2634 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
This demonstrates that a high collector dosage is required
to obtain a satisfactory WO3 recovery. However, the tung-
sten grade rather similar between the floated product and
the flotation feed, which indicated a poor selectivity of this
flotation stage. This is consistent with the very high content
in silicates in this tungsten ore (85 wt.%) since these latter
are known to massively float with amines. It was assumed
that using sodium silicate could allow depressing the sili-
cates, at least slightly, while floating scheelite. Based on the
results, it appears either the sodium silicate dosage was too
low or that sodium silicate could not allow depressing sili-
cates in presence of amines. This is probably related to the
adsorption mechanisms of amines, which mainly adsorb
by establishing hydrogen bonds. Increasing the pH seems
to further improve the recovery, rising from about 50% to
more than 65% WO3 (Figure 3), which is consistent with
the decrease of the surface charge of scheelite when the pH
is increased, as demonstrated by the zeta potential measure-
ments. However, this effect is observed only at high dos-
age in DDA (500 g·t–1) while a reverse trend is observed
for the lowest dosage. This could be attributed to the fact
that silicates also display a very negative surface charge that
decreases significantly as a function of the pH. This results
in considerable consumption of the collector by the silicates
(gangue minerals), which decreases the amount of collector
that is available for adsorbing on scheelite surfaces.
From Figure 3, the experiments allowed to obtain fur-
ther information about the effect of the pH on the WO3
recoveries. At pH 3, the WO3 recovery increases when the
collector dosage increases, rising from 21% at 121 g·t–1
to 64% at 487 g·t–1. The same trend is observed at pH 4,
where the maximal recovery of 75% WO3 is reached for a
dosage of about 700 g·t–1.
Two tests were carried out at a pH value of 3 using a
greater collector dosage, i.e., 700 g·t–1 for either the same
depressant dosage or a lower dosage, i.e., 3500 g·t–1
(Table 1). In the first case, no improvement in both grade
and recoveries were obtained, whereas in the second case,
the WO3 recovery was improved by more than 7%, reach-
ing 67% WO3, for a same WO3 grade (Table 1). In other
words, the depressant was not acting selectively and was
depressing a part of the scheelite during the previous tests.
These tests highlight the overdosage of Na2SiO3.
Design of Experiments Results
A complete design of experiments was conducted to get
insights in the effects (including the interaction effects) of
the amine dosage and the pH for the direct flotation of
scheelite from the Tabuaço complex tungsten skarn. On
overall, the recovery slightly depends upon the pH at lower
Table 1. WO3 grade and recovery for the supplementary tests
carried out to investigate the effect of the depressant dosage
at a pH value of 3 and a DDA dosage of 700
Test pH
DDA
Dosage
Na
2 SiO
3 Dosage
WO
3 Grade, %
WO
3 Recovery, %
1 3 700 4268 1.03 60.10
2 3 700 3500 1.08 67.72
Figure 3. Evolution of the WO3 recovery as a function of the pH, from 3 to 5, at two different dosages in dodecylamine (left),
and as a function of the collector dosage, from 100 to 700 g·t–1, for pH 3 and 4. For all the tests, the dosage in depressant
(Na2SiO3) was set at 4250 g·t–1
This demonstrates that a high collector dosage is required
to obtain a satisfactory WO3 recovery. However, the tung-
sten grade rather similar between the floated product and
the flotation feed, which indicated a poor selectivity of this
flotation stage. This is consistent with the very high content
in silicates in this tungsten ore (85 wt.%) since these latter
are known to massively float with amines. It was assumed
that using sodium silicate could allow depressing the sili-
cates, at least slightly, while floating scheelite. Based on the
results, it appears either the sodium silicate dosage was too
low or that sodium silicate could not allow depressing sili-
cates in presence of amines. This is probably related to the
adsorption mechanisms of amines, which mainly adsorb
by establishing hydrogen bonds. Increasing the pH seems
to further improve the recovery, rising from about 50% to
more than 65% WO3 (Figure 3), which is consistent with
the decrease of the surface charge of scheelite when the pH
is increased, as demonstrated by the zeta potential measure-
ments. However, this effect is observed only at high dos-
age in DDA (500 g·t–1) while a reverse trend is observed
for the lowest dosage. This could be attributed to the fact
that silicates also display a very negative surface charge that
decreases significantly as a function of the pH. This results
in considerable consumption of the collector by the silicates
(gangue minerals), which decreases the amount of collector
that is available for adsorbing on scheelite surfaces.
From Figure 3, the experiments allowed to obtain fur-
ther information about the effect of the pH on the WO3
recoveries. At pH 3, the WO3 recovery increases when the
collector dosage increases, rising from 21% at 121 g·t–1
to 64% at 487 g·t–1. The same trend is observed at pH 4,
where the maximal recovery of 75% WO3 is reached for a
dosage of about 700 g·t–1.
Two tests were carried out at a pH value of 3 using a
greater collector dosage, i.e., 700 g·t–1 for either the same
depressant dosage or a lower dosage, i.e., 3500 g·t–1
(Table 1). In the first case, no improvement in both grade
and recoveries were obtained, whereas in the second case,
the WO3 recovery was improved by more than 7%, reach-
ing 67% WO3, for a same WO3 grade (Table 1). In other
words, the depressant was not acting selectively and was
depressing a part of the scheelite during the previous tests.
These tests highlight the overdosage of Na2SiO3.
Design of Experiments Results
A complete design of experiments was conducted to get
insights in the effects (including the interaction effects) of
the amine dosage and the pH for the direct flotation of
scheelite from the Tabuaço complex tungsten skarn. On
overall, the recovery slightly depends upon the pH at lower
Table 1. WO3 grade and recovery for the supplementary tests
carried out to investigate the effect of the depressant dosage
at a pH value of 3 and a DDA dosage of 700
Test pH
DDA
Dosage
Na
2 SiO
3 Dosage
WO
3 Grade, %
WO
3 Recovery, %
1 3 700 4268 1.03 60.10
2 3 700 3500 1.08 67.72
Figure 3. Evolution of the WO3 recovery as a function of the pH, from 3 to 5, at two different dosages in dodecylamine (left),
and as a function of the collector dosage, from 100 to 700 g·t–1, for pH 3 and 4. For all the tests, the dosage in depressant
(Na2SiO3) was set at 4250 g·t–1