THE FIELD OF THE INVENTION
The present invention relates to an improved process for recovery of iron values
from the rejects of iron ore washing plant. The process would enable enrichment
of iron ore fines for sinter making. It would also be helpful in increasing the life of
the tailing pond.
DESCRIPTION OF KNOWN ART
Various equipment like ferrous wheel, WHIMS etc. being used for recovery of iron
values from wastes of iron ore mine followed by some dewatering process. The
above equipment are very costly.
Beneficiation of iron ore fines is achieved by the following processes as
discussed hereunder:
Treatment of the fine hematite (-0.5 mm) particles with gangue minerals in
Floatex Density Separator (FDS) to recover iron values. The principle involved in
this separator is hindered setting classification.
Use of hydrocyclone in conjunction with Slow Speed Spiral Classifier (SSSC) is
known to upgrade the slime. A battery of about twelve hydrocyclones and two
units of SSSC (90 t/hr each) are usually in operation to recover nearly 100 t/hr
enriched fines.
It is important to mention herein that in both the above known processes of
beneficiation of iron ore fines involve use of fines which are not waste and the
size of iron fines is coarser.
The above discussed known processes are not suitable for recovery of iron
values from slime (wastes) which unlike the coarser fines treated above are very
fine (70% contains - 325 mesh fractions). Recovering of iron values with such a
fine granulometry at a low operating cost is very difficult.
It is thus the basic object of the present invention to provide a process for
recovery of iron values from wastes/rejects of iron ore washing plants.
Another object is to provide a process for the recovery of iron values from
wastes/rejects of iron ore washing plants which will be on one hand simple and
effective and on the other hand commercially viable.
Yet further object is directed to a process of recovery of iron values from iron ore
fines involving fine granulometry at a low operating cost.
Yet further object is directed to a process of recovery of iron values from iron
fines which would provide for the following operative advantages :
a) Improve performance and availability of downstream equipment i.e. thickeners
and slurry pump ;
b) Increase life of tailing pond in an iron ore mine ;
c) Increase availability of process water; and
d) Decrease environmental pollution.
Thus according to the present invention there is provided an improved process
for recovery of iron values from iron ore fines such as rejects/wastes of iron ore
washing plants comprising :
subjecting the said iron ore fines to treatment in a fluidised bed classifier having
an underflow and overflow means wherein the iron ore particles are subjected to
a rising current of water whereby the dense and coarse particles reach at the
bottom and the lighter particles pushed out by the water stream through the
overflow means;
subjecting the underflow of the fluidised bed classifier comprising said dense
coarser particles to further processing in atleast one hydrocyclones;
dewatering the underflow of the hydrocyclone to thereby recover the iron values
from the ore.
Preferably, in the above process, the underflow from the fluidised bed is fed into
the hydrocyclones by means of slurry pumps.
During the above process of recovery, the feed rate of the system is operated
such that there is always an overflow from the fluidised bed classifier ensuring
continuous removal of lighter particles.
In accordance with a preferred aspect, the underflow of the fluidised bed
classifier is further processed in plurality of hydrocyclone. The size of the
hydrocyclone and its apex and vortex diameters are selectively determined to
achieve maximum recovery.
In accordance with another aspect of the present invention there is provided a
system for carrying out the method of recovery of iron values as detailed above
comprising :
fluidised bed classifier having an underflow means and an overflow means;
means for feeding water to said classifier from the bottom;
slurry pump means operatively connecting said underflow of the fluidised bed
classifier to the hydrocyclone, said hydrocyclone means having dewatering unit.
Preferably, the dewatering unit is comprised of single deck vibrating screen
consisting of variable apertures (50 to 200 micron range). In order to remove
moisture further for the recovered product there is provided a slightly inclined
conveyor for carrying forward the recovered product with such a speed so that
water trickles down through the bottom side of the conveyor having a skirt gate to
thereby further enrich the recovered product.
The details of the invention its objects and advantages would be apparent from
the further details provided hereunder in relatioin to the non-limiting exemplary
embodiments as illustrated in the accompanying figures.
Fig. 1 is an illustration of a conventional process of recovery of iron values
presently in use.
Fig. 2 is a schematic illustration of the improved process of recovery of iron
values in accordance with the present invention ; and
Fig. 3 is a schematic illustration of the system for use in the improved process of
recovery of iron values in accordance with the present invention.
Reference is first invited to Fig. 1 which shows the conventional art of recovery of
iron values from iron ore fines. As shown in said figure the slime as the classifier
overflow is first treated in the Floatex Density Separator (FDS) from where the
underflow is subjected to the treatment in the hydrocyclone for recovery of the
iron values. The amount of recovery from the initial fines is also represented in
illustration.
