pellets

Abstract

The invention relates to a process for producing pellets and pellets obtainable by the process. The process comprises: (i) providing a particulate material selected from the group consisting of carbonaceous material, metal, metal ore and mixtures thereof; and an inorganic binder comprising a metal silicate to form a mixture; (ii) compacting the mixture to form a pellet; and (iii) curing the pellet by contacting the pellet with gaseous carbon dioxide. Also described are pellets comprising a particulate material selected from the group consisting of carbonaceous material, metal, metal ore and mixtures thereof; silicon dioxide; and a metal carbonate.

Description

[0001] This invention relates to the production of pellets from particulate materials and to pellets produced in this manner. Typically, the pellets are cured with carbon dioxide.

[0002] The production of pellets from granular materials such as granular iron ore and other metallic ores is commonly known in the art. For example, pellets of this nature are frequently used in blast furnaces for producing molten iron, or in the direct iron reduction (DRI) of iron ore to produce sponge iron. Pellets are designed to be robust enough to allow for successful transport and use in blast furnaces or electric arc furnaces. For instance, when used in a blast furnace, the pellets must be able to maintain their integrity as they pass through the blast furnace into the furnace; otherwise, the performance of the blast furnace may be adversely affected.

[0003] Conventionally, a thermal process is used to form pellets, thereby producing so-called thermally bonded (hardened) billets. In hardening techniques, initially, a combination of a particulate substrate (particulate material) and a binder is used to form “green” pellets, which are then shaped into pellets (typically using a pelletizing machine). As used herein, the term “green pellet” takes its usual meaning in the art and refers to pellets that do not yet possess the strength required for their end use and require further processing or treatment. Green pellets are hardened via a series of steps including drying, preheating, firing, and cooling. The primary purpose of the drying stage is to remove moisture from the pellets, thereby making them more stable and easier to handle. Removing water in a controlled manner prevents crack formation and maintains the structural integrity of the pellets. The temperature range of the drying stage depends on the chemical and physical properties of the green pellets; however, it may last from 5 to 10 minutes in the range of 100°C to 250°C. The preheating stage typically employs a gradient heating process, from approximately 300°C to 350°C for 10 to 15 minutes, up to a maximum of approximately 1250°C to 1350°C. This preheating stage ensures that any present metal hydrates or metal carbonates decompose into their anhydrous forms. The decomposition of these types of compounds helps improve the structural integrity of the resulting pellets by removing water and / or gases that may react during firing, leading to overpressure and rupture of the pellets. The firing stage is typically carried out at temperatures above 1350°C for approximately 10 to 20 minutes (for typical capacities, e.g., 250 tph to 500 tph)) and results in the sintering of the pellets, providing the strength required to suit their end use. During the sintering process, bonds within the pellets are formed through recrystallization and bridging, resulting in ceramic bonding and the formation of large voids, which allows for some expansion and stress release. As used herein, the term "large voids" refers to voids within the pellets, with diameters ranging from approximately 50 μm to approximately 1 mm. Void formation is particularly important when the pellets are metallic ore pellets, as the reduction of the metal (e.g., the conversion of hematite to magnetite in iron ore) leads to volume changes and stress on the pellets. Since large voids do not form without firing, alternative methods are needed to prevent pellet disintegration under internal stress.

[0004] As mentioned above, a common problem associated with this type of pellet is the breakage of the agglomerates. In attempts to overcome this problem, binders such as cement or clay are typically used to bind the particles together, hoping to improve their strength for further processing. However, a problem associated with using cement or clay is that it increases the amount of silica in the iron and slag produced at the end of the process.

[0005] Furthermore, hardening processes are uneconomical because they are complex, must be carried out carefully, and require the application of significant amounts of heat. For example, the preparation of raw materials is crucial. To withstand the process, the green pellets must have an appropriate range of sizes, surface areas, and moisture content, as surface chemistry plays a vital role. Moreover, the process requires substantial energy due to the multiple heating stages involved.

[0006] Therefore, there is a need for a pellet production method that is less energy-intensive and more cost-effective. Furthermore, there is a need for a method that offers greater flexibility in the physical state of the particulate materials used, and that results in pellets with physical properties (particularly in terms of strength) comparable to or even superior to those produced using hardening methods, enabling processing and handling. The present invention aims to overcome or improve at least some aspects of this problem.

[0007] Therefore, in a first aspect of the invention, a method for producing pellets is provided, the method comprising:

[0008] (i) Provides a particulate material selected from carbonaceous materials, metals, metal ores and mixtures thereof; and an inorganic binder comprising metal silicates to form a mixture;

[0009] (ii) Compacting the mixture to form pellets; and

[0010] (iii) Solidify the pellets by contacting them with gaseous carbon dioxide.

[0011] The method of the present invention enables the rapid production of pellets with sufficient strength to be handled and transported during pellet formation without the need for heat application (although this may optionally be part of the method). These pellets also exhibit good water resistance and thermal properties suitable for the final use conditions of blast furnaces or other furnaces. For some pellet formulations, carbon dioxide enables the production of pellets with sufficient strength without the need for heat application, where heat would previously be necessary for the hardening process. For other pellet formulations, carbon dioxide acts as an acceleration agent for pellet hardening, allowing the pellets to be cold-formed over a longer period without the aid of a carbon dioxide-enhanced catalyst. Therefore, the present invention provides for the production of pellets in production sites where heat is not necessarily readily available, and provides (in some cases) a simpler design for pellet manufacturing plants. Furthermore, heat generation typically leads to production costs and, depending on the energy source used to generate the heat, can cause environmental damage through indirect carbon emissions from energy production. Therefore, its use may be undesirable unless heat is generated responsibly.

[0012] It should be noted that, as used in this general description, the terms “strength / reinforcement” and “hardening / hardening” are generally used interchangeably to indicate that the pellets possess transport and handling capabilities and ultimate robustness. The terms “granular material” and “granular substrate” are also used interchangeably to refer to pellet raw materials.

[0013] Furthermore, the use of carbon dioxide provides a means of sequestering this material, which is known to be a major contributor to greenhouse gas emissions. Carbon dioxide can compensate for waste carbon dioxide, such as that produced by heavy industry, or in cases where heating is also used for curing and green energy is unavailable. The use of carbon dioxide produced by heavy industry can be particularly beneficial in cases where the carbon dioxide is from the iron or steel production industry, as these industries traditionally generate large amounts of waste heat and carbon dioxide. For example, a typical ironmaking operation, including blast furnaces and auxiliary equipment, emits 5% to 50% carbon dioxide in waste gas, which can be equivalent to 2,000 tpd to 20,000 tpd. However, the gas flow rate will vary. For example, a medium-sized blast furnace can emit waste gas at 11,000 tpd (or 3,860 liters per minute). Furthermore, even small blast furnaces can produce 2,000 tpd of carbon dioxide (or 701 liters per minute). Therefore, although the impact is far less than, for example, that of a large power plant, the impact of blast furnace operations is significant and can be advantageous for decarbonization. Direct iron reduction (DRI) processes produce exhaust gases containing approximately 30% carbon dioxide, although some recapture is common in these systems; and electric arc furnace emissions contain exhaust gases ranging from 5% to 50% carbon dioxide. It is common practice to reuse the heat generated by industrial processes, including those mentioned above, but the carbon dioxide is typically released into the atmosphere or stored (physical or chemical storage). Such storage increases the cost of iron / steel production and wastes potentially valuable chemical carbon dioxide by locking it up without further use (despite obvious environmental benefits). Therefore, finding ways to utilize the generated carbon dioxide, and to store it in a productive and beneficial manner (as opposed to simply storing it to remove it from the atmosphere), is extremely beneficial in reducing emissions from industrial production sites (e.g., iron and steel) or fossil fuel power plants in Scopes 1 and 3. Furthermore, the method of the present invention uses carbon dioxide to produce valuable products (i.e., pellet feedstock, typically used in iron and steel in this case, but also potentially in the mining industry), storing the carbon dioxide as carbonates. Furthermore, since the pellets produced are typically intended for use in the manufacture of iron or steel (e.g., where they contain a metal or metal ore substrate), using carbon dioxide generated from the production of iron or steel (e.g., from exhaust gases from power generation or heat generated in internal combustion engines or hardening equipment at mining sites) to produce pellets (potentially at the location of the iron or steel production site) creates a desirable cycle in the process, which is both environmentally and economically beneficial, reducing the overall carbon footprint of the production site.

