Claims:We Claim:
1. A process for preparation of iron ore pellets comprising steps of:
a) mixing hematite ore fines, mill scale, iron ore slime and binder optionally along with flux maintaining basicity ranging from 0 and 0.5 to obtain a mixture,
b) pelletizing the mixture to obtain pellets, and
c) optionally indurating the pellets.
2. The process as claimed in claim 1, wherein the binder is bentonite.
3. The process as claimed in claim 1, wherein ratio of hematite ore fines, mill scale, iron ore slime and binder is ranging between 99.7:0:0:0.3 and 59:20:20:1.
4. The process as claimed in claim 1, wherein the flux is selected from a group comprising limestone, olivine and magnesium oxide or any combination thereof, at an amount ranging from about 0.1 to 7 wt%.
5. The process as claimed in claim 1, wherein the mixing is carried out for a period of about 5 to 15 minutes; and wherein the pelletizing of the mixture is carried out in a pelletizer using about 8-16 wt% of water spray.
6. The process as claimed in claim 1, wherein the indurating of the pellets is carried out at a temperature ranging from about 1050-1350°C for a time period ranging from about 5 to 15 minutes; and wherein the indurating of the pellets is carried out in a furnace.
7. The process as claimed in claim 1, wherein the pellets have a size ranging from about 7-15 mm.
8. The process as claimed in claim 1, wherein the hematite ore fines comprises about 60-68 wt% of Fetot, about 0.3-3 wt% of SiO2, about 0.3-3 wt% of Al2O3, about 0.02-0.05 wt% of S, and about 0.02-0.08 wt% of P; wherein the mill scale comprises about 25-40 wt% of Fe2O3, about 50-70 wt% of FeO, about 60-77 wt% of Fetot, about 0.1-0.07 wt% of SiO2, and about 0.1-0.7 wt% of Al2O3; and wherein the iron ore slime comprises about 40-65 wt% of Fetot, about 2-7 wt% of SiO2, about 2-7 wt% of Al2O3, about 0.02-0.05 wt% of S, and about 0.02-0.2 wt% of P.
9. The process as claimed in claim 2, wherein the bentonite comprises about 8-15% of Fe2O3, about 40-60% of SiO2, about 8-20 wt% of Al2O3, about 2.5 to 3 wt% of MgO, about 1.5 to 2 wt% of CaO, and about 1-2.5 wt% of Na2O.
10. The process as claimed in claim 4, wherein the limestone comprises about 45-53 wt% of CaO, about 0.3-3 wt% of Al2O3, about 1-6 wt% of SiO2, and about 0.5-7 wt% of MgO.
11. Iron ore pellets comprising hematite ore fines, mill scale, iron ore slime and binder.
12. The pellets as claimed in claim 11, wherein the hematite ore fines, mill scale, iron ore slime and binder are present at a ratio ranging between 99.7:0:0:0.3 and 59:20:20:1.
13. The pellets as claimed in claim 11, wherein the binder is bentonite; wherein the pellets have a size ranging from about 7-15 mm, and a basicity ranging from 0 and 0.5.
14. The pellets as claimed in claim 11, wherein the pellets have a compressive strength of at least 1.66 kg/pellet, Green Drop Strength Number of at least 31, dry compressive strength of at least 9.16 kg/pellet or a combination thereof.
15. The pellets as claimed in claim 11, wherein the pellets have a cold compression strength of at least about 225 kg/pellet, reducibility index of less than 96 wt%, Reduction Degradation Index of about less than 26 wt%, swelling index of less than 20 wt% or a combination thereof. , Description:TECHNICAL FIELD
The present disclosure relates to the field of metallurgy and material sciences. In particular, the present disclosure relates to a process for preparation of iron ore pellets comprising iron ore fines, mill scale, iron ore slime and binder. The present disclosure also relates to iron ore pellets comprising iron ore fines, mill scale, iron ore slime and binder.

BACKGROUND OF THE DISCLOSURE
In magnetite ore pellet, oxidation of magnetite occurs during induration which provides exothermic heat to the pellet and enhances diffusion bonding. However, due to the absence of this exothermic oxidation, hematite pellet requires higher roasting temperature and narrow firing ranges for the induration which gives rise to the difficulty in operation of firing equipment. Any integrated steel plant needs to continuously improve its current processes to reduce the energy consumption. This includes the development of new processes to reduce environmental impact. Also, the roasting behaviour of hematite pellets is inferior to that of magnetite pellets. Therefore, mixing of magnetite in hematite ore is carried out for its induration. Magnetite ore is however a sparse resource. Hence, low quality iron ores having high alumina and silica have not been efficiently used.

Prior art teaches use of iron ore fines along with other components such as reduced iron powder, steel making slag, blast furnace dust, etc for making cold bonded briquettes using gypsum free cement and molasses as binders. However, such studies are on briquetting and not on pelletization. Further, indurated pellets produced in the art comprise zinc making it unsuitable for use in Blast Furnace.

Accordingly, there is a need for sustained and cost-effective use of iron ores/fines, particularly low-grade iron ores or iron ore fines, to achieve good quality blast furnace grade pellet having the desirable physico-chemical properties and also addressing the aforesaid concerns of the presently practiced methods.

SUMMARY OF THE DISCLOSURE
The present disclosure relates to a process for preparation of iron ore pellets comprising steps of:
a) mixing hematite ore fines, mill scale, iron ore slime and binder optionally along with flux maintaining basicity ranging from 0 and 0.5 to obtain a mixture,
b) pelletizing the mixture to obtain pellets, and
c) optionally indurating the pellets.

The present disclosure also relates to iron ore pellets comprising hematite ore fines, mill scale, iron ore slime and binder.

