XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 611
Zn, Co, Ni, and Mn are removed from AMD2 as a group
in 3.4 min after –0.30 V is applied, while Ca, Mg, and Si
are mostly rejected. The specific recovery rates for both Cu
and Zn are as high as 0.13 g(RVC)–1 min–1. Compared to
the corresponding rates at –0.75 V in Al-depleted AMD1,
the rate for Cu is similar, while that for Zn is higher by a
factor of 3 (Figure 5). The improved uptake of these ele-
ments from AMD2 can be linked to their more dilute
concentrations than in AMD1 (Table 1). As a result, the
electrode is less passivated by the precipitates and hence
generates a higher flux of hydroxyl ions, which is the driv-
ing force of SEP. This effect can explain another interesting
feature of the uptake at –0.30 V from AMD2, namely, the
synchronization of the co-uptake of Co, Ni, and Mn with
that of Cu, Zn, and TREE (Figure 8). The co-uptake of Co,
Ni, and Mn is delayed in AMD1 and Al-depleted AMD1 at
both –0.30 V and –0.75 V (Table 2).
Since the treatment of AMD1 at –0.30 V selectively
uptakes only Cu and Al (Figure 3a,b), we treated this water
further at –0.75 V to study the further uptake Zn and REE
after the Cu and Al depletion. As shown in Figure 9, this
stage recovers 80% Zn, 85% TREE, 35% Co&Ni, along
with the remaining Cu and Al in 7.5 min. It leaves behind
77–95% Si, Ca, Mg, Mn, and Fe, the primary contami-
nants of the SEP deposit being Ca, Mg, and Mn. It fol-
lows that the two-stage treatment can separate Cu from an
Al-depleted AMD in the first stage by electro-deposition
and Zn with TREE in the second stage by SEP.
Finally, we should highlight the finding that the Cu
uptake mechanism in AMD can be either electro-deposi-
tion or SEP depending on the aqueous matrix and poten-
tial, while the Cu uptake rate by SEP is significantly higher.
At –0.30 V in AMD1, Cu is immobilized by e-deposition,
while the e-deposition rate is almost ten times slower than
in a synthetic Cu solution in Na2SO4 with the same con-
centrations of Cu and SO42– (Figure 5). The suppression
of e-deposition can be explained the passivation of the
electrode by Al (Figure 4). Surprisingly, the Cu uptake rate
at –0.75 V in AMD is twice higher than in the synthetic
Cu solutions (Figure 5). This is surprising because the
Cu e-deposition from the Na2SO4 solutions at potentials
cathodic of –0.10 V is under diffusion control and does
not depend on potential and pH [25]. The acceleration of
the Cu uptake at –0.75 V suggests that the uptake mecha-
nism switches to SEP, which is supported by the intermix-
ing of Cu with other immobilized elements in the deposit
(Figure 7). The acceleration also suggests that the mass
0 5 10 15 20
0
20
40
60
80
100
Time (min)
Mg
Ca
Mn
Fe
Co
Ni
Cu
Zn
Sr
U
Si
Y
La
Ce
Nd
6.5
7.0
7.5
8.0
8.5
9.0
9.5
Figure 8. SEP of AMD2 at –0.30 V with a RVC electrode
with size of 19×17×5 mm3 (0.114 g) in a 40 mL cell
0 1 2 3 4 5 6 7 8
0
20
40
60
80
100
Time (min)
Mg
Ca
Mn
Fe
Co
Ni
Cu
Zn
Sr
U
pH
5.5
6.0
6.5
7.0
7.5
8.0
8.5
0 1 2 3 4 5 6 7 8
0
20
40
60
80
100
Time (min)
Al
Si
Y
La
Ce
Nd
b a
Cu
U Zn
Co
Ni
Mn
0.75 V
Figure 9. Cumulative recovery of elements at –0.75 V from AMD1 treated at –0.30 V in the test shown in Figure 3a,b. The
test was conducted in a 30-mL cell with a 17×17×2 mm3 (0.041 g) RVC electrode. Copyright (C) 2023 Chernyshova, Suup,
Kihlblom, Kota, Ponnurangam
Uptake
(%)
pH
Uptake
(%)
pH Uptake
(%)
Zn, Co, Ni, and Mn are removed from AMD2 as a group
in 3.4 min after –0.30 V is applied, while Ca, Mg, and Si
are mostly rejected. The specific recovery rates for both Cu
and Zn are as high as 0.13 g(RVC)–1 min–1. Compared to
the corresponding rates at –0.75 V in Al-depleted AMD1,
the rate for Cu is similar, while that for Zn is higher by a
factor of 3 (Figure 5). The improved uptake of these ele-
ments from AMD2 can be linked to their more dilute
concentrations than in AMD1 (Table 1). As a result, the
electrode is less passivated by the precipitates and hence
generates a higher flux of hydroxyl ions, which is the driv-
ing force of SEP. This effect can explain another interesting
feature of the uptake at –0.30 V from AMD2, namely, the
synchronization of the co-uptake of Co, Ni, and Mn with
that of Cu, Zn, and TREE (Figure 8). The co-uptake of Co,
Ni, and Mn is delayed in AMD1 and Al-depleted AMD1 at
both –0.30 V and –0.75 V (Table 2).
