Description:TECHNICAL FIELD
The present disclosure is in the field of metallurgy. In particular, the present disclosure relates to a method for enhancing strength of iron ore pellets using rice husk ash. The present disclosure also relates to iron ore pellets with enhanced strength.

BACKGROUND OF THE DISCLOSURE
Iron ore and iron ore pellets are important sources of iron for manufacturing steel. The iron ore production has significantly expanded in recent years, owing to increasing steel demands in developing countries. However, the content of iron ore in deposits has deteriorated and low-grade iron ore has been processed. The fines resulting from the concentration process must be agglomerated for use in iron and steelmaking.

Iron ore pelletizing is an agglomeration process where iron ore fines are mixed with flux material, coal, bentonite and water to form green pellets which are then fired at high temperature in an indurating machine to form iron ore pellets suitable for its use in downstream ironmaking process. The pelletizing process starts with the preparation of raw materials which includes grinding and classification of as received raw materials. Iron ore, flux and coal are mixed and fed into ball mill for grinding after which the ground product gets classified to attain an adequate size range required for pelletizing. The ground product is then mixed with bentonite and water in a high intensity mixer to get a homogenized wet pellet mix. Green pellets are prepared by charging the wet mix material on a disc/drum pelletizer where the fine material gets agglomerated to form spherical balls. These green balls formed are then exposed to high temperature in an indurating machine to attain the required strength and other metallurgical properties for its use in blast furnaces.

Iron ore pellets plays vital role in the success of the steel industry across the globe. Maintaining consistent quality of pellets is very important to achieve good reducibility and productivity at both blast furnace and direct reduction processes. Physical parameters like cold crushing/compressive strength and shatter index of iron ore pellets are very critical for their handling and use. The cold compressive strength (CCS) i.e., the strength attained after firing of the green pellets is one of the most important quality parameters that allows smooth functioning of the ironmaking process in blast furnaces. High CCS of the iron ore pellets is desirable as it reduces crumbling and deterioration of iron ore pellets during charging and reduction process inside the blast furnaces. In addition to it, the targeted pellet strength that needs to be achieved determines the productivity of the pellet plant.

Various methods have been adopted in the past in the area of iron ore pelletizing to enhance the pellet CCS. Some of these works include the modification of firing cycle inside the induration furnace, use of different flux combination, use of binders and additives, etc. Particularly, there are several prior art documents that have tried to improve the pellet strength by modifying pellet chemistry by choosing appropriate flux combination and/or various additives and binders for improving the pellet properties. For instance, additives/binders like high alumina cement and silica fume, modified native starch base binder, organic binders etc. have been used. However, there are number of limitations in these processes such as high cost of certain binders/additives, low compressive strength etc.

Hence, there is a need for a simple, cost-effective/economical, environment friendly and efficient method for enhancement of strength of iron ore pellets. The present disclosure tries to address said need.

SUMMARY OF THE DISCLOSURE
The present disclosure relates to a method for enhancing strength of iron ore pellets, comprising:
a) grinding raw material comprising of an iron ore, a flux and a carbonaceous material, to obtain a ground product;
b) mixing the ground product with rice husk ash, a binder and water to obtain a wet pellet mixture;
c) pelletizing the wet pellet mixture to obtain green pellets; and
d) firing the green pellets to produce iron ore pellets with enhanced strength.
In an embodiment of the present disclosure, the rice husk ash is present in an amount at about 0.15% (w/w) to about 0.6% (w/w), including all values and ranges therebetween.

In an embodiment of the present disclosure, the rice husk ash is present in an amount at about 0.5% (w/w).

In an embodiment of the present disclosure, the rice husk ash comprises silica (SiO2) at about 90% (w/w) to about 98% (w/w), including all values and ranges therebetween.

In an embodiment of the present disclosure, particle size of the rice husk ash ranges from about less than 38 microns to about less than 1000 microns.

In an embodiment of the present disclosure, the rice husk ash is present in a granulated form or a powdered form.

In an embodiment of the present disclosure, about 87% (w/w) to about 89% (w/w) of the ground product is mixed with about 0.15% (w/w) to about 0.5% (w/w) of the rice husk ash, about 0.15% (w/w) to about 0.5% (w/w) of the binder, and about 7% (w/w) to about 9% (w/w) water in step b).

In an embodiment of the present disclosure, the strength of the iron ore pellets is cold compressive strength.

In an embodiment of the present disclosure, the cold compressive strength of the iron ore pellets increases by about 10 kg/pellet to 50 kg/pellet, including all values and ranges therebetween.

The present disclosure further relates to iron ore pellets with enhanced strength.

In an embodiment of the present disclosure, the strength of iron ore pellets is cold compressive strength.

In an embodiment of the present disclosure, the cold compressive strength of iron ore pellets is in the range of about 200 kg/pellet to about 300 kg/pellet, including all values and ranges therebetween.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

Figure 1 depicts the improved silicate slag network in the iron ore pellets with rice husk ash vis-à-vis without rice husk ash (using surface electron microscopy). Figure 1A depicts the silicate slag network in iron ore pellets without rice husk ash; and Figure 1B depicts the silicate slag network in iron ore pellets with rice husk ash.

Figure 2 illustrates a schematic representation of producing pellets without using rice husk ash.

Figure 3 illustrates a schematic representation of producing pellets using rice husk ash.

Figure 4 illustrates a schematic representation of basket test setup for pilot scale tests.

Figure 5 illustrates a schematic representation of dosing method followed for introducing rice husk ash into the mixer unit, in a commercial pellet plant.

DETAILED DESCRIPTION OF THE DISCLOSURE
With respect to the use of substantially any plural and/or singular terms herein (such as “a”, “an” and “the”), 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 suffix “(s)” at the end of any term in the present disclosure envisages in scope both the singular and plural forms of said term.

