Claims:We Claim:
1. Boron doped Iron ore pellets comprising:
Iron ore composition of
Fe(T) in amounts of 61 - 63.5 % by wt.;
SiO2 in amounts of 2.5 - 5.5 % by wt;
Al2O3 in amounts of 2.36 – 4.0 % by wt;
MgO in amounts of 0.15 - 0.25% by wt;
LOI(Loss on ignition) in amounts of 2-4.5, which is boron doped involving a boron source in an amount of 0.5 to 1.2% by wt.,
with slag covered iron ore grains having micro pores enabling a reducibility index in the range of 0.48 to 0.7 preferably 0.50 to 0.66.
2. Boron doped Iron ore pellets as claimed in claim 1 wherein said boron source includes one or more of (a) boric acid and (b) colemanite.
3. Boron doped Iron ore pellets as claimed in anyone of claims 1 or 2 wherein said iron ore has high surface area with blaine number 1800-3400 cm2/g .
4. Boron doped Iron ore pellets as claimed in anyone of claims 1 to 3 wherein said boric acid has specification of 60-70% BO3 and colemanite contains 30-35% B2O3 , 6% SiO2 , 3% MgO, 1% Al2O3.

5. Boron doped Iron ore pellets as claimed in anyone of claims 1 to 4 having reducibility index at 40% reduction is 0.45-0.70, degree of reduction 92-97% with metallization of 91-95% with strength of boron doped reduced pellets being in the range of 70-90 kg/pellets against 50-65 kg/pellets of conventional reduced pellet.

6. Boron doped Iron ore pellets as claimed in anyone of claims 1 to 5 wherein the strength of fired pellets is in the range of 265-305 kg/pellet.

7. Boron doped Iron ore pellets as claimed in anyone of claims 1 to 6 which favours slag formation in fired pellets including 1.5-4.5% B2O3 and other oxides like CaO, Al2O3, MgO, SiO2.

8. A process for manufacture of boron doped iron ore pellets as claimed in anyone of claims 1 to 7 comprising :

providing a pellet feed of a slag system including a boron source;

manufacturing pellets involving generation of green pellets followed by firing of green pellets in the temperature range of 1280-13600C .

9. A process as claimed in claim 8 wherein said pellet feed comprising iron ore fines in amount of 92-94%,limestone in amount of 1 to 1.5%, dolomite in amounts of 1 to 1.5 % ,coke breeze in amount of 0.8 to 1.4 % ,bentonite in amounts of 0.6 to 1.2 % and boron source in amount of 0.5 to 1.2%.

10. A process as claimed in anyone of claims 8 or 9 carried out such that the fired pellets have a basicity (B2) of 0.30 - 0.45 (B2 = CaO /SiO2) and basicity (B4) of 0.20 - 0.30 [B4 = (CaO+MgO) / (SiO2+Al2O3)].

11. A process as claimed in anyone of claims 8 to 10 comprising:
a) Preparing the pellet feed including iron ore fines 90-94 % having
Materials Fe(T) SiO2 Al2O3 MgO LOI(Loss on ignition)
Iron ore 61 - 63.5 2.5 - 5.5 2.36 – 4.0 0.15 - 0.25 2-4.5

limestone 1-1.5 %,dolomite 1-1.5%, coke breeze 0.8-1.4%, bentonite 0.4-1.2% and boron compound 0.5 -1.2%.
b) pelletization of aforementioned pellet feed in disc pelletizer having inclination of 42 to 45 preferably about 440 with rotation of 18 to 25 preferably about 18 rpm for 20 minutes.
c) firing of green pellets mentioned in step (b) in temperature range of 1280-1360 0C and the fired pellets having basicity (B2) of 0.30 - 0.45 (B2 = CaO /SiO2) and basicity (B4) of 0.20 - 0.30 [B4 = (CaO+MgO) / (SiO2+Al2O3)].

12. A process as claimed in anyone of claims 8 to 11 wherein said Iron ore used have high surface area with blaine number 1800 - 3400 cm2/g and maintaining same consistent with blaine number range of additives and fuel for reduction.

13. A process as claimed in anyone of claims 8 to 12 wherein said boron sources comprise boric acid having specification of 60-70% BO3 and CaO based colemanite, preferably having 30-35% B2O3 , 6% SiO2 , 3% MgO, 1% Al2O3

14. A process as claimed in anyone of claims 8 to 13 wherein the slag formed in fired pellets include 1.5-4.5% B2O3 and other oxides like CaO, Al2O3, MgO, SiO2.

