1266 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
recovery of hydrophobic particles that are too small to be
recovered by flotation using air bubbles. Huang and Yoon
(2019) studied the thermodynamic and kinetic basis for
the superiority of using the TLF process to float ultrafine
particles. A U.S. patent was awarded for further developing
the TLF process to produce higher-grade and dry products
using recyclable hydrophobic liquid (Yoon, 2016).
Table 2 shows the results obtained on a thickener
underflow sample taken from a coal beneficiation plant, KY,
using the modified TLF process. The sample was attrition
ground to d80 =2.2 mm to liberate REMs from the coal
matrix. The mill product was conditioned with potassium
octyl hydroxamate (KOH) to selectively hydrophobize the
liberated REM particles prior to the TLF separation.
As shown, a high-grade concentrate was obtained with
56.14% REE+Y. However, the recovery was only 14.2%,
which was not surprising, however. According to a libera-
tion model developed by Gaudin (1939), the less-abundant
phase, REM in this case, cannot be liberated at all unless
the particle size is less than the grain size. The REM images
shown in Figure 7 are 2–4 mm. In this regard, grinding
to d80 =2.2 mm could not have been sufficient to achieve
high REM recoveries. According to the model, the particle
size-to-grain size ratio should be 0.1 to obtain a significant
liberation, e.g., 75% (Wills and Finch, 2016). If the model
is correct, a coal byproduct should be ground to 0.5 mm to
sufficiently liberate 5 mm monazite grains from coal, which
is impractical.
Recognizing the limitations in liberating rare earth-
bearing minerals from coal, the authors explored the pos-
sibility of liberating REMs by blunging. The clay industry
in Georgia has been using this method to liberate anatase
(TiO2) from kaolinite before removing the brownish impu-
rity by flotation to obtain high-brightness coating-grade
clays. The method is based on increasing the z-potentials
of the particles using a polyelectrolyte. An increase in the
double-layer potentials causes the pressure of the thin liq-
uid films (TLFs) of water, known as disjoining pressure (P),
and thereby keeps the two dissimilar surfaces apart from
each other. The same technique has been employed to liber-
ate the pigments of oil-based inks from paper fibers (Huang
et al., 2022).
In the present work, the authors used EDTA as a poly-
electrolyte to increase P and, hence, liberate REMs from
the coal matrix. The test results obtained on a thickener
underflow sample from Virginia are presented in Figure 8.
Table 2. Recovery of REE+Y from a Leatherwood thickener underflow sample, Kentucky†
Products
Weight
(%)Grade (%REE+Y)*
Recovery
(%REE+Y)
Concentrate 0.13 56.14 14.20
Tailings 99.87 0.06 85.80
Feed 100.00 0.07 100.00
*Dry ash basis †d
80 =2.2 mm
(a) (b) Thickener
Underflow
Liberation by
Blunging
Low-Ash
Dry Coal
Activated IEX
Leaching
REE+Y
in Solution
Two-Liquid
Flotation
Reject
Passivated IAC
+REMs
Figure 8. a) Liberation of rare earth minerals by blunging rather than by ultrafine grinding b) a proposed flowsheet for
REM recovery by liberation by blunging, two-liquid flotation to obtain REM concentrate and a low-ash dry coal byproduct,
followed by activated IEX +Y leaching
recovery of hydrophobic particles that are too small to be
recovered by flotation using air bubbles. Huang and Yoon
(2019) studied the thermodynamic and kinetic basis for
the superiority of using the TLF process to float ultrafine
particles. A U.S. patent was awarded for further developing
the TLF process to produce higher-grade and dry products
using recyclable hydrophobic liquid (Yoon, 2016).
Table 2 shows the results obtained on a thickener
underflow sample taken from a coal beneficiation plant, KY,
using the modified TLF process. The sample was attrition
ground to d80 =2.2 mm to liberate REMs from the coal
matrix. The mill product was conditioned with potassium
octyl hydroxamate (KOH) to selectively hydrophobize the
liberated REM particles prior to the TLF separation.
As shown, a high-grade concentrate was obtained with
56.14% REE+Y. However, the recovery was only 14.2%,
which was not surprising, however. According to a libera-
tion model developed by Gaudin (1939), the less-abundant
phase, REM in this case, cannot be liberated at all unless
the particle size is less than the grain size. The REM images
shown in Figure 7 are 2–4 mm. In this regard, grinding
to d80 =2.2 mm could not have been sufficient to achieve
high REM recoveries. According to the model, the particle
size-to-grain size ratio should be 0.1 to obtain a significant
liberation, e.g., 75% (Wills and Finch, 2016). If the model
is correct, a coal byproduct should be ground to 0.5 mm to
sufficiently liberate 5 mm monazite grains from coal, which
is impractical.
Recognizing the limitations in liberating rare earth-
bearing minerals from coal, the authors explored the pos-
sibility of liberating REMs by blunging. The clay industry
in Georgia has been using this method to liberate anatase
(TiO2) from kaolinite before removing the brownish impu-
rity by flotation to obtain high-brightness coating-grade
clays. The method is based on increasing the z-potentials
of the particles using a polyelectrolyte. An increase in the
double-layer potentials causes the pressure of the thin liq-
uid films (TLFs) of water, known as disjoining pressure (P),
and thereby keeps the two dissimilar surfaces apart from
each other. The same technique has been employed to liber-
ate the pigments of oil-based inks from paper fibers (Huang
et al., 2022).
In the present work, the authors used EDTA as a poly-
electrolyte to increase P and, hence, liberate REMs from
the coal matrix. The test results obtained on a thickener
underflow sample from Virginia are presented in Figure 8.
Table 2. Recovery of REE+Y from a Leatherwood thickener underflow sample, Kentucky†
Products
Weight
(%)Grade (%REE+Y)*
Recovery
(%REE+Y)
Concentrate 0.13 56.14 14.20
Tailings 99.87 0.06 85.80
Feed 100.00 0.07 100.00
*Dry ash basis †d
80 =2.2 mm
(a) (b) Thickener
Underflow
Liberation by
Blunging
Low-Ash
Dry Coal
Activated IEX
Leaching
REE+Y
in Solution
Two-Liquid
Flotation
Reject
Passivated IAC
+REMs
Figure 8. a) Liberation of rare earth minerals by blunging rather than by ultrafine grinding b) a proposed flowsheet for
REM recovery by liberation by blunging, two-liquid flotation to obtain REM concentrate and a low-ash dry coal byproduct,
followed by activated IEX +Y leaching