COLUMN FLOTATION FOR THE BENEFICIATION OF IRON ORE FINES

National Metallurgical Laboratory Madras Centre

C S I R Madras Cemplex, Chennai -600113
swaprabha(cDyahoo.com
1. INTRODUCTION

"Iron ore is more integral to the global economy than any other commodity" perhaps except oil.
Indian iron ore industry is one of the world"s largest and growing at a rapid pace. Optimum utilization of
iron ore resources have become a national priority. As per the recent national steel policy, our country
will be producing about 110 million tons of steel per annum by 2020 requiring around 42 million tons of
iron ore. The iron ore exports are projected to a level of 114 million tones and it amounts to total
production of 300 million tons by 2020. In the present steel boom, many global steel producers have
projects in states of Chattisgarh, Jharkhand, Karnataka and Orissa. Research on utilization of low
grade iron ore to produce quality raw material would play a key role in future which is a fact
acknowledged by the iron and steel industry. [1,2]

India is bestowed with rich iron ore reserves in the form of hematite and magnetite. Most of the
iron ore mines produce hematite ores and have washing plants to produce lumps as well as fines.
During the washing process, around 8-10 million tons of slimes containing around 48-60% of Fe are
discarded every year. Further, hematite ores can contain significantly higher concentrations of penalty
elements, such as water content and aluminum. The challenge facing the iron ore industry is to deal
with the problem of processing alumina rich iron ore fines and slimes. Apart from these available fines,
low and off grade ores such as banded hematite quartz (BHQ) and Banded Hematite Jasper (BHJ) are
invariably ground finer sizes for liberation there by generates slimes which need suitable processing
technology.

The depletion of high grade reserves coupled with increasing market pressure for improved
product quality has forced iron ore producers to re-examine their process flow sheets and evaluate
alternate or supplemental processing routes. The requirement for higher quality iron ore demands that
the silica and alumina contents be lowered for effective use in the steel making. Reverse flotation (silica
& alumina is floated away from the concentrate) has proven to be an economical and effective method
for reducing silica & alumina content to acceptable levels. [3,4]

Iron ore is being beneficiated all around the world to meet the quality requirement of Iron and
Steel industries. However, each source of iron ore has its own peculiar mineralogical characteristics
and requires specific beneficiation and metallurgical treatment to get the best product out of it. The
choice of the beneficiation treatment depends on the nature of the gangue present and its association
with the ore structure. Beneficiation studies using various techniques such as washing, jigging,
hydrocyclone, spiral, advanced gravity separations, magnetic separation, flotation etc. were carried out
to develop a suitable process flowsheet as a step towards the upgradation of iron values and to reduce
gangue content. The required separation technique was selected based on particle size and the
properties for effective separation.

Page lof 12
 When the particles are finer in size (< 100 microns) gravity and magnetic separations are not
effective. The best alternative is flotation, which is a physio-chemical operation and was proven to be
the main unit operation in the mineral industry for treatment of fines for recovering values from gangue.
The process of flotation is mainly affected by the small mass of the particle. Low momentum, slime
coating and high reagent consumption are the most frequently discussed difficulties. As the size of the
bubble plays a vital role in flotation process, extensive research was focused on controlling the bubble
size. Conventional flotation cell has its own limitations in producing fine bubbles below 800 microns.
Keeping in view of the above aspects, the technology of column flotation has been developed.

In recent years, flotation columns are being used for improving the grade-recovery performance
of froth flotation due to their inherent selectivity would make it possible for reducing multistage
conventional flotation circuits to only one or two stage column flotation. Many iron-ore producers world-
wide are considering columns as a viable alternative to conventional flotation machine for the reduction
of silica in fine pellet feed. The technology has been used with great success at many iron ore
processing plants worldwide. NML over the years have done laboratory and pilot scale test work and
has demonstrated some significant metallurgical and economic advantages at various iron ore
beneficiation plants, which include M/s KIOCL, Kudremukh, M/s FOMENTO, Goa, M/s JSW Ltd.,
Tornagallu , Karnataka , M/s Tata Steel , Joda Mines , Orissa and M/s RBSSN Ltd ., Hospet, Karnataka.
Some of the salient results of the test works are discussed in the present paper highlighting the
application of column flotation technology in beneficiation of iron ore fines. [5]

