FIELD OF THE INVENTION
The present invention relates to a process for upgrading the chromite value
present in ultrafine tailings. In particularly, the present invention relates to
selectively flocculating the chromite particles followed by magnetic separation.
More particularly, the invention relates to a process for recovery of enriched
chromium concentrate from chromite tailings, which eliminates the above
drawbacks.
BACKGROUNDS OF THE INVENTION
Huge demand of chromite ore necessitates the use of low grade chromite ore
after beneficiation. Beneficiation of low grade chromite ore generates large
quantities of chromite tailings. The safe and environment friendly disposal of
these tailings is a persistent problem for plant operators. Normally beneficiation
of the chromite ore is carried out by one or more of these following conventional
methods like gravity separation, froth floatation and magnetic separations.
However, these conventional methods is not found to be substantially effective
for enrichment of chromite value in the ultrafine particles of chromite tailings. All
these prior art methods have limitations in handling ultrafine particles.
Generally beneficiation of the chromite ore is done by the conventional methods
like by using different gravity separators, magnetic separators or by physico-
chemical method of separations like flotation [Murthy etal.2011,Aslan.2009;
Guney etal.,1999; Smith and Allard, 1983]. But all these processes are not
capable for processing ultra-fine chromite ore because of size limitations. Form
the size distribution analysis of the generated tailings, it is observed that
around 40 to 45 % of chromite is of ultra-fine size (below 37 micron). The ultra-
fine size is used to be thrown because no process available for processing these

ultra-fines. Selective flocculation can be used an alternative method for
beneficiating the ultra-fine chromite.
The process of selective flocculation has been successfully developed and used
earlier for enrichment of iron ore as described in U.S. Patent no. 4274945.
Further enrichment of iron ore has been carried out by using magnetic
separation as disclosed in US Patent no. 4298169. However use of selective
flocculation for chromite mineral is very limited used in prior art.
A process for concentrating chromite ore has been taught in U.S. Patent No.
3473656 (1969), where 70% of the particles below 0.074 mm processed by
selective flocculation and flotation. In this process, a selective flocculation at pH
11.5 was carried-out using sodium silicate as the dispersant. Further, the
chromite value was upgraded by using flotation techniques by addition of an
anionic collector.
Akdemir and Hieylmaz, 1996 has studied a selective shear flocculation using
synthetic mixtures of chromite - serpentine, but they could not successfully
establish the process because, the used reagents Na2Si03 and IMa2SiF6 shows
detrimental effect to selective flocculation method. Similarly Beklioglu and Aral.,
2004 have attempted to establish selective flocculation on synthetic mixtures of
chromite and serpentine minerals using corn starch as a flocculant but the
established process shows some limitations like, they concluded that particular
solid concentration should be maintained to achieve the selective flocculation
between the chromite and .serpentine. Panda, 2010 have attempted selective
flocculation of chromite tailings where the chromite value was enhanced from
19.7% to 26%.
In all the prior art processes, attempts were made to enrich the chromite value

using selective flocculation without considering the possibility of further
enrichment of chromite value in combination with other unit operation. In other
words, prior art fail to teach any process developed for grade enhancement of
chromite tailings in combination of selective flocculation and magnetic
separation.
Moreover except Panda, 2010 in all other cases the researchers have used either
chromite ore or synthetic mixtures of chromite and serpentine minerals and not
chromite tailings. Although panda 2010 had used chromite tailings for
beneficiation but have not used selective flocculation in combination with
magnetic separation. Panda 2010 had also not used sodium hexa-meta
phosphate as dispersant and chromite tailings with 14% chromite grade.
The present inventors through extensive study and experimentation, recognized
that chromite tailings if processed in combination of selective-flocculation and
magnetic separation technique, a higher grade feed could be obtained for the
beneficiation circuit or the product can be blend with high grade chromite and
can be further used for various purposes.
OBJECT OF THE INVENTION
It is therefore an object of the invention to propose a process for enriching
chromite value present in chromite tailings, which eliminates the above
drawbacks.
Another object of the invention is to propose a process for recovery of enriched
chromium concentrate from chromite tailings, in which degraded wheat starch is
used as the flocculating agent for selectively flocculating ultrafine particles.

