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Journal of Minerals & Materials Characterization & Engineering, Vol. 8, No.4, pp 317-327, 2009
jmmce.org Printed in the USA. All rights reserved
Enrichment of Cobalt Values by Dry Magnetic Separation from Low-Grade
Manganese Ores of Bonai-Keonjhar Belt, Orissa
P. P. Mishra,
B. K. Mohapatra*,
P. P. Singh
Regional Research Laboratory, Bhubaneswar, India
Utkal University, Bhubaneswar, India
*Corresponding Author, contact: email@example.com, firstname.lastname@example.org
Resource potential of cobalt in India is practically negligible. Cobalt in marine manganese
nodule though known since long, its report from terrestrial manganese ore is least observed. This
paper reports the occurrence of cobalt in low-grade manganese ores of Bonai-Keonjhar belt,
Orissa, eastern India and describes methods for its possible enrichment. Cobalt is associated with
manganese minerals like lithiophorite (~CoO: 1.2%) and cryptomelane (~CoO: 0.2%). A feed of
low-grade siliceous manganese ore containing 26% Mn and 32% SiO
and 0.08% Co was
subjected to physical beneficiation. By processing the low-grade siliceous ore on a dry belt
magnetic separator, a product with 47% Mn at 60% recovery could be obtained. It was observed
that along with manganese the cobalt value gets enriched (~Co: 0.38%) more than four times in
comparison to the feed. Some other traces like Ni, Cu, Zn, Ga, Li etc. also get enriched in the
magnetic product. Thus, through simple dry magnetic separation a low-valued material cannot
only be converted to usable product but two valuable metals can also be recovered from it.
Orissa Manganese ore, Magnetic separation, Cobalt.
Occurrence of cobalt in the ferromanganese nodules of present day marine basins has been
studied in great detail over the last few decades by several workers all over the world [1-3].
However, only limited data is available on the distribution of cobalt in terrestrial manganese
ores. Delian Fan et.al.,  has reported the occurrence of Co in Mn-ores of Sichuan province of
318 P. P. Mishra, B. K. Mohapatra, P. P. Singh Vol.8, No.4
China. A worldwide review of Co-rich manganese deposits and techniques required for their
development and mining has been suggested by Tetsuo .
During detailed investigation of the manganese ores of Bonai-Keonjhar belt of Orissa, India it
was observed that the Mn-ores of this region contains appreciable quantity of trace elements in
general and cobalt in particular. Cobalt in Mn-ores of this belt is found to be associated with
manganese minerals like lithiophorite and cryptomelane. Presence of lithiophorite in
Precambrian manganese deposits of Orissa was earlier recorded by Roy  and Mohapatra et.al.
. Cobalt in Mn-deposits from this belt was first reported by Mohapatra et al. .
There is no workable deposit of cobalt in India and it is considered as a strategic metal of defense
importance. Cobalt is only won from the copper converter slag of different Cu-smelting plants in
India. So the Co-values in Mn-ores of this belt need to be characterized and recovered. This
paper reports the presence of cobalt in Bonai-Keonjhar belt, their characterization and
enrichment so as to recover two valuable metals from a low-grade siliceous manganese ore of
2. MATERIALS AND METHODS
Representative samples, mostly of oolitic/nodular and spongy varieties were collected from low-
grade siliceous manganese ore deposits like Shankar, Bhoot, and Spencer from Bonai-Keonjhar
belt. These were subjected to optical microscopy (Leitz make Orthoplan at RRL), XRD (Phillips
Diffractometer, PW-1710 at RRL) and Electron Probe Microanalyser (EPMA, JEOL make JXA
8600 Super probe, at USIC Roorkee). For beneficiation of manganese ore, high intensity dry belt
magnetic separator of type LOG 1.4 SEP operated at 50 Dc Volt and 4.17 Dc A current, suitable
for fine particle separation, (supplied by Boxmag Rapid Ltd., Birmingham, England) was
employed. The magnetic intensity was varied between 0.73 and 1.23 T. Dry samples of closed
size fractions were continuously fed to the belt magnetic separator by vibrating feeder at
controlled rate. Magnetic products were separated by moving disc at required speed and
intensity. Based on the requirement the intensity, feed rate, and gap between the belt and disc in
the magnetic separator were varied. Selective elements like Mn, Fe and SiO
were analyzed by
XRF Spectrometry on Philips (PW-1400) X-ray spectrometer with scandium and Rhodium
targets using Pentaerythritol (Al, Si), Thallium Acid Pathalate (Na, Mg), Germanium (P) and
Lithium Fluoride (LIF, for heavier elements) as analyzing crystals in vacuum medium. The trace
elements were analyzed at NGRI, Hyderabad, India using Inductively Coupled Plasma-Mass
Spectrometer (ICP-MS). The ICP-MS used was a Plasma Quad PQ1 controlled by an IBM PC-
XT microcomputer and associated software. Standard acid dissolution procedure was adopted for
sample preparation as prescribed by Balaram, et. al. . Both in-house and international ore
standards of different chemical composition (NNODA-1, MNODP-1 etc.) were analyzed along
with the sample for precision.