[0014] As described above, the method of the present invention provides robust pellets that offer one or more of the following benefits: robustness to transport, robustness to handling, good water resistance, and thermal properties suitable for the final use conditions of a blast furnace or other furnace. Not bound by theory, it is considered that strength can be obtained without the need for heat because carbon dioxide reacts with the inorganic binder (metal silicate) to form carbonates via anionic substitution. For example, in the case where the inorganic binder comprises sodium silicate, the substitution reaction is considered to be:

[0015] (Reaction 1).

[0016] This reaction (using carbon dioxide to separate silica from sodium silicate) provides pellets with higher thermal stability than pellets of the same composition that are not cured by contact with carbon dioxide. Similarly, without being bound by theory, silica is considered to have a greater affinity for reactive functional groups in particulate materials than for other silica groups. This produces pellets containing bonds between silica and particulate matter (e.g., metal / metal oxides in the particles) that would not form if metal silicates were simply mixed with the particulate matter without further processing. Essentially, the reaction with carbon dioxide to form metal carbonates as an alternative to dehydrated metal silicates allows for the provision of discrete silica particles that interact to form strong bonds with the particulate material in the pellets. This makes it possible to use carbon dioxide as a catalyst to cure bonded systems containing silicate components.

[0017] The reaction of metal silicates with carbon dioxide to form metal carbonates can be partial or complete. Since the strength of the pellets is roughly proportional to the extent of the reaction that forms free silica and carbonates, it is generally desirable for the reaction to be complete or near-complete. For example, the reaction is typically completed at least 50%, usually in the range of 50% to 100%, typically in the range of 60% to 90%, or 70% to 80%. The hardening / reinforcement of the pellets typically occurs after gas permeation of the green pellets, so that the outer surface of the pellets is usually hardened first, while the core hardens after prolonged exposure to carbon dioxide. It is for this reason that a partial reaction is often sufficient to provide pellets with the desired strength, as a hardened exterior is sufficient to protect the interior during processing.

[0018] The particulate material will typically comprise carbonaceous materials, metals, metal ores, or mixtures thereof. In many cases, the particulate material will be selected from metal ores, metals, and combinations thereof, as the application of carbon dioxide to green pellets containing such a particulate substrate provides particular benefit in terms of observed improvements in strength. The metal / metal ore may be further selected from metal residues, metal scraps, fine metal powders, iron ore sieves, and collected dust from furnaces including blast furnaces, BOS, EAF, and DRI. Collected dust will typically comprise combinations of metal oxides, partial oxides, and fine metal powders. The particulate substrate is typically derived from waste products of other industrial processes. The particulate substrate may comprise waste products from a single waste stream (where only particle size will vary) or waste products from a combination of waste streams (where mixed wastes of different compositions will be present). This is environmentally beneficial because the recycling and reuse of such materials reduces the amount of limited resources that might otherwise be wasted.

[0019] The carbonaceous material can be coke, graphite, carbon black, peat, or coal. Typically, the carbonaceous material will include graphite, coke, coal, or combinations thereof. It is possible that the carbonaceous material includes both coke and / or coal. As used herein, the term "coal" is intended to include lignite, sub-bituminous coal, bituminous coal, thermal coal, and anthracite. Coke has been found to be particularly problematic in pelletizing, and therefore the present invention provides a particular benefit in providing more robust coke pellets.

[0020] The metal can be, or the metal ore can contain: iron, zinc, nickel, copper, chromium, manganese, gold, platinum, silver, titanium, tin, lead, vanadium, cadmium, beryllium, molybdenum, uranium, aluminum or mixtures thereof; for example, as an elemental metal, or in the form of, for example, oxides or silicates.

[0021] Typically, the particulate substrate contains a metal, and more commonly, iron. The use of iron is advantageous due to its readily available availability and because it can be reused and recycled from waste products of other processes to provide environmentally sustainable accessibility to this material. When the particulate substrate contains a metallic ore, the ore will typically be an iron ore, such as goethite, pseudomorphous hematite, limonite, siderite, flint, hematite, or magnetite. Typically, when the particulate substrate is a metallic ore, it will be an iron ore, such as hematite or magnetite.

[0022] The particulate substrate can be powder or metal shavings, with the term "metal shavings" given its usual meaning in the art. Typically, the particle diameter of the particulate substrate is 4 mm or smaller (widest axis). Typically, the particle diameter will range from 30 μm to 4 mm, typically from 50 μm to 3 mm, or from 0.1 mm to 2 mm. Typically, at least 10% by weight of the particulate substrate is able to pass through a 100 μm sieve before forming pellets. The presence of a certain range of particle sizes within the sample improves the packing of material within the pellets.

[0023] It is possible that the particulate material is added in an amount of about 70% to about 99.9% by weight, typically about 80% to about 99% by weight, and more typically about 90% to about 95% by weight of the mixture in step (i). At these levels, there is a balance between the need for other components and the expectation of maximizing the level of the particulate matrix, since the reactive raw materials are the reason for granulation. It is possible that the particulate material comprises metallic ores, metals, and combinations thereof, and is added in an amount of about 70% to about 99.9% by weight, typically about 80% to about 99% by weight, and more typically about 90% to about 95% by weight. It is possible that the particulate material comprises carbonaceous material. It is possible that the particulate material is added in an amount of about 70% to about 99.9% by weight, typically about 80% to about 99% by weight, and more typically about 90% to about 95% by weight.

[0024] It is possible that the moisture content of the particulate material is less than 25%. When it is higher than these levels, the dilution of the particles affects their ability to form tight aggregates. Typically, the moisture content will be in the range of about 1% to about 25% by weight of the mixture, usually about 3% to about 20% by weight, and more typically about 5% to about 15% by weight.

[0025] The inorganic binder comprises one or more metal silicates. It is possible that the metal silicate includes Group I or Group II metal silicates, or more than one Group I and / or Group II metal silicate. While other metal silicates can be successfully used as the inorganic binder of this invention, it has been found that Group I and Group II metals are more reactive than other metals in the presence of carbon dioxide (promoting carbonate formation). As a result, in the case of Group I or Group II silicates, “free” silicates are readily formed, thereby promoting enhanced crosslinking of silicate bonds and improving the thermal properties of the pellets. Some more stable metal silicates may require the application of pressure and heat to promote crosslinking. Therefore, the metal silicate will generally be selected from sodium silicate, potassium silicate (e.g., K₂SiO₃), calcium silicate (e.g., CaSiO₃, Ca₂SiO₄), magnesium silicate (e.g., MgSiO₄), and combinations thereof. It is possible that the metal silicate is selected from sodium silicate, potassium silicate, magnesium silicate, or combinations thereof. In the case of metal silicates including calcium silicate, it can exist in its natural mineral state, such as wollastonite (i.e., CaSiO3) and clinoptilolite (i.e., Ca2SiO4). It is generally not present as a calcined product (e.g., Portland cement). It is possible that the metal silicate is selected from sodium silicate, magnesium silicate, or combinations thereof. Sodium silicate has been found to be particularly advantageous due to its high ionic reactivity. Sodium silicate is also readily available and inexpensive. It is possible that the metal silicate includes both sodium silicate and magnesium silicate. This combination of alkali metal silicates has been found to provide pellets with high cold-pressing strength. Without being bound by theory, since sodium silicate is more reactive than magnesium silicate, it should preferentially react according to the substitution reaction outlined in Equation 1 above. This should then allow magnesium silicate to co-react to form a Na-Mg complex and produce a bound salt. It is thought that magnesium silicate transforms from its generally more stable crystalline phase to an amorphous, more reactive phase during this process.

