XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1287
required, with REE sources from phosphates, coal, coal ash
being investigated alternative sources.
While coal itself may be used as a source of REE,
we focus on the post-combustion ash as the REE source
because the combustion process concentrates the REE
content by ~10X, a factor that depends on the quality of
the coal and the weight fraction of the ash remainder. The
REE oxides, being non-volatile, remain within the ash. This
effect is shown in Figure 1 for the Russian REE-rich Black
Stone coal investigated by Seredin (Serendin 2012). For the
1.4 g/cm3 density fraction coal (9.5% ash), which con-
tains 500 ppm (0.05 wt%) total REE, produces ash with
5000 ppm REE content on ash basis, split about evenly
between HREE and LREE.
Coal combustion fly ash is readily available as fine pow-
der (~10s to ~100 µm scale) from coal-fired power plants.
No pulverization is needed as would be the case for coal.
This would significantly reduce processing costs as exca-
vation, grinding, pulverizing (i.e., mine-to-mill expenses)
account for ~60% cost of production per unit mass of REE
metal product. Fly ash thus represents a readily-available
source of raw material needed for the extraction of lan-
thanides and other valuable trace elements. In 2010, U.S.
utilities produced 67.7 Mt (short tons) of fly ash (American
Coal Ash Association 2011), of which 42.7 Mt was not uti-
lized. In most cases, a large amount of ash is stored on the
plant site or in nearby ponds or landfills, providing a readily
available resource. The resource, in a larger sense, does have
some regional concentration (as shown in Figure 2). For
example, the seven Ohio River valley states (PA. OH, WV,
KY, IN, IL, MO) are among the top ten states with respect
to coal utilization for power production. The Ohio River,
along with navigable tributaries, supports a large number of
power plants. Therefore, a centrally located processing plant
could take advantage of both a wide distribution of poten-
tial individual resources and a location amenable to the full
complement of barge, rail, and truck transportation.
The objective of the reported study is to describe the
development of a physicochemical method to extract rare
earth elements from coal ash. The team first developed the
process at the bench scale (~0.5 kg/day ash throughput)
using, followed by design and implementation at the pilot
scale (~0.4 ton/day ash throughput). We then proposed the
design of a commercial-scale (~1200 ton/day ash through-
put) REE from coal ash facility. The successful develop-
ment of the REE from coal ash technology will result in a
new domestic source of REE.
MATERIALS AND METHODS
The Project team collected 15 tons of coal ash from 2 east-
ern KY coal fire power plants (referred to as Plant C and
Plant D). The impoundment contained a mixture of fly ash
and bottom ash. The ash had average particle size of ~25
μm and carbon content between 3 and 10 wt.% (deter-
mined by loss on ignition measurements).
Physical processing was used to create an ash fraction
that is a suitable feed to chemical REE separation. Key
properties are: (1) low carbon content (2) low magnetics
content and (3) small particle size. As shown in Figure 3, a
0.4 ton per day physical processing pilot plant was built at
the University of Kentucky consisting of a feed and slurry
tank, a +16 mesh coarse mesh and hydraulic classifier for
size screening, froth flotation cells to remove the carbon
rich ash fraction, and a magnetic separator. Processed ash
collected in super sacks, shipped to and processed in the
chemical pilot.
Figure 1. REE Enrichment in Coal Ash: Example of Russian Far East black Stone Coal (Serendin 2012)
required, with REE sources from phosphates, coal, coal ash
being investigated alternative sources.
While coal itself may be used as a source of REE,
we focus on the post-combustion ash as the REE source
because the combustion process concentrates the REE
content by ~10X, a factor that depends on the quality of
the coal and the weight fraction of the ash remainder. The
REE oxides, being non-volatile, remain within the ash. This
effect is shown in Figure 1 for the Russian REE-rich Black
Stone coal investigated by Seredin (Serendin 2012). For the
1.4 g/cm3 density fraction coal (9.5% ash), which con-
tains 500 ppm (0.05 wt%) total REE, produces ash with
5000 ppm REE content on ash basis, split about evenly
between HREE and LREE.
Coal combustion fly ash is readily available as fine pow-
der (~10s to ~100 µm scale) from coal-fired power plants.
No pulverization is needed as would be the case for coal.
This would significantly reduce processing costs as exca-
vation, grinding, pulverizing (i.e., mine-to-mill expenses)
account for ~60% cost of production per unit mass of REE
metal product. Fly ash thus represents a readily-available
source of raw material needed for the extraction of lan-
thanides and other valuable trace elements. In 2010, U.S.
utilities produced 67.7 Mt (short tons) of fly ash (American
Coal Ash Association 2011), of which 42.7 Mt was not uti-
lized. In most cases, a large amount of ash is stored on the
plant site or in nearby ponds or landfills, providing a readily
available resource. The resource, in a larger sense, does have
some regional concentration (as shown in Figure 2). For
example, the seven Ohio River valley states (PA. OH, WV,
KY, IN, IL, MO) are among the top ten states with respect
to coal utilization for power production. The Ohio River,
along with navigable tributaries, supports a large number of
power plants. Therefore, a centrally located processing plant
could take advantage of both a wide distribution of poten-
tial individual resources and a location amenable to the full
complement of barge, rail, and truck transportation.
The objective of the reported study is to describe the
development of a physicochemical method to extract rare
earth elements from coal ash. The team first developed the
process at the bench scale (~0.5 kg/day ash throughput)
using, followed by design and implementation at the pilot
scale (~0.4 ton/day ash throughput). We then proposed the
design of a commercial-scale (~1200 ton/day ash through-
put) REE from coal ash facility. The successful develop-
ment of the REE from coal ash technology will result in a
new domestic source of REE.
MATERIALS AND METHODS
The Project team collected 15 tons of coal ash from 2 east-
ern KY coal fire power plants (referred to as Plant C and
Plant D). The impoundment contained a mixture of fly ash
and bottom ash. The ash had average particle size of ~25
μm and carbon content between 3 and 10 wt.% (deter-
mined by loss on ignition measurements).
Physical processing was used to create an ash fraction
that is a suitable feed to chemical REE separation. Key
properties are: (1) low carbon content (2) low magnetics
content and (3) small particle size. As shown in Figure 3, a
0.4 ton per day physical processing pilot plant was built at
the University of Kentucky consisting of a feed and slurry
tank, a +16 mesh coarse mesh and hydraulic classifier for
size screening, froth flotation cells to remove the carbon
rich ash fraction, and a magnetic separator. Processed ash
collected in super sacks, shipped to and processed in the
chemical pilot.
Figure 1. REE Enrichment in Coal Ash: Example of Russian Far East black Stone Coal (Serendin 2012)