XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1875
link between sustainable energy goals and the imperative
for a consistent supply of critical minerals. Therefore, there
is a pressing need to tap into secondary sources like slags,
low-grade ores, landfills, and electronic waste to meet the
rising demand. Understanding, therefore, the characteris-
tics, sources, processing, and significance of these alternative
sources is essential for effectively navigating the challenges
and opportunities they present.
Nickel is naturally present in various environments,
sourced from rocks, soils, terrestrial and aquatic species,
and widely distributed in natural flora and fauna. It exhibits
the lowest concentrations in clays, limestone, sandstones,
and shales, while its highest concentrations are found in
igneous rocks, specifically laterites or sulfides (Begum et
al., 2022). Notably, laterites represent 72% of the world’s
nickel resources on land, with the remainder being sulfides,
from which 58% of primary nickel production is sourced
(Dalvi et al., 2004). For laterite ores, commercial recovery
processes involve sulfate medium extraction, encompassing
pressure acid leaching in a sulfate-based medium, followed
by solvent extraction and electrolytic recovery. Alternatively,
chloride medium extraction involves chloride leaching,
electrowinning of the nickel chloride solution, and puri-
fication with the collection of chlorine gas, which is then
recirculated for further leaching (Moskalyk &Alfantazi,
2002). Sulfide ores traditionally undergo pyrometallurgi-
cal processes, but recent advances in hydrometallurgical
techniques have produced significantly purer products.
Both pyrometallurgical and hydrometallurgical processing
methods may be preceded by froth flotation. Nickel sul-
fide minerals can be effectively separated from their gangue
through froth flotation, utilizing thiol group collectors like
xanthates and alkyl dithiophosphates, along with activa-
tors, dispersants, and depressants. In nickel sulfide ores,
which often contain sulfides like pyrrhotite and chalcopy-
rite alongside pentlandite, maintaining a high alkaline pH
allows for the flotation of pentlandite while depressing pyr-
rhotite with cyanide, though this approach poses challenges
of pentlandite losses to tails (Rao, 2000).
Nickel and cobalt are closely associated with the pyrite
and pyrrhotite minerals (Karppinen et al., 2024), which are
mainly the tailings of the flotation process. To recover nickel
lost to tails and other associated valuable metals, hydro-
metallurgical extraction by acid leaching proves effective,
leveraging sulfuric acid for its chemical activity (Jiang et
al., 2014). While metal oxides dissolve swiftly in acids, the
dissolution of metal sulfides is accelerated in the presence of
an oxidant. Ferric ions, in particular, serve as an oxidizing
agent with the potential to enhance the dissolution of sul-
fide minerals. (Neou-Singouna &Fourlaris, 1990 Park et
al., 2006). Ferric ions, primarily sourced from FeCl3, a rec-
ognized leaching agent, or other alternatives such as ferric
sulfate (Fe2(SO4)3), are commonly utilized. The ferric ions
derived from chloride sources pose lesser environmental
concerns because the reaction yields elemental sulfur unlike
the sulfate sources which produce sulfur dioxide, similar to
the outcomes in pyrometallurgical processes (Aydogan et
al., 2005). Although the chloride ions pose challenges in
relation to its corrosive nature, recent advances have seen
successful mitigations to these issues and now the pres-
ence of chloride ions is beneficial to the leaching process as
they form complexes with the oxidized metal ions, thereby
improving the metal recovery.
Response Surface Methodology (RSM) and Central
Composite Design (CCD) which involves the use of statis-
tical and mathematical methods to model the relationship
between input parameters and output variables for pro-
cess optimization, achieved through a second-order math-
ematical model, visually represented in 2D and 3D plots
(Kökkılıç et al., 2015) is utilized to optimize the leaching
parameters and assess the combined effect of the ferric chlo-
ride catalyst in the leaching and recovery of nickel and cop-
per. The present study therefore proposes a rather efficient
ferric chloride catalyzed acid leaching of nickel and copper
from nickel sulfide flotation tailings with ferric chloride
catalyst.
EXPERIMENTAL
Materials
The rougher flotation tailing sample used in this study was
provided by Eagle Mine, USA. A representative portion
of the material was ground in a laboratory-size ball mill at
approximately 80 rev/min for 5 and 10 min to achieve 80%
passing 75 and 38 microns. The ground sample was then
used in the leaching experiments and characterization tests.
The study used analytically pure reagents, sulfuric acid, and
ferric chloride, obtained from ThermoFisher Scientific ™.
Preliminary Leaching Studies
In the initial leaching tests, 10 g of the material was dissolved
with 1 M solutions of hydrochloric acid (HCL), nitric acid
(HNO3), and sulfuric acid (H2SO4) at a temperature of
80 °C, a liquid-to-solid ratio of 10:1, and a time interval
of 2–48 hours. 300 mL graduated flasks were used for the
tests, which were carried out in a water bath. A pipette was
used to remove samples of the slurry at predetermined inter-
vals while the mixture was being stirred at a rate of roughly
200 rev/min. The slurries were then filtered via a centrifuge,
and the filtrates were subjected to Inductively Coupled
Plasma Optical Emission Spectroscopy (ICP-OES) analysis
link between sustainable energy goals and the imperative
for a consistent supply of critical minerals. Therefore, there
is a pressing need to tap into secondary sources like slags,
low-grade ores, landfills, and electronic waste to meet the
rising demand. Understanding, therefore, the characteris-
tics, sources, processing, and significance of these alternative
sources is essential for effectively navigating the challenges
and opportunities they present.