In an embodiment, the ratio of hematite ore fines, mill scale, iron ore slime and binder is ranging between 99.7:0:0:0.3 and 59:20:20:1.

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 a 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 depicts surface morphology of different fines under SEM microscope.
Figure 2 depicts effect of induration temperature on CCS of pellet.
Figure 3 depicts thermogravimetric analysis of mill scale pellet.
Figure 4 depicts effect of slime on RDI and swelling index of basic pellet.
Figure 5 depicts effect of slime on RDI and swelling index of basic pellet.

DETAILED DESCRIPTION OF THE DISCLOSURE
The present disclosure relates to a process for preparation of iron ore pellets comprising steps of:
a) mixing hematite ore fines, mill scale, iron ore slime and binder optionally along with flux maintaining basicity ranging from 0 and 0.5 to obtain a mixture,
b) pelletizing the mixture to obtain pellets, and
c) optionally indurating the pellets.

In an embodiment, the binder is bentonite.

In another embodiment, the ratio of hematite ore fines, mill scale, iron ore slime and binder is ranging between 99.7:0:0:0.3 and 59:20:20:1.

In yet another embodiment, the flux is selected from a group comprising limestone, olivine and magnesium oxide or any combination thereof, at an amount ranging from about 0.1 to 7 wt%.

In still another embodiment, the mixing is carried out for a period of about 5 to 15 minutes; and wherein the pelletizing of the mixture is carried out in a pelletizer using about 8-16 wt% of water spray.

In still another embodiment, the indurating of the pellets is carried out at a temperature ranging from about 1050-1350°C for a time period ranging from about 5 to 15 minutes; and wherein the indurating of the pellets is carried out in a furnace.

In still another embodiment, the pellets have a size ranging from about 7-15 mm.

In still another embodiment, the hematite ore fines comprises about 60-68 wt% of Fetot, about 0.3-3 wt% of SiO2, about 0.3-3 wt% of Al2O3, about 0.02-0.05 wt% of S, and about 0.02-0.08 wt% of P; wherein the mill scale comprises about 25-40 wt% of Fe2O3, about 50-70 wt% of FeO, about 60-77 wt% of Fetot, about 0.1-0.07 wt% of SiO2, and about 0.1-0.7 wt% of Al2O3; and wherein the iron ore slime comprises about 40-65 wt% of Fetot, about 2-7 wt% of SiO2, about 2-7 wt% of Al2O3, about 0.02-0.05 wt% of S, and about 0.02-0.2 wt% of P.

In still another embodiment, the bentonite comprises about 8-15% of Fe2O3, about 40-60% of SiO2, about 8-20 wt% of Al2O3, about 2.5 to 3 wt% of MgO, about 1.5 to 2 wt% of CaO, and about 1-2.5 wt% of Na2O.

In still another embodiment, the limestone comprises about 45-53 wt% of CaO, about 0.3-3 wt% of Al2O3, about 1-6 wt% of SiO2, and about 0.5-7 wt% of MgO.

The present disclosure also relates to iron ore pellets comprising hematite ore fines, mill scale, iron ore slime and binder.

In an embodiment, the hematite ore fines, mill scale, iron ore slime and binder are present at a ratio ranging between 99.7:0:0:0.3 and 59:20:20:1.

In another embodiment, the binder is bentonite.

In yet another embodiment, the pellets have a size ranging from about 7-15 mm, and a basicity ranging from 0 and 0.5.

In still another embodiment, the pellets have a compressive strength of at least 1.66 kg/pellet, Green Drop Strength Number of at least 31, dry compressive strength of at least 9.16 kg/pellet or a combination thereof.

In still another embodiment, the pellets have a cold compression strength of at least about 225 kg/pellet, reducibility index of less than 96 wt%, Reduction Degradation Index of about less than 26 wt%, swelling index of less than 20 wt% or a combination thereof.

As used herein, the term ‘iron ore pellets’ refers to about 7–15 mm pellets comprising iron ores or iron ore files, mill scale and iron ore slime; optionally along with one or more binder such as but not limiting to bentonite; and/or flux. Iron ore pellets are suitable for use as raw material for blast furnaces.

As used herein, the term ‘green pellets’ refers to balled fines in which the ground fines such as iron ore, slime, mill scale are mixed in varying proportions along with fluxes and binder such as bentonite and rolled into oval/spherical balls with the addition of moisture.

As used herein, the term ‘indurated pellets’ refers to thermally processed green pellets heated in an electrically heated furnace in a temperature range of about 1050-1350°C for a period of about 5-15 minutes

As used herein, the term ‘green bonding property’ refers to the adhesion of ground ore fines particles in the presence of moisture.

As used herein, the terms ‘iron ore slime’ and ‘slime’ have been used interchangeably.

In all embodiments of the present disclosure, the % amount indicated is weight % unless specified otherwise.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results. Throughout this specification, the word “comprise”, or variations such as “comprises” or “comprising” or “containing” wherever used, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

The present disclosure provides for a process for preparation of iron ore pellets utilizing mill scale and iron ore slime, which obviates the drawbacks of the hitherto known prior art as detailed above.

In order to utilize both mill scale and iron ore slime, the pellets are prepared by combining and mixing iron ore such as hematite ore fines with mill scale and iron ore slime in a suitable proportion.

In an embodiment, the process of the present disclosure provides for preparation of hematite pellets for iron making with lower indurating temperature. The process provides for reducing energy consumption for hematite ore pelletization.

In an embodiment, the process of the present disclosure provides for preparation of iron ore pellets from waste materials such as mill scale and iron ore slime without increasing the gangue materials.