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. As such, the terms “a” (or “an”), “one or more”, and “at least one” can be used interchangeably herein.

Throughout this specification, the word “comprise”, or variations such as “comprises” or “comprising” or “containing” or “has” or “having” 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.

Throughout this specification, the term ‘combination thereof’ or ‘combinations thereof’ or ‘any combination thereof’ or ‘any combinations thereof’ are used interchangeably and are intended to have the same meaning, as regularly known in the field of patents disclosures.

The terms “about” or “approximately” as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, are meant to encompass variations of and from the specified value, such as variations of +/- 10% or less, +/- 5% or less, +/-1% or less, and +/-0.1% or less of and from the specified value, insofar such variations are appropriate to perform in the disclosure. It is to be understood that the value to which the modifier “about” or “approximately” refers is itself also specifically, and preferably, disclosed.

As used herein, the term “comprising” when placed before the recitation of steps in a method means that the method encompasses one or more steps that are additional to those expressly recited, and that the additional one or more steps may be performed before, between, and/or after the recited steps. For example, a method comprising steps a, b, and c encompasses a method of steps a, b, x, and c, a method of steps a, b, c, and x, a method of steps a, x, b and c, as well as a method of steps x, a, b, and c. Furthermore, the term “comprising” when placed before the recitation of steps in a method does not (although it may) require sequential performance of the listed steps, unless the content clearly dictates otherwise. For example, a method comprising steps a, b, and c encompasses, for example, a method of performing steps in the order of steps a, c, and b, the order of steps c, b, and a, and the order of steps c, a, and b, etc.

Numerical ranges stated in the form ‘from x to y’ include the values mentioned and those values that lie within the range of the respective measurement accuracy as known to the skilled person. If several preferred numerical ranges are stated in this form, of course, all the ranges formed by a combination of the different end points are also included.

As used herein, the terms “include” (any form of “include”, such as “include”), “have” (and “have”), “comprise” etc. any form of “having”, “including” (and any form of “including” such as “including”), “containing”, “comprising” or “comprises” are inclusive and 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.

As used herein, the phrase ‘rice husk ash’ is an agricultural waste by-product obtained after the incineration of rice husks in boilers at rice mills or power plants. It comprises approximately 90% to 98% (w/w) silica, preferably 95% (w/w) silica and has a very fine granulometry having size less than 45 microns.

As used herein, the phrase ‘pelletizing’ refers to a method of agglomeration, in which material fines are processed into pellets or granules. It is an agglomerating process of converting iron ore fines into uniform sized iron ore pellets which can be charged directly into a blast furnace (BF) or into a vertical furnace or rotary kiln normally used for the production of direct reduced iron (DRI).

As used herein, the term ‘iron ore pellets’ refers to iron ore fines that are agglomerated into pellets and then indurated using a furnace to create iron ore pellets. Thus, iron ore pellets are spheres of typically about 6 mm to about 16 mm to be used as raw material for production of steel. In the present disclosure, the term “iron ore pellets” has been used interchangeably with “fired pellets”.

The present disclosure relates to a method of enhancing strength of iron ore pellets using rice husk ash. The present disclosure also relates to iron ore pellets with enhanced strength. The present disclosure aims to develop a simple, cost-effective, environment friendly/low carbon footprint method for enhancing the strength of iron ore pellets, for its use in manufacturing of steel. For achieving this, the present disclosure recycles or utilizes the waste or reject of rice mills for enhancing the strength of iron ore pellets.

Particularly, the present disclosure employs a by-product of rice mills such as rice husk ash (often regarded as waste/reject) as one of the raw materials for enhancing the strength of iron ore pellets. The silica from rice husk ash in wet pellet mixture forms homogenously distributed silicate slag bond network to increase the consolidation of iron ore pellets, thereby enhancing the strength.

Thus, the present disclosure provides a method for improving/enhancing the cold compressive strength of iron ore pellets using rice husk ash. The iron ore pellets produced can be further used in steel manufacturing.

Particularly, the present disclosure relates to a method for enhancing strength of iron ore pellets, comprising:
e) grinding raw material comprising of an iron ore, a flux and a carbonaceous material, to obtain a ground product;
f) mixing the ground product with rice husk ash, a binder and water to obtain a wet pellet mixture;
g) pelletizing the wet pellet mixture to obtain green pellets; and
h) firing the green pellets to produce iron ore pellets with enhanced strength.

In an embodiment of the present disclosure, the grinding is of wet type or dry type.

In some embodiments of the present disclosure, grinding is carried out in a ball mill, a high-pressure grinding roller (HPGR), a vertical agitation mill, a vertical roller mill, or a combination thereof.

In some embodiments of the present disclosure, grinding is preferably carried out in a ball mill.

In some embodiment of the present disclosure, the ground product has a particle size of less than 150 microns, wherein about 60% to about 70% of the particles are less than 45 microns, including all values and ranges therebetween.

In some embodiments of the present disclosure, the ground product has a particle size of less than 45 microns, less than 50 microns, less than 55 microns, less than 60 microns, less than 65 microns, less than 70 microns, less than 75 microns, less than 80 microns, less than 85 microns, less than 90 microns, less than 95 microns¸ less than 100 microns¸ less than 105 microns¸ less than 110 microns¸ less than 115 microns¸ less than 120 microns¸ less than 125 microns¸ less than 130 microns¸ less than 135 microns¸ less than 140 microns¸ less than 145 microns¸ or less than 150 microns.

In some embodiments of the present disclosure, the iron ore comprises Fe at about 60% to about 64% (w/w), Al2O3 at about 2% to about 4% (w/w), SiO2 at about 2.5% to about 6% (w/w) and loss on ignition at about 2% to about 5% (w/w) and other impurities in minor or trace amounts.