[0026] Alternatively, alkali metal silicates may include magnesium silicate, potassium silicate, or combinations thereof.

[0027] Metal silicates can be in liquid form, powder form, or a combination thereof. When a metal silicate is in liquid form, it will be present in a larger quantity because the activity level is lower in liquid metal silicates compared to powdered metal silicates. In the case of a metal silicate in liquid form, it is typically present in the range of about 1% to about 6% by weight, typically about 1.5% to about 5.5% by weight, typically about 2% to about 5% by weight, and typically about 3% to about 4% by weight of the mixture in step (i). In the case of a metal silicate in powder form, it is typically present in the range of about 0.5% to about 3.5% by weight, and typically about 1% to about 3% by weight of the mixture. It is possible to have two or more metal silicates present. In the case of two or more metal silicates present, it is possible that at least one is in liquid form and at least one is in powder form. When two or more metal silicates are present, at least one is in liquid form and at least one is in powder form, typically the liquid and powder forms are present in a ratio of 5:1 to 1:1. Optionally, this ratio can be 3:1, or alternatively, it can be 3:2. Therefore, metal silicates can be present in the mixture in the range of about 0.5 wt% to about 6 wt%, typically about 1 wt% to about 5 wt%, or typically about 1.5 wt% to about 4 wt%. At these levels, sufficient metal silicates are present to ensure bonding occurs, but the binder is not used excessively, thereby avoiding a reduction in the total amount of particulate substrate available from the pellets.

[0028] Optionally, step (i) (formation of the mixture) may also include the addition of an organic binder. It has been found that the presence of organic binders, in addition to inorganic binders, increases the curing speed. Possible organic binders include: natural polymers (e.g., lignin sulfonates); synthetic polymers (e.g., polyacrylic acids, styrene-acrylate copolymers, polyvinyl alcohol, or synthetic organic resins); cellulose materials; glycerides (e.g., monoesters, diesters, or triesters of glycerol); polysaccharides; or combinations thereof. As used herein, the term "polyacrylic acid" takes its usual meaning in the art and refers to a class of synthetic polymers derived from acrylic acid or its esters. Examples of polyacrylic acids include, but are not limited to, polyacrylic acid (PAA), poly(methyl methacrylate) (PMMA), and polyacrylamide (PAM). As used herein, the term "styrene-acrylate copolymer" takes its usual meaning in the art and relates to synthetic polymers formed by copolymerization of styrene and acrylic acid or its derivatives. Examples of styrene-acrylate copolymers include, but are not limited to, styrene-2-ethylhexyl acrylate (2-EHA), styrene-ethyl acrylate (EA), styrene-methyl methacrylate (MMA), and styrene-butyl acrylate (BA). Typically, styrene-acrylate copolymers will include styrene-ethyl acrylate (EA). As used herein, the term "cellulose material" takes its usual meaning in the art and refers to any material derived from or containing cellulose. Cellulose materials include natural materials composed primarily of cellulose, but also include synthetic derivatives of cellulose. As used herein, the term "glycerol lipids" takes its usual meaning in the art and refers to a type of lipid molecule consisting of a glycerol backbone esterified with one or more fatty acids or acyl groups.

[0029] The organic binder may be selected from: natural polymers (e.g., lignin sulfonates), synthetic polymers (e.g., polyacrylic acids, styrene-acrylate copolymers, synthetic organic resins such as polyacrylamide resins or phenolic resins (including methyl phenolic resins, which are base-catalyzed phenolic resins with a formaldehyde to phenol ratio greater than one (typically about 1.5), or phenolic varnish resins with a formaldehyde to phenol molar ratio less than one) or polyvinyl alcohol); cellulose materials, such as cellulose fibers, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), or hydroxyethyl methyl cellulose (MHEC); glycerides (e.g., glyceryl acetate, glyceryl diacetate, and glyceryl triacetate); and / or polysaccharides, such as starches (e.g., wheat starch, corn starch, barley starch, and potato starch, and / or molasses) or gums (e.g., gum arabic, guar gum, and / or xanthan gum). Possible organic binders are selected from: polyacrylamide resins, polyvinyl alcohol, phenolic resins (e.g., phenolic varnish resins or methyl phenolic resins), polyacrylic acids (e.g., polyacrylic acid (PAA), poly(methyl methacrylate) (PMMA), polyacrylamide (PAM)), styrene-acrylate copolymers (e.g., 2-ethylhexyl acrylate styrene (2-EHA), ethyl acrylate styrene (EA), methyl methacrylate styrene (MMA), and butyl acrylate styrene (BA)), triacetin, diacetin, cellulose fibers, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxyethyl methyl cellulose (MHEC), wheat starch, corn starch, barley starch, potato starch, gum arabic, guar gum, xanthan gum, and combinations thereof. The organic binder may be selected from: polyacrylamide resin, polyvinyl alcohol, phenolic resin, triacetin, polyacrylamide, ethyl acrylate styrene, cellulose fiber, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), or combinations thereof.

[0030] Organic binders may include cellulose materials, polyacrylamide resins, polyvinyl alcohol, phenolic resins, or combinations thereof.

[0031] When the organic binder includes cellulose materials, it is possible that the organic binder includes carboxymethyl cellulose (CMC), cellulose fibers, hydroxyethyl methyl cellulose (MHEC), or a combination thereof. It is possible that the organic binder includes carboxymethyl cellulose (CMC) and / or hydroxyethyl methyl cellulose (MHEC). CMC is advantageous because it can be added in powder form, which allows for control of the total moisture content of the pellets. CMC also has a longer shelf life compared to other plant-derived binders. This is because other plant-derived binders are generally more susceptible to microbial attack and therefore more prone to decomposition. Sometimes, the organic binder can be hydroxyethyl methyl cellulose (MHEC), which has been found to have particularly good binding qualities and helps to enhance the strength of the pellets. However, because MHEC is highly water-soluble, this can affect the shelf life of the final pellets, resulting in a shorter shelf life compared to pellets containing CMC.

[0032] Typically, when in solution, CMC has an active polymer content of about 40% to about 90% and a pH range of about 5 to about 9, or about 6 to about 8. Furthermore, the number-average molecular weight (Mn) of CMC... n The number average molecular weight (Mn) will typically be in the range of approximately 3,000 to approximately 70,000. Optionally, the number average molecular weight of CMC will be in the range of approximately 10,000 to approximately 50,000. Without being bound by theory, it is thought that, for example, in the case of lower number average molecular weight CMCs in the range of approximately 10,000 to approximately 50,000, high-concentration solutions can be prepared, which in turn can improve the strength of the pellets. Any known technique, such as size-exclusion chromatography (SEC), gel permeation chromatography (GPC), or light scattering, can be used to determine the number average molecular weight (Mn). Specific measurement conditions (including temperature, solvent, and calibration standards) will be based on the chosen technique and selected according to appropriate industry standards.

[0033] Polyvinyl alcohol (PVA) can be used as an organic binder in place of other organic binders or other organic binders, such that the organic binder may contain about 10% to about 100% by weight, typically about 20% to about 90% by weight, or about 50% to about 75% by weight of PVA. When the organic binder contains PVA, the organic binder is typically added in the range of about 0.01% to about 2.0% by weight of the pellets, typically about 0.05% to 1.5% by weight of the pellets, or about 1% by weight of the pellets.

[0034] Unbound by theory, it is believed that PVA provides good mixing of components and high strength because the polymer network formed by PVA is strong. Furthermore, the process of pelletizing with PVA removes air from the particulate material, which reduces oxidation of the particulate substrate when it is metallic. 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.

