Claims:We Claim:

1. A binder comprising Fume Extraction System (FES) dust, humic acid and lime.

2. The binder as claimed in claim 1, wherein the binder comprises Fume Extraction System (FES) dust at a concentration of about 75 to 85 wt%, humic acid at a concentration of about 10 to 15 wt% and lime at a concentration of about 5 to 10 wt%.

3. The binder as claimed in claim 2, wherein the binder comprises Fume Extraction System (FES) dust at a concentration of about 80 wt%, humic acid at a concentration of about 13 wt% and lime at a concentration of about 7 wt%.

4. The binder as claimed in claim 1, wherein the Fume Extraction System (FES) dust is obtained from Electric Arc Furnace (EAF).

5. The binder as claimed in claim 1, wherein the Fume Extraction System (FES) dust comprises CaO at a concentration of about 1 to 10 wt%, MgO at a concentration of about 0.5 to 5 wt%, SiO2 at a concentration of about 0.5 to 2.5 wt%, Al2O3 at a concentration of about 0 to 0.5 wt% and LOI (Loss on ignition) at a concentration of about 0 to 1 wt%.

6. The binder as claimed in claim 1, wherein the humic acid is alkali based humic acid.

7. The binder as claimed in claim 6, wherein the alkali based humic acid is sodium based or potassium based.

8. A method for synthesizing the binder as claimed in claim 1, comprising steps of:
 mixing Fume Extraction System (FES) dust, humic acid and lime dissolved in water; and
 ageing the mixture to obtain granules/lumps followed by damp milling the granules/lumps to obtain the binder.

9. The method as claimed in claim 8, wherein the binder comprises Fume Extraction System (FES) dust at a concentration of about 75 to 85 wt%, humic acid at a concentration of about 10 to 15 wt% and lime at a concentration of about 5 to 10 wt%.
10. The method as claimed in claim 8, wherein the Fume Extraction System (FES) dust is obtained from Electric Arc Furnace (EAF).

11. The method as claimed in claim 8, wherein the humic acid is alkali based humic acid.

12. The method as claimed in claim 11, wherein the alkali based humic acid is sodium based or potassium based.

13. The method as claimed in claim 8, wherein the ageing is carried out for about 1 to 10 days, preferably for about 5 days.

14. The method as claimed in claim 8, wherein the damp milling is carried out for about 1 to 5 minutes, preferably for about 2 minutes.

15. A method for improving thermal shock properties of iron ore pellets comprising steps of:
 mixing of iron ore fines, flux, carbon source, bentonite and the binder as claimed in claim 1 along with moisture; and
 pelletizing the mixture to obtain the iron ore pellets with improved thermal shock properties.

16. The method as claimed in claim 15, wherein the iron ore fines are hematite - based iron ore fines.

17. The method as claimed in claim 15, wherein the flux is selected from a group comprising CaO based flux, MgO based flux and combinations thereof.

18. The method as claimed in claim 17, wherein the CaO based flux is selected from a group comprising limestone, slaked lime, calcined limestone and combinations thereof.

19. The method as claimed in claim 17, wherein the MgO based flux is selected from a group comprising olivine, pyroxenite, dolomite and combinations thereof.

20. The method as claimed in claim 15, wherein the carbon source is selected from a group comprising anthracite coal, coke fines and combinations thereof.
21. The method as claimed in claim 15, wherein the binder is mixed at a concentration of about 0.05 to 0.5 wt%.

22. The method as claimed in claim 15, wherein the method involves dry mixing of iron ore fines, flux, carbon source, bentonite and the binder followed by wet mixing with addition of moisture.

23. The method as claimed in claim 15, wherein the pelletization is carried out in a disc pelletizer to obtain green pellets followed by induration in a furnace at a temperature ranging from about 1200 to 1300°C to obtain the iron ore pellets.

24. The method as claimed in claim 15, wherein the iron ore pellets of size ranging from about 10 mm to 12.5 mm is obtained.

25. The method as claimed in claim 15, wherein the binder partially replaces bentonite in pelletization.

26. The method as claimed in claim 25, wherein the binder replaces bentonite in pelletization at a replacement ratio of about 1:1.

27. The method as claimed in claim 15, wherein the iron ore pellets show better thermal shock properties as compared to the iron ore pellets with bentonite binder alone.

