Method for manufacturing pellets

Abstract

A method for manufacturing pellets, the method comprising the steps of mixing an organic binder with water to form an organic hydrogel binder; mixing the hydrogel with a particulate substrate selected from metal ores, metal ore-containing wastes, metal fines, iron residues, iron filings, mineral wastes, carbonaceous materials, arc furnace wastes, or combinations thereof to form a substrate mixture; and forming aggregates. Alternatively, the method can include providing a wet particulate substrate selected from metal ores, metal ore-containing wastes, metal fines, iron residues, iron filings, mineral wastes, carbonaceous materials, arc furnace wastes, or combinations thereof; mixing the wet particulate substrate with an organic binder to form a wet substrate mixture; allowing the wet substrate mixture to stand to form a hydrogel of the organic binder around the particulate substrate; and forming aggregates.

Description

Technical Field

[0001] The present invention relates to a method for producing pellets, in particular iron-containing pellets, from particulate substrates and hydrogel binders, and to the pellets obtained using said method.

Background Art

[0002] Although abundant in the Earth's core, the amounts of available carbon, various metals and metal ores are finite. Environmental burdens are associated with the mining of metal ores and metals such as iron, and smelting activities, particularly in terms of pollution. Therefore, it is desirable to maximize the recycling of waste materials, thereby reducing the waste that needs to be handled and stored. Storage is typically carried out by long-term storage in heaps or ponds, for example in the case of iron waste.

[0003] The production of pellets from particulate iron and other metal ores is generally known in the art. Often, such particles are combined and integrated using a binder to produce pellets. In the pelletizing process, the binder is typically added as a powder. However, the powder can be difficult to process into pellets that have a stable and sufficiently strong form that can be transported not only to the place of use but also within the large-scale processing plants at their destination. Powder binders can also explode or easily escape into the atmosphere. This can be economically disadvantageous due to material losses and can also be dangerous as the powder in the atmosphere may be inhaled.

[0004] Furthermore, pelletization using powders often results in inconsistent outcomes and can pose problems during scale-up of manufacturing. This is because efficient powder dispersion in an industrial-scale mixer is difficult. Also, interference between binder components may exist as a result of the action of temperature and pressure. The use of powders can also affect solubilization differences in an unpredictable manner. This means that extensive testing is required before industrial-scale use, making the transition from formulation to industrial pelletization more difficult and costly.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, it is considered desirable to develop a method of pelletization in which pellets exhibit improved ease of manufacture without losing strength and stability. The present invention aims to overcome or improve at least some aspects of this problem.

Means for Solving the Problems

[0006] Accordingly, in a first aspect of the present invention, there is provided a method of manufacturing pellets, the method comprising the steps of mixing an organic binder with water to form an organic hydrogel binder; mixing the hydrogel with a particulate substrate selected from metal ores, metal ore-containing wastes, metal fines, iron residues, iron filings, mineral wastes, carbonaceous materials, arc furnace wastes, or combinations thereof to form a substrate mixture; and forming aggregates.

[0007] In a second aspect of the present invention, a method for manufacturing pellets, the method comprising: providing a wet particulate substrate selected from metal ores, metal ore-containing wastes, metal fines, iron residues, iron turnings, mineral wastes, carbonaceous materials, arc furnace wastes, or combinations thereof; mixing the wet particulate substrate with an organic binder to form a wet substrate mixture; allowing the wet substrate mixture to stand to form a hydrogel of the organic binder around the particulate substrate; and forming aggregates.

[0008] In a third aspect of the present invention, there is provided a pellet obtained by the method of the first or second aspect of the present invention, the pellet comprising a particulate substrate selected from metal ores, metal ore-containing wastes, metal fines, iron residues, iron turnings, mineral wastes, carbonaceous materials, arc furnace wastes, or combinations thereof and an organic hydrogel binder.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0010] By the methods according to the first and second aspects of the present invention, the binder can be more efficiently dispersed through the particulate substrate in the final pellet product. Without being bound by theory, the formation of a hydrogel by the organic binder binds and integrates the substrate particles, thereby not only increasing the strength of the final pellet but also acting as a processing aid. This is because in hydrogel form, the binder exhibits higher dispersibility and can thus have a lubricant effect. Overall, this improves pellet processing and results in more consistent outcomes. Furthermore, the hydrogel binder is more easily dispersed in an industrial-scale mixer than a powder binder. Thus, this leads to improved efficiency by reducing equipment load and overheating. Additionally, the final pellets produced by the method of the present invention have surprisingly been found to be stronger and have higher strength and rigidity compared to equivalent compositions without gelation, thereby reducing the need for subsequent heating (e.g., drying or curing processes) after pellet production for their stabilization towards storage, transportation, and use. This has significant environmental benefits in that less energy is required to produce pellets of sufficient strength from particulate materials and enables rapid low-temperature pelletization to be completed without the need for a heating device or delays that can be caused by additional heating steps, introducing process efficiency. Moreover, the pellets obtainable by the method according to the first or second aspect of the present invention also generally exhibit high thermal stability, which means that the pellets are reduced to carbon at a controlled rate and do not disintegrate in the furnace.

