Claims:1. A method for grinding iron ore blend, the method comprising:
charging the iron ore blend consisting of individual iron ores with variation in at least one of porosity, hardness, bond work index (BWI), particle size, texture and morphology into a grinding equipment;
charging flux and fuel into the grinding equipment;
charging a predetermined quantity of iron ore sinter fines into the grinding equipment; and
grinding a mixture of iron ore blend, flux and fuel along with iron ore sinter fines in the grinding equipment, wherein the iron ore blend processed by the method exhibits optimal ultra-fines and Blaine surface area.

2. The method as claimed in claim 1, wherein the flux is at least one of dolomite, lime, quartzite, limestone, olivine, and pyroxenite

3. The method as claimed in claim1, wherein the fuel is at least one of coke fine and anthracite coal.

4. The method as claimed in claim 1, wherein size of the optimal ultra-fines ranges from about -10 µm.

5. The method as claimed in claim 1, wherein the optimal Blaine surface area ranges from about 1800 cm2/g to 2400 cm2/g.

6. The method as claimed in claim 1, wherein the predetermined quantity of the iron ore sinter fines added to the iron ore blend ranges from about 3 wt.% to about 15 wt.%.

7. The method as claimed in claim 1, wherein the iron ore sinter fines comprise a composition of: total iron Fe (T) at about 45 wt.% to about 60 wt.%, ferrous oxide (FeO) at about 7 wt.% to about 14 wt.%, calcium oxide (CaO) at about 9 wt.% to about 14 wt.%, magnesium oxide (MgO) at about 1.50 wt.% to about 2.50 wt. %, Al2O3 at about 1.5 wt.% to about 3.0 wt. % and silicon dioxide (SiO2) at about 2.5 wt.% to about 5.0 wt. %.

8. The method as claimed in claim 1, wherein particle size of the iron ore sinter fines is -6.3 mm, preferably -5 mm.

9. The method as claimed in claim 1, wherein the bond work index (BWI) of the iron ore sinter fines is about 13.5 kWh/t.

10. The method as claimed in claim 1, wherein microstructure of iron ore sinter fines comprises crisscross lamellar morphology with acicular and columnar silico ferrite of calcium and aluminum.

11. The method as claimed in claim 1, wherein the microstructure of iron ore sinter fines promotes improved grinding of iron ore blends.

12. The method as claimed in claim 1, wherein the iron ore sinter fines exhibit mechanisms of crack tip deflection and crack tip blunting during grinding.

13. The method as claimed in claim 1, wherein the grinding equipment is a dry circuit horizonal ball mill.

14. The method as claimed in claim 1, wherein the variation in porosity of the individual iron ore in the iron ore blend ranges from about 16 vol.% to 51 vol.%.

15. The method as claimed in claim 1, wherein the variation in bond work index of the individual iron ore in iron ore blend ranges from about 7.5 kWh/t to about 15.5 kWh/t.

16. The method as claimed in claim 1, wherein the variation in top size of the individual iron ore in the iron ore blend ranges from about 4 mm to 12 mm.

17. The method as claimed in claim 1, wherein hardness of the iron ore sinter fines is comparable to hardness of the iron ore blend.

18. The method as claimed in claim 1, wherein the iron ore blend, fuel and flux and the iron ore sinter fines are charged to the grinding equipment in dry state.
, Description:TECHNICAL FIELD
The present disclosure generally relates to a field of material science and metallurgy. Particularly, but not exclusively the present disclosure relates to a method of grinding iron blend. Further, embodiment of the present disclosure discloses a method for grinding iron blend containing individual iron ores with significant variation in properties.

BACKGROUND OF THE DISCLOSURE
Mechanized mining become a common practice in extractive metallurgy filed. During, mechanized mining of iron ore, lots of fines (with particle size -10 mm) are generated along with small quantity of lumps (with particle size about 10 mm to about 40 mm). In order to utilize fines which are less than -10 mm in iron making units like blast furnaces or other packed bed furnaces, a prior agglomeration is essential. Agglomeration of iron ore is generally done by two methods i.e. sintering and pelletizing. Other methods like cold briquetting etc. are limited due to low strength and poor metallurgical performance of cold bonded agglomerates. Iron ore pelletizing is a process of formation of green or wet spherical balls by mixing powdered iron ore fines, fluxes and solid fuel with critical amount of water and binder. The green ball is then indurated, or heat hardened to obtain required quality in terms of strength and metallurgical performance for iron making unit. In comparison to sintering, pelletization is largely favored because of its capability to utilize more fine and dusty materials (less than 150 µm) as well as suitability of fired pellets for transporting over long distances such cross continent transportation. However, for pelletizing, further grinding of the less than 10 mm fines is essential to obtain an optimal fineness with suitable size and Blaine surface area.