15. A process for metallization of DRI comprising the step of involving boron doped Iron ore pellets as claimed in anyone of claims 1 to 7 comprising metallization involving reducing gases controlled based on the dosage of boron in the boron doped pellets including activating the boron source at temperature of 950-12000C such that said boron enables generation of emulsified slag which upon solidification generates desired micro-porosity the pathway for reducing gases to reach to the core of fired boron doped pellet during reduction.

16. A process as claimed in claim 15 wherein said boron doped iron ore pellets used comprise boron sources selected from boric acid and colemanite doping.

17. A process as claimed in anyone of claims 15 or 16 wherien the boron doped pellets used comprise boric acid in levels of 0.50 to 0.70 % for highest metallization in the range of 92 to 95 % at 800 to 950 0C preferably 8200C with reducing gas compostion of 60-62 % CO,30-32% H2 and balance Nitrogen and in case of colemanite doping the coleminte level in the pellets used is limited to 0.80 to 0.90%.

18. A process as claimed in anyone of claims 15 to 17 wherein said reducing gases include selectively CO,H2 and nitrogen preferably in combination of 30-35 % CO and 60-65 % H2 gas H2/CO ratio is 1.85-2, remaining Nitrogen and 58-63 % CO and 30-35% hydrogen gas H2/CO ratio is 0.51-0.55, remaining 5-7 % nitrogen.

19. A process as claimed in anyone of claims 15 to 18 wherein boron involves in reducing the melting temperature of binary, ternary and quaternary slag system and formation of two-liquid zone which makes the slag emulsified which when solidifies contains population of micro-porosity and hence it provides the pathway for reducing gases to reach to the core of the fired pellet during reduction.

20. A process as claimed in anyone of claims 15 to 19 wherein emulsified slag is formed at temperatures of 850 -9000C with uniform dispersion and generation of micro pores increasing the metallization and reducibility index of the pellets.

Dated this the 11th day of January, 2017
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

, Description:FIELD OF THE INVENTION

The present invention relates to boron doped iron ore pellets with improved reduction kinetics and a process for manufacturing such pellets. More particularly, the present invention is directed to a process for improving the reduction kinetics of ore pellets from a catalytic effect generated by the addition of boron based compound. The doping of boron helps in maintaining the two liquid zones in binary, ternary and quaternary slag system. It also helps in maintaining the slag emulsification during reduction process. The boron rich slag in fired pellets leads to increased number of micropores which provides the path way for the gases to reach to pellet core and enhance the reduction rate. The process comprises of mixing the iron ore fines with flux, binder and fuel with boric acid or colemanite or any other source of boron oxide and making green pellets using disc pelletizer. The green pellets so formed are subjected to induration at required firing temperature followed by reduction of fired pellets in presence of reduction gases CO, H2, CH4 and N2 gases. The reducibility index of boron doped pellets increases from 0.50 to 0.66 which in turn increases the metallization of direct reduced iron. The effect of boron on slag formation is confirmed by characterizing the fired / reduced pellets under EPMA which revealed emulsification effect of boron rich slag in pellets.

BACKGROUND OF THE INVENTION

Reducibility of iron ore pellets basically depend on the intrinsic characteristics of the ore grains, slag phase and inter-granular porosity of the pellet. The characteristics of the ores and additives as well as chemical composition and indurating conditions of the pellets are important factors for the physical and metallurgical qualities of the pellets. However, the rate of reaction is governed by the amount of slag phase and its distribution. The kinetics and mechanism of iron oxide reduction by CO and H2 are similar. The diffusivity of hydrogen is about four times as rapid as that of carbon monoxide and therefore the reduction by H2 is 4 to 6 times faster than that of CO. Lump ores and pellets contain iron oxide mostly as Fe2O3. The fundamental measure of the extent of reduction is the degree of reduction (a) defined as:
a = (weight loss due to removal of oxygen / weight of total removable oxygen in iron ore) x 100.
Iron oxide (Fe2O3) reduces in stages, e.g., Fe2O3 ? Fe3O4 ? FeO ? Fe. Reduction is characterized by the formation of a porous product layer. When hematite is reduced to magnetite, additional porosity develops, enhancing the rate of further reduction of hematite. Hence, hematite is more reducible than magnetite. Additional porosity develops during reduction is due to the density difference of the product solids. The overall reduction rate would depend on temperature, gas composition, size of the particle, and nature of the solid in terms of its structure and composition. The higher the reducibility of iron oxides, the faster is the rate of reduction. Hence, the rate of reduction (da/dt) may be considered as a measure of reducibility.