[0011] Typically, the particulate substrate is selected from metal ores, metal ore-containing wastes, metal fines, iron residues, iron filings, mineral wastes, carbonaceous materials, arc furnace wastes, or combinations thereof. The particulate substrate is often selected from metal ores, metal ore-containing wastes, metal fines, iron residues, iron filings, carbonaceous materials, arc furnace wastes, or combinations thereof. The particulate substrate is often supplied from the wastes of other industrial processes. The particulate substrate can include waste products derived from a single waste stream (in this case, the variation is only in the particle size), or waste products derived from a combination of each waste stream (in this case, there are mixed wastes with different compositions). This is environmentally beneficial because recycling and reusing such materials reduces the amount of finite resources that would otherwise be discarded.

[0012] The carbonaceous material can be coke, graphite, carbon black, peat, or coal. The carbonaceous material often includes coke and / or coal. As used herein, the term "coal" is intended to include lignite, sub-bituminous coal, bituminous coal, steam coal, and anthracite. Coke has been found to be particularly problematic during pellet forming, and thus the present invention provides a particular benefit in terms of providing stronger coke pellets.

[0013] Mineral wastes can include mill scale, mill sludge, ore-derived fines, and / or metal-containing wastes.

[0014] Without being bound by theory, it is believed that the use of the gel binder aids in the distribution of the waste in the suspect matrix, whether the particulate substrate includes a single type of waste or a combination of different types of waste, before the aggregates are formed prior to curing.

[0015] The metal may be any of the following, and the mineral waste of metal ore may contain the following: iron, zinc, nickel, copper, chromium, manganese, gold, platinum, silver, titanium, tin, lead, vanadium, cadmium, beryllium, molybdenum, uranium, aluminum or a mixture thereof; or a simple metal, or in the form of, for example, an oxide or a silicate. The metal is often a transition metal, such as iron, zinc, nickel, copper, chromium, manganese, gold, platinum, silver, titanium, tin, lead, vanadium, cadmium, molybdenum, aluminum or a mixture thereof, but the metal may be uranium.

[0016] The particulate substrate often contains a metal, and relatively often contains iron. The use of iron is advantageous because iron is readily available. This is because iron can be reused and recycled from the waste products of other processes, thereby providing an environmentally sustainable access to this material. When the particulate substrate contains metal ore, often the ore is iron ore, such as goethite, limonite, siderite, taconite, hematite or magnetite. Often, when the particulate substrate is metal ore, this is iron ore, such as hematite or magnetite.

[0017] The particulate substrate may be a powder or a scrap, and the term "scrap" has its ordinary meaning in the art. Often, the particulate substrate has a particle size (widest axis) of 4 mm or less. Often, the particle size ranges from 30 μm to 4 mm, often from 50 μm to 3 mm or from 0.1 mm to 2 mm. Often, at least 10% by weight of the particulate substrate can pass through a 100 μm sieve before being formed into pellets. The presence of a range of particle sizes within the sample improves the filling of the material within the aggregates during extrusion. The term "aggregate" has its ordinary meaning in the art, i.e., a particulate material formed from an aggregate of physically or chemically bonded and integrated particles.

[0018] Typically, the particulate substrate is added in an amount of about 70 wt% to about 99.9 wt%, preferably about 80 wt% to about 99 wt%, more preferably about 90 wt% to about 95 wt% of the pellets.

[0019] An auxiliary binder may be present, such that the binder used in the described method may comprise one or more organic binders, or a combination of one or more organic binders and one or more auxiliary binders. Typically, the binder is present in the pellets in the range of about 0.05 wt% to about 4 wt%, often in the range of about 0.5 wt% to about 4 wt%, often in the range of about 0.5 wt% to about 2.5 wt%.

[0020] Organic binders have the advantage that they can be used at low concentrations and do not significantly affect the metallurgical or physical properties of the substrate mixture per se. Organic binders can be added in powder form, gel form, or other pre-solubilized forms (i.e., organic binders in a liquid suspension). In an example where the organic binder is added as a powder, the presence of water promotes in-situ gelation of the organic binder. By providing the organic binder as a powder or gel, the total water content of the pellets can be better controlled compared to the case of liquid addition. Forming a gel in the organic binder (either before or after addition to the substrate) improves the low-temperature strength of the pellets, thereby reducing or eliminating the need for long heating or drying processes and the energy input required for such processes. Such advantages may not exist if the organic binder does not form a hydrogel and instead takes, for example, the form of a film. An example of the situation where the organic binder forms a film is when the amount of water in the mixture is limited, resulting in reduced dissolution of the organic binder in water and prevention of hydrogel formation.

[0021] Typically, the organic binder is selected from organic resins (e.g., polyacrylamide resins), cellulose materials (e.g., carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), or hydroxyethyl methyl cellulose (MHEC)), polyvinyl alcohol (PVA), phenol-formaldehyde resins (e.g., resol resins where the ratio of formaldehyde to phenol in the base-catalyzed phenol-formaldehyde resin exceeds 1, usually about 1.5, or novolac resins where the molar ratio of formaldehyde to phenol is less than 1), and / or polysaccharides (e.g., starch such as wheat, corn, barley, and potato starch, gum arabic, guar gum, or xanthan gum). Often, the organic binder is selected from organic resins, cellulose materials, polyvinyl alcohol, and / or phenol-formaldehyde resins.