[0035] Commercially, PVA is typically formed from polyvinyl acetate by saponification of polyvinyl acetate with sodium hydroxide, replacing the acetate groups with hydroxyl groups. Partial saponification means that some of the acetate groups have been replaced by hydroxyl groups, thereby forming at least partially saponified polyvinyl alcohol residues. Typically, the degree of saponification of PVA is at least about 80%, typically at least about 5%, at least about 90%, at least about 95%, at least about 99%, or about 100%. Typically, it is used as a solution in water. PVA can be modified to include, for example, sodium hydroxide. Typically, when in solution, PVA-bound materials have an active polymer content of about 12% to about 13% and a pH in the range of about 4 to about 7. Furthermore, the number-average molecular weight (M) of PVA... n The number average molecular weight will typically be in the range of about 15,000 to about 150,000. Optionally, the number average molecular weight of PVA will typically be in the range of about 30,000 to about 120,000. Without being bound by theory, it is thought that, for example, at a lower number average molecular weight in the range of about 15,000 to about 60,000, high-concentration solutions can be prepared, which in turn can improve the strength of the pellets.

[0036] In cases where the organic binder includes polyacrylamide resin, it will typically have a medium to high number-average molecular weight (M). n This includes anionic polyacrylamide resins with medium to high charge densities. For example, the number average molecular weight can range from 100,000 to 2,000,000, typically from 500,000 to 1,500,000. The charge density will typically be in the range of 25% to 50%. The charge density of the polymer can be measured using any technique known in the art. Suitable methods include, but are not limited to, potentiometric titration, conductivity titration, electrophoretic mobility, light scattering, and nuclear magnetic resonance (NMR). Specific measurement conditions (e.g., temperature, solvent, and calibration criteria) will be selected based on the chosen technique and in accordance with appropriate industry standards.

[0037] When the organic binder includes a polysaccharide, it can be starch or amylase starch. For example, it can be pregelatinized potato starch. It can be added in an amount of about 0.8% by weight of the final pellet, typically about 0.6% by weight. Using polysaccharides as a component of the mixture may be desirable because polysaccharides often also act as thickeners.

[0038] The organic binder may be present in the mixture in the range of about 0.2% by weight to about 5% by weight, optionally about 0.25% by weight to about 0.45% by weight, optionally about 0.3% by weight to about 0.4% by weight.

[0039] The viscosity of the organic binder may be in the range of about 1,000 MPa·s to about 16,000 MPa·s, typically in the range of about 2,000 MPa·s to about 10,000 MPa·s, or in the range of about 3,000 MPa·s to about 7,000 MPa·s. Viscosity can be measured using standard techniques known in the art, such as capillary viscometers, rotational viscometers, and oscillating rheometers. Specific measurement conditions (including temperature, solvent, and calibration criteria) will be selected based on the chosen technique and in accordance with appropriate industry standards. Typical measurement conditions include a temperature ranging from 20°C to 25°C, the use of a solvent such as water or an organic solvent, and calibration with a standard viscosity reference material.

[0040] The mixture of step (i) may also contain flux additives to promote the flowability of the mixture during subsequent processing. Where flux additives are present, they may be selected from silica, dolomite, fluorite, calcium oxide, magnesium oxide, carbon, aluminum, pure peridotite, basalt, and combinations thereof. Where present, the flux additives will typically be present in the range of about 0.5% by weight to about 2% by weight, and typically about 1% by weight to 1.5% by weight of the mixture.

[0041] As described above, it is possible that the carbon dioxide used to solidify the pellets is produced by one or more industrial processes. This may be referred to as “waste” carbon dioxide, or, when used, as “recycled” carbon dioxide. Therefore, the method of the present invention may also include the step of capturing carbon dioxide produced by one or more industrial processes for use in solidifying the pellets. The step of solidifying the pellets includes contacting the pellets (green pellets) with gaseous carbon dioxide. Contact will typically involve placing the pellets in a gas stream. This can be achieved by passing a carbon dioxide stream through a static bed of pellets, or by transporting the pellets via a moving gas stream. The gas stream may be almost entirely carbon dioxide (e.g., “pure” or “purified” carbon dioxide), or it may be carbon dioxide mixed with an inert carrier gas such as argon or nitrogen. As used herein, the term “inert carrier gas” is intended to include any gas that will not react with the carbon dioxide or the material in the green pellets. However, typically, carbon dioxide will comprise about 70% to about 100% by weight of the gas stream, usually about 80% to about 99% by weight, or about 90% to about 95% by weight, to maximize the contact between the reactive carbon dioxide gas and the pellets, thereby ensuring that hardening occurs as quickly as possible and minimizing the time spent in the curing step (iii). One advantage of using a gas stream is that the carbon dioxide supply is continuously replenished, which would not occur, for example, if the pellets are placed in a sealed chamber and allowed to react in a static atmosphere of carbon dioxide.

[0042] Typically, pellet solidification is achieved by contacting the pellets with gaseous carbon dioxide. This is done by introducing the pellets into a gas stream containing carbon dioxide, at a flow rate ranging from about 1 liter / min to about 100 liters / min, typically from about 2 liters / min to about 50 liters / min, or from about 2 liters / min to about 20 liters / min. At these rates, sufficient carbon dioxide is present to ensure good contact with the pellets, without excessive unreacted carbon dioxide exceeding the contact point (which would require recirculation to avoid waste). As a skilled reader will understand, the flow rate will be adjusted within this range for the load of solidified pellets, pellet volume, residence time, pressure, and temperature used.

[0043] Pellet solidification can be carried out at atmospheric pressure, although it is typically carried out at slightly increased pressures, such as in the range of about 1 bar to about 3 bar (1 bar = 0.1 MPa), typically about 1.5 bar to about 2.5 bar, or about 1.5 bar to about 2 bar. At these pressures, carbon dioxide permeation of the pellets is enhanced relative to atmospheric pressure. As a skilled reader will understand, the pressure will be adjusted within this range for the solidified pellet load, pellet volume, residence time, carbon dioxide flow rate, and temperature.

[0044] The pellets will remain in the gas stream until the hardening reaction (i.e., the silicate turns into carbonate, subsequently releasing silica) proceeds to a point where the pellets are sufficiently robust. As a skilled reader will understand, this will depend on the load on the solidified pellets, the pellet volume, the pressure, the carbon dioxide flow rate, and the temperature.

[0045] While pellets can be cured at ambient temperature (cold forming), for some formulations this will require an extended curing time to provide the desired level of strength. Therefore, it is possible that the step of curing the pellets (step iii) additionally includes applying heat at a temperature ranging from about 50°C to about 1000°C. Heating the pellets during contact with gaseous carbon dioxide reduces the curing time.

[0046] The term "cold forming" refers to processes such as non-curing, sintering, or heating to above about 50°C, above about 40°C, or about 30°C, such that if any heat is applied, the pellets will typically be heated to below 50°C. In other words, it is generally likely that if heat is applied during pellet formation, only a low level of heat will be applied. Furthermore, while frictional heat may be generated during pellet formation through any pressing and / or extrusion processes used, and the binder may undergo an in-situ exothermic reaction, this is sometimes the only heat present and does not constitute heating as described above, as it is not an application of external heat. These inherent heating mechanisms are not expected to generate sufficient heat to affect pellet formation. Compared to commonly used hardening manufacturing techniques, cold forming offers significant advantages in reducing energy consumption. High-temperature furnaces are also unnecessary for pellet production, resulting in a simpler, more economical, and environmentally friendly manufacturing process.

