Process for sintering iron ore

Abstract

A process for sintering iron ore includes the steps of providing iron ore, colloidal silica, and water, combining the iron ore, the colloidal silica, and the water to form a mixture, granulating the mixture to form granules, and sintering the granules to form sintered ore. The present disclosure is further directed to the use of colloidal silica for reducing the amount of dust produced by a sintering process. The present disclosure is further directed to the use of colloidal silica for increasing the strength of sinter in a sintering process. The present disclosure is further directed to the use of colloidal silica for increasing productivity in a sintering process.

Description

PROCESS FOR SINTERING IRON ORECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 579,425, filed August 29,2023.TECHNICAL FIELD

[0002] The present disclosure generally relates to a process for sintering iron ore. More specifically, this disclosure relates to a process for sintering iron ore using colloidal silica. The present disclosure is further directed to the use of colloidal silica for reducing the amount of dust produced by a sintering process. The present disclosure is further directed to the use of colloidal silica for increasing the strength of the sinter in a sintering process. The present disclosure is further directed to the use of colloidal silica for increasing productivity in a sintering process.BACKGROUND

[0003] In the iron ore sintering process, lime (calcium oxide, CaO) is commonly used as a fluxing agent to help remove impurities from the raw materials and to improve the overall efficiency of the process. The sintering process involves agglomerating fine iron ore particles and other materials, such as coke fines and fluxes, into a porous mass known as sinter. This sinter is then heated in a sintering furnace to create a product that can be used in the blast furnace for iron production.

[0004] Much of the iron ore which remains in some of the world's principal iron ore deposits is too fine to serve as a desirable blast furnace feed. Therefore, it must be agglomerated into larger, more useful particles. An important means of effecting such agglomeration is sintering. During the sintering process, the fine ore is heated to such a temperature that, while complete fusion does not occur, the small solid particles in contact with one another adhere and agglomerate into larger particles. While this process is simple in principle, a difficulty has heretofore existed in that the finished sinter often lacks uniformity in its physical and chemical properties and is, therefore, less effective as blast furnace fed than uniform sinter. To this end, various additives including lime have been used.

[0005] Lime plays several important roles in the sintering process. Lime acts as a fluxing agent by combining with impurities and forming slag. This slag helps to separate impurities,such as silica (SiCh) and alumina (AI2O3), from the iron ore, allowing them to be removed more easily during the later stages of iron production. Lime also helps in binding the sinter particles together by forming calcium silicates and calcium aluminate compounds. These compounds create a cohesive structure within the sinter bed, which is important for maintaining the structural integrity of the sinter during the high-temperature sintering process. Lime further contributes to the control of the sintering temperature. Lime has a relatively high melting point (2600 °C) and hence does not melt during sintering process. However, as it fuses during the sintering process, for instance with SiCL and other impurities, it helps to maintain the appropriate temperature range for sintering to occur efficiently by forming lower melting point compounds, for instance, calcium silicate.

[0006] As iron ore is removed from mines with more fine particles, higher lime dosages are required. However, it is not possible to simply continue adding additional lime because there is a specific CaO / SiCh ratio from the sinter that the Blast furnace specifies and the current lime dosage already reaches this limit.

[0007] The lime particles employed in iron ore sintering are not fine and actually quite coarse. They are difficult to handle because they react rapidly with water or CO2 from the atmosphere forming Ca(OH)2 and CaCCL, respectively. Both reactions produce lower-density products, therefore, they are expansive and can crumble the sintering products.

[0008] During the sintering process, various raw materials including iron ore fines, coke fines, fluxes like lime, and sometimes other additives are mixed and granulated to form a feedstock that is charged onto a sintering bed. This feedstock is typically spread over a permeable bed of previously ignited coke, and the whole bed is ignited to initiate the sintering process.

[0009] The sintering furnace is operated at elevated temperatures, typically in the range of about 1,200 to 1,400 degrees Celsius (-2,200 to 2,550 degrees Fahrenheit). As the feedstock materials heat up, they undergo various physical and chemical transformations. Limestone, being a major component of the feedstock (also due to its formation from lime as described above), undergoes thermal decomposition, releasing carbon dioxide gas in the process. This chemical reaction is known as calcination: CaCCL (limestone) —> CaO (quicklime) + CO2.

[0010] The released carbon dioxide gas can carry fine particles of quicklime (unreacted lime) along with it, creating dust in the furnace environment. This dust can become airborne and potentially be carried by the hot gases present in the furnace. Factors such as the particle sizeof the lime, the temperature, the airflow patterns, and the design of the sintering furnace can all influence the formation and dispersion of dust particles.

[0011] In industrial operations, measures are often taken to minimize the formation and dispersion of dust, including optimizing feedstock composition, controlling sintering conditions, and employing dust collection and abatement technologies to mitigate environmental and health impacts associated with dust emissions.

[0012] More specifically, there are generally recognized ways to reduce such dust. Careful selection and preparation of raw materials, including iron ore fines, coke fines, and fluxes like lime, can help minimize the formation of fine dust particles during the sintering process. Using materials with appropriate particle sizes and characteristics can lead to better agglomeration and reduced dust generation.

[0013] Improved agglomeration techniques, such as pelletizing or granulating the raw materials before introducing them into the sintering process, can help reduce the amount of fine particles that can contribute to dust formation.

[0014] Proper moisture control in the sinter mix can also be important for controlling dust emissions. Adding the right amount of moisture to the feedstock materials can improve their granulation and cohesion properties, leading to reduced dust generation.

[0015] Some advanced sintering technologies, such as fluidized bed sintering, can offer better control over the sintering process and reduce dust emissions compared to traditional sintering methods. Moreover, adjusting the sintering temperature and residence time within the sintering furnace can influence the extent of calcination and dust generation. Fine-tuning these parameters can help optimize the sintering process for reduced dust emissions.

[0016] Even further, installing dust collection systems, such as baghouses, electrostatic precipitators, or cyclones, can capture airborne dust particles before they are released into the environment. These systems effectively collect and remove dust from the furnace off-gas, improving air quality and minimizing environmental impact. Furthermore, proper design and control of airflow patterns and gas distribution within the sintering furnace can help prevent the entrainment of dust particles in the hot gases and promote their capture by dust collection systems.

[0017] Maintaining an appropriate permeability of the sinter bed can also be important for even gas distribution and efficient dust capture. Ensuring proper sinter bed structure and porosity can help prevent the escape of dust particles from the bed. Nevertheless, strategies for dust reduction can vary depending on the specific sintering process and facility. Acombination of these measures, along with adherence to environmental regulations and guidelines, has helped to achieve effective dust control and minimize the impact of sintering operations on the environment and the health of workers. Still, these methods are expensive and time-consuming and can be complex in their implementation. Therefore, there remains the opportunity for improvement.

[0018] Other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description of the disclosure and the appended claims, taken in conjunction with the accompanying drawings and the background of the disclosure.SUMMARY

[0019] This disclosure provides a process for sintering iron ore. The process includes the steps of providing iron ore, colloidal silica, and water, combining the iron ore, the colloidal silica, and the water to form a mixture, granulating the mixture to form granules, and sintering the granules to form sintered ore. This disclosure further provides a use of colloidal silica for reducing the amount of dust produced by a sintering process. This disclosure further provides a use of colloidal silica for increasing the strength of the sinter in a sintering process. This disclosure further provides a use of colloidal silica for increasing productivity in a sintering process. This disclosure further provides a use of colloidal silica for reducing the sintering temperature in a sintering process. This disclosure further provides a use of colloidal silica for preparing sinter from ore fines. This disclosure further provides a use of colloidal silica for decreasing the temperature in a sintering process. This disclosure further provides a use of colloidal silica for lowering the CO2 emissions in a sintering process.BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present disclosure will hereinafter be described in conjunction with the following drawing Figs, wherein like numerals denote like elements, and FIG. l is a process diagram of one embodiment of this disclosure.