Reference is now invited to Fig. 2 which shows the method in accordance with
the present invention. As shown in said figure the slime from the classifier
overflow preferably is fed (tangentially at the rate of about 1000 t/hr slurry) to the
Fluidised Bed Classifier (FBC) by gravity. The fludised bed classifier is preferably
a conical vessel having larger overflow pipe diameter and smaller underflow
diameter. A stream of water in injected from the bottom of the FBC through a
valve means. The iron ore particles are subjected to the rising current of water
and expanded into a state of 'teeter' which means the fine particles coated with
thin film of water are in perfect suspension. The whole mass acts as a viscous
liquid, which allows only the heavy particles, which have specific gravity more
than the teeter bed to penetrate. The iron ore grains are predominantly classified
by density. Dense and coarse particles report at the bottom of FBC whereas the
lighter particles are pushed out by the water stream through the overflow pipe.
The feed rate to the system is operated in such a way that there is always an
overflow from the FBC, ensuring removal of lighter particles. The underflow of the
FBC is further processed in a battery of hydrocyclones preferebly 4 Nos. by a
slurry pump. The size of the hydrocyclone and its apex and vortex diameters are
so chosen such that the recovery is maximum. Here the basic purpose is to
discard the subsieve fraction as well as quality upgradation. The underflow of
hydrocyclone is dewatered through a dewateriser. The recovery of iron value
achieved is also represented in the said illustration.
The upgradation in iron (Fe) in the product is about 11% (absolute) with about
20% material recovery. The hydrocyclone underflow product contain about 40%
water. The dewateriser unit is preferably comprised of a single deck vibrating
screen consisting of variable apertures (50 to 200 micron range). In order to
remove moisture further from the product, the product is conveyed through a
slightly inclined conveyor with such a speed so that water trickles down through
the bottom side of the conveyor having a skirt grate and the final product gets
further enriched and thus become a suitable feed to sinter grade fines.
Reference is now invited to accompanying Fig. 3 which schematically illustrates
the system for carrying out the improved method of recovery of iron values from
wastes/rejects of iron ore washing plants. As shown in said figure, the system
comprises of the fluidised bed classifier (FBC) which is a conical vessel having
larger over flow pipe diameter and smaller underflow diameter. Importantly, the
waste/rejects (slime) is required to be fed tangentially into said fluidised bed
classifier (FBC) and for the purpose the FBC is adapted accordingly. The system
also includes means for controlling the feed rate into the said fluidised bed
classifier (FBC) of said slime. In such a way that there is always an overflow from
the fluidised bed classifier (FBC) ensuring removal of lighter particles. Also, the
fluidised bed classifier (FBC) is also adapted to be injected with stream of water
from the bottom through a valve means.
The fluidised bed classifier (FBC) is further operatively connected to
hydrocyclone (HC) by a slurry pump (SP) such that the underflow from the
fluidised bed classifier (FBC) is fed into the hydrocyclone (HC) for further
processing. The size and nos. of the hydrocyclone and its apex and vortex
diameters are chosen based on the desired recovery of the iron values. The
underflow from the hydrocyclone is dewatered through a dewateriser. The
dewateriser unit is specially developed with single deck vibrating screen
consisting of variable apertures (50-200) micron range.
In order to further remove the moisture, the recovered product is further
conveyed on a slightly inclined conveyor with such a speed such that water
trickles down to the bottom side of the conveyor having skirt grate and the final
product gets further enriched and thus become a suitable feed to sinter grade
fines.
It is thus possible by way of the above disclosed improved method of recovery of
iron values from iron fines and system for use in such method to achieve
recovery of iron values from iron fines following a cost-effective and simple
process and importantly from iron ore fines involving very fine granulometry at
low operating cost.
The process of the invention avoids the drawbacks of the methods presently in
use. Importantly, in FBC, due to tangential feeding (unique feature) coupled with
density separation in fludised material bed, the enrichment in Fe is very high and
which makes it cost effective. Also, the selective use of FBC and the
hydrocyclones provide for avoiding the costly and maintenance prone
equipments such as disc filter or pressure filter.
WE CLAIM
1. An improved process for recovery of iron values from iron ore fines such as

rejects/wastes of iron ore washing plants comprising :
subjecting the said iron ore fines to treatment in a fluidised bed classifier having an
underflow and overflow means wherein the iron ore particles are subjected to a rising
current of water whereby the fine particles are coated with a film of water and
maintained in suspension to constitute a mass of viscous liquid, the dense and
coarse particles reaching at the bottom and the lighter particles pushed out by the
water stream through the overflow means ; subjecting the underflow of the fluidised
bed classifier to further processing in one or more hydrocyclones ;
dewatering the underflow of the hydrocyclone to thereby recover the iron values from
the ore.
2. An improved process for recovering of iron values from iron ore fines as claimed in
claim 1 wherein the underflow from said fluidised bed classifier is fed into plurality of
hydrocyclone preferably four hydrocyclones.
3. An improved process for recovering of iron values from iron ore fines as claimed in
anyone of claims 1 or 2 wherein said underflow from said fluidised bed classifier is
fed into plurality of hydrocyclone preferably from hydrocyclones (HC).
4. An improved process for recovering of iron values from iron ore fines as claimed in
anyone of claims 1 to 3 wherein the rejects/waste (slime) is tangentially fed into said
fluidised bed classifier (FBC) by gravity.
5. An improved process for recovering of iron values from iron ore fines as claimed in
claim 4 wherein the slime containing 10-20% solids is fed tangentially at a rate of 800
to 1400 t/hr preferably 1000 t/hr.
