A functionalized core-shell structured binder for hydrogen-based direct reduction pellets, its preparation method, and oxidized pellets for hydrogen-based direct reduction.

Abstract

This application provides a functionalized core-shell structured binder for hydrogen-based direct reduction pellets, its preparation method, and oxidized pellets for hydrogen-based direct reduction, relating to the fields of green metallurgy and pellet binder technology. The binder is a core-shell structured unit composed of a composite functional core and a chemically grafted polymer shell; the polymer shell is a polyacrylamide crosslinked network bridged and covalently bonded to the surface of the composite functional core; calculated based on 100% of the total mass of the raw materials of the composite functional core, it includes: 50-85% bentonite matrix, 10-25% dispersant, and 5-25% magnesium-containing grain boundary reinforcing agent. This application solves the core problem of easy failure under shear force and thermal stress in physical mixtures due to weak interfacial bonding, significantly improving the structural stability and reliability of the product; and through the innovative design of the core-shell structure and the introduction of the magnesium-containing grain boundary reinforcing agent, it endows it with the special functions of actively inhibiting the hydrogen reduction expansion of pellets and improving high-temperature strength.

Description

Technical Field

[0001] This application relates to the fields of green metallurgy and pellet binder technology, and in particular to a functionalized core-shell structure binder for hydrogen-based direct reduction pellets, its preparation method, and oxidized pellets for hydrogen-based direct reduction. Background Technology

[0002] Against the backdrop of the global steel industry's efforts to achieve its goals, hydrogen-based direct reduction technology, using hydrogen as the primary or sole reducing agent, is widely recognized as the most promising disruptive process. However, the unique reaction kinetics of hydrogen reduction impose almost stringent requirements on the metallurgical properties of its feedstock—oxidized pellets. First, under a hydrogen-reducing atmosphere, iron oxides (Fe2O3) in the pellets are rapidly reduced to metallic iron (Fe). Due to the lack of CO inhibition, the newly formed α-Fe whiskers tend to overgrow and intertwine, generating enormous internal stress and causing severe volume expansion of the pellets, known as "reduction expansion." Excessively high reduction expansion rates (typically >20%) can lead to pellet pulverization, deteriorating the permeability of the shaft furnace or reactor, and disrupting normal production. This is one of the core technological bottlenecks facing hydrogen metallurgy. Second, to ensure reduction efficiency and stable reactor operation, the pellets must possess extremely high room-temperature strength to withstand the pressure of the feed column, as well as excellent medium- and high-temperature strength to maintain integrity during rapid heating and reduction processes. In addition, to obtain high-quality direct reduced iron (DRI) and reduce the energy consumption of subsequent electric arc furnace smelting, the pellets themselves must have the highest possible iron grade and the lowest possible gangue content.

[0003] Pellet binders are key auxiliary materials affecting pellet quality, energy consumption, and the final economic and technical indicators of ironmaking. Currently, widely used industrial pellet binders (such as bentonite) and their physically compounded improved versions mainly focus on improving the drop strength and bursting temperature of green pellets. Their design concepts and performance targets are derived from the traditional oxidative roasting-blast furnace smelting process, which is no longer suitable for the high-temperature reduction conditions of hydrogen metallurgy. These binders have two fundamental defects: first, the addition of high-silica and aluminum minerals such as bentonite is usually 1.5%-3.0%, which significantly reduces the iron grade of the pellets; second, the components are mostly physically adsorbed or weakly bonded, which cannot provide durable and stable microstructural support under the harsh conditions of high-temperature reduction, and they do not have the function of actively regulating the reduction behavior of pellets (such as inhibiting whisker growth).

[0004] Therefore, developing a novel special binder that can construct a stable synergistic structure through chemical bonding, possesses high-efficiency bonding, low impurity introduction, and can actively improve the high-temperature reduction metallurgical properties of pellets is a key material problem that urgently needs to be solved to promote the large-scale industrial application of hydrogen-based direct reduction technology from the laboratory. Summary of the Invention

[0005] The purpose of this application is to provide a functionalized core-shell structured binder for hydrogen-based direct reduction pellets, a method for preparing the same, and oxidized pellets for hydrogen-based direct reduction, in order to solve the above-mentioned problems.