[0022] When the organic binder is a cellulose material, it is often carboxymethyl cellulose (CMC). CMC is advantageous because it can be added in powder form, thereby enabling control of the total moisture content of the pellets. CMC also has a longer shelf life than other plant-derived organic binders. This is because other plant-derived organic binders are more susceptible to microbial attack and thus decompose more easily. Sometimes, the organic binder may be hydroxyethyl methyl cellulose (MHEC), which has been found to have particularly good adhesion quality and helps to increase the strength of the pellets. However, because MHEC has high water solubility, this may affect the shelf life of the final pellets, which is reduced compared to CMC-containing pellets.

[0023] Generally, the organic binder includes carboxymethyl cellulose (CMC), polyacrylamide, phenol-formaldehyde resin, polyvinyl alcohol (PVA), or a combination of these organic binders with each other, or a combination of these organic binders with other organic binders, such as those listed above. Alternatively, the organic binder may consist essentially of one or more of CMC, polyacrylamide, phenol-formaldehyde resin and / or PVA; may consist of CMC, polyacrylamide, phenol-formaldehyde resin and / or PVA; or may consist of only one of CMC, polyacrylamide, phenol-formaldehyde resin and / or PVA, such as CMC or PVA.

[0024] Often, CMC may be used as the organic binder instead of or in addition to other organic binders, such that the organic binder can contain from about 10 wt% to about 100 wt%, often from about 20 wt% to about 90 wt%, or from about 50 wt% to about 75 wt% of CMC. When the organic binder contains CMC, this is typically added in the range of about 0.01 wt% to about 1.5 wt%, often about 0.1 wt% to about 1 wt% of the pellets.

[0025] Typically, CMC organic binders have an active polymer content of about 40% to about 90% and a pH in the range of about 5 to about 9, or about 6 to 8 in the case of a solution. Further, CMC often has a molecular weight in the range of about 3,000 to about 70,000. Optionally, CMC often has a molecular weight in the range of about 10,000 to about 50,000. Without being bound by theory, it is believed that in the case of relatively low molecular weight CMC, such as in the range of about 10,000 to about 50,000, it is possible to prepare high-concentration organic binder solutions, thereby improving the strength of the pellets.

[0026] Organic binders often contain polyvinyl alcohol (PVA). PVA may be used as an organic binder instead of or in addition to other organic binders. As a result, the organic binder can contain from about 10 wt% to about 100 wt%, often from about 20 wt% to about 90 wt%, or from about 50 wt% to about 75 wt% of PVA. When the organic binder contains PVA, this is typically added in the range of from about 0.01 wt% to about 1.5 wt% of the pellets, often in the range of from about 0.05 wt% or 1 wt% to about 1 wt% of the pellets.

[0027] Without being bound by theory, it is believed that PVA provides rapid curing and high strength because the polymer network formed by PVA is strong. Furthermore, in the pelletization process using PVA, air is excluded from the bulk raw material, which can reduce the oxidation of the metallic substrate. Metal oxidation is undesirable for the simple reason that it reduces the amount of metal (e.g., metallic iron) available for processing by the end user due to the oxidation of the metal.

[0028] Polyvinyl alcohol is typically commercially formed from polyvinyl acetate, which is done by reacting polyvinyl acetate with sodium hydroxide in a process called saponification to replace the acetate radical of the acetate ester with a hydroxyl radical. By partially saponified is meant that some of the acetate ester groups are replaced with hydroxyl groups, thereby forming at least partially saponified polyvinyl alcohol groups.

[0029] Typically, PVA has a degree of saponification of at least about 80%, typically at least about 85%, at least about 90%, at least about 95%, at least about 99% or about 100%. PVA can be commercially obtained, for example, from Kuraray Europe GmbH, Germany. Typically, this is utilized as an aqueous solution. PVA may be modified, for example, to contain sodium hydroxide content.

[0030] Typically, the PVA organic binder has an active polymer content of about 12% to about 13% and has a pH in the range of about 4 to about 7 in the case of a solution. Further, the PVA often has a molecular weight in the range of about 15,000 to about 150,000. Optionally, the PVA often has a molecular weight in the range of about 30,000 to about 120,000. Without being bound by theory, it is believed that in the case of a relatively low molecular weight, for example, in the range of about 15,000 to about 60,000, it is possible to prepare a high-concentration organic binder solution, whereby the strength of the pellets can be improved.

[0031] When the organic binder is a polysaccharide, this may be starch or amylose starch. For example, this may be pre-gelatinized potato starch. This can be added in an amount of about 0.8% by weight, preferably about 0.6% by weight, of the final pellet. It may be desirable to use a polysaccharide as the organic binder because polysaccharides often also function as thickeners.

[0032] The organic binder (alone or in combination with one or more auxiliary binders) can be present in the range of about 0.05% to about 1.5% by weight of the pellet. Often, it is in the range of about 0.07% to about 1.0% by weight, or about 0.1% to about 0.9% by weight. When the organic binder present is less than about 0.05% by weight, it has been found that the structural integrity of the aggregates is low.

[0033] In the method of the first aspect of the present invention, the organic binder is mixed with water to form an organic hydrogel binder.