2. COLUMN FLOTATION TECHNOLOGY AND APPLICATIONS

Column flotation offers mineral processors several opportunities to significantly improve process
economics. Properly designed and operated columns can deliver high recoveries and concentrate
grades, reduce reagent consumption, cut energy costs and lower capital expense. High recoveries are
possible because of the column"s ideal hydrodynamic environment and its ability to operate at relatively
high volume fractions of air. Grade performance is enhanced because a deep froth layer can be
maintained and rinsed with a water wash W remove gangue material. Because feed conditioning and
flotation are carried out separately , flotation takes place in a quiescent environment that encourages
bubble/particle attachment.

Improved metallurgical performance is assured by column flotation as a result of:

Less entrainment and entrapment through froth washing
Independent control of operating variables
Flotation of coarse and slimes particles
Can also be used as roughers and scavengers

Reduced running costs as a result of:

No moving parts
Lower reagent consumption
Lower energy consumption (40 - 50% lower than an equivalent mechanical flotation circuit)
Reduced downtime
Page 2 of 12
 Low maintenance and low inventory requirements.

Reduced capital costs as a result of:

Lower residence time
Higher gas holdup
Substantial reduction in floor area
One stage of column flotation is equivalent to 3 stage conventional flotation
Simplification of circuit configuration

A comparison between column flotation and conventional flotation cells is presented below for better
understanding.

Conventional Flotation Cell Column Flotation Cell

1. Relatively large air bubble generation at the 1. Positive air pressure generates fine air bubbles
impeller zone through air bubbler at the bottom

2. Recovery: Very low for fine and coarse particle 2. Recovery: High for fine and coarse particles

3. Turbulent pulp body 3. Quiescent pulp body

(i) Not favorable for the flotation of the large , less (i) Good for flotation of large, less floatable
floatable particles particles
(ii) Contamination of the froth bed by non- (ii) Less contamination of the froth bed by the non-
floatable particles floatable materials

4. Mineral particle air bubble attachment in the 4. Counter current flow of the gravity induced settling
active impeller zone mineral particles and rising air bubbles

(i) Effective residence time and mineral particles (i) Effective residence time is 100% of the
and air bubbles at the active zone is very short residence time for the mineral particle and air
(ii) Small relative velocity between air bubble bubbles in the recovery zone
mineral in the ideally mixed pulp body (ii) Mineral particles & air bubbles move air
opposite directions for head on collision

5. Limitation in froth depths 5. Long cleaning zone

6. High operating costs 6. Low operating costs

(i) High power consumption (i) Low power consumption

(ii) High maintenance costs (ii) Low maintenance costs
(iii) Low recovery (iii) Loser control points, low manpower
7. Long floor space 7. Small floor space

(i) Flat configuration (i) Vertical configuration

(ii) Low capacity (ii) Large capacity
8. High costs for instrumentation and auxiliary unit 8. Low costs for instrumentation and auxiliary units

9. Unit operation capability of small capacity 9. Unit operation capability at large capacity

(i) Improved metallurgical performance

(ii) Process simplification

Page 3 of 12
3. NML'S EXPERTISE IN COLUMN FLOTATION TECHNOLOGY

NML Madras Centre by its extensive R&D efforts had developed indigenous automated laboratory and
pilot flotation column units. The Centre made a pioneering effort in demonstrating the technology by
installing and conducting feasibility studies at the plant premises of various mineral beneficiation
industries both in public and private sector covering base metals, iron ore, industrial minerals, gold etc.

3.a Design and Development

Fully automated laboratory model and pilot size flotation columns were designed, fabricated and
extensively field tested by the Centre. Spargers, both internal and external types were developed to
suit different applications. Special attention was paid in sparger design to generate required bubble size
and bubble flux to suit a wide range of applications. The overall column design facilitates the variation
of column height, feed injection point, froth depth etc.

