FIELD OF INVENTION
The present invention relates to a method for cold bonded pelletizing of ferrous or non-
ferrous ores or mineral fines by mixture of organic and inorganic binders adaptable to
metallurgical application.
BACKGROUND OF INVENTION
Pelletizing is one of the widely used methods of agglomerating iron ore fines to produce a
quality feedstock for the iron making furnaces. The first large plant (with a capacity in
excess of 6 million tons per annum) in the United States that commenced operation in
1955 and by the year 1975 iron ore pellet production in the United States was almost 60
million tons per annum. The Pelletizing plants are now operated in many countries.The
iron ore pelletising capacity is around 400 million tones per annum throughout the world.
This widely practiced conventional pelletizing process to produce indurated or heat
hardened pellets consists of two distinct operations. First is preparing pellets at ambient
temperature and second is firing them at high temperature in the range of 1250-1350° C
depending upon the material. In the first operation, pellets are formed by the rolling
moist fine ore of proper fineness (60% - 80% less than 45 microns) in either a horizontal
drum, or more usually an inclined disk, and are known as "green balls" or pellets. At this
stage the pellets are required to have adequate strength to withstand handling to the
firing stage and sometimes a minimum quantity of an inorganic or an organic binder is
added to achieve an adequate strength. In the second operation the pellets are fired. The
resulting fired pellets are typically a spherical in shape of 9-16 mm in diameter, and have
a cold compression strength of in the range of 200-250 kg/pellet. "Coldcompression
strength (CCS)" is a measure of the load required to be applied to cause crushing of a
spherical pellet of 10-12.5 mm diameter placed between two plates of an compression
testing machine. Sufficient CCS is required to withstand the bulk handling for loading to
railway cars, unloading of railway cars, at port facilities, at steel works etc.
Firing of Pellets is normally carried out using gas, oil or coal as fuel. The firing operation
consists of large, complicated furnaces, like the grate-kiln, straight grate or shaft furnace
to carry out the firing on a continuous basis. The high temperature firing /induration
process requires large quantities of thermal energy, ranging from 90000 to 250000
kcal/tonne of pellets and electrical energy of 35 kWh per ton of pellets, depending on
whether the iron oxide in the ore is in the form of magnetite or hematite. A significant
environmental problem like high thermal NOx emission is also associated with the high
temperature in duration process. This is a serious concern for the iron ore producers and
pollution control agencies.
Many attempts have been made to find an alternative agglomeration processes and in
particular the processes which could avoid the necessity of firing/in duration step which
needs a huge amount of energy and a high capital investment. Over the years cold
bonded pelletizing (CBP) has emerged as an alternative to heat hardened pelletizing
route. The cold bonded pelletizing does not required firing or in duration of pellets at high
temperature to* attain the required strength (CCS). The required strength is achieved by
using a proper binder or binder combinations and curing the pellets at relatively very low
temperatures. Cold bonded pelletizing process needs a minimum amount of energy and
does not require complicated equipment. Since its inception in 1971 and especially during
1980's it has become evident that cold bonded pelletizing is an economically feasible
method for agglomerating iron ore fines and in particular, recycling of dust and sludge.
The general requirements for good quality agglomerates include sufficient strength of
pellets for handling and for long distance transportation, the ability to withstand outside
storage without having substantial detrimental effectes, and complete reducibility in iron
and steel furnaces without having premature degradation or excessive swelling.
Till date numerous CBP processes have been developed in which inorganic binders such
as cement, lime, magnesia, clays, bentonite or organic binder materials such as tars,
petroleum residues, starches, waxes, flours, paper industry by products and polymers
have been employed. In general the resulting pellets have been either too expensive to
produce and/or have been deficient in quality. Some inorganic binders also add unwanted
slag making constituents to the pellets.
• Liu Hanqing et al.'s, Patent (US 20050061207) DATED 24 March. 2005, describes
use of 10-26% Portland cement clinker as binder in making self reducing pellets of
iron ore fines, steel making dust, BF dust and mill scale and curing for 14-28 days
to attain 78-200 kg pellet strength.
• Graham Roderick et al.'s, Patent (US 4402736) dated 6 September 1983, describes
use of 0.5-10% raw starch as binder in making cold bonded pellets of iron ore
fines and curing at 70-170oC to attain strength of 136 kg/pellet.
• Hideomi Yanaka et al/s, Patent (US 5066327) dated 19 Nov 1991, describes use of
6% cement as binder and curing in a traveling grate in C02 atmosphere at 90°C in
making cold bonded pellets of iron ore fines for use in blast furnace.
• Aota Jay Kanata et al/s, Patent (US 6409964) dated 25 June. 2002, describes use
of 7% high alumina cement as binder in making pellets of ferrous ores and plant
wastes by heat treatment at 100 to 200° C temperature.
