WE CLAIM:
1. A pellet composition comprising- chrome ore fines, binder and additive selected from a group comprising heating additive, fluxing additive, and a combination thereof.
2. The composition as claimed in claim 1, wherein the binder is bentonite.
3. The composition as claimed in claim 1, wherein the heating additive is selected from a group comprising rice husk, carbon soot, high ash Indian coal, medium ash South African coal, low ash high volatile Indonesian Coal, anthracite coal, graphite powder, calcined pet coke, charcoal and any combinations thereof.
4. The composition as claimed in claim 1, wherein the fluxing additive is selected from a group comprising dolomite, magnesium oxide, magnesium chloride, magnesium chromite refractory powder, magnesium carbon powder, cryolite, activated carbon (AC) powder and any combinations thereof.
5. The composition as claimed in claim 1, wherein the chrome ore fines is in an amount ranging from about 90% to 95%.
6. The composition as claimed in claim 1, wherein the binder is in an amount ranging from about 0.01% to 3 %.
7. The composition as claimed in claim 1, wherein the heating additive is in an amount ranging from about 0.01% to 3 %.
8. The composition as claimed in claim 1, wherein the fluxing additive is in an amount ranging from about 0.01% to 3 %.
9. The composition as claimed in claim 1, wherein the heating additive has particle size ranging about <1mm (D80 :100µm); and the fluxing additive has particle size ranging about <0.5mm (D80 :250µm).
10. The composition as claimed in claim 3, wherein the heating additive is rice husk or carbon soot or a combination thereof.
11. The composition as claimed in claim 4, wherein the fluxing additive is cryolite or magnesium chromite refractory powder or a combination thereof.
12. The composition as claimed in claim 10, wherein the rice husk has particle size ranging about <0.150mm; and the carbon soot has particle size ranging about <0.050mm.
13. The composition as claimed in claim 11, wherein the cryolite has particle size ranging about <0.250mm; and the magnesium chromite refractory powder has particle size ranging from about <0.250mm.
14. The composition as claimed in claim 1, wherein the chrome ore fines comprises- Cr2O3 ranging from about 48% to 52%, Fe (t) ranging from about 11% to 15%, MgO ranging from about 7% to 11%, Al2O3 ranging from about 9% to 14% and SiO2 ranging from about 3% to 6%; and the chrome ore fines has particle size ranging from about 0 to 0.500mm.
15. The composition as claimed in claim 10, wherein the composition comprises chrome ore fines, binder and rice husk.
16. The composition as claimed in claim 11, wherein the composition comprises chrome ore fines, binder and cryolite.
17. The composition as claimed in claim 10 or 11, wherein the composition comprises chrome ore fines, binder, rice husk and cryolite.
18. A method of preparing the composition as claimed in claim 1, said method comprises- mixing the chrome ore fines, the binder and the additive selected from a group comprising the heating additive, the fluxing additive and a combination thereof, followed by milling to obtain the composition.
19. Chromite ore pellet comprising the composition as claimed in claim 1.
20. The chromite ore pellet as claimed in claim 19, wherein the pellet has particle size ranging from about 8 mm to 18mm.
21. The chromite ore pellet as claimed in claim 19, wherein the pellet has moisture content ranging from about 10 % to 16%.
22. The chromite ore pellet as claimed in claim 19, wherein the pellet has cold compressive strength (CCS) ranging from about 63 kgf/pellet to 197 kgf/pellet; has swelling index ranging from about 5.7 to 8.2; has porosity ranging from about 34.17 to 41.53%; and has green strength ranging from about 6 drops to 15 drops.
23. A method of preparing the chromite ore pellet as claimed in claim 19, said method comprising:
- preparing the composition as claimed in claim 1, according to the method as claimed in claim 18; and
- adding solvent to the composition and preparing pellet, followed by heating the pellet to obtain the chromite ore pellet.
24. The method as claimed in claim 23, wherein the preparing pellet comprises pelletizing mixture of the solvent and the composition to obtain the pellet.
25. The method as claimed in claim 23, wherein the heating is carried out at a temperature ranging from about 300 °C to 1250 °C.
26. The method as claimed in claim 23, wherein the solvent is water; and wherein the solvent is in an amount ranging from about 10 % to 16 % per weight of the composition.

Dated this 03rd day of January 2022
Signature:
Name: Sridhar R
To: Of K&S Partners, Bangalore
The Controller of Patents Agent for the Applicant
The Patent Office, at Kolkata IN/PA-2598

, Description:TECHNICAL FIELD
The present disclosure relates to field of metallurgy and material sciences. The disclosure particularly relates to pellet composition comprising chromite ore fines, binder and additive. The disclosure further relates to chromite ore pellet comprising the pellet composition. The disclosure also relates to methods of preparing said pellet composition and said chromite ore pellet.