[0047] However, similar to the use of carbon dioxide from industrial methods described above, these methods also generate excess heat, which can be used to heat the pellets during the curing step of the present invention, thereby mitigating the heat consumption of industrial processes by designing the system (e.g., by using a heat exchanger) to reuse waste heat generated elsewhere. Therefore, it is possible that the application of heat includes applying heat generated by one or more industrial processes, such as heat generated by the steelmaking or ironmaking industries. As described above, it may be advantageous to heat the pellets during curing to a temperature in the range of about 50°C to about 1000°C. It is also possible that the pellets are heated during curing to a temperature in the range of about 60°C or about 100°C to about 900°C, typically about 150°C to about 800°C, typically about 200°C to about 600°C, or typically about 200°C to about 400°C. Finally, it is possible that the pellets are heated during curing to a temperature in the range of about 400°C to about 800°C, or about 600°C to about 800°C. At these temperatures, pellets can solidify within minutes, for example, from about 30 seconds to about 30 minutes, typically from about 1 minute to about 15 minutes, or from about 2 minutes to about 10 minutes, making pellet formation very rapid compared to the much longer curing time (hours, and in some cases days) that might be required without using heat as part of the method.

[0048] The method of the present invention includes the step of compacting a substrate mixture to form pellets. This can be achieved via any of a range of compaction techniques, such as passing the substrate mixture through compaction rollers (e.g., on a roller press), compaction screws, hammer mills, hydraulic presses, mechanical presses, or pressure plates. Pellets can be formed by extrusion, such that the step of forming pellets includes extruding the mixture. The extrusion process can be carried out at temperatures ranging from about 30°C to about 70°C, typically from about 35°C to about 55°C, with the temperature rise caused by frictional heat generated during the extrusion process. Furthermore, the process can be carried out at atmospheric pressure or under a vacuum. As used herein, the term "under a vacuum" takes its usual meaning in the art, since the extrusion process can be carried out at pressures below atmospheric pressure. One method that can be used is a roller pressing process (RPP), in which the step of compacting the substrate mixture includes passing the mixture through a roller press configured to produce pellets. The rollers apply continuous pressure, thereby forming the substrate mixture into pellets as it passes through the gaps between the rollers. This method allows for continuous production and can process a variety of materials, thereby producing pellets with consistent size and density. Another method that can be used is the cold-pressing technique (CTS), in which the substrate mixture is placed in a mold or die and subjected to high pressure using a hydraulic or mechanical press. The pressure compacts the material into solid pellets without the use of heat, thus ensuring that the pellets are dense and cohesive. This method is advantageous due to its energy efficiency, as it eliminates the need for heating.

[0049] When using the RPP method, the hydraulic pressure applied in step (ii) is typically in the range of about 50 bar to about 300 bar, typically in the range of about 100 bar to about 250 bar, or about 150 bar to about 200 bar.

[0050] When using the CTS method, the pressure is calculated at 6 tons of force. The pressure at 6 tons of force will vary depending on the size of the mold used (i.e., the inner diameter of the mold). For example, for a 10 mm mold, the pressure applied in step (ii) can range from about 6000 bar to about 8000 bar, typically from about 6500 bar to about 7500 bar. For a 16 mm mold, the pressure applied in step (ii) can range from about 2000 bar to about 5000 bar, typically from about 2500 bar to about 4000 bar, typically from 2750 bar to 3500 bar. For a 20 mm mold, the pressure applied in step (ii) can range from about 800 bar to about 3500 bar, typically from about 1000 bar to about 3000 bar, typically from about 1500 bar to about 2500 bar.

[0051] It is possible that the pellets are subjected to an inert atmosphere prior to step (iii) of the method according to the first aspect of the invention. As used herein, the term "inert atmosphere" takes its usual meaning in the art and refers to an environment containing gases that are non-reactive under specific conditions, more specifically gases that do not react with carbon dioxide or the materials in the green pellets. Incorporating this additional step prior to step (iii) can prevent any undesirable side reactions, thereby improving the quality of the resulting pellets. It is possible that the pellets are subjected to an inert atmosphere by introducing the pellets into a stream of inert gas with a flow rate in the range of about 1 liter / min to about 100 liters / min, typically about 2 liters / min to about 50 liters / min, or about 2 liters / min to about 20 liters / min. Where the method includes the additional step of subjecting the pellets to an inert atmosphere, the pellets may be heated to a temperature in the range of about 50°C to about 1000°C, about 60°C, or typically about 100°C to about 800°C, typically about 150°C to about 700°C, or more typically about 200°C to about 600°C before contact with gaseous carbon dioxide. The gas used to provide the inert atmosphere may include nitrogen or argon. It is possible that the gas used to provide the inert atmosphere includes nitrogen.

[0052] It is possible that the method may also include an additional step (iv) of cooling the resulting pellets under an inert atmosphere. The inert atmosphere may include nitrogen or argon. Typically, the inert atmosphere will include nitrogen. Cooling under an inert atmosphere is advantageous because it prevents any undesirable reactions from occurring. Due to the ease of controlling the atmosphere in small-scale reactions, treatment under an inert atmosphere is frequently used under experimental conditions.

[0053] In a second aspect of the invention, pellets obtainable by the method according to the first aspect of the invention are provided, and in a third aspect of the invention, pellets comprising: particulate material selected from carbonaceous materials, metals, metal ores, and mixtures thereof; silica; and metal carbonates, wherein the metal carbonates are generally formed by the reaction of an inorganic binder comprising metal silicates with gaseous carbon dioxide. As described above, the pellets of the second and third aspects of the invention have been found to have unique chemical structures. The reaction of metal silicates with carbon dioxide provides metal carbonates and silica, which are believed to form bonds with the particulate matter, for example, with metal / metal oxides in metal-containing particulate matter, bonds that would not exist without curing in carbon dioxide.

[0054] Silica typically exists as discrete particles, whose surfaces are usually bonded together via hydrogen bonds between hydroxyl groups present in the particulate material and oxide groups in the silicate, thus forming composite materials.

[0055] The volume and size of the pellets will depend on their final application. For example, pellets used in steelmaking will typically be larger than those used in DRI (Damage Reinforced Plastic) because the pellets must have sufficient mass to be submerged in molten steel during steelmaking. Typically, the average volume of a pellet is approximately 2.5 cm³. 3 approximately 25 cm 3 Within a range, usually around 3 cm 3 Approximately 15 cm 3 or about 5 cm 3 approximately 10cm 3 Within a certain range. The size of the pellets will typically be manufactured to minimize the surface area, and will typically be, for example, roughly spherical, oval, cylindrical, or cubical in shape.

[0056] Unless otherwise stated, each of the described elements may be used in combination with any other elements as will be understood by those skilled in the art. Furthermore, while all aspects of the invention preferably “comprise” the features described with respect to that aspect, it is particularly contemplated that they may “consist” or “substantially constitute” those features outlined in the claims. Moreover, unless specifically defined herein, all terms are intended to give their meaning as commonly understood in the art.

[0057] Furthermore, in the discussion of this invention, unless otherwise stated, the disclosure of optional values ​​for the upper or lower limits of the permissible range of a parameter should be interpreted as the following implied statement: each intermediate value of the parameter (between the smaller and larger alternatives) is itself disclosed as a possible value of the parameter.

[0058] Furthermore, unless explicitly excluded, 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 refer to the percentage of a component by weight in the final pellet by weight. If 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.

[0059] To make the invention easier to understand, it will be further described below with reference to the accompanying drawings and specific embodiments.

[0060] Figure 1 A schematic diagram of a laboratory test bench (an iron ore test bench from the Polish ITR equipment) used in the method of the present invention;

[0061] Figure 2 for Figure 1 An exploded view of the test bench, focusing on the furnace;

[0062] Figure 3The images, obtained by XRD / SEM, show carbonate formation as a function of the relative percentage of carbonate / silicate in the pellets. The pellets on the left of the image are solidified in carbon dioxide and are crystalline, indicating carbonate formation. The pellets on the right of the image are solidified in air and show no signs of carbonate formation.