Laboratory scale

A 75mm. laboratory column was designed, developed and installed at NML Madras Centre during 1990
that has several unique features. The sparger is of internal type fitted with sintered bronze disc of
desired porosity. Differential Pressure Transmitter (DPT) coupled with a micro processor based dual -
loop controller was adopted to maintain the interface between slurry and froth. The interface can be
monitored from display on the LCD screen of the controller. At the steady state, the interface level
could be maintained within +/- 2 cm. Various instruments were incorporated to monitor variables like
airflow, slurry flow, wash water flow etc. The system was extensively field tested and standardized.
Similar systems were supplied to the R&D Centre of NMDC to study the beneficiation of iron ore fines
and Golden Valley Institute of Technology for academic purposed.

Pilot scale

The experience gained in design and development of laboratory and the successful execution of in
plant trials at different mineral processing plants with a wide range of ores, culminated in the
development of a pilot scale model to treat part of the plant stream (50-100 tpd). Accordingly, a 500
mm dia. column (maximum height 14 metres with flanged sections) was fabricated equipped with
suitable pumps, electronic level controls, magnetic flow meters, automatic sampling valves etc.
Different types of bubble generators (spargers) have been designed, suitable to process various
minerals in plant conditions.

Page 4 of 12
 Wash water
WS W-`yl'y_W

Schematic diagram of NML column flotation system

SV

Concentrate

DPT

Feed
--------------
AF2 PG2 PG3
FS

AFM
PG1
ST
__WFM

PC FF
1 01J00 Control Panel

0000
0000 SV
AF1 0000

FCV
Compressor

4 0 Drain
Cv Sv DV line
AS Air flow Sensor DAT•• Differential Pressure Transmitter
AF1&AF2 Air filters FCV Feed Control Valve
AST Air sparger tank FFM Feed Flow Meter
PC Column Controller PG1 Line Pressure gauge
CV Control Valve PG2 Valve Pressure gauge
DV Drain Valve PG3 Transducer Pressure gauge
FS Feed Flow Sensor SV Auto sampling valve
WS Wash Water Flow Sensor WFM Washwater flow meter
AFM Air flow meter ST Sampling timer

Page 5 of 12
Chronology of the development and field tests with laboratory/pilot scale flotation column at various
mineral processing plants:

Year Project Title Sponsor Test Site

Design & development of semi-
1996 commercial, 0.5m dia column with NML Internal resources NMLMC
automatic controls.
Kolar Gold
Demo of 0.5M dia flotation column for
1996-97 Bharat Gold Mines Ltd. Fields,
gold ore beneficiation at BGML
Karnataka
Field testing of 0. 5M dia column at
Gujarat Mineral Kadipani,
1999-00 Kadipani, GMDC, for fluorspar
Development Corpn. Gujarat
beneficiation
OSCOM,
Demo of flotation column for sillimanite Indian Rare Earths
20 01 - 02 Chatrapur ,
beneficiation at OSCOM, Orissa Limited
Orissa
Column flotation of iron ore fines at Sociedade De Fomento Madgaon,
2002-03 Industrial Ltd. Goa
Fomento, Goa
Demo of 0.5M dia flotation column for Calpro Mineral
Salem,
2003-04 the beneficiation of Limestone at Technologies India Pvt.
Tamilnadu
Salem Ltd.
Indian Ocean Garnet Tuticorin,
2004-05 Studies on the Beneficiation of Garnet
Sands Co. Pvt. Ltd. Tamilnadu
Vijayanagar,
Amenability studies at JSW Steel Ltd.
2006-07 JSW Steels Ltd. Gallery,
0. 5M dia. semi-commercial column
Karnataka
Pilot Scale Column Flotation Stt•dies Joda, Barbil,
2008-09 TATA Steel Ltd.
on the Iron Ore Fines at JEIM Orissa

Industrial scale

Based on the successful demonstration of pilot scale column (0.5 m diameter) for the beneficiation of
sillimanite and limestone, industrial size columns were designed and commissioned for the following
industries:

Beneficiation of sillimanite (150 tons/day), Indian Rare Earths Ltd., Chatrapur, Orissa
Beneficiation of sillimanite (150 tons/day), Indian Rare Earths Ltd., Chavara, Kerala
Beneficiation of limestone (100 tons/day), Calpro Mineral Technologies Ltd., Salem, Tamilnadu