[0006] To achieve the above objectives, this application adopts the following technical solution: This application provides a functionalized core-shell structured binder for hydrogen-based direct reduction pellets. The binder is a core-shell structured unit composed of a composite functional core and a chemically grafted polymer shell. The polymer shell is a polyacrylamide crosslinked network that is bridged and covalently bonded to the surface of the composite functional core. The total mass of the raw materials for the composite functional core is 100%, including: 50-85% bentonite matrix, 10-25% dispersing reinforcing agent, and 5-25% magnesium-containing grain boundary reinforcing agent.

[0007] Optionally, the bentonite matrix includes sodium-based bentonite and / or calcium-based bentonite.

[0008] Optionally, the dispersing enhancer includes at least one of lignin sulfonate, humate, and polycarboxylate.

[0009] Optionally, the magnesium-containing grain boundary strengthener is at least one of magnesium oxide, magnesium hydroxide, magnesium carbonate, and lightly calcined magnesium oxide powder.

[0010] Optionally, the polyacrylamide crosslinking network is formed by copolymerizing acrylamide monomers and a crosslinking agent.

[0011] Optionally, the crosslinking agent is N,N′-methylenebisacrylamide and / or ethylene glycol dimethacrylate.

[0012] This application also provides a method for preparing a functionalized core-shell structured binder for hydrogen-based direct reduction pellets, comprising: Bentonite matrix, dispersing agent, and magnesium-containing grain boundary reinforcing agent were dispersed in water in a certain proportion to obtain a uniform slurry; cationic surfactants were added for intercalation and surface organic modification to obtain organic composite functional core powder. The organic composite functional core powder was dispersed in an organic solvent, and a vinyl-containing silane coupling agent was added under an inert atmosphere to carry out a reflux reaction to obtain a silanized modified core. The silanized modified core is dispersed in water and mixed with acrylamide monomer, crosslinking agent and water-soluble initiator to carry out free radical polymerization reaction to obtain the binder.

[0013] Optionally, the cationic surfactant comprises hexadecyltrimethylammonium bromide or hexadecylaminotrimethylammonium chloride, and is added in an amount of 30-60% of the mass of the bentonite matrix.

[0014] Optionally, the silane coupling agent includes at least one of vinyltrimethoxysilane, vinyltriethoxysilane, and γ-(methacryloyloxy)propyltrimethoxysilane; the mass ratio of the silane coupling agent to the organic composite core powder is 0.15-0.35:1.

[0015] Optionally, the mass ratio of the acrylamide monomer to the silanized modified core is 3-10:1.

[0016] Optionally, the amount of crosslinking agent added is 0.2-1.0% of the mass of the acrylamide monomer.

[0017] Optionally, the water-soluble initiator includes at least one of ammonium persulfate, potassium persulfate, and azobisisobutyramidine hydrochloride; the amount of the water-soluble initiator added is 0.1-0.8% of the mass of the acrylamide monomer.

[0018] Compared with the prior art, the beneficial effects of this application include: The functionalized core-shell structured binder for hydrogen-based direct reduction pellets provided in this application is a chemical composite with a clearly defined core-shell phase interface. Through a strategy of "silanization bridging + in-situ copolymerization," covalent bonds are established between the inorganic "core" and the organic "shell," forming a uniform and stable core-shell structure. This fundamentally solves the core problem of easy failure under shear and thermal stress caused by weak interfacial bonding in physical mixtures, significantly improving the product's structural stability and reliability. By adding magnesium-containing functional components, the binder is transformed from a traditional passive adhesive into a functionalized material that actively participates in and optimizes the high-temperature metallurgical process of pelletizing, providing a solution for achieving stable and smooth hydrogen-based direct reduction.

[0019] The reduction expansion rate of the oxidized pellets for hydrogen-based direct reduction provided in this application is significantly reduced (and can be stably below 15%). The high-temperature strength of the reduced pellets is significantly improved (>350N / piece), and fewer impurities are introduced, which helps to improve the iron grade of the pellets and reduce the energy consumption and slag volume of the entire ironmaking process from the source.