Reducibility is a determining factor for the performance of iron making units, viz., Blast Furnace, Corex or DRI plants. Unlike smelting units, in direct reduction reactors, the maximum temperatures reached are much lower than the melting temperature of iron. In literature, very little information is available on the effect of metal-oxides other than that of oxides of calcium and magnesium on the reducibility of iron ore agglomerates.

Generally, the alkali elements like sodium and potassium helps in faster melting of slag in pellets and facilitates better distribution of slag. However, the presence of sodium and potassium in slag drastically reduce the temperature when slag gets saturated with alkalies which help in uniform distribution of slag in pellets. The slag starts melting in the temperature range of 950 - 1000 oC. The slag so formed covered the most of the micro-pores and iron grains which become the barrier for the reducing gases to get in contact with iron oxides and so excessive addition or presence of alkalies will hinder the reduction rate of the pellets. However, its usage will increase the alkali load.

Khalafalla and Weston (S.E. Khafalla and P.L. Weston, Jr.; Promoters for Carbon Monoxide Reduction of Wustite; Transactions of Metallurgical Society of AIME; pp. 1484-1499, Vol. 239; October 1967) studied the effect of alkaline metals and alkaline earth metals on FeO reduction in CO atmosphere at 1000 0C., and they found that small concentrations of these metals, approximately 0.7%, improved the reducibility of the FeO due to disturbances generated in the crystalline reticulate by interstitial ions with high atomic rays regarding Fe.

Chinje and Jueffes (U.F. Chinjee and I.H.E. Jueffes; Effects of chemical composition of iron oxides on their rates of reduction: Part-1 Effect of trivalent metal oxides on reduction of hematite to lower iron oxides; Iron making and Steelmaking, pp. 90-95; Vol. 16, No 2, 1989) evaluated the effect of trivalent metallic oxides, more specially of Cr and Al, in the reduction of pure iron oxide, in an atmosphere with 18% CO and 82% CO2 at 960 0C, and concluded that Cr has a positive effect on the reduction of iron oxide with additions varying from 1.6 to 5%. The reduction was found increasing as their concentration increases. The hypothesis formulated to explain this effect is that Cr acts as a catalyst in the CO absorption process on the surface of the oxide, which is a characteristic of transition metals such as Ni.

El-Geassy et al. (El-Geassy et al.; Effect of nickel oxide doping on the kinetics and mechanism of iron oxide reduction; ISIJ International; pp. 1043-1049; Vol. 35; No. 9, 1995) investigated the effect of NiO doping, varying from 1 to 10%, on the kinetics and reduction mechanisms of pure iron oxides in H2 atmosphere and temperatures between 900 and 1100 0C and noted a positive and significant effect of that addition on the reduction. The reducibility increased in the initial and final stages of the process throughout the temperature range and this increase has been attributed to the formation of a nickel ferrite (NiFe2O4) and the increase in porosity of the sintered material.

Similarly, US Patent 0096650 dated April 10, 2014 discloses the patent which describes the increase in reducibility of pellet which mentions a new process for the improvement of reducibility of iron ore pellets comprising the steps for preparing raw material mixture which contain a metallic nickel powder, pelletizing the said mixture obtained, burning the said raw pellets, and reducing the said burnt pellets under reducing conditions in the presence of CH4.
There has been thus a need for developing a formulation and process of producing iron ore pellets involving less costly metal oxides as having catalytic effect on improving reducibility of pellets and enhanced metallization to economically benefit metal extraction from such pellet products. None of the literature and patents discloses the usage of boron compound for increase in metallization of pellets after reduction. Similarly, the gases and their composition used for the reduction are fully different from the above mentioned work. The rate of oxygen removal is also a key factor in reduction kinetic of pellet which is taken in present invention.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to provide boron doped iron ore pellets with improved reduction kinetics and a process for producing such iron ore pellets favouring improved reducibility and metallization.

