Title of Invention

AN IMPROVED PROCESS FOR THE PREPARATION OF COLED FONDED IRON

Abstract Title: An An improved process for the preparation o f cold bonded iron ore pellets. An improved process for the preparation of cold bonded iron ore pellets which comprises mixing with 94 - 96 % iron ore fines (having granulometry -2mm + 600 µ (18-30%), -600 µ + 75 u (40-60%), -75 µ (20-30%)), 4-6% ground Portland cement clinker having surface area in the range of 3300 - 4750 cm. sq./g with or without silica fines and then pilletizing with a constant spray of water and the green pellets are cured for 7-28 days at room temperature and humid condition followed by drying in air at temperature of 120-150°C for 2-3 hours to have crushing strength of 100-310 kg. /pettet.
Full Text This invention relates to an improved process for the preparation of cold bonded iron ore pellets.
The process of the present invention particularly relates to the pelletization of iron ore fines to produce cold bonded pellets which may be used as burden material either alone or along with lump ore, sinter or the like ones in cupola, low/moderate or conventional blast furnace and the like ones for extraction of metal.
Huge quantity of naturally occurring iron ore fines (Blue dust) with iron content 60 - 65% and fines (50 -55% iron content) generated during ore processing and washing plants remain almost unutilized because these fines as such cannot be charged as burden material into the furnaces. These fines need to be agglomerated prior to use as burden. The agglomerate (in pellet form) should exhibit adequate crushing strength of 100-150 kg/pellet for cupola/low/moderate shaft furnaces and 200 kg/pellet or more for conventional high capacity blast furnace besides other desired physico-metallurgical characteristics.
Conventional heat indurated pelletization processes require 80 - 85 % fines below 75(J. size and temperature of 1200 - 1300° C. The heat requirement for the purpose is considerably high. Thus, the process is energy intensive and has become almost uneconomical particularly in India due to high cost of firing fuel.
Several energy saving cold bonded iron ore pelletization processes have been developed for agglomerization of ore fines. Various types of binders like ordinary Portland cement, cement clinker, clinkers-silica, lime-silica, lime-carbondioxide etc. are used as binders. Trials conducted in low shaft/blast furnace have established the cement-bonded pellets as good burden material.
In grang cold process (J. Svensson, the Grang cold pellet process, Steel times, May 1969, P-362-364), about 10 % cementitious binder was used in making iron ore pellets. The green
pellets were mixed up with ore fines to avoid sticking of the pellets and then stored for hardening for a few days, after which the fines were screened and the pellets were cured for about 28 days under normal condition for attaining the final strength. The strength of the pellets varies from 100-250 kg/pellet depending upon the size of the pellets i.e. from 12.5 - 25 mm diameter.
A process for making iron ore pellets from hematite ore fines and/or from blue dust with cement, as binder has been described in Indian Patent No. 119163. In this process 10 % or more amount of binder (ordinary Portland cement) is used and pellets are cured under normal/and or autoclave condition for attaining final crushing strength of 145 - 165 kg/pellet. Successfully trial has been conducted using cement bonded iron ore pellets where 9 - 10 % ordinary portland cement was used and cured for about 28 days (Minerals and Metals Review, 1981, March 3: 53).
In MTU process (M. A. Goksel, Cold Bond Peptization for steel production process, Met. Mater. (1978), 19-26), COBO process (B. Hassler et.al., Cold Bonding Agglomeration, Proc. 2nd. Int. Symp. on Agglomeration, Atlanta, 1977, 901-909) and other similar processes, lime-silica, slag and the like ones were used as binders for making pellet. The pellets were autoclaved for 1-2 hours under steam pressure of about 21 atm. To develop strength of around 200 kg/pellet.