BACKGROUND OF THE DISCLOSURE
Ferrochrome is an important alloy and used as a raw material during production of stainless steel. It is mainly produced by smelting reduction of chromite ores using cokes as a reductant in a submerged electric arc furnace. This process needs lumpy feed to maintain desired gas flow rate in the reactor, however mining of friable chrome ores generates significant quantity of fines during the process, which cannot be used directly in the process. Thus, agglomeration techniques, such as briquetting, pelletisation and sintering were developed.

Chrome ore pelletisation involves fine wet grinding, filtration, granulation and sintering. However, it is noted that technoeconomic impact of the pellets of chrome ore fines depends on the physical and chemical properties of the pellets. Pellet mix composition and pelletisation process parameters impact overall physical and chemical properties of chrome ore pellets. It was noted that pellets with low compressive strength (for e.g., <100 kgf/pellet) crumbles during pellet making process and during transportation and melts in alloy making submerged arc furnace. The low strength pellets which crumble in the submerged arc furnace during melting process reduces furnace permeability and adversely impact smelting reduction process. It was noted that low strength pellets adversely impact techno-economics of overall ferrochrome making process.

Improvement or optimization of grinding, pelletisation and sintering was carried out to improve pellet strength. However, it was noted that said improvement or optimization of process parameters were not able to provide high quality pellets consistently due to variable ore composition and inability to maintain highly precise process control(s).

Thus, there was a need for developing chromite ore pellets with improved pellet properties, such as green strength, cold compressive strength and smelting reduction properties. The present disclosure addresses said need.

STATEMENT OF THE DISCLOSURE
Accordingly, the present disclosure describes novel and an improved pellet composition for preparing chromite ore pellet having improved pellet properties. The pellet composition comprises- chrome ore fines, binder and additive selected from a group comprising heating additive, fluxing additive, and a combination thereof.

The present disclosure further describes a method of preparing the pellet composition, said method comprises- mixing the chrome ore fines, the binder and the additive, followed by milling to obtain the pellet composition which is homogenous in nature.

The present disclosure further describes chromite ore pellet having cold compressive strength (CCS) ranging from about 63 kgf/pellet to 197 kgf/pellet; swelling index ranging from about 5.7 to 8.2; porosity ranging from about 34 to 42%; and green strength ranging from about 6 drops to 15 drops.

The present disclosure further describes a method of preparing the chromite ore pellet, said method comprises: preparing the composition described above; and adding solvent to the composition and preparing pellet, followed by heating the pellet to obtain the chromite ore pellet having improved pellet properties.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
In order that the present 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, where:

Figure 1 illustrates a plot describing cold compressive strength of chromite ore pellets made from using various fluxing additive in the composition.

Figure 2 illustrates a plot describing cold compressive strength of chromite ore pellet made from using optimum fluxing additive dosage in the composition.

Figure 3 illustrates a plot describing cold compressive strength of chromite ore pellet with preferred optimum fluxing additive dosage in the composition.
Figure 4 illustrates hot stage microscopy image of base pellet mix (plant pellet), chromite ore pellet composition comprising cryolite (Cry-Pellet) and chromite ore pellet composition comprising magnesium chromite refractory powder (MagCr- pellet).

Figure 5 illustrates a plot describing degree of reduction (O2 reduced pellet/O2 unreduced pellets) of chromite ore pellets comprising cryolite and MgCr (magnesium chromite refractory powder), respectively.

DETAILED DESCRIPTION OF THE DISCLOSURE
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 disclosure belongs. By means of further guidance, term definitions are included for better understanding of the present disclosure.

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.

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.

Reference throughout this specification to ‘some embodiments’, ‘one embodiment’ or ‘an embodiment’ means that a particular feature, structure or characteristic described in connection with the embodiment may be included in at least one embodiment of the present disclosure. thus, the appearances of the phrases ‘in some embodiments’, ‘in one embodiment’ or ‘in an embodiment’ in various places throughout this specification may not necessarily all refer to the same embodiment. It is appreciated that certain features of the disclosure, which are for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The present disclosure relates to pellet composition for preparing chromite ore pellets having improved pellet properties

In some embodiments of the present disclosure, the pellet composition comprises chrome ore fines, binder and additive selected from a group comprising heating additive, fluxing additive and a combination thereof.

In some embodiments of the present disclosure, the pellet composition comprises chrome ore fines, binder and heating additive.

In some embodiments of the present disclosure, the pellet composition comprises chrome ore fines, binder and fluxing additive.

In some embodiments of the present disclosure, the pellet composition comprises chrome ore fines, binder, heating additive and fluxing additive.