[0034] As used herein, the term "hydrogel" means a material that is not an easily flowable liquid nor a solid, but a gel that contains a gel-forming material, such as a hydrophilic polymer that is insoluble in water. In other words, a hydrogel may be a semi-solid substance. Typically, a hydrogel is formed through a gel-forming material, such as a hydrophilic polymer, which forms an interconnected cross-linked network that can capture, absorb, and / or otherwise retain water, thereby enabling the formation of a gel. Some hydrogels can be diluted with another liquid, such as water, which breaks the interconnected network, resulting in a solution. Typically, however, the hydrogels of the present invention are cross-linked hydrogels that do not dissolve upon dilution.

[0035] Typically, the amount of water in the hydrogel ranges from about 1 wt% to about 5 wt%, or from about 2 wt% to about 4 wt%, or from about 2.5 wt% to about 4.5 wt%, or about 3 wt%. Without being bound by theory, it is believed that not all of the water mixed with the organic binder prior to addition to the substrate is present in the final hydrogel. This is because a small amount serves to ensure the dissolution or mixing of other components.

[0036] The formation of the organic hydrogel binder may take a time in the range of about 20 minutes to about 2 hours, preferably about 30 minutes to about 1 hour. The time required for the formation of the organic hydrogel binder can vary depending on factors such as additional processing, temperature (often in the range of about 10°C to about 60°C, or about 15°C to about 40°C, or about 20°C to about 30°C for optimal solubilization), CMC grade selection, iron ore grade selection, and mixing. At these temperatures, the formed pellets have been found to be particularly strong compared to pellets of the same formulation that have not undergone gel-forming treatment.

[0037] In the method of the second aspect of the present invention, by allowing the wet base material mixture to stand, a hydrogel of the organic binder is formed around the particulate base material. As used herein, the terms "standing" or "aging" are given their ordinary meaning in the art, i.e., the wet base material mixture is left without external interference such as heating, shearing or mixing for a period sufficient for the organic binder and the particulate base material to form a hydrogel.

[0038] Without being bound by theory, as described above with respect to the first aspect of the present invention, it is believed that not all of the water associated with the wet base material is present in the final hydrogel. This is because a small amount acts to ensure the dissolution or mixing of the other components.

[0039] Typically, the ratio of the organic binder to the particulate base material is from about 0.1% to about 0.8% of the organic binder to about 99.9% to about 99.2% of the particulate base material, preferably from about 0.15% to about 0.5% of the organic binder to about 99.85% to about 99.5% of the particulate base material.

[0040] The standing of the wet base material mixture to form a hydrogel of the organic binder around the particulate base material may require a range from about 5 minutes, 15 minutes or 30 minutes to about 2 days, often from 1 hour to 1 day (i.e., 24 hours) or less than 1 day, for example 9 hours, 6 hours or 3 hours. The time required depends on the nature of the binder selected. Often, the standing time is in the range of 15 minutes to about 2 hours, especially when a co-binder is present. For example, cellulose materials often form a gel after standing for a certain period, such as 15 minutes to 3 hours, or 1 to 2 hours. On the other hand, organic resins and phenol-formaldehyde resins can beneficially be allowed to stand for a relatively long time, such as 3 hours to 2 days, or 6 hours to 1 day.

[0041] The method of the present invention can further include the step of adding a co-binder to the base material mixture. The base material mixture can be the dry base material mixture of the first aspect of the present invention or the wet base material mixture of the second aspect of the present invention.

[0042] The auxiliary binder forms a bond with the particulate substrate, such as iron ore, thereby enabling the final pellets to withstand heat and pressure during furnace passage.

[0043] Typically, the auxiliary binder includes an inorganic binder. The inorganic binder can include one or more silicates (e.g., silicates in the form of sodium salts), or refractory materials, which include, but are not limited to, oxides, carbides, or nitrides of silicon, aluminum, magnesium, calcium, and zirconium and combinations thereof.

[0044] For example, the refractory material can include alumina, fireclay, bauxite, chromite, dolomite, magnesite, silicon carbide, zirconia, or combinations thereof. As used herein, the term "refractory material" refers to a material that exhibits resistance to thermal stress, high pressure, or corrosion by chemical reagents.

[0045] Often, the inorganic binder includes one or more silicates. Often, the inorganic binder includes two to four different silicates. The one or more silicates can be in liquid form, powder form, or a combination thereof. The auxiliary binder can be in powder form.

[0046] Often, the inorganic binder (alone or in combination with one or more organic binders) is present in the pellets in the range of about 0.5 wt% to about 2.5 wt%, often in the range of about 1 wt% to about 2 wt%, or in the range of about 1.25 wt% to about 1.75 wt%.

[0047] When silicate is present and one or more silicates are in liquid form, this is often present in relatively large amounts. This is because the activity level is lower in liquid silicate than in powdered silicate. When one or more silicates are in liquid form, this is often present in the pellet in the range of about 0.5 wt% to about 2.5 wt%, often in the range of about 1 wt% to about 2 wt%, or in the range of about 1.25 wt% to about 1.75 wt%.

[0048] When one or more silicates are in powdered form, this is often present in the pellet in the range of about 0.5 wt% to about 2.5 wt%, often in the range of about 1 wt% to about 2 wt%, or in the range of 1.25 wt% to about 1.75 wt%.

[0049] The method of the present invention can further include the step of adding one or more additional additives to the base material mixture.