• Schierloh Uwe et al/s, Patent (US 3765869) dated 16 October 1973, describes use
of starch/dextrin (0.2-0.5%) and iron powder up to 6% as binder in making cold
bonded pellets of iron ore fines for DRI making shaft furnaces.
• Kelly J James et al/s, Patent (US 5100464) dated 31 March 1992, describes use of
sucrose residue/molasses (0-10%) and gypsum free hydraulic cement (3-10%) as
binder and drying at 150-200 °C and further curing in making cold bonded pellets
from steel mill byproduct material.
• Nayak Bansidhar et al/s, Patent (US20040107800) dated 10 June 2004, describes
use of 4-10% iron bearing hydraulic mineral as binder and curing for 3-20 days in
making cold bonded pellets from ferrous and nonferrous ore or mineral fines for
use in Blast furnace, shaft furnace and rotary kiln.
• Shimada Shunsaku et al.'s, Patent (US 3925069) dated 9 Dec 1975, describes use
of 2-40% cement & iron containing powder mix as binder in making cold bonded
pellets for use in Blast furnace.
• Pirtle James et al/s, Patent (US 6384126) dated 7 May 2002, describes use of 2%
colloidal silica and 2% polyvinyl alcohol as binder and drying at 150°C in making
cold bonded pellets of iron ore fines for making DRI in coal or gas based furnaces.
• Matsul Seiji et al/s, Patent (US 4597790) dated 1 July 1986, describes use of 5-
15% cement and 5-30% reduced iron powder or mill scale powder as binder and
curing in C02 atmosphere and drying at 250 °C in making cold bonded pellets of
iron ore fines for making DRI in shaft furnaces.
The drawbacks of the earlier processes in the prior art as illustrated herewith are the use
of wide varieties of binding materials, steam curing, heat hardening and very long curing
times (up to 30 days) in making pellets which are energy intensive. In some cases
organic binders like raw starch or dextrin were used in pelletizing but the pellets lose their
strength very quickly at low temperatures due to the burn off of these binders. In some
cases binders consisting of bentonite and/or clays have employed minor amounts (for
example 0.25% by weight of iron ore) of gelatinized starch. However the gelatinized
starch was then present for the purpose of lubrication the binding composition and those
binders were used prior to firing rather than as a substitute for firing. It has not
previously been proposed to use dextrin and bentonite combination as a binder in cold
bonded pelletizing. Most of the cement based and caustic based binders also add
deleterious impurities in the metallurgical process and create emission of hazardous and
corrosive gases which cause destruction of furnace life and air pollution. Thus there exists
a need to provide a process or method that overcomes the aforesaid limitations
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a method for cold bounded
pelletizing of ore or mineral fines by a mixture of organic and inorganic binders which
eliminates the disadvantages of prior art.
Another object of the present invention is to propose a method for cold bounded
pelletizing of ore or mineral fines by a mixture of organic and inorganic binders which
produces pellets of sufficient strength to permit handling, transportation and uses in the
manner mostly usual for fired pellets.
A further object of the present invention is to propose a method for cold bounded
pelletizing of ore or mineral fines by a mixture of organic and inorganic binders which
does not contaminate the pellets by stag forming constituents.
A still further object of the present invention is to propose a method for cold bounded
pelletizing of ore or mineral fines by a mixture of organic and inorganic binders which
reduces the curing time of pellets for achieving the required strength
An yet further object of the present invention is to propose a method for cold bounded
pelletizing of ore or mineral fines by a mixture of organic and inorganic binders which is
suitable for use in Basic Oxygen Furnace (BOF), Electric Arc Furnace (EAF) submerged
Arc furnace (SAF) Ladle furnace (LF) and Rotary hearth furnace (RHF).
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig -1 shows the effect of dextrin dosage on the wet drop number and green
compression strength of cold bonded pellets.
Fig -2 shows the effect the drying temperature on the dry drop number of cold bonded
pellets.
Fig -3 Microstructure of cold bonded pellets.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The cold bonded pelletizing of the ore or mineral fines involves the following steps;
1. Raw material preparation to prepare the green pelletizing mix.
2. Mixing the binder or binders
3. Preparation of green pellets
4. Curing the green pellets
To prepare green pellets the ore or mineral fines are ground to the required fineness
(60% to 80% less than 45 microns) in the ball mill. If the fines to be pelletized already
posses the required fineness and size distribution, then there is no need of grinding.
In the present method, ground mineral fines are mixed with composite binder to prepare
the pelletizing mix. The composite binder, consist of a combination of Dextrin and
Bentonite is added to the ore fines. Dextrin is a polysaccharide intermediate between
Starch and Sugars. Dextrins are a group of low-molecular-weight carbohydrates produced
by the hydrolysis of starch. Bentonite is naturally occurring plastic clay under
montmorillonite group. Bentonite, (Na Ca) (Al Mg) Si4O10(OH)2 is basically an alumino-
silicate clay. Chemical composition of bentonite is shown in Table. 1.