6. An improved process for recovering of iron values from iron ore fines as
claimed in anyone of claims 1 to 5 wherein the feed rate is adapted such that
there is always an overflow from the fluidised bed classifier (FBC) of lighter
particles ensuring content removal of lighter particles.
7. An improved process for recovering of iron values from iron ore fines as
claimed in anyone of claims 1 to 6 wherein said stream of rising water is
injected through the bottom of the fluidised bed classifier.
8. An improved process for recovering of iron values from iron ore fines as
claimed in anyone of claims 1 to 7 wherein said water is injected form the
bottom of the fluidised bed classifier whereby the iron ore particles are
subjected to the rising current of water and expanded into a state of 'teeter'
such that fine particles coated with thin film of water are in perfect suspension
and the whole mass acts as a viscous liquid and allows only the coarser
particles having a specific gravity more than the teeter bed to penetrate and
constitute the underflow of the fluidised bed classifier.
9. An improved process as claimed in anyone of claims 1 to 8 wherein the size
of the hydrocyclone and its apex and vortex diameters are selectively chosen
based on the character of the waste/reject and the desired recovery.
10. An improved process as claimed in anyone of claims 1 to 9 wherein after
said step of dewaterising in said hydrocyclones the recovered product is
conveyed through a slightly inclined conveyor such that the water trickles
down to the bottom side of the conveyor having skirt grate and the final
product is enriched.
11. An improved process as claimed in anyone of claims 1 to 10 comprising
screening the waste/rejects prior to feeding such that materials with particle size
upto 2 mm are fed into said FBC and preferably maintain very fine granulometry
70% max of-300 mesh.
12. An improved process as claimed in anyone of claims 1 to 11 wherein the
slime fed into FBC is obtained after usual sizing of iron ore comprising steps
of crushing, screening and classification.
13. A system for carrying out the improved method of the recovery of iron values
from iron ore wastes/rejects (slimes) as claimed in anyone of claims 1 to 12
comprising :
a fluidised bed classifier having an underflow and an overflow means;
means for feeding of the wastes/rejects (slime) into said fluidised bed
classifier preferably tangentially and by gravity ;
means for supply of rising current of water into the said fluidised bed classifier
(FBC) through the bottom thereof ;
atleast one hydrocyclone means;
means for transferring the heavier particles from the underflow of the FBC into
said atleast one hydrocyclone ; and
means for dewaterising the hydrocyclone.
i
14. A system as claimed in claim 13 wherein the FBC is a conical vessel with a
larger overflow diameter and a smaller underflow diameter.
15. A system as claimed in anyone of claims 13 or 14 comprising valve means to
inject the stream of water from the bottom of the fluidised bed classifier.
16. A system as claimed in anyone of claims 13 to 15 wherein said means for
supply of heavier particles from the underflow of the FBC to said
hydrocyclone comprise slurry pumps.
17. A system as claimed in anyone of claims 13 to 16 wherein said FBC is
connected to plurality of hydrocyclone.
18. A system as claimed in anyone of claims 13 to 17 wherein the size of the
hydrocyclone and its apex and vortex diameters are selected based on the
desired recovery rate.
19. A system as claimed in anyone of claims 13 to 18 wherein a dewateriser unit
is provided in said hydrocyclone.
20. A system as claimed in anyone of claims 13 to 19 wherein dewateriser unit
comprise of single deck vibrating screen consisting of variable apertures in
the range of 50-200 microns.
21. A system as claimed in anyone of claims 13 to 20 comprising an inclined
conveyor operatively connected to said hydrocyclone such that the recovered
product is conveyed slightly inclined and thereby effecting further drying and
enriching of the product.
22. A system as claimed in anyone of claims 13 to 21 wherein the bottom side of
the inclined conveyor is provided with skirt grate which is adapted for allowing
water to trickle down to thereby effectuate the desired further drying of the
product.
23. An improved process for recovering of iron values from iron ore fines and a
system for use in such process substantially as hereindescribed and
illustrated with reference to the accompanying examples.

An improved process for recovery of iron values from the rejects of iron ore
washing plant for enrichment of iron ore fines using fluidised bed classifier
comprising subjecting the said iron ore fines to treatment in a fluidised bed
classifier whereby the dense and coarse particles reach at the bottom and the
lighter particles pushed out by the water stream through the overflow means ;
subjecting the underflow of the fluidised bed classifier comprising said dense
coarser particles to further processing in atleast one hydrocyclones
anddewatering to thereby recover the iron values.
It is possible by way of the above process for recovery of iron values from
wastes/rejects of iron ore washing plants which will be on one hand simple and
effective and on the other hand commercially viable. Also the process is directed
to recovery of iron values from iron ore fines involving fine granulometry at a low
operating cost. Importantly the above process provide for the following operative
advantages:
a) Improve performance and availability of downstream equipment i.e. thickeners
and slurry pump;
b) Increase life of tailing pond in an iron ore mine ;
c) Increase availability of process water; and
d) Decrease environmental pollution.