28. Use of the binder of any of the claims 1-7 in preparation of iron ore pellets.

29. Iron ore pellets obtained by the method of any of the claims 15-27.
, Description:TECHNICAL FIELD
The present disclosure relates to the field of material sciences and metallurgy. In particular, the present disclosure relates to a binder for improving thermal shock properties of iron ore pellets. The binder comprises Fume Extraction System (FES) dust, humic acid and lime. Also disclosed are corresponding method for synthesizing the binder and a method for improving thermal shock properties of iron ore pellets using the binder.

BACKGROUND AND PRIOR ART
Iron ore pelletization involves the process of making spherical ball of size 9-16 mm diameter by rolling raw materials like, mixture of iron ore fines, fluxes (such as limestone, dolomite, dunite, olivine, pyroxenite, etc.), carbon source (such as anthracite, coke breeze, etc.) together with the binder such as bentonite and moisture. The prepared wet balls are then indurated in travelling grate/rotary grate kiln furnace at 1300°C, so that they can be used as a feed material for iron making units.
One of the major problems with respect to iron ore pellets is its tendency to have lower thermal shock properties. Thermal shock properties can be described as tendency of green/wet pellets to resist internal pressure due to sudden evaporation of moisture during drying. Therefore, green/wet pellets should be dried slowly to avoid sudden release of moisture which results in bursting/spalling. But, this takes longer time and requires excessive amount of heat which is not economically feasible.
Various materials have been used to improve thermal shock properties of iron ore pellets. Conventionally, bentonite is most commonly used because it provides acceptable green, dried and fired strength along with thermal shock properties. Green strength is necessary to endure the load caused due to two kinds of forces i.e., impact force and compressive force (a) impact force act while dropping through several conveyors on the way from disc pelletizer to induration furnace and (b) compressive force act due to load of wet pellet bed inside the furnace. Dry strength is required when there is no plasticity in the pellet to protect it from cracking during induration. Fired strength is crucial for transportation of fired pellets to iron making unit.
However, bentonite usage contributes to high alumina, silica and undesirable constituents to final pellet chemistry which is not desirable. Also, it reduces total iron content of pellets and is expensive due to its limited availability.
Several prior arts teach to improve thermal shock properties of iron ore pellets as discussed below:
Guitang et al., in their Patent No. CN101469366A prepared additive to reduce bentonite content which comprises of bentonite, industrial alkali (sodium carbonate/sodium hydroxide) and cellulose ether/ultra-micro building material. These materials are prepared in a manner to obtain the pellet additive which improves green strength, fired properties, burst temperature, quality and yield of the finished pellets. Drawbacks associated with this method is that during the preparation of additive, it was aged for 3-6 days and then dried due to which they become hard and then they are ground to ultrafine size (1200-1500 mesh) which makes the process very costly and not so efficient. Moreover, the patent is completely silent on dry crushing strength of pellets.
Chengan et al., in their Patent No. CN101348862A prepared iron ore pellet adhesive to completely replace the sodium bentonite. The raw materials used are calcium oxide, calcium carbonate, silicon dioxide, alumina, magnesium oxide, ferric oxide and calcium chloride. The adhesive prepared increases the bursting temperature and the crushing strength of the fired pellets. Major drawbacks associated with this is the addition of chloride which increases the corrosion of machine parts such as grate bars. Moreover, addition of alumina also increases alumina load in the blast furnace. Also, the patent is completely silent on green and dry properties of pellets.
Fang et al., in their Patent No. CN110894572A prepared an additive to replace bentonite partially by using raw materials like pellet return fines, sodium humate and slaked lime. With the help of this additive, firing temperature was reduced and crushing strength was also improved remarkably. However, the drawback associated is that the alkali content of the final pellets significantly increases due to excess addition of sodium humate as claimed in the art. Moreover, recycling of pellet return fines or return ore further results in cyclical increase in alkali in pellets. It is also to be noted that pellet return ore are coarser fines. Coarser particles are not expected to undergo enough ageing due to less surface area of coarse particles and hence higher dosage of sodium humate is suggested. Also, another drawback is that pellet return ores are different in chemistry from one plant to another and hence, different chemistry return ore from different plant is not necessarily expected to behave in the same manner. The patent is also completely silent on dry crushing strength and thermal shock properties of pellets.
Iwaskai et al., in their Patent No. JP2000239752A used converter dust and hot metal pre-treatment dust as binder to completely replace bentonite. The additive was used to achieve necessary dropping resistance without using expensive binder bentonite. Major drawbacks related to this prior art is that it is silent about the physical strength of pellet such as green crushing strength, dry crushing strength, fired strength and thermal shock properties.
Guitang et al., in their Patent No. CN102329951A used the additive cellulose ether and iron powder to replace bentonite in pellet making. This additive improved the green drop strength properties, burst temperature and fired ball properties. However, the drawback associated with this method is that the raw material like cellulose ether and iron powder are costly. The prepared additive was ground to 600-1000 mesh for approximately 40 minutes which increases the cost further. Also, the patent does not talk about green crushing strength and dry crushing strength of the pellets.
Haiyong et al., in their Patent No. CN104988308A prepared iron rich composite binder which comprises of iron mud and carboxymethyl cellulose to replace bentonite. This binder improved the green ball properties and burst temperature. The downside effect of this binder is majorly the moisture content of iron mud which is about 25% and must be brought down to less than 5% to be used as a binder. Further, drying of iron mud requires a lot of energy, capital investment and its availability is also an issue. Moreover, the patent is completely silent on dry crushing strength and fired crushing strength.
Thus, there exists a need for binder/method for improving thermal shock properties of iron ore pellets and the present disclosure achieves the same.

