3398 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
influence of reductant to manganese dioxide ratio and acid
concentration were consistent with that of iron metal.
The use of ferrous ions is less favourable compared to
metallic iron, since the dissolution of metallic iron ensures
constant availability of ferrous ions to the system as the
reaction progresses, whereas ferrous ions introduced to the
system as ferrous sulfate would be expected to speciate and
oxidize to form a portion of ferric iron (Bafghi et al., 2008)
Organic Acids and Other Organic Reductants
The use of organic acids and other organic reductants have
garnered attention as reductants due to their propensity to
release less harmful gasses compared to inorganic reduc-
tants (Sinha and Purcell, 2019). Organic materials such
as biomass and agricultural wastes are also inexpensive in
nature, making them an attractive proposition.
Oxalic Acid
Oxalic acid was studied as a reductant in sulfuric acid media
at elevated temperatures (Sahoo et al., 2001). The proposed
reaction is as follows:
MnO2 (s) +C2H2O4 (aq) +2H+(aq) →
Mn2+
(aq) +2CO2
(aq) +2H2O
(l) (10)
Oxalic acid could effectively reduce manganese, achieving
extractions efficiencies up to 98.4% in 105 min. The study
found that reductant concentration, acid concentration
and temperature all had a positive effect on the extraction
of manganese.
Glucose and Sucrose
The use of sucrose (Wang et al., 2017) and a combination
of sucrose and glucose in the form of cane molasses (Su
et al., 2008) have been investigated. Su et al. presents the
following stoichiometry for the reduction reactions with
sucrose and glucose respectively:
24MnO2
(s) +C12H22O11
(aq) +24H2SO4
(aq) →
24MnSO4
(aq) +12CO2
(aq) +35H2O
(l) (11
12MnO2
(s) +C6H12O6
(aq) +12H2SO4
(aq) →
12MnSO4 (aq) +6CO2 (aq) +18H2O (l) (12)
Both authors indicated positive relationships between
manganese extraction and reductant concentration, acid
concentration and temperature. Manganese extraction effi-
ciencies above 90% were achieved at 90°C under 120 min.
A similar study was completed using glucose to leach fines
rejects from an EMD production circuit where the same
effects of reductant, acid and temperature were observed
(Konighofer, 2004).
The use of biomass and agricultural wastes have also
been studied for use as reductants in the extraction of man-
ganese since cellulose is a linear polymer of glucose (Sinha
and Purcell, 2019). Sawdust was used as a reductant dur-
ing an investigation where the finding was that 98% Mn
extraction could be achieved from a low-grade ore at 90°C
in 8 h in the presence of sulfuric acid (Hariprasad et al.,
2007). A positive relationship between manganese extrac-
tion and reductant concentration, acid concentration and
temperature were observed.
Hydrogen Peroxide
The leaching of high-grade manganese dioxide using
hydrogen peroxide was studied by Nayl et al in sulfuric acid
medium. While the reagent is commonly used as a strong
oxidant, it behaves as a reductant owing to the strong oxi-
dizing nature of manganese dioxide. The proposed reaction
mechanism is presented below (Sinha and Purcell, 2019):
MnO2 (s) +H2O2 (aq) +H2SO4 (aq) → MnSO4 (aq) +
2H2O
(l) +O2
(g) (13)
A positive relationship between manganese extraction
and reductant concentration, acid concentration and tem-
perature was observed during the study by Nayl et al. The
highest manganese extraction achieved was found to be
92%.
Aqueous Sulfur Dioxide
By far, the most predominant reductant studied for the
leaching of manganese dioxide is aqueous sulfur dioxide,
due to its dual function as a reductant and weak acid.
When using sulfur dioxide as reductant, it is important
to consider its speciation in solution. As per Sinha and
Purcell, it is commonly thought that the speciation of SO2
is pH dependent and the predominant species at various
pH intervals occurs as shown in Table 1. This is highlighted
in Figure 2.
Leaching of manganese dioxide predominantly takes
place according to Equation 14, but other reactions with
different sulfur species and other side reactions will also
occur depending on reactor conditions (Das et al., 2000
Kejie He et al., 2018 Sinha and Purcell, 2019):
MnO2
(s) +SO2
(aq) → MnSO4
(aq) (14)
Table 1. Speciation of SO2 as a function of pH
pH Range Predominant Species
1.5 SO2
1.5–5.5 HSO3–
5.5 SO
3
2–
influence of reductant to manganese dioxide ratio and acid
concentration were consistent with that of iron metal.
