604 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
A method potentially capable of meeting the afore-
mentioned requirements is surface electro-precipitation
(SEP) [25]. It is an electrochemical method that has been
developed for depositing metal hydroxide coatings but
largely ignored in the decontamination of water and the
extraction of valuable elements [26]. In this method, metal
ions are precipitated as hydroxides or hydroxycarbonates on
the surface of the cathode (Figure 1). For a divalent metal
cation M2+, this reaction can be written as
M2+ +2OH– =M(OH)2¯ (1)
A key feature of this method is that the hydroxyls needed
for this reaction are generated by this cathode through elec-
trocatalytic reduction of water (hydrogen evolution reac-
tion, HER)
2H+ +2e– =H2, E0 =0.0 V (NHE) (2)
or dissolved O2 (oxygen reduction reaction, ORR):
O2 +2H+ +2e– =H2O2, E0 =0.695 V (NHE) (3)
O2 +2H+ +4e– =2H2O E0 =1.23 V (NHE) (4)
If concentrations of the target metal cations are in
the mg/L range, these cations precipitate on the electrode
surface (Figure 1), which significantly facilitates their recov-
ery/discharge compared to the precipitates formed in the
solution bulk. In addition, precipitated metal hydroxides
are thermodynamically much easier to dissolve/discharge in
acidic solutions by applying a positive potential compared
to the electro-deposited metals. By its design, SEP borrows
the fast kinetics from chemical precipitation, while high
adsorption capacity and the technical simplicity to recover
a new phase already immobilized at a solid-solution inter-
face are borrowed from electro-deposition. Moreover, as
in the case of electro-deposition, SEP can operate without
employing chemicals, while its rate and selectivity can be
controlled by applying different potentials to the electroac-
tive cathode [25]. Finally, SEP can be powered by renew-
able energy resources, which would further improve its
environmental sustainability.
The objectives of this study are (1) to test SEP in the
uptake of Cu, Zn, Co, Ni, U, and REE from hard AMD
waters of a polymetallic sulfide ore origin and (2) to study
the effect of potential and Al on the separation of the valu-
able elements.
MATERIALS AND METHODS
Duocel ® reticulated vitreous carbon (RVC) foam pan-
els with porosity of 100 ppi and 3% relative density were
purchased from Duocel. All glassware was washed with
Sparkleen ™ detergent (Fisher) and rinsed many times
with Nanopure water. pH was adjusted with NaOH and
H2SO4 solutions. AMD samples were provided by Boliden
Minerals, Sweden.
SEP experiments were conducted at room temperature
(23±2°C) in a lab-made batch-type cylindrical two-com-
partment glass cell with a 5-mL counter electrode com-
partment and a pH probe in the main (working electrode)
compartment (Figure 2a). Potential was applied using a
Bio-logic VSP-300 potentiostat (Figure 2b). The working
SEP electrode was made from a RVC panel (Figure 2c).
Pt served as a counter electrode. An Ag/AgCl (3M NaCl)
electrode was the reference. All potentials are reported vs the
Figure 1. Schematics of SEP: An electrocatalytically active cathode generates a high flux of hydroxyls that
precipitate hydrolyzable metal cations on the cathode surface
A method potentially capable of meeting the afore-
mentioned requirements is surface electro-precipitation
(SEP) [25]. It is an electrochemical method that has been
developed for depositing metal hydroxide coatings but
largely ignored in the decontamination of water and the
extraction of valuable elements [26]. In this method, metal
ions are precipitated as hydroxides or hydroxycarbonates on
the surface of the cathode (Figure 1). For a divalent metal
cation M2+, this reaction can be written as
M2+ +2OH– =M(OH)2¯ (1)
A key feature of this method is that the hydroxyls needed
for this reaction are generated by this cathode through elec-
trocatalytic reduction of water (hydrogen evolution reac-
tion, HER)
2H+ +2e– =H2, E0 =0.0 V (NHE) (2)
or dissolved O2 (oxygen reduction reaction, ORR):
O2 +2H+ +2e– =H2O2, E0 =0.695 V (NHE) (3)
O2 +2H+ +4e– =2H2O E0 =1.23 V (NHE) (4)
If concentrations of the target metal cations are in
the mg/L range, these cations precipitate on the electrode
surface (Figure 1), which significantly facilitates their recov-
ery/discharge compared to the precipitates formed in the
solution bulk. In addition, precipitated metal hydroxides
are thermodynamically much easier to dissolve/discharge in
acidic solutions by applying a positive potential compared
to the electro-deposited metals. By its design, SEP borrows
the fast kinetics from chemical precipitation, while high
adsorption capacity and the technical simplicity to recover
a new phase already immobilized at a solid-solution inter-
face are borrowed from electro-deposition. Moreover, as
in the case of electro-deposition, SEP can operate without
employing chemicals, while its rate and selectivity can be
controlled by applying different potentials to the electroac-
tive cathode [25]. Finally, SEP can be powered by renew-
able energy resources, which would further improve its
environmental sustainability.
The objectives of this study are (1) to test SEP in the
uptake of Cu, Zn, Co, Ni, U, and REE from hard AMD
waters of a polymetallic sulfide ore origin and (2) to study
the effect of potential and Al on the separation of the valu-
able elements.
MATERIALS AND METHODS
Duocel ® reticulated vitreous carbon (RVC) foam pan-
els with porosity of 100 ppi and 3% relative density were
purchased from Duocel. All glassware was washed with
Sparkleen ™ detergent (Fisher) and rinsed many times
with Nanopure water. pH was adjusted with NaOH and
H2SO4 solutions. AMD samples were provided by Boliden
Minerals, Sweden.
SEP experiments were conducted at room temperature
(23±2°C) in a lab-made batch-type cylindrical two-com-
partment glass cell with a 5-mL counter electrode com-
partment and a pH probe in the main (working electrode)
compartment (Figure 2a). Potential was applied using a
Bio-logic VSP-300 potentiostat (Figure 2b). The working
SEP electrode was made from a RVC panel (Figure 2c).
Pt served as a counter electrode. An Ag/AgCl (3M NaCl)
electrode was the reference. All potentials are reported vs the
Figure 1. Schematics of SEP: An electrocatalytically active cathode generates a high flux of hydroxyls that
precipitate hydrolyzable metal cations on the cathode surface