SUMMARY OF THE DISCLOSURE
The present disclosure relates to a binder which enables integrating reduction in bentonite consumption, better thermal shock properties and cost effectiveness in pellet making.

In an embodiment of the present disclosure, the binder comprises Fume Extraction System (FES) dust, humic acid and lime.

In another embodiment of the present disclosure, The Fume Extraction System (FES) dust is obtained from Electric Arc Furnace (EAF).
The present disclosure also relates to a method for synthesizing the binder, comprising steps of:
 mixing Fume Extraction System (FES) dust, humic acid and lime dissolved in water; and
 ageing the mixture to obtain granules/lumps followed by damp milling the granules/lumps to obtain the binder.
The present disclosure also relates to a method for improving thermal shock properties of iron ore pellets comprising steps of:
 mixing of iron ore fines, flux, carbon source, bentonite and the binder along with moisture; and
 pelletizing the mixture to obtain the iron ore pellets with improved thermal shock properties.
The present disclosure also relates to use of the binder in preparation of iron ore pellets.
The present disclosure also relates to Iron ore pellets obtained by the above method.
In an embodiment of the present disclosure, the binder partially replaces bentonite in pelletization.

In another embodiment of the present disclosure, the iron ore pellets so obtained show better thermal shock properties as compared to the iron ore pellets with bentonite binder alone.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
In order that the disclosure may be readily understood and put into practical effect,
reference will now be made to exemplary embodiments as illustrated with reference to
the accompanying figures. The figures together with detailed description below, are
incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the
present disclosure where:

Figure 1: Illustrates the conventional method of preparing iron ore pellet: Part no 1.1(a) is iron ore fines bin, 1.1(b)- is flux bin, 1.1(c)- is carbon bearing solid fuel bin 1.1(d)- is bentonite bin, 1.2- is mixer, 1.3- is disc pelletizer, 1.3(a)- are wet pellets, 1.4- is conveyor belt, 1.5- is travelling grate furnace.

Figure 2: Illustrates the proposed method of preparing composite binder and its inclusion in the industrial practice of iron ore pellet making: Part no 2.1(a) – is FES dust, 2.1(b)- is humic acid, 2.1(c)- is lime water, 2.2- is mixed additive, 2.3- is aged composite binder and 2.4- is dried and damp milled composite binder. Part no 2.5(a) is iron ore fines bin, 2.5(b)- is flux bin, 2.5(c)- is carbon bearing solid fuel bin 2.5(d)- is bentonite bin, 2.4- is dry and damp milled composite binder as proposed in the present disclosure, 2.6- is mixer, 2.7- is disc pelletizer, 2.7(a)- are wet pellets, 2.8- is conveyor belt, 2.9- is travelling grate furnace.