[0021] FIG. 2 is a plot of the wet apparent density vs. the amount of silica solids for various test samples as described herein.

[0022] FIG. 3 is a plot of the dry apparent density vs. the amount of silica solids for various test samples as described herein.

[0023] FIG. 4 shows photographs of various test samples after drying at 120°C (on the left) and after firing at 1100°C (on the right).

[0024] FIG. 5 shows a plot of cold compression strength of various test samples after drying at 120°C as described herein vs. the amount of silica solids added.

[0025] FIG. 6 shows a plot of cold compression strength of various test samples after firing at 1100°C as described herein vs. the amount of silica solids added.

[0026] FIG. 7 is a diagram summarizing for samples containing a particular colloidal silica the effect of the amount of solid silica on the cold compression strength for different sintering temperatures.

[0027] FIG. 8 is a diagram summarizing for samples containing a particular colloidal silica the effect of the amount of solid silica on the percentual mass loss of the samples as fine powder during a drumming test for different sintering temperatures.

[0028] FIG. 9 is a plot comparing the wet apparent density vs. the amount of silica solids for colloidal silica samples and microsilica samples.

[0029] FIG. 10 is a plot comparing the dry apparent density vs. the amount of silica solids for colloidal silica samples and microsilica samples.

[0030] FIG. 11 is a diagram summarizing for samples containing a particular microsilica the effect of the amount of solid silica on the cold compression strength for different sintering temperatures.

[0031] FIG. 12 is a diagram summarizing for samples containing a particular microsilica the effect of the amount of solid silica on the percentual mass loss of the samples as a fine powder during a drumming test for different sintering temperatures.DETAILED DESCRIPTION

[0032] The following detailed description is merely exemplary in nature and is not intended to limit the current composition. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

[0033] Embodiments of the present disclosure are generally directed to processes for sintering iron ore and compositions used therein. For the sake of brevity, conventional techniques related to sintering may not be described in detail herein. Moreover, the various tasks and process steps described herein may be incorporated into a more comprehensive procedure or process having additional steps or functionality not described in detail herein. In particular, various steps in sintering iron ore are well-known and so, in the interest of brevity, many conventional steps will only be described briefly herein or will be omitted entirely without providing the well-known process details.

[0034] In this disclosure, the terminology “about” can describe values ± 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10%, in various embodiments. Moreover, it is contemplated that, in various non-limiting embodiments, it is to be appreciated that all numerical values as provided herein, save for the actual examples, are approximate values with endpoints or particular values intended to be read as “about” or “approximately” the value as recited. It is also contemplated that all isomers and chiral options for each compound described herein are hereby expressly contemplated for use herein in various non-limiting embodiments.

[0035] Throughout this disclosure, the terminology percent "actives" is well recognized in the art and means the percent amount of active or actual compound or molecule present as compared to, for example, the total weight of a diluted solution of a solvent and such a compound. Some compounds, such as a solvent, are not described relative to a percent actives because it is well known to be approximately 100% actives. Any one or more of the values described herein may be alternatively described as percent actives as would be understood by the skilled person.

[0036] In various embodiments, the terminology “free of’ describes embodiments that include less than about 5, 4, 3, 2, 1, 0.5, or 0.1, weight percent (or weight percent actives) of the compound or element at issue using an appropriate weight basis as would be understood by one of skill in the art. In other embodiments, the terminology “free of’ describes embodiments that have zero weight percent of the compound or element at issue.

[0037] The term “dust” as used herein describes extremely fine, dusty particles. As the skilled person will appreciate, ore dust is different from ore fines. While ore fines particles are actually quite coarse particles at least in the cm-range, i.e. larger than 1 cm in its maximum diameter, such as a DnlO or DvlO of above 1 cm or even above 2 cm, dust particles are at a maximum in the lower mm-range, i.e. dust particles usually have a maximum diameter of 1 mm, preferably a maximum diameter of less than 0.8 mm, such as less than 0.5 mm, less than 0.3 mm, less than 0.1 mm, less than 0.05 mm, less than 0.02 mm, or even less than 0.01 mm, such as a Dn90 or Dv90 of 1 mm, preferably a maximum diameter of less than 0.8 mm, such as less than 0.5 mm, less than 0.3 mm, less than 0.1 mm, less than 0.05 mm, less than 0.02 mm, or even less than 0.01 mm.

[0038] The terminology “consists essentially of’ may describe various non-limiting embodiments that are free of one or more optional compounds described herein and / or free of one or more additives, additional compounds, etc.

[0039] The compositions disclosed herein may suitably comprise, consist of, or consist essentially of the components, elements, and process delineations described herein. The embodiments illustratively disclosed herein suitably may be practiced in the absence of any element which is not specifically disclosed herein.Production of Sintered Iron Ore

[0040] Generally speaking, production of sintered iron ore used as a raw material in ironmaking can be formed using a method that includes mixing and granulation with raw material tanks and a mixer, such as a drum mixer, and sintering with an ore feed hopper and a sintering machine. The sintering raw material tends to include iron ore, such as iron ore powder or even iron ore dust having a particle size (e.g. Dn50 or Dv50) of about 10 mm or less, such as 8 mm or less, 5 mm or less, 3 mm or less, 1 mm or less, or even 0.5 mm or less, or even an Dn90 or Dv90 of about 10 mm or less, such as 8 mm or less, 5 mm or less, 3 mm or less, 1 mm or less, 0.5 mm or less, 0.3 mm or less, 0.1 mm or less, 0.05 mm or less, 0.02 mm or less, or even 0.01 mm or less, auxiliary materials, such as lime stone, quick lime, silica rock and serpentine; and solid fuel, such as coke. These components can be stored in raw material tanks and then charged into a mixer, such as a drum mixer, at a predetermined composition. Then, a desired amount of water can be added thereto. The components can then be combined or mixed and optionally granulated in the mixer. The granules are then optionally packed or arranged for a sintering machine at a predetermined height by an ore feed hopper. Moreover, solid fuel can then be added to a top surface of the packaged / arranged granules and ignited. After ignition, burning of the solid fuel can be continued while air is moved downward and the sintering raw material is sintered by a combustion heat to form a sinter cake. This sinter cake can then be pulverized and ground or otherwise filtered to achieve a desired particle size of iron ore.

[0041] Sintered iron ore requires high strength as a raw material in ironmaking. This minimizes not only reduction in production yield due to pulverization of sintered ore in the course of charging into a blast furnace but also deterioration in blast furnace operating conditions due to reduction in air flowing-through property through a blast furnace from pulverization of sintered ore in the furnace.

[0042] To improve the strength of the sintered iron ore, a high temperature is typically generated in the granules by combustion of solid fuel in the granules. This high temperature is typically maintained so that a sufficient amount of a melt for sintering of iron ore powder is formed in a uniform manner in the bulk of the sintering raw material. The melt is typicallyformed by a slag reaction between iron ore and auxiliary materials wherein the melt is typically a multi-component system that includes calcium-ferrite. With the melt, liquid phase sintering of iron ore powder is affected and after cooling, bonds between particles of the iron ore powder are formed.

[0043] It is generally known that the strength of a sintered iron ore is increased either when a bond is wide or when bonds are constructed in a network structure. For this reason, it has been understood that the strength of a sintered iron ore can be improved when a sufficient amount of a melt for sintering iron ore powder is produced to extend the width of a bond and in addition, the melt is produced in a uniform manner in the bulk of the sintering raw material to achieve a uniform network structure of bonds.

[0044] Reduction of airflow resistance of the granules has also been targeted in order that a high temperature is generated and maintained by the combustion of solid fuel included in the granules as described above. With the reduced air flowing-through resistance, much of the air can be passed through and the solid fuel can be efficiently burned in a uniform manner, thereby enabling a high temperature at which a high strength sintered iron ore can be produced (sintered) to be achieved and maintained.