Vol.8, No.4 Enrichment of Cobalt Values by Dry Magnetic Separation 319
3. RESULTS AND INTERPREATION
3.1. Mineralogical Characteristics
X-ray diffraction and optical microscopic studies are exclusively employed for mineralogical
characterization of Mn-ores. X-ray diffraction pattern of Mn-ore clearly reveals the presence of
lithiophorite as a major manganese mineral in oolitic/nodular and spongy types of ore (Fig. 1).
Other minerals present include pyrolusite (Mn-phase) and quartz (gangue mineral). Presence of
cryptomelane (Mn-phase) is also recorded in some sample.
Fig. 1: X-ray diffraction pattern of feed and enriched products of low-grade siliceous Mn-ore
Lithiophorite and cryptomelane were found to contain Co values as brought out through EPMA
study (Table-1). Hence, detailed characteristics of these phases were further studied under optical
microscope. Lithiophorite exhibits a well-developed bireflection, from pearly gray to brownish
gray and strong anisotropism, making crystallites appear black and white under crossed polar
(Fig.2). The mineral has lowest VHN values (40-60) amongst its co-existing phases. The
lithiophorite exhibits mamillary growth with undulose segmented twinning (Fig.2A).
Lithiophorite mosaics show different reflection (Fig. 2B). Occasionally, it is thinly banded where
coarse radiating crystals are arranged in zig-saw pattern (Fig. 2C). It often occurs as dense
masses of micron-sized acicular to pea shaped crystallites (Fig. 2D). It also occurs as polyhedral
mosaic grains (Fig. 2E) along the periphery of vugs (Fig. 2 E & F). Other associated Mn-
minerals include cryptomelane and pyrolusite. The former exhibits colloform banding while later
occurs as large prismatic crystals to tiny needle shaped acicular grains. Hematite, quartz/illite
form iron and gangue minerals respectively.
320 P. P. Mishra, B. K. Mohapatra, P. P. Singh Vol.8, No.4
Table 1: Composition of Lithiophorite and Cryptomelane phases in low-grade siliceous Mn-ore,
as obtained through EPMA.
1 to 4: Cryptomelane, 5 to 9: Lithiophorite. ©:Calculated value
3.2. Chemical Characteristics
The bulk sample of the siliceous manganese ore contains 26.4% Mn, 2.78% Fe and more than
(Table 2). Such low-grade manganese ore sample contains appreciable Co values
ranging from 691 ppm to 1002 ppm (avg. 791 ppm) in the bulk sample. The EPMA results
shown in Table 1 distinctly indicate that both lithiophorite and cryptomelane are Co-bearing.
However, the lithiophorite mostly shows higher Co value than cryptomelane. Besides Co value,
lithiophorite also contains appreciable Ni in its lattice. The X-ray image maps of Mn, Fe, Al, Si,
Co, Ni, K and Ba elements in selected location (SL) occupied by lithiophorite and cryptomelane
show the former phase to be rich in Co-concentration (Fig. 3).
Vol.8, No.4 Enrichment of Cobalt Values by Dry Magnetic Separation 321
Fig 2: Photomicrograph of lithiophorite mineral showing different microstructures x200
(A) Mamillary growth of lithiphorite showing undulose segmented twinning (B) Lithiophorite
mosaics showing different reflection and traversed by a cryptomelane veinlet. (C) Thinly banded,
coarse grained, lithiphorite (bottom) showing zig-saw pattern. Alternate bands at the top are that
of cryptomelane (white) and quartz/clay (black) D) Acicular aggregates of lithiophorite (E)
Prismatic growth of lithiophorite encrusting a vug. (F) Mosaic of polyhedral crystallites of
lithiophorite lining a vug.