Figure 3: Illustrates drop strength of green pellets; Set 1- pellets prepared using 99.5% GOC and 0.5% bentonite (bentonite based pellets); Set 2- pellets prepared using 99.5% GOC and 0.4% bentonite and 0.1% composite binder; Set 3- pellets prepared using 99.5% GOC and 0.4% bentonite (bentonite based pellets)

Figure 4: Illustrates green crushing strength of green pellets; Set 1- pellets prepared using 99.5% GOC and 0.5% bentonite (bentonite based pellets); Set 2- pellets prepared using 99.5% GOC and 0.4% bentonite and 0.1% composite binder; Set 3- pellets prepared using 99.5% GOC and 0.4% bentonite (bentonite based pellets)

Figure 5: Illustrates dry crushing strength of dried pellets; Set 1- pellets prepared using 99.5% GOC and 0.5% bentonite (bentonite based pellets); Set 2- pellets prepared using 99.5% GOC and 0.4% bentonite and 0.1% composite binder; Set 3- pellets prepared using 99.5% GOC and 0.4% bentonite (bentonite based pellets)

Figure 6: Illustrates relative change in un-cracked pellets with base case as 100%; Set 1- pellets prepared using 99.5% GOC and 0.5% bentonite (bentonite based pellets); Set 2- pellets prepared using 99.5% GOC and 0.4% bentonite and 0.1% composite binder; Set 3- pellets prepared using 99.5% GOC and 0.4% bentonite (bentonite based pellets)

Figure 7: Illustrates relative change in burst pellets with base case as 100%; Set 1- pellets prepared using 99.5% GOC and 0.5% bentonite (bentonite based pellets); Set 2- pellets prepared using 99.5% GOC and 0.4% bentonite and 0.1% composite binder; Set 3- pellets prepared using 99.5% GOC and 0.4% bentonite (bentonite based pellets)

Figure 8: Illustrates cold crushing strength of pellets at 1280°C; %; Set 1- pellets prepared using 99.5% GOC and 0.5% bentonite (bentonite based pellets); Set 2- pellets prepared using 99.5% GOC and 0.4% bentonite and 0.1% composite binder; Set 3- pellets prepared using 99.5% GOC and 0.4% bentonite (bentonite based pellets)

DETAILED DESCRIPTION

The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the description of the disclosure. It should also be realized by those skilled in the art that such equivalent product/methods do not depart from the scope of the disclosure.

Definitions:
Unless otherwise defined, all terms used in the disclosure, including technical and scientific terms, have meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

As used herein, the singular forms ‘a’, ‘an’ and ‘the’ include both singular and plural referents unless the context clearly dictates otherwise.

The term ‘comprising’, ‘comprises’ or ‘comprised of’ as used herein are synonymous with ‘including’, ‘includes’, ‘containing’ or ‘contains’ and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. Likewise, certain terms may be interchangeably used throughout the specification and thus have the same meaning even when they are referred interchangeably. For example, lime dissolved in water may be interchangeably referred as lime and moisture or lime water, FES dust as EAF dust, binder of the present disclosure as composite binder/composite based binder, iron ore pellets with bentonite binder alone as bentonite based pellet or bentonite-based pellet, etc.

The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within the respective ranges, as well as the recited endpoints.

The term ‘about’ as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of ±10% or less, preferably ±5% or less, more preferably ±1% or less and still more preferably ±0.1% or less of and from the specified value, insofar such variations are appropriate to perform the present disclosure. It is to be understood that the value to which the modifier ‘about’ refers is itself also specifically, and preferably disclosed.