The amount of binder required is a compromise between cost of the binder, strength of
the final pellet and decreased ore value,. To get satisfactory quality, 1-5 wt% of dextrin
by weight of the mineral fines and 1-3 wt% of bentonite by weight of the mineral fines is
added. First premix the binders thoroughly in the required ratio, for example, 75:25 of
dextrin: bentonite or 80:20 of dextrin: bentonite and then add this composite binder to
the pelletizing mix. This method of premixing both the organic and inorganic binders
produces a homogeneous pelletizing mixture. Prewetting of the mixture comprising of ore
fines and composite binder is done by adding adequate of water, normally in the range of
4-6% by weight of the mixture. After prewetting the mixture is called green pelletizing
mixture. Pelletizing is carried out in the normal manner with water being added as
appropriate to the mineral during this operation. The amount of water used being that
required for satisfactory pelletizing, normally in the range of 9-11% by weight of the
pelletizing mix, but changes as per the type of ore or mineral whether they are
hydrophilic or hydrophobic in nature. The pellets, in the size range of 8-16 mm in
diameter are then dried, either by allowing them to dry in air at ambient temperature for
one to two days or in the oven at around 75-150°C. Dried pellets of having average drop
strength of 20-25 are produced by using 4% dextrin and 1% bentonite.
In another embodiment of this invention, to produce cold bonded pellets from chromite
fines for smelting in Submersed arc furnace solid reductant like coal fines is added to the
cold bonding pelletising mix before the preparation of pellets. The carbonaceous material
in the pellets helps in the in situ reduction of oxides during the smelting operation. The
carbonaceous material also aids the early reduction of iron oxides to metallic phase that
improves the high temperature strength.
Application case study-1: Cold bonded composite chromite-coal pellets for direct
reduction in RHF or SAF.
Ground chromite fines, solid reductant fines, flux powder, bentonite and dextrin as given
in the Table.2 are premixed in the dry state to form a homogeneous mixture. Prewetting
of the dry pelletizing mixture is done by adding 8-9% water. Pelletizing experiments are
conducted on a laboratory balling disc. Diameter of the disc is 600 mm and angle of
inclination and rpm of the disc were set at 45° and 25 respectively during balling. During
pelletizing 1-2% water was added on the disc. Time taken for pelletizing 2kg batch is
approximately 20 minutes.

1.1 Drying of green pellets:
Green pellets are dried in a laboratory hot air dryer at different temperatures ranging
from room temperature, 100°C, 150°C, 200°C, 250°C, 300°C, 350°C and 400°C for one
hour.
1.2 Testing of cold bonded pellets:
The green pellets are tested for compression strength and drop strength whereas the
dried pellets are tested for drop strength. The drop strength measures the ability of the
pellets to survive drops during transportation and handling. The drop strength is
measured by means of dropping the pellets on a steel plate from a height of 1 meter.
The number of drops the pellet withstands without damage is measured as drop strength
of the pellets. Pellets of 10-12.5mm diameter are used for drop test and average value of
the 20 pellets is used as drop strength.
Compressive strength measures the ability of wet pellets to retain their shape under the
compressive forces acting on them. The strength of green pellet originates mainly in the
capillary negative pressure in the liquid saturated pores. Saturation degree, i.e., the
volume fraction of pores taken up by the water, has an important influence on the
compressive strength of pellets. A single pellet was compressed manually on an electronic
balance and the load required to fracture the pellet was recorded. This was repeated for
10 pellets and the results were averaged.
1.3 Results:
Fig. 1 shows the drop strength and compression strength of cold bonded pellets before
drying. With increasing dextrin dosage, drop number of the green pellets is increasing,
but green compression strength is decreasing. This could be attributed to the increasing
fluid viscosity in the green pellets. Drop number of the dried pellets is increasing with
increasing dextrin dosage as shown in the figure. Natural curing of green pellets at room
temperature for 24 hours is also imparting considerable drop strength, but drying at 150°
C in the oven is yielding the maximum strength at 4% dextrin.
It was found through drying experiments that green pellets are losing nearly 40% of the
water during room temperature curing and most of the added water is removed at 100
°C. A temperature range of 100-150 °C seems to be better for the drying of green pellets.
A steady state weight loss beyond 150 °C temperature indicates the start of burning of
dextrin which is not desirable and deteriorated the pellet quality. Beyond 200 °C, the dry
drop strength of pellets falls to zero, i.e. dextrin is completely burning off at this
temperature.
