FIELD OF THE INVENTION
This invention relates to a process for recovery of chromite values from the
tailings of chrome ore benefication plant.
BACKGROUND OF THE INVENTION
Large amounts of fine sized chromite tailings naturally occur during production
and processing and this causes severe environmental hazards as well as source
losses due to the high chromite content. There has been numerous research
studies reported on the beneficiation of the tailings in recent years. Generally,
after crushing and grinding, spirals and shaking tables are used as the
concentrators, therefore fine size chromite particles are removed as tailings
(Guney et al., 1999, 2000, 2001). The beneficiation of the valuable minerals
contained in fine particles is a complicated problem in mineral processing and
particularly in gravity separation. The fines are generally discarded as gangue
from gravity concentration processes which ultimately reports to tailing through
process water stream. To recover these fines, investigation results of Feng and
Aldrich (2004) on the Western Chromite Mines in South Africa, shows that
maximum 95.6% of chromite fines can be recovered by using column flotation
with the optimum conditions of parameters. Flotation recovery of many minerals
decreases as the particle size decreases. Based on this fact, the studies of
Akdemir and Hicyilmaz (1996), reveals that shear flocculation of chromite is
possible in aqueous solution of sodium oleate to recover the ultrafine chromite
particles.
Mining and processing operations leads to generation of enormous quantities of
fines, which are major concern in respect of handling, storage and environmental
safety. More than 25% of the mineral value is lost in tailings during the

processing operations. The importance of utility of these vast accumulated fines
through recovery of chromite from these rejected tailings is well-conceived within
the Research community. To cater for the demand of chromium by ferro alloys
industry, and considering insufficient high grade deposits, a relatively economical
method for upgrading or beneficiating these tailings is much required.
Prior art discloses technique for benefication of low grade ferruginous ore by
flotation (Indian Patent No.200700651). Beneficiation of low-grade chromite ores
of abandoned mine was reported by Tevfik Agacayak et. Al., published in
Directory of Open Access Journals, 2011, Lund University Libraries at pp 323-
327. Indian Patent No. 200250012 discloses a method of recovering chromite
from tailing of coarse scavenger tailings, fine scavenger tailing and slime.
During preparation of tailored product, large quantities of fines or superfine -
relatively of lower grade, are being generated and discarded into the tailing
ponds. Further, some of the chromite deposits are either relatively of lower
grade or a mixture of hard and friable matrix which makes them uneconomical
for direct use.
Indian Patent No.200300593 discloses a process to beneficiate lumpy chromite
ore reject to recover lumpy chromite concentrate.
Soviet Union patent No. 1030024 discloses a method to increase the extraction
rate of chromite from chromium ores containing olivine, produced by the fourth
flotation process, is ensured by modification of the flotation properties of the
pulp so that olivine is removed with the first foam prod. U.S. patent No.
2006123951 discloses a method for increasing the chrome to iron ratio of a
chromite product selected from the group consisting of ore and ore concentrate.

Prior art processes although attempted to beneficiate low grade chromite ores
using a number of techniques but for tailings having Cr2O3 content less than
20%, however, no attempts were made Flotation techniques have also been
tried but have not been widely used due to low recoveries.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a process for recovery of
chromite values from the process plant tailings generated in large volume by
processes plants.
Another object of the invention is to propose a process for recovery of chromite
values from the process plant tailings generated in large volume by processes
plants, which is enabled to reduce the chromite losses into the tailings of chrome
ore beneficiation plant to <10% Cr2O3 using existing unit operations.
A further object of the invention is to propose a process for recovery of chromite
values from the process plant tailings generated in large volume by processes
plants, which are finely distributed in a host goethite and/or silica gangue.
SUMMARY OF THE INVENTION
According to the invention, the process utilizes the differences between the
densities of the valuable mineral (chromite) and the associated gangue minerals
(goethite, alumina, silica). The process of the invention comprises the steps of
(a) Classification of the tailings
(b) Concentrating the classified products
(c) Recovery of the free chromite values as concentrate.

Process steps (b) through (c) are influenced corresponding to a change in the
particle size or pulp density. High recoveries of chromite containing significantly
reduced amounts of iron and silica are obtained.
The inventive process is of particular value for concentrating chromite which is
finely distributed along with goethite, alumina, silica and other gangue materials
is herein described. Thus it appears that economic savings are possible by
performing both functions simultaneously.
The present invention proposes an improved process for the recovery of
chromite values from tailings through physical beneficiation methods. It is found
that most of the liberated chromite particles are segregated in the fine size
fraction below 38pm whereas free gangue minerals like quartz, iron silicates and
aluminium silicates were present in the intermediate size fractions. It is
necessary to have detailed information on the liberation and association
characteristics of minerals before selecting unit operations and its process
parameters for achieving desire quality product. Material was classified into
different size fractions and liberation analysis of these three fractions was carried
out using QEMSEM. It reveals that chromite particles are in fully liberated form.
Theoretically 20% weight recovery can be achieved with the concentrate having
59% Cr2O3. At coarser size, chromite is associated with goethite and gibbsite and
in the finer size fraction most of the chromite grains are in liberated form and
iron mineral is the dominant gangue mineral. The challenging task for
beneficiation is recovery of fully liberated chromite particles present in the
ultrafine size ranges followed by selection and optimization of unit operations.
Individual unit operations according to the inventive process has shown the
following increasing order performance.
Wet shaking table>hydrocyclone>floatex density separator