The present disclosure relates to a binder which enables integrating reduction in bentonite consumption, better thermal shock property and cost effectiveness in pellet making. Particularly
the present disclosure relates to a binder comprising Fume Extraction System (FES) dust, humic acid and lime.
In another embodiment of the present disclosure, the binder comprises Fume Extraction System (FES) dust at a concentration of about 75-85 wt%, humic acid at a concentration of about 10-15 wt% and lime at a concentration of about 5-10 wt%.
In another embodiment of the present disclosure, the binder comprises Fume Extraction System (FES) dust at a concentration of about 80 wt%, humic acid at a concentration of about 13 wt% and lime at a concentration of about 7 wt%.
In another embodiment of the present disclosure, the Fume Extraction System (FES) dust is obtained from Electric Arc Furnace (EAF).
In another embodiment of the present disclosure, the Fume Extraction System (FES) dust comprises CaO at a concentration of about 1-10 wt%, MgO at a concentration of about 0.5-5 wt%, SiO2 at a concentration of about 0.5-2.5 wt%, Al2O3 at a concentration of about 0 to 0.5 wt% and LOI (Loss on ignition) at a concentration of about 0-1 wt%.
In another embodiment of the present disclosure, the humic acid is alkali based humic acid.
In another embodiment of the present disclosure, the alkali based humic acid is sodium based or potassium based.
The present disclosure also relates to a method for synthesizing the binder, comprising steps of:
 mixing Fume Extraction System (FES) dust, humic acid and lime dissolved in water; and
 ageing the mixture to obtain granules/lumps followed by damp milling the granules/lumps to obtain the binder.

