XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1607
group of particles in the column. While these adaptations
enable extracting solid or solution samples from interme-
diate positions within the leaching system, they are not
expected to affect how the solution, or the solids would
behave if the column had not been divided.
A dilute sulphuric acid solution containing ferric and
ferrous sulphates was considered for the leaching feed. The
iron (II) and iron (III) ions were added to emulate the
oxidising conditions typical of bioleaching. A small amount
of copper sulphate was added to act as a baseline for cop-
per concentration estimations during the leaching period.
The estimated sulphuric acid and metal concentrations
considered for the leaching feed are reported in Table 2.
The reagents used for this preparation were sulphuric acid
(95.0–97.0%) AnalaR NORMAPUR ® (VWR Chemicals),
iron (II) sulphate heptahydrate, ≥96%, technical grade
(VWR Chemicals), iron (III) sulphate pentahydrate, 97%
(Thermo Scientific), and copper (II) sulphate pentahydrate,
≥98%, ACS reagent (Thermo Scientific).
The solution was fed to the first column in the system
(see Figure 1) at a rate of ~10 mL/h or ~10.3 L/(h.m2). This
irrigation rate was kept constant during the 78 days that the
experiment lasted, except for six days when the irrigation
was stopped to allow for solution and solid analysis to be
performed. All three columns were kept at a constant tem-
perature of ~40ºC throughout the experiment. The feed
always consisted of a fresh solution prepared according to
the concentrations displayed in Table 2.
Solution Assays
Solutions were collected at different times from four
locations within the system (initial feed and the outlet of
each of the three columns, see Figure 1). These aliquots were
used to measure the pH and oxidation-reduction potential
(ORP) of the solutions, as well as to determine their con-
centration of copper, total iron, and ferrous ion. pH and
ORP were measured using a pH-130 pH/ORP meter from
VWR. Total copper and iron concentration in solution
were obtained via Inductively Coupled Plasma-Optical
Emission Spectroscopy (ICP-OES) using a Thermo iCAP
6300. Ferrous ion determination was performed through
redox titration with potassium permanganate following a
well-established method (Metrohm -Titration Application
Note H-128, n.d.). Ferric ion was then calculated as the
difference between the determined concentration of total
iron and of ferrous ion. ICP-OES was also used to deter-
mine total copper and iron in the pregnant leach solutions
collected throughout the leaching period. This information
was then used to estimate how much copper and iron was
extracted from the particles over time, thus quantifying the
extent of leaching.
3D Imaging with Micro Computed Tomography
(micro-CT)
A region from each column was scanned using micro
computed tomography (micro-CT) to assess changes that
may be occurring at a volumetric scale in the particles.
The same regions were scanned throughout the leaching
period to evaluate the temporal heterogeneity of the pro-
cess. Each scan consisted in the acquisition of 1800 X-ray
projections, obtained using a voltage of 90 kV, a current of
320 µA and an exposure time of 1 s per projection. Three
radiographs were averaged per projection to improve image
quality, with each full scan lasting about 2 hours. The voxel
(3D equivalent of a pixel) size for each of the scans was of
~17.3 µm. The scanner used for the image acquisition was
a General Electric Phoenix ® Nanotom S. The images were
reconstructed using the built-in reconstruction software
employing cone-beam filtered back-projection algorithms.
The results of the reconstruction of one of the columns
before leaching are shown in Figure 2. Figure 2a shows a
3D rendering of one of the columns and Figure 2b shows
a 2D slice of the same column. The main components in
the sample are highlighted in yellow (sulphide grains), grey
(rock matrix), and black (interparticle and intraparticle
pores).
Surface-Level Techniques
Four particles (4–8 mm in diameter) were prepared for
surface-level analysis via scanning electron microscopy with
energy dispersive X-ray spectroscopy (SEM/EDX) and
X-ray photoelectron spectroscopy (XPS). Sample prepara-
tion included producing a flat surface through grinding.
These particles were placed in the designated sample cham-
bers at the top of the first column (removable sample A in
Figure 1) and at the bottom of all columns (removable sam-
ples B-D in Figure 1). For surface-level analysis, the par-
ticles were removed from their respective chambers, washed
with deionised water and dried in an oven at ~40°C for 12
hours, before analysing them with SEM/EDX and XPS.
Table 2. Estimated concentration of sulphuric acid, ferrous
ion, ferric ion, and copper added to the leaching feed
Species Concentration (g/L)
H
2 SO
4 12.0
Fe(II) 1.6
Fe(III) 1.8
Cu 0.5
group of particles in the column. While these adaptations
enable extracting solid or solution samples from interme-
diate positions within the leaching system, they are not
expected to affect how the solution, or the solids would
behave if the column had not been divided.