[0020] Although the preparation of this invention involves multiple chemical reactions, the overall benefits it brings, such as improved pellet grade, optimized metallurgical performance, and potentially reduced ironmaking coke ratio, make it irreplaceable in the production of pellets for hydrogen-based direct reduction. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0022] Figure 1A schematic diagram of the process flow for preparing a functionalized core-shell structured binder for direct reduction of hydrogen-based pellets, provided in the embodiments; Figure 2 This is a photograph of the oxidized pellets for direct reduction of hydrogen-based compounds prepared in Example 1. Detailed Implementation

[0023] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0024] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0025] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0026] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0027] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (where K is any number representing a multiplier). It is important to understand that, unlike parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0028] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0029] To better illustrate the technical solution provided in this application, a general description of the technical solution provided in this application will be given before proceeding with specific implementation methods.

[0030] In a first aspect, this application provides a functionalized core-shell structured binder for hydrogen-based direct reduction pellets, wherein the binder is a core-shell structured unit composed of a composite functional core and a chemically grafted polymer shell; the polymer shell is a polyacrylamide crosslinked network that is bridged and covalently bonded to the surface of the composite functional core. The total mass of the raw materials for the composite functional core is 100%, including: 50-85% bentonite matrix, 10-25% dispersing reinforcing agent, and 5-25% magnesium-containing grain boundary reinforcing agent.

[0031] Optionally, based on the total mass of the raw materials of the composite functional core being 100%, the amount of bentonite matrix can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or any value between 50% and 85%; the amount of dispersing reinforcing agent can be 10%, 15%, 20%, 25%, or any value between 10% and 25%; and the amount of magnesium-containing grain boundary reinforcing agent can be 5%, 10%, 15%, 20%, 25%, or any value between 5% and 25%.

[0032] In an alternative embodiment, the bentonite matrix comprises sodium-based bentonite and / or calcium-based bentonite.

[0033] In an optional embodiment, the dispersion enhancer includes at least one of lignin sulfonate, humate, and polycarboxylate.

[0034] In one optional embodiment, the magnesium-containing grain boundary strengthener is at least one of magnesium oxide, magnesium hydroxide, magnesium carbonate, and lightly calcined magnesia powder.

[0035] In an optional embodiment, the polyacrylamide crosslinking network is formed by copolymerizing acrylamide monomers with a crosslinking agent.

[0036] In an optional embodiment, the crosslinking agent is N,N′-methylenebisacrylamide and / or ethylene glycol dimethacrylate.

[0037] It is understandable that the composite functional core is a multiphase composite system, composed of three functional components tightly bonded together through physicochemical interactions. Bentonite matrix, as the main framework material, utilizes its layered structure, cation exchange capacity, and water absorption and swelling properties to provide basic adhesion, water retention, and structural support. The preferred dispersant is lignin sulfonate, whose abundant sulfonic acid groups, hydroxyl groups, and other hydrophilic functional groups on its molecular chain effectively improve the dispersibility of bentonite and iron ore powder particles in the aqueous phase, reduce slurry viscosity, and encapsulate the ore powder to form a denser green pellet structure. At high temperatures, the gases produced by its decomposition can form micropores, facilitating the inward diffusion of reducing gases. The magnesium-containing grain boundary strengthener is key to achieving the core function of this invention. Highly active, fine-grained magnesium compounds (such as lightly calcined magnesium oxide) are selected. During the preheating (~1000℃) and calcination (>1200℃) processes of the pellets, Mg... 2+ It can diffuse into the iron oxide (Fe2O3) lattice and grain boundaries. During the subsequent high-temperature hydrogen reduction stage (>800℃), these Mg²⁺ molecules that have pre-diffused to the grain boundaries... + It can react with the FeO generated during reduction and impurities such as SiO2 and Al2O3 inherent in the raw materials to generate high-melting-point mineral phases such as magnesium iron spinel ((Mg,Fe)Fe2O4) or forsterite (Mg2SiO4) in situ. These high-melting-point phases act like "nails" between iron grains, significantly strengthening the grain boundaries and effectively hindering the excessive growth of iron whiskers and the formation of interwoven networks during reduction. This mechanistically suppresses the volume expansion of the pellets and helps to improve the high-temperature structural strength of the pellets in the reduced state.

[0038] The polymer shell is chemically grafted onto the surface of the composite functional core using a "silanization bridging-in-situ copolymerization" process, forming a three-dimensional cross-linked network of polyacrylamide. This shell is connected to the core via strong Si-OC covalent bonds, ensuring the stability of the organic-inorganic phase interface. Utilizing the entanglement of the long PAM molecular chains and the elasticity of the cross-linked network, multiple "functional core" units are strongly bridged to a large number of surrounding iron ore powder particles, providing excellent macroscopic bonding strength. During pelletizing, drying, and the initial stages of reduction, the cross-linked network effectively buffers and disperses internal stress, preventing the generation and propagation of microcracks. Simultaneously, the sequential decomposition of PAM and lignin sulfonate during calcination forms a well-connected and uniformly distributed microporous structure, optimizing the mass transfer channels for reducing gases within the pellets.