Blast furnace utilizes different types of iron ore processed products as feed in the form of lump and pellets. These feed materials are required to possess alumina content about 2 wt.% to about 2.5 wt.% in order to achieve lower slag rate, efficient fuel consumption and high productivity of blast furnaces. Ores containing alumina content more than 3 wt.% to 4 wt.% is processed to decrease alumina to 2 wt.% to 3 wt.% by using process such as but not limited to washing, magnetic separation, hydro-cyclone and jigging etc. Similarly, run-of-mine (ROM) ores content, containing alumina less than 1 wt.% to 2 wt.% also may be crushed resulting in the production of high-grade fines along with small quantity of lumps.

In order to increase mining resource life and to utilize natural resources more effectively, these two types of iron ores are mixed to form iron ore blend, which is further employed in pellet making. Iron ore blending is done to achieve desirable chemical composition as generally dictated by iron making units.

Each kind of iron ore require specific grinding requirements. Hence, grinding two different iron ores having different properties such as but limited to porosity, hardness, bond work index (BWI), particle size, texture and morphology may lead to difference in size and surface area of the particles. The iron ores which are softer and friable generate excess ultra-files. This condition may be not only damage to the iron ores; but also lead to lower productivity during pelletization demanding slower drying, slower preheating rate in order to avoid pellet bursting. On the other hand, the iron ores which may be hard to grind may generate excess coarse particles, beyond the required optimal limit leading to poor green ball quality and fired pellet quality.

Particle size distribution and Blaine surface area has a significant effect on green ball and fired pellet quality. Therefore, controlling the same is an essential aspect for producing quality pellets economically. During grinding of the ore blend, from at least one of mines and a set of ores purchased from different sources (which may be generally blended in terms of chemical composition like alumina, silica, phosphorous and sulphur etc.), controlling the ground product quality in terms of ultra-fines and Blaine surface area is very challenging. Since the ore blends are prepared for grinding according to chemistry, suitable grinding characteristics are rarely achieved.

Grinding behavior of iron ore blend with variation in texture is illustrated in figure 1. A massive ore or equiaxed ore (1a) and a laminated or banded ore (1b) may be subjected for grinding. The hardness, porosity, chemical composition, extent of weathering characteristics of massive ore is generally uniform throughout the grains while the same characteristics in a laminated or banded ore fines are different in different bands or lamellae. Due to different weathering rate of different bands in banded ore, one layer may be predominantly hard while other can be weak. When subjected to grinding operation in ball mill, massive or equiaxed iron ore may generally experience trans-granular or through-grain fracture as strength across the grain is similar at all points in the ore. Laminated or banded ores, specially which have been weathered, will have a variation in strength and are generally weak at the interface of two layers. These ores tend to fracture at the interface resulting in generation of platy fines. Additionally, the laminated ores due to erosion of sharp edges in the ground product have tendency to produce more ultra-fines particles less than 2µm to 7 µm. Blaine number is associated with the surface area of particles, and with platy fines along with more ultra-fines, weathered laminated ores generate powder with higher blaine and increased ultra-fines which is very difficult to control. Hence, grinding of massive and laminated type of ores together may be difficult in terms of control over ground product quality.

Furthermore, grinding behavior of iron ore blend with variation in porosity is illustrated in figure 2. A less porous ore (2a) and high porous (2b) may be subjected for grinding. In general, ores containing less pores may be compact enough due to which they tend to break into small number of particles and require long time, more energy for fine grinding. On the other hand, the ores containing large number of pores during grinding may generate finer particles and require less time and energy for fine grinding. Additionally, when they are grinded together, less porous ores act as grinding media for high porous ores resulting in over grinding of porous ores. This condition results in uncontrolled increase in fineness of final ground product along with excessive high Blaine surface area.

