnamurthy
(2004) and others.
In general, metals typically exist in the environment in several different forms, depending on ambient
chemical conditions (e.g., pH, organic carbon, presence of other chemicals). The chemical form of a
metal, or its speciation, can play a large role in its fate and bioavailability and, thus, in its potential to
produce toxic effects (Langmuir et al., 2004). Because of the high variability in both biotic and abiotic
factors (e.g., pH) affecting the speciation and bioavailability of metals within and between environmental
media, risks posed by metals often can vary by orders of magnitude depending on the speciation.
Environmental conditions can change significantly, even over small spatial scales (e.g., a few centimeters
in a sediment transitioning from an aerobic zone downward to an anaerobic zone), and such significant
shifts in conditions can lead to significant changes in metals speciation and risk. Evidence found
pertaining to the toxicity and health effects of lanthanides is provided in Section 6 of the main document
to this appendix.
The rare earths are so chemically similar to one another that separation of individual elements from the
host minerals is difficult (see Section 4). Their similarity is also demonstrated by their occurrence
together in the same geological deposits; however, that does not imply that these metals respond equally
to changes in natural systems (Weber, 2008). It is believed that the lanthanide group elements also have
very similar electronic configurations; however, due to the complexity of the electron spectra and
difficulty of analysis the electron configuration is not known with complete certainty (Gupta and
Krishnamurthy, 2004).
There are observed distributions for lanthanide group elements in the natural environment indicating that
they will, under the right conditions, separate from the each other. Preferences for the occurrence of
certain lanthanides have been observed in different mineral types. In aqueous solution, separation also
occurs due to variable stability constants, indicating the strength of the chemical bond of lanthanide-
ligand complexes (Weber, 2008). Observations like these have suggested a subdivision of the lanthanides
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Rare Earth Elements Review Appendix A - Selected Chemical Properties
into various groupings as presented by Gupta and Krishnamurthy (2004) from other sources and that are
presented below. Previously the lanthanides were categorized into three groups according to Kramers in
1961:
Light (or cerium) lanthanide group - lanthanum (La) through samarium (Sm);
Middle (or terbium) lanthanide group - europium (Eu) through dysprosium (Dy);
« Heavy (or yttrium) lanthanide group - holmium (Ho) through lutetium (Lu) and including
yttrium.
More recently, two other attempts have been made to subdivide the lanthanides into groups:
(after Jackson and Christiansen, 1993):
Light (or cerium) lanthanide group - lanthanum (La) through gadolinium (Gd); and
« Heavy (or yttrium) lanthanide subgroup - terbium (Tb) through lutetium (Lu), including yttrium.
(after Sabot and Maestro, 1995)
« Light lanthanide group - lanthanum (La) through neodymium (Nd);
Middle lanthanide group - samarium (Sm) through dysprosium (Dy);
Heavy lanthanide group - holmium (Ho) through lutetium (Lu) and including yttrium.
Other groupings continue to be developed based on newer studies and observations and according to
purpose.
The chemical properties of metals are determined by the valence electrons or the number of bonds that
can be formed by an atom. Rare earths differ from other metals since their valence electrons are not
located in the outermost shell of the atom, rather the valence electrons of the lanthanide group are
positioned in the (4f) subshell that is shielded by two larger closed (or full) subshells (5s2 and 5p6).
Regardless of the attempted groupings, this atomic configuration supporting stable outermost electron
shells results in the very similar chemical properties of the lanthanide group in general and the difficulty
in their separation during processing.
Contrary to the general trend in the periodic table, it has been observed in the lanthanide group that the
atomic radii of the elements and their ions decrease slightly as the atomic numbers increase (starting with
cerium). Lanthanum has the largest radius and lutetium the smallest, owing to the incremental increase of
4f orbital electrons by one across the group. In very general terms, a current theory considers that the
atomic nucleus of the lanthanide elements is poorly shielded, and therefore with the increase in atomic
number, the nuclear charge experienced by the 4f orbital electrons increases as well. The effect of this
shielding pattern results in a contraction of the 4f shell as that subshell's electrons are pulled closer to the
nucleus. This reduction in ionic radii across the lanthanides with increasing ionic charge is referred to as
the "lanthanide contraction." The difference in ionic radius of adjacent rare earths is very small. For
example, the ionic radius of Ce+3 is 1.06 A and that of Lu+3 is 0.85 A. The lanthanide contraction controls
many of the features observed for REE chemistry. The chemistry of lanthanides is predominantly ionic
and is determined primarily by the size of the trivalent ion.