A further object of the present invention is directed to said process to improve reducibility of ore pellets wherein a catalytic effect generated by the addition of metallic boron based compound increase the reduction kinetics of iron ore pellets.
A still further object of the present invention is directed to said process to improve reducibility of ore pellets wherein boron rich slag in fired pellets leads to increased number of micropores thereby providing the pathway for reducing gases (H2 and CO) to reach to the core of the pellets.

Another object of the present invention is directed to said process to improve reducibility of ore pellets wherein addition of boron compound helps in maintaining two liquid slag formed basically of primary boron silicate and primary boron richer calcium silicate in binary, ternary and quaternery slag system.

Yet another object of the present invention is directed to said process to improve reducibility of ore pellets wherein in presence of boron during firing of the pellets, the two liquid along with one solid in slag melts results in dispersed solid-liquid slag.

A further object of the present invention is directed to said process to improve reducibility of ore pellets wherein the slag covered iron grains with lots of micro-pores results in easy access for the reducing gases to reach to the core of the pellets and hence the reduction kinetics gets enhanced.

A still further object of the present invention is directed to said process to improve reducibility of ore pellets wherein the reducibility index of boron doped pellets increases from 0.50 to 0.66 which in turn increases the metallization of direct reduced iron.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to provide Boron doped Iron ore pellets comprising:
having Iron ore composition of
Fe(T) in amounts of 61 - 63.5 % by wt.;
SiO2 in amounts of 2.5 - 5.5 % by wt;
Al2O3 in amounts of 2.36 – 4.0 % by wt;
MgO in amounts of 0.15 - 0.25% by wt;
LOI(Loss on ignition) in amounts of 2-4.5, which is boron doped involving a boron source in an amount of 0.5 to 1.2% by wt.,
with slag covered iron ore grains having micro pores enabling a reducibility index in the range of 0.48 to 0.7 preferably 0.50 to 0.66.
A further aspect of the present invention is directed to said Boron doped Iron ore pellets wherein said boron source includes one or more of (a) boric acid and (b) colemenite.
A still further aspect of the present invention is directed to said Boron doped Iron ore pellets wherein said iron ore has high surface area with blaine number 1800-3400 cm2/g .
A still further aspect of the present invention is directed to said Boron doped Iron ore pellets wherein said boric acid has specification of 60-70% BO3 and colemanite contains 30-35% B2O3 , 6% SiO2 , 3% MgO, 1% Al2O3.

Another aspect of the present invention is directed to said Boron doped Iron ore pellets having reducibility index at 40% reduction is 0.45-0.70, degree of reduction 92-97% with metallization of 91-95% with strength of boron doped reduced pellets being in the range of 70-90 kg/pellets against 50-65 kg/pellets of conventional reduced pellet.

Yet another aspect of the present invention is directed to said Boron doped Iron ore pellets wherein the strength of fired pellets is in the range of 265-305 kg/pellet.

A further aspect of the present invention is directed to said Boron doped Iron ore pellets which favours slag formation in fired pellets including 1.5-4.5% B2O3 and other oxides like CaO, Al2O3, MgO, SiO2.

A still further aspect of the present invention is directed to a process for manufacture of boron doped iron ore pellets as described above comprising :

providing a pellet feed of a slag system including a boron source;

manufacturing pellets involving generation of green pellets followed by firing of green pellets in the temperature range of 1280-13600C .

A further aspect of the present invention is directed to said process wherein said pellet feed comprising iron ore fines in amount of 92-94%,limestone in amount of 1 to 1.5%, dolomite in amounts of 1 to 1.5 % ,coke breeze in amount of 0.8 to 1.4 % ,bentonite in amounts of 0.6 to 1.2 % and boron source in amount of 0.5 to 1.4%

A still further aspect of the present invention is directed to said process carried out such that the fired pellets have a basicity (B2) of 0.30 - 0.45 (B2 = CaO /SiO2) and basicity (B4) of 0.20 - 0.30 [B4 = (CaO+MgO) / (SiO2+Al2O3)].