The present disclosure relates to a process for preparation of iron ore pellets comprising steps of:
a) combining iron ore, mill scale, iron ore slime optionally along with binder such as bentonite by maintaining basicity between 0 and 0.5 to obtain a mixture, and
b) pelletizing the mixture to obtain pellets.

The process of pelletizing comprises mixing finely ground particles of iron ore fines with additives such as but not limiting to bentonite and subsequently shaping them into oval/spherical pellets of about 7-15 mm in diameter by a pelletizer and hardening the balls by firing with a fuel.

In an embodiment, the process for preparation of iron ore pellets comprises:
- Preparation of raw material, in which the raw materials such as iron ore fines, slime and mill scale are individually ground in a ball mill to a Blaine fineness of about 2200 cm2/g.
- Formation of green pellets, in which the ground fines such as iron ore, slime, mill scale is mixed in varying proportions optionally along with fluxes and binder such as but not limiting to bentonite and rolled into oval/spherical balls with the addition of moisture.
- Drying of pellets, is done by placing the green pellets in an oven maintained at a temperature of about 110°C for about four hours to remove the surface moisture.
- Induration of the pellets, involves the thermal processing of pellets heated in an electrically heated furnace in a temperature range of about 1050-1350°C for a period of about 5-15 minutes.
- Cooling and storage of pellets is done by cooling the pellets under furnace atmosphere and further storing of the thermally processed pellets in a desiccator.

The present disclosure also relates to a process for preparation of iron ore pellets comprising steps of:
a) combining iron ore, mill scale, iron ore slime by maintaining basicity between 0 and 0.5 to obtain a mixture, and
b) pelletizing the mixture to obtain green pellets, in which the ground fines such as iron ore, slime, mill scale is mixed in varying proportions along with fluxes and binder such as but not limiting to bentonite and rolled into oval/spherical balls with the addition of moisture.
c) indurating the pellets to obtain indurated pellets by thermal processing of pellets heated in an electrically heated furnace in a temperature range of 1050-1350°C for a period of 5-15 minutes.

In embodiments of the present disclosure, the term ‘combining’ as used herein includes contacting the components and optionally mixing the same.

In preferred embodiments, the iron ore employed in the process for preparation of iron ore pellets is hematite ore or hematite ore fines.

The basicity of the mixture/pellet is maintained by addition of one or more flux selected from a group comprising but not limiting to limestone, olivine and magnesium oxide or any combination thereof. In an embodiment, the flux is added at an amount ranging from about 0.1 to 7 wt%. In an embodiment, the basicity is maintained between 0 and 0.5 for a period of about 5 to 15 minutes.

In an embodiment of the present disclosure, the process comprises addition of binder such as but not limiting to bentonite to iron ore, mill scale and iron ore slime. In embodiments of the present disclosure, the iron ore, mill scale, iron ore slime and binder such as bentonite are combined in the process for preparation of the iron ore pellet at a ratio (in weight %) ranging between 99.7:0:0:0.3 and 59:20:20:1. In a preferred embodiment, the said ratio is ranging from about 99.5:0.1:0.1:0.3 to 59:20:20:1. In another preferred embodiment, the said ratio is ranging from about 89.7:5:5:0.3 to about 59.5:20:20:05. In yet another preferred embodiment, the said ratio is ranging from about 89.7:5:5:0.3 to about 69.5:15:15:0.5. In yet another preferred embodiment, the ratio of iron ore, mill scale, iron ore slime and binder combined in the process for preparation of the iron ore pellet is 69.5:15:15:0.5.

In embodiments of the present disclosure, the process for preparation of iron ore pellets comprises:
a) combining iron ore such as hematite iron ore or hematite iron ore fines, mill scale, iron ore slime and binder such as bentonite in a ratio ranging between 99.7:0:0:0.3 and 59:20:20:1, preferably from 95.5:0.1:0.1:0.3 to 59:20:20:1, more preferably from 89.7:5:5:0.3 to about 59.5:20:20:05, and most preferably from 89.7:5:5:0.3 to about 69.5:15:15:0.5, with or without flux maintaining basicity between 0 and 0.5 for a period of about 5 to 15 minutes to obtain a mixture,
b) pelletizing the mixture to obtain pellets, and
c) optionally indurating the pellets.

In an embodiment, the process for preparation of iron ore pellets comprises steps of:
a) combining hematite ore fines, mill scale, iron ore slime and bentonite with or without flux maintaining basicity between 0 and 0.5 for a period of about 5 to 15 minutes to obtain a mixture,
b) pelletizing the mixture to obtain pellets, and
c) optionally indurating the pellets.

In embodiments of the present disclosure, the pelletizing of the mixture comprising the components of the iron ore pellets as per the process of the present disclosure is carried out in a pelletizer. In an embodiment, the pelletizing of the mixture is carried out using about 8-16 wt% of water spray.

In embodiments of the present disclosure, the indurating of the pellets in the process is carried out at a temperature ranging from about 1050-1350°C, preferably about 1275 °C for a time period ranging from about 5 to 15 minutes. In an embodiment, the induration of the pellets is carried out in a furnace.

In an embodiment, the process for preparation of iron ore pellets utilizing mill scale and iron ore slime comprises,
a) mixing hematite ore fines, mill scale, iron ore slime and binder such as bentonite in the ratio ranging between 99.7:0:0:0.3 and 59:20:20:1 with or without fluxes maintaining basicity between 0 and 0.5 for a period of 5 to 15 minutes,
b) pelletizing the mixture as obtained in step (a) to pellets of size range, 7-15 mm in a pelletizer using 8-16 wt% of water spray,
c) optionally characterizing the green and pellets through techniques such as but not limiting to green compressive strength, drop strength, dry compressive strength measurement, etc.,
d) indurating pellets in a furnace at the temperature ranging from about 1050-1350°C, and
e) optionally characterizing the pellets obtained in step (d) through techniques such as but not limiting to compressive strength, reducibility index, reduction degradation index, swelling index, apparent porosity measurement etc.