In some embodiments of the present disclosure, the iron ore is selected from a group comprising hematite, magnetite, goethite, limonite, siderite, or combinations thereof.

In some embodiments of the present disclosure, the iron ore in the raw material mixture is present in an amount in the range at about 85% (w/w) to about 90% (w/w), including all values and ranges therebetween.

In some embodiments of the present disclosure, the iron ore in the raw material mixture is present in an amount at about 85% (w/w), about 86% (w/w), about 87% (w/w), about 88% (w/w), about 89% (w/w), or about 90% (w/w).

In some embodiments of the present disclosure, the flux is selected from a group comprising limestone, olivine, pyroxenite, dolomite, magnesite, wollastonite, or combinations thereof.

In some embodiments of the present disclosure, the flux in the raw material mixture is present in an amount in the range at about 0.5% (w/w) to about 7% (w/w), including all values and ranges therebetween.

In some embodiments of the present disclosure, the flux in the raw material mixture is present in in an amount at about 0.5% (w/w), about 1% (w/w), about 1.5% (w/w), about 2% (w/w), about 2.5% (w/w), about 3% (w/w), about 3.5% (w/w), about 4% (w/w), about 4.5% (w/w), about 5% (w/w), about 5.5% (w/w), about 6% (w/w), about 6.5% (w/w), or about 7% (w/w).

In some embodiments of the present disclosure, the carbonaceous material is selected from a group comprising anthracite coal, coke breeze, nut coke, blast furnace flue dust, gas cleaning plant sludge, or combinations thereof.

In some embodiments of the present disclosure, the carbonaceous material in the raw material mixture is present in an amount in the range at about 1% (w/w) to about 3% (w/w), including all values and ranges therebetween.

In some embodiments of the present disclosure, the carbonaceous material in the raw material mixture is present in in an amount at about 1% (w/w), about 1.5% (w/w), about 2% (w/w), about 2.5% (w/w), or about 3% (w/w).

In some embodiments of the present disclosure, the raw material comprises of the iron ore in the range at about 85% to 90% (w/w), the flux material at about 0.5% to 7% (w/w), and the carbonaceous material at about 1% to 3% (w/w).

In some embodiments of the present disclosure, the raw material comprises of the iron ore in the range at about 85% to 89% (w/w), the flux material at about 0.5% to 7% (w/w), and the carbonaceous material at about 1% to 6% (w/w).

In some embodiments of the present disclosure, the raw material comprises of the iron ore in the range at about 88.4%(w/w), the flux material at about 6.2% (w/w), and the carbonaceous material at about 5.4% (w/w).

In some embodiments of the present disclosure, the mixing is carried out in a high intensity mixer, a horizontal paddle mixer, a pug mill, a muller mixer, or a combination thereof.

In some embodiments of the present disclosure, the mixing is carried out in a high intensity mixer.

In some embodiments of the present disclosure, the rice husk ash is present in an amount at about 0.15% (w/w) to about 0.6% (w/w), including all values and ranges therebetween.

In some embodiments of the present disclosure, the rice husk ash is present in an amount at about 0.15% (w/w), about 0.2% (w/w), about 0.25% (w/w), about 0.3% (w/w), about 0.35% (w/w), about 0.4% (w/w), about 0.45% (w/w), about 0.5% (w/w), about 0.55% (w/w), or about 0.6% (w/w).

In some embodiments of the present disclosure, the rice husk ash is present in an amount at about 0.5% (w/w).

In some embodiments of the present disclosure, the rice husk ash comprises silica (SiO2) at about 90% (w/w) to about 98% (w/w), including all values and ranges therebetween.

In some embodiments of the present disclosure, the rice husk ash comprises silica (SiO2) at about 90% (w/w), about 91% (w/w), about 92% (w/w), about 93% (w/w), about 94% (w/w), about 95% (w/w), about 96% (w/w), about 97% (w/w), or about 98% (w/w).

In some embodiments of the present disclosure, the rice husk ash comprises moisture between about 3% to about 12%, including all values and ranges therebetween.

In some embodiments of the present disclosure, the rice husk ash comprises moisture at about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, or about 12%.

In some embodiments of the present disclosure, the rice husk ash has a density in the range of about 0.15 g/cm3 to about 0.4 g/cm3, including all values and ranges therebetween.
In some embodiments of the present disclosure, the rice husk ash has a density of about 0.15 g/cm3¬, about 0.2 g/cm3, about 0.25 g/cm3, about 0.3 g/cm3, about 0.35 g/cm3, or about 0.4 g/cm3.

In some embodiments of the present disclosure, particle size of the rice husk ash ranges from about less than 38 microns to about less than 1000 microns.

In some embodiments of the present disclosure, particle size of the rice husk ash is less than 38 microns, less than 45 microns, less than 50 microns, less than 60 microns, less than 70 microns, less than 80 microns, less than 90 microns, less than 100 microns, less than 150 microns, less than 200 microns, less than 250 microns, less than 300 microns¸ less than 350 microns¸ less than 400 microns¸ less than 450 microns¸ less than 500 microns¸ less than 550 microns¸ less than 600 microns¸ less than 650 microns¸ less than 700 microns¸ less than 750 microns¸ less than 800 microns¸ less than 850 microns, less than 900 microns, less than 950 microns, or less than 1000 microns.

In some embodiments of the present disclosure, the rice husk ash is in a granulated form or a powdered form.

In some embodiments of the present disclosure, the size of about 97% of the particles of the powdered form of the rice husk ash is less than 45 microns.

In some embodiments of the present disclosure, the binder is an organic binder or an inorganic binder.

In some embodiments of the present disclosure, the binder is selected from a group comprising of starch, guar gum, dextrin, acrylamide, bentonite, fly ash, or combinations thereof.