Page 6 of 12
3.b Studies conducted by NML on iron ore beneficiation by flotation columns:

Gangue minerals in iron ores generally comprise of quartz or silicates such as alumino-silicates and
their proportion is relatively less. This type of ores are generally beneficiated by flotation using cationic
reagents like amines as collectors and the process is called „reverse flotation". The cationic flotation
(reverse flotation) is advantageous in plant practice because the cationic collectors need less induction
time and provides high contact angles facilitating tenacious bond with the minerals to be separated out.
Hence, they are being widely used world over in iron ore flotation practice. NML-Madras Centre has
been carrying out pioneering work in this area on iron ores of different regions of the country for the
past few decades. Few case studies are discussed below.

1. Feasibility Studies of Column Flotation to Improve the Quality of Iron Ore Concentrate at Kudremukh
(M/s Kudremukh Iron Ore Company Ltd., July 1992) [6]

The objective was to reduce the silica content

---IFT
in the concentrate while improving the iron
-A
recovery using a lab model flotation column FEED
(74mm dia) at the plant site. Reverse flotation L
tests were conducted on four different ^S
PMS NON MAC CYCLONE
samples viz ., spiral rougher concentrate T A ILS
DOUBLE DRUM
(ground ), feed to secondary magnetic Ui F hf LOATH
separator, mixed feed of spiral rougher
concentrate and feed to secondary magnetic BALL MILL
ROUGHER
SPIRALS
separator in the ratio 1:2 and another mixed
feed consisting of secondary and tertiary CYCLONE
magnetic tail in the ratio 4 : 1. Among these, r 0IF
f-RTO FLa ION
the first three have shown excellent BALL MILL
SMS
improvement in both grade and recovery. It
was possible to obtain a concentrate v.ith
SIGLE DRUM
H
CLEANER
SPIRALS
silica content of 2.0% and iron recovery of
RECLEANEA
over 90% from existing 80% apart from circuit 1 I SINGLEED
DRUM SPIRALS
configuration simplification . The results of the J
column tests given in Table indicate clearly
MAG CONC- NON MAG.COM1C• FLOTATION
that the performance of the column compared
with that of the conventional mechanical cells was excellent and capable of improving the recovery of
both magnetic and non-magnetic iron minerals.

Page 7 of 12
 Salient results of column flotation tests:

Feed Wt% Con. Wt.%

Sample Fe Fe SiO2 Tailings Recovery,

No. Wt% %

Rougher spiral concentrate

1 51.48 65.23 2.97 6.03 97.28
2 52.09 65.69 2.07 8.09 96.33
3 54.98 65.81 2.71 98.44
Feed to secondary magnetic
1 separator 68.16 1.65 15.98 96.72
2 61.57 68.31 2.05 34.08 92.14
63.31

2. Beneficiation of Iron Ores by pilot scale Flotation Column ( M/s Sociedado De Fomento Industrial
Ltd., Goa, June 2002) [71

0.5 m dia flotation column was installed at Greater Ferromet plant of M/s Fomento, Goa, to test the
application of column flotation technology for iron ore beneficiation. Reverse flotation process, i.e.,
flotation of gangue minerals was adopted for the removal of SiO2 and AI2O3. Microscopic examination of
the samples collected from four different mines has revealed the presence of hematite, goethite,
martite, magnetite while quartz and clay form the silicate gangue. The flotation results clearly
suggested that iron ore concentrate assaying 67% Fe and 2% SiO2 & A1203 could be obtained with a
recovery of 85-90% by single stage column operation. Better quality of concentrate by flotation column
could be attributed to deeper froth bed and wash water addition. Wash water addition improves the
froth rheology and product discharge. Concentrates with better quality could be achieved if the slimes
are removed before feeding into the flotation column. Thus the iron ore fines generated during mining
and milling operations could be converted to most valuable products by the column flotation technology
besides resolving the environmental issues.

Error! Objects cannot be created from editing field codes.

Page 8 of 12
 Feed assay% Conc. Assay
S.No.
Fe A1203 Si02 Fe A1203 Si02 Fe% Rec.

