TITLE:
Method for preparing high-purity manganese carbonate and by-products through low and
Medium Grade Manganese Oxide Ores
FIELD OF INVENTION:
This invention relates to a method for preparing high purity manganese carbonate and by-
products from medium and low grade manganese oxide.
BACKGROUND OF THE INVENTION:
High purity manganese carbonate is a strategic material for production of various end products
like electrolytic manganese dioxide (EMD), chemical manganese dioxide (CMD), electrolytic
manganese metal (EMM) and other manganese bearing oxide materials. Other than being raw
material, it has direct application in the manufacturing of communications equipment in a high-
performance magnetic materials Mn-Zn ferrite, acts as cattle feed, and even acts as pigment in
paint industries. Current method for production of high purity manganese carbonate is by
dissolution and leaching of manganese based oxide material or manganese metal in nitric acid
solution and followed by precipitation of manganese carbonate. The main drawback of this
commercial process is having higher cost involved, as starting raw material are manganese metal

or synthetic manganese dioxide and nitic acid as leaching medium. Thus, in order to lower the
production costs, manganese bearing ores can be utilized as potential raw material for leaching
with sulfuric acid or ammonical leaching along with sulfur dioxide as reductant.
Secondly, naturally occurring rhodochrosite (manganese carbonate) ores have depleted due to
heavy utilization as raw materials for making manganese based chemicals. In place of high grade
low grade rhodochrosite ores can be used for extraction, but those lead to heavy leaching cost
involved to due to complex mineralogy of these ores leads to higher CAPEX and OPEX. As the
mineralogy of these low grades of manganese ores are very complex due to presence of gangue
minerals like iron, alumina and silica along with manganese. Thus, in order to extract manganese
as manganese carbonate there is additional step of beneficiation which need to be addressed in
the process separation. Low grade ferrogenois manganese oxide ores are another potential
material which can be used as potential material from production of high purity manganese
carbonate using hydrometallurgical steps without having environmental pollution.
Manganese carbonate is valuable material for many industrial products like pigments, for
preparation of soft magnets, cattle feed and as food supplement Other than this, manganese
carbonate is raw material for production of manganese based salts. Secondly, utilization of high
iron bearing low grade manganese ore for preparation of high purity manganese carbonate has
not being explored. Few patents describe the method for preparation of manganese salt based on
low grade manganese carbonate ores. For example, a method for preparation of manganese
carbonate from low grade rodhochrosite ore has been disclosed in CN105152152A, wherein low

grade rhodochrosite was leached with sulphuric acid followed by solution preparation to obtain
primarily manganese carbonate along with other by products. The specific process comprises the
steps that 1, N and P compound fertilizer base materials are prepared; 2, orthophosphoric acid
iron powder is recycled; 3, cobalt, nickel and copper concentrate is recycled; 4, aluminium
hydroxide powder is recycled; 5, land plaster is recycled; 6, high-purity manganese carbonate
powder is prepared; 7, magnesium ammonium phosphate slow-release compound fertilizer is
prepared. In patent application CN104294038A, manganese carbonate is prepared from silver-
manganese ores. In their process, silver-manganese ore is used as primary raw material for
extraction of manganese by sulphuric acid route followed by removal of iron was carried out by
addition of pure MnO2 or MnCO3 as oxidant Subsequently, heavy metals are extracted from
leach liquor by sulfuration process. Ammonium carbonate was used for precipitation of
manganese as manganese carbonate. Silver was subsequently leached in second stage and
extracted with recovery of 95%. A similar process was described by CN1101328A, where
primary raw material used was rodhochrosite ore and leaching with sulphuring acid and finally
precipitation was carried out by ammonium carbonate. In patent application CN104480314A, a
innovative method for recycling of waste reside from manganese residue for production
manganese carbonate has been elaborated. The method comprises of specific steps: (a) pre-
processing of filter residue; (b) leaching the manganese and iron value with sulphuric acid; (c)
recovery of iron value as hematite powder; (d) recovery of manganese carbonate concentrate;
and (e) preparation of a nitrogen-phosphorus compound fertilizer base material. Another patent