Application case study-2: Cold bonded pellets for recycling iron ore slimes in Basic
oxygen furnace in this study cold bonded pellets are prepared for recycling iron ore slimes
in BOF furnace. These pellets can replace some of the scrape that is used in BOF as a
coolant. Iron ore slimes of fineness (80% minus 45 microns) and composite binder (4%
dextrin and 1% bentonite) are premixed in the dry state in a turbo mixer to form a
homogeneous mixture. Prewetting of the dry pelletizing mixture is done by adding 8-9%
water. Pelletisation experiments are conducted on a laboratory balling disc. Diameter of
the disc is 600mm and angle of inclination and rpm of the disc were set at 45° and 25
respectively during balling. During pelletizing 1-2% water was added on the disc. Time
taken for pelletizing 2kg batch is approximately 20 minutes.
The dried cold bonded pellets are tested for drop strength and abrasion resistance.
Resistance to abrasion is the ability of the pellets to suppress the dust generation during
handling. It is tested by rotating 500 grams of dry pellets in 200 mm X 345 mm drum for
1 minute at a speed of 52 rpm. The resistance is reported as wt% of the fraction of
particles more than 3 mm.
To compare the performance of composite binder, pellets are also prepared with 10%
cement as binder. As shown in the Table.2, cement bonded pellets even after 7 days
curing time, could not develop enough drop strength. But composite binder pellets
developed required drop strength after one day curing. Similarly composite binder pellets
have shown remarkable abrasion resistance compared to cement bonded pellets.

The present method of cold bonded pelletizing is not limited for recycling iron ore slimes
in BOF. Innoculants, hot toppings and steel additives can be used through this method
where they subjected to limited handling and the requirement for compression strength is
not as severe.
It will be understood that the examples described herein, case study-1 and case study-2,
are in no way limiting and that the order of the steps and the relative concentrations and
conditions may be altered to an extent which will be apparent to those skilled in the art
without departing from the inventive concept described.
The composite binder (mixture of dextrin and bentonite) mentioned in this invention need
not be limited to pelletizing process and can also be used as a binder in the conventional
briquetting process of ore or mineral fines.
It is to be understood that the invention is not limited by the specific examples and
embodiments described hereinabove, but includes such changes and modifications as
may be apparent to one skilled in the art upon reading the appended claims.
WE CLAIM
1. A method for cold bonded pelletizing of ferrous or non-ferrous ores or mineral
fines by a mixture of organic and inorganic binders comprises:-
- grinding the ore or mineral into a size of 60-80% less than 45 micron;
- mixing the ore fines with composite binder and adequate amount of water (2-8%)
to prepare the green pelletizing/briquetting mixture,
- pelletizing / briquetting the green mixture to form green pettels /briquettes;
- drying the pellets either at ambient temperature or at temperature substantially
below firing temperature used in conventional heat hardened pelletizing process.
2. The method as claimed in claim 1 wherein the composite binder is a mixture of
organic and inorganic binder in the ratio 75-80: 25-20.
3. A method as claimed in claim 2 wherein the organic binder includes dextrin, starch
and their derivatives; lignin, lignosulfonate and their derivatives.
4. A method as claimed in claim 2 wherein the inorganic binder includes bentonite,
montmorillonite, colloidal silica, silica fume/micro silica and other water expanding
clays.
5. A method as claimed in claim 2 wherein said organic binder comprises from 1 to 5
wt% by weight of the pelletizing mix.
6. A method as claimed in claim 2 wherein said inorganic binder comprises from 1 to
4 wt% by weight of the pelletizing mix.
7. A method as claimed in claim 1 wherein the said composite binder is added to the
mineral fines prior to pelletizing or briquetting.
8. A method as claimed in claim 1 wherein said drying is conducted at a temperature
in the range of 75° C. to 150° C.
9. A method as claimed in claim 1 wherein said drying is conducted at ambient
temperature in air for 1-3 days.
10. A method as claimed in claim 1, wherein said ore or mineral fines include iron ore
fines, chromite or chrome ore fines, manganese ore fines, ilmenite fines, blast
furnace dust and sludge, basic oxygen furnace (BOF) dust and sludge, mill scale
and oil and carbon contaminated sludge and fines, lime, limestone, dolomite,
dunite, pyroxenite, quartizite, coke, coal, carbonaceous materials and mixtures.
11. A method as claimed in claim 1 wherein said agglomeration includes disc or drum
pelletizing, briquetting, cylindrical blocks making and granulation.

The present invention relates to a method for cold bonded pelletizing of ferrous or non-
ferrous ores or mineral fines by a mixture of organic and inorganic binders comprises
grinding the ore or mineral into a size of 60-80% less than 45 micron and mixing the ore
fines with composite binder and adequate amount of water (2-8%) to prepare the green
pelletizing/briquetting mixture and pelletizing / briquetting the green mixture to form
green pettels /briquettes and drying the pellets either at ambient temperature or at
temperature substantially below firing temperature used in conventional heat hardened
pelletizing process.