XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1263
which will be costly. A more logical approach would be to
extract them from fine coal refuse for obvious reasons.
In this regard, we considered the case of extracting
REMs from fine coal refuse only. Normalizing the annual
REE production, each plant may be considered to produce
87 tons per year (TPY) of REEs. Multiplying this with
248, the number of coal beneficiation plants operating in
the U.S. in 2014, one would obtain 21,700 TPY REEs.
Assuming a 50% recovery, the US coal industry can pro-
duce 10,850 TPY REEs, which was close to the annual
consumption of REOs in the same year. Much of the REEs
would be HREEs, as discussed in conjunction with the
data presented in Figure 2. According to the 2024 Mineral
Commodity Summaries (MCS), the U.S. consumed 9,680
short tons of REOs in 2023. It is estimated that ~4 billion
tons of fine coal refuse has been discarded over the years
to numerous impoundments. At a 50% recovery, the pond
fines can become an REE resource for the next ~60 years at
the current rate of REO consumption.
Figure 3 shows the XPS spectra of the La3+ ions
absorbed on the surface of the ash-forming minerals iso-
lated from a high-ash middlings sample taken from an
operating coal mine in West Virginia. The two shoulders at
839.3 and 835.7 represent the La 3d5/2 doublet with a mul-
tiplet splitting of 4.1 eV. The multiplet splitting varies from
one compound to another. For La(OH)3 and La2O3, the
values are 3.7 and 3.9 eV, respectively. The strongest peak is
the F KLL band. The spectra may serve as direct evidence
for the presence of IACs in U.S. coal as suggested by Bryan
et al. (2015) and Foley and Ayuso (2015).
The standard IEX leaching process may be represented
by the following reaction,
Clay-Ln3+ +3NH4+ → Clay-3NH4+ +Ln3+ (1)
in which one mole of Ln3+ ions is displaced by three moles
of NH4+ ions for charge balance. The driving force for the
ion exchange mechanism is the large difference in DH°
between the tri- and mono-valent cations, as discussed.
The process works well when the Ln3+ ions are physically
adsorbed on a clay surface but not when they are chemically
bonded to the clay surfaces and/or to passivating agents and
form chemical compounds.
Figure 4a shows the XPS spectra of an IAC sample con-
taining ~500 ppm La before and after an IEX leaching test
conducted at 0.5 M (NH4)2SO4 and pH 4 As shown, the
characteristic La 3d5/2 peaks disappeared almost completely
in the presence of the ammonium sulfate (AS) lixiviant,
Figure 3. The XPS spectra of the mineral matter from a
Beckley coal middlings sample
Figure 4. a) A synthetic IAC coated with ~500 ppm La has been subjected to IEX at 0.5 M ammonium sulfate (AS) to remove
La ions from the surface b) at 0025 M NaH
2 PO
4 ,IEX leaching was stopped
which will be costly. A more logical approach would be to
extract them from fine coal refuse for obvious reasons.
In this regard, we considered the case of extracting
REMs from fine coal refuse only. Normalizing the annual
REE production, each plant may be considered to produce
87 tons per year (TPY) of REEs. Multiplying this with
248, the number of coal beneficiation plants operating in
the U.S. in 2014, one would obtain 21,700 TPY REEs.
Assuming a 50% recovery, the US coal industry can pro-
duce 10,850 TPY REEs, which was close to the annual
consumption of REOs in the same year. Much of the REEs
would be HREEs, as discussed in conjunction with the
data presented in Figure 2. According to the 2024 Mineral
Commodity Summaries (MCS), the U.S. consumed 9,680
short tons of REOs in 2023. It is estimated that ~4 billion
tons of fine coal refuse has been discarded over the years
to numerous impoundments. At a 50% recovery, the pond
fines can become an REE resource for the next ~60 years at
the current rate of REO consumption.
Figure 3 shows the XPS spectra of the La3+ ions
absorbed on the surface of the ash-forming minerals iso-
lated from a high-ash middlings sample taken from an
operating coal mine in West Virginia. The two shoulders at
839.3 and 835.7 represent the La 3d5/2 doublet with a mul-
tiplet splitting of 4.1 eV. The multiplet splitting varies from
one compound to another. For La(OH)3 and La2O3, the
values are 3.7 and 3.9 eV, respectively. The strongest peak is
the F KLL band. The spectra may serve as direct evidence
for the presence of IACs in U.S. coal as suggested by Bryan
et al. (2015) and Foley and Ayuso (2015).
The standard IEX leaching process may be represented
by the following reaction,
Clay-Ln3+ +3NH4+ → Clay-3NH4+ +Ln3+ (1)
in which one mole of Ln3+ ions is displaced by three moles
of NH4+ ions for charge balance. The driving force for the
ion exchange mechanism is the large difference in DH°
between the tri- and mono-valent cations, as discussed.
The process works well when the Ln3+ ions are physically
adsorbed on a clay surface but not when they are chemically
bonded to the clay surfaces and/or to passivating agents and
form chemical compounds.
Figure 4a shows the XPS spectra of an IAC sample con-
taining ~500 ppm La before and after an IEX leaching test
conducted at 0.5 M (NH4)2SO4 and pH 4 As shown, the
characteristic La 3d5/2 peaks disappeared almost completely
in the presence of the ammonium sulfate (AS) lixiviant,
Figure 3. The XPS spectra of the mineral matter from a
Beckley coal middlings sample
Figure 4. a) A synthetic IAC coated with ~500 ppm La has been subjected to IEX at 0.5 M ammonium sulfate (AS) to remove
La ions from the surface b) at 0025 M NaH
2 PO
4 ,IEX leaching was stopped