application CN105084421A, proposes a process for producing carbonates of manganese by
reduction-roasting followed by acid leaching of low grade pyrolusite. The method comprises of
reduction roasting followed by magnetic separation of iron value from the product to form ferric
phosphate powder. Manganese based residue is leached with sulphuric acid to produce
manganese carbonate in similar fashion as described by other patent literatures discussed above.
Other than manganese carbonate, aluminium hydroxide, gypsum powder and N-P compound
fertilizer is produced. A similar method for preparation of manganese carbonate has been
described in other patent applications as well (CN105152153A, CN102660689A,
CN102605186A and CN102220491 A). As can been seen from the prior art references that
almost all the inventions have used rodhochrosite as manganese source for preparation of
carbonate following sulphuric acid route. Secondly, low grade rodhochrosite ores doesn't have
iron which, thus iron removal and hence the loss of intermittent loss of manganese is not a
problem. In ano pyrolusite ore was roasted followed by leaching with sulphuric acid to produce
manganese carbonate. All the studies pertaining to manganese carbonate preparation was through
sulphuric acid route. Since most of manganese in low grade manganese ore is present in Mn(IV)
oxidation state and in order to reduce the manganese, reductant needs to added. Overall
manganese carbonate production through leaching in sulphuric acid of low grade rodhochrosite
is established process route, but no study has been published which deals with low grade
manganese ores with iron content with Mn:Fe ratio: 0.9-1.1. Therefore, a new one step process

route for production of manganese carbonate from low grade pyrolusite ore has been established
while leaching in hydrochloric acid, followed by removal of iron via solvent extraction. Iron
which is removed is obtained as hematite powder and manganese is precipitated as manganese
carbonate with recovery of copper, nickel and cobalt concentrate. Hydrochloric acid (HC1) has
employed as leaching agent for leaching manganese from pyrolusite since HC1 leads to form
more stable metal-chloro complex. Since the complex the stable, the activity of manganese ion in
solution is less, leads to enhance more manganese dissolution from the ore and hence leads
recovery in leaching.
OBJECTS OF THE INVENTION:
An object of the present invention is to propose a method for preparing high purity manganese
carbonate and by-products from medium and low grade manganese oxide.
Another object of the present invention is to propose a single step hydrometallurgical process for
treating low grade high iron bearing pyrolusite ore for production of high purity manganese
carbonate as primary product
Still another object of this invention is to obtain by products like copper-nickel-cobalt
concentrate, nano size hematite powder and gypsum.

Further object of the present invention is to use leaching combined with solvent extraction for
removal of iron from the pregnant leach liquor using combination of two extraction organic
solvents: D2EPHA and diethyl ether.
Still further object of this invention to usage of hydrochloric acid as primary leaching agent
along with hydrogen peroxide as oxidant for leaching of low grade manganese oxide ores.
A still another object of this invention is to produce calcium sulphate from the solution after
manganese carbonate precipitation.
BRIEF DESCRIPTION OF THE INVENTION:
This invention relates to a method for preparing high purity manganese carbonate and by-
products from medium and low grade manganese oxide comprising:
crushing and pulverizing the manganese raw material,
subjecting the crushed and pulverized ore to the step of leaching with an acid and reductant,
separating the residue from the leach liquor by solid-liquid separation;
subjecting the leach liquor to the step of solvent extraction to separate iron,
remaining iron and aluminum from the liquor in the form of hydroxide and copper, nickel and
cobalt in the form of sulphide,
adding ammonium bicarbonate to the leach liquor to increase the pH followed by addition of
sodium carbonate to precipitate manganese carbonate,