In an embodiment of the present disclosure, the binder comprises Fume Extraction System (FES) dust at a concentration of about 75-85 wt%, humic acid at a concentration of about 10-15 wt% and lime at a concentration of about 5-10 wt%.
In another embodiment of the present disclosure, the binder comprises Fume Extraction System (FES) dust at a concentration of about 80 wt%, humic acid at a concentration of about 13 wt% and lime at a concentration of about 7 wt%.
In another embodiment of the present disclosure, the Fume Extraction System (FES) dust is obtained from Electric Arc Furnace (EAF).
In another embodiment of the present disclosure, the humic acid is alkali based humic acid.
In another embodiment of the present disclosure, the alkali based humic acid is sodium based or potassium based.
In another embodiment of the present disclosure, lime is dissolved in water to obtain a slurry. Fume Extraction System (FES) dust and humic acid are mixed in the slurry to obtain a mixture;
In another embodiment of the present disclosure, lime at a concentration of about 5-10% is dissolved in water at a concentration of about 20-30% to obtain the slurry;
In another embodiment of the present disclosure, the ageing is carried out for about 1 to 10 days.
In another embodiment of the present disclosure, the ageing is carried out for about 5 days.
In another embodiment of the present disclosure, the damp milling is carried out for about 1 to 5 minutes.
In another embodiment of the present disclosure, the damp milling is carried out for about 2 minutes.
In another embodiment of the present disclosure, the binder obtained is a grounded binder. The present disclosure also relates to a method for improving thermal shock properties of iron ore pellets comprising steps of:
 mixing of iron ore fines, flux, carbon source, bentonite and the binder of the present disclosure along with moisture; and
 pelletizing the mixture to obtain the iron ore pellets with improved thermal shock properties.
The present disclosure also relates to a method for improving thermal shock properties of iron ore pellets comprising steps of:
 mixing of Ground Ore Concentrate (GOC), bentonite and the binder of the present disclosure along with moisture; and
 pelletizing the mixture to obtain the iron ore pellets with improved thermal shock properties.
In an embodiment of the present disclosure, the binder is mixed at a concentration of about 0.05 to 0.5 wt%.
In another embodiment of the present disclosure, the iron ore fines are hematite-based iron ore fines.
In another embodiment of the present disclosure, the flux is selected from a group comprising CaO based flux, MgO based flux and combinations thereof.
In another embodiment of the present disclosure, the CaO based flux is selected from a group comprising, but not limiting to, limestone, slaked lime, calcined limestone and combinations thereof.
In another embodiment of the present disclosure, the MgO based flux is selected from a group comprising, but not limiting to, olivine, pyroxenite, dolomite and combinations thereof.
In another embodiment of the present disclosure, the carbon source is selected from a group comprising, but not limiting to, anthracite coal, coke fines and combinations thereof.
In another embodiment of the present disclosure, the Ground Ore Concentrate (GOC) comprises of iron ore fines, limestone fines, pyroxenite fines and carbon bearing solid fuel such as anthracite coal, coke and plant industrial by-product Gas Cleaning Plant (GCP) sludge.
In another embodiment of the present disclosure, the method involves dry mixing of iron ore fines, flux, carbon source, bentonite and the binder followed by wet mixing with addition of moisture.
In another embodiment of the present disclosure, the method involves dry mixing of GOC, bentonite and the binder followed by wet mixing with addition of moisture.
In another embodiment of the present disclosure, the pelletization is carried out in disc pelletizer to obtain green pellets followed by induration in a furnace at a temperature ranging from about 1200°C - 1300°C to obtain the iron ore pellets.
In another embodiment of the present disclosure, the iron ore pellets of size ranging from 10 mm to 12.5 mm is obtained.
In another embodiment of the present disclosure, the binder partially replaces bentonite in pelletization.
In another embodiment of the present disclosure, the binder replaces bentonite in pelletization at a replacement ratio of 1:1.
In another embodiment of the present disclosure, the iron ore pellets show better thermal shock properties as compared to the iron ore pellets with bentonite binder alone.
The present disclosure also relates to use of the binder in preparation of iron ore pellets.
The present disclosure also relates to Iron ore pellets obtained by the above method.
In an embodiment of the present disclosure, the iron ore pellets of the present disclosure show better thermal shock properties as compared to the iron ore pellets with bentonite binder alone.
In another embodiment of the present disclosure, the iron ore pellets of the present disclosure show comparable physical strength such as green crushing strength, drop strength and dry crushing strength as that of the iron ore pellets with bentonite binder alone.
In another embodiment of the present disclosure, the iron ore pellets of the present disclosure show better cold crushing strength as that of the iron ore pellets with bentonite binder alone.
In an embodiment of the present disclosure, the composite binder based pellets show better thermal shock properties as compared to the bentonite based pellets.
In another embodiment of the present disclosure, the composite binder based pellets show comparable physical strength such as green crushing strength, drop strength and dry crushing strength as compared to the bentonite based pellets.
In another embodiment of the present disclosure, the composite binder based pellets show better cold crushing strength as compared to the bentonite based pellets.
In another embodiment of the present disclosure, use of the binder of the present disclosure leads to decrease in alumina and silica content in iron ore pellets produced by conventional methods. The composite based binder of the present disclosure does not add any impurity material more than the bentonite binder such as Alkali and decreases gangue addition such as SiO2, Al2O3 etc.
In another embodiment, the binder of the present disclosure is easier to produce in terms of processing steps and decreases the cost of binders used in iron ore pelletizing.
In another embodiment, the present disclosure aims to decrease the bentonite consumption which contributes to higher alumina and silica in finished pellets.
In another embodiment, the Fume Extraction System (FES) dust used in the binder of the present disclosure is ultrafine in nature and does not require any grinding or milling process like bentonite. Due to its finer nature, it will age more properly along with humic acid and lime water. Moreover, the LOI is much lower than the bentonite.
Thus, the present disclosure relates to a composite binder and methods thereof. The disclosure comprises of development of a binder wherein alkali content is the same as that of bentonite so that alkali content does not increase in pellets due to binder dosage. The composite binder is prepared by mixing Fume Extraction System (FES) dust from Electric Arc Furnace (EAF), humic acid and lime water solution. The Fume Extraction System (FES) dust has no/negligible amount of Loss on Ignition (LOI) and therefore, it also helps in decreasing the overall LOI content of a binder and hence in pellets. The prepared mix is then aged for 1-10 days for surface activation of FES dust particles. Due to addition of lime water, small granules and lumps are formed, therefore, the aged material is then damp milled for 1-5 minutes to achieve finer particle size. The composite binder is then added to pellet feed in certain amount such as about 0.05-0.5% to partially replace bentonite in the pellet feed. Humic acid in the binder shows higher water absorbing capacity than bentonite and the binder results in decreasing the bentonite consumption without affecting physical properties of wet, dried and fired pellets.

