FIELD OF THE INVENTION
The present invention relates to a process for upgrading values of ultrafine
chromite particles from rejected chromite tailings in a known beneficiation circuit.
BACKGROUND OF THE INVENTION
A huge amount of chromite tailings are generated during the beneficiation
process of the chromite ores. These generated particles are discarded and
normally stored in the tailing ponds. Safe storage and handling of these
generated tailings is a major problem for the plant management. Safer and
better way is to further process the generated tailings. It has been noticed that
the generated tailings contain mostly ultra-fines which cannot not be captured by
the known beneficiation circuit. Many attempts i.e gravity separation, magnetic
separation, physico chemical method of separation i.e flotation etc., are known
to have been applied to beneficiate the stored tailings. However, all these
methods are having some kind of limitations for handling the ultra-fines because
of the particle size limitations.
Selective flocculation is an alternative method for beneficiation of ultra-fines.
Previously reported literatures show that attempts were made in the past to
enrich the ultrafine chromite particles by using the selective flocculation process.
Akdemir and Hieylmaz, 1998 taught that selective shear flocculation can be
achieved by using synthetic mixtures of ultrafine chromite - serpentine ores of
less than < 10 µm of particles. They conducted all the tests by using 2g of
synthetic mixtures of chromite and serpentine. The used reagents Na2SiO3 and
Na2SiF6 shows detrimental effect to selective flocculation method. Becklioglu and
Arol, 2004 have attempted to establish selective flocculation by using the

synthetic mixtures of chromite and serpentine ores of particle size less than 20
µm. They used corn starch as a flocculant and sodium silicate solution as
dispersant. Their findings shows selective separation of chromite from synthetic
mixture of chromite and serpentine is possible if the solid concentration (%) of
the serpentine should be low in the feed slurry.
Indian Patent No. (291/KOL/2013) teaches a technique for up gradation of low
grade chromite tailings by using selective flocculation followed by magnetic
separation by using chromite tailings of < 37 µm of particle size. For selective
flocculation method, this prior art proposed use of causticized wheat starch as
the flocculant and sodium hexameta phosphate as the dispersant. This
acknowledged prior art establishes that it is possible to achieve Cr2o3 (%) up to
28.11% with 31.89% of Fe (T) % from 14% Cr2o3 of feed assay. IN patent
application 316/KOL/2014 teaches enrichment of the chromite tailings in a
desliming technique followed by selective flocculation process by using wheat
starch as the flocculant (316/KOL/2014). The reported literatures show it is
possible to enrich the ultrafine chromite particles by using selective flocculation
method by using degraded wheat starch as the flocculant. The limitation of the
known process is that the flocculant should be freshly prepared (Weissenborn
etal.,1995).
US Patent No. 3473656(1969) teaches using the Carboxyl methyl cellulose
reagent for enrichment of the ultrafine particles present in the low grade ores.
However, the prior art shows use of< 74 µm particles which contains 18.13%
Cr2O3. In this prior art, the test was conducted at pH 11 by using carboxyl
methylcellulose as the flocculant, and sodium silicate as the dispersants. The
invention achieved the concentrate 52.16(%) Cr2O3 (%) with approximately 80

(%) of recovery after processing the ores by selective flocculation followed by
flotation.
This known process is still having few limitations. Specifically, the used CMC
grade for pretreatment of CMC flocculants including the process methodology
was not disclosed in details. Accordingly, the prior art fail to teach or suggest a
detail process for up-gradation of ultrafine chrome value in chromite tailings
using selective flocculation technique.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a process for upgrading
values of ultrafine chromite particles from rejected chromite tailings in a known
beneficiation circuit.
Another object of the invention is to propose a process for upgrading values of
ultrafine chromite particles from rejected chromite tailings in a known
beneficiation circuit, in which a freshly available flocculant selective to chromite
minerals, is used.
Another object is to propose a process for upgrading values of ultrafine chromite
particles from rejected chromite tailings in a known beneficiation circuit, in which
low grade chromite particles of size (<37 µm) is used.
Still another object of the invention is to propose [Δ] in which selective
flocculation of the ultrafine chromite particles is established by using carboxyl
chromite (CMC) as the flocculant.