Still another object of the invention is to propose a process for recovery of
enriched chromium concentrate from chromite tailings, in which selective
flocculating is followed by a step of magnetic separation for enhancement of
chromite grade of the pre-concentrated chromite tailings by selective
flocculation.
Yet another object of the invention is to propose a process for recovery of
enriched chromium concentrate from chromite tailings, where in the selective
flocculation is conducted in the alkali region.
A further object of the invention is to propose a process for recovery of enriched
chromium concentrate from chromite tailings, adapts sodium hexa-
metaphosphate as the dispersing agent.
SUMMARY OF THE INVENTION
According to the invention, the received tailing sample is classified below 400
mesh or 37 micron. In this present work, Sodium hexa meta phosphate was used
as the dispersant. Required amount of sodium hexa meta phosphate was added
to the feed slurry and mixing of the dispersant is done by the shearing action of
a mechanical stirrer. Level of pH in the slurry is maintained by addition of sodium
hydroxide. After the dispersion of the particles, the flocculent is added. Then the
shearing action is maintained slowly. The flocculent get adsorb on the chromite
particles and the floe formation occurs with the chromite particles and other
associated gangue minerals remains in the dispersed conditions.
The flocculated pulp is passed through the magnetic separator to separate the
siliceous minerals that are present in the pre-concentrate from selective
flocculation. By the magnetic separation technique, the siliceous materials

present in the floc is removed, thereby enhancing the grade of the final
concentrate.
DETAIL DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Generally the Chrome Ore beneficiation Plant produces tailings which contain
ultrafine chromite particles. These ultra-fine chromite particles cannot be
recovered primarily due to their ultrafine particle size by the existing
conventional beneficiation processes. The tailings sample used in this invention
contains around 14% Cr203. Along with the chromite minerals, goethite and
siliceous minerals are the major associated gangue minerals that are present in
the ultrafine tailings. Liberation study by QEM-SEM, had shown that the tailings
still contain around 50% of chromite minerals in liberated state which can be
recovered.
In this present invention, degraded wheat starch is used as the flocculant which
flocculates the chromite minerals selectively from the gangues like goethite,
siliceous minerals etc. Sodium hexa-meta phosphate is used as the dispersant
which allows all the minerals present in the feed slurry should remains in
dispersed phase, and after addition of the flocculant, the flocculant will adsorb
on the surface of desired mineral.
Sodium hexa- metaphosphate is added to the slurry, then pH of the slurry is
maintained at 9-11 using sodium hydroxide. After addition of the dispersant,
mixing is done by a high shearing action. Then the freshly prepared flocculent
(degraded wheat starch) is added to the well dispersed slurry. After addition of
the flocculants, mixing of the flocculants in the slurry is carried out by
maintaining a very low shearing action. Then by the shearing action, the

flocculants gets in contact with the minerals including the gangue minerals. By
the virtue of surface properly, the floe formation however, occurs only on the
desired minerals and the other gangue minerals remains in the dispersed phase.
For further up-gradation of the chromite value, the floe formed is subjected to
magnetic separation process magnetic intensity of 14000 gauss. This process of
selective flocculation followed by the magnetic separation of the pre-concentrate
from selective flocculation enables enrichment of the chromite grade in tailings to
twice the value in the final concentrate.
The example is given by way of illustration of the present invention and
therefore should not be interpreted to limit the scope of the present invention.
Example, Raw tailing samples were collected from the chrome ore beneficiation
pant. The raw chromite sample was classified at 400 mesh and the particles
passing through 400 mesh were collected for processing. This is a substantial
amount which contains around 14% of chromite and could not be beneficiated
using conventional methods. The chemical analysis of the particles passing
through 400 mesh, is used here in as feed sample contains 14.7%Cr203 along
with 14.06%AI2O3, and 8%SIO2.The detail chemical analysis of feed sample is
shown in Table 1.
Feed slurry was used for selective flocculation test was prepared with 5%
weight of feed sample in a 1000ml of water in a glass beaker. In the first stage
before addition of the flocculant to the slurry, dispersant of 400 g/t was added
to the slurry. Sodium hexa-metaphosphate was used as the dispersant.After
addition of the dispersant, mixing was done in a mechanical stirrer at a rate of
2000 r.p.m. Then the slurry pH was maintained at pH range of 9-11 by addition
of sodium hydroxide, 280 g/t of causticized wheat starch was added to the alkali
slurry and the speed of the srirrer maintained very slowly with very slow shearing
action and slowly the stirring was brought to zero. The floc formed is allowed to

settle down. The addition of the flocculent selectively floes the chromite particles
and the siliceous gangue allowed to remain in the dispersed state. The enriched
chromite floc was separated from the supernatant liquid by decantation, After
selective flocculation, Cr2O3% was up-graded to 24.45% from 14.4%. And the
SiO2% value decreases to 6.08% in the treated concentrate. The chemical
analysis of both the selective flocculation concentrate and tailings was shown in
given in Table 2 and 3.
After selective flocculation process, the chromite minerals grade was enriched
from 14.4% to 24.45% and then the enriched grade (%) was further processed
by magnetic separators for further enrichment of the grade. The collected
chromite floc was again mixed with water to prepare the slurry with 20% solid
concentration. The prepared slurry was subjected to wet high intensity magnetic
separation at magnetic intensity of 1400 gauss. Magnetic fraction was collected
as the final chromite concentrate and the non magnetic fraction was collected as
the final tailings. The chemical analysis of the final chromite concentrate and non
magnetic tailings is given in Table 4 and 5 respectively. From the chemical
analysis, it is observed that Cr2O3% was up-graded to 28.11% from 24.45%,
with SiO2% 4.13% in the concentrate