[0063] Figure 4 To illustrate after partial curing Figure 3 A 1200×1200 pixel optical microscope image with 140x magnification formed by carbonates on the surface of the left-hand pellet;

[0064] Figure 5 To show what happens after curing is complete Figure 3 A 1200×1200 pixel optical microscope image of the surface of the left-hand sphere at 140x magnification;

[0065] Figure 6 This illustrates the formation of carbonates on the surface. Figure 3 Magnified optical microscope image of the surface of the left-hand sphere;

[0066] Figure 7 The illustration of the results for tests ID 1 through ID 8 highlights how curing atmosphere and duration affect the cold crushing strength (CCS) of the pellets. Specifically, Figure 7 (a) Illustrations of Test ID 1 (i.e., cured under CO2) and Test ID 2 (i.e., cured under air) at 200°C; Figure 7 (b) Illustrations of test ID 3 (i.e., cured under CO2) and test ID 4 (i.e., cured in air) at 400°C; Figure 7 (c) Illustrations of Test ID 5 (i.e., cured under CO2) and Test ID 6 (i.e., cured in air) at 600°C; and Figure 7 (d) Illustrations of Test ID 7 (cured under CO2) and Test ID 8 (cured in air) at 800°C; and

[0067] Figure 8This is a graph illustrating the cold compressive strength (CCS) of pellets containing different silicate / silicate combinations under different curing conditions. The left-hand bar graph (i) shows the CCS of pellets containing solid sodium silicate (black filler), pellets containing a combination of liquid sodium silicate and magnesium silicate (rising diagonal stripes from left to right), and pellets containing a combination of liquid sodium silicate and calcium silicate (horizontal stripes) after curing in an oven under air for 120 minutes. The right-hand bar graph (ii) shows the CCS of pellets containing solid sodium silicate (black filler), pellets containing a combination of liquid sodium silicate and magnesium silicate (rising diagonal stripes from left to right), pellets containing a combination of liquid sodium silicate and calcium silicate (horizontal stripes), pellets containing magnesium silicate (vertical stripes), and pellets containing calcium silicate (falling diagonal stripes from left to right) after curing in an ITR device under CO2.

[0068] Example

[0069] The embodiments described herein include the formation of pig iron ore pellets, which are agglomerated at ambient temperature using a roller press or cylindrical die press. As used herein, the term "ambient temperature" takes its common meaning in the art and refers to the temperature of the air surrounding the component, typically in the range of 15°C to 25°C. The green pellets are solidified under controlled conditions, including under a CO2 gas stream, and various physical properties are measured. Specifically, cold compressive strength (CCS), thermal durability, water resistance, and appearance under an optical microscope are measured.

[0070] method

[0071] Formation of green pellets

[0072] The formation of green pellets involves thoroughly mixing iron ore particles with a binder material to form a blend. The blend is then pressed into aggregates to form green pellets.

[0073] The two agglomeration methods used in the embodiments described herein (both performed at ambient temperature) are (i) cylindrical test specimens (CTS) formed by a cylindrical molding machine, and (ii) roller-pressed pellets (RPP) formed by a roller press.

[0074] (i) CTS

[0075] Using a Hobart N50-G mixer at speed setting 2, a measured mass of iron ore particles was mixed with one or more binders for 3 minutes. A portion of the resulting blend was placed into a stainless steel cylindrical mold with a height of 90 mm and an inner diameter of 20 mm, allowing the material to fill the mold without compaction. A Baileigh Industrial H-frame 20-ton Shop Press (equivalent to HSP-20A) was used to push the piston down into the mold and compact the material. The calculated pressure at 6 tons of force was 1,873 bar (i.e., 187.3 mPa). Specifically, pressure was applied to the piston until a force equivalent to 6 tons (metric tons) was measured. Once this value was reached, the pressure was immediately released. The Baileigh press was then used to expel the agglomerated pellets of material from the mold. This process was repeated to form several pellets from the batch of blended material.

[0076] (ii) RPP

[0077] The iron ore and binder formulation were mixed for 3 minutes in a Wirtgen WLM30 paddle mixer (high shear 45 rpm). After mixing, the material was removed from the mixer and a sample was produced as follows.

[0078] The material is fed into the Hutt roller press under a gauge pressure of 160 bar to produce a size of approximately 27 mm × 18 mm × 10 mm (4.86 cm). 3 ) oval-shaped roller-pressed pellets.

[0079] Within one hour of production, the pellets are transferred to the CO2 curing stage. The gas stream contains 100% carbon dioxide at a flow rate of approximately 5 liters per minute at atmospheric pressure.

[0080] The synthesis on the test bench is easily scalable, for example, to recover carbon dioxide generated as waste gas in industrial processes through appropriate engineering design.

[0081] Pellet solidification

[0082] (i) Curing in air atmosphere (comparison)

[0083] To simulate typical curing conditions in an air atmosphere, the pellets were placed on a metal tray inside a ventilated drying oven at a specified temperature for a specified duration without forced airflow.

[0084] (ii) Curing in the presence of gaseous carbon dioxide

[0085] A test bench is used to solidify the pellets under carbon dioxide conditions. A schematic diagram of the test bench is shown below. Figure 1 and Figure 2 The general procedure is as follows:

[0086] A sample of 500 g of green pellets 16 is placed on a bed of ceramic beads 17 in reactor 2 (e.g., a reaction vessel), and the system power module 14 is activated via main switch 4. Gas flow through the reactor is initiated via process start button 8. The sample is heated to the desired temperature at atmospheric pressure with a flow of N2 at a rate of 5 L / min, entering through gas inlet 3 and exiting through outlet 18. After reaching the desired temperature, the gas input is switched from N2 to CO2, exiting through gas inlet 3 and outlet 18 at 5 L / min and atmospheric pressure. The temperature is controlled by a heating system including furnace 1, heater off button 5, heater on button 6, LED indicator 7 (to indicate whether furnace 1 is on or off), temperature controller 9, thermometer 10, and heater transformer 15. The on / off buttons (6 and 7) are manually operated to maintain the sample at the desired temperature. The temperature is maintained at 200°C, 400°C, 600°C, and 800°C for residence times of 2 minutes, 5 minutes, or 10 minutes, respectively. The process is monitored using thermocouple 10, CO2 signal LED 11, N2 signal LED 12, and gas flow meter 13. For example... Figure 1 and Figure 2 As shown in the image.

[0087] After the prescribed CO2 exposure, the sample was cooled under an inert N2 atmosphere to prevent any further reaction.

[0088] Optical microscopy

[0089] Images were captured in bright field configuration on an Olympus DSX system. Scale bars are shown in the illustration.

[0090] carbonate formation

[0091] Observe from microscopic images 3 to 5.

[0092] Water resistance

[0093] The samples were immersed in water at ambient temperature for 1 hour and 5 hours, and the compressive strength was tested after drying.

[0094] Cold compressive strength (CCS)

[0095] The CCS values ​​described herein were determined using the standard method according to ISO 4700:2015, employing a Mecmesin Omnitest material testing apparatus 10. Results are presented in kilonewtons (kN) or kilogram-forces (kgf). As used herein, 1 kgf = 0.00980665 kN.

[0096] thermal properties

[0097] Using the standard method according to ISO 4696-2:2015, the following Figure 1 and Figure 2 The test ITR apparatus shown is used to determine the thermal properties of pellets. This ISO provides a method for evaluating the degree of size degradation of iron ore under conditions similar to those in a low-temperature reduction zone in a blast furnace (i.e., a reducing environment at 550°C).

[0098] Example 1 - Sodium silicate and magnetite

[0099] Using the above RPP method, 2.0 wt% sodium metasilicate was mixed with 10 kg of magnetite iron ore (D... v (90 = 186 µm, >97 wt% Fe3O4, >68 wt% Fe) were mixed at 15 °C. The resulting substrate mixture was formed into an agglomerate and cured at room temperature (approximately 20 °C).

[0100] The resulting pellets contain 2% by weight of sodium metasilicate.