Yet another object of the invention is to propose a process for upgrading values
of ultrafine chromite particles from rejected chromite tailings in a known
beneficiation circuit, wherein the selective flocculation is conducted in a pH value
of 7 and 11 of the feed slurry.
A further object of the invention is to propose a process for upgrading values of
ultrafine chromite particles from rejected chromite tailings in a known
beneficiation circuit, in which sodium hexa-metaphosphate solution is used as
the dispersing agent.
SUMMARY OF THE INVENTION
Accordingly, there is provided a process for upgrading values of ultrafine
chromite particles from rejected chromite tailings in a known beneficiation circuit.
Thus, the inventive process allows enrichment of ultrafine chromite minerals by
using carboxyl methyl cellulose as the flocculant and sodium hexameta
phosphate as the dispersant. Sodium hexametaphosphate solution is added in
the feed slurry to cause all the feed particles dispressed so that the silicate
particles remain in the dispersed stages. Proper pH of the feed slurry was
maintained. After addition of the required amount of the flocculant dose, the floc
formation occurs only on the chromite minerals only.
BRIEF DESCRIPTION OF THE ACCOMPANING DRAWING
FIGURE 1 shows a flow sheet of the process of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Approximately 1 ton of chromite tailing sample was collected from
representative points of a tailing pond. The sample was selected through
sampling of approximately 200kg of the samples by coning and quartering
method. From the 200kg of the samples again by coning and quartering
methods, the representative samples were collected and subjected tor size
analysis.
The selected sample is subjected to seiving to get the particles of size less than
37 µm. After getting the representative samples the samples are subjected to
mineralogical characterization analysis (detail mineral analysis, liberation analysis
etc). The mineralogical analysis also shows that the particles present in the
sample exists in the liberated phase, and therefore, beneficiation by selective
flocculation is possible by using that sample. The feed sample contains 16.81(%)
of Cr2O3, 8.48(%) SiO2 and 31.63(%) Fe(T) assay along with few minor
elements.
Subsequently the samples are subjected for selective flocculation analysis. In the
first step required amount of dispersant dose was added, subsequently the
required pH was maintained. Thereafter, required amount of flocculant dose was
added to the system. Next, the samples are subjected to selective flocculation
process.
GENERAL PROCEDURE
Approximately 1 ton of tailing sample was collected from the representative
points of tailing pond. After proper sampling by coning and quartering

approximately 200kg of the samples were taken. From the 200kg of the samples
again by coning and quartering methods, the representative samples were taken
and subjected for size analysis. From the size analysis it was observed that
around 50 % by weight of the sample is less than 45 micron. After the size
analysis, the sample has undergone for detail mineralogical analysis i.e XRD
analysis, QEM-SCAN analysis etc. The detail schematic diagram of the process is
given in Fig .1. The minerological analysis shows different phases present in the
sample along with the liberation of the individual particles. Liberation study and
the mineralogical analysis shows beneficiation of the particular sample is
possible. The laboratory test work were carried out at 1000ml beaker. For all
tests 12% of solid concentration was maintained. Sodium hexametaphosphate
was added as the dispersant. After addition of the dispersant to the system,
required pH of the feed slurry was maintained. After addition of the dispersant
dose to the feed slurry, the stirrer speed was maintained very highly so that the
dispersant can act on the individual particles present in the system and the
stirrer speed was maintained approximately 2000RPM.
After addition of the floculant dose, stirrer speed was reduced slowly to prevent
breakage of the floc. After selective flocculation process, the flocculated part was
separated from the dispersed part. After drying both the parts were subjected for
further analysis.
Before addition of the flocculant to the system, the pretreatment of the
flocculant was done.
CMC (Carboxyl Methyl Cellulose) of medium viscosity used as the flocculant for
this study.

