2556 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
This approach relies heavily on subjectivity and empiri-
cism, overlooking the complexity and variability of miner-
alogy, as well as the intricate interactions between chemical,
physical-mechanical, and operational factors in the plant.
The reagents selected are often not robust enough to meet
industrial requirements, and laboratory tests provide lim-
ited knowledge for the operational environment (Nagaraj
2005). In 2020, our group introduced colloidal silica as a
potential calcite depressant in scheelite flotation (Kupka
et al. 2020). Single mineral microflotation experiments
demonstrated that increasing the dosage of colloidal sil-
ica decreased the recovery of calcite without affecting the
recovery of scheelite. To systematically optimize and scale
up the patented technology with minimal trials, we devel-
oped a methodology that combines design of experiments
(DoE) approach in the batch-scale with the Nelder Mead
optimization method at pilot- and industrial-scale.
MATERIAL AND METHODS
Reagents
The collector used was sodium oleate C18H33Na2 (NaOl)
from Carl Roth with a purity of 90%. pH modifiers are
hydrochloric (HCl) acid and sodium hydroxide (NaOH)
from Carl Roth GmbH, and frother is 4-methyl-2-penta-
nol (MIBC) supplied by Alfa Aesar. Seven types of Levasil ®
Colloidal Silica (CS) provided by Nouryon ® were tested as
calcite depressant, differing in modification and specific
surface area, as summarized in Table 1.
Microflotation of Scheelite and Calcite
160 ml of KCl was mixed with one gram of each min-
eral, and the mixture was agitated at 400 rpm in a beaker
equipped with a magnetic bar. With a two-minute condi-
tioning period, 1 M HCl or NaOH feedstock solutions
were used to modify the slurry’s pH. Depressant and col-
lector conditioning were carried out sequentially after pH
stabilization, each lasting three minutes at 400 rpm. After
that, the suspension was transferred to the Hallimond tube
and agitated at 800 rpm for two minutes. Two minutes of
microflotation were conducted at a 20 cm3/min air flow
rate. The collected concentrates and tailings were filtered
and dried overnight at 50°C–60 °C.
Batch Flotation Experiments
Ore and Overall Flotation Procedure
The low-grade scheelite ore under investigation contains
1.1% (w/w) calcite and 0.5% (w/w) scheelite. As shown
in Figure 1, the primary gangue minerals are quartz,
Table 1. Summary of colloidal silica suspensions and their
specifications. *calculated from the specific surface area
Specific
Surface Area,
m2/g Modification
Particle Size*
(nm) Acronym
250 None 9 CS_250
500 None 4.5 CS_500
220 Silane 10 CS_S_220
500 Silane 4.5 CS_S_500
250 Aluminate 9 CS_Al_250
500 Aluminate 4.5 CS_Al_500
1100 Aluminate 2 CS_Al_1100
Figure 1. Mineralogical composition of the ore in %(w/w) obtained by X-ray diffraction (XRD) and mineral liberation
analyser (MLA)
This approach relies heavily on subjectivity and empiri-
cism, overlooking the complexity and variability of miner-
alogy, as well as the intricate interactions between chemical,
physical-mechanical, and operational factors in the plant.
The reagents selected are often not robust enough to meet
industrial requirements, and laboratory tests provide lim-
ited knowledge for the operational environment (Nagaraj
2005). In 2020, our group introduced colloidal silica as a
potential calcite depressant in scheelite flotation (Kupka
et al. 2020). Single mineral microflotation experiments
demonstrated that increasing the dosage of colloidal sil-
ica decreased the recovery of calcite without affecting the
recovery of scheelite. To systematically optimize and scale
up the patented technology with minimal trials, we devel-
oped a methodology that combines design of experiments
(DoE) approach in the batch-scale with the Nelder Mead
optimization method at pilot- and industrial-scale.
MATERIAL AND METHODS
Reagents
The collector used was sodium oleate C18H33Na2 (NaOl)
from Carl Roth with a purity of 90%. pH modifiers are
hydrochloric (HCl) acid and sodium hydroxide (NaOH)
from Carl Roth GmbH, and frother is 4-methyl-2-penta-
nol (MIBC) supplied by Alfa Aesar. Seven types of Levasil ®
Colloidal Silica (CS) provided by Nouryon ® were tested as
calcite depressant, differing in modification and specific
surface area, as summarized in Table 1.
Microflotation of Scheelite and Calcite
160 ml of KCl was mixed with one gram of each min-
eral, and the mixture was agitated at 400 rpm in a beaker
equipped with a magnetic bar. With a two-minute condi-
tioning period, 1 M HCl or NaOH feedstock solutions
were used to modify the slurry’s pH. Depressant and col-
lector conditioning were carried out sequentially after pH
stabilization, each lasting three minutes at 400 rpm. After
that, the suspension was transferred to the Hallimond tube
and agitated at 800 rpm for two minutes. Two minutes of
microflotation were conducted at a 20 cm3/min air flow
rate. The collected concentrates and tailings were filtered
and dried overnight at 50°C–60 °C.
Batch Flotation Experiments
Ore and Overall Flotation Procedure
The low-grade scheelite ore under investigation contains
1.1% (w/w) calcite and 0.5% (w/w) scheelite. As shown
in Figure 1, the primary gangue minerals are quartz,
Table 1. Summary of colloidal silica suspensions and their
specifications. *calculated from the specific surface area
Specific
Surface Area,
m2/g Modification
Particle Size*
(nm) Acronym
250 None 9 CS_250
500 None 4.5 CS_500
220 Silane 10 CS_S_220
500 Silane 4.5 CS_S_500
250 Aluminate 9 CS_Al_250
500 Aluminate 4.5 CS_Al_500
1100 Aluminate 2 CS_Al_1100
Figure 1. Mineralogical composition of the ore in %(w/w) obtained by X-ray diffraction (XRD) and mineral liberation
analyser (MLA)