The use of ferrous ions is less favourable compared to
metallic iron, since the dissolution of metallic iron ensures
constant availability of ferrous ions to the system as the
reaction progresses, whereas ferrous ions introduced to the
system as ferrous sulfate would be expected to speciate and
oxidize to form a portion of ferric iron (Bafghi et al., 2008)
Organic Acids and Other Organic Reductants
The use of organic acids and other organic reductants have
garnered attention as reductants due to their propensity to
release less harmful gasses compared to inorganic reduc-
tants (Sinha and Purcell, 2019). Organic materials such
as biomass and agricultural wastes are also inexpensive in
nature, making them an attractive proposition.
Oxalic Acid
Oxalic acid was studied as a reductant in sulfuric acid media
at elevated temperatures (Sahoo et al., 2001). The proposed
reaction is as follows:
MnO2 (s) +C2H2O4 (aq) +2H+(aq) →
Mn2+
(aq) +2CO2
(aq) +2H2O
(l) (10)
Oxalic acid could effectively reduce manganese, achieving
extractions efficiencies up to 98.4% in 105 min. The study
found that reductant concentration, acid concentration
and temperature all had a positive effect on the extraction
of manganese.
Glucose and Sucrose
The use of sucrose (Wang et al., 2017) and a combination
of sucrose and glucose in the form of cane molasses (Su
et al., 2008) have been investigated. Su et al. presents the
following stoichiometry for the reduction reactions with
sucrose and glucose respectively:
24MnO2
(s) +C12H22O11
(aq) +24H2SO4
(aq) →
24MnSO4
(aq) +12CO2
(aq) +35H2O
(l) (11
12MnO2
(s) +C6H12O6
(aq) +12H2SO4
(aq) →
12MnSO4 (aq) +6CO2 (aq) +18H2O (l) (12)
Both authors indicated positive relationships between
manganese extraction and reductant concentration, acid
concentration and temperature. Manganese extraction effi-
ciencies above 90% were achieved at 90°C under 120 min.
A similar study was completed using glucose to leach fines
rejects from an EMD production circuit where the same
effects of reductant, acid and temperature were observed
(Konighofer, 2004).
The use of biomass and agricultural wastes have also
been studied for use as reductants in the extraction of man-
ganese since cellulose is a linear polymer of glucose (Sinha
and Purcell, 2019). Sawdust was used as a reductant dur-
ing an investigation where the finding was that 98% Mn
extraction could be achieved from a low-grade ore at 90°C
in 8 h in the presence of sulfuric acid (Hariprasad et al.,
2007). A positive relationship between manganese extrac-
tion and reductant concentration, acid concentration and
temperature were observed.
Hydrogen Peroxide
The leaching of high-grade manganese dioxide using
hydrogen peroxide was studied by Nayl et al in sulfuric acid
medium. While the reagent is commonly used as a strong
oxidant, it behaves as a reductant owing to the strong oxi-
dizing nature of manganese dioxide. The proposed reaction
mechanism is presented below (Sinha and Purcell, 2019):
MnO2 (s) +H2O2 (aq) +H2SO4 (aq) → MnSO4 (aq) +
2H2O
(l) +O2
(g) (13)
A positive relationship between manganese extraction
and reductant concentration, acid concentration and tem-
perature was observed during the study by Nayl et al. The
highest manganese extraction achieved was found to be
92%.
Aqueous Sulfur Dioxide
By far, the most predominant reductant studied for the
leaching of manganese dioxide is aqueous sulfur dioxide,
due to its dual function as a reductant and weak acid.
When using sulfur dioxide as reductant, it is important
to consider its speciation in solution. As per Sinha and
Purcell, it is commonly thought that the speciation of SO2
is pH dependent and the predominant species at various
pH intervals occurs as shown in Table 1. This is highlighted
in Figure 2.
Leaching of manganese dioxide predominantly takes
place according to Equation 14, but other reactions with
different sulfur species and other side reactions will also
occur depending on reactor conditions (Das et al., 2000
Kejie He et al., 2018 Sinha and Purcell, 2019):
MnO2
(s) +SO2
(aq) → MnSO4
(aq) (14)
Table 1. Speciation of SO2 as a function of pH
pH Range Predominant Species
1.5 SO2
1.5–5.5 HSO3–
5.5 SO
3
2–