In some embodiments of the present disclosure, the chrome ore fines in the composition is present in an amount ranging from about 90% to 95%, including all the values in the range, for instance, 90.1%, 90.2%, 90.3%, 90.4% and so on and so forth.

In some embodiments of the present disclosure, the chrome ore fines comprises Cr2O3 ranging from about 48% to 52%, including all the values in the range, for instance, 48.1%, 48.2%, 48.3%, 48.4% and so on and so forth.

In some embodiments of the present disclosure, the chrome ore fines comprises Fe (t) ranging from about 11% to 15%, including all the values in the range, for instance, 11.1%, 11.2%, 11.3%, 11.4% and so on and so forth.
In some embodiments of the present disclosure, the chrome ore fines comprises MgO ranging from about 7% to 11%, including all the values in the range, for instance, 7.1%, 7.2%, 7.3%, 7.4% and so on and so forth.

In some embodiments of the present disclosure, the chrome ore fines comprises Al2O3 ranging from about 9% to 14%, including all the values in the range, for instance, 9.1%, 9.2%, 9.3%, 9.4% and so on and so forth.

In some embodiments of the present disclosure, the chrome ore fines comprises SiO2 ranging from about 3% to 6%, including all the values in the range, for instance, 3.1%, 3.2%, 3.3%, 3.4% and so on and so forth.

In some embodiments of the present disclosure, the chrome ore fines has particle size ranging from about 0 mm to 0.5 mm, including all the values in the range for instance, 0.01 mm, 0.02 mm, 0.03 mm, 0.04 mm and so on and so forth.

In some embodiments of the present disclosure, the chrome ore fines has fine particle size of less than 0.5 mm.

In some embodiments of the present disclosure, the binder in the composition is in an amount ranging from about 0.01% to 3%, including all the values in the range, for instance, 0.02%, 0.03%, 0.04%, 0.05% and so on and so forth.

In some embodiments of the present disclosure, the binder includes but it is not limited to bentonite.

In some embodiments of the present disclosure, the heating additive in the composition is present in an amount ranging from about 0.01% to 3%, including all the values in the range, for instance, 0.1%, 0.2%, 0.3%, 0.4% and so on and so forth.

In some embodiments of the present disclosure, the heating additive in the composition is selected from a group comprising- rice husk, carbon soot, high ash Indian coal, medium ash South African coal, low ash high volatile Indonesian coal, anthracite coal, graphite powder, calcined pet coke, charcoal and any combinations thereof. Described heating additive is a low temperature (300 ºC to 800 ºC) heating additive which can burn at low temperature and can improve pellet strength in preheating zone during heating/sintering in the furnace.

In some embodiments of the present disclosure, the heating additive has particle size ranging from about <1 mm (D80:100 µm), including all the values range for instance, 0.01 mm, 0.02 mm, 0.03 mm, 0.04 mm and so on and so forth.

In some embodiments of the present disclosure, the heating additive is rice husk. The rice husk has particle size ranging about <0.15 mm, including all the values in the range for instance, 0.01 mm, 0.02 mm, 0.03 mm, 0.04 mm and so on and so forth.

In some embodiments of the present disclosure, the heating additive is carbon soot. The carbon soot has particle size ranging about <0.05 mm. In some embodiments, the carbon soot has particle size of about 0.01 mm, about 0.02 mm, about 0.03 mm, about 0.04 mm or about 0.05 mm.

In some embodiments of the present disclosure, the fluxing additive in the composition is present in an amount ranging from about 0.01 % to 3%, including all the values in the range, for instance, 0.1%, 0.2%, 0.3%, 0.4% and so on and so forth.

In some embodiments of the present disclosure, the fluxing additive is selected from a group comprising dolomite, magnesium oxide, magnesium chloride, magnesium chromite refractory powder, magnesium carbon powder, cryolite, activated carbon (AC) powder and any combination thereof. The described fluxing additive can burn at high temperature (800 ºC to 1300 ºC) and can make low temperature liquid phases using chromite spinal.

In some embodiments of the present disclosure, the fluxing additive has particle size ranging about <0.5 mm (D80: 250 µm), including all the values in the range, for instance, 0.01 mm, 0.02 mm, 0.03 mm, 0.04 mm and so and so forth.

In some embodiments of the present disclosure, the fluxing additive is cryolite. The cryolite has particle size ranging about <0.25 mm, including all the values in the range, for instance, 0.01 mm, 0.02 mm, 0.03 mm, 0.04 mm and so on and so forth.

In some embodiments of the present disclosure, the fluxing additive is magnesium chromite refractory powder. The magnesium chromite refractory powder has particle size ranging about < 0.25 mm, including all the values in the range, for instance, 0.01 mm, 0.02 mm, 0.03 mm, 0.04 mm and so on and so forth.

In some embodiments of the present disclosure, the pellet composition comprises chrome ore fines ranging from about 90% to 95%, binder ranging from about 0.01% to 3% and heating additive ranging from about 0.01 % to 3%.

In some embodiments of the present disclosure, the pellet composition comprises chrome ore fines ranging from about 90% to 95%, binder ranging from about 0.01% to 3% and fluxing additive ranging from about 0.01 % to 3%.

In some embodiments of the present disclosure, the pellet composition comprises chrome ore fines ranging from about 90% to 95%, binder ranging from about 0.01% to 3%, heating additive ranging from about 0.01 % to 3% and fluxing additive ranging from about 0.01 % to 3%.

In some embodiments of the present disclosure, the pellet composition comprises chrome ore fines ranging from about 90% to 95%, bentonite ranging from about 0.01 % to 3% and rice husk ranging from about 0.01 % to 3%.

In some embodiments of the present disclosure, the pellet composition comprises chrome ore fines ranging from about 90% to 95%, bentonite ranging from about 0.01 % to 3% and carbon soot ranging from about 0.01 % to 3%.

In some embodiments of the present disclosure, the pellet composition comprises chrome ore fines ranging from about 90% to 95%, bentonite ranging from about 0.01 % to 3% and cryolite ranging from about 0.01 % to 3%.

In some embodiments of the present disclosure, the pellet composition comprises chrome ore fines ranging from about 90% to 95%, bentonite ranging from about 0.01 % to 3% and magnesium chromite refractory powder ranging from about 0.01 % to 3%.

In some embodiments of the present disclosure, the pellet composition comprises chrome ore fines ranging from about 90% to 95%, bentonite ranging from about 0.01 % to 3%, rice husk ranging from about 0.01 % to 3% and cryolite ranging from about 0.01 % to 3%.

In some embodiments of the present disclosure, the pellet composition comprises chrome ore fines ranging from about 90% to 95%, bentonite ranging from about 0.01 % to 3%, rice husk ranging from about 0.01 % to 3% and magnesium chromite refractory powder ranging from about 0.01 % to 3%.

In some embodiments of the present disclosure, the pellet composition comprises chrome ore fines ranging from about 90% to 95%, bentonite ranging from about 0.01 % to 3%, carbon soot ranging from about 0.01 % to 3% and cryolite ranging from about 0.01 % to 3%.

In some embodiments of the present disclosure, the pellet composition comprises chrome ore fines ranging from about 90% to 95%, bentonite ranging from about 0.01 % to 3%, carbon soot ranging from about 0.01% to 3% and magnesium chromite refractory powder ranging from about 0.01% to 3%.

In some embodiments of the present disclosure, the pellet composition comprises about 95% chrome ore fines, about 2% bentonite, about 2% rice husk and about 1% cryolite.

The present disclosure further relates to method of preparing the composition described above.

In some embodiments of the present disclosure, the method of preparing the composition comprises- mixing the chrome ore fines, the binder and the additive selected from a group comprising the heating additive, the fluxing additive and a combination thereof, followed by milling to obtain composition which is homogenous in nature.

In some embodiments of the present disclosure, the method of preparing the composition comprises- mixing the chrome ore fines, the binder and the heating additive, followed by milling to obtain composition which is homogenous in nature.

In some embodiments of the present disclosure, the method of preparing the composition comprises- mixing the chrome ore fines in an amount ranging from about 90% to 95%, the binder in an amount ranging from about 0.01 % to 3% and the heating additive in an amount ranging from about 0.01 % to 3%, followed by milling to obtain the composition which is homogenous in nature.

In some embodiments of the present disclosure, the method of preparing the composition comprises- mixing the chrome ore fines in an amount ranging from about 90% to 95%, the binder in an amount ranging from about 0.01 % to 3% and the fluxing additive in an amount ranging from about 0.01 % to 3%, followed by milling to obtain the composition which is homogenous in nature.

In some embodiments of the present disclosure, the method of preparing the composition comprises- mixing the chrome ore fines in an amount ranging from about 90% to 95%, the binder in an amount ranging from about 0.01 % to 3%, the heating additive in an amount ranging from about 0.01 % to 3% and the fluxing additive in an amount ranging from about 0.01 % to 3%, followed by milling to obtain the composition which is homogenous in nature.

In some embodiments of the present disclosure, the method of preparing the composition comprises- mixing the chrome ore fines ranging from about 90% to 95%, the bentonite ranging from about 0.01 % to 3% and the rice husk ranging from about 0.01 % to 3%, followed by milling to obtain the composition which is homogenous in nature.

In some embodiments of the present disclosure, the method of preparing the pellet composition comprises- mixing the chrome ore fines ranging from about 90% to 95%, the bentonite ranging from about 0.01 % to 3% and the carbon soot ranging from about 0.01 % to 3%, followed by milling to obtain the composition which is homogenous in nature.

In some embodiments of the present disclosure, method of preparing the pellet composition comprises- mixing the chrome ore fines ranging from about 90% to 95%, bentonite ranging from about 0.01 % to 3% and cryolite ranging from about 0.01 % to 3%, followed by milling to obtain the composition which is homogenous in nature.

In some embodiments of the present disclosure, method of preparing the pellet composition comprises- mixing the chrome ore fines ranging from about 90% to 95%, the bentonite ranging from about 0.01% to 3% and the magnesium chromite refractory powder ranging from about 0.01 % to 3%, followed by milling to obtain the composition which is homogenous in nature.

In some embodiments of the present disclosure, method of preparing the pellet composition comprises- mixing the chrome ore fines ranging from about 90% to 95%, the bentonite ranging from about 0.01% to 3%, the rice husk ranging from about 0.01% to 3% and the cryolite ranging from about 0% to 3%, followed by milling to obtain the composition which is homogenous in nature.

In some embodiments of the present disclosure, method of preparing the pellet composition comprises chrome ore fines ranging from about 90% to 95%, bentonite ranging from about 0.01% to 3%, rice husk ranging from about 0.01% to 3% and magnesium chromite refractory powder ranging from about 0.01% to 3%, followed by milling to obtain the composition which is homogenous in nature.

In some embodiments of the present disclosure, method of preparing the pellet composition comprises- mixing the chrome ore fines ranging from about 90% to 95%, the bentonite ranging from about 0.01% to 3%, the carbon soot ranging from about 0.01% to 3% and the cryolite ranging from about 0.01% to 3%, followed by milling to obtain the composition which is homogenous in nature.

In some embodiments of the present disclosure, method of preparing the pellet composition comprises- mixing the chrome ore fines ranging from about 90% to 95%, the bentonite ranging from about 0.01% to 3%, the carbon soot ranging from about 0.01% to 3% and the magnesium chromite refractory powder ranging from about 0.01% to 3%, followed by milling to obtain the composition which is homogenous in nature.

In some embodiments of the present disclosure, method of preparing the pellet composition comprises- mixing about 95% of the chrome ore fines, about 2% of the bentonite, about 2% of the rice husk and about 1% of the cryolite, followed by milling to obtain the composition which is homogenous in nature.

The inventors have identified that, mixing the chrome ore fines, the binder such as bentonite and additive selected from a group comprising heating additive, the fluxing additive and a combination thereof described above provides for improved homogenous pellet composition for preparing the chromite ore pellet having improved pellet properties. The inventors have particularly identified that use of the heating additive, such as rice husk and carbon soot and use of the fluxing additive, such as cryolite and magnesium chromite refractory powder provides for pellet composition which when prepared into chromite ore pellet has improved pellet properties better than the chromite ore pellets conventionally known.

The inventors have further identified that the heating additive described above improves ballability of the pellet composition and thereby improves cold compressive strength of the pellet in the pre-heating zone condition. It is identified that the cold compressive strength is improved from about 18% to 32% when compared to pellets made from pellet mixes having coke fines as carbonaceous materials.

The present disclosure further relates to chromite ore pellet.

In some embodiments of the present disclosure, the chromite ore pellet comprises the composition described above.

In some embodiments of the present disclosure, the chromite ore pellet has size ranging from about 8 mm to 18 mm, including all the values in the range for instance, 8.1 mm, 8.2 mm, 8.3 mm, 8.4 mm and so on and so forth.

In some embodiments of the present disclosure, the chromite ore pellet has moisture content ranging from about 10% to 16%, including all the values in the range for instance, 10.1%, 10.2%, 10.3%, 10.4% and so on and so forth.

In some embodiments of the present disclosure, the chromite ore pellet has cold compressive strength (CCS) ranging from about 63 kgf/pellet to 197 kgf/pellet, including all the values in the range for instance, 63.5 kgf/pellet, 64 kgf/pellet, 64.5 kgf/pellet, 65 kgf/pellet and so on and so forth.

In some embodiments of the present disclosure, the chromite ore pellet has swelling index ranging from about 5.7 to 8.2, including all the values in the range for instance, 5.71, 5.72, 5.73, 5.74 and so on and so forth.

In some embodiments of the present disclosure, the chromite ore pellet has porosity ranging from about 34 % to 42%, including all the values in the range for instance, 34.10%, 34.11%, 34.12%, 34.13% and so on and so forth.

In some embodiments of the present disclosure, the chromite ore pellet has green strength ranging from about 6 drops to 15 drops, including all the values in the range, for instance, 6.1 drops, 6.2 drops, 6.3 drops, 6.4 drops and so on and so forth.

In some embodiments of the present disclosure, the chromite ore pellet comprising the pellet composition comprising chrome ore fines, bentonite and rice husk has an increased compressive strength of about 31% when compared to pellet having base mix pellet composition (Ore fines: 95 %, Bentonite :<2 %; Coke fines <3 %) in pre-heating zone of shaft furnace which helps to maintain proper spherical shape and uniform heating gas flow around pellet for improved induration. Further, it was noted that the pellet porosity was improved by about 5% which aided in proper heat and gas flow during induration of pellets.

In some embodiments of the present disclosure, the chromite ore pellet comprising the pellet composition comprising chromite ore fines, bentonite and carbon soot has an increased compressive strength of about 19% when compared to pellet having base mix pellet composition in pre-heating zone.

The inventors identified that, the cellulose and lignin in rice husk in the pellet composition help in green pellet formations and its low temperature burning carbonaceous content improve pellet strength in the low temperature zone. The amorphous silica in the rice husk also help in high temperature binding phases in the chromite pellets. The inventors further identified that, the carbon soot has high surface area and its quick burning improve microporosity of green strength of pellets. The activated functional groups in the carbon soot improve dispersion of the carbon soot in the pellet mix and help in ballability of the composition mix while pellet preparation.

In some embodiments of the present disclosure, the chromite ore pellet comprising the pellet composition comprising chromite ore fines, bentonite and cryolite has an increased cold compressed strength (CCS) of about 190% when compared to pellet having basemix pellet composition. Further, it was noted that the chromite ore pellet has about 30% less swelling index (SI) when compared to pellet having basemix pellet composition. The chromite ore pellet comprising the pellet composition having cryolite attains about 53% reduction whereas the pellet made from the basemix pellet composition attains only 30% reduction during reduction using coal in 1:2 ratio with ore at 1400 ºC for 2 hours duration (total cycle time:8 hours). Further, it was identified that the chromite pellets comprising the pellet composition having cryolite showcases low sulphur level due to partial removal of sulphur in the form of SF6.

The inventors have identified that, the chromite ore pellets comprising the pellet composition having cryolite in an amount ranging from about 0.5% to 2% provides for improved cold compressive strength by about 190% when compared to pellet comprising basemix pellet composition. Further, it was identified that the chromite ore fines comprising the composition having cryolite in an amount ranging from about 0.5% to 2% provides for about 30% reduced swelling index when compared to pellet comprising basemix pellet composition.

In some embodiments of the present disclosure, the chromite ore pellets comprising the pellet composition having cryolite in an amount ranging from about 0.5% to 2% has cold compressive strength of about 187 kgf/pellet.

In some embodiments of the present disclosure, the chromite ore pellets comprising the pellet composition having cryolite in an amount ranging from about 0.5% to 2% has swelling index of about 5.7.

In some embodiments of the present disclosure, the chromite ore pellet comprising the pellet composition comprising chrome ore fines, bentonite and magnesium chromite refractory has an increased cold compressive strength (CCS) of about 20% when compared to pellet comprising basemix pellet composition. Further, it was noted that the chromite ore pellet has about 30% less swelling index when compared to pellet comprising basemix pellet composition.

The inventors have identified that, the chromite ore pellets comprising the composition having magnesium chromite refractory in an amount ranging from about 0.5% to 2% provides for improved cold compressive strength by about 20% when compared to pellet comprising basemix pellet composition. Further, it was identified that the chromite ore fines comprising the pellet composition having magnesium chromite refractory in an amount ranging from about 0.5% to 2% provides for about 30% reduced swelling index when compared to pellet comprising basemix pellet composition.

In some embodiments of the present disclosure, the chromite ore fines comprising the composition having magnesium chromite refractory in an amount ranging from about 0.5% to 2% has cold compressive strength of about 72 kgf/pellet.

In some embodiments of the present disclosure, the chromite ore fines comprising the composition having magnesium chromite refractory in an amount ranging from about 0.5% to 2% has swelling index of about 5.7.

In some embodiments of the present disclosure, the chromite ore pellet comprising the pellet composition comprising about 95% of chrome ore fines, about 2% of bentonite, about 2% of rice husk, about 1% of cryolite has cold compressive strength of about 197 kgf/pellet and has moisture content of about 14%.

The present disclosure further relates to method of preparing the chromite ore pellet described above.

In some embodiments of the present disclosure, the method of preparing the chromite ore pellet comprises:
- preparing the pellet composition described above by mixing the chrome ore fines, the binder and the additive selected from a group comprising the heating additive, the fluxing additive and a combination thereof in a predetermined amounts as described above, followed by milling;
- adding solvent to the composition and preparing pellet, followed by heating the pellet to obtain the chromite ore pellet.

In some embodiments of the present disclosure, preparing the pellet comprises pelletizing mixture of the solvent and the composition to obtain the pellet. As mentioned above, the heating additive present in the pellet composition improves the ballability of the pellet and does not allow the pellets to collapse during heating.

In some embodiments of the present disclosure, the heating is carried out at a temperature ranging from about 300 ºC to 1250 ºC, including all the values in the range for instance, 301 ºC, 302 ºC, 303 ºC, 304 ºC and so on and so forth.

In some embodiments of the present disclosure, the solvent includes but it is not limited to water.

In some embodiments of the present disclosure, the solvent is in an amount ranging from about 10% to 16%, including all the values in the range, for instance, 10.1%, 10.2%, 10.3%, 10.4% and so on and so forth.

The chromite ore pellet obtained by the above described method has improved pellet properties. The chromite ore pellet has cold compressive strength (CCS) ranging from about 63 kgf/pellet to 197 kgf/pellet; has swelling index ranging from about 5.7 to 8.2; has porosity ranging from about 34.17 to 41.53%; and has green strength ranging from about 6 drops to 15 drops.

The pellet composition and the chromite ore pellet described in the present disclosure provides for the following advantages-
- The heating additive present in the pellet composition burns at low temperature (300-800°C) and improves pellet strength in preheating zone during sintering process by maintaining pellet shape and size intact, which helps in uniform heating and gas flow to improve pellet sintering.
- The heating additive and the fluxing additive present in the pellet composition dissolves hard chromite ore spinal to make a liquid phase during high temperature induration (800°C to 1300 °C) of pellets and improves its physical and metallurgical properties.
- The heating additive and the fluxing additive present in the pellet composition improves chromite ore pellets strength without impacting slag chemistry of ferroalloy making process.
- The heating additive and the fluxing additive present in the composition enables the pellets to be cured uniformly and remain intact as a sphere in the lower part of preheating zone of the shaft furnace, thus improving pellet induration and thermal profile of the furnace.
- The pellet composition minimizes (to negligible extent) pellet breakage and fines generation in shaft furnace induration process and significantly improves pellet making.
- The chromite ore pellet has improved pellet properties such as- higher cold compressive strength, reduced swelling index, improved porosity and improved green strength when compared to conventionally known chromite ore pellet having coke fines as carbonaceous material.

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: Preparing Chromite ore pellet
i. Preparing pellet composition
Raw materials: chrome ore fines; bentonite; heating additive selected from a group comprising: rice husk, carbon soot, high ash Indian coal, medium ash South African coal, low ash high volatile Indonesian Coal, anthracite coal, graphite powder, calcined pet coke, charcoal and any combinations thereof; and fluxing additive selected from a group comprising dolomite, magnesium oxide, magnesium chloride, magnesium chromite refractory powder, magnesium carbon powder, cryolite, activated carbon (AC) powder and any combinations thereof.

The said raw materials were grounded separately in ball mill, followed by mixing the milled materials in separate batches in turbo mixture to obtain various compositions having different heating additive, fluxing additive or combination thereof alongside chrome ore fines and bentonite. Table 1 describes proportions of the raw materials employed to prepare different pellet composition.

Raw material (wt%) Composition-A Composition-B Composition-C Composition-D Composition-E
Chrome ore fines 90-95 90-95 90-95 90-95 95
Bentonite 2 2 2 2 2
Rice husk 2 - - - 2
Carbon soot - 3 - - -
Cryolite - - 1 - 1
MgCr - - - 2 -

Table 1:

ii. Preparing chromite ore pellets.
The compositions described in Table 1 were mixed with about 10% to 16% of water per total weight of the composition, respectively to obtain a mixture (green mix material). The mixtures were pelletized separately in pelletizing disc. The obtained pellets have size ranging from about 8 mm to 18 mm. The moisture content of the pellets was measured, and it was found to be in the range of about 10% to 16%.

Firing (heating) of the pellets was carried out in Inconel basket (100 mm*100 mm*100mm) in an electrically heated rapid heating nabertherm furnace at a temperature of about 1250ºC in oxidizing temperature atmosphere. The pellets were cooled by air and subjected to analysis. The properties of the pellets are tabulated in Table 2
Parameter Pellets from Composition- C
Pellets from Composition- D
Pellets from Composition- E

Cold compressive strength (kgf/pellet) 184 72 197
Swelling index 5.74 5.71
Table 2:

Data in Table 3 describes the chromite ore pellet properties in pre-heating zone having different types of heating additives in the pellet composition.

S. No. Pellet Mix Heating additive Properties Green Pellet Properties Drying & Pre-heating (2h)
Filter Cake (Wt, g) Bentonite (Wt., g) Carbon additive (heating additive)

Composition (%) TGA (Deg. C) CCS (kgf/pellet)
Porosity
Swelling Binding
Phases
Name (Wt,g) VM ASH FC Ts Te Drops Ballability 800°C 1000°C
1 190 4 Coke fines 6 5.98 20.21 73.81 500 1200 7 Good 5 31.76 39.41 No MF, F, MS
2 190 4 Rice Husk 6 38 20 40.6 150 500 12 Excellent 9.9 41.90 41.53 No MF, F, MS
3 190 4 Anthracite 6 6.28 7.08 86.64 550 1100 10 Good 5.1 37.32 39.69 No MF, F, MS
4 190 4 Graphite 6 0.78 11.13 88.1 700 850 9 Good 7.3 32.92 39.48 No MF, F, MS
5 190 4 Charcoal 6 27.28 5.4 67.32 250 800 10 Good 3.6 16.70 43.86 Shrink MF, F, MS
6 190 4 Indian Coal 6 31.06 30.17 38.77 400 900 6 Good 5.66 29.94 40.51 No MF, F, MS
7 190 4 SA coal 6 26.21 24.61 49.18 350 900 6 Good 3.96 25.64 41.76 No MF, F, MS
8 190 4 Indon. Coal 6 43.89 14.48 41.63 250 600 13 Good 5.1 28.58 42.42 No MF, F, MS
9 190 4 CPC 6 0.4 0.69 98.1 750 1000 10 Good 3.49 16.92 42.88 Swell MF, F, MS
10 191 4 Carbon soot 6 21.45 8.98 69.57 400 600 15 Excellent 6.3 37.74 38.69 No MF, F, MS
Drop = 1m height on cement floor; Ts = Burning Starts; Te = Burning Ends; MF- Magnesium ferrite; Fylite; Magnesium Silicate

It was noted that, use of about 2% to 3% coke fines in the pellet mix composition led to improper pre-heating of pellets in drying zone. The ineffectively heated weak pellets crumbled in the heating zone and changed their shape due to load of the upper layers and impact flow of gas and caused improper sintering operation and also caused lump formation in the shaft furnace. However, this was not observed when other heating additives mentioned in Table 3 were employed in the pellet composition for preparing the chromite ore pellet. Further, the results in Table 3 demonstrates that use of rice husk and carbon soot in the pellet composition provides for improved induration properties of pellets than the conventionally used coke fines in the preheating zone. The chromite ore pellets made from the pellet composition having rice husk and carbon soot achieved 12 drops and 15 drops green pellet strength, respectively which is significantly better than use of coke fines in the pellet composition for preparing chromite ore pellet. Further, it was observed that the ballability of green pellet mix was excellent when a composition comprising rice husk and carbon soot was employed for pellet making.

The green pellets obtained from a composition having rick husk and carbon soot, respectively along with chrome ore fines and bentonite were heat treated at the process conditions similar to the pre-heating zone of a shaft furnace. The pellets were heated at about 800°C and about 1000°C for about 2 hours duration and cold compressive strength (CCS) was measured. It was observed that the pellets attained cold compressive strength of 41.90 kgf/pellet and 37.74 kgf/pellet strength for pellets prepared from the composition having rice husk and carbon soot, respectively. The obtained CCS were about 32% and 18% higher than the pellets prepared from a composition having coke fines along with chrome ore fines and bentonite.

The data in the figures 1 to 3 demonstrates that the use of fluxing additive, such as cryolite and Magnesium chromite refractory powder in the pellet composition provides for improved cold compressive strength of about 19% and 190%, respectively for the chromite ore pellets when compared to the base pellet mix.

It was observed that, the fluxing additive, such as cryolite and magnesium chromite refractory powder in the pellet composition improve pellet properties and reduce any possibility of lump formation inside the furnace during the induration and provides for smoother operation of shaft furnace. It was observed that cryolite melts at 1000 ºC and it dissolves the spinal phases and provide additional liquid phases which helps the pellets to attain high cold compressive strength after cooling. The magnesium chromite refractory powder provides additional Fe and Mg for bonding with silica in the ores and produce silicate phases to improve pellet strength.

The data in Figures 5 and 6 demonstrates that pellets made from a pellet composition having cryolite reduces faster when compared to the pellets made from basemix composition. The Scanning Electron Microscopy (SEM) analysis of the reduced pellets indicate that the pellets made from the pellet composition having cryolite shows 53.2% reduction (oxygen loss) when heated at 1400 ºC for about 2 hours using coal as a reducing agent in a ratio of about 1:2, whereas the pellet made from basemix composition (conventional pellets) showed only 30.2% reduction in similar condition.