[0039] Secondly, this application also provides a method for preparing a functionalized core-shell structured binder for hydrogen-based direct reduction pellets, comprising: Prefabrication and surface organication of the core structure: Bentonite matrix, dispersing agent, and magnesium-containing grain boundary reinforcing agent are dispersed in water in a certain proportion to obtain a uniform slurry; cationic surfactants are added for intercalation and surface organic modification to obtain organic composite functional core powder; Covalent anchoring of polymerizable functional groups on the core surface: The organic composite functional core powder is dispersed in an organic solvent, and a vinyl-containing silane coupling agent is added under an inert atmosphere to carry out a reflux reaction to obtain a silanized modified core; In-situ free radical copolymerization to construct a crosslinked shell: The silanized modified core is dispersed in water and mixed with acrylamide monomer, crosslinking agent and water-soluble initiator to carry out a free radical polymerization reaction to obtain the binder.

[0040] In an optional embodiment, the cationic surfactant comprises hexadecyltrimethylammonium bromide or hexadecylaminotrimethylammonium chloride, and is added in an amount of 30-60% of the mass of the bentonite matrix.

[0041] Optionally, the amount of cationic surfactant can be 30%, 35%, 40%, 45%, 50%, 55%, or 60% of the mass of the bentonite matrix, or any value between 20% and 60%.

[0042] In an optional embodiment, the silane coupling agent includes at least one of vinyltrimethoxysilane, vinyltriethoxysilane, and γ-(methacryloyloxy)propyltrimethoxysilane; the mass ratio of the silane coupling agent to the organic composite nucleus powder is 0.15-0.35:1.

[0043] Optionally, the mass ratio of silane coupling agent to organic composite core powder can be 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, or any value between 0.15 and 0.35:1.

[0044] In one optional embodiment, the mass ratio of the acrylamide monomer to the silanized modified core is 3-10:1.

[0045] Optionally, the mass ratio of acrylamide monomer to silanized modified core can be 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, or any value between 3 and 10:1.

[0046] In an optional embodiment, the amount of crosslinking agent added is 0.2-1.0% of the mass of the acrylamide monomer.

[0047] Optionally, the amount of crosslinking agent can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% of the mass of acrylamide monomer, or any value between 0.2% and 1%.

[0048] In an optional embodiment, the water-soluble initiator includes at least one of ammonium persulfate, potassium persulfate, and azobisisobutyramidine hydrochloride; the amount of the water-soluble initiator added is 0.1-0.8% of the mass of the acrylamide monomer.

[0049] Optionally, the amount of water-soluble initiator can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% of the mass of acrylamide monomer, or any value between 0.1% and 0.8%.

[0050] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0051] Example 1 This embodiment provides a functionalized core-shell structured binder for hydrogen-based direct reduction pellets: The adhesive is a core-shell structural unit composed of a composite functional core and a chemically grafted polymer shell; the polymer shell is a polyacrylamide crosslinked network that is bridged and covalently bonded to the surface of the composite functional core. The polyacrylamide crosslinked network is formed by copolymerizing acrylamide monomers and a crosslinking agent, specifically N,N'-methylenebisacrylamide (MBA).

[0052] The raw materials for the composite functional core include: 60g of sodium bentonite (purchased from Shanghai Maclean Biochemical Technology Co., Ltd., montmorillonite content >80%), 25g of sodium lignosulfonate (industrial grade, dry basis), and 15g of lightly calcined magnesium oxide powder (purchased from Haicheng Magnesium Mine Group Co., Ltd., MgO≥92%, particle size -5μm).