All the REMs typically occur in the trivalent (M3+) state in terrestrial environments. However, a few of
the REMs occur in other ionic forms such as samarium (Sm2+), thulium (Tm2+), and ytterbium (Yb2+), but
only the alternate forms of cerium (cerous, Ce4+), and Europium (Eu2+), are commonly found in natural
systems (Railsback, 2008). Since the outer orbitals of lanthanides have higher energy, they tend not to
form covalent bonds (Weber, 2008). Some covalency is exhibited and increases slightly with increasing
A-2
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Rare Earth Elements Review Appendix A - Selected Chemical Properties
atomic number; however, bonding is predominantly ionic, even with extra electrons in the d-orbitals of
some lanthanides.
An important chemical property is that the lanthanides will form strong complexes with a number of
different ligands. Water is a strong ligand for trivalent (M3+) lanthanides (Weber, 2008). Trivalent (M3+)
lanthanides strong affinity for water allows them to form a hydration shell around the Ln3+ ion. The
number of molecules of water that a lanthanide ion can bond with in an aqueous solution varies between 8
and 9, depending on the element and species (Weber, 2008). Weber (2008) points out that the basic
physico-chemical properties of lanthanides in natural aqueous systems (e.g., interstitial soil water in the
unsaturated zone) depend significantly on the presence of other coordinating compounds that can displace
the water molecules from around the lanthanide metal ion.
In aqueous environments, the water ligand would only be displaced if ligands with small ionic radius
were present with a high oxidation state, high electronegativity, and with the highest occupied molecular
orbitals having low energy; examples of these chemical species are the hydroxyl anion (OH"), fluorine
(F~), chlorine (CO, ammonia (NH3), acetic acid (CH3COO~), carbonic acid (CO32~), nitrate (NO3"), sulfate
(SO42~), phosphate (PO43~), oxide (O2~), alcohols (R -OH), amines (R-NH2), and others containing highly
electronegative donor atoms such as O and F. These chemical species would tend to form mainly an ionic
bond with the lanthanides molecules within their unoccupied lower high-energy orbitals. Lanthanides
preferentially bond with oxygen atoms in aqueous solutions, but one-to-one bonding between lanthanides
and other compatible ions has been shown to be weak compared to bonding with oxygen or flourine
atoms and easily hydrolyzed by water (Gupta and Krishnamurthy, 2004; Weber, 2008). However,
polydentate ligands, which have multiple pairs of electrons that can bond to the lanthanide metal ion, will
form stronger bonds that may be more stable in aquatic environments. In general, the lanthanide ion
preference for donor atoms is O>N>S (Weber, 2008).
At ambient temperatures, all REMs are not affected by air the same way. The ionization energies (or
strength of the nuclear charge) of lanthanides are comparatively low, meaning it takes less energy to
remove valence electrons. These elements are therefore highly electropositive and, as previously stated,
form compounds that are essentially ionic in nature (Gupta and Krishnamurthy, 2004). Like most metals,
the lanthanides have a gray luster or bright silvery appearance. Five of the elements (lanthanum, cerium,
praseodymium, neodymium, and europium) are very reactive. When exposed to the air, they react with
oxygen to form an oxide coating that tarnishes the surface almost immediately. A block of europium will
be converted to an oxide in a few days or weeks. Under the same conditions, surface corrosion of a
massive block of lanthanum or neodymium will occur in a few days, and a thick crust of oxide will
develop in a few months.
Analytical Methods
There are a variety of methods employed to determine REE concentrations in environmental samples,
such as (1) atomic absorption spectroscopy; (2) neutron activation; (3) isotope dilution thermal ionization
mass spectrometry (ID-TIMS); and (4) inductively coupled plasma-mass spectrometry (ICPMS).
Concentrations of REEs in unpolluted freshwater systems typically range in from parts-per-billion (ppb)
to parts-per-trillion (ppt) (Lawrence et al., 2006). Therefore, a pre-concentration step such as ion
exchange chromatography, Fe(OH)3 co-precipitation, or liquid-liquid extraction may be required prior to
analysis. The specific method selected for analysis will provide guidance on sample preparation prior to
analysis (e.g., an EPA 3000 series method).
