The present invention relates to a method of recovering improved grade lumpy
chromite concentrates from lumpy ore rejects.
Chromite resources from mines at Sukinda in the State of Orissa, are mostly
enriched with ferrugenous type ore.
During mining operation lumpy ores of siliceous type is also mined along with the
friable ferrugenous type.
The mined lumpy ore is manually sorted out for separating the high grade ore.
The remaining lumpy ore can be treated in a lump ore processing (LOP) plant for
producing the desired grade of products.
In this process low grade lumpy ore with approximately 26% Cr2O3 is also
generated which is usually dumped as rejects.
For Sukinda mines, for example, mined at the rate of about 4.5 million tones per
annum, rejects of low grade lumpy ore generated is about 50,000 tonnes per
annum. A stock pile of around 1.0 million tonnes of the rejects built up over
years and there exists a need to process these ore objects for recovering
improved grade lumpy chromite concentrate.
The principal object of this invention is to provide a method of recovering
improved grade lumpy chromite concentrates from this low grade lumpy ore
rejects.
The characterization studies indicates that the rejects
analyse 25.77% Cr 0 and 15.7% SiO , and the sample has a
2 3 2
Cr/Fe ratio of 2.42. '
Granulometric studies of —75 mm crushed sample indicated
that about 83% material is between 75 and 10 mm containing 88% of
chromite values. The fines below 0.075 mm are only 5%, analysing
6.6% Cr 0 .
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The fines from the sample is contributed by clay particles
originally present as coatings on the lumps.
A liberation study indicated that the sample contained
around 60% chromite rich pieces, 23% chromite and gangue locked
pieces and 17% gangue rich pieces.
Sink—float studies indicated that by gravity methods it
is possible to produce lumpy concentrates analysing about 41%
Cr 0 and 3.0% Cr/Fe ratio at a yield of about 61%.
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On the basis of the above characterization studies, further
benefication studies were carried out for developing a process
for additional recovery of marketable grade lumpy concentrates
from lumpy ore rejects.
By jigging of —40+10 mm fraction it is possible to produce
a concentrate with about 41% Cr 0 , and 3.0 Cr/Fe ratio.
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Figure 1 of the accompanying drawing shows the flow sheet
of the present invention for a method of recovering marketable
grade lumpy chromite concentrates from lumpy ore rejects.
The low grade lumpy ore rejects are to be fed for
example through wobbler feeder and crushed to below 40 mm in
closed crushing circuit.
The crushed sample is to be wet screened at 10mm.
The -40+10mm fraction is to be fed to mineral Jig by
using ragging material of specific gravity higher than 3.5.
The Jig concentrates produced are suitable for refractory
use and analyse more than 31.1 Cr/Fe and 40% Cr 0 .
2 3
The - 10 mm fraction is subjected to classification to
remove slimes
The Jig middlings and — 10 mm deslimed sand fraction
together can become a feed to the present COB plant to produce
normal marketable grade concentrates.
The Jig tails, slimes, together analysing less than 10%
Cr 0 , can be rejected.
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The jig concentrate produced by the method of present
invention is the product for direct sale in the market.
Thus it is possible to produce ~ 31% lumpy ore concentrates
analysing about 40% Cr 0 and 3.0 Cr/Fe ratio at about
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-40+10 mm size by Jigging from lumpy ore rejects analysing
~ 26% Vr 0 .
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Simultaneously material analysing around 20% Cr 0 are
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also produced which can be used as a feed material for the chrome
ore benefication plant after grinding to —0.5 mm.
The tailing generated ( 29,000 tpa) contain less than 10%
Cr 0 and can be rejected.
2 3
The additional quantities of concentrates produced can
generate handsome return on investments.
WE CLAIM
1. A method of recovering improved grade lumpy chromite concentrates
from lumpy ore rejects, comprising the steps of:
(a) feeding low grade lumpy ore rejects and crushing to -40mm size in a
closed crushing circuit;
(b) wet screening crushed sample at 10mm, yielding -40+10 and -10mm
fractions;
(c) feeding the -40+10mm fraction to a mineral jig using ragging material of
specific gravity higher than 3.5; and
(d) collecting jig concentrates produced which analyse 31:1 Cr/Fe and 40%
Cr2O3, as the final product.
2. The method as claimed in claim 1 comprising the steps of:
(e) subjecting the -10mm fraction to classification after step (b) to remove
slimes;
(f) collecting the -10mm deslimed (sand) fractions, and the jig middlings
from step (d); and
(g) feeding -10mm deslimed fraction and jig middlings for processing as in
steps (a) to (d) to produce normal marketable grade concentrate.
3. A method of recovering improved grade lumpy chromite concentrates
from lumpy ore rejects substantially as herein described and illustrated in
the flow sheet of accompanying drawing.
Dated this 17th day of November 2003

A method of recovering improved grade lumpy chromite concentrates from
lumpy ore rejects, comprising the steps of feeding low grade lumpy ore rejects
and crushing to -40mm size in a closed crushing circuit; wet screening crushed
sample at 10mm, yielding -40+10 and -10mm fractions; feeding the -40+10mm
fraction to a mineral jig using ragging material of specific gravity higher than 3.5;
and collecting jig concentrates produced which analyse 31:1 Cr/Fe and 40%
Cr2O3, as the final product.