In an embodiment, the method of preparing the binder involves mixing lime at about 5-10% (dissolved in water), humic acid at about 10-15% and FES dust at about 75-85% and then aged for 1-10 days. After aging, the composite binder thus obtained is dried at 50-60°C and then damp milled to crush-grind the lumps formed so that size acceptable for pellet making is achieved. FES does not require excess grinding because of its powdery nature and hence, only a damp milling is enough. Moreover, FES dust is very fine powder, hence, it is easier and more efficient to age it in the presence of lime water and humic acid. Finer particles give the higher surface area for surface activation during ageing. The binder thus developed in the present disclosure helps to replace bentonite partially without compromising physical strength and thermal shock properties of iron ore pellets.
After preparing the binder, it is mixed uniformly with other raw materials like iron ore fines, fluxes, carbon bearing solid fuel and bentonite. Thus, the present disclosure is also directed to a method of producing iron ore pellets by using iron ore (hematite), CaO based fluxes (limestone, slaked lime, calcined limestone) and MgO based fluxes (olivine, pyroxenite and dolomite), carbon bearing solid fuel (anthracite coal, coke fines), bentonite and the composite binder along with moisture. Alternately, GOC from steel plant collected from Tata Steel Pellet Plant containing iron ore fines, limestone fines, pyroxenite fines and carbon bearing solid fuel such as anthracite coal, coke and plant industrial by-product Gas Cleaning Plant (GCP) sludge is used in the process.
The conventional way of producing iron ore pellets is shown in Figure 1. Raw materials from bin i.e. iron ore fines, fluxes, carbon bearing solid fuel and bentonite [1.1(a)- 1.1(d)] is mixed in the mixer (1.2). Moisture is then added in the mixed material (about 6-9%) to prepare wet mixture which is moved to disc pelletizer (1.3) through the conveyor belt and pellet is made by sprinkling water as per requirement. Wet pellet (1.3a) made with help of disc pelletizer is passed through different size roller screen (1.4) so that, right size pellet (say 9-16 mm.) can be charged into travelling grate furnace (1.5) and, the oversized and undersized pellets are made again to meet this size. Once, the pellets are fired by passing through different zone in travelling grate furnace, it is carried to iron making unit.
Iron ore pellet preparation according to the present disclosure is represented in Figure 2. Raw materials - FES dust, humic acid and lime water are mixed in certain amount such that total alkali content does not exceed by about 2.5-3% which is the limit in bentonite. This is then aged for 1-10 days. After aging, composite binder formed is moist and granular which are dried and damp milled, to bring the particle size down which is suitable for pellet making. This is then used in iron ore pellet making as in Figure 2 where material from bins [2.5(a)-2.4] goes into the mixer (2.6), which provides uniform mixing of raw materials. Water is added to the mixed material in required amount, for example ~8%, and then the material is charged into an inclined circular disc known as pelletizer (2.7). Wet pellets of 9-16 mm size [2.7(a)] are prepared in disc pelletizer and through the conveyor belt (2.8), these are charged into travelling grate furnace (2.9) where the pellets are fired at suitable temperature.
It is to be understood that the foregoing description is illustrative not a limitation. While considerable emphasis has been placed herein on particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. Those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Similarly, additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon description provided herein.
Descriptions of well-known/conventional methods/steps and techniques are omitted so as to not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for examples illustrating the above-described embodiments, and in order to illustrate the embodiments of the present disclosure, certain aspects have been employed. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments may be practiced and to further enable those of skill in the art to practice the embodiments. Accordingly, following examples should not be construed as limiting the scope of the embodiments herein.
Examples:
Example 1: Synthesis of composite binder
In synthesizing the binder of the present disclosure, 80% Fume Extraction System (FES) dust, 13% humic acid and 7% lime dissolved in 28% moisture is mixed and aged for 5 days. The binder prepared is damp milled and then used to replace bentonite partially.
Initially, 7% lime is dissolved in 28% moisture/water to obtain a slurry. 80% Fume Extraction System (FES) dust and 13% humic acid are mixed in the slurry to obtain a mixture which is aged for 5 days to obtain the binder. The binder prepared is damp milled and then used to replace bentonite partially.
Particle size analysis of raw materials used for preparing the red oxide based binder is done by using wet sieving method and is provided in Table 1.
Table 1: Particle size analysis of raw material used for composite binder preparation

Size range (μm) EAF dust (wt.%) Lime (wt. %) Humic acid (wt. %)
-45 96.4 82.8 94

Example 2: Green Pellet Preparation
Four sets of green pellets [Table 3] were prepared to observe the improvement in thermal shock properties based on the composite binder. Comparison was done between bentonite-based pellet and bentonite plus composite binder based pellet. Chemical analysis of raw material used for pellet preparation is provided in Table 2.

