3396 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Various commercializing projects outside of China, at dif-
ferent investment stages, have been announced by new and
existing players (Fleming, 2023). This paper reviews the
state of art within the hydrometallurgical processing indus-
try, paying attention to the processing options that have
been developed for leaching, purification and recovery of
Mn as products for use in the battery industry.
OVERVIEW OF THE
HYDROMETALLURGICAL RECOVERY OF
MANGANESE
The first step in the hydrometallurgical recovery of man-
ganese for ore is leaching. For most manganese ores this
requires a reduction process, to convert insoluble Mn4+
to soluble Mn2+. Even in high-grade deposits, Mn will be
associated with multiple base metals (Al, Fe) as well as Si.
Processing of low-grade waste dumps (often containing
reject fines material, which is partially liberated) can be
expected to introduce higher levels and greater varieties of
impurities.
Battery grade manganese sulfate has extremely strict
requirements for various base metal impurities especially
Fe, Ca, Cu, Cr, Mg, Na, Pb and Zn. The bulk of base metal
impurities are usually rejected from the pre-leach solution
by using either precipitation, cementation and or solvent
extraction. Although the use of ion exchange to reject traces
of base metal impurities in the impure Mn sulfate has not
been widely practised commercially, this is one of the tech-
nologies currently being explored for this purpose.
Manganese is recovered from solution either as a salt
or metal by using various processes such as evaporative
crystallisation, precipitation, and electrowinning. The tol-
erable metal impurities prior to Mn recovery depends on
the recovery route that is chosen. For example, when using
electrowinning to recover the Mn metal, impurities which
plates before the Mn must be rejected to a very low level to
prevent contamination of the Mn during electrowinning.
LEACHING OF MANGANESE ORE
Manganese ore often has extremely complex mineralogy,
with manganese present in minerals in both the divalent
(Mn2+) and tetravalent (Mn4+) oxidation states. Divalent
manganese is able to be leached under typical acid leach
conditions. However, tetravalent Mn (e.g., in the form of
pyrolusite) is known to be insoluble in dilute acidic and
alkali solutions. Extraction of manganese is facilitated by
either reductive roasting the feed stock prior to leaching or
direct leaching. Regardless of the approach, the objective is
consistent: the reduction of insoluble tetravalent manga-
nese to its soluble divalent form. The traditional approach
has been to roast manganese ore in the presence of a suit-
able reductant such as coal (Harris et al., 1977), graphite,
carbon monoxide, pyrite, elemental sulfur (Zhang et al.,
2013) or biomass such as cornstalk (Cheng et al., 2009) at
elevated temperatures (500–550°C for sulfur and biomass
and 700–950°C for coal) to convert the mineral to manga-
nese oxide prior to dissolution. Processing low-grade feed-
stocks pyrometallurgically is unfavourable both in terms of
environmental impact as well as economic feasibility due to
the high cost of operation and infrastructure in contrast to
the low manganese value contained in the feedstock.
Harris et al. reported on successful leaching of man-
ganese oxide using sulfuric acid in the presence of an
ammonium sulfate buffer following the reduction of a
high-grade manganese feed source in a rotary kiln using
coal as reductant.
Different direct leaching technologies have been
applied successfully for the extraction of manganese from
different sources. The extraction of manganese in nitrate
medium by leaching manganese dioxide with nitrogen
dioxide, resulting in the formation of manganese nitrate,
has been patented (Welsh et al., 1981). A similar patented
process from 1942 has been described (Zhang and Cheng,
2007). Another patent described involves the reaction of
manganese oxide with strong hydrochloric acid to form
manganese chloride (Zhang and Cheng, 2007). In all these
cases the cost of reagent and notorious challenges associ-
ated with material of construction are noted as significant
challenges. The leaching of low-grade manganese carbon-
ate using sulfuric acid without the need for reductant has
also been reported on (Xie et al., 2013). However, such
an option is limited to available manganese carbonate ore
bodies.
DIRECT REDUCTIVE LEACHING
Direct reductive dissolution of manganese ore has been
emphasised in research due to favourable economics and
its comparatively benign impact on the environment. The
Pourbaix diagram for manganese is presented in Figure 1
and highlights the need to operate in an acidic environment
with a low Eh to facilitate the extraction of manganese into
solution. This implies that, during direct reductive leach-
ing, some protons and a reducing agent are required to
facilitate the extraction of manganese.
Iron and iron compounds as reductants
Various authors have investigated the use of iron as reduc-
ing agent owing to the inexpensive nature and widespread
availability of iron. The use of iron from different sources in
sulfuric acid medium is discussed below.
