1262 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
reasons for the difficulties and found promising solutions,
as reported herewith.
EXPERIMENTAL
Ion Adsorption Clay
According to Bryan et al. (2015), there are 5.9 million met-
ric tonnes of REEs embedded in the aluminum-rich coal
deposits in the four states (Pennsylvania, West Virginia,
Virginia, and Kentucky) in Central Appalachia. The authors
of the present work took a series of coal samples from a
total of 15 coal preparation plants operating in Central
Appalachia and analyzed them for their REE contents, with
the results presented in Figure 2. On average, the concen-
trations of LREEs are higher than those of HREEs, which
is consistent with the crustal abundance (Krishnamurthy
and Gupta, 2016). It was interesting to find, however, that
the HREE/LREE ratio increased with decreasing ash con-
tents (Luttrell, et al., 2019).
All the solid-solid separation processes employed in
coal beneficiation plants are physical separation processes,
e.g., dense-medium separation (DMS), flotation, spirals,
etc. In general, the smaller the particle size, the lower the ash
content due to improved liberation. In this regard, flota-
tion concentrates should represent the lowest-ash products.
Flotation feeds usually consist of 150 mm × 0 materials
however, the process does not work well for particle sizes
(d1) below ~20 mm (Wells and Finch, 2016). Therefore,
the lower-ash coal data points given in Figure 2 may rep-
resent the flotation products consisting primarily of kaolin
clays. Thus, the sharp increase in the HREE/LREE ratio
with decreasing ash content may be due to the presence of
the ion-adsorption clays in the Appalachian coal.
The results obtained from auditing the 15 coal ben-
eficiation plants are presented in Table 1. As reported by
Bryan et al. (2015), REEs in the eastern U.S. coal are pref-
erentially partitioned to the inorganic mineral matter rather
than the organic coal matrix. Each plant produces two inor-
ganic refuse streams, i.e., coarse and fine refuse materials. It
would be difficult to extract REEs from the coarse refuse as
it will entail crushing and grinding a large volume of refuse,
Figure 2. HREE/LHREE ratio as a function of ash contents in the coal samples taken in
15 operating coal preparation plants in Central Appalachia
Table 1. Production of Mass, Ash and REEs for the 15 Beneficiation Plants Audited*
Stream Mass TPY Ash TPY REE TPY REE/Whole REE/Ash
Plant Feed 78,567,376 36,986,176 9,899 126 268
Clean Coal 36,697,676 3,435,608 1,620 44 472
Coarse Refuse 33,279,712 28,160,683 6,285 189 223
Fine Refuse 8,589,993 5,227,936 1,313 153 251
*in short tons
reasons for the difficulties and found promising solutions,
as reported herewith.
EXPERIMENTAL
Ion Adsorption Clay
According to Bryan et al. (2015), there are 5.9 million met-
ric tonnes of REEs embedded in the aluminum-rich coal
deposits in the four states (Pennsylvania, West Virginia,
Virginia, and Kentucky) in Central Appalachia. The authors
of the present work took a series of coal samples from a
total of 15 coal preparation plants operating in Central
Appalachia and analyzed them for their REE contents, with
the results presented in Figure 2. On average, the concen-
trations of LREEs are higher than those of HREEs, which
is consistent with the crustal abundance (Krishnamurthy
and Gupta, 2016). It was interesting to find, however, that
the HREE/LREE ratio increased with decreasing ash con-
tents (Luttrell, et al., 2019).
All the solid-solid separation processes employed in
coal beneficiation plants are physical separation processes,
e.g., dense-medium separation (DMS), flotation, spirals,
etc. In general, the smaller the particle size, the lower the ash
content due to improved liberation. In this regard, flota-
tion concentrates should represent the lowest-ash products.
Flotation feeds usually consist of 150 mm × 0 materials
however, the process does not work well for particle sizes
(d1) below ~20 mm (Wells and Finch, 2016). Therefore,
the lower-ash coal data points given in Figure 2 may rep-
resent the flotation products consisting primarily of kaolin
clays. Thus, the sharp increase in the HREE/LREE ratio
with decreasing ash content may be due to the presence of
the ion-adsorption clays in the Appalachian coal.
The results obtained from auditing the 15 coal ben-
eficiation plants are presented in Table 1. As reported by
Bryan et al. (2015), REEs in the eastern U.S. coal are pref-
erentially partitioned to the inorganic mineral matter rather
than the organic coal matrix. Each plant produces two inor-
ganic refuse streams, i.e., coarse and fine refuse materials. It
would be difficult to extract REEs from the coarse refuse as
it will entail crushing and grinding a large volume of refuse,
Figure 2. HREE/LHREE ratio as a function of ash contents in the coal samples taken in
15 operating coal preparation plants in Central Appalachia
Table 1. Production of Mass, Ash and REEs for the 15 Beneficiation Plants Audited*
Stream Mass TPY Ash TPY REE TPY REE/Whole REE/Ash
Plant Feed 78,567,376 36,986,176 9,899 126 268
Clean Coal 36,697,676 3,435,608 1,620 44 472
Coarse Refuse 33,279,712 28,160,683 6,285 189 223
Fine Refuse 8,589,993 5,227,936 1,313 153 251
*in short tons