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Rare Earth Elements Review
Appendix A - Selected Chemical Properties
Although each method has their advantages and disadvantages, the predominant method utilized today is
ICP-MS. Listed in Table A-l are three established ICP-MS methods that can be utilized for the analysis
of REEs. It is important to note that the EPA methods do not list REE as being successfully demonstrated
by these methods. However, if REEs are to be measured they need to meet the provisions outlined in the
method. Chapter K of the USGS document presented in Table A-l was written specifically for the
analysis of REEs and addresses the common matrix interference issues associated with this group of
metals. Although not specifically mentioned in the EPA methods, REEs can be measured with these
methods as long as the elements of interest are validated by the procedures outlined in the perspective
method.
Table A-1. Analytical Methods and Sample Preservation and Holding Times
for the Analysis of Rare Earth Elements
Reference
Method
EPA 6020A
EPA 200.8
USGS Open
File Report 02-
223-K
USGS Open
File Report 02-
223-H
Method
Description
Metals in
environmental
samples by ICP-
MS
Metals in
environmental
samples by ICP-
MS
REEs in geologic
samples by ICP-
MS
Metals in
aqueous samples
by ICP-MS
Holding
Time
6 months
6 months
6 months
6 months
Container
Solid -(1)4
oz. glass jar
Liquid - (1)
500 ml_ plastic
bottle
Solid -(1)4
oz. glass jar
Liquid - (1)
500 mL plastic
bottle
(1)4 oz. glass
jar
(1)500mL
plastic bottle
Preservation and
Storage
Solid -
Refrigerate at
4EC
Liquid -
Refrigerate at
4EC; HNO3 to pH
<2
Solid -
Refrigerate at
4EC
Liquid -
Refrigerate at
4EC; HNO3 to pH
<2
Refrigerate at
4EC
Refrigerate at
4EC; HNO3 to pH
<2
Demonstrated
Acceptable
Elements
Al, Sb, As, Ba, Be,
Cd, Ca, Cr, Co,
Cu, Fe, Pb, Mg,
Mn, Hg, Ni, K, Se,
Ag, Na, Tl, V, Zn
Al, Sb, As, Ba, Be,
Cd, Cr, Co, Cu,
Pb, Mn, Hg, Mo,
Ni, Se, Ag, Tl, Th,
U, V, Zn
La, Ce, Pr, Nd,
Sm, Eu, Gd, Tb,
Dy, Ho, Er, Tm, Yb
Ag, Al, As, Ba, Be,
Ca, Cd, Co, Cr,
Cs, Cu, Fe, Ga, k,
Li, Mg, Mn, Na, Ni,
Pb, Rb, Se, Sr, Tl,
U, V, Zn, Ge, Mo,
Nb, P, S, Si, Ta, Ti,
W, Zr, Ce, La, Nd,
Sc, Y, Fe, Al, Si
References
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Lexington, MA: ERG.
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natural waters by ICP-MS. Applied Geochemistry, 21, 839-848.
Railsback, B. (2008). An Earth Scientist's Periodic Table of the Elements and Their Ions. University of
Georgia Department of Geology, Athens, Georgia; Internet resource:
http://www.gly.uga.edu/railsback/PT.html
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Rare Earth Elements Review Appendix A - Selected Chemical Properties
Weber, R. (2008). An experimental study of fractionation of the rare earth elements in poplar plants
(populous eugenei) grown in a calcium-bearing smectite soil. Master's Thesis, Kansas State
University, Manhattan. 5Op.
A-5
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Rare Earth Elements Review
Appendix B - REE Mines and Mineral Deposits in the U.S.
Appendix B
Locations of REE-Producing Mines and REE-Containing Mineral Deposits in the U.S.
State /
Province
Alaska
Deposit Type
Alkalic Igneous
Carbonatite
Other Igneous-
Affiliated
(including
Pegmatites and
Veins)
Other-
Uncertain
Placer, Alluvial
Map
Reference
No (Figure
3-1)
226
160
175
77
312
753
627
629
630
635
636
655
665
670
680
Deposit Name
Mount Prindle
(Roy Creek)
Bokan
Mountain
(Ross-Adams)
Dora Bay
Salmon Bay
Wolf Mountain
Eagle Creek
Circle
El Dorado
Creek area
Fortymile
Hot Springs
Iditarod
McGrath
Port Clarence
Ruby Meadows
Tolovana
Status
Occurrence
Potential
resource REE,
Past Prod. U
Prospect
Occurrence
Occurrence
Occurrence
Occurrence
Occurrence
Occurrence
Occurrence
Occurrence
Occurrence
Occurrence
Occurrence
Occurrence
Company
Comments
Selected material contained ama 25% REE and 15%
Th. LREE more abundant in the quartz-bearing
syenites.