After process optimization on individual unit operations, a synchronization and
combination of unit operations for the inventive process has been proposed. Two
alternative process routes have been provided using combination of floatex
density separator, hydrocyclone and wet shaking table. The first process route
comprises Floatex density separator, wet shaking table and hydrocyclone
whereas the second process comprises hydrocyclone and wet shaking table. The
final product produced from these two process routes assays between 40-50%
Cr2O3 with Cr2O3 recovery of 40.0-45% by weight obtained from a feed value of
19-24% Cr2O3. The Cr: Fe of the obtained product varies from 1.5-1.8 and the
produced tailings contains Cr2O3 between 9.0%-12.0% using combination of a
floatex density separator, a hydrocyclone, and a wet shaking table (Figure 1 &
2). The first process route comprises of classification by Floatex density
separator followed by concentration of floatex underflow in a wet shaking table
and further dewatering of floatex overflow in a hydrocyclone. Similarly in the
second process route wherein two stage classification using hydrocyclone
followed by concentration using wet shaking table was done. From these process
routes a concentrate obtained assays between 40-50% Cr2O3 with Cr2O3
recovery of 40.0 - 45% by weight was obtained from a feed value of 19-24%
Cr2O3. The Cr. Fe of the obtained product varies from 1.5-1.8 and the produced
tailings contains Cr2O3 between 9.0%-12.0%.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Shows a process flow chart using a combination of floatex density
separator, a hydrocyclone, and a wet-shaking table.
Figure 2 - Shows a process flow chart using a combination of a two stage
hydrocyclone and a wet-shaking table.

DETAIL DESCRIPTION OF THE INVENTION
As shown in figures 1 and 2, two process flow sheets are generated using
combination of a floatex density separator, a hydrocyclone, and a wet shaking
table (Figure 1 & 2). The first process route comprises of classification by Floatex
density separator followed by concentration of floatex underflow in a wet shaking
table and further dewatering of floatex overflow in a hydrocyclone. Similarly in
the second process route wherein two stage classification using hydrocyclone
followed by concentration using wet shaking table was done. From these process
routes a concentrate obtained assays between 40-50% Cr2O3 with Cr2O3
recovery of 40.0 - 45% by weight was obtained from a feed value of 19-24%
Cr2O3. The Cr. Fe of the obtained product varies from 1.5 - 1.8 and the produced
tailings contains Cr2O3 between 9.0% -12.0%.

WE CLAIM :
1. A process for beneficiating chromite ores, comprising:
characterization of a sample to estimate the liberation of chromite and
associated gangue phase; adapting benefication technique in individual
unit operations; generating process flow parameters by combining
individual unit operations, recovering chromite values and discarding the
tailings with chrome values less than 12% Cr2O3, the recovered
concentrate containing reduced levels of undesirable gauge.
2. The process as claimed in claim 1, wherein said step of characterization is
carried to estimate the fully liberated chromite and maximum achievable
grade.
3. The process as claimed in claim 1, wherein said step of beneficiation on
individual unit operations is carried out on floatex density separator,
hydrocyclone, and wet shaking table.
4. The process as claimed in claim 1, wherein said step of process flow
parameters are generated after optimizing the actual process parameters
for obtaining maximum recovery and maximum grade.
5. The process as claimed in claim 1, wherein two process flow parameters
are generated, which comprises :

• combination of floatex density separator, hydrocyclone and wet
shaking table; and
• combination of hydrocyclone, and wet shaking table.

6. The process as claimed in any of the preceding claims, wherein the final
product produced from these two process routes assays between 40-50%
Cr2O3 with Cr2O3 recovery of 40.0-45% by weight obtained from a feed
value of 19-24% Cr2O3.
7. The process as claimed in any of the preceding claims, wherein the Cr: Fe
of the obtained product varies from 1.5-1.8 and the produced tailings
contains Cr2O3 between 9.0%-12.0%.

The invention relates to an disclosed is a process for beneficiating
chromite gravity plant tailings. The process is also adaptable to reduce
chromite losses from the existing circuit. A sample is first classified using
hydrocyclone and floatex density separator followed by concentration
using wet shaking table. The desired concentrate recovered in this
manner contains significantly reduced levels of undesirable gangue. The
beneficiated chromite ore shows improved chromium concentrations and
chromium to iron ratios when compared to the original ore.