XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1723
products. (Rozelle et al., 2021 Shekarian et al., 2022
Vaziri Hassas 2022).
Staged precipitation has been investigated as a poten-
tial method for selectively recovering critical elements from
AMD. For example, the authors developed a patented
staged carbonate precipitation process for selective recovery
of Fe, Al, and REEs from AMD at pH values below the
target treatment pH (i.e., 7) (Rezaee et al., 2021). However,
recovery of Co and Mn while neutralizing AMD is a chal-
lenge due to the required elevated pH or use of costly oxi-
dants for their precipitation. Typically, the precipitation
of these elements starts at pH ~9 through conventional
hydroxide or ammonical AMD treatment, and achieving a
high recovery needs an even higher pH (~10.5) (Balintova
and Petrilakova., 2011 Shekarian et al., 2022). Oxidative
precipitation has been documented to be very effective in
the hydrometallurgical processing of Co-Mn (Bolton et al.,
1981 Zhang and Cheng, 2007 Zhang et al., 2010 Freitas
et al., 2013 Shekarian et al., 2022). Various oxidants,
including SO2/O2, ozone (O3), Caro’s acid (H2SO5), per-
oxydisulfuric acid (H2S2O8), hypochlorite (ClO–) and
chlorite, sodium persulfate (Na2S2O8), and potassium
permanganate (KMnO4), have been used for Mn and Co
recovery from aqueous solutions (Van Rooyen et al., 2007
Zhang and Cheng, 2007 Zhang et al., 2010 Joo et al.,
2013 Freitas et al., 2013). As an example, utilizing SO2/
air mixture, Zhang et al., 2010 recovered more than 99%
of Mn from laterite waste solutions with minimal Ca-Mg
co-precipitation and chemical consumption, offering oxi-
dative precipitations as an efficient and selective recovery
approach for treating hydrometallurgical waste streams. A
previous study found that parameters including flow rate,
ion concentration, ozone partial pressure, and temperature,
impact the Co recovery from a chloride solution utilizing
ozone (Tian et al., 2017). In previously published work by
the authors, ozone was identified as the most effective oxi-
dizing agent for extracting Co and Mn from AMD at cir-
cumneutral pH, providing a chemical-less and eco-friendly
extraction process (Shekarian et al., 2022). Ozone, a potent
oxidizing agent, reacts with Co-Mn to form insoluble metal
oxides or oxyhydroxides, that precipitate out of the solu-
tion. The following reactions could represent the overall
reactions:
Co2+ +O3 +H2O → CoO(OH) +O2 (R1)
2Mn2+ +2O3 → 2MnO2 +O2 (R2)
Moreover, ozone has the potential to recover other
critical elements like Ni, Pb, Cu, Mn, Ag, and Pd if present
in aqueous solutions, such as AMD. The effects of process
parameters, including flow rate, stirring rate, and tempera-
ture, and their interaction on ozone oxidative precipitation
of Co and Mn have not been reported in the published lit-
erature. Moreover, the existing literature on the kinetics of
Co and Mn precipitation using ozone is limited (Jing et al.,
2014 Cruz-Díaz et al., 2015 Tian et al., 2017 Oruê et al.,
2021 Qu et al., 2022). Therefore, a detailed exploration of
the kinetics is essential to enhance our understanding of the
ozone-based recovery process.
In this study, the effects of stirring rate, oxygen flow
rate, and temperature on the oxidative precipitation of
ozone were investigated to determine the significant fac-
tors and maximize the recovery of Co-Mn from AMD.
Furthermore, the kinetics of Co and Mn precipitations
were measured to determine their precipitation rates. For
this purpose, various kinetics models, including Linear,
Higbie, and Pseudo-homogeneous, were evaluated to fit
the data obtained from kinetic experiments, and activation
energy values were calculated. The outcomes of this study
carry significant implications for the development, design,
and scale-up of the ozone oxidative precipitation process
aimed at recovering Co and Mn from AMD.
MATERIAL AND METHODS
Materials
For this study, about 800 liters of representative sam-
ples of AMD were collected from a treatment facility in
Pennsylvania operated by the Pennsylvania Department of
Environmental Protection (PADEP). Sampling AMD from
the Lower Kittanning coal seam was conducted at feed
points to the treatment facility. The elemental composition
of AMD, with a pH of 3.5, showed a significant concen-
tration of critical elements, such as Al (45.6 ppm), REE
(0.5 ppm), Co (0.9 ppm), and Mn (41.8 ppm), underscor-
ing its potential as a secondary resource of multiple critical
elements.
Methods
Solution Chemistry
The saturation index (SI) is an aqueous processing concept
that can be applied to any scenario of the dissolution or
precipitation of a solid from a solution. SI provides infor-
mation about whether the solution is at equilibrium, under-
saturated, or supersaturated with respect to the product
mineral (i.e., CoOOH and MnO2). SI for Co and Mn at
different pH with the corresponding precipitants were cal-
culated utilizing the Visual MINTEQ software. Pourbaix
diagrams of Co and Mn at 25 °C were constructed utilizing
MEDUSA software. For the solution chemistry study, the
concentration of Co and Mn were similar to those of the
products. (Rozelle et al., 2021 Shekarian et al., 2022
Vaziri Hassas 2022).