subjecting the manganese carbonate thus obtained to the step of washing and drying,
precipitating calcium finally from the liquor in the form of gypsum.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1.Process flow diagram for manganese carbonate from lean grade manganese ores.
Figure 2.Microstructure for low grade manganese ore.
Figure 3. Final form of manganese carbonate obtained
Figure 4. Dissolution of iron in organic solvent during solvent extraction
Figure 5. Iron precipitated as iron hydroxide during pH adjustment after solvent extraction.
Figure 6.Copper-nickel-cobalt sulphide precipitated from solution.
DETAILED DESCRIPTION OF THE INVENTION:
A process for utilization of lean high iron bearing manganese ores as a feedstock for production
of high purity manganese carbonate as primary product and by-products has been described. In
this process, manganese ore is crushed and sized to a specific size fraction followed by leaching
with hydrochloric acid and hydrogen peroxide as reductant while maintaining the solid to liquid
ratio during leaching to 1:10 to 1:20. During leaching acid concentration was allowed to be kept
between 1-8 M with concentration of H202 was between 0.2-2 M. Process conditions for

leaching were: T: 35-100°C and time was between 30-180 minutes. Conditions were optimized
based on series of experiments and mineralogy of the feed material.Leach residue was separated
by solid-liquid separation using filter press and the leach liquor is sent to solvent extraction unit
for separation of iron from leach solution. In solvent extraction, iron was extracted from aqueous
phase by employing mixture of organic media: D2EPHA and diethyl ether. Loaded organic
phase is sent to stripping section to recover iron value as iron sulphate and organic phase is
recycled to solvent extraction unit. Recovery of iron in solvent extraction was between 65-80%
and rest of the iron is precipitated as iron hydroxide by addition of lime and blowing of air. Iron
hydroxide obtained is further processed to obtain nano powder of hematite. Some amount of
alumina from solution is also precipitated as alumina hydroxide by increasing the pH of the
solution. Copper-nickel-cobalt based concentrate was obtained after sulfurization treatment with
sodium sulphide (Na2S) or sodium hydrogen sulphide (NaHS) at a pH of 5.5-6. The leach liquor
contained mostly has dissolved manganese cations whose pH is increased by addition of
ammonium bicarbonate to 8, followed by addition of sodium carbonate to precipitate manganese
carbonate. Manganese carbonate obtained was subject to washing to remove traces of acid and
dried at 125°C for 4-6 hours. The liquor obtained after manganese carbonate precipitation
contains mostly calcium cations which are which is subject to precipitation by addition of
sulphuric acid in the liquor, leads to lowering of the pH of the solution to 5-5.5 resulting in
gypsum formation. The solid is separated from liquid in filter press and dried to obtain industrial
gypsum powder.

The object of the present invention is to provide a direct utilization of low-grade oxide based
ores of manganese for preparing high purity manganese carbonate and a simultaneous extraction
of iron from the residue or leach liquor. Another by product while producing manganese
carbonate arenickel-copper-cobalt recovery of precious metal concentrateand secondly
beneficiation enrichment has been carried out without any high temperature reduction. Thus, the
process proposed achieves clean and environmental friendly waste water discharge.
The described innovative process can be achieved by the following specific process steps while
preparing high purity manganese carbonate from lean grade manganese ores: (1) reductive
leaching of manganese ore using H2O2 as reductant in hydrochloric acid as medium; (2) recovery
iron value as nano hematite powder (3)cobalt, nickel, copper concentrate recovery; (4) recovery
of industrial gypsumpowder; and (5) preparation of high purity manganese carbonate powder.
Milling and grinding of the low grade manganese ore is carried out to a particle size with dso of
200 micron (US series). Leaching has been carried out according to liquid solid ratio of 10-20:1
ratio and leaching solution was added slowly followed by stir to avoid pulp thickening. Leaching
was carried out with HC1 solution in stirred reactors. The pulp density will be somewhere
between 12 to 20% by weight to facilitate subsequent solid liquid separation with a leach tank
thickener. The material breaks downs into finer particles as a result of the agitation in this stage.
In order to reduce the reduction potential of manganese, which is mostly present as Mn(IV) in
M11O2, a catalyst in the form of hydrogen peroxide (H2O2) is added. H2O2 behaves as a reducing
agent only towards very strong oxidizing agents such as Mn(^ and chloride ion is not a reductant
in dilute acid solutions. Hydrochloric acid is chosen as leaching medium and about 80-85% by