[0045] In the past, in order to reduce air flow resistance, a sintering raw material was prepared so as to be coarse granules by either making primary particles of the sintering raw material larger in size or promoting a granulating nature of the sintering raw material and thereby improving a degree of agglomeration.

[0046] In order to promote the granulating nature of the sintering raw material, a binder, such as quick lime, bentonite, cement or cement clinker in powder, can be added to the raw material. However, where too much binder is added, production costs increase along with production problems, especially in blast furnaces.

[0047] Accordingly, this disclosure provides in a first aspect a process for sintering iron ore including the steps of providing iron ore, colloidal silica, and water, combining the iron ore, the colloidal silica, and the water to form a mixture, granulating the mixture to form granules, and sintering the granules to form sintered ore. One embodiment of this process is shown in FIG. 1.Providing the Iron Ore, the Colloidal Silica, and the Water (Step A.)

[0048] The step A. of providing the iron ore is not particularly limited. In various embodiments, the iron ore comprises a powder, for instance in the diameter range of 1-10 mm. In some embodiments, the iron ore is provided as a powder. In some embodiments, theiron ore comprises dust. In some embodiments, the iron ore is provided as dust. The powder or dust may have any particle size. In various embodiments, the particle size is as described above. The particle size may be measured using any technique in the art including use of sieves with different openings, or laser diffraction (such as used by a Malvern Mastersizer). The particle size may be further described as DvlO, DnlO, Dv50, Dn50, Dv90, Dn90, or any Dv or Dn between 1 and 100.

[0049] Similarly, the steps of providing the colloidal silica and the water are not particularly limited. The iron ore, colloidal silica, and water can be provided batch wise or continuously and in one or more parts or in whole amounts. Moreover, any one or more of the iron ore, the colloidal silica, and the water may be provided with any of the other of the iron ore, the colloidal silica, and the water. Moreover, the water may be provided separately and independently from the components or may be part of the components themselves, such as part of the colloidal silica.Combining The Iron Ore, The Colloidal Silica, and The Water To Form a Mixture (Step B.)

[0050] Just as described above, in a step B. the iron ore, the colloidal silica, and the water may be combined continuously or batchwise and in one or more parts or in whole amounts. Moreover, any one or more of the iron ore, the colloidal silica, and the water may be combined with any of the other of the iron ore, the colloidal silica, and the water. Moreover, the water may be combined separately and independently from the components or may be part of the components themselves, such as part of the colloidal silica. The step of combining forms a mixture. In an embodiment, the colloidal silica and the water are combined first, and the combined mixture of colloidal silica and water is than combined with the iron ore. In another embodiment, the colloidal silica and the water are added separately but at the same time to the iron ore.

[0051] Albeit the amount of the iron ore present in the mixture is not particularly limited, typically, in the mixture, the amount of iron ore present is from about 50 to 96.99 wt.%, such as from 60 to 96.99 wt.%, from 70 to 96.99 wt.%, from 75 to 94.99 wt.%; from 80 to 93.99 wt.%, from 80 to 91.99 wt.%, from 82 to 89.99 wt.%, or from 84 to 86.99 wt.%, the wt.% in each case being based on a total weight of the mixture. Albeit the amount of the colloidal silica present in the mixture is not particularly limited, typically, the amount of the colloidal silica present is from is from about 0.01 to 10 wt.%, such as from 0.02 to 8 wt.%, from 0.03 to 5 wt.%, from 0.04 to 3 wt.%, from 0.05 to 1 wt.%, from 0.07 to 0.8 wt.%, or from 0.1 to 0.5 wt.%, the wt.% in each case is based on total weight of the mixture. Albeit the amount ofwater present in the mixture is not particularly limited, typically, the amount of water present is from about 3 to 20 wt.%, such as from 4 to 18 wt.%, from 5 to 15 wt.%, or from 8 to 12 wt.%, the wt.% in each case being based on the total weight of the mixture. Moreover, the mixture may include, or be free from, any one or more conventional additives such as fluxes, coke, solid waste, etc. In various additional non-limiting embodiments, all values and ranges of values, both whole and fractional, including and between those described above are hereby expressly contemplated for use herein.

[0052] In various embodiments, the mixture has a melting point of less than about 1500, 1400, 1300, 1200, 1100, 1000, or 900 °C. Hence, in some embodiments, the mixture is sintered at a processing temperature of less than about 1500, 1400, 1300, 1200, 1100, 1000, or 900 °C, such as at about 1500, 1400, 1300, 1200, 1100, 1000, or 900 °C. Since the mixture if formed with water, particles of the iron ore may be coated with silica particles. These coated particles may then be dried in a later step using any method known in the art. Without intending to be bound by theory, it is contemplated that the silica particles may react with the iron ore particles at temperature to form a melt, with the result that melt formation through a slag reaction between the iron ore powder and the colloidal silica can be accelerated in the presence of the melt such that a sufficient amount of a melt for sintering the iron ore powder is additionally produced, which enables the strength of a sintered iron ore to be improved. In various additional non-limiting embodiments, all values and ranges of values, both whole and fractional, including and between those described above are hereby expressly contemplated for use herein.

[0053] In other embodiments, it is contemplated that migration (diffusion) of components of the iron ore powder and the silica particles may become easier with the help of the melt which may accelerate the production of an additional melt through a slag reaction between the iron ore powder and the silica particles, whereby, it is estimated, sintering of iron ore powder is sufficiently progressed.

[0054] It is further contemplated that a component of a melt produced by the aforementioned reaction can reduce the formation temperature of the additional melt through a slag reaction. As a result, more of the melt than in a conventional case of sintered iron ore could be produced, thereby enabling formation of a wider bond contributable to increased strength of a sintered iron ore.

[0055] A melting point of the melt can decrease as a result of a slag reaction between the iron ore powder and the silica particles. Moreover, the viscosity of the melt may also decrease. Even further, it may be easier for the melt to migrate over the surfaces of particles of the iron ore powder. As a result, the melt may be able to spread over the surfaces of particles of the iron ore powder in a uniform distribution, which makes it possible for a network structure of bonds contributing to the increased strength of a sintered iron ore to be formed with spatial uniformity.Granulating The Mixture To Form Granules (Step C.)

[0056] The method also includes the step C: of granulating the mixture to form granules. The step of granulating is not particularly limited and may be accomplished using any techniques known in the art.

[0057] Granulation is a process used to agglomerate fine particles into larger, more cohesive granules or pellets. In the context of iron ore processing, granulation is often employed to create feedstock materials that are more suitable for downstream processes like sintering and pelletizing. The granulation process can involve one or more steps to transform fine iron ore particles into well-defined granules.

[0058] In one embodiment, granulation involves adding a controlled amount of moisture to the fine iron ore particles. Moisture acts as a binding agent, helping to promote the formation of cohesive granules.

[0059] In another embodiment, moistened iron ore particles are mixed thoroughly to ensure an even distribution of moisture throughout the material. This helps in achieving consistent granule properties and preventing the formation of dry or wet spots.

[0060] In a further embodiment, the moistened particles are brought together to form larger granules. This can be achieved through various techniques such as tumbling, pan granulation, extension, pressure agglomeration, etc. In tumbling, the moistened particles are tumbled in a drum or other agitating equipment. The tumbling action causes the particles to adhere to each other, forming granules. In pan granulation, the particles are placed in a pan or disc granulator, where they are subjected to rotating blades or rollers that compress and shape them into granules. In extrusion granulation, the moistened particles are forced through a die or screen to produce cylindrical or other shaped granules. In pressure agglomeration, high pressure is applied to the particles causing them to compact and form granules.

[0061] During agglomeration, the size of the granules is controlled by adjusting factors like moisture content, agitation intensity, and equipment parameters. The aim is to produce granules of a specific size range that is suitable for the intended application.

[0062] After granulation, the formed granules often include excess moisture. Drying is typically performed to remove this moisture and stabilize the granules. The drying process can take place in various types of drying equipment, such as rotary dryers or fluidized bed dryers.