Similarly, different ores may have different hardness depending upon chemical composition, geological effect, weathering etc. Figure 3 illustrates the grinding behavior of iron ore blends having variation in hardness. Energy utilization is more for grinding hard ores (3a) than soft ores (3b). Soft ores during grinding produces large amounts of fines in comparison to hard ores. When two ores with variation in hardens are grinded together, the harder ores will act as grinding media for soft ores. The soft ores will be over grounded with additional action of harder ores and generate even more fines which is not desirable for pellet making.

Conventionally, many methods have been tried for grinding iron ore blend. One such method in Patent No CN202191938U describes a simple wet ball milling in a vertical grinding barrel. However, this process may consume large quantity of water, and require a filter press/vacuum press to remove the excess moisture. The wet mill products may possess difficulty in transport due to moisture in present in final product. Further, problem may be associated with disposal of waste liquid. Another method described in Patent No CN102728445A in the conventional art involves dry grinding of iron ore blend in a roller mill. The method involves the first step of breaking coarse ores in a high-pressure roller mill followed by a second step of classifying the fine power into a dust collector by emptying a classifier sort. Third step of the method involves sorting the coarse powder which may be then returned back into the high-pressure roller for further processing. This process may be cumbersome and require a lot of capital investment.

Yet another method described in Patent No US3202502 includes a high temperature autogenous grinding of ores. The method involves tumbling and autogenously grinding lump iron ore in a grinding drum with a chemically active atmosphere at around 200 °C to about 300 °C. This may be a complex process and require sophisticated equipment and hence economically may not be an attractive process in iron ore plants. Usage of microwave pretreatment in order to improve the grinding characteristic also has been tried and described by P.Kumar et.al in their research article “Iron ore grindability improvement by microwave pre-treatment”. However, having microwave plant for iron ore grinding may require huge capital investment and enormous amount of electrical energy. Another type of wet ball milling process by controlling distance between the grinding parts in a stirring device has been tried for grinding iron ore blend and described in Patent No CN105032563A. Open laminar flow grinding may be achieved so that over mixing of materials may not occur and accordingly over-grinding may be avoided. The final product obtained in form of slurry has narrow particle size distribution. However, this method may not help in controlling the ground product quality and additional drying step may be essential to obtain final product.

The present disclosure is directed to overcome one or more limitations stated above or any other limitation associated with the conventional methods.

SUMMARY OF THE DISCLOSURE
One or more shortcomings of the prior art are overcome by a method as disclosed and additional advantages are provided through the method as described in the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined together to form a further embodiment of the disclosure.

In one non-limiting embodiment of the present disclosure, there is provided a method of grinding iron ore blend. In the method, the iron ore blend consisting of individual iron ores with variation in at least one of porosity, hardness, bond work index (BWI), particle size, texture and morphology is charged into a grinding equipment. Flux and fuel are charged into the grinding equipment. Further, a predetermined quantity of iron ore sinter fines is charged into the grinding equipment. Finally, a mixture of iron ore blend, flux and fuel along with iron ore sinter fines is ground in the grinding equipment. The iron ore blend processed by this method exhibits optimal ultra-fines and Blaine surface area.

In an embodiment, the flux is at least one of dolomite, lime, quartzite, limestone, olivine, and pyroxenite.

In an embodiment, the fuel is at least one of coke fine and anthracite coal.

In an embodiment, size of the optimal ultra-fines ranges from about -10 µm.

In an embodiment, the optimal Blaine surface area ranges from about 1800 cm2/g to about 2400 cm2/g.

In an embodiment, the predetermined quantity of the iron ore sinter fines added to the iron ore blend ranges from about 3 wt.% to about 15 wt.%.

In an embodiment, the iron ore sinter fines comprise a composition of: total iron Fe (T) at about 45 wt.% to about 60 wt.%, ferrous oxide (FeO) at about 7 wt.% to about 14 wt.%, calcium oxide (CaO) at about 9 wt.% to about 14 wt.%, magnesium oxide (MgO) at about 1.50 wt.% to about 2.50 wt. %, Al2O3 at about 1.5 wt.% to about 3.0 wt. % and silicon dioxide (SiO2) at about 2.5 wt.% to about 5.0 wt. %.

In an embodiment, particle size of the iron ore sinter fines is -6.3 mm, preferably -5 mm.