REE-bearing pegmatites, dikes, and shear
zones/fractures in central part of the complex and in
veins in the outer parts & nearby country rocks.
Produced 98,000 mt of approx. 1 % U308. Because
dikes generally < 1 m thick and mineralogically
complex, econo
Veins.
U, Th, and REE minerals along margins of alkaline
dikes.
Panned concentrate contained 0.029% Eu and 0.02%
U.
Buried bench gravels.
Buried placer deposit.
Orris, et
al.a
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Long, et
al."
Y
Y
Gupta,
et al.c
Schiiler,
et al.d
Y
B-l
-------
Rare Earth Elements Review
Appendix B - REE Mines and Mineral Deposits in the U.S.
State /
Province
Arizona
Arkansas
California
Colorado
Deposit Type
Other Igneous-
Affiliated
(including
Pegmatites and
Veins)
Carbonatite With
Residual
Enrichment
Carbonatite
Metamorphic
Other Igneous-
Affiliated
(including
Pegmatites and
Veins)
Placer, Shoreline
Carbonatite
Other Igneous-
Affiliated
(including
Pegmatites and
Veins)
Map
Reference
No (Figure
3-1)
297
306
128
59
342
305
563
104
31
36
307
Deposit Name
Mineral X
Signal district
Magnet Cove
Mountain Pass
Music Valley
Pomona Tile
Company
Soledad
Wet Mountains
Gem Park
Iron Hill
(Powderhorn,
Cebolla Creek)
South Platte
District
Status
Occurrence
Occurrence
Past small
producer rut,
mag
Current
producer
Occurrence
Occurrence
Occurrence
Occurrence
Past prod of
vrm, Ni, Ag
Ti resource/
prospect
Occurrence
Company
Molycorp
(2000)
Teck
Resources
Corp.
Comments
REE, Nb, and Th occur in veins and Carbonatite
dikes. Province includes Gem Park, McClure Mtn-
Iron Mtn, Democrat Creek, and other occurrences.
In Los Angeles County.
REE, Nb, and Th occur in veins and Carbonatite dikes.
Province includes Gem Park, McClure Mtn-lron Mtn,
Democrat Creek, and other occurrences.
Carbonatitic dikes. Concentrations of Th, REE, Cu, P,
and vermiculite have not been fully appraised.
Orris, et
al.a
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Long, et
al."
Y
Y
Y
Y
Gupta,
et al.c
Y
Y
Y
Y
Schiller,
et al.d
Y
B-2
-------
Rare Earth Elements Review
Appendix B - REE Mines and Mineral Deposits in the U.S.
State /
Province
Florida
Georgia
Georgia
Florida
Idaho
Deposit Type
Placer, Shoreline
Placer, Shoreline
Placer, Shoreline
Carbonatite
Metamorphic
Map
Reference
No (Figure
3-1)
439
495
575
377
580
382
411
428
611
388
68
337
339
340
341
Deposit Name
Green Cove
Springs
Maxville
Trail Ridge
(Highland Trail
Ridge, Starke
Trail Ridge)
Boulougne
Vero Beach
Brunswick-
Altamaha
Cumberland
Island
Folkston
Yulee
Cabin Bluff
North Fork area
Indian Creek
District
Lemhi Pass
Mineral Hill
District
Monumental
Summit
Status
Active mine
(1999); Past
byproduct
monazite
producer
Occurrence
Occurrence
Past producer
Past small
producer
byproduct
mon
Occurrence
Occurrence
Past producer
Occurrence
Occurrence
Occurrence
Occurrence
Occurrence
Company
Westralian
Sands
(1999)
DuPont
Humphrey's
Mining Co.
(1979)
Riz Mineral
Co. (1945)
Humphrey's
Mining Co.
(1979)
Comments
Stopped producing mon in 1 994.
Extension of Green Cove Springs deposit.
Marine placer.
Deposit is exhausted.
Marine placer.
Barrier island. In National Park so development
unlikely.
Deposit exhausted.
Includes Wilkey Evans and Reese Esker claims,
Radiant group.
Veins. Thorium is dominant mineralization.
Orris, et
al.a
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Long, et
al."
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Gupta,
et al.c
Y
Y
Y
Y
Y
Schiller,
et al.d
B-3
-------
Rare Earth Elements Review
Appendix B - REE Mines and Mineral Deposits in the U.S.
State /
Province
Idaho
(cont.)