REFERENCES: PATENTS PUBLICATIONS
1. Method of concentrating a chromite containing Ore (Patent IMo.3473656).
2. Iron Ore beneficiation by Selective flocculation (Plant no. 4274945).
3. Selective Flocculation, Magnetic Separation, and Flotation Of Ores (Patent
no 4298169).
REFERENCES: NON-PATENTS LITERATURE
1. Y. Rama Murthy, Sunil Kumar Tripathy, C. Raghu Kumar, Chrome ore
beneficiation challenges and opportunities - A review, Minerals Engineering,
Volume 24, Issue 5, April 2011, Pages 375-380.
2. N. Asian, Beneficiation Of Chromite Concentration Waste By Multi-Gravity
Separator And High intensity Induced-Roll Magnetic Separator, The Arabian
Journal for Science and Engineering, Volume 34, 2009, pp, 285-296.
3. A. Guney, G. Onal, M.S. Celik., 1999. A new flowsheet for processing
chromite fines by column flotation and the collector adsorption mechanism.
Minerals Engineering, 12(9), 1999, pp. 1041-1049.
4. R.W. Smith, S.G. Ailard, Effects of pre-treatment and aging on chromite
flotation, International Journal of Mineral Processing, Volume 11, Issue 3,
October 1983, Pages 163-174.
5. Akdemir, U., Hicyilmza, C, 1996. Shear flocculation of chromite fines in
sodium oleate solutions. Colloids and Surfaces A: Physicochemical and
Enginerring Aspects 110(1), 87-93).

6. Baris Beklioglu, AN Ihsan Arol* ... 2004. Selective flocculation behaviour of
chromite and serpentine. Physicochemical Problems of Minerals Processing,
38, 103-112.
7. Pandal Lopamudra Recovery of Chromite Value from Chromite Ore
Beneficiation Plant Tailings by Selective Flocculation, 2010. journal of
sustainable planet.

WE CLAIM
1. A process for recovering enriched chromite concentrated from chromite
tailings, comprising:
(a) classifying the chromite tailings below 400 mesh or 37 micron;
(b) mixing the classified particles to produce a slurry with 5% solid
concentration;slurry was prepaired with mixing 5% by weight of feed
sample in 1000ml of water in a beaker;
(c) conditioning the slurry with sodium silicate and sodium hydroxide;
(d) Selectively flocculating the chromite particles by addition of proper
reagent then separation of floc from supernant liquid by decantation.
(e) for further enrichment of chromite value, the floc collected after
selective flocculation was subjected to magnetic separation by using
a wet high intensity magnetic separation.

2. The process as claimed in claim 1 wherein pH of the slurry is maintained
at a pH range from 9-11 while it is subjected to selective flocculation.
3. The process as claimed in claim 1 wherein the slurry of enriched chromite
floe contains about 20% solid concentration.
4. The process as claimed in claim 1 wherein sodium hexa meta-phosphate
is used as the dispersing agent.

5. The process as claimed in claim 1, where in degraded wheat starch is
used as the floccuiant for selective flocculating.
6. The process as claimed in claim 1, wherein chemical analysis of a feed
sample classified tailings exhibit 10.8%LOI, 14.7 %Cr2O3/2.35%
MgO,8.22% Si02/.5% CaO,33.52% Fe(T) respectively.
7. The process as claimed in claim 1, wherein a chemical analysis of a
sample slurry concentrated after selective flocculation exhibits 8.08% LOI,
24.45 %Cr2O3, 15.620/oAI2O3, 4.24% MgO,6.08%SiO2/.38%CaO,37.9%
Fe(T) respectively.
8. The process as claimed in claim 1, wherein a chemical analysis of a
sample concentrated after magnetic separation exhibits weight percentage
of 6.06%LOI, 28.11%Cr2O3, 10.11%AI2O3/ 4.72%
MgO,4.13%SiO2,.11%CaO,31.89%Fe(T).

ABSTRACT

Huge amount of chromite processing plant tailings are getting deposited in the
tailing pond. These tailings contain substantial amount of chromite value in them
which are ultra-fine particles. Ultra-fine chromite tailings cannot be effectively
up-graded by conventional beneficiation method, because of the smaller particle
size. The present invention provides a process for up-gradation of chromite
values in the tailings. In the inventive process selective flocculation is applied for
pre concentration of chromite values and the further enrichment of the chromite
value is achieved by applying a step of magnetic separation. In the selective
flocculation process degraded wheat starch can be used as flocculent and sodium
hexa-meta phosphate as the dispersing agent. The process enriches the chromite
value to around twice the value of chromite present in the tailings.