[0053] This embodiment also provides a method for preparing the adhesive, the process flow of which is as follows: Figure 1 As shown, the specific steps are as follows: Construction and surface pretreatment of the composite functional core: Weigh 60.0 g sodium bentonite, 25.0 g sodium lignosulfonate, and 15.0 g lightly calcined magnesium oxide powder. Add 500 mL of deionized water, first disperse at 20,000 rpm for 15 minutes by high-speed shearing, then sonicate (800 W) for 30 minutes to obtain a uniform slurry A. Transfer slurry A to a reactor equipped with stirring and heating, heat to 70 °C, slowly add 28.0 g cetyltrimethylammonium bromide (CTAB), and stir at a constant temperature for 3 hours. After the reaction, centrifuge, wash the precipitate three times alternately with hot water and ethanol, dry in an 80 °C vacuum drying oven to constant weight, and grind to obtain the organic composite functional core powder.

[0054] Construction of polymerizable active sites on the core surface: 30.0 g of powder was dispersed in 200 mL of anhydrous toluene and bubbled with nitrogen for 15 minutes to remove oxygen. 6.0 g of vinyltrimethoxysilane (VTMS) was added, and the mixture was heated to 85 °C under nitrogen protection and refluxed for 8 hours. After the reaction was completed, the mixture was cooled, centrifuged, washed three times with toluene to remove unreacted material, and dried under vacuum at 60 °C to obtain a vinyl-modified silanized core.

[0055] In-situ free radical graft copolymerization of the polymer shell: 200 mL of deionized water was added to a 500 mL four-necked flask, and stirring was started while nitrogen was introduced. 10.0 g of silanized core, 70 g of acrylamide (AM) monomer, and 0.42 g of N,N'-methylenebisacrylamide (MBA) crosslinking agent were added sequentially. After stirring to dissolve and purging with nitrogen for 30 minutes, the temperature was raised to 60 °C in a water bath. 0.28 g of ammonium persulfate (APS, dissolved in 5 mL of water) initiator was quickly added, and the reaction was maintained at this temperature for 4 hours, during which the system gradually transformed into an elastic gel. The gel was removed, chopped, and dried in an 85 °C forced-air drying oven for 12 hours. It was then pulverized and passed through a 100-mesh sieve to obtain the final functionalized core-shell structure binder, labeled F-1.

[0056] Example 2 This embodiment provides a functionalized core-shell structure binder for hydrogen-based direct reduction pellets. The only difference from Embodiment 1 is that the raw materials for the composite functional core include: 70g of sodium bentonite, 15g of sodium lignosulfonate, and 15g of lightly calcined magnesium oxide powder.

[0057] This embodiment also provides a method for preparing the adhesive, which differs from Example 1 only in that the amount of CTAB added is adjusted to 33.6g (based on 48% of the bentonite mass). The remaining steps are the same as in Example 1, and adhesive F-2 is obtained.

[0058] Example 3 This embodiment provides a functionalized core-shell structure binder for hydrogen-based direct reduction pellets. The only difference from Embodiment 1 is that the raw materials for the composite functional core include: 85g of sodium bentonite, 10g of sodium lignosulfonate, and 5g of lightly calcined magnesium oxide powder.

[0059] This embodiment also provides a method for preparing the adhesive, which differs from Example 1 only in that the amount of CTAB added is adjusted to 40.8g (based on 48% of the bentonite mass). The remaining steps are the same as in Example 1, and adhesive F-3 is obtained.

[0060] Example 4 This embodiment provides a functionalized core-shell structure binder for hydrogen-based direct reduction pellets. The only difference from Embodiment 1 is that the raw materials for the composite functional core include: 50.0g of sodium bentonite, 25g of sodium lignosulfonate, and 25g of lightly calcined magnesium oxide powder.

[0061] This embodiment also provides a method for preparing the adhesive, which differs from Example 1 only in that the amount of CTAB added is adjusted to 24.0g (based on 48% of the bentonite mass). The remaining steps are the same as in Example 1, and adhesive F-4 is obtained.

[0062] Example 5 This embodiment provides a functionalized core-shell structure binder for hydrogen-based direct reduction of pellets. The only difference from Example 1 is that sodium lignosulfonate is replaced with an equal mass of sodium humate, while the other conditions remain unchanged.

[0063] This embodiment also provides a method for preparing the adhesive, with the same steps as in Embodiment 1, except that sodium lignosulfonate is replaced with an equal mass of sodium humate to obtain adhesive F-5.

[0064] Example 6 This embodiment provides a functionalized core-shell structure binder for direct reduction of hydrogen-based pellets. The only difference from Example 1 is that the lightly calcined magnesium oxide is replaced with an equal mass of magnesium hydroxide, while the other conditions remain unchanged.