Another aspect of the present invention is directed to said process comprising:
a) Preparing the pellet feed including iron ore fines 90-94 % having
Materials Fe(T) SiO2 Al2O3 MgO LOI
(Loss on Ignition)
Iron ore 61 - 63.5 2.5 - 5.5 2.36 – 4.0 0.15 - 0.25 2-4.5

limestone 1-1.5 %,dolomite 1-1.5%, coke breeze 0.8-1.4%, bentonite 0.4-1.2% and boron compound 0.5 -1.2%.
b) pelletization of aforementioned pellet feed in disc pelletizer having inclination of 42 to 45 preferably about 440 with rotation of 18 to 25 preferably about 18 rpm for 20 minutes.
c) firing of green pellets mentioned in step (b) in temperature range of 1280-1360 0C and the fired pellets having basicity (B2) of 0.30 - 0.45 (B2 = CaO /SiO2) and basicity (B4) of 0.20 - 0.30 [B4 = (CaO+MgO) / (SiO2+Al2O3)].

Yet another aspect of the present invention is directed to said process wherein said Iron ore used have high surface area with blaine number 1800 - 3400 cm2/g and maintaining same consistent with blaine number range of additives and fuel for reduction.

A further aspect of the present invention is directed to said process wherein said boron sources comprise boric acid having specification of 60-70% BO3 and CaO based colemanite preferably having 30-35% B2O3 , 6% SiO2 , 3% MgO, 1% Al2O3

A still further aspect of the present invention is directed to said process wherein the slag formed in fired pellets include 1.5-4.5% B2O3 and other oxides like CaO, Al2O3, MgO, SiO2.

Another aspect of the present invention is directed to a process for metallization of DRI comprising the step of involving boron doped Iron ore pellets comprising metallization involving reducing gases controlled based on the dosage of boron in the boron doped pellets including activating the boron source at temperature of 950-12000C such that said boron enables generation of emulsified slag which upon solidification generates desired micro-porosity the pathway for reducing gases to reach to the core of fired boron doped pellet during reduction

A further aspect of the present invention is directed to said process wherein said boron doped iron ore pellets used comprise boron sources selected from boric acid and colemanite doping.

A still further aspect of the present invention is directed to said process wherein the boron doped pellets used comprise boric acid in levels of 0.50 to 0.70 % for highest metallization in the range of 93 to 95 at 800 to 950 0C preferably 8200C with reducing gas composition of 60-62 % CO,30-32% H2 and balance Nitrogen and in case of colemanite doping the colemanite level in the pellets used is limited to 0.80 to 0.90%.

A still further aspect of the present invention is directed to said process wherein said reducing gases include selectively CO,H2 and nitrogen preferably in combination of 30-35 % CO and 60-65 % H2 gas remaining Nitrogen and 58-63 % CO and 30-35% hydrogen gas remaining 5-7 % nitrogen.

A still further aspect of the present invention is directed to said process wherein boron involves in reducing the melting temperature of binary, ternary and quaternary slag system and formation of two-liquid zone which makes the slag emulsified which when solidifies contains population of micro-porosity and hence it provides the pathway for reducing gases to reach to the core of the fired pellet during reduction.

A still further aspect of the present invention is directed to said process wherein emulsified slag is formed at temperatures of 850 -9000C with uniform dispersion and generation of micropores increasing the metallization and reducibility index of the pellets.

The above and other objects and advantages of the present invention are described hereunder in greater details with reference to following accompanying non limiting illustrative drawings and example.

BRIEF DESCRIPTION OF THE ACCOMPNAYING DRAWINGS
Figure 1a: Ternary slag system of FeO-CaO-B2O3 showing the effect of boron and melting temperature of calcium ferrite and boron rich iron compounds.
Figure 1b: Ternary slag system of SiO2-CaO-B2O3 showing the effect of boron and melting temperature of calcium rich silicate and boron rich calcium silicate iron compounds.
Figure 2a: Result of EPMA analysis of fired pellets (Electron Probe Micro-analyzer) JXA-8230 wherein the photomicrographs of pellets along with elemental mapping of silica, alumina, calcium, boron in pellets are presented which is doped with boric acid.
Figure 2b: Result of EPMA analysis of fired pellets (Electron Probe Micro-analyzer) JXA-8230 wherein the photomicrographs of pellets along with elemental mapping of silica, alumina, calcium, boron in pellets are presented which is doped with colemanite.
Figure 3a: Represents graphically the influence of boric acid on metallization, reducibility, percent reduction and FeO content in reduced pellet or DRI.
Figure 3b: Represents graphically the influence of Colemanite on metallization, reducibility, percent reduction and FeO content in reduced pellet or DRI.
Figure 4a: Result of EPMA analysis of fired pellets (Electron Probe Micro-analyzer) JXA-8230 which reveals the slag composition of boric acid doped pellets.
Figure 4b: Result of EPMA analysis of fired pellets (Electron Probe Micro-analyzer) JXA-8230 which reveals the slag composition of colemanite doped pellet.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
The present invention is directed to provide boron doped iron ore pellets and a process for increasing the reduction kinetics of iron ore pellets which in turn increases the metallization of DRI. The working of the invention is illustrated with the help of following example:

Example:

According to an embodiment of the present invention iron ore pellets are produced by doping of iron ore pellets with boric acid or colemanite. The raw material consists of iron ore, limestone, dolomite, coke breeze, bentonite and boron compound. The pellet feed consists of 92-94% iron ore fines, 1-1.5% limestone, 1-1.5% dolomite, 0.8-1.4% coke breeze, 0.6-1.2% bentonite and 0.5-1.5% boron compound. The said boron compound is analytical grade boric acid which contains 60-70% BO3 having chemical formula 2CaCO3.B2O3.5H2O. The another source of boron used in present invention is CaO based colemanite which contain 30-35% B2O3, 6% SiO2, 3% MgO and 1% Al2O3.

The green pellets having the mean particle size of 10.50 -11.50 mm are fired at the temperature of 1280-1320 OC, which is based on the amount of boron compound present in pellets. The composition of reducing gases used in invention is of (i) 30-35% CO and 60-65% H2 gas remaining nitrogen and (ii) 58-63% CO and 30-35% hydrogen gas remaining is 5-7% nitrogen. The fired pellets are reduced at temperature of 950 OC and the reducibility index at 40% reduction lies in the range of 0.50 - 0.66.

Accompanying Figure 1a shows the ternary slag system in which the presence of boron compound in oxide form helps in reducing the melting and softening temperature of FeO rich calcium and silicate ferrite slag. The ternary system helps in executing the formation of two liquid zone. The mechanism behind the reduction in melting temperature is as follows.
1. Boron oxide helps formation of emulsified slag at temperature of 850 - 900 oC and forms thin slag film with larger micro-pores.
2. The boron oxide forms complex compounds and resides in the slag and does not affect the iron grains.

Similarly, Figure 1b shows the ternary slag system of SiO2-CaO-B2O3 , wherein
1. The dosage of doping chemical is to be optimized to operate in the boundary condition for
emulsified porous slag phase.
2. shifting of the operating range towards right will result in excess amounts of fluid slag which will block the micro pores.
3. Similarly shifting towards the left will result in formation of hard non porous slag resulting in
thicker slag wall and blocked micro pores.

The mixing of raw materials during pelletization is the major issue and the ionic charge of the participating materials makes the mixture heterogeneous. By way of the present advancement as per accompanying Figures 2a and 2b elemental mapping of silicon, alumina, calcium and boron with boric acid and colemanite doped green pellets respectively was carried out.

It was found by way of the present advancement that the reducibility is largely governed by the amount of boron present in slag phase in fired pellet. Appropriate amount of boron in slag helps in emulsification of ternary and binary slag system available in fired pellet. Figures 3a and figure 3b reveal that the optimized dosage of boric acid is 0.50-0.70% and the highest metallization is achieved at 800 0C with reducing gas composition 60-62% CO, 30-32% H2 and balance nitrogen. Higher dosage of boron compound in the system lowers down the melting temperature of slag. Drastic reduction in melting temperature of slag causes pores blockage and less generation of micro-pores in two-zone slag layer. This results in lowering of metallization of direct reduced iron. In case of colemanite doping, the maximum metallization is achieved at 0.80-0.90% colemanite addition. However, the metallization and reducibility achieved with colemanite is lower than that of boric acid due to its high boron content.