1 66.7 1.36 1.99 67.4 1.04 0.90 94.4

2 66.0 1.24 2.21 67.2 1.09 0.86 87.6

3 65.4 1.28 2.67 67.2 1.10 0.71 94.2

3. Pilot Scale Column Flotation Studies on the Iron Ore Fines (M/s JSW Steel Ltd., Toranagallu,
Karnataka, June 2007) [4]

The aim of the work was to reduce

alumina and improve upon present weight
recovery (45%) of iron values from screw Feed

classifier overflow (d80 = 40.5pm) in the ,0 mm Screen r +,0 mm

beneficiation plant by adopting reverse

and column flotation so as to increase the C,esef,er
quality of the product and productivity of i
the beneficiation plant. A typical feed of L_
_._..,s ^mes

60.54% Fe, 5.95% Si02 and 3.67% A1203

could be improved to 64.21% Fe, 2.64%
Si02 and 2.20% A1203 at concentrate
weight recovery of 82.7% and Fe recovery
Npr:zoniai tW; fill%r
of 84.7%, a significant gain in the weight
recovery. This in turn leads to increasing
the feed availability to the pellet plant. The PeYel,*ant Feed

process developed is being implemented

on commercial scale columns to be
installed shortly.

4. Pilot Scale Column Flotation Studies on the Iron Ore Fines at Joda East Iron Mines (M/s Tata Steel
Limited, March 2009)

Extensive test work was done at laboratory tests level and at the beneficiation plant site to improve the
quality of screw classifier overflow (d80 = 45.6pm) by reduction of alumina and silica by direct, reverse
and column flotation. By reverse flotation at laboratory level tests, feed of 58.70% Fe, 5.30% Si02 and
5.79% Al O3 could be improved to 63.16% Fe, 3.04% Si02 and 4.51% A1203 at concentrate weight
recovery of 54.26%, which is not significant in terms of reduction of alumina to less than 2.5%. Direct
flotation tests at laboratory level and on-site plant trials met with little success and are insignificant from
industrial practice point of view. The reasons attributed are the predominant form of alumina (gibbsite)
and its intricate and interlocked association with hydrated iron oxides and silica bearing minerals.

Page 9 of 12
Apart from the above case studies exploratory work was done on different ore samples received from
various companies and the salient results are given in the following Table.

Exploratory studies on iron ore beneficiation:

Sponsor Aim Feed to column Conc. produced Remark

To reduce Si02
from iron ore ultra Fe : 63-65
M/s Chowgule, Fe : 47-50% Fe Rec. >90%
fines / slimes Si0 2 :3 . 5-4 . 5%
Goa Si02 : 23-27%
(60% < 45pm)

A low grade ore

Fe 34.95% Fe 53.87% Weight recovery
Si02 26.73% Si02 11.26% .4 0 0
M/s RBSSN, Reduction of AI203 1.82%
AI203 5.54%
Hospet, silica and alumina
Karnataka from iron ore Medium grade ore
Fe 55.56% Fe 64.73% Weight recovery
Si02 10.86% Si02 3.16% 46.7%
A1203 2.98% A1203 0.49%

Reduction of Reverse flotation

M/s Jagannath Fe 61.25% Fe 66.53%
silica and alum i na adopted .
Steels, Orissa Si02 3.89% Si02 1.04%
from iron ore Weight recovery
A1203 : 2.17% A1203 : 0.85%
64.8%
Flotation carried in
To reduce Si02 industrial scale
M/s Fe :32-33% Fe : 63-64%
from Banded column of 7 tph plant
Hospet, Si02 :50-52% Si02 : 5-7 /o
pe, Hematite Fe Rec. : 35-40%
Karnataka Quartzite (BHQ) (one cleaning)
Flotation carried out
Fe : 5 8.08 %
To recover Fe : 61.88 % after de-sliming
M/s JSW,
values from Si02 : 5 7.49% 4.81 /° ( slimes wt
wt /° 32.16
A1203 : 3 Si02 .81
K rna a 2.52 % Fe : ,
plant tailings
arnat aka a
Kt LOI .38%
4.38%
dam LOI : 3.30% Si02:11.89%
A1203: 5.80% )

NML as an integral solution provider

NML has collaboration with M/s Somu Organo Chem . Ltd.(SOCPL), Bangalore , since 2008, for
developing tailor made reagents for the beneficiation of various ores , minerals and coal. The reagents
developed by SOCPL were successful evaluated by NML to reduce silica and alumina content in
different types of iron ores from variety of sources in our country.