322 P. P. Mishra, B. K. Mohapatra, P. P. Singh Vol.8, No.4
Table 2: Size and chemical analysis results of low-grade siliceous Mn-ore
m Wt% Mn% Fe% SiO
% Co in
Bulk - 26.41 2.78 32.42 791
+500 40.1 24.84 2.78 34.93 668
+250 33.4 25.47 2.92 33.78 585
+150 9.5 28.93 3.06 27.98 1002
+75 9.4 28.93 3.06 27.49 1180
-75 7.6 27.00 4.22 32.11 726
Head 100 25.96 2.98 32.95 724
3.3. Beneficiation Characteristics
In order to assess the upgradation potential and possible enrichment of manganese and other
valuable traces in general and cobalt in particular, the siliceous manganese ore was subjected to
physical beneficiation study. The bulk sample was crushed and subjected to sieve analysis using
standard BSS sieves of 500, 250, 150 and 75µm size. Each fraction was analyzed for Mn, Fe,
and Co values. The size and chemical analysis of the feed and classified fractions are
presented in Table 2. The analytical results reveal that there is a marginal improvement in the
Mn values through size classification. As Co is intimately associated with manganese it also
shows a marginal rise.
All the classified fractions, excepting -75µm size, were subjected to dry magnetic separation at
different current intensities, viz. 10A (0.73 T), 15A (1.00 T) and 20A (1.23 T). The classified
sample below 75 µm size was not processed through magnetic separator because of its low
volume (7.5 wt.%) in the bulk sample. Moreover, it is difficult to process –75 µm size sample
through dry magnetic separator. This needs wet magnetic separation, which may not be cost
The magnetic products recovered through magnetic separation in different size fractions were
analyzed for Mn content. The grade and recovery of Mn-values at different magnetic intensities
are given in Table-3. It can be seen from Table-3 that best grade of Mn-ore is obtained at 1.00 T.
In order to ascertain the concentration level of valuables and impurities in all the magnetic
products, obtained at 1.00 T, each fraction was analyzed for Mn, Fe, SiO
and Co. The results are
presented in Table-4. A significant rise in the concentration level of manganese and cobalt values
in the magnetic product with respect to the feed is noticed (Table-4). The values of Mn and Co in
each fraction when plotted in a graph (Fig. 4) both were found to follow more or less a common
trend line. This further substantiates the adsorption of Co values in Mn-phase.
Vol.8, No.4 Enrichment of Cobalt Values by Dry Magnetic Separation 323
Fig. 3: X-ray image map of Manganese minerals with respect to Mn, Fe, Si, Co, Ni, Al, K and
Ba. The SL image shows the occurrence of cryptomelane (Cy) and Lithiophorite (Li).
The magnetic product so obtained at –150+75 µm size fraction at 1.00 T was also analyzed for
other traces like Li, Ni, Cu, Zn and Mo, as it showed the highest value of Mn (47.48%, Table.4)).
324 P. P. Mishra, B. K. Mohapatra, P. P. Singh Vol.8, No.4
One can note from the table (Table-5) that along with Co; some of the traces like Ni, Cu and Zn
also show enhancement in their values around four times than that of feed.