In an embodiment, the bond work index (BWI) of the iron ore sinter fines is about 13.5 kWh/t.

In an embodiment, microstructure of iron ore sinter fines comprises crisscross lamellar morphology with acicular and columnar silico ferrite of calcium and aluminum. The microstructure of iron ore sinter fines promotes improved grinding of iron ore blends.

In an embodiment, the iron ore sinter fines exhibit mechanisms of crack tip deflection and crack tip blunting during grinding.

In an embodiment, the grinding equipment is a dry circuit horizonal ball mill.

In an embodiment, the variation in porosity of the individual iron ore in the iron ore blend ranges from about 16 vol.% to 51 vol.%.

In an embodiment, the variation in bond work index of the individual iron ore in iron ore blend ranges from about 7.5 kWh/t to about 15.5 kWh/t.

In an embodiment, the variation in top size of the individual iron ore in the iron ore blend ranges from about 4 mm to 12 mm.

In an embodiment, hardness of the iron ore sinter fines is comparable to hardness of the iron ore blend.

In an embodiment, the iron ore blend, fuel and flux and the iron ore sinter fines are charged to the grinding equipment in dry state.

It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined together to form a further embodiment of the disclosure.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The novel features and characteristics of the disclosure are set forth in the appended description. The disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:

Figure 1 illustrates grinding behavior of iron ore blend with variation in texture using conventional methods.

Figure 2 illustrates grinding behavior of iron ore blend with variation in porosity using conventional methods.

Figure 3 illustrates grinding behavior of iron ore blend with variation in hardness using conventional methods.

Figure 4 is a flowchart illustrating a method of grinding iron ore blend, according to an exemplary embodiment of the present disclosure.

Figures 5a, 5b and 5c illustrate optical micrographs of the microstructure of iron ore sinter fines, according to an exemplary embodiment of the present disclosure.

Figures 6a and 6b illustrate crack tip deflection and crack tip blunting mechanism of iron ore sinter fines, according to an exemplary embodiment of the present disclosure.

Figures 7a and 7b illustrate optical micrographs of the microstructure of dense hard laminated ore and porous fragile laminated ore present in iron ore blend respectively, according to an exemplary embodiment of the present disclosure.

Figure 8 is a graphical representation of variation in Blaine surface of the iron ore fines after grinding, according to an exemplary embodiment of the present disclosure.

Figure 9 is a graphical representation of variation in ultrafine after grinding, according to an exemplary embodiment of the present disclosure.

Figures 10a and 10b are graphical representation of trend in Blaine surface area during trial and base period respectively, according to an exemplary embodiment of the present disclosure.

Figures 11a and 11b are graphical representation of variation in Blaine surface area during trial and base period respectively, according to an exemplary embodiment of the present disclosure.

Figures 12a, 12b and 12c are graphical representation of trend in ultra-fines generation during trial and base period respectively, according to an exemplary embodiment of the present disclosure.

The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION
The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the description of the disclosure. It should also be realized by those skilled in the art that such equivalent methods do not depart from the scope of the disclosure. The novel features which are believed to be characteristic of the disclosure, as to method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.

In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the disclosure.

The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a method that comprises a list of acts does not include only those acts but may include other acts not expressly listed or inherent to such method. In other words, one or more acts in a method proceeded by “comprises… a” does not, without more constraints, preclude the existence of other acts or additional acts in the method.

Conventional methods available for grinding iron ore blend containing individual iron ores with variation may require huge amount of water, high temperature, controlled atmosphere, and special requirements such as microwaves. These methods may not be economical for large scale production owing to the requirements of enormous capital and energy. Furthermore, available techniques produce particles in uncontrollable fashion. i.e. coarse particles with size greater than 250 µm and ultra-fines with particles size less than 2 µm. Utilization coarser particles for subsequent palletizing may result in poor green ball quality and fired pellet quality. On the other hand, utilization of very fine particles during palletizing may demand slower drying and preheating rates in order to avoid the pellet bursting during subsequent palletization process.

From the discussion of prior arts, it is evident that grinding iron blend containing individual iron ores with variation in at least one of porosity, hardness, bond work index (BWI), particle size, texture and morphology is still a challenge. Hence, there a great need for a simple, easy, economical and efficient method for grinding of iron ore blends which produce particles in well controllable manner as required by pelletization process. Herein, the present disclosure is directed towards a method of grinding iron ore blend to obtain optimal ultra- fines and Blaine surface area.