Experimental Results:
The invention of the present process was established by conducting series of trials to produce pellets by doping different proportion of boric acid and colemanite in iron ore fines having different blaine number and limestone, dolomite, bentonite and coke breeze.Table1a showing the raw material along with composition used for pelletization; table1b showing the proportion of mix bled at different level of boric acid and colemanite; table1c shows the fired pellet chemistry. The chemical doped green pellets having different levels of dpoing were fired and tested for metallurgical properties as shown in Table 2.It was surpisingly found that the addition of boron compound helps in increasing the cold crushing strength with reduce in porosity as shown in Table 2. The reduction degradation index reduces as boron compound helps in maintaining the proper distribution of calcium and silicate rich slag in pellets.

Further studies as per Table 3 shows a dynamic reduction test carried out at 8200C for 4 hours at H2/CO ratio of 1.92. It was found following the above studies that the addition of boron compounds either boric acid or colemanite surprisingly favoured in increasing the metallization and reducibility index of the pellets. Similarly, the fines generation under dynamic condition is also decreased with doping of boron compound.

Table1a-Raw material composition used for pellet making
Materials Fe(T) FeO SiO2 Al2O3 CaO MgO LOI Moisture
IRON ORE 62.23 0.43 4.13 3.26 0.05 0.05 3.4 2
DOLOMITE 1.06 0.00 6.80 0.96 28.98 18.76 45.4 1.5
BENTONITE 2.00 0.00 43.17 15.74 3.72 2.91 11.2 0
LIMESTONE 0.40 0.00 2.37 0.13 53.52 1.03 44.02 3.00

Table1b-Proportion of Raw material with boric acid and colemanite (%)
IRON ORE 93.2 93 92.8 92.5
Boric acid 0.5 0.7 0.9 1.2
DOLOMITE 3 3 3 3
BENTONITE 0.8 0.8 0.8 0.8
LIMESTONE 1.5 1.5 1.5 1.5
COKE BREEZE 1 1 1 1

IRON ORE 93.6 93.4 93.2 92.9
Colemanite 0.5 0.7 0.9 1.2
DOLOMITE 2.6 2.6 2.6 2.6
BENTONITE 0.8 0.8 0.8 0.8
LIMESTONE 1.5 1.5 1.5 1.5
COKE BREEZE 1 1 1 1

Table1c-Fired pellet chemistry Doped with Boric acid and Colemanite
Boric acid % 0.5 0.7 0.9 1.2
Fe(T) 61.24 61.112 60.97 60.77
FeO 0.423 0.422 0.421 0.420
SiO2 4.594 4.585 4.576 4.562
Al2O3 3.361 3.354 3.347 3.337
CaO 1.436 1.435 1.435 1.435
MgO 0.421 0.421 0.421 0.420
MnO 0.234 0.234 0.233 0.233
TiO2 0.223 0.223 0.222 0.222
Na2O 0.045 0.045 0.044 0.044
K2O 0.034 0.034 0.034 0.034
B 0.164 0.229 0.295 0.393
B2 0.313 0.313 0.314 0.315
Colemanite% 0.5 0.7 0.9 1.2
Fe(T) 61.402 61.27 61.13 60.93
FeO 0.424 0.42 0.42 0.42
SiO2 4.619 4.62 4.63 4.63
Al2O3 3.372 3.37 3.36 3.36
CaO 1.500 1.55 1.61 1.69
MgO 0.392 0.40 0.40 0.41
MnO 0.234 0.23 0.23 0.23
TiO2 0.224 0.22 0.22 0.22
Na2O 0.045 0.04 0.04 0.04
K2O 0.034 0.03 0.03 0.03
B 0.087 0.122 0.157 0.209
B2 0.325 0.34 0.35 0.36

Table 2: Properties of the pellets
Boric acid (%) CCS (kg/pellet) Porosity (%) Mean particle size (mm) Reduction Degradation Index (%) Abrasion Index (%)
0.0 272 28.23 11.23 11.23 4.69
0.5 285 27.43 11.64 9.25 4.21
0.7 296 26.35 11.35 9.12 4.10
0.9 297 25.80 11.42 9.26 3.80
1.2 301 25.63 11.56 9.20 3.52
Colemanite (%)
0.5 280 28.37 11.45 10.21 5.52
0.7 288 27.13 11.49 10.10 5.20
0.9 296 24.35 11.68 9.56 5.00
1.2 305 22.13 11.90 9.23 4.80