[0101] Test data shows that sodium silicate partially reacts to form sodium carbonate and silicon dioxide, as evidenced by the approximately 50 kgf increase in strength after one hour of curing. The shell is distinctly white, indicating carbonate formation. Figures 3 to 5 As shown in the figure. It is expected that under these conditions, smaller pellets that are closer in size to those typically used in industrial processes will solidify more quickly.

[0102] Example 2 - Sodium silicate, iron ore and carboxymethyl cellulose

[0103] Using the RPP method described above, 10 kg of magnetite ore (D80 = 500 µm, >97 wt% Fe3O4) and 2.0 wt% sodium metasilicate were mixed at ambient temperature. Then, 0.25 wt% carboxymethyl cellulose was added, and the mixture was mixed for another 3 minutes. The resulting matrix mixture formed agglomerates.

[0104] The pellets contain 2% by weight silicate and 0.25% to 0.5% by weight carboxymethyl cellulose. Curing is promoted under the test conditions described in Example 3.

[0105] Example 3 - Curing at a range of temperatures with and without carbon dioxide

[0106] Four different curing temperatures were used in tests ID 1 through ID 8: 200°C, 400°C, 600°C, and 800°C. At each temperature, both air and CO2 curing atmospheres were used. As detailed above, air curing was performed in a drying oven, while CO2 curing was performed in an ITR device. Under each of these conditions, the pellet samples were cured for different durations: 2 minutes, 5 minutes, and 10 minutes.

[0107] In test ID 1, as described above, the green pellets were solidified at approximately 200°C, under atmospheric pressure, and in carbon dioxide.

[0108] In Test ID 2 (Comparative Test), the green pellets were solidified at approximately 200°C, at atmospheric pressure, and in air (i.e., without the addition of carbon dioxide).

[0109] Test IDs 3 through 8 were used to repeat tests ID 1 and ID 2 at different temperatures, as shown in Table 1 below. The results are shown in Table 2, with each of test IDs 2, 4, 6, and 8 serving as a comparative example.

[0110] Table 1 - Conditions for Test IDs 1 to 8

[0111]

[0112] Table 2 - Effect of curing atmosphere and duration on cold compress strength (CCS) of pellets.

[0113]

[0114] As can be seen, at all temperatures, curing in the presence of carbon dioxide significantly increased the hardness of the pellets relative to the green pellet strength (Test ID 1, Test ID 3, Test ID 5 and Test ID 7) and relative to comparative tests in which the pellets were not exposed to carbon dioxide (Test ID 2, Test ID 4, Test ID 6 and Test ID 8).

[0115] Furthermore, these increases were observed over a very short period (only two minutes), and in many cases, little improvement was observed with longer exposure times, making it sufficient to expose pellets to carbon dioxide for just a few minutes to provide pellets that can be processed and transported as needed. This means that exposing pellets to CO2 for just a few minutes is sufficient to produce pellets that are strong enough to be processed and transported according to industry requirements. This is crucial because pellet production typically occurs at iron ore mining sites, and therefore the pellets must be able to withstand transport to ironmaking sites that may be located far away.

[0116] Furthermore, while curing at 200°C provides pellets strong enough to meet transport and handling standards, data shows that greater strength can be achieved by increasing the curing temperature, with the highest CCS value observed at 800°C. Therefore, additional heat can be applied for pellet formulations with higher resistance to curing.

[0117] Because this is early data, minor deviations from the trend are reported and attributed to experimental error. For example, in Test ID 1 and Test ID 3, the 5-minute values ​​were lower than the 2-minute and 10-minute values, or in Test ID 2, Test ID 4, and Test ID 6, the initial results were lower than the raw ball strength; however, the overall trend clearly supports this approach, leading to an increase in strength over time.

[0118] The results of tests ID 1 through ID 8 highlight how curing atmosphere and duration affect pellet strength (CCS), as shown in... Figure 7 (a) to 7(d).

[0119] Example 4 - Effect of curing in carbon dioxide on water resistance

[0120] The effect of CO2 curing on the water resistance of pellets was investigated on test ID 5 (exposed to carbon dioxide for 10 minutes) and test ID 6 (exposed to air for 10 minutes). The water resistance of the pellets on test ID 5 and test ID 6 was then measured by immersion for 1 hour. The results are shown in Table 3 below.

[0121] Table 3 - Water resistance tests for test IDs 5 and 6

[0122]

[0123] As can be seen, despite immersion in water for 1 hour, the strength of the pellets of the present invention (Test ID 5) decreased by only about 50%, remaining at a CCS value that would allow for transportation, storage, and handling without loss of integrity. However, the comparative test pellets (Test ID 6) showed a decrease of about 60%, a greater decrease in relative strength, and a level that posed a risk of degradation during handling.

[0124] Example 5 - Effect of curing in carbon dioxide on the thermal properties of pellets

[0125] The thermal properties of pellets with test IDs 5 and 6 were determined to ensure that there was no loss of thermal strength in pellets cured in carbon dioxide. The pellets were subjected to reduction conditions according to RDI ISO testing, and then CCS was tested. The results are shown in Table 4 below.

[0126] Table 4 - Thermal Characteristics Tests for Test ID 5 and Test ID 6

[0127]

[0128] These results indicate that although the expected low level of degradation (20% to 30%) occurred during the test, neither test showed a significant loss in pellet strength, suggesting that curing in carbon dioxide has minimal impact on the thermal properties of the pellets.

[0129] Example 6 - Analysis of metal silicates under different curing conditions

[0130] This study demonstrates the effect of curing in an ITR device for 10 minutes in a CO2 atmosphere compared to curing in an air atmosphere for 120 minutes in a drying oven. Furthermore, this study also shows the effect of CO2 curing on different types of silicate binders (and combinations). Pelletizing was performed using CMC in combination with the following metal silicate / metal silicate combinations:

[0131] • Sodium silicate (solid)

[0132] • Calcium silicate (solid)

[0133] • Magnesium silicate (solid)

[0134] • Magnesium silicate (solid) and sodium silicate (liquid)

[0135] • Calcium silicate (solid) and sodium silicate (liquid)

[0136] Details of the pellet formulation are shown in Table 5. The pellets were formed using the CTS method detailed above and cured (i) in a drying oven under air at 150°C or (ii) in an ITR device under CO2 at the same temperature. Details of the curing conditions are shown in Table 5.

[0137] The CCS of the cured pellets were tested, and the results are shown in Table 5 and 6. Figure 8 In the data, it is evident that the CCS of pellets cured at 150°C under CO2 for 10 minutes in an ITR apparatus is greater than that of comparative pellets cured at 150°C for 120 minutes in a drying oven. Therefore, this embodiment provides evidence of the increase in CCS resulting from the method according to the first aspect of the invention, and also illustrates the speed at which this benefit is achieved (10 minutes vs. 120 minutes). The accelerated curing process is advantageous because it not only improves pellet production efficiency but also reduces operating costs.

[0138] As the results show, sodium silicate produced the best-performing pellets. Calcium silicate and magnesium silicate, when cured in air, exhibited poor performance. However, when using the method according to the invention, specifically when produced according to the first aspect of the invention, pellets formed with calcium silicate and magnesium silicate as metal silicates showed significant improvements in CCS. Furthermore, unexpectedly, magnesium silicate, when combined with liquid sodium silicate, produced robust pellets.

[0139] This study demonstrates the effect of curing at 150°C for 10 minutes in an ITR apparatus under a CO2 atmosphere and curing at 150°C for 120 minutes in a drying oven under an air atmosphere on the structural integrity of the pellets. The results are shown in Table 6 below.

[0140] As can be seen from the results in the following list, pellets produced according to the method of the first aspect of the invention solidify in a significantly shorter time. This shorter solidification time offers key benefits, such as high energy savings and improved production efficiency. Furthermore, pellets produced according to the method of the first aspect of the invention have a lower RDI%. A low RDI% is a key indicator of high-quality pellets, which can withstand the harsh conditions of the ironmaking process, resulting in improved efficiency and productivity. Therefore, pellets manufactured according to the method of the first aspect of the invention are less likely to break and have better structural integrity. Moreover, lower pulverization is advantageous because it means less dust and fine powder will be generated during reduction, thereby minimizing material loss and reducing the risk of operational problems associated with dust accumulation.