Nickel is naturally present in various environments,
sourced from rocks, soils, terrestrial and aquatic species,
and widely distributed in natural flora and fauna. It exhibits
the lowest concentrations in clays, limestone, sandstones,
and shales, while its highest concentrations are found in
igneous rocks, specifically laterites or sulfides (Begum et
al., 2022). Notably, laterites represent 72% of the world’s
nickel resources on land, with the remainder being sulfides,
from which 58% of primary nickel production is sourced
(Dalvi et al., 2004). For laterite ores, commercial recovery
processes involve sulfate medium extraction, encompassing
pressure acid leaching in a sulfate-based medium, followed
by solvent extraction and electrolytic recovery. Alternatively,
chloride medium extraction involves chloride leaching,
electrowinning of the nickel chloride solution, and puri-
fication with the collection of chlorine gas, which is then
recirculated for further leaching (Moskalyk &Alfantazi,
2002). Sulfide ores traditionally undergo pyrometallurgi-
cal processes, but recent advances in hydrometallurgical
techniques have produced significantly purer products.
Both pyrometallurgical and hydrometallurgical processing
methods may be preceded by froth flotation. Nickel sul-
fide minerals can be effectively separated from their gangue
through froth flotation, utilizing thiol group collectors like
xanthates and alkyl dithiophosphates, along with activa-
tors, dispersants, and depressants. In nickel sulfide ores,
which often contain sulfides like pyrrhotite and chalcopy-
rite alongside pentlandite, maintaining a high alkaline pH
allows for the flotation of pentlandite while depressing pyr-
rhotite with cyanide, though this approach poses challenges
of pentlandite losses to tails (Rao, 2000).
Nickel and cobalt are closely associated with the pyrite
and pyrrhotite minerals (Karppinen et al., 2024), which are
mainly the tailings of the flotation process. To recover nickel
lost to tails and other associated valuable metals, hydro-
metallurgical extraction by acid leaching proves effective,
leveraging sulfuric acid for its chemical activity (Jiang et
al., 2014). While metal oxides dissolve swiftly in acids, the
dissolution of metal sulfides is accelerated in the presence of
an oxidant. Ferric ions, in particular, serve as an oxidizing
agent with the potential to enhance the dissolution of sul-
fide minerals. (Neou-Singouna &Fourlaris, 1990 Park et
al., 2006). Ferric ions, primarily sourced from FeCl3, a rec-
ognized leaching agent, or other alternatives such as ferric
sulfate (Fe2(SO4)3), are commonly utilized. The ferric ions
derived from chloride sources pose lesser environmental
concerns because the reaction yields elemental sulfur unlike
the sulfate sources which produce sulfur dioxide, similar to
the outcomes in pyrometallurgical processes (Aydogan et
al., 2005). Although the chloride ions pose challenges in
relation to its corrosive nature, recent advances have seen
successful mitigations to these issues and now the pres-
ence of chloride ions is beneficial to the leaching process as
they form complexes with the oxidized metal ions, thereby
improving the metal recovery.
Response Surface Methodology (RSM) and Central
Composite Design (CCD) which involves the use of statis-
tical and mathematical methods to model the relationship
between input parameters and output variables for pro-
cess optimization, achieved through a second-order math-
ematical model, visually represented in 2D and 3D plots
(Kökkılıç et al., 2015) is utilized to optimize the leaching
parameters and assess the combined effect of the ferric chlo-
ride catalyst in the leaching and recovery of nickel and cop-
per. The present study therefore proposes a rather efficient
ferric chloride catalyzed acid leaching of nickel and copper
from nickel sulfide flotation tailings with ferric chloride
catalyst.
EXPERIMENTAL
Materials
The rougher flotation tailing sample used in this study was
provided by Eagle Mine, USA. A representative portion
of the material was ground in a laboratory-size ball mill at
approximately 80 rev/min for 5 and 10 min to achieve 80%
passing 75 and 38 microns. The ground sample was then
used in the leaching experiments and characterization tests.
The study used analytically pure reagents, sulfuric acid, and
ferric chloride, obtained from ThermoFisher Scientific ™.
Preliminary Leaching Studies
In the initial leaching tests, 10 g of the material was dissolved
with 1 M solutions of hydrochloric acid (HCL), nitric acid
(HNO3), and sulfuric acid (H2SO4) at a temperature of
80 °C, a liquid-to-solid ratio of 10:1, and a time interval
of 2–48 hours. 300 mL graduated flasks were used for the
tests, which were carried out in a water bath. A pipette was
used to remove samples of the slurry at predetermined inter-
vals while the mixture was being stirred at a rate of roughly
200 rev/min. The slurries were then filtered via a centrifuge,
and the filtrates were subjected to Inductively Coupled
Plasma Optical Emission Spectroscopy (ICP-OES) analysis