In our Indian Patent No. 171191, we hve disclosed a process for the preparation of cold bonded iron ore pellets with granulated blast furnace slag along with lime or ordinary portland cement with or without gypsum and nodulizing the resultant mixture in the presence of water in a disc nodulizer and curing the green pellets under normal/autoclaving condition, developed crushing strength of around 120 -200 kg/pellets in a period of 5 - 7 days. The amount of binder used was 8-12 % and consisted of granulated blast furnace slag and lime or ordinary portland cement.
In our another Indian Patent No. 171192 we hve disclosed a process for the preparation of iron ore pellets of crushing strength of 140 -200 kg/pellet by using 10 - 12 % cement as binder and curing under accelerated condition.
We have also disclosed, in our yet another Indian Patent No. 171194, a process for the preparation of cold bonded iron ore pellets of ore fines using binders consisting of 7 - 10 % cement clinker and 0.4-1.5 % chemical accelerator. The pellets were cured under hydrothermal condition and developed crushing strength of around 200 kg/pellet.
In our still another co-pending Indian Patent Application No. 261/DEL/92, we have disclosed a process for the preparation of cold bonded iron ore pellets where 7 - 9 % cement clinker along with 0.5 - 1.0 % silica fines was used as binder and curing under different conditions for developing crushing strength of 100 - 225 kg/pellets.
Hitherto known processes of cold bonded pelletization of ore fines as described above are associated with the draw back that requirement of cementitious binder is quite high i.e. in the range of 7 - 10 % or above. The high amount of binder besides increases the cost of the pellets also increases considerable amount of unwanted materials, particularly alumina, which is an essential constituent of cement. The aluminous gangue materials adversely affect the iron making process. Thus from the point of cost of the pellets and extraction of iron from the same, it is essential to reduce the binder requirement in making the pellets.
The main object of the present invention is to provide an improved process for making cold bonded iron ore pellets using relatively small quantity of binder and thus reduce the amount of undesirable gangue content in the burden materials, by using quality cement clinker as well as by increasing the efficiency of the binder through increase of its surface area or incorporating pozzolanic materials like reactive silica.
Accordingly, the process of the present invention provides an improved process for the preparation of cold bonded iron ore pellets which comprises mixing with 94 - 96 % iron ore fines (having granulometry -2mm + 600 u (18-30%), -600 \i + 75 p. (40-60%), -75 ^i (20-30%)), 4-6% ground Portland cement clinker having surface area in the range of 3300 - 4750 cm. sq./g with or without silica fines and then palletizing with a constant spray of water and curing the green pellets are cured for 7-28 days at room temperature and humid condition followed by drying in air at temperature of 120-150 C for 2-3 hours to have crushing strength of 100 - 310 kg. /pellet.
In a preferred embodiment of the invention, the silica fines (quartz fines having silica content more than 99.5 %) used had particle size below 63 µ and its amount ranges from 0.4 to 0.6 %. The pellets obtained may preferably be cured for a few days at room temperature under humid condition followed by drying at 120-150° C for 2-3 hours to develop crushing strength of around 100-300 kg/pellet. Alternatively, the green pellets may be cured for 1-3 days under humid condition followed by autoclaving at about 150 psi for a period of 3 hours followed by drying at 120-150°C for 2-3 hours to develop crushing strength of around 100-130 kg/pellet.
The details of the process of the present invention are given in the following examples which are provided for illustration only and should not be construed to limit the scope of the invention.
The composition of the raw materials used in the present invention are shown in the Table 1.
Table 1. Chemical composition of the raw materials
Table Removed