Deposit Type
Other Igneous-
Affiliated
(including
Pegmatites and
Veins)
Phosphorite
Map
Reference
No (Figure
3-1)
286
733
719
721
722
725
727
730
731
735
726
729
736
734
723
Deposit Name
Hall Mountain
Group
Smoky Canyon
Blackfoot
Bridge
Caldwell
Canyon
Champ
Gay and South
Forty
Husky
Mountain Fuel
North Henry
Trail Creek
Henry
Maybe Canyon
(Maybie)
Wooley Valley
Swan Lake
Gulch
Conda
Status
Occurrence
Byproduct
producer?
Occurrence
Occurrence
Occurrence
Occurrence
Occurrence
Occurrence
Occurrence
Occurrence
Past
byproduct
producer?
Past
byproduct
producer?
Past
byproduct
producer?
Potential
producer
Company
Comments
Mining ceased in the 1940's.
P mine.
? 0.1% REE in Pore.
? 0.1% REE in Pore.
? 0.1% REE in Pore. Phosphate mining ceased in
1986.
? 0.1% REE in Pore.
? 0.1% REE in Pore.
? 0.1% REE in Pore.
? 0.1% REE in Pore.
? 0.1% REE in Pore.
? 0.12% REE in Pore.
? 0.1% REE in Pore.
? 0.11% REE in Pore.
Production planned for 2004.
? 0.1% REE in Pore. Phosphate mining ceased in
1984.
Orris, et
al.a
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Long, et
al."
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Gupta,
et al.c
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Schiller,
et al.d
B-4
-------
Rare Earth Elements Review
Appendix B - REE Mines and Mineral Deposits in the U.S.
State /
Province
Idaho
(cont.)
Idaho/
Caribou
Idaho/
Valley
County
Illinois
Missouri
Montana
Nebraska
Deposit Type
Placer, Alluvial
Other Igneous-
Affiliated
(including
Pegmatites and
Veins)
Placer, Alluvial
Carbonatite
Hydrothermal Fe-
Oxide
Carbonatite
Metamorphic
Other- F
Deposits
Carbonatite
Map
Reference
No (Figure
3-1)
624
667
650
663
283
670
632
279
619
35
274
11
74
345
747
26
Deposit Name
Chamberlin
District
Ramey
Meadows
Long Valley
Pearsol Creek
Diamond Creek
Ruby Meadows
Gold Fork-Little
Valley
Big Creek
Bear Valley
Hicks Dome
Pea Ridge
Bearpaw
Mountains
(Rocky Boy)
Ravalli County
Sheep Creek
Snowbird
Elk Creek
Status
Occurrence
Occurrence
Past producer
Prospect
Occurrence
Past producer
Small past
producer
Potential
resource
Potential
resource
Occurrence
Occurrence
Past small
producer
Occurrence
Company
Merlin
Mining NL
(1987)
Comments
7 claims near Burgdorf. Preliminary estimates indicate
about 100 Mm3 with amaO. 16% Y and 0.85 g/tTa.
Past gold placer producer.
Includes Porter placer.
Ore contains 0.42% REO and 0.15% Th02.
95 km SW of St. Louis.
Lat-long is for the Rocky Boy stock.
REE in carbonate veins and dikes in metamorphic
rocks.
Hydrothermal fluorite and quartz-bearing carbonate
veins.
NearUsakos. REE 0.35-1 .86% in Carbonatite 200m
below Quaternary and Pennsylvanian sediments.
Orris, et
al.a
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Long, et
al."
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Gupta,
et al.c
Y
Y
Y
Y
Y
Y
Schiller,
et al.d
Y
Y
B-5
-------
Rare Earth Elements Review
Appendix B - REE Mines and Mineral Deposits in the U.S.
State /
Province
Nevada
New Jersey
New
Mexico
New
Mexico,
Texas
Deposit Type
Other Igneous-
Affiliated
(including
Pegmatites and
Veins)
Hydrothermal Fe-
Oxide
Alkalic Igneous
Alkalic Igneous
Alkalic Igneous
Alkalic Igneous
Carbonatite
Other- F
Deposits
Other Igneous-
Affiliated
(including
Pegmatites and
Veins)
Alkalic Igneous
Map
Reference
No (Figure
3-1)
281
275
166
269
233
Location N/A
Location N/A
745
302
Location n/a
Location n/a
Location n/a
Location n/a
172
Deposit Name
Crescent Peak
Scrub Oaks
Caballo
Mountains
Wind Mountain
(see Cornudas
Mtns)
Pajarito
Mountain
Red Hills District
Lemitar and
Chupadera
Mountains
Gallinas
Mountains
Petaca District
Captain
Mountains
El Porvenir
District/ Hermit
Mountain
Gold Hill Area
and White Signal
District
Laughlin Peak
Area
Cornudas Mtns
- Diablo Plateau
Pnd Mtn.)