weight of acid was added in the leach reactor to the slurry of minerals. Acid injection is
controlled to keep the temperature between 70-90°C. Eventually H2O2 is added to the solution in
between of 1-5 weight percent of solution and keeping the temperature close to set point As the
reaction proceeds for 60-180 mins, temperature drops to 65-70°C. During the reaction, Fe(H)
content from the solution is detected periodically using atomic absorption spectrometer. The
leach liquor obtained is having some fine and unsettled material which was thickened by adding
flocculent in the leaching tank and allowed to settle for 30 minutes. Following reactions which
occur during the leaching stage are provided below:
Mn02 + 4HCl(aq) = MnCl2 (aq) + H20 + C12 (g)
Fe304 + 8HCl(aq) =FeCl2 (aq) + 2FeCl3(aq) + 4H20
FeCl2 (aq) + 02 + 4HCl(aq) = 4FeCl3(aq) + 2H20
MnC^ + H202 (aq) + 2¥t = Mn2+ + 2H20 + (^AE0 = 0.549 eV
After leaching stage, the slurry enters a thickener to subsequently separate the pregnant leach
liquor solution (PLS) from the residue. Adequate settling is achieved by operating at a lower
pulp density (in the range of 12 to 20% by weight) without the need for auto-dilution(by
recycling of the overflow back to the same thickener) to increase settling rates. Secondly,
flocculation can be facilitated by addition of flocculent and allowed to settle for 30 minutes.
Although the pulp density is low, the Mn concentration is maintained at an adequately highlevel
in the PLS. Incoming water used in the leach contains Mn recovered from the CCD wash.

Iron from the PLS is recovered in solvent extraction unit, where the iron dissolved in PLS was
extracted using D2EHPA in kerosene as the solvent was used. Other than D2EHPA, diethyl ether
along with kerosene was also used to estimate the distribution coefficient for iron. The extraction
behaviour of 0.20 M Fe(III), 0.25 M Mn(II), 0.253 ppm Cu, 1.786 ppm Ni, 3.244 ppm Co, 2.322
ppm Zn from 1-3 M hydrochloric acid was carried out using diethyl ether and D2EHPA in
kerosene as the solvent. Extraction efficiency for removal of iron increases with increase of
extractant concentration. Extraction efficiency for diethyl ether shows that, 80 % of iron is
recovered along with organic phase. The diethyl ether alone as extractant was varied by weight
between: 20 - 75 % with iron removal up to 30- 80% respectively. Iron which was present in
PLS as Fe(III) state along with chloride ion, leads to form a co-ordination compound of iron with
diethyl ether generally called as Tetrameric Ethernal iron complex. This iron complex is mostly
containing iron as dissolve phase without appreciable dissolution of any other metallic ions in the
organic phase. Iron is recovered from the organic phase as ferric chloride compound with
recovery of organic phase from the distillation unit with condensation back to solvent extraction
unit Secondly, with D2EHPA used as extraction phase in kerosene for extraction of Fe(in) from
chloride solution, maximum 0.5 M D2EHPA is used with 75% recovery of iron in organic phase.
Other metals doesn't partition in organic phase with reaming with PLS. The iron loaded organic
phase will be taken to stripping section, where the organic was stripped with sulphuric acid as
main iron stripper. Iron will be realised from organic phase and report to acid phase and lead to
form iron sulphate.

PLS main stream contains rest of Fe (II) ions dissolve, Mn(II) and other metallic cations (Cu, Ni,
Co, AI, Ca and Zn) is taken to downstream reactor for further iron removal by increasing the pH
of the solution. PLS from solvent extraction unit varies between 2.5-2.8 and in order to remove
iron, Al as hydroxide, pH of the solution need to be increased to range of 3.5-4.0. In this step,
PLS pH is increased by addition of lime in one reactor followed by bubbling air in second
reactor with close monitoring of pH to between 3.8-4.0. Iron from PLS leads to form hydroxide
of iron ad precipitates out of the solution as per the solubility diagram (Ref). The equilibrium of
a metal hydroxide precipitation can be expressed by the general equation:
Mn+ + nOH = M(OH)„
The equilibrium constant for the following reaction can be written as:

Where Ks is the solubility productThe equilibrium of metal hydroxides precipitation is often
represented graphically at 25°C. At mis temperature, it is predicted that Fe3+, Al3*, Pb2+ and Cu2+
can be readily separated from Mn2+ by hydroxide precipitation while separation of Zn2+ from
Mn2+ is possible but that of Co2+, Ni2+ from Mn2+ is difficult by a hydroxide precipitation
method due to their closeness on the solubility diagram. At the pH 4.0, the iron gets precipitated
asFeO.OH and aluminium as aluminium hydroxide with gelatinous brown precipitate. In order to
precipitate iron, lime is dissolved in the warm water to make it sparingly soluble. Lime
containing solution is slowly added in the PLS with continuous measurement of pH. Some
quantity of dilute sodium hydroxide with pH maintained at 10.0 was also added. Iron oxide

hydrodoxide obtained is separated from PLS by passing it through a press filter where, the cake
of Fe(OH)3 is obtained. This cake is rinsed with fresh water to dissolve any manganese from the
thickened solid and this water is send back to leaching section to concentrate the manganese in
the circuit. The filter cake obtained from the filter press after washing was dried to obtain iron
oxide hydroxide.
Cobalt, nickel, copper recovery was said after the complete removal of iron from PLS. These
metallic compounds are present in the solution in the form of [Co 2+], [Ni2+], [Cu24], [Pb2 *] and
[Zn 2+] having following concentration: 3.244, 1.786,0.253 and 2.322 ppm respectively.
Ammonium bicarbonate solution was added to the PLS to take the pH to 5.5-6 along with
addition of disodium sulphide solution to precipitate precious metals. Solution was slowly added
with stirring for 55-70min. The solid-liquid system was taken to separation membrane filter press
to obtain a filtrate and cake. The pressed cake has liquid to solid ratio of 3-5:1 ratio. The filter
cake obtained after washing and drying, cobalt, nickel, copper concentrate. PLS obtained after
removal of Cu, Ni, Zn and Co is subject to analysis is having following analysis: 0.012, 0.883,
1.143 and 1.223 PPM respectively.
PLS free of major metallic ions are subject for manganese carbonate precipitation. Precipitation
of the MnCO3 proceeds according to the following reactions:
MnC12 (aq) + Na2CO3(s) = MnCO3 (ppt) + 2NaCl (aq)

Manganese precipitation was carried out by addition of 150 g/L Na2CC>3 slurry, at a
stoichiometric ratio of 0.8 carbonate to manganese, to the pregnant leach solution in a stirred
tank reactor. Precipitation of MnCO3 occurred instantaneously after the addition of Na2CO3 to
the pregnant leach solution. The solid laden solution was sent to filter press to recover solid
product from the rest solution and the filtrate was taken for recovery of gypsum.
Gypsum powder is recovered from the filtrate obtained after separation of MnCO3 cake. After
the separation of MnCO3, solid-liquid separation resulting filtrate was sampled to detect [Mn2 +]
and [Ca 2+] molar concentration of the filtrate. pH of this solution varies between 10-11.
Subsequently .ammonium bicarbonate solution was added 2mol / L added into filtrate which
contains Ca2+ cations along with some amount of Mn2+ with pH of the solution to 7.1-8.5. After
stirring for 30-50 minutes, the solution is taken to another reactor where 90% by weight of
sulphuric acid was added until the pH of the above slurry is reduced to 5.5. After stirring for 60-
70 minutes, the slurry was sent to filter press to obtain a filtrate and cake. Filter cake obtained
after twice washing and drying provides industrial gypsum powder.
The specific examples for manganese carbonate as per the flowsheet shown in Figure 1 is
described below.

Example-1
• Low grade manganese ore lumps with Mn:Fe: 1.5 (detailed chemical analysis shown in
Table 1) is crushed to size distribution below