[0063] Once the granules are dried, they may undergo screening to remove any oversized or undersized particles. This helps to achieve a uniform size distribution of granules. The resulting granules tend to be more cohesive, have improved handling properties, and can be more easily processed in subsequent steps of iron ore production, such as sintering or pelletizing. Granulation helps to mitigate issues related to dust generation, material handling, and the segregation of fine particles, thereby enhancing the overall efficiency of iron ore processing.Sintering The Granules To Form Sintered Ore (Step D.)

[0064] The method also includes the step D. of sintering the granules to form sintered ore (in the following also called “sinter”). The step of sintering is also not particularly limited and may be accomplished using any techniques known in the art.

[0065] Sintering is a high-temperature process used to convert iron ore fines and other materials into a porous mass known as sinter. The sintering process typically involves the agglomeration of iron ore granules, which are created through a prior granulation process, followed by heating to a temperature that causes the particles to bond together and form a cohesive structure.

[0066] In one embodiment, sintering involves the preparation of the granules, e.g. as described above.

[0067] In another embodiment, sintering involves sinter bed formation wherein the prepared iron ore granules are spread evenly over a sintering bed, which is typically a permeable layer of previously ignited coke fines. The coke layer provides the necessary heat for the sintering process and also serves as a structural support for the sinter bed.

[0068] In another embodiment, sintering involves ignition wherein the sintering bed, including the layer of iron ore granules, is ignited. The ignition process typically involves introducing a controlled amount of ignition fuel, such as natural gas or coke breeze, and igniting it. The ignited fuel generates the heat required for the sintering reactions to occur.

[0069] During sintering, several reactions take place. One reaction is calcination wherein if any unreacted limestone (CaCOs) is present in the iron ore granules, it undergoes calcination, releasing carbon dioxide gas. In other reactions, various minerals present in the iron ore granules undergo thermal decomposition, releasing gases and generating a porous structure within the granules. In still other reactions, the elevated temperature causes certain minerals to melt and form a liquid phase. This liquid phase acts as a binding material, helping to bond the granules together. Moreover, as the granules come into contact with each other and the liquid phase, they start to bond together. This creates a cohesive structure within the sinter bed.

[0070] In still other embodiments, the liquid phase created during the sintering reactions wets the surfaces of the granules and acts as a bridge between them. As the temperature continues to rise, the liquid phase solidifies, further strengthening the bonds between granules.

[0071] The temperature of the sintering step (Step D) as such is not particularly limited. However, as already described above, in some embodiments, the mixture is sintered at a processing temperature of less than about 1500 °C, preferably less than about 1400 °C, such as less than about 1300 °C, less than about 1200 °C, less than about 1100 °C, less than about 1000 °C, or even less than about 900 °C. In some particularly preferred embodiments, the mixture is sintered at a processing temperature of about 1500 °C, such as of about 1400 °C, of about 1300 °C, of about 1200 °C, of about 1100 °C, of about 1000 °C, or even of about 900 °C.

[0072] After a desired level of sintering is achieved, the sinter bed is then allowed to cool down. During this cooling phase, the sinter solidifies and forms a porous mass with a defined structure. Once the sinter bed has cooled, the sintered product is removed from the furnace. The sinter is then broken down into smaller pieces suitable for transportation and further processing.

[0073] The resulting sinter is typically a porous material with improved physical and chemical properties compared to the original iron ore granules. The sinter can be used as a feedstock material in blast furnaces for the production of iron and steel. The porous structure of the sinter allows for better gas flow and chemical reactions within the blast furnace, contributing to efficient iron production.

[0074] The resulting sinter can in a further step E. be crushed into pieces of appropriate size by using any commonly known crushing techniques, and in a further step F. be fed into a blast furnace. The advantage of the process of the present disclosure is that during step E of crushing dust and fines formation is efficiently suppressed so that merely the crushed pieces of appropriate size but no dust or fines are fed into the blast furnace and can be properly processed without any disadvantages connected with dust formation as set forth above. The appropriate size of the crushed pieces is not particularly limited but is selected by the skilled person such that the crushed pieces are heavy enough to not be blown away in the blast furnace, i.e. to not form dust. In other words, the skilled person can select the size of the crushed particles based on the specific technical setup of a particular blast furnace as well as the density of a particular resulting sinter. For instance, a particle size (e.g. Dn50 or Dv50) of the crushed resulting sinter may be 10 mm or more, such as 20 mm or more, such as 50 mm or more, 100 mm or more, 200 mm or more, 300 mm or more, or even 500 mm or more. In various additional non-limiting embodiments, all values and ranges of values, both whole and fractional, including and between those described above are hereby expressly contemplated for use herein.Iron Ore

[0075] Referring now to the iron ore itself, iron ore is a heterogeneous mixture of various minerals and rock fragments. The different types of iron ore particles can be classified based on their mineral composition, physical characteristics, and origin. The main types of iron ore particles include hematite, magnetite, limonite, geothite, siderite, taconite, itabirite, oolitic iron ore, and pisolitic iron ore.

[0076] Hematite (Fe20s) is one of the most abundant and widely distributed iron oxide minerals. It is often the primary iron-bearing mineral in iron ore deposits. Hematite ore typically has a reddish-brown color and a metallic luster. It can vary in texture from finegrained to coarser, and it is often found as massive ore deposits or as individual crystals.

[0077] Magnetite (FesCU) is another common iron oxide mineral. It is known for its strong magnetic properties and black color. Magnetite ore is often found in igneous and metamorphic rock formations. It usually has a fine-grained texture and can be easily recognized by its magnetic attraction.

[0078] Limonite (FeO(OH)-nH2O) is a hydrated iron oxide mineral that can vary in color from yellow to brown. It often forms as a weathering product of other iron minerals and canbe found in sedimentary rocks. Limonite ore is typically soft and friable, and it often contains impurities such as clay minerals.

[0079] Goethite (FeO(OH)) is another hydrated iron oxide mineral that is closely related to limonite. It has a yellowish to reddish-brown color and is often found in soil and weathered rock formations. Goethite can occur as individual crystals or as earthy aggregates.

[0080] Siderite (FeCCL) is an iron carbonate mineral that can vary in color from brown to gray or even green. It is less common than hematite and magnetite and is often associated with sedimentary iron ore deposits.

[0081] Taconite is a type of low-grade iron ore that is often found in banded iron formations. It contains a mixture of minerals, including hematite, magnetite, and chert. Taconite needs to undergo beneficiation processes to extract the iron content for use in steelmaking.

[0082] Itabirite is a type of iron ore found in Brazil, particularly in the Quadrilatero Ferrifero region. It is composed of alternating layers of hematite and chert, giving it a banded appearance. Itabirite ores are often beneficiated to improve their iron content.

[0083] Oolitic Iron Ore includes small, rounded particles called ooids. These particles are usually composed of iron minerals, typically hematite or goethite, and are often cemented together with minerals like chert.

[0084] Pisolitic Iron Ore includes small, rounded concretions called pisoliths. Like ooids, these concretions are often composed of iron minerals and other materials, and they can be found in various sedimentary environments.

[0085] Any one or more of these types of iron ore can be utilized in this disclosure.Sol Including Colloidal Silica

[0086] Referring now to the colloidal silica, the silica may be described as a silica sol including colloidal silica. Herein, the terminology “sol” typically describes a stable dispersion of colloidal silica (SiCL) particles in a liquid, such as water. The silica sol may also be described as a colloidal silica dispersion.

[0087] The sol includes colloidal silica, e.g. silica particles. In various embodiments, the terms “silica sol” and “colloidal silica” have the same meaning. In other embodiments, the term “colloidal silica” refers to a dispersion comprising about 1 to about 50 wt% silica particles dispersed in an aqueous medium. The aqueous medium may comprise organic solvent, but where it does so it typically comprises less than 10 wt% organic solvent. If an organic solvent is present, the aqueous medium more typically includes no more than about 5wt% organic solvent. Typical organic solvents, when present, are water-miscible, for example being chosen from one or more of C1-4 alkyl alcohols, C1-4 aldehydes, C1-4 ketones, C1-4 carboxylic acids their C1-4 alkyl esters, and combinations thereof. In various additional nonlimiting embodiments, all values and ranges of values, both whole and fractional, including and between those described above are hereby expressly contemplated for use herein.