Run-of-mine (ROM) sample of blue dust was screened to obtain - 2mm fraction. The + 2 mm fraction or the ROM sample was ground in a ball mill so as to pass 80-90 % through 75µ sieve. About 60 % of the - 2mm sieved fraction was mixed with a mix having granulometry in the following range :
-2mm + 600µ ' - 18-30%

600 u + 75u

40 - 60 %

- 75 µ - 20-30 %
37.6 kg of the ore mix was mixed thoroughly with 2.4 kg of ground ordinary Portland cement clinker having surface area 3300 cm2/g. Green pellets were prepared using about 3 liters of water in a disc pelletizer having the following specifications, diameter 75 cm, color height 25 cm, angle of inclination 45 degree and rpm 36. The pellets formed were screened to size 14 -22 mm diameter and stored aside at room temperature under humid condition. After 7, 14 and 28 days curing, the crushing strength developed were 86, 144 and 202 kg/pellet respectively. EXAMPLE 2
37.6 kg of the ore mix consisting 60 % - 2 mm and 40 % ground fractions (as in example 1) was mixed with 2.4 kg of ground ordinary Portland cement clinker having surface area 3300 cm /g thoroughly. Green pellets were prepared using about 3 liters of water in a disc pelletizer having the following specifications, diameter 75 cm, color height 25 cm, angle of inclination 45 deg. And rpm 36. The green pellets were screened, to size 14-22 mm diameter
and stored aside at room temperature under humid condition. After 7, 14 and 28 days curing, the pellets were dried in air oven at 120-150° C for a period of 2-3 hours to develop crushing strength of 130, 220 and 260 kg/pellet respectively. EXAMPLE 3
37.6 kg of the ore mix consisting 60 % - 2 mm and 40 % ground fractions (as in example 1) was mixed thoroughly with 2.4 kg of ground ordinary Portland cement clinker having surface area 4130 cm2/g. Green pellets were prepared using about 3 liters of water in a disc pelletizer having the following specifications, diameter 75 cm, color height 25 cm, angle of inclination 45 deg. and rpm 36. The green pellets were screened to size 14 - 22 mm diameter and stored aside at room temperature under humid condition. After 7, 14 and 28 days curing, the pellets showed crushing strength of 90,160 and 210 kg/pellet respectively. EXAMPLE 4
37.6 kg of the ore mix consisting 60 % - 2 mm and 40 % ground fractions (as in example 1) was mixed thoroughly with 2.4 kg of ground ordinary Portland cement clinker having surface area 4130 cm2/g. Green pellets were prepared using about 3 liters of water in a disc pelletizer having the following specifications, diameter 75 cm, color height 25 cm, angle of inclination 45 deg. and rpm 36. The green pellets were screened to size 14-22 mm diameter and stored aside at room temperature under humid condition for 7, 14 and 28 days. The pellets were dried in air oven at 120 -150° C for a period of 2-3 hours to develop crushing strength of 160, 235 and 298 kg/pellet. EXAMPLE 5
37.6 kg of the ore mix consisting 60 % - 2 mm and 40 % ground fractions (as in example 1) was thoroughly mixed with 2.4 kg of ground ordinary Portland cement clinker
having surface area 4740 cm2/g. Green pellets were prepared using about 3 liters of water in a disc pelletizer having the following specifications, diameter 75 cm, color height 25 cm, angle of inclination 45 deg. and rpm 36. The green pellets were screened to size 14-22 mm diameter and stored aside at room temperature under humid condition. The 7, 14 and 28 days normal cured pellets showing crushing strength of 108,165 and 215 kg/pellet respectively. EXAMPLE 6
37.6 kg of the ore mix consisting 60 % - 2 mm and 40 % ground fractions (as in example 1) was mixed thoroughly with 2.4 kg of ground ordinary Portland cement clinker having surface area 4740 cm2/g. Green pellets were prepared using about 3 liters of water in a disc pelletizer having the following specifications, diameter 75 cm, color height 25 cm, angle of inclination 45 deg. and rpm 36. The green pellets were screened to size 14-22 mm diameter and stored aside at room temperature under humid condition. The 7, 14 and 28 days normal cured pellets were dried at 120 - 150° C in an air oven for about 2-3 hours to develop crushing strength of 165,238 and 310 kg/pellet. EXAMPLE 7
37.6 kg of the ore mix consisting 60 % - 2 mm and 40 % ground fractions (as in example 1) was mixed with 2.4 kg of ground ordinary Portland cement clinker having surface area 3300 cm2/g thoroughly. Green pellets were prepared using about 3 liters of water in a disc pelletizer having the following specifications, diameter 75 cm, color height 25 cm, angle of inclination 45 deg. and rpm 36. The green pellets were screened to size 14 - 22 mm diameter and stored aside at room temperature under humid condition. The 1 day normal cured pellets were autoclaved at 150 psi for about 3 hours to develop crushing strength of about 90 kg/pellet and after drying 120-150° C for about 2-3 hours the strength enhanced to about 110 kg/pellet.
EXAMPLE 8