[0050] As described above, the hydrogel formed by the organic binder can act as a processing aid. The method of the present invention can optionally further include the step of adding a separate processing aid to the base material mixture. Examples of processing aids include, but are not limited to, dilute solutions of cationic, anionic or non-ionic polymers, typically acrylic flocculants, carbon (often in the form of graphite), lubricants, surfactants (e.g., sodium lauryl sulfate), stearates (e.g., calcium stearate or sodium stearate), stabilizing fibers, or combinations thereof. The processing aids can make the overall process more efficient, thereby saving both cost and energy.

[0051] The step of forming the pellets can include the extrusion molding of the aggregates. The extrusion molding process can be carried out at a temperature in the range of about 30°C to about 70°C, often in the range of about 35°C to about 55°C. Further, this process can be carried out at atmospheric pressure or under vacuum. As used herein, the term "under vacuum" has its ordinary meaning in the art in that the extrusion molding process can be carried out at a pressure below atmospheric pressure.

[0052] The step of forming the pellets can include the cold forming of the aggregates. The term "cold formed" means, for example, not performing curing, sintering, or heating above about 60°C, or above about 40°C, or up to about 30°C. In other words, when heat is applied during the formation of the aggregates, only low levels of heat are often applied. Further, when pelletizing the aggregates, frictional heat may be generated by any of the pressing and / or extrusion molding processes used, and the binder may undergo an exothermic reaction in situ, but this is sometimes the only heat applied. Such inherent heating mechanisms would not be expected to generate sufficient heat to affect the formation of the pellets.

[0053] Alternatively, low levels of heat may be applied, such as heating in the range of about 100°C to about 250°C. The low-level heating enables more rapid pellet formation and can be in the range of about 100°C to about 250°C, or often about 150°C to 200°C. When applying low-level heating, it can be applied over a period in the range of about 1 minute to about 24 hours. By applying heat, drying and curing of the pellets are generally promoted, and the pellets are reliably prepared for transportation and use when needed. One skilled in the art will understand and recognize that factors such as the external ambient temperature, the nature of each component in the formulation, and the desired properties of the pellets to be produced (e.g., low water content) affect the need for external heat, the level of heat applied, and the duration. Thus, one skilled in the art will consider such factors when determining the duration and level of heat applied in the process, and for example, by providing an environment of about 30°C to 50°C (based on either the external ambient temperature or heating) for 6 to 24 or 9 to 18 hours, pellet formation can be assisted. Alternatively, it may be desirable to apply the heating in the range of 125°C to 175°C for a shorter period, such as 1 minute to 3 hours, or 15 minutes to 100 minutes. Thus, the aggregates, and thus the pellets, can be cold-formed or formed by applying low levels of heat such that they are formed at temperatures in the range of about 10°C to about 250°C, or about 15°C to about 200°C, or about 20°C to about 150°C.

[0054] The advantage of cold-forming, or forming by low levels of heat only, is significant in that it consumes less energy compared to commonly used curing manufacturing techniques. Also, a high-temperature furnace for producing the pellets is not required, resulting in a simpler, more economical, and environmentally beneficial manufacturing process.

[0055] Traditionally, pellets were formed using a heat treatment process to produce so-called hot bond (cure) briquettes. In the curing technique, first, "green" pellets are formed from a combination of particulate substrate and binder, and then this is formed into pellets (often using a pelletizer). As used herein, the term "green pellet" has its ordinary meaning in the art, which refers to a pellet that does not yet have the strength required for its end use and requires further treatment or processing. Green pellets are cured through a series of steps including drying, preheating, firing, and cooling of the green pellets. By removing water in a controlled manner, crack formation is prevented and the structural integrity of the pellets is maintained. The temperature range of the drying stage depends on the chemical and physical properties of the green pellets but is expected to be in the range of 100°C to 250°C for 5 to 10 minutes. The preheating stage is typically carried out at about 300°C to 350°C for 10 to 15 minutes using a ramp heating process up to about 1250°C to 1350°C. The preheating stage ensures that the existing metal hydrates or metal carbonates are decomposed into their anhydrous forms. The decomposition of these types of compounds helps to improve the structural integrity of the resulting pellets by removing water and / or gases that could react and cause overpressure and cracking in the pellets during firing. The firing stage is often carried out at temperatures above 1350°C for approximately 10 to 20 minutes (for typical throughput such as 250 - 500 tph), resulting in the sintering of the pellets and providing the strength required to make the pellets suitable for their end use. During the sintering process, bonds within the pellets are formed by recrystallization and cross-linking, ceramic bonds are generated, and macroboids are formed, which allow for some expansion and stress relief. As used herein, the term "macroboid" refers to voids within the pellets and has a size range of about 50 μm to about 1 mm in diameter. Void formation is particularly important when the briquette is a metal ore briquette because the reduction of the metal (e.g., the conversion of hematite to magnetite in iron ore) causes volume changes and stresses to the briquette.Macrovoid formation does not occur without firing, so an alternative method is needed to prevent pellet disintegration when placed under internal stress. The gelation techniques described herein provide such an alternative by providing improved chemical bond strength.