[0141] Table 6 - RDI% values ​​for test IDs 17 to 20

[0142]

[0143] Example 8 - Comparison between CMC and polysaccharide binders

[0144] This study investigated the differences between CMC and polysaccharides when used as binders in pellets cured under CO2 according to the method of the present invention. A batch of pellets (ID 21) was produced and cured according to test ID 12, but instead contained polysaccharides instead of CMC as binders. The polysaccharides were present at 0.25% by weight. The polysaccharides used in this example were starches from Cargill, USA.

[0145] The CCS of each batch of pellets was tested, and the results are shown in Table 7. The CCS of pellets formulated with polysaccharides as binders was lower than that of pellets formulated with CMC as binders.

[0146] While the CCS of pellets containing polysaccharide binders is acceptable for iron ore pellets, this embodiment illustrates that when formed using the method according to the invention, the CCS is significantly higher when the binder is a cellulose material such as CMC.

[0147] Table 7: Pellet formulation used in Example 5, and CCS results.

[0148]

[0149] It will be understood that the methods and apparatus of the present invention can be implemented in a variety of ways, and only a few of them have been illustrated and described above.

Claims

1. A method for producing pellets, the method comprising: (i) Provide particulate materials selected from carbonaceous materials, metals, metal ores and mixtures thereof; and an inorganic binder containing metal silicates to form a mixture; (ii) The mixture is compacted to form pellets; as well as (iii) The pellets are solidified by contacting them with gaseous carbon dioxide.

2. The method according to claim 1 further includes adding an organic binder.

3. The method according to claim 1 or claim 2, wherein the hydraulic pressure applied in step (ii) is applied in the range of 50 bar to 300 bar using a roll pressing process (RPP).

4. The method according to claim 1 or claim 2, wherein the pressure applied in step (ii) is applied using cold pressing technology (CTS) with a 10 mm die, wherein the applied pressure is in the range of 6000 bar to 8000 bar calculated at 6 tons of force.

5. The method according to claim 1 or claim 2, wherein the pressure applied in step (ii) is applied using cold pressing technology (CTS) with a 16 mm die, wherein the applied pressure is in the range of 2000 bar to 5000 bar calculated at 6 tons of force.

6. The method according to claim 1 or claim 2, wherein the pressure applied in step (ii) is applied using cold pressing technology (CTS) with a 20 mm die, wherein the applied pressure is in the range of 800 bar to 3500 bar calculated at 6 tons of force.

7. The method according to any of the preceding claims, wherein the carbon dioxide in step (iii) is carbon dioxide produced by one or more industrial processes.

8. The method according to any of the preceding claims further comprises the additional step of capturing carbon dioxide produced by one or more industrial processes for use in step (iii).

9. The method according to any of the preceding claims, wherein step (iii) further comprises applying heat at a temperature in the range of 50°C to 1000°C.

10. The method of claim 9, wherein applying heat comprises applying heat generated by one or more industrial processes.

11. The method according to any of the preceding claims, wherein step (iii) involves solidifying the pellets at atmospheric pressure.

12. The method according to any one of claims 1 to 10, wherein step (iii) involves solidifying the pellets under a pressure ranging from 1 bar to 3 bar.

13. The method according to any of the preceding claims, wherein the particulate material is added in an amount of about 70% by weight to about 99.9% by weight of the mixture in step (i).

14. The method according to any of the preceding claims, wherein the particulate material comprises metal ore, metal, and combinations thereof.

15. The method of claim 14, wherein the particulate material comprises iron.

16. The method according to any one of claims 13 to 15, wherein the particulate material comprises a carbonaceous material.

17. The method according to any of the preceding claims, wherein the moisture content of the particulate material is less than 25%.

18. The method according to any of the preceding claims, wherein the metal silicate is present in the mixture in the range of 0.5% to 5% by weight.

19. The method according to any of the preceding claims, wherein the metal silicate comprises a Group I metal silicate or a Group II metal silicate.

20. The method according to any of the preceding claims, wherein the metal silicate is selected from sodium silicate (Na2SiO3), calcium silicate (CaSiO3, Ca2SiO4), potassium silicate (K2SiO3), magnesium silicate (MgSiO4), and combinations thereof.

21. The method according to any of the preceding claims, wherein the metal silicate is selected from sodium silicate, potassium silicate, magnesium silicate, and combinations thereof.

22. The method according to any of the preceding claims, wherein the metal silicate is selected from sodium silicate, magnesium silicate, and combinations thereof.

23. The method according to any of the preceding claims, wherein the metal silicate is selected from potassium silicate, magnesium silicate, and combinations thereof.

24. The method according to any one of claims 2 to 23, wherein the organic binder is present in the mixture in the range of 0.2% by weight to 5% by weight.

25. The method according to any one of claims 2 to 24, wherein the organic binder comprises natural polymers, synthetic polymers, glycerides, cellulose materials, polysaccharides, and combinations thereof.

26. The method according to claim 25, wherein the organic binder comprises polyacrylamide resin, phenolic resin, polyacrylic acid, styrene-acrylate polymer, cellulose fiber, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxyethyl methyl cellulose (MHEC), triacetin, diacetin, polyvinyl alcohol, wheat starch, corn starch, barley starch, potato starch, gum arabic, guar gum, xanthan gum, and combinations thereof.

27. The method according to claim 25 or claim 26, wherein the organic binder comprises polyacrylamide resin, phenolic resin, cellulose fiber, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxyethyl methyl cellulose (MHEC), triacetin, diacetin, polyacrylamide, ethyl acrylate styrene (EA), polyvinyl alcohol, and combinations thereof.

28. The method according to any one of claims 25 to 27, wherein the organic binder comprises polyacrylamide resin, phenolic resin, cellulose fiber, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxyethyl methyl cellulose (MHEC), polyvinyl alcohol, triacetin, or combinations thereof.

29. The method according to any one of claims 25 to 28, wherein the organic binder comprises polyacrylamide resin, cellulose fiber, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), or combinations thereof.

30. The method according to any one of claims 25 to 29, wherein the organic binder comprises carboxymethyl cellulose (CMC), cellulose fibers, hydroxyethyl methyl cellulose (MHEC), or combinations thereof.

31. The method according to any one of claims 25 to 30, wherein the organic binder comprises carboxymethyl cellulose (CMC).

32. The method according to any one of claims 25 to 28, wherein the organic binder comprises polyvinyl alcohol.

33. The method according to any one of claims 2 to 32, wherein the viscosity of the organic binder is in the range of 3,000 MPa·s to 16,000 MPa·s.

34. The method according to any of the preceding claims further comprises adding a flux additive to the mixture.

35. The method according to claim 34, wherein the flux additive is selected from silica, dolomite, fluorite, calcium oxide, magnesium oxide, carbon, aluminum, pure peridotite, basalt, and combinations thereof.

36. The method of claim 35, wherein the flux additive is selected from fluorite, aluminum, pure peridotite, basalt, and combinations thereof.

37. The method according to any preceding claim, wherein solidifying the pellets by contacting them with gaseous carbon dioxide is performed by introducing the pellets into a gas stream containing carbon dioxide, the gas stream having a flow rate in the range of 1 liter / minute to 100 liters / minute.

38. A pellet that can be obtained by the method according to any of the preceding claims.

39. A pellet comprising particulate material selected from carbonaceous materials, metals, metal ores and mixtures thereof; silicon dioxide; and metal carbonates.

40. The pellets of claim 39, wherein the metal carbonate is formed by reacting with an inorganic binder comprising a metal silicate and gaseous carbon dioxide.

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