The present disclosure provides a a method of grinding iron ore blend. In the method, the iron ore blend consisting of individual iron ores with variation in at least one of porosity, hardness, bond work index (BWI), particle size, texture and morphology may be first charged into a grinding equipment. Flux and fuel may be subsequently charged into the grinding equipment. Further, a predetermined quantity of iron ore sinter fines may be charged into the grinding equipment. Finally, a mixture of iron ore blend, flux and fuel along with iron ore sinter fines is subjected for grinding in the grinding equipment. The iron ore blend processed by this method exhibits optimal ultra-fines and Blaine surface area.

In the following detailed description of the embodiments of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense.

In the present disclosure, a method of grinding iron ore blend is explained with the help of figures. However, such exemplary embodiments should not be construed as limitations of the present disclosure, since the method may be used for other types of ore blends other than iron ore blend. A person skilled in the art may envisage various such embodiments without deviating from scope of the present disclosure.

Figure 4 illustrates a flow chart for a method of grinding iron ore blend. The method may be particularly applicable for producing optimal ultra-fines (about 2 µm to 10 µm) and Blaine surface area. At block 101, the iron ore blend consisting of individual iron ores with variation in at least one of porosity, hardness, bond work index (BWI), particle size, texture and morphology may be charged in dry condition into a grinding equipment. In an embodiment, grinding equipment used may be involve such as but no limited to dry circuit horizontal ball milling. Later, charging of flux and fuel in dry condition into the ball milling may be carried out as shown in block 102. The flux may be at least one of dolomite, lime, quartzite, limestone, olivine, and pyroxenite the fuel is at least one of coke fine and anthracite coal. Later, a predetermined quantity of iron ore sinter fines in dry condition may be charged into the ball milling as shown in block 103. Finally, a mixture of iron ore blend, flux and fuel along with iron ore sinter fines may be subjected to grinding (a shown in block 104) for about 15 minutes at ambient conditions to obtain optimal ultra-fines of particle size -10 µm and optimal Blaine surface area ranges from about 1800 to 2400 cm2/g.

In an embodiment, during grinding of iron ore blend, iron ores may undergo brittle type fracture at room temperature or at ambient temperature range generally observed in industrial ball mill. In iron ore particle, when subjected to grinding operation in ball mill, cracks may be initiate at weak points such as but not limited to pores, lower hardness points and interfaces with weak bonding (in laminated type ores). Cracks may be then propagated by means of stress applied by impact forces which may work normally to the surface of particle, abrasive forces which may work tangentially to the surface of particle or angular force which may work at angle in between normal and tangential forces. Finally, the cracks may terminate by being stopped or by crossing through the material resulting in fracture or disintegration of particle. If the crack propagation is easy and resulting in crack termination after particle disintegration, then the material may generate excessive ultra-fines and high Blaine surface area during grinding. If the crack propagation is such that it gets terminated a few steps before finally crossing the material for fracture, then the material may not generate powder with excessive ultra-fines and high Blaine surface area. Hence, the microstructural features, texture, size and hardness etc. of an iron ore may play an important role in deciding the grinding behavior of that mineral in horizontal ball milling. In a ball mill, three types of forces may act on a particle during grinding.

In an embodiment, in order to control the generation of excessive ultra-fines and to optimize Blaine-surface area during grinding of iron ore, iron ore sinter fines with a particles size less than -6.3 mm, preferably -5 mm obtained from sinter returns may be added in 3 wt.% to about 15 wt.% to the iron ore blend. The iron ore sinter fines comprise a composition of: total iron Fe (T) at about 45 wt.% to about 60 wt.%, ferrous oxide (FeO) at about 7 wt.% to about 14 wt.%, calcium oxide (CaO) at about 9 wt.% to about 14 wt.%, magnesium oxide (MgO) at about 1.50 wt.% to about 2.50 wt. %, Al2O3 at about 1.5 wt.% to about 3.0 wt. % and silicon dioxide (SiO2) at about 2.5 wt.% to about 5.0 wt. %. The bond work index (BWI) of the iron ore sinter fines is about 13.5 kWh/t.

In an embodiment, mechanism of grinding of a base blend comprising ores with significant variation in textural features, porosity, size, hardness etc. vis-à-vis the same blend containing sinter return fines with size - 6.3 mm, preferably -5 mm may be described herewith.

Grinding behavior during impact loading:

Hard Massive Ore Soft Massive Ore Hard Laminated Ore Fragile Laminated Ore Dense Ore Porous Ore
Disintegration Behavior Breakage into less particles owing to their high hardness Breakage into more particles owing to their low hardness Breakage into less particles owing to their high hardness Breakage into more particles owing to their fragile nature Breakage into less particles owing to their dense structure Breakage into more particles owing to their porous structure
Breakage into less particles owing to their generally bigger size of +6 mm Breakage into more particles owing to their generally smaller size of -6 mm Breakage into less particles owing to their generally bigger size of +6 mm Breakage into more particles owing to their generally smaller size of -6 mm Breakage into less particles owing to their generally bigger size of +6 mm Breakage into more particles owing to their generally smaller size of -6 mm

Disintegrating Behavior or Behavior as Grinding Media Owing to large size, High Hardness and Presence of Softer ores, it also works as grinding media significantly for softer ores Does not work as grinding media at All Owing to large size, High Hardness and Presence of Softer ores, it also works as grinding media significantly for softer ores Does not work as grinding media at All Owing to large size, High Hardness and Presence of Softer ores, it also works as grinding media significantly for softer ores Does not work as grinding media at All

Over Grounding DO not face over grounding Face Excess or Over grounding because of presence of large harder ores DO not face over grounding Face Excess or Over grounding because of presence of large harder ores DO not face over grounding Face Excess or Over grounding because of presence of large harder ores

Ultra-fines Generation Behavior Less ultra-fines generation High Ultra fines Generation Slightly more ultra-fines generation because of erosion of sharp edges form broken particles Excessively high generation of ultra-fines Less Ultra-fines generation High Ultra-fine generation

Table-1

With addition of iron ore sinter fines, characteristic behavior of these iron ores changes Sinter fines results in decreasing the percentage of iron ores in the blend to same extent to which sinter fines are added. Addition of sinter ore fines may subsequently result in:
a) Hard massive, laminated and dense ore participation in getting grinded may increase.
b) Hard massive, laminated and dense ore behavior as grinding media may decrease because of decrease in both harder ores and softer ores i.e. material which may act as grinding media (harder ores) and material which is undergoing excess grinding (softer ores).
c) Behavior of softer, porous and fragile ores to generate more ultra-fines may decrease because of decrease in large sized harder ores.
d) Additionally, iron ore sinter fines may undergo optimum impact grinding because of their relatively smaller size of -6.3 mm and at the same time, they do not undergo excessive grinding because of optimum mix of columnar and acicular ferrite structure (which cause crack deflection during crack propagation) and pores (which cause crack tip blunting during crack propagation).

Grinding behavior during angular loading:

Hard Massive Ore Soft Massive Ore Hard Laminated Ore Fragile Laminated Ore Dense Ore Porous Ore
Chips Generation Behavior Less chips generation owing to high hardness and generally large size of +6 mm High Chips generation behavior owing to low hardness and generally small size of -6 mm Slightly high chips generation owing to angular fractured or sharp edge fractured particle Very high chips generation owing to angular fractured or sharp edge fractured particle with low hardness Less chips generation owing to dense structure and generally large size of +6 mm High Chips generation behavior owing porous structure and generally small size of -6 mm

Table-2

With addition of iron ore sinter fines, chipping of ores may slightly decrease during ball milling. Again, iron ore sinter fines may undergo optimum chipping because of their relatively smaller size of -6.3 mm, preferably -5 mm. At the same time, sinter return fines may not undergo excessive grinding because of optimum mixture of columnar and acicular ferrite structure present in the morphology.

Grinding behavior during tangential loading or abrasion:

Hard Massive Ore Soft Massive Ore Hard Laminated Ore Fragile Laminated Ore Dense Ore Porous Ore
Ultra-fines Generation Behavior Less ultra-fines generation High Ultra fines Generation Slightly more ultra-fines generation because of erosion of sharp edges form broken particles Excessively high generation of ultra-fines Less Ultra-fines generation High Ultrafine generation

Table-3

With addition of iron ore sinter fines, abrasion may significantly decrease during grinding in the ball mill. Further, sinter return fines may undergo less abrasion during grinding because of their relatively high BWI of about 13.5 kWh/t. Another reason for sinter fines may not undergo excessive abrasive grinding may be optimum mixture of columnar and acicular ferrite structure in the morphology.

In an embodiment, sinter return fines contain crisscross lamellar morphology with acicular and columnar silico ferrite of calcium and aluminum. It may also contain primary and secondary hematite along with magnetite and pores as depicted in figures 5a, 5b and 5c. This structure may provide the ability to absorb stresses leading to lower fine generation and Blaine surface area during grinding. Mechanism of sinter fines breakage may promote better control over Blaine surface area and ultra-fines generation during grinding of iron ore blend as depicted in figures 6a and 6b. When crack from one lamellae of ferrite pass into adjacent lamellae, its direction is changed because of crystallographic orientation of lamellae. This mechanism is called as “crack tip deflection mechanism” (as shown in figure 6a). The crack tip deflection mechanism increases the actual crack length and toughness of material and hence results in less generation of ultrafine fraction. Also, due to the presence of acicular ferrites along with columnar ferrite, the structure may stabilize a huge number of uniformly distributed pores. When a propagating crack encounters a pore in front of it, its tip gets blunt and require more energy for further crack initiation. This mechanism of crack growth impediment is called as “crack tip blunting mechanism” (as shown in figure 6b). Both crack tip deflection and crack tip blunting mechanism may cause crack growth impediment preventing excessive high ultra-fines and high Blaine surface area. However, due to relatively small size of -6.3 mm, preferably -5 mm, the iron ore sinter fines may undergo only moderate grinding as per required fineness.

Following paragraphs now enumerates examples grinding iron ore blend using a method of the present disclosure:

EXAMPLES:

Case 1: Establishing the effect of iron ore sinter fines addition on ultrafine generation and Blaine surface area at laboratory scale grinding

In an exemplary embodiment, iron ore sinter fines may be added to iron ore blend in order to decrease excessive ultra-fine generation and to optimize Blaine surface area and also to decrease variation if ultra-fines generation and Blaine surface area. 3 series of experiments were conducted at laboratory scale. For the preparation of iron ore blend, ore A is mixed with Ore B, wherein percentage of Ore A and Ore B may be varied from about 0 wt.% to about 100 wt.% with 25 wt.% change in each step. These series may be as explained below:

Series 1: Size of ore A is +6 mm to -10 mm and size of ore B is- 6 mm. This may be chosen so as ore A is a dense hard laminated ore and ore B is a porous fragile laminated ore. Hardness or BWI of ore A is around 14.83 kWh/t while BWI of ore B is around 7.71 kWh/t. Ore A and ore B were obtained from Joda region in Odisha. Micrographs of ore A and ore B are as duplicated in figures 7a and 7b respectively. Because of difference in size, porosity, friable nature, Bond Work Index (BWI), textural features, it is concluded that the iron ore blend is a complex feed for ball mill. The iron ore blends prepared were grounded for about 15 min in lab scale ball mill and product obtained may be screened at 0.5 mm mesh. -0.5 mm sized powder may be considered as ground product while +0.5 mm sized power were considered as unground material.

Series 2: Size of ore A is -6 mm and size of ore B is- 6 mm. This may be chosen so as ore A is a dense hard laminated ore and ore B is porous fragile laminated ore. Hardness or BWI of ore A is around 14.83 kWh/t while BWI of ore B may be around 7.71 kWh/t. Ore A and ore B were obtained from Joda region in Odisha. Micrographs of ore A and ore B are as duplicated in figures 7a and 7b respectively. The iron ore blend prepared were grounded for about 15 min in lab scale ball mill and product obtain were screened at 0.5 mm mess. -0.5 mm sized power has been considered as ground product while +0.5 mm sized power has been considered as unground material.