The CMC flocculant was prepared by mixing the CMC salt with required quantity
of water and proper temperature was adjusted approximately 80 to 850c by
using a magnetic stirrer. During preparation of the flocculant, it should be
observed that the CMC powder should be homogeneously mixed with the water
solution.
After following the same procedures, few tests were carried out at different
conditions. Test examples were presented in Example 1 and Example 2.
Example 1
General procedure was followed and one test was conducted at flocculant dose
375.(g/t) and at 527.91 (g/ton) dispersant dose (g/t) and at pH 7, it was
observed that Cr2O3(%) was increased from 16.81(%) to 31.34(%),SiO2(%)
achieved 6.42(%),Fe(T)% was achieved 19.66.(%) in the product obtained
approximately 19.66(%) with 32.086 wt(%).
Example 2
General procedure was followed , another test was conducted at flocculant
dose 375(g/t) and at 527.91 dispersant dose (g/t) and at pH 11, it was observed
that Cr2O3(%) was increased from 16.81(%) to 29.6(%),SiO2(%) obtained was
6.68(%), Fe(T)% was obtained approximately 20.35(%) with 33.235(%) wt(%).
REFERENCES: PATENTS PUBLICATIONS
1. A process for recovery of enriched chromium concentrates from chromite
tailings, Indian Patent No. (291/KOL/2013 of 14.3.2013).

2. A process for enriching chromite values of ultrafine particles in chromite
tailings by selective flocculation technique to produce higher grade of Cr203
concentrate, Indian Patent No. (316/KOL/2014).
3. Method of concentrating a chromite containing Ore (Patent No.3473656).
REFERENCES: NON-PATENTS PUBLICATIONS
1.Baris Beklioglu, Ali Ihsan Arol, Selective flocculation behavior of chromite and
serpentine, Physicochemical Problems of Mineral Processing, 38 (2004) 103-112.
2.Udnal Akdemir ", Cahit Hiwilmaz, Shear flocculation of chromite fines in sodium
oleate solutions, Colloids and Surfaces A: Physicochemical and Engineering
Aspects 110 (1996) 87 93.
3. P.K. Weissenborn, L.J. Warren,., J.G. Dunn a.K. L.J. Warren b,., J.G. Dunn ,
Selective flocculation of ultrafine iron ore.1.Mechanisim of adsorption of starch
onto hematite.Colloids and Surfaces.A:Physiological and Engineering Aspects
99(1995)11-27.

WE CLAIM :
1. A process for upgrading values of ultrafine chromite particles from
rejected chromite tailings in a known beneficiation circuit, comprising the
steps of :
(a) classifying the chromite tailings below 400 mesh or 37 micron;
(b) mixing the classified particles to produce a slurry with 12% solid
concentration;

(c) conditioning the slurry with sodium hexameta phosphate acting as
a dispersant solution ;
(d) maintaining the agitator speed at a higher value after addition of
the dispersant dose to the system;
(e) maintaining the desired pH of the feed slurry;
(f) pre-treating the flocculant before addition of the flocculant to the
feed;
(g) adding a desired flocculant dose to the slurry, after addition of the
dispersant dose;
(h) adjusting the stirrer speed after addition of the flocculant dose in
correspondence to the system speed; and
(i) separating the flocculated part from the dispersed part.
2. The process as claimed in claim 1, wherein the flocculant is a freshly
prepared medium viscosity grade of carboxyl methyl cellulose (CMC).
3. The process as claimed in claim 1, wherein the dispersant dose is
prepared by mixing water with sodium hexametaphosphate.
4. The process as claimed in claim 1, wherein the slurry is maintained at a
pH range from 7-11 while it is subjected to selective flocculation.

5. The process as claimed in claim 1, wherein the chemical analysis of a
classified sample tailings exhibits a weight percentage of Cr2CO3, MgO,
SiO2, Fe(T) respectively around 16.36(%), 2.89(%), 8.1(%), and 31.035
(%).
6. The process as claimed in claim 1, wherein a chemical analysis of a
sample slurry concentrated after selective flocculation exhibits a weight
percentage of Cr2O3, SiO2 and Fe(T) respectively about 31.34(%),
6.42(%), 19.66.(%) with 32.086 wt(%) at flocculant dose 375.(g/t),
dispersant dose 527.91(g/t) and pH value of 7.
7. The process as claimed in claim 1, wherein a chemical analysis of a
sample slurry concentrated after selective flocculation exhibits weight
percentage of Cr2O3, SiO2 and Fe(T) respectively 29.6(%),6.68(%) and
20.35(%) with 33.235 wt(%) at flocculant dose 375.(g/t), dispersant dose
527.91(g/t) and pH value of 11.