Table 1: Raw material chemical analysis

Raw Material Fe(T) FeO CaO SiO2 MgO Al2O3 K2O Na2O C LOI
GOC 58.4 9.68 1.6 4.65 1.87 2.87 0.05 0.02 0.87 5.59
Bentonite 10.23 - 1.48 38.02 1.98 13.99 0.08 2.23 - 24.6
EAF (FES) Dust 65.98 4.51 1.53 0.92 0.88 0.16 0.37 0.021 0.24 0.77
Lime 0.45 - 89.85 1.02 0.84 0.04 - - - 7.11
Composite binder 51.9 -
7.75
2.13
0.94
0.54
-
-
- 13.3
The process of green pellet preparation involves use of Ground Ore Concentrate (GOC) collected from Tata Steel Pellet Plant. It contains iron ore fines, limestone fines, pyroxenite fines and carbon bearing solid fuel such as anthracite coal, coke and plant industrial by-product Gas Cleaning Plant (GCP) sludge.
Mass balance of ingredients for preparing green pellets is shown in Table 3. Based on the mass balance, 5 kg of raw material on a dry basis was weighed. First, dry mixture was prepared in a turbo mixer (make- Insmart, capacity 10L) wherein material was mixed for 30 minutes in dry condition. Wet mixture was prepared in high intensity bladed mixer with 8% moisture. The wet mixture was then used for making green pellet of size 10-12.5 mm in a disc pelletizer.

Table 3: Mass balance for preparing green pellet

Pellet Id GOC Bentonite Composite binder
Set 1
(base case) 99.5% 0.5% 0.0%
Set 2 99.5% 0.4% 0.1%
Set 3 99.5% 0.4% 0.0%

Example 3: Moisture absorbing capacity of Pellet raw material containing bentonite and proposed composite binder
Moisture absorbing capacity was measured for both mixtures i.e. Ground Ore Concentrate (GOC) with bentonite and GOC with bentonite plus composite binder. Experiment was conducted for measuring the water absorbing capacity by using a cylindrical tube of 100 mm height and 15 mm diameter which was open from both ends. The cylindrical tube was placed on a porous bed of filter papers so that water can be absorbed from bottom by capillary forces without material falling from the bottom. 100 g of mixture was filled in it. The full set up was placed in a tray in which water was poured till the height of filter paper and it was kept for 24 hours to absorb the moisture fully. After 24 hours, moistened mixture from the cylinder was taken out and with the help of moisture analyzer equipment, moisture percentage was measured as mentioned in Table 4.

Table 4: Moisture absorption test

GOC+0.5% Bentonite GOC+0.4%Bentonite+0.1% composite binder GOC+0.3%Bentonite+0.2% composite binder
%Moisture absorbed 17.86 18.17 18.49

It is evident from Table 4 that GOC with bentonite plus composite binder absorbed more moisture than GOC with bentonite only. Thus, the composite binder can replace bentonite in iron ore pellet making because of its good water absorbing capacity.

Example 4: Comparing physical properties of Bentonite based pellets and composite binder-based pellets
Tests like drop strength test (Figure 3) and GCS - green crushing strength (Figure 4) was performed on green pellets so prepared in Example 2. After drying green pellet at temperature 105°C ±5, dry crushing strength (DCS) test was done (Figure 5). The green pellets were also subjected to the thermal shock test designed with heating patterns like Tata Steel 6 MTPA Pellet plant. The peak shock temperature given to pellet was 500 °C wherein pellets were heated to reach 500 °C at a heating rate of ~67 °C/min. The number of un-cracked pellets (Figure 6) and burst pellets (Figure 7) were counted and relative percentage, with Set 1 being the reference, is reported. Further, pellets were also fired at 1280 °C to see its effect on CCS (Figure 8).
According to Figures 3-5, green strength (drop strength, GCS and DCS) of pellets for all sets are comparable. According to figure 6, relative percentage of un-cracked pellets for Set 2 was higher than the Set 1. Even relative percentage of burst pellets (Figure 7) was reduced by half for Set 2 in comparison with set 1. Set 2 also showed better thermal shock property than Set 3 as both Set 2 and 3 contain same amount of bentonite but due to addition of the composite binder in Set 2, it shows better property. Fired strength for Set 1 and Set 2 are comparable and even better than set 3 as shown in Figure 8.
Thus, Set 2 pellets show better thermal shock properties in comparison with only bentonite-based pellets (Sets 1 and 3).