[0088] It is contemplated that the sol may include one or more individual types of colloidal silica. In such embodiments, at least one is of the type described herein and one or more additional types may be of the type described herein or of the type not described herein or may be a mixture of both. Moreover, it is contemplated that the composition as a whole may include one or more independent sols. In such embodiments, at least one is of the type described herein and one or more additional types may be of the type described herein or of the type not described herein or may be a mixture of both.

[0089] The sol itself is not particularly limited and can have a SiCh content of from about 5 to about 60 wt% depending on particle size. In various embodiments, this content is from about 10 to about 55, about 15 to about 50, about 20 to about 45, about 25 to about 40, or about 30 to about 35, weight % based on a total weight of the sol. The sol may or may not be diluted for use herein. In various additional non-limiting embodiments, all values and ranges of values, both whole and fractional, including and between those described above are hereby expressly contemplated for use herein.

[0090] Aqueous silica sols can be acidic, having a pH below 7, such as pH 2-4, neutral having a pH of around 7 or basic, having a pH of more than 7, such as from about 7 to about 11, preferably from about 8.0 to about 11.0, for example from about 8.5 to about 10.5. In a preferred embodiment, the aqueous silica sols have a basic pH. Other optional components of such sols include the presence of alkali metals, typically one or more of lithium, sodium, and potassium. Typically sodium is the sole or predominant alkali metal. The alkali metals can be derived from soluble silicate solutions (e.g. water glass) that can be used to make the colloidal silica using conventional processes. Examples of suitable aqueous alkali metal silicates or water glass that can be used to make aqueous silica sols include lithium, sodium and potassium silicates, typically sodium silicate. In various additional non-limiting embodiments, all values and ranges of values, both whole and fractional, including and between those described above are hereby expressly contemplated for use herein.

[0091] The silica particles are typically amorphous nanoparticles, and most typically have a particle diameter of from about 2 to about 170 nm. In various embodiments, the colloidalsilica particles typically have an average particle diameter of from about 2 to about 100 nm or from about 3 to about 75 nm. In further embodiments, the particle diameter is from about 4 to about 50 nm, from about 5 to about 30 nm or from about 7 to about 25 nm. In other embodiments, the particle diameter is from about 5 to about 25, about 10 to about 20, about 10 to about 15, etc. In various additional non-limiting embodiments, all values and ranges of values, both whole and fractional, including and between those described above are hereby expressly contemplated for use herein.

[0092] The particle diameter can be calculated from the titrated specific surface area using a method described in "The Chemistry of Silica", by Iler, K. Ralph, page 465, John Wiley & Sons (1979). Based on the assumption that the silica particles have a density of 2.2 g.cm'3, and that all particles are of the same size, have a smooth surface area, and are spherical, then the particle diameter (PD) can be calculated from Equation 1 : PD (nm) = 2727 / Surface Area (m2.g-1) Equation 1

[0093] Other ways of measuring average particle diameters include ES-DMA (electro- spray differential mobility analysis), CLS (centrifugal liquid analysis), SEM (scanning electron microscopy) and TEM (transmission electron microscopy).

[0094] In other embodiments, e.g. for unmodified colloidal silica, the colloidal silica has an S value of from about 20 to about 95 %, for example from about 30% to about 90% or from about 50 to about 85% The S-value is measured and calculated as described by Iler & Dalton (Iler & Dalton; J. Phys. Chem. 60(1956), 955-957). The S-value indicates a degree of aggregate or microgel formation and a lower S-value is indicative of a higher degree of aggregation. In various additional non-limiting embodiments, all values and ranges of values, both whole and fractional, including and between those described above are hereby expressly contemplated for use herein.

[0095] In various embodiments, the colloidal silica is made from particle growth from a soluble silicate or a polysilicic acid solution and is not prepared by creating a dispersion from a solid form of silica nanoparticle. For example, in some embodiments, the colloidal silica is not derived from solid forms of silica such as amorphous forms of fumed silica, silica fume, and precipitated silica.Optionally, the colloidal silica is not derived from crystalline forms of silica, such as microquartz or nano-quartz, which suffer the additional disadvantage of potential health risks. Soluble silicate-derived colloidal silicas tend to have less aggregation of the silica particles compared to dispersions made from solid forms of silica. This is because, ingeneral, solid forms of silica nanoparticles tend to be in the form of agglomerates of the primary nanoparticles, and it is not usually possible to disperse such silicas to create a colloidal silica comprising predominantly the discrete primary particles because larger agglomerates tend to remain. The silica particles in such colloidal silicas therefore tend to settle (precipitate) relatively rapidly. In contrast, colloidal silicas made from particle growth from a soluble silicate or a polysilicic acid solution do not include such large silica agglomerates. They tend to be stable and do not typically noticeably gel or precipitate for many months, typically for greater than 12 months.

[0096] In various embodiments, the colloidal silica is made by converting soluble alkali metal silicate to polysilicic acid (with a pH typically of from about 1 to about 3) by ion exchange or treatment with acid, and raising the pH to about 7 or more, typically about 8 to about 11, for example about 9 to about 10.5, using a basic alkali metal salt such as alkali metal hydroxide or alkali metal silicate. The content of alkali metals in the starting silica sol can be of from about 0.1 to about 5.0 wt%, expressed as alkali metal oxide. In some embodiments, this content is from about 0.2 to about 3.0 wt%. In other embodiments, the silica concentration in the colloidal silica is from about 1 to about 50 wt%, from about 1 to about 40 wt%, from about 2 to about 35 wt% or from about 3 to about 30 wt%. As used here, silica concentrations are typically expressed as SiCh. A typical minimum concentration is about 5 wt%, and most typical ranges are therefore about 5 to about 50 wt%, and more typically about 5 to about 40 wt%, for example about 5 to about 35 wt% or about 5 to about 30 wt%. In various additional non-limiting embodiments, all values and ranges of values, both whole and fractional, including and between those described above are hereby expressly contemplated for use herein.

[0097] In various embodiments, the colloidal silica particles typically have a surface area of from about 30 to about 1500 m2g-1, for example of from about 30 to about 1200 m2g-1, from about 30 to about 1000 m2g’1, from about 40 to about 700 m2g’1, such as of from about 60 to about 550 m2g'1or from about 60 to about 500 m2g-1, and more typically from about 90 to about 400 m2g’1, such as from about 100 to about 400 m2g'1and most typically from about 120 to about 250 m2g-1, such as from about 130 to about 250 m2g-1. The specific surface area of colloidal silica particles in a silica sol can be calculated from NaOH titration following the method of Sears (Sears; Anal. Chem., 1956, 28(12), 1981-1983). In various additional non-limiting embodiments, all values and ranges of values, both whole andfractional, including and between those described above are hereby expressly contemplated for use herein.

[0098] The density of the silica sol is at least in part dependent on the silica content, and is typically of from about 1.01 to about 1.45 g em'3, and typically of from about 1.01 to about 1.30 g em'3. As an example, a silica sol of density 1.2 g em'3has typically a silica content of 30 wt.-% SiCh while a silica sol of density 1.4 g em'3has typically a silica content of 50 wt.- % SiCh. Density can be determined using ASTM D4052-18a. In various additional nonlimiting embodiments, all values and ranges of values, both whole and fractional, including and between those described above are hereby expressly contemplated for use herein.

[0099] The viscosity of the silica sol is typically less than about 40, 35, 30, 25, or 20, 15, 10, or 5 cP, measured at about 20°C. Viscosities of silica sols, including those described herein, can be measured using a conventional rotational viscometer. A method that can be used is ASTM D4016-14. In various additional non-limiting embodiments, all values and ranges of values, both whole and fractional, including and between those described above are hereby expressly contemplated for use herein.

[0100] In aqueous systems, the colloidal silica particles can be dispersed in the presence of stabilizing cations, which can be chosen from alkali metals (e.g. K+, Na+, Li+), ammonium (NH4+), organic cations, quaternary amino, tertiary amino, secondary amino, and primary amino, or mixtures thereof. Typically, they are selected from alkali metals and ammonium. Examples of sols that can be used as starting aqueous silica sols include silica sols marketed under the name Levasil™ from Nouryon Chemicals International B. V.

[0101] In exemplary embodiments, the colloidal silica particles can be alkali metal stabilized colloidal silica, such as preferably sodium stabilized colloidal silica, with a solid content of above 5 wt.%, preferably above 15 wt.%, and more preferably above 30 wt.% the wt.% in each case based on the colloidal silica sol. In some embodiments, the colloidal silica particles can be alkali metal stabilized colloidal silica, such as preferably sodium stabilized colloidal silica, with a solid content of between 5 and 60 wt.%, such as between 5 and 50 wt.%, between 15 and 50 wt.%, between above 30 and 50 wt.%, such as between 31 and 50 wt.%, between 35 and 45 wt.%, or between 38 and 42 wt.%, typically about 40wt%, the wt.% in each case based on the colloidal silica sol, and further preferably having a surface area of from 80-1100 m2 / g, such as from 100 to 800 m2 / g, from 120 to 500, from 150 to 300 m2 / g, from 200 and 250 m2 / g, or from 210 to 240 m2 / g. In a particularly exemplary embodiment, the colloidal silica has a solid content between 15-40 w% and a surface area of 130-500 m2 / g.In further exemplary embodiments, the colloidal silica of the exemplary embodiments can rather than being sodium stabilized be modified with aluminate, silane, or other counter ions, such as potassium (K+) and ammonium (NH4 ). In various additional non-limiting embodiments, all values and ranges of values, both whole and fractional, including and between those described above are hereby expressly contemplated for use herein.

[0102] It is contemplated that the utilization of the colloidal silica can reduce an amount of dust produced by the sintering process. Moreover, the utilization of colloidal silica enables use of iron ore of less quality from the mines, i.e. iron ore which contains already high amounts of dust and fines. Even further, due to the reduction of dust formation in the sintering process, the sintering process of the present invention has overall a higher productivity. This is beneficial from an environmental as well as economical viewpoint. Even further, the sintering process of the present invention increases the strength of sinter in sintering process.

[0103] According to another aspect, the present disclosure is directed to the use of colloidal silica for reducing an amount of dust produced by a sintering process. In this regard, the colloidal silica and the sintering process may be the same as already described above in the context of the process of the present disclosure.

[0104] According to another aspect, the present disclosure is directed to the use of colloidal silica for increasing strength of sinter in a sintering process. In this regard, the colloidal silica and the sintering process may be the same as already described above in the context of the process of the present disclosure.

[0105] According to another aspect, the present disclosure is further directed to the use of colloidal silica for increasing productivity in a sintering process. In this regard, the colloidal silica and the sintering process may be the same as already described above in the context of the process of the present disclosure.Additional Embodiments

[0106] Nowadays, sintering ore processes considers the mixing of many different raw materials like sinter iron ore, coke, lime, limestone, water, etc., which are heated at temperatures above 1200°C and, then cooled and crushed to the right size before transported to the blast furnace. This sinter iron ore needs to present high mechanical strength as well as suitable chemical composition to withstand the Blast furnace conditions. Fines and ultrafine particles of sinter are typically released during transportation from the sintering process to the blast furnace, resulting in high dust generation. Higher mechanical strength of the sinter ironore is also desirable to withstand all the blast furnace severe conditions. Additionally, the quality of the iron ore coming from the mines is also decreasing when related to the particle size distribution (higher fines particles coming from the mines) and the need of a more sustainable technology binder that can reduce the CO2 footprint was also requested. The improved retention of fines and increase strength results in an improved productivity in the sintering plant. Therefore, this disclosure provides use of colloidal silica as high temperature binder aiming to increase the sinter iron ore mechanical strength, act as binder for sinter the fine / ultra fine particles as well as promote the possibility of reducing the firing temperature or reduce its firing time. The present disclosure is further directed to the use of colloidal silica for decreasing the temperature in a sintering process. The present disclosure is further directed to the use of colloidal silica for lowering the CO2 emissions in a sintering process

[0107] In various embodiments, the colloidal silica dosage can vary from greater than about 0 up to about 10% in weight, e.g. from greater than about 0 up to about 2 wt% or from about 0.05 to about 1 wt%. It is theorized that colloidal silica increases the sinter-fired mechanical resistance and also reduces dust generation and energy consumption of the furnace.

[0108] In further embodiments, the colloidal silica is sodium stabilized colloidal silica with a solid content of about 40wt% and a surface area of from about 200 to about 250 m2 / g. In various embodiments, colloidal silica having a solids content of from about to about 50 wt% and a surface area of from about 80 to about 1100 m2 / g can be used. In further embodiments, the colloidal silica has a solids content of from about 15 to about 40w% and a surface area of from about 130 to about 500 m2 / g. Moreover, in still other embodiments, the colloidal silica can be modified with various modifications (aluminate, silane etc.) or counter ions (K, NH3).

[0109] In still other non-limiting embodiments, this disclosure may include one or more process steps, compounds, apparatuses, etc. as described in U.S. Pat. No. 2884320, which is expressly incorporated herein by reference in its entirety.

[0110] In a second aspect, this disclosure further provides a use of colloidal silica for reducing an amount of dust produced by a sintering process. In a third aspect, this disclosure further provides a use of colloidal silica for increasing the strength of the sinter in a sintering process. In a fourth aspect, this disclosure further provides a use of colloidal silica for increasing productivity in a sintering process. In a fifth aspect, this disclosure further provides a use of colloidal silica for reducing the sintering temperature in a sintering process.In a sixth aspect, this disclosure further provides a use of colloidal silica for preparing sinter from ore dust. In a seventh aspect, this disclosure is further directed to the use of colloidal silica for decreasing the temperature in a sintering process. In an eighth aspect, this disclosure is further directed to the use of colloidal silica for lowering the CO2 emissions in a sintering process. The colloidal silica and the sintering process as well as any product and process parameters thereof according to the second, third, fourth, fifth, sixth, seventh, and eighth aspects of this disclosure can be the same as described above in the context of the process of the present invention, i.e. in the context of the first aspect of this disclosure. The uses according to the second, third, fourth, fifth, sixth, seventh, and eighth aspect of this disclosure in particular concern sintering processes for sintering iron ore.

[0111] As regards the fifth aspect of this disclosure, with the use of colloidal silica, sintering temperatures can be significantly reduced, in particular below 1100°C, such as below 1000°C, or even below 950°C, without impairing the properties of the obtained sintered product.

[0112] While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims.

[0113] In the following, the present invention and the merits achieved therewith will be further illustrated by means of examples. However, these examples are not intended to restrict the scope of the present invention in any way.Examples Materials

[0114] Iron ore raw material containing agglomerates was obtained from an iron core processing plant and used as received. The iron ore raw material contained around 85 wt.% iron ore, around 4 wt.% coke, and around 11 wt.% limestone, the wt-% being based on the solids of the iron ore raw material. The iron ore raw material further contained around 10.1 wt.% water, based on the total weight of the iron ore raw material. The iron ore had a D90 of20 mm, a D50 of 100 microns and a DIO of 10 microns. Hence, the iron ore also contained a considerably amount of dust.

[0115] The as-received iron ore raw material was initially homogenized intensively inside a thick plastic bag. Most of the weak agglomerates were broken to equalize water content. Such procedure was followed for all preparations.