Table 3 :
Boric acid (%) Size analysis (%) Chemical analysis of DRI (%) Gas analysis (%)
6
mm 4 mm 1
mm -1 mm Fe(T) Fe(M) Metallization H2 N2 CH4 CO
0 94.56 3.10 0.90 1.44 83.45 77.13 92.43 63.02 0.93 0.47 32.78
0.5 96.05 2.60 0.58 0.80 84.86 79.5 93.68
0.7 96.17 2.50 0.64 0.78 85.66 80.92 94.47
0.9 96.12 2.40 0.72 0.85 84.55 78.30 92.65
1.2 95.93 2.60 0.55 0.96 82.23 76.95 92.56

The EPMA analysis of pellets revealed that the boron saturated slag moves the ternary slag point towards two-liquid and one-solid region. It is also observed that the boron has diffused into iron grains which are indicative of the pathway for gases to reach to core of the pellets (Figures 4a and 4b). The slag saturation with 2.1 - 4.2% boron is a good indicative of faster slag melting and uniform dispersion of slag leading to the generation of more micro-pores which in turn increase the reduction kinetics of pellets. The slag composition of boric acid doped pellets and slag composition of colemanite doped pellet are presented in the following tables 4 & 5. The shelled wustite is converted to iron by the neighboring iron nuclei via solid diffusion. The retardation in reduction may be due to slow diffusion in solid phase. The difference in the degree of reduction at the surface and core of DRI indicates that the rate of reduction decreases with the progress of reduction. The cause of such retardation may be the binding of iron oxides in the acid slag phase or the formation of dense iron shells around the remaining wustite particles.
Table 4:

Spot CaO B2O3 Al2O3 SiO2 FeO
1 26.32 3.20 45.19 22.71 3.12
2 6.50 2.12 7.72 27.88 55.92
3 3.33 3.21 6.92 14.14 73.62
4 0.23 2.23 0.50 0.12 96.00
5 0.59 4.19 0.62 1.49 93.11

Table 5:
Spot CaO B2O3 Al2O3 SiO2 FeO
1 24.35 2.85 44.21 23.21 6.12
2 6.50 2.12 7.80 27.88 55.92
3 3.60 3.45 6.72 16.23 70.23
4 3.00 2.10 0.58 0.10 96.00
5 0.59 2.13 0.70 0.20 96.82

The results of comparative study of pellets with and without Boron compounds are presented in following Table 6.

Table 6:

Doping chemical 0% 0.5%B 0.7 %B 0.9%B 1.2%B 0.5%C 0.7%C 0.9%C 1.2%C
Fe(T) 61.74 61.25 61.11 60.98 60.77 61.4 61.27 61.13 60.93
FeO 0.43 0.42 0.42 0.42 0.42 0.42 0.42 0.42 0.42
SiO2 4.61 4.59 4.58 4.58 4.56 4.62 4.62 4.63 4.63
Al2O3 3.38 3.36 3.35 3.35 3.34 3.37 3.37 3.36 3.36
CaO 1.36 1.44 1.44 1.44 1.43 1.5 1.55 1.61 1.69
MgO 0.38 0.42 0.42 0.42 0.42 0.39 0.4 0.4 0.41
Na2O 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04
K2O 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03
Boron 0 0.164 0.229 0.295 0.393 0.087 0.122 0.157 0.209
B2 0.3 0.31 0.31 0.31 0.31 0.325 0.34 0.35 0.36
B4 0.22 0.23 0.23 0.23 0.23 0.24 0.24 0.25 0.26
Metallization 91.56 93.68 94.47 92.65 92.56 91.56 92.16 94.12 93.12
Reducibility dr/dt 0.48 0.65 0.68 0.58 0.45 0.51 0.56 0.62 0.56
Firing temperature 0C 1310
Reduction temperature 0C 820
Reduction time(hrs) 4
H2/C0 ratio (gas) 1.92

It is thus possible by way of the present invention to provide boron doped iron ore pellet composition for improvement in reducibility and reduction kinetics of iron ore pellets. The process comprises of mixing the iron ore fines with flux, binder and fuel with boric acid or colemanite or any other source of boron oxide and making green pellets using disc pelletizer. The green pellets so formed are subjected to induration at required firing temperature followed by reduction of fired pellets in presence of reduction gases CO, H2, CH4 and N2 gases. The reducibility index of boron doped pellets increases from 0.50 to 0.66 which in turn increases the metallization of direct reduced iron alongwith emulsification effect of boron rich slag in pellets.