In embodiments of the present disclosure, the pellets obtained by the process have a size ranging from about 7-15 mm.

In embodiments of the present disclosure, the hematite ore fines comprises about 60-68 wt% of Fetot, about 0.3-3 wt% of SiO2, about 0.3-3 wt% of Al2O3, about 0.02-0.05 wt% of S, and about 0.02-0.08 wt% of P;

In embodiments of the present disclosure, the mill scale comprises about 25-40 wt% of Fe2O3, about 50-70 wt% of FeO, about 60-77 wt% of Fetot, about 0.1-0.07 wt% of SiO2, and about 0.1-0.7 wt% of Al2O3.

In embodiments of the present disclosure, the iron ore slime comprises about 40-65 wt% of Fetot, about 2-7 wt% of SiO2, about 2-7 wt% of Al2O3, about 0.02-0.05 wt% of S, and about 0.02-0.2 wt% of P.

In embodiments of the present disclosure, the bentonite comprises about 8-15% of Fe2O3, about 40-60% of SiO2, about 8-20 wt% of Al2O3, about 2.5 to 3 wt% of MgO, about 1.5 to 2 wt% of CaO, and about 1-2.5 wt% of Na2O.

In embodiments of the present disclosure, the limestone comprises about 45-53 wt% of CaO, about 0.3-3 wt% of Al2O3, about 1-6 wt% of SiO2, and about 0.5-7 wt% of MgO.

In embodiments of the present disclosure, the olivine comprises about 40.3 wt% of SiO2, about 0.5 wt% of Al2O3, and about 48.1 wt% of MgO.

The present disclosure also relates to iron ore pellets obtained by any of the afore-described process of the present disclosure.

The present disclosure further relates to iron ore pellets comprising hematite ore fines, mill scale and iron ore slime.

In an embodiment, the present disclosure provides for development of hematite ore pellets utilizing mill scale and slime.

Mill scale is a by-product generated during casting and rolling process of steel. Mill scale is generated from steel mills area, which includes rolling mills, merchant mills, reheating furnaces etc. Mill scale is constituted with high Fe content with very less gangue content. Mill scale mainly contains magnetite and woustite with negligible gangue oxides. These lower oxides of iron get oxidized to hematite if reheated at moderate to high temperature in presence of air. Thus, mill scale in pellet is oxidized during induration which provides in-situ heat and improves diffusion bond and recrystallization. Mixing of mill scale in hematite ore improves its bonding property and reduces induration temperature. Although, mill scale is gangue free iron oxide, it has very poor green bonding property.

Iron ore slime is also a waste material generated in very fine form in the ore washing plant. Slime is very fine material and has good green bonding property. The wet processing of iron ore results in the generation of sizeable amounts of iron ore slime. Even though iron ore slime is constituted with high Fe% (about 55-60%), its use in blast furnace is restricted because of the presence of high gangue content which includes alumina and silica. Further, due to its high alumina and silica content and excessive fineness it cannot be used alone in pelletization.

Hematite ore pellets have poor roasting properties and do not achieve adequate strength until the induration temperature is >1300°C which makes the process highly energy intensive. The mixing of hematite ore with mill scale and iron ore slime in suitable proportions, generates good quality pellets with improved pellet property, which is suitable for use in blast furnace, Direct Reduced Iron (DRI) production etc. The high alumina and silica in slime are balanced by the mill scale, and thus both the materials will be utilized which improves pellet property. The iron ore pellets of the present disclosure have improved exothermic oxidation and diffusion bonding, and reduced induration temperature which helps in decrease in energy consumption.

The present disclosure also relates to iron ore pellets comprising hematite ore fines, mill scale and iron ore slime. In another embodiment, the pellets have a size ranging from about 7-15 mm.

In an embodiment, the iron ore pellet further comprises a binder such as bentonite. In embodiments of the present disclosure, the iron ore pellet comprises iron ore, mill scale, iron ore slime and binder at a ratio ranging between 99.7:0:0:0.3 and 59:20:20:1. In a preferred embodiment, the said ratio is ranging from about 99.5:0.1:0.1:0.3 to 59:20:20:1. In another preferred embodiment, the said ratio is ranging from about 89.7:5:5:0.3 to about 59.5:20:20:05. In yet another preferred embodiment, the said ratio is ranging from about 89.7:5:5:0.3 to about 69.5:15:15:0.5. In yet another preferred embodiment, the ratio of iron ore, mill scale, iron ore slime and binder in the iron ore pellet is 69.5:15:15:0.5.

The iron ore pellets of the present disclosure include green pellets and indurated pellets. In an embodiment, the green pellets are obtained on combining the components prior to subjecting the pellet to induration. In another embodiment, the indurated pellets are obtained on induration of the green pellets.

In an exemplary embodiment, the green pellet of the present disclosure has a green compressive strength of at least 1.66 kg/pellet, GDSN / drop strength of at least 31, and/or a dry compressive strength of at least 9.16 kg/pellet.

In an exemplary embodiment, the indurated pellet of the present disclosure has a cold compression strength of at least about 225 kg/pellet, reducibility index of less than 96 wt%, Reduction Degradation Index of about less than 26 wt%, swelling index of less than 20 wt% or a combination thereof.

In an embodiment, the CCS is ranging from about 225 to 450 kg/pellet, the reducibility index is ranging from about 80 to 96 wt%, the Reduction Degradation Index is ranging from about 6 to 25 wt% and the swelling index is ranging from about 9.5 to 19.9 wt%.

In an embodiment, the induration temperature is reduced by at least 75°C.

The present disclosure provides for use of mill scale and iron ore slime for developing iron ore pellets which are suitable for application in blast furnace.

In an embodiment, the green and indurated pellets obtained by the processes of the present disclosure are characterised by techniques known in the art.

In an embodiment, green pellets are characterized by analysing green pellet properties such as but not limiting to Green Compressive Strength (GCS), Green Drop Strength Number (GDSN), Dry Compressive Strength (DCS), SEM and moisture content of the green pellets. In an exemplary embodiment, the GCS of pellets is measured using a Hounsfield Material testing Machine (Model: H10K-S), indicates ability of green pellets to withstand the compressive load of the pellet bed at the initial stage of induration process. The average compressive load sustained by 20 green pellets having 10-11 mm diameter before breaking is given as GCS. GCS of at least 1 kg/pellet is industrially acceptable. In an exemplary embodiment, the DCS of oven dried pellets was tested in a Hounsfield Material testing Machine (Model: H10K-S), it indicates the strength of pellet at the time of drying when the moisture in green pellet evaporates and the pellet becomes fragile. The machine is connected with a PC having data capturing system. In an exemplary embodiment, the GDSN is measured by repeatedly dropping individual green pellets on a mild steel plate from a height of about 450 mm and counting the number of drops sustained by the pellet before cracking. In an exemplary embodiment, the moisture content in green pellets is measured by heating a representative sample of about 30-40 g at a temperature of about 110°C for about four hours and subsequently measuring the weight loss in the sample in wt%, indicates the amount of moisture adsorbed by pellet during green balling. Optimum moisture is critical to maintain productivity. Less moisture may result in keeping fines dry whereas more moisture though results in growth rate but high moisture may result in easy deformation. In an exemplary embodiment, the Scanning Electron Microscope (SEM) Imaging is done to study the morphology of the pellets.

In an embodiment, indurated pellets are characterized by analysing indurated pellet properties such as but not limiting to Cold compression strength (CCS), Reducibility Index (RI), Reduction Degradation Index (RDI), Swelling Index (SI), Apparent porosity (AP) etc. In an exemplary embodiment, the CCS of the indurated pellets is measured as per the standard ISO 4700, using Hounsfield Material testing Machine (Model: H10K-S), indicates the strength of indurated pellet which is required by a pellet to withstand the load in blast furnace. In an exemplary embodiment, the RI is measured as per the standard JIS: M 8713-2000, indicates the ease with which oxygen combined with iron could be removed from iron ore pellets with a reducing gas at the time of reduction. In an exemplary embodiment, the RDI is measured as per the standard JIS: M 8720-2001, indicates the degradation of pellets in the upper part of blast furnace. In an exemplary embodiment, the Swelling Index (SI) is measured after reduction as per JIS: M 8713-2000 at a temperature of 900°C by measuring its volume change percentage between before and after reduction by mercury displacement method, and indicates the volume increase in pellet during reduction making the reduced pellet fragile. In an exemplary embodiment, the AP of indurated pellets is measured as per the standard IS: 1528 (Part VIII) – 1974 (Reaffirmed 2002), indicates the porosity in pellets after induration.

In an embodiment of the present disclosure, the pelletization properties of slime, mill scale and iron ore such as hematite iron ore is studied individually. Pellets cannot be prepared from mill scale or iron ore slime individually (100%). Pure mill scale pellet has very poor green bonding property. Pure slime pellet shows very good green and dry strength, however, during pelletization coagulation of ores/fines occurs due to its excessive fineness. Therefore, green pelletization is very difficult with these two materials individually. However, their suitable proportion of mixing allows for pelletization and provides for quality improvement of the iron ore pellet and energy consumption.

In an embodiment, addition of iron ore slime in pellet deteriorates the strength properties and reduction degradation properties of iron ore pellet both in acidic and basic condition. Therefore, slime alone cannot be used with iron ore in pellet. In an embodiment, use of mill scale in hematite ore pellet provides very good strength even at 1200°C, because of the oxidation of FeO and Fe3O4 which facilitates diffusion bonding and recrystallization. FeO oxidation in mill scale added pellets takes place from the surface towards the centre gradually during isothermal heating without forming any duplex structure of magnetite core and hematite shell like magnetite ore pellet. Mill scale addition can reduce the induration temperature of pellet and decreases the energy consumption in induration strand. It is also possible to produce the lime free acidic pellet which has very good properties to be suitable for blast furnace use. In an embodiment, iron ore slime has good green properties. The addition of iron ore slime provides for application of the potential of mill scale in hematite ore pellet to reduce the induration temperature to decrease energy consumption.

Due to the combined addition of slime and mill scale, pellets properties are, induration temperature is reduced and the increase of gangue content due to addition of slime has almost been counterbalanced by the addition of mill scale (almost pure). Thus, the combined mixture of slime and mill scale in hematite pellet has a very good application potential which help utilizing wastes and reduces energy consumption.

The present disclosure provides for good quality iron ore pellets, and process for obtaining the same, which are suitable for iron making through blast furnace and DRI production. In an embodiment, the acidic pellet has a very good importance in blast furnace operation as a mix material with basic sinter. The present disclosure provides for combined use of mill scale and slime in pellet without increasing gangue content, and also helps in utilizing waste materials.

In a non-limiting embodiment, the various advantages of the process and iron ore pellets of the present disclosure include but are not limited to:
1. Pellet quality improves. Good quality pellets produced suitable for iron making through blast furnace and DRI.
2. Helps in utilizing waste materials such as mill scale and iron ore slime.
3. Suitably for use of low quality iron ore such as hematite ore fines.
4. Mill scale helps in diffusion bond formation and provide exothermic in-situ heat. This may save energy for induration of pellets.
5. Preparation of iron/hematite pellets with lower indurating temperature.
6. Overall alumina and silica content of pellet does not increase in spite of using slime.
7. Reducing energy consumption for iron ore, such as hematite ore fines, pelletization.

The foregoing descriptive matter is illustrative of the disclosure and not a limitation. Descriptions of well-known/conventional methods and techniques are omitted so as to not unnecessarily obscure the embodiments herein.

Further, the invention herein provides for examples illustrating the above described embodiments, and in order to illustrate the embodiments of the present invention, 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 herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. While considerable emphasis has been placed herein on the 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. Accordingly, the following examples should not be construed as limiting the scope of the embodiments herein.

EXAMPLES
EXAMPLE 1:
Example 1.1: Raw materials and their preparation
Hematite iron ore fines from Noamundi, India was taken as the principal raw material for pelletization. 2 kg each of hematite ore fines and mill scale have been taken for the sieve analysis test. All the other raw materials were received from Tata Steel Ltd., Jamshedpur, India. The size fraction of iron ore fines and mill scale used in the study is shown in Table 1.

Table 1: Size fraction of iron ore fines and mill scale

The chemical analysis of iron ore fines, fluxes, bentonite and mill scale used in the study are shown in Table 2.

Table 2: Chemical analysis of raw materials, wt%
Fe2O3 FeO Fetot SiO2 Al2O3 MgO P Na2O CaO
Hematite ore fines 91.26 0.52 63.9 2.247 2.34 0.013 0.07 - 0.001
Mill Scale 34.32 63.21 73.19 0.49 0.28 0.06 0 - 0.7
Slime 83.36 0 58.35 4.67 5.18 0.15 0.173 - 0.21
Bentonite 12.58 0.1 8.81 45.62 11.43 2.79 0 1.59 1.65
Limestone 0 0 0 1.4 0.3 0.5 0 - 51.51
Olivine 0 0 0 40.3 0.5 48.1 0 - 0

The raw materials were ground in ball mill at 6 kg/batch for varying time of retention. Specific surface area of ground particles in terms of Blaine fineness (cm2/g) or Blaine number (B.No.) was measured by standard Blaine permeability apparatus (ASTM C-204, 2007). The fluxes, limestone and olivine were ground to less than #200 BIS mesh.

Example 1.2: Preparation of green pellets
Pellets of 9-16 mm diameter size range were prepared in a laboratory scale disk pelletizer. The raw materials for pelletization were combined and mixed in various proportions as shown in Table 3. The blend compositions were designed as per the desired amount of mill scale addition, MgO percentage and basicity (CaO/SiO2) of the pellet.

Table 3: Raw Material blend percentages (wt%) for various types of pellets prepared
Pellet type Pellet
code Hematite ore fines % Mill
scale
% Slime
% Olivine % Limestone % Bentonite % Desired
MgO % Desired
Basicity
(CaO/SiO2)
Only iron
Ore A1 96.5 0 0 2 0.92 0.5 1 0.15
A2 95.65 0 0 2 1.85 0.5 1 0.3
A3 94.4 0 0 2 3.1 0.5 1 0.5
Only mill
scale B1 0 99 0 0 0 1 0 0
B2 0 99.5 0 0 0 0.5 0 0
Varying
mill scale
(Acidic) C1 99.5 0 0 0 0 0.5 0 -
C2 94.5 5 0 0 0 0.5 0 -
C3 89.5 10 0 0 0 0.5 0 -
C4 84.5 15 0 0 0 0.5 0 -
C4a 84.13 15 0 0.37 0 0.5 0.2 -
C4b 83.5 15 0 1.0 0 0.5 0.5 -
Varying
mill scale
(Basic) D1 90.77 5 0 2 1.73 0.5 1 0.3
D2 85.9 10 0 2 1.6 0.5 1 0.3
D3 81 15 0 2 1.5 0.5 1 0.3
Varying
slime in iron
ore pellet
(Acidic) E1 94.5 0 5 0 0 0.5 0 -
E2 89.5 0 10 0 0 0.5 0 -
E3 84.5 0 15 0 0 0.5 0 -
E4 0 0 99.5 0 0 0.5 0 -
Varying
slime in iron
ore pellet
(Basic) F1 90.6 0 5 2 1.9 0.5 1 0.3
F2 85.55 0 10 2 1.95 0.5 1 0.3
F3 80.5 0 15 2 2 0.5 1 0.3
F4 0 0 95.7 2 2.8 0.5 1 0.3
Varying
slime in iron
ore + 15%
mill scale
pellet
(Acidic) G1 79.5 15 5 0 0 0.5 0 -
G2 74.5 15 10 0 0 0.5 0 -
G3 69.5 15 15 0 0 0.5 0 -
Varying
slime in iron
ore + mill
scale pellet
(Basic) H1 75.95 15 5 2 1.55 0.5 1 0.3
H2 73.43 15 7.5 2 1.57 0.5 1 0.3
H3 70.9 15 10 2 1.60 0.5 1 0.3
H4 65.85 15 15 2 1.65 0.5 1 0.3
H5 75.78 10 10 2 1.72 0.5 1 0.3
H6 70.73 10 15 2 1.77 0.5 1 0.3

EXAMPLE 2: Characterization of green pellets
Green pellets were prepared from different pellet mix and their green and dry properties were measured and the results obtained are shown in Table 4(a) and Table 4(b). Green Compressive Strength (GCS), Green Drop Strength Number (GDSN, also referred to as Drop Nos.), Dry Compressive Strength (DCS) and moisture content of the green pellets was analysed. The GCS of pellets was measured using a Hounsfield Material testing Machine. The average strength of 20 green pellets has been recorded as the GCS. The GDSN was measured by repeatedly dropping individual green pellets on a mild steel plate from a height of 450 mm and counting the number of drops sustained by the pellet before cracking. The moisture content in green pellets was measured by heating a representative sample of about 30-40 g at a temperature of 110°C for four hours and subsequently measuring the weight loss in the sample in wt%. The DCS of the oven dried pellets was tested in a Hounsfield Material testing Machine (Model: H10K-S). The machine is connected with a PC having data capturing system. Further, Scanning Electron Microscope (SEM) Imaging was done to study the morphology of iron ore fines, mill scale and iron ore slime.

EXAMPLE 2.1: Green and dry properties of pellets with iron ore, mill scale and slime individually
Green properties of pellets with the individual materials, i.e. the iron ore, mill scale and slime are presented in the Table 4(a). GDSN values of Mill scale is the lowest and below the acceptable limit of 5, and hence is completely unsuitable for pellet making. The GDSN of slime is the highest indicating highest drop strength. Mill scale has very poor green properties because of its smooth surface properties as shown in Figure 1. Due to this smooth surface property it has good wettability and less water holding capacity which is unfavourable for green bonding. Though mill scale is a very pure iron oxide, it cannot be pelletized individually. On the other hand, slime shows very good green properties because of its uneven surface properties (Figure 1) and adhesiveness. However, pellet preparation with only slime has been observed to be very difficult due to its coagulation problem and high gangue content.

Table 4(a): Green and dry properties of pellets made from iron ore, mill scale and slime individually
Pellet Code GCS, kg/pellet DCS, kg/pellet GDSN Moisture content of green pellet, wt%
Hematite ore C1 2.02 9.73 30.5 9.55
Hematite ore A2 1.90 5.51 22.2 9.62
Mill scale B2 1.81 8.18 2.4 6.57
Iron ore slime E4 1.77 7.86 71.2 10.33

EXAMPLE 2.2: Green and dry properties of pellets with iron ore, mill scale and slime individually
Green properties of pellets made from different mix composition are presented in the Table 4(b). The results obtained show that the pellet properties on addition of a combination of mill scale and slime to Hematite ore does not deteriorate, while it deteriorates on addition of only mill scale. Mill scale has very poor green properties mainly GDSN which is much below the industrially acceptable limit of 5 GDSN.

Table 4(b): Green and dry properties of pellets made from different mix composition
Sl. No Code Pellet mix composition, wt% GCS, kg/pellet DCS, kg/pellet GDSN
Hematite ore Mill scale Slime Bentonite
1 C1 99.5 0 0 0.5 2.13 9.73 30.5
2 C4 84.5 15 0 0.5 2.085 6.85 26.8
3 G3 69.5 15 15 0.5 1.66 9.16 31.9

EXAMPLE 3: Characterization of indurated pellets with addition of mill scale
Cold compression strength (CCS) of the indurated pellets was measured as per the standard ISO 4700, using Hounsfield Material testing Machine (Model: H10K-S). Reducibility Index (RI) was measured as per the standard JIS: M 8713-2000, indicates the ease with which oxygen combined with iron could be removed from iron ore pellets with a reducing gas at the time of reduction. Reduction Degradation Index (RDI) was measured as per the standard JIS: M 8720-2001, indicates the degradation of pellets in the upper part of blast furnace. Swelling Index (SI) was measured after reduction as per JIS: M 8713-2000 at a temperature of 900°C by measuring its volume change percentage between before and after reduction by mercury displacement method.

EXAMPLE 3.1: Induration and characterization of indurated pellets
The green pellets in various batch sizes ranging between 0.1kg and 1.5 kg were indurated in an electrically heated chamber furnace (Heating element: Mo-Si2) at temperature of 1275°C for 15 minutes at the set temperature. The furnace gets switched off after 15 minutes holding, at a temperature of 1275°C and the indurated pellets are left to be cooled in the furnace as its slowly reaches the ambient atmospheric temperature. The furnace cooled pellets are then checked for CCS and other properties viz. reducibility index, reduction degradation index, swelling index with increase in mill scale content of acidic hematite pellet.

Hematite ore pellets have very high induration temperature because of absence of any oxidation and limited amount of diffusion bonding at lower temperature. The results tabulated in Table 5 show that all the properties of the indurated pellets are improved by increasing mill scale content in the pellet. For mill scale comprising pellet, a lower induration temperature is sufficient, hence the decrease in energy consumption is possible

Table 5: Properties of acidic hematite pellets with mill scale addition
Sl. No. Code Wt% of mill scale added CCS, kg/pellet Reducibility index,(RI) % Reduction degradation index, (RDI) % Swelling index, (SI)%
1 C1 0 231 96.11 86.76 18.86
2 C2 5 255.7 92.13 75.26 18.8
3 C4 15 328.1 85.40 25 9.5

EXAMPLE 3.2: Characterization of indurated pellets with mill scale
The pellets were indurated at varying set temperature in a muffle furnace in slow heating scheme and after furnace cooling, the CCS was measured. Effects of induration temperature on CCS of pellets are shown in Figure 2. The indurated pellet with 15% mill scale shows much higher CCS than without mill scale even at 1100°C and its strength increases with much higher rate. The mill scale added pellet shows more than 225 kg/pellet CCS at only 1200°C, while the pellet without mill scale shows around 120 kg/pellet CCS at the identical temperature. Therefore, there is a substantial increase in CCS due to the addition of mill scale in pellet as mill scale facilitates sintering of fine particles in pellets. As mill scale mainly contains FeO and Fe3O4, the oxidation of these oxides during induration at high temperature in air atmosphere takes place which may provide exothermic heat. It may also enhance diffusion bonding favouring diffusion of Fe2+ ions towards the reaction interface.

Thermo-gravimetric experiment of mill scale pellet is shown in Figure 3. The weight gain starts to increase from 200ºC temperature as oxidation reactions starts at this temperature and it continues up to high temperature (>1200 °C) resulting in better strength development in mill scale added pellet.

EXAMPLE 4: Characterization of indurated pellets with addition of slime
CCS, RDI, RI and SI of pellets with addition of slime are measured as afore-described.

Example 4.1: Pellet with only iron ore and only slime
Properties of indurated pellets with only iron ore and only slime at acidic and basic conditions are shown in Table 6. Slime pellets shows much lower CCS than only iron ore pellets in basic condition because of high alumina which increases the melting point of slag and deceases fluidity which is unfavourable to form a homogeneous slag bond. Hence, the CCS decreases. Both slime pellets and iron ore pellets in acidic condition have very poor RDI (more than 80%). For basic pellets, RDI of both the pellets decreases to lower level. However, basic slime pellets has relatively higher RDI and is not suitable for blast furnace. Therefore, suitable technology is required for using slime in blast furnace.

Table 6: Comparison of iron ore pellet and slime pellets indurated at 1275°C
Pellet Code Basicity CCS, Kg/pellet RDI, %
Only iron ore (Acidic) pellet C1 - 231 86.76
Only iron ore (Basic) pellet A2 0.3 408 19.81
Only slime (Acidic) pellet E4 - 160 73.24
Only slime (Basic) pellet F4 0.3 337 45.4

Example 4.2: Pellet with mill scale and varying slime
Properties of pellets made of only hematite pellet and the pellets with 15% slime and 15% mill scale indurated at 1275°C temperature is shown in Table 7. CCS and other properties are measured as afore-described and are found to be good on addition of slime along with mill scale.

It is envisaged from the table that addition of mill scale in hematite pellet improves CCS to a great extent that indicates a much lower temperature requirement in induration. When 15% slime is added to this pellet, CCS deteriorates but it is much higher than the pellets without addition of mill scale and slime. RDI, RI and swelling index are also good. It also indicates a lower temperature requirement in induration. Thus, energy saving and quality improvement, both are possible by addition of these two materials. Further, this establishes that alumina and silica content does not increase significantly, on addition of silica to mill scale comprising iron ore pellets, and is within the range for blast furnace operation. Thus, pellet with superior quality is produced using mill scale and slime.

Table 7: Properties of pellets with varying amount of slime
Sl. No. Code No. Pellet mix composition, wt% Induration Temp, °C CCS, % RI, % RDI, % SI, %
Hematite ore Mill scale Slime Bentonite
1 C1 99.5 0 0 0.5 1275 231 93 86.76 23.07
2 C4 84.5 15 0 0.5 1275 328.1 85.4 25 9.5
3 G3 69.5 15 15 0.5 1275 246 91.9 45.6 12.69

Example 4.3: Iron ore pellet with mill scale and varying slime content
From above it is evident that addition of mill scale in hematite ore pellet shows very good physical and metallurgical properties even at very low induration temperature. Varying addition of slime has been done in 15% mill scale added pellet to investigate its effect on the pellet properties. Properties with various slime content are shown in Table 8. Figure 4 shows that CCS of basic mill scale added (15%) pellet is much higher than hematite ore basic pellet. However, CCS does not change so much when varying amount of slime has been added without mill scale pellet (Figure 5). The reason is due to sufficient slag bond formation. Slight deterioration of RDI is due to the increase in alumina content. More or less constant character of swelling index and RI has been observed with increase in slime content. RI is very appreciable in all level of slime content swelling index is also within the tolerable limit.

Table 8: Properties of pellet with varying slime content in 15% mill scale added pellet
% Slime in 15% mill scale pellet CCS, kg/pellet RDI, % RI, % SI, %
0 411 6.4 81.99 17.72
5 403 11.22 84.78 18.79
10 441 10.39 19.69
15 442 12.66 81.71 18.29

Example 4.4: Iron ore pellet with mill scale and slime at varying induration temperature
Table 9 shows the properties of pellets with iron ore, 15 wt% mill scale and 15 wt% slime at varying induration temperature. On lowering the induration temperature, CCS decreases but it is well within the acceptable limit; however, RI, RDI and swelling properties improve to a great extent. This result indicates that a very high temperature such as 1275°C is not required for induration because, excessive fusion may happen which is responsible for deteriorating the swelling index. Thus, the combination of slime and mill scale in hematite pellet reduces induration temperature which in turn reduces the energy consumption in induration.

Table 9: Properties of Pellet with iron ore + 15%mill scale+15% slime in varying temperature
Sl. No. Induration temperature,
°C CCS, kg/pellet RI, % RDI,% SI, %

1 1175 303 87.91 12.68 6.86
2 1200 366 82.44 8.5 12.81
3 1275 447 81.71 18.29 17.92

EXAMPLE 5:
Effect of a little amount of fluxes which increases basicity are shown in Table 10. At 1250°C, slime and mill scale added pellets shows much higher strength and other properties. RDI also improves. Thus, a good quality pellet making from hematite ore utilizing slime and mill scale is possible which indicates a lower temperature requirement in induration.

Table 10: Effect of addition of minor amount of slag (increase the basicity slightly)
Sl. No Code No. Pellet mix composition, wt% Basicity CCS % RI
% RDI % SI
%
Hematite ore Mill scale Slime Bentonite Fluxes
1 A2 95.65 0 0 0.5 3.85 0.3 408 81.1 19.2 17.9
2 H4 65.85 15 15 0.5 3.65 0.3 447 85.3 12.6 18.3