Table 3: Mn-value (wt. %) and recovery (%) in magnetic products at different size fractions and
0.72 T 1.00 T 1.23 T
Size, in µm Wt. %
% Mn %
-1000+500 38.8 41.9 23.9 39.3 43.51 26.0 41.9 42.7 33.9
-500+250 33.0 44.7 21.7 32.8 45.91 23.0 32.6 44.6 27.5
-250+150 14.2 42.9 8.9 13.8 45.91 9.7 12.4 41.5 9.7
-150+75 14.0 46.4 9.6 14.1 47.48 10.3 13.1 46.8 11.5
Table 4: Size and chemical analysis results of magnetic products at 1.00 T
m Wt, % Mn, % Fe, % SiO
% Co, ppm
-1000+500 39.3 43.51 4.45 8.01 2956
-500+250 32.8 45.91 5.78 3.45 2894
-250+150 13.8 45.91 5.01 3.68 3658
-150+75 14.1 47.48 4.73 2.31 3843
Table 5: Concentration level of selected trace elements in feed and best enriched product
Element in ppm Feed
Li 105 250
Co 791 3843
Ni 437 1546
Cu 423 1557
Zn 170 961
Mo 5 23.4
Vol.8, No.4 Enrichment of Cobalt Values by Dry Magnetic Separation 325
500 250 15075
Size in um
Concentration of Mn, wt. %
500 250 15075
Size in um
Concentration of Co in ppm
Fig. 4: Schematic diagram showing the distribution pattern of Mn and Co in bulk and enriched
The beneficiation studies thus revealed that the low-grade siliceous manganese ores of Bonai-
Keonjhar belt, Orissa are amenable to upgradation and better utilization through a simple means
of dry magnetic separation. Enrichment of Mn content from a feed of 26% to more than 47% in
processed product (–150+75 µm size fraction at 1.00 T) is definitely a significant achievement.
Enrichment of Mn-content by wet high intensity magnetic separation and dry magnetic
separation from Chikla manganese ore, India has also been reported by Mohapatra et. al.,  and
Rao et al., , respectively. However, enrichment of Co-values with that of Mn is reported
here. A cobalt value of 791 ppm in the Mn-ore feed can be upgraded to an average value of 3157
ppm through simple magnetic separation technique.
326 P. P. Mishra, B. K. Mohapatra, P. P. Singh Vol.8, No.4
Mineralogical and geochemical characterization of low-grade siliceous manganese ores from
Bonai-Keonjhar belt indicated that lithiophorite is the dominant Mn-mineral and quartz is the
major gangue. The electron probe microanalysis and X-ray image map of different elements in
such an ore clearly reveal that the lithiophorite is cobalt bearing i.e. Co is present in adsorbed
state within Mn-phase. The manganese minerals are para-magnetic in nature while quartz is non-
magnetic. So the undesired non-magnetic quartz can easily be separated from magnetic
manganese phase by simple physical separation process (dry magnetic separation). Thus the
trace elements in general and Co in particular present in the lattices of Mn-minerals are upgraded
automatically along with the Mn-values. A four-fold increase in the cobalt and other trace values
(Ni, Cu & Zn) has been recorded in the enriched product with respect to the feed sample.
Following the above simple flow sheet, the low-grade manganese ore (26% Mn), which has
negligible market value, can be upgraded to a valuable product (>47% Mn). Co enrichment
further adds to the value.
Methods have been developed to recover Co and Ni metals associated with marine manganese
nodules [11-13] by different leaching processes. Applicability of this method to the Orissa
manganese ores needs to be studied. If 50, 000 tonnes of manganese ores with 0.5% of cobalt on
an average is smelted electrically, about 250 tonnes of cobalt will be obtained. In view of
advantage of recovering Co as a by-product with electro-manganese and the availability of
substantial resources of low-grade siliceous manganese ores in Orissa, the feasibility of
conversion of a part of manganese ore from this part of India deserves further detail study.
The occurrence of Co with lithiophorite phase in the low-grade siliceous manganese ores of
Bonai-Keonjhar belt and their amenability to upgradation through dry magnetic separation is
reported. A low-grade siliceous ore containing 26% Mn and 791 ppm Co can be enriched up to a
product of 47% Mn and 3843 ppm Co with 69% recovery. Thus a waste can be converted to a
wealth at very low cost and minimum unit operations. Sincere efforts are needed to recover these
two valuable metals by suitable extractive metallurgical methods like chemical, bio-chemical,
biological, electro-metallurgical and hydro-metallurgical process routes.
The authors are highly thankful to the Director, Institute of Minerals and Materials Technology,
Bhubaneswar for his kind permission to publish this paper. Thanks are due to Mr. P.S.R. Reddy,
Sct. G for his critical review of the manuscript and Dr. S. Prakash, Sr. Sct. for his assistance in
magnetic separation work. The authors are also thankful to the Department of Science &
Vol.8, No.4 Enrichment of Cobalt Values by Dry Magnetic Separation 327
Technology, New Delhi, India for their financial support in the form of a project
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