Status
Occurrence
Byproduct
Occurrence
Occurrence
Potential
resource
Prospect
Prospect
Very small
past producer
Occurrence
Potential
Resource
Potential
Resource
Potential
Resource
Prospect
Occurrence
Company
Comments
Magnetite-hematite orebody in metamorphic rocks.
Potassic dikes with postulated alkaline body at depth.
Eudialyte in dikes, sills, and laccoliths.
Quartz-bearing syenite contains ama 20% eud and 5%
flu. Apatite containing ama 19.2% REO has been
found in the peralkaline granites. Check Mining
Engineering, 1989, July, p. 515 for tonnage.
About 65 1 of bas concentrate produced in the 1 950's
from Cu-F veins and breccia fillings probably
associated with alkalic trachyte.
Lincoln county; Est Resources: Thorium content
measured from 0.01 to 1 .12 percent
McLemore and others (1 988) report that samples of
quartzite contain traces of Th, La, and Y.
Thorium-bearing minerals form pods and lenses within
pegmatites of granite, Burro Mountains .
Orris, et
al.a
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Long, et
al."
Y
Y
Y
Y
Y
Y
Y
Y
Y
Gupta,
et al.c
Y
Y
Schiller,
et al.d
B-6
-------
Rare Earth Elements Review
Appendix B - REE Mines and Mineral Deposits in the U.S.
State /
Province
New York
North
Carolina
North
Carolina
South
Carolina
Georgia
Oregon
South
Carolina
Tennessee
Texas
Deposit Type
Hydrothermal Fe-
Oxide
Placer, Alluvial
Placer, Alluvial
Carbonatite
Placer
Placer, Alluvial
Placer, Shoreline
Placer, Alluvial
Placer,
Paleoplacer
Placer, Shoreline
Other Igneous-
Affiliated
(including
Pegmatites and
Veins)
Map
Reference
No (Figure
3-1)
272
654
Location n/a
23
Location n/a
634
451
662
675
662
511
518
473
291
Deposit Name
Mineville
dumps
Marion
Carolina
monazite belt
Deep Creek
Aiken County
Horse Creek
(Aiken County)
Hilton Head
Island
Oak Grove
Silica Mine
Oak Grove
Natchez Trace
deposit
North Camden
(Kerr-McGee
deposit)
Kerr-McGee
deposit
Llano County
(Williams Mine,
others)
Status
Past Fe
producer;
REE resource
Past
byproduct
producer
Occurrence
Occurrence
Past producer
of monazite
Potential
resource
Occurrence
Producer, but
does not
recover REO
Occurrence
Occurrence
Occurrence
Occurrence
Small Past
Producer
Company
Rhone-
Poulenc
Imperial
Mining Co.
(1990)
National
Kaolin Co.
Ethyl Corp.
(1989)
Kerr-
McGee
(1971)
Comments
Apatite in mill tailings averages from 4 to more than
1 1 % REO. Magnetite-hematite orebody in
metamorphic rocks.
SE of Crane Mountain.
Closed in 1958.
Flood plain. Reconcentration of heavy minerals from
Tuscaloosa Fmt. Includes Hollow (Holley) Creek and
other drainages.
Mining unlikely, resort area.
Alluvial terrace.
HM stockpiled from past production of silica sand.
Marine placer.
Marine placer.
Several tons of pegmatite were mined prior to 1909.
Orris, et
al.a
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Long, et
al."
Y
Gupta,
et al.c
Y
Y
Y
Y
Y
Schiller,
et al.d
B-7
-------
Rare Earth Elements Review
Appendix B - REE Mines and Mineral Deposits in the U.S.