Since the treatment of AMD1 at –0.30 V selectively
uptakes only Cu and Al (Figure 3a,b), we treated this water
further at –0.75 V to study the further uptake Zn and REE
after the Cu and Al depletion. As shown in Figure 9, this
stage recovers 80% Zn, 85% TREE, 35% Co&Ni, along
with the remaining Cu and Al in 7.5 min. It leaves behind
77–95% Si, Ca, Mg, Mn, and Fe, the primary contami-
nants of the SEP deposit being Ca, Mg, and Mn. It fol-
lows that the two-stage treatment can separate Cu from an
Al-depleted AMD in the first stage by electro-deposition
and Zn with TREE in the second stage by SEP.
Finally, we should highlight the finding that the Cu
uptake mechanism in AMD can be either electro-deposi-
tion or SEP depending on the aqueous matrix and poten-
tial, while the Cu uptake rate by SEP is significantly higher.
At –0.30 V in AMD1, Cu is immobilized by e-deposition,
while the e-deposition rate is almost ten times slower than
in a synthetic Cu solution in Na2SO4 with the same con-
centrations of Cu and SO42– (Figure 5). The suppression
of e-deposition can be explained the passivation of the
electrode by Al (Figure 4). Surprisingly, the Cu uptake rate
at –0.75 V in AMD is twice higher than in the synthetic
Cu solutions (Figure 5). This is surprising because the
Cu e-deposition from the Na2SO4 solutions at potentials
cathodic of –0.10 V is under diffusion control and does
not depend on potential and pH [25]. The acceleration of
the Cu uptake at –0.75 V suggests that the uptake mecha-
nism switches to SEP, which is supported by the intermix-
ing of Cu with other immobilized elements in the deposit
(Figure 7). The acceleration also suggests that the mass
0 5 10 15 20
0
20
40
60
80
100
Time (min)
Mg
Ca
Mn
Fe
Co
Ni
Cu
Zn
Sr
U
Si
Y
La
Ce
Nd
6.5
7.0
7.5
8.0
8.5
9.0
9.5
Figure 8. SEP of AMD2 at –0.30 V with a RVC electrode
with size of 19×17×5 mm3 (0.114 g) in a 40 mL cell
0 1 2 3 4 5 6 7 8
0
20
40
60
80
100
Time (min)
Mg
Ca
Mn
Fe
Co
Ni
Cu
Zn
Sr
U
pH
5.5
6.0
6.5
7.0
7.5
8.0
8.5
0 1 2 3 4 5 6 7 8
0
20
40
60
80
100
Time (min)
Al
Si
Y
La
Ce
Nd
b a
Cu
U Zn
Co
Ni
Mn
0.75 V
Figure 9. Cumulative recovery of elements at –0.75 V from AMD1 treated at –0.30 V in the test shown in Figure 3a,b. The
test was conducted in a 30-mL cell with a 17×17×2 mm3 (0.041 g) RVC electrode. Copyright (C) 2023 Chernyshova, Suup,
Kihlblom, Kota, Ponnurangam
Uptake
(%)
pH
Uptake
(%)
pH Uptake
(%)