[0065] This embodiment also provides a method for preparing the binder, with the same steps as in Embodiment 1, except that lightly calcined magnesium oxide is replaced with an equal mass of magnesium hydroxide to obtain binder F-6.

[0066] Comparative Example 1 This comparative example provides a functionalized core-shell structure binder for hydrogen-based direct reduction pellets. The only difference from Example 1 is that the raw materials for the composite functional core include: 75g of sodium bentonite and 25g of sodium lignosulfonate.

[0067] This comparative example also provides a method for preparing the adhesive, which differs from Example 1 only in that the amount of CTAB added is adjusted to 36g (based on 48% of the bentonite mass). The remaining steps are the same as in Example 1, and adhesive D-1 is obtained.

[0068] Comparative Example 2 This comparative example provides a functionalized core-shell structure binder for hydrogen-based direct reduction pellets. The only difference from Example 1 is that the raw materials for the composite functional core include: 75g of sodium-based bentonite and 25g of lightly calcined magnesium oxide.

[0069] This comparative example also provides a method for preparing the adhesive, which differs from Example 1 only in that the amount of CTAB added is adjusted to 36g (based on 48% of the bentonite mass). The remaining steps are the same as in Example 1, and adhesive D-2 is obtained.

[0070] Comparative Example 3 This embodiment provides a functionalized core-shell structure binder for hydrogen-based direct reduction pellets: the raw materials include: 60g of sodium bentonite, 25g of sodium lignosulfonate, and 15g of lightly calcined magnesium oxide powder (MgO≥92%, particle size-5μm).

[0071] This comparative example also provides a method for preparing the adhesive, wherein the dry powders of the above raw materials are physically mixed in a mixer for 1 hour and passed through a 100-mesh sieve to obtain physically mixed adhesive D-3.

[0072] Comparative Example 4 Sodium-based bentonite (purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with montmorillonite content >80%) was used as a control and labeled as D-4.

[0073] Pellet preparation and routine performance testing: Examples F-1 to F-6 and Comparative Examples D-1 to D-4 all used the same batch of high-grade hematite concentrate (TFe 68.2%, SiO2 1.8%, Al2O3 0.7%, CaO+MgO 0.5%, particle size -200 mesh 97%) as pelletizing raw material for comparison. In the following cases, except for Comparative Example D-4 where the binder addition was 2.0%, the binder was added at 1.0% (percentage of dry weight of iron concentrate) and mixed with iron ore powder in a laboratory disc pelletizer (diameter 1m, side height 0.2m, inclination angle 45°, rotation speed 25rpm). The pellet moisture content was controlled at 8.0%-8.5%, and the green pellet size was screened to 12.5-13.0mm. Conventional performance indicators of green pellets, dry pellets, and roasted pellets were tested according to international standard methods. The pellets obtained in F-1 are as follows... Figure 2 As shown.

[0074] Unless otherwise specified (e.g., 2.0% binder addition in Comparative Example D-4), all binders were added at a fixed rate of 1.0% (percentage of dry iron concentrate mass) and mixed with the aforementioned iron concentrate in a laboratory disc pelletizer (Φ1000mm) to form pellets. The moisture content of the pellets was controlled at 8.0%-8.5%, and the green pellet size was screened to 12.5-13.0mm. After drying, the green pellets were oxidatively roasted in a box-type resistance furnace under a simulated belt roasting regime (1250℃, 15 minutes) to obtain oxidized pellets.

[0075] The conventional physical properties of green pellets and oxidized pellets were tested according to the international standard (ISO) method, and the results are shown in Table 1.

[0076] Table 1. Conventional physical properties of pellets prepared with different binders

[0077] Table 1 shows that, in all embodiments of the present invention (F-1 to F-6), the strength of both green pellets and oxidized pellets is significantly better than that of sodium bentonite (D-4) with 2.0% added, demonstrating the ultra-high bonding efficiency of the core-shell structure. Regarding the composite functional core components, Embodiments F-1 (sodium bentonite: sodium lignosulfonate: lightly calcined magnesia powder = 60:25:15) and F-2 (sodium bentonite: sodium lignosulfonate: lightly calcined magnesia powder = 70:15:15) exhibit relatively balanced performance across various aspects, representing the preferred range, while F-3 and F-4 demonstrate the boundary conditions of performance. The strength of Comparative Example D-1 (without MgO) is slightly lower than that of the embodiments of the present invention, indicating that the magnesium-containing grain boundary reinforcing agent also contributes to the strength. Comparative Example D-2 (without dispersing reinforcing agent) shows a significant decrease in the strength of both green pellets and oxidized pellets, indicating that the dispersing reinforcing agent in the composite functional core structure makes a significant contribution to the pellet strength. The performance of Comparative Example D-3 (physical mixture) is significantly different from that of the embodiments of the present invention (F1~F6), highlighting the importance of chemical bonding structure in improving the conventional physical properties of pellets.