State /
Province
Utah
Virginia
Wyoming
Wyoming/
Albany
County
Wyoming/
Carbon
County
Deposit Type
Placer, Shoreline
Other Igneous-
Affiliated
(Including
Pegmatites And
Veins)
Other-
Uncertain
Placer, Shoreline
Carbonatite
Alkalic Igneous
Other Igneous-
Affiliated
(Including
Pegmatites And
Veins)
Placer,
Paleoplacer
Other Igneous-
Affiliated
(Including
Pegmatites And
Veins)
Placer, Alluvial
Placer,
Paleoplacer
Map
Reference
No (Figure
3-1)
Location n/a
290
775
525
10
215
310
707
279
618
714
Deposit Name
Deep Sands
Little Friar
Mountain
(Massie)
Little Friar
Mountain
Old Hickory
(Stony Creek)
Bear Lodge
Mountains
(southern)
Laramie
Anorthosite
Complex
Tie Siding
Bald Mountain
Big Creek
Bates Hole area
Onemile Creek
area
Status
Prospect
Small Past
Producer
Occurrence
Active Mine
(1999), no
REE prod
Large, low-
grade
resource of
REE-Th
Occurrence
Occurrence
Potential
resource
Occurrence
Occurrence
Occurrence
Company
Great
Western
Minerals
Group
Westralian
Sands
(1999)
Comments
Exploratory drilling in 2008; preliminary feasibility
study occurring.
Pegmatite dike in hypersthene granodiorite.
Mine had startup problems with mining and in the
separation plant.
Veins and disseminated deposits. Samples ranged
from 1 12 to 30000 ppm with REE more abundant than
Th. Area incompletely explored.
T20-22N R70-71W
Fossil fluvial placer. Little Big Horn River area. Two
sites contain at least 1 .0 kg mon/t of rock. Resource is
poorly defined.
T30N, R80-81W
High radioactivity.
T18NR78Wsec6andN/2sec7.
Orris, et
al.a
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Long, et
al."
Y
Gupta,
et al.c
Y
Y
Y
Schiller,
et al.d
Y
Y
B-8
-------
Rare Earth Elements Review
Appendix B - REE Mines and Mineral Deposits in the U.S.
State /
Province
Wyoming/
Fremont
County
Wyoming/
Hot Springs
County
Wyoming/
Sublette
County
Deposit Type
Placer, Alluvial
Placer,
Paleoplacer
Other-
Uncertain
Map
Reference
No (Figure
3-1)
683
711
765
Deposit Name
Warm Spring
Creek placers
Grass Creek
area
Fremont Butte
Status
Occurrence
Occurrence
Occurrence
Company
Comments
Fremont County, WY
Paleo-beach placers. North segment- T46N R98W
sees. 8, 9, 16.
Mineralization along cracks and veins; fault and shear-
zone related. T32N R107W sec. 21 , NW/4.
Orris, et
al.a
Y
Y
Y
Long, et
al."
Gupta,
et al.c
Schiiler,
et al.d
Orris, Greta J. and Richard I. Grauch, 2002. Rare Earth Element Mines, Deposits, and Occurrences; Open-File Report 02-189 Version 1.0; United State Geological Survey (USGS); Internet
resource: http://pubs.usgs.gov/of/2002/of02-189/
Long, Keith R. and Bradley S. Van Gosen, Nora K. Foley, and Daniel Cordier, 2010. The Principal Rare Earth Elements Deposits of the United States - A Summary of Domestic Deposits and a
Global Perspective; USGS Scientific Investigation Report 2010-5220; US Geological survey, Reston, Virginia; Internet Resource: http://pubs.usgs.gov/sir/2010/5220/
Gupta, C.K., Krishnamurthy, N. (2004) Extractive Metallurgy of Rare Earths. CRC Press.
Schiiler, D, Buchert, M, Liu, R, Dittrich, S, Merz, C. (2011). Study on rare earths and their recycling, OKO-insititut e.v., January.
B-9
-------
Rare Earth Elements Review Appendix B U.S. Mines and Mineral Deposits
References
Gupta, C.K., Krishnamurthy, N. (2004) Extractive Metallurgy of Rare Earths. CRC Press.
Long, Keith R. and Bradley S. Van Gosen, Nora K. Foley, and Daniel Cordier, 2010. The Principal Rare
Earth Elements Deposits of the United States - A Summary of Domestic Deposits and a Global
Perspective; USGS Scientific Investigation Report 2010-5220;
Orris, Greta J. and Richard I. Grauch, 2002. Rare Earth Element Mines, Deposits, and Occurrences;
Open-File Report 02-189 Version 1.0;
Schiller, D, Buchert, M, Liu, R, Dittrich, S, Merz, C. (2011). Study on rare earths and their recycling,
OKO-insititut e.v., January.