Considering the success of NML flotation column in the beneficiation of various minerals M/s McNally
Bharat Engineering Co. Ltd.(MBE), Bangalore, a leading mineral processing equipment manufacturer

Page 10 of 12
and marketing organization showed interest in providing engineering support and marketing the NML
flotation column technology. In year 2008 both the organizations signed an MOU to promote and
market column flotation technology.

The above collaborations enabled NML to provide a holistic solution for the beneficiation problems of
low grade ores which involve developing a viable reagent scheme followed by an industrial scale
processing plant on a turnkey basis involving design, installation and commissioning.

Following projects were taken up under the above collaborations:

1. Fully automatic laboratory flotation column (74 mm diameter) with advanced controls - NEIST
(CSIR), Jorhat, Assam. Successfully commissioned and working satisfactorily at NEIST
laboratory.
2. Pilot scale column (0.5m dia.) for the beneficiation of low grade iron ores with fully automatic
controls - M/s RBSSN, Hospet, Karnataka. Supplied, erected and commissioned.
3. Industrial scale column of 35 tph capacity for the beneficiation of barites - M/ s Andhra Barites
Corporation Ltd., Kadapa, AP. Work is in progress. The reagent to be used in this plant is
developed by NML-SOCPL.

SUMMARY

Over two decades of R&D work NML has gained experience in beneficiating various minerals by
flotation columns on laboratory, pilot and industrial scale.

Based on test results obtained by NML on continuous operation, flotation columns were found to
be beneficial to achieve high grade concentrates from all types of iron ores.

Three industrial scale columns based on NML technology are in operation for beneficiation of
sillimanite and limestone in our country.

Reverse flotation of iron ore places different demands on a flotation column than do other
flotation applications. High froth grade is less important than complete recovery of all floatable
material from the non-floatable product. Columns perform best in this application in an
arrangement that maximizes recovery, rather than one that maximizes froth grade.

Column cells are slowly gaining acceptance for use in roughing applications. With each new
successful installation, the degree of confidence in this technology is increases.

Page 11 of 12
References:

1. Mishra, B.K., Reddy, P.S.R., Das, B., Biswal , S.K., Prakash, S., Das, S.K., Issues relating to
characterization and beneficiation of low grade iron ore fines,
Steel World, Nov., 2007, 34-36.

2. Pradip, Processing of alumina-rich Indian iron ore slimes,

Journal of Minerals , Metals and Materials Engineering , 59 (5), 2006, 551-568.

3. Eisele , T.C. and Kawatra , S.K., Reverse column flotation of iron ore,
Minerals & Metallurgical Processing , Vol. 24, No., May, 2007 , 61-66.

4. Vijayakumar, T.V., Rao, D.S., Subba Rao, S., Prabhakar , S., Bhaskar Raju, G., Reverse
flotation studies on an Indian low grade iron ore slimes,
International Journal of Engineering Science and Technology, Vol. 2(4), 2010, 637-648.

5. Prabhakar, S., Bhaskar Raju, G., Subba Rao , S., Vijayakumar, T.V., Column flotation
technology - NML Experience,
MPT 2010, NML, Jamshedur, Dec., 2010.

6. Bhaskar Raju, G ., Prabhakar , S., Sankaran , C., Beneficiation of iron ores by column flotation,
Trans . Of Institution of Mining and Metallurgy : Sec. C Mineral Processing and Extractive
Metallurgy, Vol. 102, 1993, C132.

7. Vijayakumar, T.V., Rao, D.S., Subba Rao, S., More, P., Reddy, Y.S., Prabhakar, S., Bhaskar
Raju, G, Beneficiation of iron ore fines by conventional flotation, flotation column and dual
extraction column - A pilot scale study,
Power Handling & Processing, Vol. 17, No.2, March/April, 2005, 88-93.

Page 12 of 12