37.6 kg of the ore mix consisting 60 % - 2 mm and 40 % ground fractions (as in example 1) was mixed thoroughly with 2.16 kg. of ground ordinary Portland cement clinker having surface area 3300 cm2/g. Green pellets were prepared using about 3 liters of water in a disc pelletizer having the following specifications, diameter 75 cm, color height 25 cm, angle of inclination 45 deg. and rpm 36. The green pellets were screened to size 14 - 22 mm diameter and stored aside at room temperature under humid condition. The pellets were cured for 1 day under normal condition followed by 3 hours autoclaving at 150 psi to develop crushing strength of about 98 kg/pellet and the pellets on drying at 120-150° C for about 2-3 hours developed crushing strength of about 130 kg/pellet. EXAMPLE 9
38.4 kg of the ore mix consisting 60 % - 2 mm and 40 % ground fractions (as in example 1) was mixed with 1.6 kg. of ground ordinary Portland cement clinker having surface area 3300 cm /g thoroughly. Green pellets were prepared using about 3 liters of water in a disc pelletizer having the following specifications, diameter 75 cm, color height 25 cm, angle of inclination 45 deg. and rpm 36. The green pellets were screened to size 14-22 mm diameter and stored aside at room temperature under humid condition. The 7, 14 and 28 days normal cured pellets showed crushing strength of 55, 82 and 100 kg/pellet respectively. EXAMPLE 10
38.4 kg of the ore mix consisting 60 % - 2 mm and 40 % ground fractions (as in example 1) was mixed with 1.6 kg. of ground ordinary Portland cement clinker having surface area 3300 cm /g thoroughly. Green pellets were prepared using about 3 liters of water in a disc
pelletizer having the following specifications, diameter 75 cm, color height 25 cm, angle of inclination 45 deg. and rpm 36. The green pellets were screened to size 14-22 mm diameter and stored aside at room temperature under humid condition. The 7, 14 and 28 days normal cured pellets on air drying at 120-150° C for 2-3 hours developed crushing strength of 80, 110 and 120 kg/pellet respectively. EXAMPLE 11
38.4 kg of the ore mix consisting 60 % - 2 mm and 40 % ground fractions (as in example 1) was mixed with 1.6 kg. of ground ordinary Portland cement clinker having surface area 4130 cm2/g thoroughly. Green pellets were prepared using about 3 liters of water in a disc pelletizer having the following specifications, diameter 75 cm, color height 25 cm, angle of inclination 45 deg. and rpm 36. The green pellets were screened to size 14 - 22 mm diameter and stored aside at room temperature under humid condition. The 7, 14 and 28 days normal cured pellets showed crushing strength of 70,100 and 115 kg/pellet respectively. EXAMPLE 12
38.4 kg of the ore mix consisting 60 % - 2 mm and 40 % ground fractions (as in example 1) was mixed with 1.6 kg. of ground ordinary Portland cement clinker having surface area 4130 cm2/g thoroughly. Green pellets were prepared using about 3 liters of water in a disc pelletizer having the following specifications, diameter 75 cm, color height 25 cm, angle of inclination 45 deg. and rpm 36. The green pellets were screened to size 14 - 22 mm diameter and stored aside at room temperature under humid condition. The 7, 14 and 28 days normal cured pellets on air drying at 120-150° C for about 2-3 hours developed crushing strength of 110, 160 and 165 kg/pellet respectively.
EXAMPLE 13
38.4 kg of the ore mix consisting 60 % - 2 mm and 40 % ground fractions (as in example 1) was mixed with 1.6 kg. of ground ordinary Portland cement clinker having surface area 4740 cm2/g thoroughly. Green pellets were prepared using about 3 liters of water in a disc pelletizer having the following specifications, diameter 75 cm, color height 25 cm, angle of inclination 45 deg. and rpm 36. The green pellets were screened to size 14 - 22 mm diameter and stored aside at room temperature under humid condition. The 7, 14 and 28 days normal cured pellets showed crushing strength of 75,102 and 118 kg/pellet. EXAMPLE 14
38.4 kg of the ore mix consisting 60 % - 2 mm and 40 % ground fractions (as in example 1) was mixed with 1.6 kg. of ground ordinary Portland cement clinker having surface area 4740 cm2/g thoroughly. Green pellets were prepared using about 3 liters of water in a disc pelletizer having the following specifications, diameter 75 cm, color height 25 cm, angle of inclination 45 deg. and rpm 36. The green pellets were screened to size 14 - 22 mm diameter and stored aside at room temperature under humid condition. The 7, 14 and 28 days normal cured pellets on air drying at 120-150° C for 2-3 hours developed crushing strength of 118, 165 and 170 kg/pellet respectively. EXAMPLE 15
38.4 kg of the ore mix consisting 60 % - 2 mm and 40 % ground fractions (as in example 1) was mixed with 1.44 kg. of ground ordinary Portland cement clinker having surface area 4740 cm /g and 0.16 kg. f silica fines thoroughly. Green pellets were prepared using about 3 liters of water in a disc pelletizer having the following specifications, diameter 75 cm, color
height 25 cm, angle of inclination 45 deg. and rpm 36. The green pellets were screened to size 14 - 22 mm diameter and stored aside at room temperature under humid condition. The pellets were cured for 2 days under normal condition followed by autoclaving at 150 psi for about 3 hours and air dried at 120-150 ° C for 2-3 hours developed crushing strength of 105 kg/pellet.