In some embodiments of the present disclosure, the binder is present in an amount ranging from about 0.15% (w/w) to about 1.5% (w/w), including all values and ranges therebetween.

In some embodiments of the present disclosure, the binder is present in an amount at about 0.15% (w/w), about 0.2% (w/w), about 0.3% (w/w), about 0.4% (w/w), about 0.5% (w/w), about 0.6% (w/w), about 0.7% (w/w), about 0.8% (w/w), about 0.9% (w/w), about 1.0% (w/w), about 1.1% (w/w), about 1.2% (w/w), about 1.3% (w/w), about 1.4% (w/w), or about 1.5% (w/w).

In some embodiments of the present disclosure, about 85% (w/w) to about 90% (w/w) of the ground product is mixed with about 0.1% (w/w) to about 1% (w/w) of the rice husk ash, about 0.2% (w/w) to about 1% (w/w) of the binder, and about 7% (w/w) to about 11% (w/w) water in step b).

In some embodiments of the present disclosure, about 87% (w/w) to about 89% (w/w) of the ground product is mixed with about 0.15% (w/w) to about 0.5% (w/w) of the rice husk ash, about 0.15% (w/w) to about 0.5% (w/w) of the binder, and about 7% (w/w) to about 9% (w/w) water in step b).

In some embodiments of the present disclosure, about 89.9% (w/w) of the ground product is mixed with about 0.5% (w/w) of the rice husk ash, about 0.46% (w/w) of the binder, and 9.2% (w/w) water in step b).

In some embodiments of the present disclosure, size of the wet pellet mixture is in the range of about 45 microns to about 150 microns, including all values and ranges therebetween.

In some embodiments of the present disclosure, size of the wet pellet mixture is about 45 microns, about 50 microns, about 55 microns, about 60 microns, about 65 microns, about 70 microns, about 75 microns, about 80 microns, about 85 microns, about 90 microns, about 95 microns, about 100 microns, about 105 microns, about 110 microns, about 115 microns, about 120 microns, about 125 microns, about 130 microns, about 135 microns, about 140 microns, about 145 microns, or about 150 microns.

In some embodiments of the present disclosure, the wet pellet mixture comprises carbon at about 1% (w/w) to 2% (w/w), including all values and ranges therebetween.

In some embodiments of the present disclosure, the wet pellet mixture comprises carbon at about 1% (w/w), about 1.05% (w/w), about 1.1% (w/w), about 1.15% (w/w), about 1.2% (w/w), about 1.25% (w/w), about 1.3% (w/w), about 1.35% (w/w), about 1.4% (w/w), about 1.45% (w/w), about 1.5% (w/w), about 1.55% (w/w), about 1.6% (w/w), about 1.65% (w/w), about 1.7% (w/w), about 1.75% (w/w), about 1.8% (w/w), about 1.85% (w/w), about 1.9% (w/w), about 1.95% (w/w), or about 2% (w/w).

In some embodiments of the present disclosure, pelletizing is carried out in a disc pelletizer or a drum pelletizer.

In some embodiments of the present disclosure, the steps b) and c) of the method are carried out in a laboratory or a commercial pellet plant.

In some embodiments of the present disclosure, the size of the green pellets is in the range of about 2 mm to about 20 mm, including all values and ranges therebetween.

In some embodiments of the present disclosure, the size of the green pellets is in the range of about 2 mm, about 4 mm, about 6 mm, about 8 mm, about 10 mm, about 12 mm, about 14 mm, about 16 mm, about 18 mm, or about 20 mm.

In some embodiments of the present disclosure, the green pellets contain moisture in the range of about 7% to about 13%, including all values and ranges therebetween.

In some embodiments of the present disclosure, the green pellets contain moisture at about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, or about 13%.

In some embodiments of the present disclosure, the green pellets have compressive strength in the range of about 1.1 kg/pellet to about 1.9 kg/pellet, including all values and ranges therebetween.

In some embodiments of the present disclosure, the green pellets have compressive strength of about 1.1 kg/pellet, about 1.2 kg/pellet, about 1.3 kg/pellet, about 1.4 kg/pellet, about 1.5 kg/pellet, about 1.6 kg/pellet, about 1.7 kg/pellet, about 1.8 kg/pellet, or about 1.9 kg/pellet.

In some embodiments of the present disclosure, the green pellets have a drop number in the range of about 3 to about 40.

In some embodiments of the present disclosure, the green pellets have a drop number of about 3, about 5, about 7, about 9, about 11, about 13, about 15, about 17, about 19, about 21, about 23, about 25, about 30, about 35, or about 40.

In some embodiments of the present disclosure, the firing of green pellets is carried out in an induration furnace selected from a group comprising of a tube furnace, a muffle furnace, a straight grate furnace, a grate kiln furnace, a vertical shaft furnace or a rotary hearth furnace.

In some embodiments of the present disclosure, the firing of green pellets is carried out in a straight grate furnace.

In some embodiments of the present disclosure, the furnace is in a commercial pellet plant, a laboratory scale muffle furnace, or a laboratory scale tube furnace.

In some embodiments of the present disclosure, the green pellets are fired at a temperature of about 1100 oC to about 1350 oC, including all values and ranges therebetween.

In some embodiments of the present disclosure, the green pellets are fired at a temperature of about 1100oC, about 1150oC, about 1200 oC, about 1250 oC, about 1300 oC, or about 1350 oC.

In some embodiments of the present disclosure, the green pellets are fired for a time period of about 20 minutes to about 60 minutes, including all values and ranges therebetween.

In some embodiments of the present disclosure, the green pellets are fired for a time period of about 20 minutes, about 25 minutes, about 30 minutes, about 35 minutes, about 40 minutes, about 45 minutes, about 50 minutes, about 55 minutes, or about 60 minutes.

In some embodiments of the present disclosure, the fired pellet basicity (CaO/SiO2) is in the range of about 0.1 to about 0.9.

In some embodiments of the present disclosure, the fired pellet basicity (CaO/SiO2) is about 0.1, about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, or about 0.9.

In some embodiments of the present disclosure, the method comprises:
a) grinding raw material comprising the iron ore in the range at about 85% (w/w) to about 90% (w/w), the flux material at about 0.5% (w/w) to about 7% (w/w), and the carbonaceous material at about 1% (w/w) to about 3% (w/w), to obtain the ground product,
wherein the ground product has a particle size of less than 150 microns;
b) mixing the ground product in a high intensity mixer with rice husk ash, a binder material and water to obtain a wet pellet mixture,
wherein the rice husk ash comprises of silica (SiO2) at about 90% (w/w) to about 98% (w/w);
c) pelletizing the wet pellet mixture in a disc pelletizer or a drum pelletizer to obtain green pellets; and
d) firing the green pellets in an induration furnace at a temperature of about 1100oC to about 1350oC to produce iron ore pellets with enhanced strength.

In some embodiments of the present disclosure, the method comprises:
a) grinding raw material comprising the iron ore, the flux material, and the carbonaceous material in a ball mill, to obtain a ground product of particle size of less than 150 microns,
wherein the iron ore is selected from a group comprising hematite, magnetite, goethite, limonite, or siderite, or combinations thereof;
b) mixing in a high intensity mixer of about 87% (w/w) to about 89% (w/w) of the ground product with about 0.15% (w/w) to about 0.5% (w/w) of the rice husk ash, about 0.15% (w/w) to about 0.5% (w/w) of the binder and about 7% (w/w) to about 9% (w/w) to obtain the wet pellet mixture;
c) pelletizing the wet pellet mixture in a pelletizing device to obtain green pellets of size about 2 mm to about 20 mm; and
d) firing the green pellets in an induration furnace of a commercial pellet plant or a laboratory scale muffle furnace or laboratory scale tube furnace at a temperature of about 1100oC to about 1350oC to produce iron ore pellets with enhanced strength.
In some embodiments of the present disclosure, the method comprises:
a) grinding raw material comprising the iron ore in the range at about 85% to 90% (w/w), the flux material at about 0.5% to 7% (w/w), and the carbonaceous material at about 1% to 3% (w/w), in a ball mill to obtain the ground product,
wherein the ground product has particle size of less than 150 microns,
b) mixing in a high intensity mixer about 87% (w/w) to about 89% (w/w) of the ground product with about 0.15% (w/w) to about 0.5% (w/w) of the rice husk ash, about 0.15% to 0.5% (w/w) of the binder and about 7% (w/w) to about 9% (w/w) water to obtain the wet pellet mixture with particle size in the range of about 45 microns to about 150 microns, in a laboratory or a commercial pellet plant;
c) pelletizing the wet pellet mixture in a disc pelletizer or drum pelletizer with water to obtain green pellets of size of about 2 mm to about 20 mm, in a laboratory or a commercial pellet plant; and
d) firing the green pellets in an induration furnace of a commercial pellet plant or a laboratory scale muffle furnace or laboratory scale tube furnace at a temperature of about 1100oC to about 1350oC for 20 minutes to 60 minutes to produce iron ore pellets with enhanced strength,
wherein the strength is cold compressive strength, and
wherein the cold compressive strength of the iron ore pellets increases by about 10 kg/pellet to 50 kg/pellet.
In some embodiments of the present disclosure, the method comprises:
a) grinding raw material comprising the iron ore in the range at about 85% to 90% (w/w), the flux material at about 0.5% to 7% (w/w), and the carbonaceous material at about 1% to 3% (w/w), in a ball mill to obtain the ground product,
wherein the ground product has particle size of less than 150 microns,
b) mixing in a high intensity mixer about 87% (w/w) to about 89% (w/w) of the ground product with about 0.15% (w/w) to about 0.5% (w/w) of the rice husk ash, about 0.15% to 0.5% (w/w) of the binder and about 7% (w/w) to about 9% (w/w) water to obtain the wet pellet mixture with particle size in the range of about 45 microns to about 150 microns, in a laboratory or a commercial pellet plant;
c) pelletizing the wet pellet mixture in a disc pelletizer or drum pelletizer with water to obtain green pellets of size of about 2 mm to about 20 mm, in a laboratory or a commercial pellet plant; and
d) firing the green pellets in an induration furnace of a commercial pellet plant or a laboratory scale muffle furnace or laboratory scale tube furnace at a temperature of about 1100oC to about 1350oC for 20 minutes to 60 minutes to produce iron ore pellets with enhanced strength,
wherein the strength is cold compressive strength,
wherein the cold compressive strength of the iron ore pellets increases by about 10 kg/pellet to 50 kg/pellet,
wherein the cold compressive strength of iron ore pellets is in the range of about 200 kg/pellet to about 300 kg/pellet, and
size of about 95% to about 100% of the iron ore pellets is in the range of about 6 mm to about 16 mm.
In some embodiments of the present disclosure, the strength of the iron ore pellets is cold compressive strength.

In some embodiments of the present disclosure, the cold compressive strength of the iron ore pellets increases by about 10 kg/pellet to 50 kg/pellet, including all values and ranges therebetween.

In some embodiments of the present disclosure, the cold compressive strength of the iron ore pellets increases by about 10 kg/pellet, about 15 kg/pellet, about 20 kg/pellet, about 25 kg/pellet, about 30 kg/pellet, about 35 kg/pellet, about 40 kg/pellet, about 45 kg/pellet, or about 50 kg/pellet.

In some embodiments of the present disclosure, the cold compressive strength of the iron ore pellets increases by about 30 kg/pellet.

The present disclosure further relates to iron ore pellets with enhanced strength.

In some embodiments of the present disclosure, the strength of iron ore pellets is cold compressive strength.

In some embodiments of the present disclosure, the cold compressive strength of iron ore pellets is in the range of about 200 kg/pellet to about 300 kg/pellet, including all values and ranges therebetween.

In some embodiments of the present disclosure, the cold compressive strength of iron ore pellets is about 200 kg/pellet, about 210 kg/pellet, about 220 kg/pellet, about 230 kg/pellet, about 240 kg/pellet, about 250 kg/pellet, about 260 kg/pellet, about 270 kg/pellet, about 280 kg/pellet, about 290 kg/pellet, or about 300 kg/pellet.

In some embodiments of the present disclosure, the size of about 95% to about 100% of the iron ore pellets is in the range of about 6 mm to about 16 mm, including all values and ranges therebetween.

In some embodiments of the present disclosure, the size of about 95% to about 100% of the iron ore pellets is about 6 mm, about 7 mm, about 8 mm, about 9 mm, about 10 mm, about 11 mm, about 12 mm, about 13 mm, about 14 mm, about 15 mm, or about 16 mm.

In some embodiments of the present disclosure, the iron ore pellets are used in ironmaking process in blast furnace and Direct Reduced Iron (DRI) gas based and coal-based processes.

The present disclosure relates to a simple, cost-effective, and environment friendly method of enhancing the cold compressive strength of iron ore pellets, that can be subsequently employed in steel manufacturing. In particular, the process employs rice husk ash as an additive that is added into the wet pellet mixture to improve the iron ore pellet strength. The additive gets generated as a reject after the incineration of rice husks in boilers at rice mills or power plants. It comprises approximately 90% to 98% (w/w) silica, preferably 95% (w/w) silica and has a very fine granulometry having size less than 45 microns.

Two main mechanism which governs the strength of iron ore pellets are a) solid state bonds between haematite particles, and b) silicate slag bonds which is a result of the melt formation that takes place between iron ore particles, gangue contents and flux materials. Silica in the pellets interacts with iron ore particles, flux material and other gangue contents during firing process to form silicate slag bonds. Rice husk ash which has silica in very fine form gets homogeneously distributed in the wet pellet mixture which can lead to a finely distributed silicate slag bond network in fired iron ore pellets. This type of slag network increases the consolidation of pellets and results in enhancement of cold compressive strength of iron ore pellets.

In addition, the silica present in rice husk ash is in amorphous form which means it has high reactivity and can form silicate bonds even at a slightly low temperature. This allows the pellet to attain high strength at a certain set process conditions of iron ore pellet plant.

The mechanism of silicate slag formation in the present disclosure is as follows:

The induration process constitutes firing of green pellets at around 1300oC in which melt formation takes place in silica rich region which is in contact with iron oxide and results in slag formation. The first melt is formed at a location inside the pellet which has the lowest melting point which is also called liquidus temperature of a particular composition in a binary system of iron oxide and silica. The binary phase diagram between iron oxide and SiO2 shows that the liquidus temperature decreases from 1370oC to as low as 1178oC with the increase in silica concentration in a binary system of iron oxide and silica particle. Hence, the tendency of silicate formation increases at a particular temperature for the increased concentration of silica in pellets. Figure 1 clearly depicts the improvement/increase in the silicate slag network formation in the iron ore pellets with rice husk ash (Figure 1B) as compared to the silicate slag network in the iron ore pellets without the rice husk ash (Figure 1A).

Silicate slag bonds is one of the main factors governing pellet strength apart from the recrystallized haematite iron ore particles. While silica input in pellet mixture increases the amount of slag formed but the formation of slag network is limited to the particle size and its homogenization in the mix introducing SiO2 rich material i.e., rice husk ash which is a finer form of SiO2 allows improvement of cold compressive strength by modifying the slag network in the fired iron ore pellet.

To summarize, the silica in the rice husk ash contributes to the improvement of CCS of iron pellets as follows:
• It forms silicate slag bonds upon interaction with iron ore particles, flux material and other gangue contents during firing process, thereby increasing the amount of slag.
• Silica from rice husk ash has a very fine granulometry and thus it gets homogeneously distributed in the pellet mixture, thereby forming an extensive and finely distributed silicate slag bond network which increases the consolidation of pellets.
• Silica from rice husk ash is in amorphous form, which has high reactivity and forms silicate bonds even at relatively lower temperatures.

Additionally, the present method results in complete and effective utilization of rice husk ash as it is considered a reject/waste material discharged from the boiler units of rice mills and power plants. Thus, the present method is also useful from environment perspective as it ensures safe, effective, and complete utilization of rice husk ask (a by-product/waste of rice mills and power plants) in the enhancement of CCS of iron ore pellets.

The present invention also relates to iron ore pellets with enhanced strength, particularly the cold compressive strength. The iron ore pellets of the present invention have a cold compressive strength in the range of about 200 kg/pellet to about 300 kg/pellet.

The present invention primarily possesses at least the following advantages:
a) the present method is simple, economical, efficient, and eco-friendly method for manufacturing of iron pellets with improved CCS; and
b) the process results in effective and complete utilization of the rice husk ash – which is considered a waste or a reject of rice mills or power plants.

It is to be understood that the foregoing descriptive matter is illustrative of the disclosure and not a limitation. 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. 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 herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the following examples should not be construed as limiting the scope of the embodiments herein.

EXAMPLES

EXAMPLE 1: This example provides flow diagrams describing the conventional method used for preparing the iron ore pellets and method of the present disclosure using rice husk ash.

A flow diagram indicative of the conventional method is shown in Figure 2. The description of the figure allows for a complete and comprehensive understanding of the process. The steps are detailed as follows:
Step 1 - Iron ores, flux and coke breeze enters drying unit (1).
Step 2 - The dried material is then ground in a ball mill grinding unit (2) and further classified using an air classifier (3).
Step 3 - The oversize material is again recycled back to the ball mill for further grinding. The ground material after classification enters the mixer unit (4) wherein water and bentonite are added.
Step 4 - The moistened mixed material then goes to the pelletizing disc (5) for agglomeration process.
Step 5 - The agglomerated green pellets are then released from the pelletizing disc and enters the induration furnace (6) where proper firing of green pellets are done to attain enough strength.

Figure 3 depicts a flow diagram of the present method of preparing ore pellets using rice husk ash. In the above stated step 3 (of the conventional process), rice husk ash is added in the mixer unit (4) along with water and bentonite which gets mixed properly and forms a part of the mixed material that goes to the pelletizing discs (5). The green pellets with rice husk ash then enters the induration machine (6) to produce the final iron ore pellets as product.

EXAMPLE 2: This example highlights the impact of addition of 0.5% (w/w) rice husk ash in the wet pellet mixture on the iron ore pellet strength on a pilot scale. The set up used for carrying out the pilot scale testing is shown in Figure 4. The set up consists of a set of Inconnel baskets (1) of dimension 10 X 10 X 10 cm which is filled with lab prepared green pellets of desired composition. These baskets are attached to 1.3-meter-long Inconnel rod (2) of 10 mm diameter using Inconnel wires (3). This whole set of baskets filled with iron ore pellets and assembled is inserted into the green pellet bed from the feed side of the induration machine in running conditions.

The particle size range of the rice husk ash used in this study is shown in Table 1.

Table 1: Complete size distribution of rice husk ash
Cumulative size fraction UoM Rice husk ash
< 38 microns % 10.3
< 45 microns % 13.2
< 75 microns % 32.5
< 150 microns % 66.4
< 250 microns % 83.8
< 1000 microns % 100

In this example, the green pellets were prepared at laboratory using the lab scale disc pelletizer and fired in the induration furnace of a commercial pellet plant. Two sets of green pellets were prepared at the lab - with and without rice husk ash in the wet pellet mixture which were then fired in the induration furnace of pellet plant. The green pellets prepared with rice husk ash comprised of 89.9% ground product, 0.5% rice husk ash, 0.46% binder and 9.2% water. While the green pellets without rice husk ash had no rice husk ash in the mixture. The baskets filled with pellets were introduced at the feed end of the indurating machine under running condition and taken out from the discharge end by stopping the machine. Table 2 shows the pellet CCS of the two set of basket test fired pellets taken out from the induration machine. An increase of 20 kg/pellet was observed over the base case iron ore pellets.

Table 2: Pellet CCS for the samples prepared with and without rice husk ash
Sl. No. Samples CCS (kg/pellet)
1 Pellet without rice husk ash 205
2 Pellets with 0.5% rice husk ash 225

EXAMPLE 3:
This example highlights the impact of addition of 0.5% (w/w) powdered rice husk ash in the wet pellet mixture on the iron ore pellet strength on a pilot scale (set up illustrated in Figure 4). Powdered rice husk ash was produced by grinding the rice husk ash to attain a size of 97% of particles passing through 45 microns mesh size. For this example, the green pellets were prepared at lab using the lab scale disc and fired in the induration furnace of a commercial pellet plant. Two sets of green pellets were prepared at the lab - with and without powdered rice husk ash in the wet pellet mixture which were then fired in the induration furnace of pellet plant, as explained in the Example 2. The baskets filled with pellets were introduced at the feed end of the indurating machine under running condition and taken out from the discharge end by stopping the machine.
Table 3 shows the pellet CCS of the two set of basket test fired pellets taken out from the induration machine. An increase of 40 kg/pellet was observed over the base case iron ore pellets.
Table 3: Pellet CCS for the samples prepared with and without powdered rice husk ash
Sl. No. Samples CCS (kg/pellet)
1 Pellet without rice husk ash 205
2 Pellets with 0.5% powdered rice husk ash 245

EXAMPLE 4:
This example demonstrates the impact of addition of 0.5% (w/w) rice husk ash on the iron ore pellet CCS in a commercial pellet plant. Rice husk ash was introduced at a rate of 0.5% in wet pellet mixture of a 6mpta capacity pellet plant of 768 m2 of grate area. Rice husk ash was carefully introduced in the mixer during the trial using the conventional dosing method as practiced for bentonite (set up illustrated in Figure 5). The rice husk ash filled in the bin (1) was extracted through a loss in weigh feeder (2) and a screw weigh feeder arrangement (3) into the mixer (4) unit. This arrangement allowed precise addition of rice husk ash in the pellet mix before going to the disc pelletizer for green ball formation.

Table 4 compares the key process parameter of the pellet plant and the pellet strength i.e., pellet CCS for base case and trial period. An increase in pellet CCS by 33 kg/pellet was evident during the plant trial.

Table 4: Comparison of pellet CCS and process parameters during base case period and trial period with 0.5% addition of rice husk ash

Sl. No. Parameters UoM Base case Trial period
1 Pellet CCS kg/pellet 188 221
2 Machine feed rate tph 1074 1080
3 Heat input MJ/t feed 693 688
4 Firing zone temperature deg C 1244 1249
5 Burn through temperature deg C 388 380
6 Internal RF % 1.12 0.80

Thus, the iron ore pellets produced by the method of present invention have desirable strength and quality for steel manufacturing along with possessing additional advantages such as method being simple, cost -effective, and resulting in economical use of rice husk ash (by-product of rice mills and power plants) as discussed above.

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 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.