Staged precipitation has been investigated as a poten-
tial method for selectively recovering critical elements from
AMD. For example, the authors developed a patented
staged carbonate precipitation process for selective recovery
of Fe, Al, and REEs from AMD at pH values below the
target treatment pH (i.e., 7) (Rezaee et al., 2021). However,
recovery of Co and Mn while neutralizing AMD is a chal-
lenge due to the required elevated pH or use of costly oxi-
dants for their precipitation. Typically, the precipitation
of these elements starts at pH ~9 through conventional
hydroxide or ammonical AMD treatment, and achieving a
high recovery needs an even higher pH (~10.5) (Balintova
and Petrilakova., 2011 Shekarian et al., 2022). Oxidative
precipitation has been documented to be very effective in
the hydrometallurgical processing of Co-Mn (Bolton et al.,
1981 Zhang and Cheng, 2007 Zhang et al., 2010 Freitas
et al., 2013 Shekarian et al., 2022). Various oxidants,
including SO2/O2, ozone (O3), Caro’s acid (H2SO5), per-
oxydisulfuric acid (H2S2O8), hypochlorite (ClO–) and
chlorite, sodium persulfate (Na2S2O8), and potassium
permanganate (KMnO4), have been used for Mn and Co
recovery from aqueous solutions (Van Rooyen et al., 2007
Zhang and Cheng, 2007 Zhang et al., 2010 Joo et al.,
2013 Freitas et al., 2013). As an example, utilizing SO2/
air mixture, Zhang et al., 2010 recovered more than 99%
of Mn from laterite waste solutions with minimal Ca-Mg
co-precipitation and chemical consumption, offering oxi-
dative precipitations as an efficient and selective recovery
approach for treating hydrometallurgical waste streams. A
previous study found that parameters including flow rate,
ion concentration, ozone partial pressure, and temperature,
impact the Co recovery from a chloride solution utilizing
ozone (Tian et al., 2017). In previously published work by
the authors, ozone was identified as the most effective oxi-
dizing agent for extracting Co and Mn from AMD at cir-
cumneutral pH, providing a chemical-less and eco-friendly
extraction process (Shekarian et al., 2022). Ozone, a potent
oxidizing agent, reacts with Co-Mn to form insoluble metal
oxides or oxyhydroxides, that precipitate out of the solu-
tion. The following reactions could represent the overall
reactions:
Co2+ +O3 +H2O → CoO(OH) +O2 (R1)
2Mn2+ +2O3 → 2MnO2 +O2 (R2)
Moreover, ozone has the potential to recover other
critical elements like Ni, Pb, Cu, Mn, Ag, and Pd if present
in aqueous solutions, such as AMD. The effects of process
parameters, including flow rate, stirring rate, and tempera-
ture, and their interaction on ozone oxidative precipitation
of Co and Mn have not been reported in the published lit-
erature. Moreover, the existing literature on the kinetics of
Co and Mn precipitation using ozone is limited (Jing et al.,
2014 Cruz-Díaz et al., 2015 Tian et al., 2017 Oruê et al.,
2021 Qu et al., 2022). Therefore, a detailed exploration of
the kinetics is essential to enhance our understanding of the
ozone-based recovery process.
In this study, the effects of stirring rate, oxygen flow
rate, and temperature on the oxidative precipitation of
ozone were investigated to determine the significant fac-
tors and maximize the recovery of Co-Mn from AMD.
Furthermore, the kinetics of Co and Mn precipitations
were measured to determine their precipitation rates. For
this purpose, various kinetics models, including Linear,
Higbie, and Pseudo-homogeneous, were evaluated to fit
the data obtained from kinetic experiments, and activation
energy values were calculated. The outcomes of this study
carry significant implications for the development, design,
and scale-up of the ozone oxidative precipitation process
aimed at recovering Co and Mn from AMD.
MATERIAL AND METHODS
Materials
For this study, about 800 liters of representative sam-
ples of AMD were collected from a treatment facility in
Pennsylvania operated by the Pennsylvania Department of
Environmental Protection (PADEP). Sampling AMD from
the Lower Kittanning coal seam was conducted at feed
points to the treatment facility. The elemental composition
of AMD, with a pH of 3.5, showed a significant concen-
tration of critical elements, such as Al (45.6 ppm), REE
(0.5 ppm), Co (0.9 ppm), and Mn (41.8 ppm), underscor-
ing its potential as a secondary resource of multiple critical
elements.
Methods
Solution Chemistry
The saturation index (SI) is an aqueous processing concept
that can be applied to any scenario of the dissolution or
precipitation of a solid from a solution. SI provides infor-
mation about whether the solution is at equilibrium, under-
saturated, or supersaturated with respect to the product
mineral (i.e., CoOOH and MnO2). SI for Co and Mn at
different pH with the corresponding precipitants were cal-
culated utilizing the Visual MINTEQ software. Pourbaix
diagrams of Co and Mn at 25 °C were constructed utilizing
MEDUSA software. For the solution chemistry study, the
concentration of Co and Mn were similar to those of the