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Extraction of Rare Earth Elements from
Nonconventional Resources
Wei Liu, Kaiwu Huang, Oznur Onel, Rahaf Rousan,
Mohit Gupta, Aaron Noble, Roe-Hoan Yoon
Center for Advanced Separation Technologies, Virginia Tech, Blacksburg, VA
ABSTRACT: Of the 15 rare earth elements, heavy rare earth elements (HREEs) are of lower concentrations in
nature, more difficult to extract, and hence are of higher prices. Currently, 80% of HREEs are extracted from
the ion-adsorption clays (IACs) mined in South China. Foley et al. (2014) discovered small IAC deposits along
the Appalachian Mountains, while studies of the USGS coal database led to a conclusion that REEs in coal are
partitioned mostly to clayey materials (Bryan et al., 2015). Based on these reports, we developed methods of
extracting HREEs from clayey materials from domestic resources with promising results.
INTRODUCTION
As is well-known, rare-earth elements (REEs) are not rare.
What makes them rare is the difficulty in separation. Most
of the light elements (from La to Eu) are of higher crustal
abundance and easier to separate from each other and
gangue minerals, while the rest (from Gd to Lu plus Y)
that are of lower crustal abundance are referred to as heavy
rare earths (HREEs). In fact, the crustal abundance of rare
earths is about the same as the sum of the critical materials
(CMs: Cu, Ni, Pb, Zn, Sn) that are readily recovered by
flotation. REEs occur in dispersed phases as phosphates,
carbonates, and silicates while CMs occur in concentrated
forms of simple sulfides, oxides, and native metals. Also,
rare earth minerals (REMs) are salts of hard acids and hard
bases, making them difficult to decompose for leaching
under mild acidic or basic conditions. Despite these dif-
ficulties, there are enough rare earths to last for another
century or more (Krishnamurthy and Gupta, 2016).
Liu et al. (2023) compiled a list of 32 major rare
earth mining and extraction projects ongoing around the
world. These projects may be subdivided into four different
groups, depending on the minerals being mined. Bastnäsite
((REE,Ce)CO3F) is by far the largest rare earth resource
with REO contents in the 65–75% range, followed by
monazite ((Ce,La,Y,Th)PO4) with ~70% REOs, xenotime
(YPO4) with 67% REOs, and ion-adsorption clays (IACs)
with REO contents of ~0.02%. The first three REM ores
are upgraded by flotation to minimize the volume of the
materials going into the next steps involving the use of
aggressive chemical leaching processes and, hence, signifi-
cant waste generation and processing costs.
IAC ores are formed by the adsorption of the lan-
thanide ions (Ln3+) derived from the weathering of the
primary REMs present in a host rock, e.g., granite. The
lanthanide ions adsorb on the surface of the clay miner-
als, e.g., kaolinite, and form IACs in situ. Due to the small
particle size and lamella structure, the layer-structured
mineral provides a large negatively charged surface area on
which Ln3+ ions adsorb via electrostatic interactions. Some
of the Ln3+ ions adsorb on the surface as fully hydrated
ions with coordination numbers (CN) of 8–11, while oth-
ers adsorb with CN =6–8, as shown in Figure 1. Borst et
al. (2020) showed that the fully hydrated lanthanide ions
can be readily desorbed by mono-valent cations, e.g., NH4+
Extraction of Rare Earth Elements from
Nonconventional Resources
Wei Liu, Kaiwu Huang, Oznur Onel, Rahaf Rousan,
Mohit Gupta, Aaron Noble, Roe-Hoan Yoon
Center for Advanced Separation Technologies, Virginia Tech, Blacksburg, VA
ABSTRACT: Of the 15 rare earth elements, heavy rare earth elements (HREEs) are of lower concentrations in
nature, more difficult to extract, and hence are of higher prices. Currently, 80% of HREEs are extracted from
the ion-adsorption clays (IACs) mined in South China. Foley et al. (2014) discovered small IAC deposits along
the Appalachian Mountains, while studies of the USGS coal database led to a conclusion that REEs in coal are
partitioned mostly to clayey materials (Bryan et al., 2015). Based on these reports, we developed methods of
extracting HREEs from clayey materials from domestic resources with promising results.
INTRODUCTION
As is well-known, rare-earth elements (REEs) are not rare.
What makes them rare is the difficulty in separation. Most
of the light elements (from La to Eu) are of higher crustal
abundance and easier to separate from each other and
gangue minerals, while the rest (from Gd to Lu plus Y)
that are of lower crustal abundance are referred to as heavy
rare earths (HREEs). In fact, the crustal abundance of rare
earths is about the same as the sum of the critical materials
(CMs: Cu, Ni, Pb, Zn, Sn) that are readily recovered by
flotation. REEs occur in dispersed phases as phosphates,
carbonates, and silicates while CMs occur in concentrated
forms of simple sulfides, oxides, and native metals. Also,
rare earth minerals (REMs) are salts of hard acids and hard
bases, making them difficult to decompose for leaching
under mild acidic or basic conditions. Despite these dif-
ficulties, there are enough rare earths to last for another
century or more (Krishnamurthy and Gupta, 2016).
Liu et al. (2023) compiled a list of 32 major rare
earth mining and extraction projects ongoing around the
world. These projects may be subdivided into four different
groups, depending on the minerals being mined. Bastnäsite
((REE,Ce)CO3F) is by far the largest rare earth resource
with REO contents in the 65–75% range, followed by
monazite ((Ce,La,Y,Th)PO4) with ~70% REOs, xenotime
(YPO4) with 67% REOs, and ion-adsorption clays (IACs)
with REO contents of ~0.02%. The first three REM ores
are upgraded by flotation to minimize the volume of the
materials going into the next steps involving the use of
aggressive chemical leaching processes and, hence, signifi-
cant waste generation and processing costs.
IAC ores are formed by the adsorption of the lan-
thanide ions (Ln3+) derived from the weathering of the
primary REMs present in a host rock, e.g., granite. The
lanthanide ions adsorb on the surface of the clay miner-
als, e.g., kaolinite, and form IACs in situ. Due to the small
particle size and lamella structure, the layer-structured
mineral provides a large negatively charged surface area on
which Ln3+ ions adsorb via electrostatic interactions. Some
of the Ln3+ ions adsorb on the surface as fully hydrated
ions with coordination numbers (CN) of 8–11, while oth-
ers adsorb with CN =6–8, as shown in Figure 1. Borst et
al. (2020) showed that the fully hydrated lanthanide ions
can be readily desorbed by mono-valent cations, e.g., NH4+