[0116] Three different grades of colloidal silica material which are all commercially available from Noury on Chemicals International B.V. as a dispersion in water were used. The colloidal silica was used as received. The properties of the colloidal silica are summarized in the following Table 1.Table 1Example 1 : Compacting tests

[0117] Compacting tests were performed to determine the apparent density (AD) during the transportation (green state), after initial drying (dried), and after firing (sintering).

[0118] A larger batch (approximately 500 g for each condition) of as-received iron ore raw material was intensively homogenized in a paddle mixer (1000 rpm, 5 min). Following, smaller portions of 100 g were weighted in separated plastic beakers, kept under 600 rpm in the paddle mixer while different grades of colloidal silica or distilled water (0.125 wt% - 1 wt%) were added using a dropper. Water was added to those samples to which no colloidal silica was added (i.e. the reference samples) to compensate for the non-added colloidal silica.

[0119] Cylindrical plastic molds (60 mm length x 40 mm inner diameter) lined with anti-stick vaseline and closed bottom were filled with an initial mass of 150 g of material and vibrated for 30 s (sieve shaker). After extraction, samples were weighed and their height measured. For each sample, three measurements were carried out. From the obtained data the wet apparent density was calculated. The results are illustrated in FIG 2. In the next step drying was performed at 120°C for 24 h to remove free water and afterward samples wereweighed and measured again. During the whole procedure no external pressure was applied on the greenling to mimic an industrial conveyer belt situation. From the obtained data the dry apparent density was calculated. The results are illustrated in FIG 3.

[0120] FIG. 2 shows a plot of the wet apparent density of the greenling vs. the amount of silica solids added (in wt.%; also referred to herein as “solid silica”) and shows that the wet apparent density in general increases with the amount of colloidal silica added until a certain maximum is achieved. This effect is particularly pronounced for colloidal silica which is highly concentrated, i.e. the addition of FO830 achieves a higher apparent density than the addition of RD2180 and the addition of FO 1440 achieves even a higher apparent density than the addition of FO830. Generally, a higher apparent density is desirable as it indicates that more iron ore is contained in the greenling per volume which leads to improved productivity of the overall iron processing process. FIG. 3 confirms that the increase in apparent density is also observed after the greenling has been dried at 120°C for 24 h.

[0121] In a next step the samples were subjected to a thermal treatment procedure, i.e. a sintering procedure (also referred herein to as “firing”). An electric furnace was pre-heated up to 900°C, 1000°C, or 1100°C. The samples previously dried at 120°C for 24 h were then placed inside the chamber and left for 15 min. After 15 min, samples were removed from furnace and placed on a ceramic fiber blanket to cool naturally down to room temperature. FIG. 4 shows photographs of the samples before (on the left) and after sintering at 1100°C (on the right). It can be seen that the samples containing colloidal silica are more compact than the reference sample without colloidal silica but merely with 1 wt. added water. A visual assessment between the colloidal silica-containing samples revealed that the sample containing FO1440 is the most compact, followed by the sample containing FO830.Example 2: Compression tests

[0122] Compression tests were performed on cylindrical samples (40 mm height x 40 mm diameter which were prepared in a similar manner as described above in Example 1 and dried at 120°C for 24 h (dried samples; greenling) or fired at 900°C, 1000°C, or 1100°C for 15 min. After cooling to room temperature, the samples were then subjected to an uniaxial compression test using a deformation rate of 0.5 mm / min. Three samples per condition were measured to ensure reproducibility. The maximum cold compression strength sc (in MPa) was calculated using the formula sc = 4 x FRUpture / (p x D2), wherein FRUpture is the maximum force recorded during a test, and D is the sample’s average diameter (in mm). The resultsobtained are illustrated in FIG.5 (for the greenling dried at 120°C) and in Fig 6 (for the sintered / fired samples at 1100°C).

[0123] FIG.5 shows a plot of the cold compression strength of the greenling vs. the amount of solid silica added and shows that the cold compression strength in general increases with the amount of colloidal silica added (in wt.%). This effect is particularly pronounced for colloidal silica which is more concentrated, i.e. the addition of FO830 achieves a higher cold compression strength than the addition of RD2180 and the addition of FO1440 achieves even a higher cold compression strength than the addition of FO830. Generally, higher cold compression strength is desirable as it indicates that the sample is more robust against external forces and hence is less prone to dust-forming abrasion during further processing thereof. FIG. 6 illustrates that the increase in cold compression strength is even much more pronounced after sintering the greenling at 1100°C for 15 min.

[0124] FIG. 7 further shows for samples containing FO1440 the effect of the amount of solid silica (in wt.%) on the cold compression strength for different sintering temperatures (i.e. 900°C, 1000°C, and 1100°C). The black dotted line indicates the strength level shown by the as-received iron ore raw material fired at 1100°C which represents commercial standard conditions. As can be seen, the sample containing just the as-received iron ore raw material after firing at only 900°C has very poor cold compression strength. In contrast, the sample containing 0.5 wt.% FO1440 (which equals 0.2 wt.% silica solids) after firing at only 900°C nearly achieves the cold compression strength of the as-received iron ore raw material after firing at 1100°C. Higher amounts of silica up to 1 wt.% FO1440 (which equals 0.4 wt.% silica solids) significantly enhances this effect. Hence, it is apparent that with the addition of silica, sintering temperatures can be significantly reduced without impairing the cold compression strength of the sintered product. Alternatively, at higher sintering temperatures such as at the standard sintering temperature of 1100°C the addition of silica achieves significantly higher cold compression strength. The following Table 2 summarizes the experimental data which is the basis for Fig. 7.Table 2 (Cold compression strength for samples fired at different temperatures):Example 3: Drumming tests

[0125] Drumming tests were performed to further assess stability of the samples. Samples (cylindrical shape, 40 x 40 mm) were sintered for 15 min at 900°C, 1000°C, or 1100°C and after cooling were cleaned with a gentle puff of compressed air to remove dust and loose particles and weighted (Minitiai, g). Each sample was placed individually inside a rotating drum (high abrasion resistant PET flask with an inner diameter of 150 mm and 300 mm length) and kept revolving at 60 rpm for up to 5 min. The test was stopped if a sample was completely destroyed before reaching the maximum test time of 5 min. Following, samples were cleaned and weighed again (Mrinai, g). The drumming index (DI, wt.%) was calculated using the following formula: DI = 100 % x (Minitiai - Mrinai) / Minitiai. The test was performed with samples containing just the as-received iron ore material and samples containing 0,125 wt.%, 0,25 wt.%, 0,5 wt.%, 0,75 wt, or 1 wt.% FO1440.

[0126] The results are summarized in the following Table 3.Table 3 (Percentual mass loss for samples fired at different temperatures in a drumming test after 15 minutes):

[0127] FIG. 8 illustrates the obtained results and shows the percentual mass loss of the samples as fine powder during the drumming test. The black dotted line indicates the mass loss level shown by the as-received iron ore raw material fired a 1100°C. As can be seen, the samples containing just the as-received iron ore raw material after firing of only 900°C or 1000°C were destroyed before the test ended (in Fig. 8 a value of 24 or above means that the sample was destroyed) and, hence, showed only very poor stability. In contrast, the sample containing 0.5 wt.% FO1440 (which equals to 0.2 wt.% silica solids) after firing of only 900°C nearly achieves the stability of the as-received iron ore raw material after firing at 1100°C. Higher amounts of silica up to 1 wt.% FO1440 (which equals to 0.4 wt.% solid silica) significantly enhance this effect. Hence, it is apparent that with the addition of silica, sintering temperatures can be significantly reduced without impairing the stability of the sintered product. Alternatively, at higher sintering temperatures such as at the standard sintering temperature of 1100°C the addition of silica achieves significantly higher stability. A higher stability of the sintered product is desirable as the sintered product is then less prone to potentially dust-forming abrasion during further processing.T1Example 4

[0128] The effects of adding microsilica (MS) or colloidal silica (CS) to iron ore raw material were compared in compacting, compression, and drumming tests. As microsilica commercially available Elkem Microsilica® Grade 971 (MS 971; suspension of 40 wt.% silica in water; D50 = 80nm) was used. As colloidal silica FO1440 as described above was used.

[0129] The compacting tests were performed in the same manner as described above in Example 1. FIG. 9 and FIG. 10 summarize the obtained results. FIG. 9 shows a plot of the wet apparent density of the greenling vs. the amount of solid silica added (in wt.%) for colloidal silica and microsilica. FIG. 9 shows that the wet apparent density in general increases with the amount of silica added. However, for the colloidal silica the increase in wet apparent density is more pronounced already for lower amounts of solid silica added compared to the samples containing microsilica. Hence, the addition of colloidal silica can improve the productivity in a more efficient way than the addition of microsilica because less solid silica is required to achieve a similar increase in apparent density. FIG. 10 confirms that this effect is also observed for the samples after the greenling has been dried at 120°C for 24 h.

[0130] The compression tests were performed in the same manner as described above in Example 2. FIG. 11 summarizes the results obtained for microsilica. FIG. 11 shows for samples containing microsilica U971 the effect of the amount of solid silica (in wt.%) on the cold compression strength for different sintering temperatures (i.e. 900°C, 1000°C, and 1100°C). The black dotted line indicates the strength level shown by the as-received iron ore raw material fired at 1100°C which represents commercial standard conditions. As can be seen, the sample containing just the as-received iron ore raw material after firing of only 900°C has very poor cold compression strength. In contrast, the sample containing 1.0 wt.% microsilica suspension (which equals to 0.4 wt.% silica solids) after firing at only 900°C achieves a cold compression strength of the as-received iron ore raw material after firing at 1100°C. Hence, also with the addition of microsilica, sintering temperatures can in principle be reduced compared to sintered as received iron ore raw material without impairing the cold compression strength of the sintered product. However, the effect achieved with the addition of microsilica is not as pronounced as the effect achieved with the addition of colloidal silica. If one compares the results illustrated in FIG. 7 (which presents the results obtained for the addition of colloidal silica as already described above in a similar way as FIG. 11) with theresults illustrated in FIG.11, it is apparent that the colloidal silica achieves a much higher improvement of the cold compression strength for the same amount of silica solids added as well as a much higher absolute performance. For instance, for the addition of 0.5 wt.% colloidal silica FO1440 (which equals to 0.2 wt.% solid silica), after sintering at 900°C a cold compression strength of 0.49 MPa is achieved, whereas for the addition of 0.5 wt.% microsilica U971 (which equals to 0.2 wt.% solid silica), after sintering at 900°C a cold compression strength of only 0.30 MPa is achieved. For the samples containing 1 wt.% of the silica products (which equals to 0.4 wt.% solid silica), after sintering at 1100°C, the cold compression strength for the colloidal silica sample is 2.52 MPa which is much higher than the 1.59 MPa determined for the microsilica sample. The following Table 4 summarizes the experimental data which is the basis for Fig. 11.Table 4 (Cold compression strength for samples fired at different temperatures):

[0131] The drumming tests were performed in the same manner as described above in Example 3. The results are summarized in the following Table 5.Table 5 (Percentual mass loss for samples fired at different temperatures in a drumming test after 15 minutes):

[0132] FIG. 12 summarizes the results obtained for microsilica. FIG. 12 shows for samples containing microsilica U971 which have been sintered at 900°C, 1000°C, and 1100°C the percentual mass loss of the samples as fine powder during the drumming tests. The black dotted line indicates the mass loss determined for the as-received iron ore raw material fired at 1100°C which represents commercial standard conditions. As can be seen, the samples containing just the as-received iron ore raw material after firing of only 900°C or 1000°C were destroyed before the test ended and, hence, showed only very poor stability. Also, the samples containing only small amounts of microsilica (such as. 0.125 wt.% silica product which equals to 0.05 wt.% silica solids) and fired at 900°C or 1000°C were destroyed during the drumming test. Samples containing higher amounts of microsilica performed slightly better, in particular those containing 1 wt.% microsilica U971 (which equals to 0.4 wt.% silica solids). Hence, also with the addition of microsilica, drumming test performance and hence stability of a sintered product can be enhanced compared to sintered as received iron ore raw material. However, the effect achieved with the addition of microsilica is by far not as pronounced as the effect achieved with the addition of colloidal silica. If one compares the results illustrated in FIG. 8 (which presents the results obtained for the addition of colloidal silica as already described above in a similar way as FIG. 12) with the resultsillustrated in FIG.12, it is apparent that the colloidal silica achieves a much higher improvement in stability for the same amount of silica solids added as well as a much higher absolute performance. For instance, for the addition of 0.5 wt.% colloidal silica FO1440 (which equals to 0.2 wt.% silica solids), after sintering at 900°C a mass loss of only 4.87 wt.% is observed, whereas for the addition of 0.5 wt.% microsilica U971 (which equals to 0.2 wt.% solid silica), after sintering at 900°C a mass loss of 22.20 wt.% is observed. For the samples containing 1 wt.% of the silica products (which equals to 0.4 wt.% silica solids), after sintering at 1100°C, the mass loss is only 0.2 wt.% which is much lower than the 0.98 wt.% determined for the microsilica sample.

Claims

CLAIMSWhat is claimed is:

1. A process for sintering iron ore, said process comprising the steps of:A. providing iron ore, colloidal silica, and water;B. combining the iron ore, the colloidal silica, and the water to form a mixture;C. granulating the mixture to form granules; andD. sintering the granules to form sintered ore.

2. The method of claim 1 wherein the mixture has a melting point of less than about 1200°C.

3. The method of claim 1 or 2 wherein the iron ore is further defined as a powder.

4. The method of any preceding claim wherein the iron ore is further defined as dust.

5. The method of any preceding claim wherein the colloidal silica is alkali metal-stabilized colloidal silica, and preferably is sodium stabilized colloidal silica.

6. The method of any preceding claim wherein the colloidal silica is alkali metal-stabilized colloidal silica with a solid content of above 30 wt.%, preferably about 30 wt.% to about 60 wt.%, more preferably above 30 wt.% to about 50 wt.%, and most preferably above 15 to about 40 wt.%, the wt.% in each case being based on the total weight of the colloidal silica sol.

7. The method of any preceding claim wherein the colloidal silica has a surface area of about 100 to about 500 m2 / g, preferably of about 130 to about 500 m2 / g, and more preferably of about 130 to about 400 m2 / g.

8. The method of any preceding claim wherein the colloidal silica is present in the mixture in an amount of from about 0.01 to about 10 wt.% based on the total weight of the mixture.

9. The method of any one of claims 1-7 wherein the colloidal silica is present in the mixture in an amount of from about 0.05 to about 1 wt.% based on the total weight of the mixture.

10. The method of any preceding claim wherein the water is present in the mixture in an amount of from about 3 to about 20 wt.% based on the total weight of the mixture.

11. The method of any one of claims 1-10 wherein the water is present in the mixture in an amount of from about 8 to about 12 wt.% based on the total weight of the mixture.

12. The method of any preceding claim wherein the iron ore is present in the mixture in an amount of from about 50 to about 96.99 wt.% based on the total weight of the mixture.

13. The method of any one of claims 1-12 wherein the iron ore is present in the mixture in an amount of from about 80 to about 91.99 wt.% based on the total weight of the mixture.

14. The method of any preceding claim comprising further stepE. crushing the sintered ore into pieces.

15. The method of any preceding claim comprising further stepF. feeding the pieces of crushed sintered ore obtained in step E. into a blast furnace.

16. Use of colloidal silica for reducing an amount of dust produced by a sintering process.

17. Use of colloidal silica for increasing strength of sinter in a sintering process.

18. Use of colloidal silica for increasing productivity in a sintering process.

19. Use of colloidal silica for reducing the sinter temperature in a sintering process.

20. Use of colloidal silica for preparing sinter from ore dust.

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