A dilute sulphuric acid solution containing ferric and
ferrous sulphates was considered for the leaching feed. The
iron (II) and iron (III) ions were added to emulate the
oxidising conditions typical of bioleaching. A small amount
of copper sulphate was added to act as a baseline for cop-
per concentration estimations during the leaching period.
The estimated sulphuric acid and metal concentrations
considered for the leaching feed are reported in Table 2.
The reagents used for this preparation were sulphuric acid
(95.0–97.0%) AnalaR NORMAPUR ® (VWR Chemicals),
iron (II) sulphate heptahydrate, ≥96%, technical grade
(VWR Chemicals), iron (III) sulphate pentahydrate, 97%
(Thermo Scientific), and copper (II) sulphate pentahydrate,
≥98%, ACS reagent (Thermo Scientific).
The solution was fed to the first column in the system
(see Figure 1) at a rate of ~10 mL/h or ~10.3 L/(h.m2). This
irrigation rate was kept constant during the 78 days that the
experiment lasted, except for six days when the irrigation
was stopped to allow for solution and solid analysis to be
performed. All three columns were kept at a constant tem-
perature of ~40ºC throughout the experiment. The feed
always consisted of a fresh solution prepared according to
the concentrations displayed in Table 2.
Solution Assays
Solutions were collected at different times from four
locations within the system (initial feed and the outlet of
each of the three columns, see Figure 1). These aliquots were
used to measure the pH and oxidation-reduction potential
(ORP) of the solutions, as well as to determine their con-
centration of copper, total iron, and ferrous ion. pH and
ORP were measured using a pH-130 pH/ORP meter from
VWR. Total copper and iron concentration in solution
were obtained via Inductively Coupled Plasma-Optical
Emission Spectroscopy (ICP-OES) using a Thermo iCAP
6300. Ferrous ion determination was performed through
redox titration with potassium permanganate following a
well-established method (Metrohm -Titration Application
Note H-128, n.d.). Ferric ion was then calculated as the
difference between the determined concentration of total
iron and of ferrous ion. ICP-OES was also used to deter-
mine total copper and iron in the pregnant leach solutions
collected throughout the leaching period. This information
was then used to estimate how much copper and iron was
extracted from the particles over time, thus quantifying the
extent of leaching.
3D Imaging with Micro Computed Tomography
(micro-CT)
A region from each column was scanned using micro
computed tomography (micro-CT) to assess changes that
may be occurring at a volumetric scale in the particles.
The same regions were scanned throughout the leaching
period to evaluate the temporal heterogeneity of the pro-
cess. Each scan consisted in the acquisition of 1800 X-ray
projections, obtained using a voltage of 90 kV, a current of
320 µA and an exposure time of 1 s per projection. Three
radiographs were averaged per projection to improve image
quality, with each full scan lasting about 2 hours. The voxel
(3D equivalent of a pixel) size for each of the scans was of
~17.3 µm. The scanner used for the image acquisition was
a General Electric Phoenix ® Nanotom S. The images were
reconstructed using the built-in reconstruction software
employing cone-beam filtered back-projection algorithms.
The results of the reconstruction of one of the columns
before leaching are shown in Figure 2. Figure 2a shows a
3D rendering of one of the columns and Figure 2b shows
a 2D slice of the same column. The main components in
the sample are highlighted in yellow (sulphide grains), grey
(rock matrix), and black (interparticle and intraparticle
pores).
Surface-Level Techniques
Four particles (4–8 mm in diameter) were prepared for
surface-level analysis via scanning electron microscopy with
energy dispersive X-ray spectroscopy (SEM/EDX) and
X-ray photoelectron spectroscopy (XPS). Sample prepara-
tion included producing a flat surface through grinding.
These particles were placed in the designated sample cham-
bers at the top of the first column (removable sample A in
Figure 1) and at the bottom of all columns (removable sam-
ples B-D in Figure 1). For surface-level analysis, the par-
ticles were removed from their respective chambers, washed
with deionised water and dried in an oven at ~40°C for 12
hours, before analysing them with SEM/EDX and XPS.
Table 2. Estimated concentration of sulphuric acid, ferrous
ion, ferric ion, and copper added to the leaching feed
Species Concentration (g/L)
H
2 SO
4 12.0
Fe(II) 1.6
Fe(III) 1.8
Cu 0.5