As regards the embodiments characterized in this specification, it is intended that each embodiment be read independently as well as in combination with another embodiment. For example, in case of an embodiment 1 reciting 3 alternatives A, B and C, an embodiment 2 reciting 3 alternatives D, E and F and an embodiment 3 reciting 3 alternatives G, H and I, it is to be understood that the specification unambiguously discloses embodiments corresponding to combinations A, D, G; A, D, H; A, D, I; A, E, G; A, E, H; A, E, I; A, F, G; A, F, H; A, F, I; B, D, G; B, D, H; B, D, I; B, E, G; B, E, H; B, E, I; B, F, G; B, F, H; B, F, I; C, D, G; C, D, H; C, D, I; C, E, G; C, E, H; C, E, I; C, F, G; C, F, H; C, F, I, unless specifically mentioned otherwise.

Any discussion or reference of documents, acts, materials, devices, articles and the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application. Particularly, mention of any reference, article, publication, patent, patent publication, and patent application cited herein is not, and should not be taken as, an acknowledgment or any form of suggestion that they constitute valid prior art or form part of the common general knowledge in any country in the world. , Claims:1. A method for enhancing strength of iron ore pellets, comprising:
i) grinding raw material comprising of an iron ore, a flux and a carbonaceous material, to obtain a ground product;
j) mixing the ground product with rice husk ash, a binder and water to obtain a wet pellet mixture;
k) pelletizing the wet pellet mixture to obtain green pellets; and
l) firing the green pellets to produce iron ore pellets with enhanced strength.

2. The method of claim 1, wherein grinding is of wet type or dry type.

3. The method of claim 1, wherein grinding is carried out in a ball mill, a high-pressure grinding roller (HPGR), a vertical agitation mill, a vertical roller mill, or a combination thereof.

4. The method of claim 1, wherein the ground product has a particle size of less than 150 microns, wherein about 65% to about 68% of the particles are less than 45 microns.

5. The method of claim 1, wherein the iron ore comprises Fe at about 60% to about 64% (w/w), Al2O3 at about 2% to about 4% (w/w), SiO2 at about 2.5% to about 6% (w/w) and loss on ignition at about 2% to about 5% (w/w).

6. The method of claim 1, wherein the iron ore is selected from a group comprising hematite, magnetite, goethite, limonite, siderite, or combinations thereof; wherein the flux is selected from a group comprising limestone, olivine, pyroxenite, dolomite, magnesite, wollastonite, or combinations thereof; and wherein the carbonaceous material is selected from a group comprising anthracite coal, coke breeze, nut coke, blast furnace flue dust, gas cleaning plant sludge, or combinations thereof.

7. The method of claim 1, wherein the raw material comprises of the iron ore in the range at about 85% (w/w) to about 89% (w/w), the flux at about 0.5%(w/w) to about 7% (w/w), and the carbonaceous material at about 1%(w/w) to about 6% (w/w).

8. The method of claim 1, wherein the mixing is carried out in a high intensity mixer, a horizontal paddle mixer, a pug mill, a muller mixer, or a combination thereof.

9. The method of claim 1, wherein the rice husk ash is present in an amount at about 0.15% (w/w) to about 0.6% (w/w).

10. The method of claim 9, wherein the rice husk ash is present in an amount at about 0.5% (w/w).

11. The method of claim 1, wherein the rice husk ash comprises silica (SiO2) at about 90% to about 98% (w/w).

12. The method of claim 1, wherein the rice husk ash comprises moisture between about 3% to about 12%; and wherein the rice husk ash has a density in the range of about 0.15 g/cm3 to about 0.4 g/cm3.

13. The method of claim 1, wherein particle size of the rice husk ash ranges from about less than 38 microns to about less than 1000 microns.

14. The method of claim 1, wherein the rice husk ash is in a granulated form or a powdered form.

15. The method of claim 1, wherein the binder is an organic binder or an inorganic binder selected from a group comprising of starch, guar gum, dextrin, acrylamide, bentonite, fly ash or combinations thereof, and is in an amount ranging from about 0.15% (w/w) to about 1.5% (w/w).
16. The method of claim 1, wherein about 85% (w/w) to about 90% (w/w) of the ground product is mixed with about 0.1% (w/w) to about 1% (w/w) of the rice husk ash, about 0.2% (w/w) to about 1% (w/w) of the binder, and about 7% (w/w) to about 11% (w/w) water in step b).
17. The method of claim 1, wherein size of the wet pellet mixture is in the range of about 45 microns to about 150 microns.

18. The method of claim 1, wherein the pelletizing in step c) is carried out in a disc pelletizer or a drum pelletizer.

19. The method of claim 1, wherein the firing of green pellets is carried out in an induration furnace selected from a group comprising of a tube furnace, a muffle furnace, a straight grate furnace, a grate kiln furnace, a vertical shaft furnace or a rotary hearth furnace.

20. The method of claim 1, wherein the green pellets are fired at a temperature of about 1100oC to about 1350oC for a time period of about 20 minutes to about 60 minutes.

21. The method of claim 1, wherein size of the green pellets is in the range of about 2 mm to about 20 mm.

22. The method of claim 1, wherein the strength of the iron ore pellets is cold compressive strength.

23. The method of claim 22, wherein the cold compressive strength of the iron ore pellets increases by about 10 kg/pellet to 50 kg/pellet.

24. The method of claim 22, wherein the cold compressive strength of the iron ore pellets increases by about 30 kg/pellet

25. Iron ore pellets with enhanced strength produced by the method of claim 1.

26. The iron ore pellets of claim 25, wherein the strength is cold compressive strength, and the cold compressive strength is in the range of about 200 kg/pellet to about 300 kg/pellet.

27. The iron ore pellets of claim 25, wherein size of about 95% to about 100% of the iron ore pellets is in the range of about 6 mm to about 16 mm.
Dated this 09th day of July 2022

To: Signature:
The Controller of Patents Name: Durgesh Mukharya (IN/PA No. 1541)
The Patent Office, at Kolkata Of K&S Partners, Bangalore, Agent for the Applicant