3428 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
The high iron (~18% Fe2O3) and silica (~10% SiO2)
contents render this ore unsuitable for beneficiation by the
conventional dense media separation (DMS) route. The
manganese was present mainly as pyrolusite (manganese
dioxide, MnO2), which is insoluble in either acidic or alka-
line media. Reducing it to Mn(II) would render it soluble
in acidic media. Thus, a reductive leaching route in dilute
sulfuric acid followed by a purifying step consisting of sev-
eral separation techniques including iron removal step to
address the high iron content, which is soluble in acidic
media, selective precipitation, ion exchange and solvent
extraction was conceived.
REDUCTIVE LEACHING OF MANGANESE
The reductive leaching of manganese dioxide (MnO2)
using sulfur dioxide as reductant has long been known.
Other reductants have been used too such, for example,
pyrite (Chen et al. 2021) and even sucrose (Veglio and
Toro 1993). A review of reducing agents in the leaching of
manganese ores by Sinha and Purcell (2019) is particularly
informative work. Most works, however, used pure man-
ganese dioxide. No industrial application of the technique
was found in the literature. In the present work, the reduc-
tive leaching was carried out using dilute sulfuric acid (0.5
M) and sulphur dioxide (SO2) gas as reductant. Equation 1
(EQ 1) represents the leaching reaction.
MnO2(s) +SO2(g) → Mn2+(aq) +SO42– (1)
Figure 1 shows the leaching setup consisting of a
wide-neck glass reactor to accommodate an overhead stir-
rer and inlets for the reducing gas, Eh and pH measure-
ment, temperature measurement and withdrawal of assay
samples. The reactor was mounted on a hotplate to allow
temperature control. An overhead stirrer was used to agitate
the slurry.
The sulphur dioxide (SO2) gas was introduced through
a gas sparger from an SO2 gas cylinder. The temperature
was controlled using a digital thermocouple immersed in
the leach vessel. The slurry was agitated at 550 rpm using
a twin blade impellor driven by an overhead stirrer. The
temperature, redox potential and pH were monitored using
in-situ probes and recorded at the sampling time intervals.
Dried composite sample was weighed (1 kg) and
charged into the reactor. Dilute sulfuric acid (0.5 M) was
added such that the solid to liquid ratio was 1:4. The mix-
ture was stirred to form a slurry and the hotplate was turned
on to reach the target temperature. Then, the SO2 gas was
added at a flow rate of 1.0 L/min to achieve a 500% stoichi-
ometry target. The results are summarised in Table 2 while
Figure 2 shows the manganese extraction as a function of
added SO2 and leaching time.
Nearly all the manganese (99%) was extracted
but it also generated a highly contaminated PLS. Iron
(11,290 mg/L) and aluminium (1,932 mg/L) were the
main contaminants of the PLS but more than ninety per-
cent of each of the soluble oxides namely calcium, potas-
sium, magnesium and sodium were also also extracted.
Substantial amounts of the other transition metals such as
cobalt (129 mg/L), copper (75 mg/L), nickel (64 mg/L),
and zinc (10 mg/L) were also extracted. Clearly, the puri-
fying step is the main challenge and would determine the
viability of the process.
It is reasonable to suggest that significant improvement
in terms of efficiency of process is achievable but, at this
Figure 1. Reductive leaching set up
Table 2. Assay of the pregnant liquor solution (PLS)
Element
Concentration
(mg/L) Extraction (%)
Al 1,932 62.75
Ba 1 0.09
Ca 470 93.69
Co 129 97.10
Cr 16 23.78
Cu 74.6 94.89
Fe 11,290 31.67
K 3630 95.08
Mg 524 91.61
Mn 115,000 99.29
Na 652 94.56
Ni 67.5 63.81
P 110 78.77
Pb 17 38.13
Ti 21 16.99
Zn 10.4 84.38
The high iron (~18% Fe2O3) and silica (~10% SiO2)
contents render this ore unsuitable for beneficiation by the
conventional dense media separation (DMS) route. The
manganese was present mainly as pyrolusite (manganese
dioxide, MnO2), which is insoluble in either acidic or alka-
line media. Reducing it to Mn(II) would render it soluble
in acidic media. Thus, a reductive leaching route in dilute
sulfuric acid followed by a purifying step consisting of sev-
eral separation techniques including iron removal step to
address the high iron content, which is soluble in acidic
media, selective precipitation, ion exchange and solvent
extraction was conceived.
REDUCTIVE LEACHING OF MANGANESE
The reductive leaching of manganese dioxide (MnO2)
using sulfur dioxide as reductant has long been known.
Other reductants have been used too such, for example,
pyrite (Chen et al. 2021) and even sucrose (Veglio and
Toro 1993). A review of reducing agents in the leaching of
manganese ores by Sinha and Purcell (2019) is particularly
informative work. Most works, however, used pure man-
ganese dioxide. No industrial application of the technique
was found in the literature. In the present work, the reduc-
tive leaching was carried out using dilute sulfuric acid (0.5
M) and sulphur dioxide (SO2) gas as reductant. Equation 1
(EQ 1) represents the leaching reaction.
MnO2(s) +SO2(g) → Mn2+(aq) +SO42– (1)
Figure 1 shows the leaching setup consisting of a
wide-neck glass reactor to accommodate an overhead stir-
rer and inlets for the reducing gas, Eh and pH measure-
ment, temperature measurement and withdrawal of assay
samples. The reactor was mounted on a hotplate to allow
temperature control. An overhead stirrer was used to agitate
the slurry.
The sulphur dioxide (SO2) gas was introduced through
a gas sparger from an SO2 gas cylinder. The temperature
was controlled using a digital thermocouple immersed in
the leach vessel. The slurry was agitated at 550 rpm using
a twin blade impellor driven by an overhead stirrer. The
temperature, redox potential and pH were monitored using
in-situ probes and recorded at the sampling time intervals.
Dried composite sample was weighed (1 kg) and
charged into the reactor. Dilute sulfuric acid (0.5 M) was
added such that the solid to liquid ratio was 1:4. The mix-
ture was stirred to form a slurry and the hotplate was turned
on to reach the target temperature. Then, the SO2 gas was
added at a flow rate of 1.0 L/min to achieve a 500% stoichi-
ometry target. The results are summarised in Table 2 while
Figure 2 shows the manganese extraction as a function of
added SO2 and leaching time.
Nearly all the manganese (99%) was extracted
but it also generated a highly contaminated PLS. Iron
(11,290 mg/L) and aluminium (1,932 mg/L) were the
main contaminants of the PLS but more than ninety per-
cent of each of the soluble oxides namely calcium, potas-
sium, magnesium and sodium were also also extracted.
Substantial amounts of the other transition metals such as
cobalt (129 mg/L), copper (75 mg/L), nickel (64 mg/L),
and zinc (10 mg/L) were also extracted. Clearly, the puri-
fying step is the main challenge and would determine the
viability of the process.
It is reasonable to suggest that significant improvement
in terms of efficiency of process is achievable but, at this
Figure 1. Reductive leaching set up
Table 2. Assay of the pregnant liquor solution (PLS)
Element
Concentration
(mg/L) Extraction (%)
Al 1,932 62.75
Ba 1 0.09
Ca 470 93.69
Co 129 97.10
Cr 16 23.78
Cu 74.6 94.89
Fe 11,290 31.67
K 3630 95.08
Mg 524 91.61
Mn 115,000 99.29
Na 652 94.56
Ni 67.5 63.81
P 110 78.77
Pb 17 38.13
Ti 21 16.99
Zn 10.4 84.38