We claim
1. An improved process for the preparation of cold bonded iron ore pellets which comprises mixing with 94 - 96 % iron ore fines (having granulometry -2mm + 600 µ (18-30%), -600 µ + 75 µ (40-60%), -75 µ (20-30%)), 4-6% ground Portland cement clinker having surface area in the range of 3300 - 4750 cm. sq./g with or silica fines and then pelletizing with a constant spray of water and the green pellets are cured for 7-28 days at room temperature and humid coridition followed by drying in air at temperature of 120-150 C for 2-3 hours to have crushing strength of 100 - 310 kg. / pellet..
2. An improved for the preparation of cold bonded iron ore pellets substantially as herein described with reference to the examples.

Documents:

508-del-2008-abstract.pdf

508-del-2008-claims.pdf

508-del-2008-correspondence-others.pdf

508-del-2008-correspondence-po.pdf

508-del-2008-description (complete).pdf

508-del-2008-form-1.pdf

508-del-2008-form-2.pdf

508-DEL-2008-Form-3.pdf

508-DEL-2008-Form-4.pdf


Patent Number 242162
Indian Patent Application Number 508/DEL/1996
PG Journal Number 34/2010
Publication Date 20-Aug-2010
Grant Date 17-Aug-2010
Date of Filing 11-Mar-1996
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110001, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 DIPOK BORDOLOI REGIONAL RESEARCH LABORATORY, JORHAT 785006, ASSAM.
2 DIPAK KUMAR DUTTA REGIONAL RESEARCH LABORATORY, JORHAT 785006, ASSAM.
3 PRAKASH CHANDRA BORTHAKUR REGIONAL RESEARCH LABORATORY, JORHAT 785006, ASSAM.
PCT International Classification Number C21B 1/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA