XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2227
has been reported in the literature that polyelectrolytes are
good depressants for typical minerals such as quartz and
clay (Raleigh and Aplan, 1993).
Another series of TLF tests were conducted on a ground
sample. The grinding was performed using a stirred ball
mill for 4 hours with 2 mm alumina spheres as grinding
media. The particle size was reduced from 11.2 to 4.9 μm
after grinding. The TLF products obtained with the ground
sample assayed 1% ash and 2% moisture as shown in the
last two rows in Table 2. The substantial decrease in the ash
contents was most likely due to the improved liberation of
mineral matter from the coal matrix. The ultra-clean coal
products obtained from the TLF process can be blended
with heavy oil for combustion in large internal combustion
engines, which can open a broader market potential for fine
coal wastes.
Table 3 shows the results of a bench-scale TLF test con-
ducted on an Eastern Kentucky bituminous coal sample. It
was a fine coal waste excavated from an impoundment. The
sample had been upgraded via four stages of column flota-
tion to obtain 3.88% ash coal with very high moisture. The
flotation product with d80 =7.8 μm was subjected to a sin-
gle-stage TLF flotation test to obtain a clean coal product
with 1.74% ash and 2.04% moisture at an overall organic
recovery of 99.36%.
SIMULATIONS
In a typical closed-circuit flotation plant, CSTs are recycled
back to the rougher flotation bank to provide the materials
in circulating loads (CLs) with additional retention times
for recovery. The authors of the present investigation sug-
gested that the CST is where the slowest-floating particles
congregate. The slow kinetics arise from small particle size
(20 µm), composite particles, and superficial oxidation
(Gupta et al., 2023). An obvious solution to this problem
would be a longer retention time, which could exacerbate
the oxidation problem. In a laboratory setting, the contact
angle of a KAX-coaled chalcopyrite surface decreased from
68.3° to 40° in 8 hours of immersion in water. Although the
contact angle decreases during recirculation cycles would
be a small fraction of this observation, any decrease in con-
tact angle should affect the kinetics and, hence, recovery.
As discussed in the foregoing paragraph, feeding a CST
to a rougher bank as a CL should certainly improve the
recovery of slow-floating particles. However, this process
entails a significant cost, which arises from the fact that
a volume of the CL consisting of slow-floating particles
replaces the same volume of the fast-floating particles pres-
ent in the freshly mined ore. The authors of the present
investigation used a flotation model to estimate the cost
(Huang et al., 2022 Gupta et al., 2022 2023). The major
input to the model is the size-by-class mineral liberation
matrix (mij), in which m is the mass fraction of particles
in particle size i and liberation class j. From the mij matrix,
one can use the Cassie-Baxter equation (1944) to deter-
mine the contact angle matrix (qij), which in turn can be
used to determine the size-by-class flotation rate constants
(kij) under various operating conditions. The kij in the pulp
phase can be predicted using the flotation rate equation
in the form of the Arrhenius equation (Gupta and Yoon,
2024),
expd- k Z
E Ehh
El
Wa
*
ij
k
12
1 -
+-^n (1)
In Eq. (1), Z *
12 and E '
k represent the collision frequency
and the energy fluctuation due to turbulence in the pulp
Table 2. Production of ultra-clean coal using the TLF process
Feed d80,
µm
Feed Ash,
%
Proprietary
Reagents
TLF Product Refuse
Ash,
%
Organic
Recovery,
%
Ash,
%
Moisture,
%
11.21 4.97 — 2.30 2.12 79.79 99.50
4.97 Reagent A 2.04 2.19 83.83 99.64
4.92 5.69 Reagent A 0.91 1.50 79.26 99.06
5.69 Reagent B 0.72 1.40 81.31 99.20
Table 3. TLF test results obtained on an impoundment coal
Feed d80,
μm
Feed Ash,
%
TLF Product Refuse
Ash,
%
Organic Recovery,
%
Ash,
%
Moisture,
%
7.8 3.88 1.74 2.04 73.54 99.36
1As-received sample 2After attrition milling
has been reported in the literature that polyelectrolytes are
good depressants for typical minerals such as quartz and
clay (Raleigh and Aplan, 1993).
Another series of TLF tests were conducted on a ground
sample. The grinding was performed using a stirred ball
mill for 4 hours with 2 mm alumina spheres as grinding
media. The particle size was reduced from 11.2 to 4.9 μm
after grinding. The TLF products obtained with the ground
sample assayed 1% ash and 2% moisture as shown in the
last two rows in Table 2. The substantial decrease in the ash
contents was most likely due to the improved liberation of
mineral matter from the coal matrix. The ultra-clean coal
products obtained from the TLF process can be blended
with heavy oil for combustion in large internal combustion
engines, which can open a broader market potential for fine
coal wastes.
Table 3 shows the results of a bench-scale TLF test con-
ducted on an Eastern Kentucky bituminous coal sample. It
was a fine coal waste excavated from an impoundment. The
sample had been upgraded via four stages of column flota-
tion to obtain 3.88% ash coal with very high moisture. The
flotation product with d80 =7.8 μm was subjected to a sin-
gle-stage TLF flotation test to obtain a clean coal product
with 1.74% ash and 2.04% moisture at an overall organic
recovery of 99.36%.
SIMULATIONS
In a typical closed-circuit flotation plant, CSTs are recycled
back to the rougher flotation bank to provide the materials
in circulating loads (CLs) with additional retention times
for recovery. The authors of the present investigation sug-
gested that the CST is where the slowest-floating particles
congregate. The slow kinetics arise from small particle size
(20 µm), composite particles, and superficial oxidation
(Gupta et al., 2023). An obvious solution to this problem
would be a longer retention time, which could exacerbate
the oxidation problem. In a laboratory setting, the contact
angle of a KAX-coaled chalcopyrite surface decreased from
68.3° to 40° in 8 hours of immersion in water. Although the
contact angle decreases during recirculation cycles would
be a small fraction of this observation, any decrease in con-
tact angle should affect the kinetics and, hence, recovery.
As discussed in the foregoing paragraph, feeding a CST
to a rougher bank as a CL should certainly improve the
recovery of slow-floating particles. However, this process
entails a significant cost, which arises from the fact that
a volume of the CL consisting of slow-floating particles
replaces the same volume of the fast-floating particles pres-
ent in the freshly mined ore. The authors of the present
investigation used a flotation model to estimate the cost
(Huang et al., 2022 Gupta et al., 2022 2023). The major
input to the model is the size-by-class mineral liberation
matrix (mij), in which m is the mass fraction of particles
in particle size i and liberation class j. From the mij matrix,
one can use the Cassie-Baxter equation (1944) to deter-
mine the contact angle matrix (qij), which in turn can be
used to determine the size-by-class flotation rate constants
(kij) under various operating conditions. The kij in the pulp
phase can be predicted using the flotation rate equation
in the form of the Arrhenius equation (Gupta and Yoon,
2024),
expd- k Z
E Ehh
El
Wa
*
ij
k
12
1 -
+-^n (1)
In Eq. (1), Z *
12 and E '
k represent the collision frequency
and the energy fluctuation due to turbulence in the pulp
Table 2. Production of ultra-clean coal using the TLF process
Feed d80,
µm
Feed Ash,
%
Proprietary
Reagents
TLF Product Refuse
Ash,
%
Organic
Recovery,
%
Ash,
%
Moisture,
%
11.21 4.97 — 2.30 2.12 79.79 99.50
4.97 Reagent A 2.04 2.19 83.83 99.64
4.92 5.69 Reagent A 0.91 1.50 79.26 99.06
5.69 Reagent B 0.72 1.40 81.31 99.20
Table 3. TLF test results obtained on an impoundment coal
Feed d80,
μm
Feed Ash,
%
TLF Product Refuse
Ash,
%
Organic Recovery,
%
Ash,
%
Moisture,
%
7.8 3.88 1.74 2.04 73.54 99.36
1As-received sample 2After attrition milling