Series 3: Size of ore A is +6 mm to -10 mm and size of ore B is- 6 mm. This may be chosen so as ore A is a dense hard laminated ore and ore B is a porous fragile laminated ore. Hardness or BWI of ore A is around 14.83 kWh/t while BWI of ore B is around 7.71 kWh/t. Ore A and ore B were obtained from Joda region in Odisha. Micrographs of ore A and ore B are as duplicated in figures 7a and 7b respectively. To the iron ore blend of ore A and ore B, 10 wt.% iron ore sinter fines were added. i.e. 90 wt.% iron ore blend (of ore A and ore B) with 10 wt.% iron ore sinter fines. The iron ore blend along with iron ore fines were grounded for 5 min in lab scale ball mill and product obtain were screened at 0.5 mm mesh. -0.5 mm sized powder has been considered as ground product while +0.5 mm sized powder has been considered as unground material.

Blaine surface area and ultra-fines (-7 µm) for 15 iron ore blends i.e. 5 blends in each series are plotted as box plots for studying variation and shown in figures 8 and 9 respectively. Figure 8 clearly shows that with addition of iron ore sinter fines to the iron ore blend containing individual ores with variation in properties, Blaine surface area decreased significantly as well as variation in Blaine also decreased significantly (series 3 vs. series 1). Though decrease in the size of harder ore fraction may also lead to decrease the Blaine surface areas (series 2 vs. series 1), but the decrease in Blaine surface area as well as decrease in variation of Blaine surface area is prominent only for series 3 with 10wt. % iron ore sinter fines.

Similarly, figure 9 clearly indicates that with addition of iron ore sinter fines to the iron ore blends, quantity of ultra-fines also decreased significantly as well as variation in size of ultra-fines also decreased significantly (series 3 vs series 1). Though decrease in the size of harder ore fraction may also lead to decrease in the ultra-fines (series 2 vs series 1), but the decrease in ultra-fines variation may be prominent only for series 3 when 10 wt.% sinter fines.

Case 2: Establishing the effect of iron ore sinter fines addition on Blaine surface area and ultrafine generation at 6 MTPA pellet plant ball mill operation.

In an exemplary embodiment, addition of iron ore sinter fines is tried at commercial pellet plant of Tata Steel in Jamshedpur India, which has a grate area of 4 m (w) X 192 m (L) = 768 m2. The pellet plant contains two separate lines of drying, grinding followed by mixing with each lines having capacity of 550 TPH. Sinter fines were added at 4 wt.% to the iron ore blend along with required flux and fuel.

With the addition of iron ore sinter fines at 4 wt.%, there were a notable changes in the generation of ultra-fines and Blaine surface area values. Figures 10a and 10b depict a graphical representation of trend in Blaine surface area values of both ball mill #1 and #2 respectively during base period and trail period. It is clearly seen that the base period has high Blaine surface area with higher fluctuation as compared to trial period (shaded region). Variation in Blaine surface area for ball mill #1 and # 2 during base period and trial period is shown in figures 11a and 11b respectively. Figures 11a and 11b indicate reduced Blaine surface area and reduced variation in Blaine surface area. Hence, addition of the iron ore sinter fines not only decreases the Blaine surface area but also reduce the variation in Blaine surface area so as to keep the range which is suitable subsequent pelletizing process.

Referring now to figures 12a, 12b and 12c which illustrate the effect of addition of iron ore sinter fines on generation of ultra-fines during grinding. It can be seen clearly that with sinter fines addition ultrafine below 2 µm and 10 µm decreased (shaded regions in figure 12a and 12b respectively). At the same time, coarse fines which is greater than 250 µm in size and detrimental for green and fired pellet quality have not increased (shared region in figure 12c). Hence, addition of the iron ore sinter fines not only decrease the generation of ultra-fines but also reduce the variation in ultra-fines size which is a favorable condition for pelletizing process.

In an embodiment, grinding of iron ore blends with iron ore sinter fines provides optimal ultra-fines and Blaine surface area. Addition of iron ore sinter fines also decrease the variation in generation of ultra-fines and Blaine surface area. The iron ore blend grinding with iron ore sinter fines is favorable conditions for subsequent palletizing process. The present disclosure is thus successful in providing a simple, easy, economic and efficient method of grinding iron ore blends.

Equivalents:

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Referral Numerals

Referral Numerals Description
101-104 Flowchart blocks for method of grinding iron ore blend
101 Charging individual iron ores
102 Charging flux and coal
103 Charging iron ore sinter fines
104 grinding a mixture of iron ore blend, flux and fuel