[0056] Furthermore, compared to the method of the present invention, the curing process is uneconomical because it is complex, requires careful implementation, and requires the addition of a significant amount of heat. For example, raw material preparation is critical. Each component of the green pellet must be within an appropriate size range, surface area, and moisture content to withstand this process because surface chemistry plays an important role. Furthermore, since this process involves multiple heating stages, it requires a large amount of energy. Therefore, there is a need for an energy-saving and more cost-effective pellet manufacturing method. Furthermore, there is a need for a method that is more flexible in terms of the physical state of the particulate material used and that results in the production of pellets having physical properties equivalent to or better than those produced using the curing process. The method of the present invention aids in providing a solution to this problem through the use of a hydrogel binder.

[0057] In the method according to the second aspect of the present invention, the wet particulate substrate can contain water in the range of about 1 wt% to about 40 wt%, preferably about 3 wt% to about 25 wt%, more preferably about 5% to about 15%.

[0058] Pellets obtained by either method of the first and second aspects of the present invention can be cold formed and can also be formed by low-level heating such as in the temperature range of 10°C to 250°C.

[0059] Typically, pellets according to the third aspect of the present invention are in the range of 2.5 to 15 cm 3 often in the range of 3 to 12 cm 3 or in the range of 7 to 11 cm 3It has an average volume within the range. The pellets generally have a size that minimizes the surface area and often have a structure such as a substantially spherical, oval, cylindrical or cubic shape.

[0060] Unless otherwise specified, each integer described can be used in combination with any other integer as understood by those skilled in the art. Further, all aspects of the present invention preferably "include" the features described in relation to that aspect, but it is specifically contemplated that they can "consist of" or "substantially consist of" those features outlined in the claims. Further, any term is intended to be given the meaning generally understood in the art unless specifically defined herein.

[0061] Further, in the discussion of the present invention, unless the contrary is stated, the disclosure of alternative values for the upper or lower limits of the tolerance range of a parameter is to be interpreted as an implicit statement that each intermediate value of said parameter lying between the smaller and larger alternative values is also disclosed as a possible value of said parameter.

[0062] Further, unless otherwise specified, all numerical values appearing in this application should be understood to be modified by the term "about". The term "weight %" and similar terms are intended to mean the weight percentage of the raw materials in the final pellets. When additives, impurities and / or water are present in the particulate starting material in step (i), the term "weight %" includes said additives, impurities and / or water.

[0063] To make the present invention more easily understood, the present invention will be further described with reference to the drawings and the following specific examples.

[0064] Figure 1 shows the results of the variation of the moisture content with respect to the cold crushing strength (CCS) of carboxymethyl cellulose.

[0065] Figure 2 shows the results of the iterative CCS test. The pellets represented by the black bars contain 0.5 wt% CMC added to >68 wt% Fe concentrate without performing the pre-gelation step, and the white bars contain 0.5 wt% CMC added to >68 wt% Fe concentrate after performing the pre-gelation step. In this case, this CMC was added to water according to the present invention to form a hydrogel and then added to >68 wt% Fe concentrate.

[0066] Figure 3 shows the results of the variation of temperature with respect to CCS for CMC.

Example

[0067] Example 1 - Molding of roller-pressed pellets (pre-gelation) CMC powder was mixed with water at a ratio of 1 part CMC to 16 parts water at 30 °C until all of this powder was dissolved and a gel was formed. The temperature was maintained at 30 °C. The 600 g of the obtained organic hydrogel binder was mixed with 7.5 kg of dry hematite >65 wt% Fe iron ore (dried to a constant weight at 105 °C) in a high-shear mixer at 45 rpm for 3 minutes. After adding sodium silicate, this mixture was further mixed for 3 minutes. The obtained base material mixture was molded using a hat roller press to form an aggregate, and oval roller-pressed pellets (approx. 15×26×36 mm, 11.2 cm 3 ) were produced and cured at 40 °C for 24 hours. The obtained pellets contained 0.25 wt% CMC and 2 wt% silicate.

[0068] Example 2 - Molding of roller-pressed pellets (pre-gelation) The method of Example 1 was repeated using magnetite iron ore >68 wt% Fe (the moisture content of >68 wt% Fe was adjusted to 8% so that the total water content in the system was the same as the total water content in the system of Example 1).

[0069] Comparative Example 3 - Molding of roller-pressed pellets (powder binder) The method of Example 1 was repeated using hematite iron ore, except that the gelation of CMC was not carried out before addition to >65 wt% Fe iron ore (dried to constant weight at 105 °C to provide pellets having the same moisture content as in Example 1).

[0070] Comparative Example 4 - Roller - pressed pellet forming (powder binder) The method of Example 1 was repeated using magnetite iron ore, except that the gelation of CMC was not carried out before addition to >68 wt% Fe iron ore (the moisture content of >68 wt% Fe was adjusted to 8% so that the total water content in the system was the same as the total water content in the system of Example 1).

[0071] Example 5 - Roller - pressed pellet forming (pre - gelation) The method of Example 1 was repeated, except that the subsequent addition of sodium silicate was not carried out, so the resulting pellets contained 0.25 wt% of CMC.

[0072] Example 6 - CCS test The CCS of each of Example 1, 2 and 5, and Comparative Examples 3 and 4 was determined using a Mecmesin Omnitest Materials Tester 10 with a standard methodology compliant with ISO 4700:2015. The results are shown in Table 1 below.