Various commercializing projects outside of China, at dif-
ferent investment stages, have been announced by new and
existing players (Fleming, 2023). This paper reviews the
state of art within the hydrometallurgical processing indus-
try, paying attention to the processing options that have
been developed for leaching, purification and recovery of
Mn as products for use in the battery industry.
OVERVIEW OF THE
HYDROMETALLURGICAL RECOVERY OF
MANGANESE
The first step in the hydrometallurgical recovery of man-
ganese for ore is leaching. For most manganese ores this
requires a reduction process, to convert insoluble Mn4+
to soluble Mn2+. Even in high-grade deposits, Mn will be
associated with multiple base metals (Al, Fe) as well as Si.
Processing of low-grade waste dumps (often containing
reject fines material, which is partially liberated) can be
expected to introduce higher levels and greater varieties of
impurities.
Battery grade manganese sulfate has extremely strict
requirements for various base metal impurities especially
Fe, Ca, Cu, Cr, Mg, Na, Pb and Zn. The bulk of base metal
impurities are usually rejected from the pre-leach solution
by using either precipitation, cementation and or solvent
extraction. Although the use of ion exchange to reject traces
of base metal impurities in the impure Mn sulfate has not
been widely practised commercially, this is one of the tech-
nologies currently being explored for this purpose.
Manganese is recovered from solution either as a salt
or metal by using various processes such as evaporative
crystallisation, precipitation, and electrowinning. The tol-
erable metal impurities prior to Mn recovery depends on
the recovery route that is chosen. For example, when using
electrowinning to recover the Mn metal, impurities which
plates before the Mn must be rejected to a very low level to
prevent contamination of the Mn during electrowinning.
LEACHING OF MANGANESE ORE
Manganese ore often has extremely complex mineralogy,
with manganese present in minerals in both the divalent
(Mn2+) and tetravalent (Mn4+) oxidation states. Divalent
manganese is able to be leached under typical acid leach
conditions. However, tetravalent Mn (e.g., in the form of
pyrolusite) is known to be insoluble in dilute acidic and
alkali solutions. Extraction of manganese is facilitated by
either reductive roasting the feed stock prior to leaching or
direct leaching. Regardless of the approach, the objective is
consistent: the reduction of insoluble tetravalent manga-
nese to its soluble divalent form. The traditional approach
has been to roast manganese ore in the presence of a suit-
able reductant such as coal (Harris et al., 1977), graphite,
carbon monoxide, pyrite, elemental sulfur (Zhang et al.,
2013) or biomass such as cornstalk (Cheng et al., 2009) at
elevated temperatures (500–550°C for sulfur and biomass
and 700–950°C for coal) to convert the mineral to manga-
nese oxide prior to dissolution. Processing low-grade feed-
stocks pyrometallurgically is unfavourable both in terms of
environmental impact as well as economic feasibility due to
the high cost of operation and infrastructure in contrast to
the low manganese value contained in the feedstock.
Harris et al. reported on successful leaching of man-
ganese oxide using sulfuric acid in the presence of an
ammonium sulfate buffer following the reduction of a
high-grade manganese feed source in a rotary kiln using
coal as reductant.
Different direct leaching technologies have been
applied successfully for the extraction of manganese from
different sources. The extraction of manganese in nitrate
medium by leaching manganese dioxide with nitrogen
dioxide, resulting in the formation of manganese nitrate,
has been patented (Welsh et al., 1981). A similar patented
process from 1942 has been described (Zhang and Cheng,
2007). Another patent described involves the reaction of
manganese oxide with strong hydrochloric acid to form
manganese chloride (Zhang and Cheng, 2007). In all these
cases the cost of reagent and notorious challenges associ-
ated with material of construction are noted as significant
challenges. The leaching of low-grade manganese carbon-
ate using sulfuric acid without the need for reductant has
also been reported on (Xie et al., 2013). However, such
an option is limited to available manganese carbonate ore
bodies.
DIRECT REDUCTIVE LEACHING
Direct reductive dissolution of manganese ore has been
emphasised in research due to favourable economics and
its comparatively benign impact on the environment. The
Pourbaix diagram for manganese is presented in Figure 1
and highlights the need to operate in an acidic environment
with a low Eh to facilitate the extraction of manganese into
solution. This implies that, during direct reductive leach-
ing, some protons and a reducing agent are required to
facilitate the extraction of manganese.
Iron and iron compounds as reductants
Various authors have investigated the use of iron as reduc-
ing agent owing to the inexpensive nature and widespread
availability of iron. The use of iron from different sources in
sulfuric acid medium is discussed below.