U.S. Geological Survey (USGS); Internet resource: http://pubs.usgs.gov/of/2002/of02-189/
U.S. Geological Survey (USGS), Reston, Virginia; Internet Resource: http://pubs.usgs.gov/sir/2010/5220/
B-10
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Rare Earth Elements Review
Appendix C - Process Flow Diagrams
Appendix C
Process Flow Diagrams for Extraction and Processing Operations
Steam
Reagents
Concentrate
Product
Concentrate
Product
Materials Science Forum
Bastnaesite Ore
7% REO
CRUSH
I
GRINDS CLASSIFY
-100 mesh
(40% calcite, 25% barite+celestite,
10% strontianite, 12% basinaesite,
8% quartz)
I
MULTI-STAGE
CONDITIONERS
ROUGHER
FLOTATION
I
CLEANER
FLOTATION
-> Tails
60% RED
SCAVENGER
FLOTATION
I
REGRIND
LEACHING <--
T Of low
THICKENING ]
I
FILTRATION
DRYING
70% REO
CALCINATION > CO2
85-90% REO
DISSOLUTION
I
SOLVENT EXTRACTION
10% HCI
to pH1
to waste
Light (La, Ce, Pr) ^^
SOLVENT EXTRACTION
Light (Nd, Sm, Eu)
Heavy (Gd, Tb, Y)
SOLVENT EXTRACTION
Nd-Pr Carbonate T Ce concentrate
La hydrate
I
j oxide
SOLVENT EXTRACTION
\ \
Sm oxide Gd oxide Tb oxide Y oxide
Figure C-1. Simplified flow sheet used by Molycorp at Unocal Plant,
Mountain Pass, California, for recovering bastnasite (Apian, 1988).
C-1
-------
Rare Earth Elements Review Appendix C - Process Flow Diagrams
Figure C-1. (continued)
It is recognized that the reference date for the figure above is 1988. Given the opportunity to comment on this
diagram, Molycorp's Scott Honan provided the following clarifications (personal communications, 2011):
"-after the dissolution step, the insoluble fraction was a cerium product that contained about 60% REO by weight.
The other product from dissolution was the liquor that fed solvent extraction.
- the light RE elements are La, Ce, Nd, Pr. The first SX step separated these from everything else (Sm and the
other heavies). Molycorp did run solvent extraction and other unit operations to further separate the heavies,
and produced Eu products, Y-Eu co-precipitates, Sm, Gd and Tb products. As far as I know, Y was never
produced at Mountain Pass, but it was purchased to combine with the Eu to make co-precipitates.
- the chemical form of the Nd, Nd-Pr, Ce and La products varied. I would simply call these "products" instead of
specifying a chemical form."
C-2
-------
Rare Earth Elements Review
Appendix C - Process Flow Diagrams
Rare Earth Minerals and Minerals for Electronic Uses
Dredged Sands
I
TROMMEL
-5 mm
ROUGHER JIGS
8, 2-Cell Pan-Am Placer
Heavies
CLEANER JIGS
1 Pan-Am Placer
Heavies
AMALGAMATOR
RECLEANERJIGS
1 Pan-Am Pulsator
Heavies
FINAL SEPARATION JIG
1 Pan-Am Pulsator
Heavies
O' size
-> Tails
-> Au-Ag Amalgam
Lights
SHAKING TABLE
Cone.
i
Tails
Monazite
Garnet
Figure C-2. Treatment of a placer monazite concentrate by dredging (Apian, 1988).
C-3
-------
Rare Earth Elements Review
Appendix C - Process Flow Diagrams
La oxide 99.995%
Ce oxide 99.5%
Pr oxide 96%
Nd oxide 95%
Rare Earth Minerals and Minerals for Electronic Uses
Monazite Concentrate
GRINDING
70% NaOH
-> CAUSTIC LEACH
- Caustic recycle
j > Trisodium phosphate
Water
-> FILTRATION
Waste water
I
Rare Earth Chloride Solution
I
SOLVENT EXTRACTION
I
LIGHT RARE
EARTHS
HEAVY RARE
EARTHS
Finishing
I
Finishing
La Ce Pr Nd Sm
Ce Pr Nd Sm Eu
High Purity
Products
I
Pr Nd Sm Eu Gd
Y
Sm Eu Gd Tb
Sm Eu
Y
Eu oxide
99.99%
Y
Gd Tb Y -
Gd oxide Tb oxide
99.99% 99.99%
Y oxide 99.9%
Figure C-3. Treatment of monazite concentrate for the processing of rare earths
(Hart and Levins).
C-4
-------
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