Table 1

[0073] Table 1 clearly shows that when the binder is gelled before being added to the substrate, the CCS is higher than when using the comparative prior art. Also, with CMC alone, it was possible to prepare robust pellets with a CCS just slightly below 200 kgf, and a significant increase in strength was observed compared to the typical values of CMC without gelation. The typical values of CMC without gelation tend to be in the range of 30 - 50 kgf and are prone to disintegration. Also, when the moisture content of the substrate increases, it was found that this has an adverse effect on the CCS. This is shown in Figure 1.

[0074] Example 7 The CCS test using a standard methodology in accordance with ISO 4700:2015 was carried out using a Mecmesin Omnitest Materials Tester 10 on cylindrical pellets (approx. 16 mm diameter × 16 mm length, 3.2 cm 3 ) of two sample types containing 0.5 wt% CMC added to >68 wt% Fe concentrate. The first sample type included a pre - gelation step, and for the second sample type, the prior art was used. Tests were carried out on 10 various grades of CMC (from 3 various suppliers).

[0075] The results are provided in Figure 2, comparing various grades of CMC under the same conditions. The black bars represent pellets formed without performing gelation of the CMC before addition to >68 wt% Fe concentrate, and the white bars represent pellets formed after performing gelation of the CMC before addition to >68 wt% Fe concentrate. Thus, this data is generally equivalent to the test data for Example 1 (with gelation) and Example 4 (without gelation).

[0076] As shown in Figure 2 (where "Strength" on the y - axis corresponds to CCS in units of kilonewtons (kN), and here 1 kgf = 0.0098 kN), in all cases where the pellets were formed with the gelation step (represented by the white bars), an improvement in CCS is demonstrated compared to pellets formed without the gelation step.

[0077] Example 8 - Temperature for Gel Formation (Pre-Gelation) A series of experiments were conducted to determine the optimum temperature for solubilization for a grade of CMC with a molecular weight of 30,000 as an example of an organic binder. The CMC was treated by adding the powder to water at 20 °C, 30 °C, 40 °C, and 50 °C at a weight ratio of 1:16 until a gel was formed. The resulting gels were used in a standard formulation with the addition of an 8% solution of magnetite iron ore >68 wt% Fe to produce cylindrical test pellets (approx. 16 mm diameter × 16 mm length, 3.2 cm 3 ) and these were tested for CCS in accordance with ISO 4700:2015 using a Mecmesin Omnitest Materials Tester 10. The results are shown in Figure 3. As can be seen, the optimum temperature for solubilization is relatively low, for example in the range of 15 °C to 35 °C, the highest strength was observed at 20 °C or 30 °C, and it was found that the best results were obtained at 30 °C.

[0078] Example 9 - Forming Roller-Pressed Pellets (In-Situ) 0.3 wt% of CMC was mixed with 7.5 kg of hematite >65 wt% Fe iron ore (wet iron ore) with a water content of 5.5% in a high-shear mixer at 45 rpm for 3 minutes. The resulting wet base mixture was left to stand at ambient temperature (in the range of 20 °C to 25 °C) for 1 hour to form a hydrogel of CMC around the iron ore. After adding 2 wt% of sodium silicate, the mixture was mixed for a further 3 minutes. This base mixture was then formed into aggregates using a hat roller press to produce oval roller-pressed pellets (approx. 15 × 26 × 36 mm, 11.2 cm 3 ) and cured at 40 °C for 24 hours.

[0079] Example 10 - Forming Roller-Pressed Pellets (In-Situ) The method of Example 9 was repeated using magnetite iron ore >68 wt% Fe.

[0080] Comparative Example 11 - Forming Roller-Pressed Pellets (In-Situ) The method of Example 9 was repeated using hematite >65 wt% Fe iron ore, except that the standing step was not carried out, and thus the hydrogel was not formed around the iron ore.

[0081] Comparative Example 12 - Roller Compression Pellet Forming (In Situ) The method of Example 9 was repeated using hematite magnetite iron ore >68 wt% Fe, except that the standing step was not carried out, and thus the hydrogel was not formed around the iron ore.

[0082] Example 13 - CCS and Tumble Strength Index Test The CCS and Tumble Index (TI) of each of Examples 9, 10, and Comparative Examples 11 and 12 were determined using standard methodologies, in accordance with ISO 4700:2015, using a Mecmesin Omnitest Materials Tester 10, and in accordance with ISO 3271:1995. The results are shown in Table 2 below.

Table 2

[0083] Table 2 clearly shows that when the binder and substrate mixture is left standing to form a gel, the CCS is higher than when using comparative conventional techniques. Furthermore, the tumble strength index of the samples is higher, indicating that stronger pellets are produced. The industrial standard for TI is in the range of 90 - 95, and Examples 9 and 10 meet this industrial standard, while Comparative Examples 11 and 12 do not.

[0084] Example 14 - Roller Compression Pellet Forming (In Situ) 0.5 wt% of polyacrylamide (two different grades) was mixed with 7.5 kg of magnetite iron ore (>68 wt% Fe) (wet iron ore) with a water content of 5.5% at 45 rpm for 3 minutes using a high-shear mixer. The resulting wet substrate mixture was allowed to stand at ambient temperature (in the range of 20 °C to 25 °C) for the times shown in Table 3 below to form a hydrogel of polyacrylamide around the iron ore. In some examples, after adding 2.0 wt% of sodium silicate, the mixture was further mixed for 3 minutes. This substrate mixture was then formed into aggregates using a hat roller press, and "rectangular" roller-compressed pellets (approx. 15×26×36 mm, 2.5 cm 3 ) were produced and cured at 40 °C for 24 hours.

Table 3

[0085] As can be seen, higher strength is generally observed for both polyacrylamide alone and the silicate / polyacrylamide system when standing is carried out, and the improvement can be observed with a standing period of just 30 minutes. However, in the absence of silicate, polyacrylamide requires more time to form strong bonds (values exceeding 60 provide use without disintegration), which is up to 1 day. Generally, the presence of silicate significantly increases the strength compared to the case of polyacrylamide alone, which indicates the benefit of the auxiliary binder of the present invention.

[0086] Example 15 - Molding of Roller-Compressed Pellets (In Situ) The method of Example 14 was repeated using 0.5 wt% of polyvinyl alcohol and 0.5 wt% of phenol-formaldehyde resin, where the polyvinyl alcohol was provided in dry form. The results are shown in Table 4 below.

Table 4

[0087] As can be seen, when gel formation is provided, the strength increases significantly compared to the case where no gel is formed (it increases from 26 kgf to 65 kgf for PVA alone and from 20 kgf to 103 kgf for PVA + phenol-formaldehyde resin). At a strength of 20 kgf, the pellets can be molded but not in their original state. The gelation process enables the formation of stable pellets using PVA alone, and the combination of PVA and phenol-formaldehyde provides additional strength.

[0088] Similar results are achieved when polyvinyl alcohol is provided in liquid form.

[0089] It will be understood that the methods and apparatuses of the present invention can be implemented in various ways, and those illustrated and described above are only a very small part of them.

Claims

1. A method for producing pellets, wherein the method is a. A step of mixing an organic binder with water to form an organic hydrogel binder, b. A step of mixing the hydrogel with an iron-containing particulate substrate selected from metal ore, metal ore-containing waste, metal powder, iron residue, iron scrap, mineral waste, carbonaceous material, arc furnace waste, or a combination thereof, to form a substrate mixture. c. The process of forming aggregates and Includes, The method further comprises the step of adding an auxiliary binder to the base material mixture, wherein the auxiliary binder comprises an inorganic binder, and the inorganic binder is present in the pellet in an amount of 0.5% to 2.5% by weight.

2. A method for producing pellets, wherein the method is a. A process of providing a wet particulate substrate selected from metal ore, metal ore-containing waste, metal powder, iron residue, iron scrap, mineral waste, carbonaceous material, arc furnace waste, or a combination thereof, b. A step of mixing the wet particulate substrate with an organic binder to form a wet substrate mixture, wherein the organic binder is selected from an organic resin, a cellulose material, polyvinyl alcohol, a phenol-formaldehyde resin, or a combination thereof. c. A step of allowing the wet substrate mixture to stand to form a hydrogel of the organic binder around the particulate substrate, d. The process of forming aggregates and Includes, The method further comprises the step of adding an auxiliary binder to the wet substrate mixture, wherein the auxiliary binder comprises an inorganic binder, and the inorganic binder is present in the pellet in an amount of 0.5% to 2.5% by weight.

3. The method according to claim 2, wherein the particulate substrate contains a metal.

4. The method according to claim 2 or 3, wherein the particulate substrate contains iron.

5. The method according to claim 1 or 2, wherein the particulate substrate is added in an amount of 70% to 99.9% by weight of the pellets.

6. The method according to claim 1, wherein the organic binder is selected from organic resins, cellulose materials, polyvinyl alcohol, phenol-formaldehyde resins and / or polysaccharides.

7. The method according to claim 1 or 2, wherein the organic binder comprises carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), or a combination thereof.

8. The method according to claim 1 or 2, wherein the organic binder is added in an amount of 0.05% to 1.5% by weight of the pellets.

9. The method according to claim 1 or 2, wherein the inorganic binder comprises one or more silicates or refractory materials, and the refractory materials include oxides, carbides, or nitrides of silicon, aluminum, magnesium, calcium, and zirconium, and combinations thereof.

10. The method according to claim 1 or 2, wherein the inorganic binder comprises one or more silicates.

11. The method according to claim 1 or 2, wherein the inorganic binder is in powder form.

12. The method according to claim 1 or 2, further comprising the step of adding a separate processing aid to the base material mixture.

13. The method according to claim 1, wherein the organic hydrogel binder is formed at a temperature in the range of 10°C to 60°C.

14. The method according to claim 1 or 2, wherein the step of forming the pellets includes extrusion molding of the aggregate.

15. The method according to claim 1 or 2, wherein the step of forming the pellets includes heating the aggregate to a temperature in the range of 10°C to 250°C.

16. The method according to claim 2, wherein the wet particulate substrate contains water in an amount of 1% to 40% by weight.

17. A pellet obtained by the method of claim 1 or 2, wherein the pellet comprises a particulate substrate, an organic binder, and an inorganic binder, and a hydrogel binder is formed by mixing these binders with water.

18. The pellet according to claim 17, wherein the pellet is heated to a temperature in the range of 10°C to 250°C.

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