[0078] Key metallurgical performance tests for direct hydrogen reduction: To evaluate the behavior of pellets under hydrogen reduction conditions, a simulation experiment was conducted using a high-temperature horizontal tubular reduction furnace. Ten intact pellets (Φ12.5mm) were randomly selected from each type of oxidized pellet and placed in a corundum crucible. After the temperature was programmed to reach the predetermined temperature, high-purity hydrogen gas (flow rate 5 L / min) was introduced for isothermal reduction.

[0079] Test 1: Reduction Swelling Index (RSI). The pellets were isothermally reduced at 900℃ for 60 minutes. The pellet volume was measured before and after reduction using a laser volume scanner, and the RSI was calculated.

[0080] Test 2: Strength evolution during reduction. Pellet pellets were isothermally reduced at 800℃ and 900℃ for 30 minutes respectively. After being quickly removed and cooled in an inert atmosphere, their compressive strength after reduction (CCS after reduction) was tested using a universal press. This index directly reflects the structural integrity of the pellets in the reduced state.

[0081] The hydrogen-based reducing metallurgical properties of the pellets are shown in Table 2: Table 2 Hydrogen-based reducing metallurgical properties of pellets

[0082] As shown in Table 2, the reduction expansion control: the reduction expansion rate (RSI) of Examples F-1 to F-6 of this invention is significantly lower than 15%, with the optimal RSI of F-1 being only 11.8%. In contrast, the expansion rate of Comparative Example D-1 without magnesium-containing agent reaches 19.5%, and that of physically mixed D-3 and sodium-based bentonite D-4 even exceeds 20%. The data in Table 2 significantly demonstrate the decisive role of the magnesium-containing grain boundary reinforcing agent in suppressing hydrogen reduction expansion in this invention. The expansion rate of Example F-5 (using sodium humate) is slightly higher than that of the other three examples (13.8%), indicating a better synergistic effect between lignin sulfonate and magnesium-containing agent.

[0083] High-Temperature Structural Strength: After reduction at 800℃ and 900℃, the pellets in the embodiments of the present invention maintained extremely high compressive strength (510 N / pelle and 385 N / pelle for F-1, respectively), far exceeding all comparative examples. This indicates that even under intense reduction reactions and high temperatures, the pellet skeleton constructed by the functionalized core-shell structure binder remains stable. The simultaneous achievement of "low expansion" and "high strength" is the key success of the present invention, meeting the extreme requirements of hydrogen-based shaft furnaces for burden strength.

[0084] As can be seen, the technical solution provided in this application successfully prepared a functionalized core-shell structure binder specifically for hydrogen-based direct reduction pellets. By introducing a magnesium-containing grain boundary reinforcing agent and constructing a chemically bonded stable structure, this binder not only provides excellent conventional bonding performance, but also endows the pellets with superior resistance to hydrogen reduction expansion and high-temperature structural stability, solving a key material bottleneck restricting the development of hydrogen metallurgy.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0086] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A functionalized core-shell structured binder for direct reduction of hydrogen-based pellets, characterized in that, The adhesive is a core-shell structural unit composed of a composite functional core and a chemically grafted polymer shell; the polymer shell is a polyacrylamide crosslinked network that is bridged and covalently bonded to the surface of the composite functional core. Based on the total mass of the raw materials of the composite functional core being 100%, it includes: 50-85% bentonite matrix, 10-25% dispersing reinforcing agent, and 5-25% magnesium-containing grain boundary reinforcing agent; The bentonite matrix includes sodium-based bentonite and / or calcium-based bentonite; The dispersion enhancer includes at least one of lignin sulfonate, humate, and polycarboxylate; The magnesium-containing grain boundary strengthening agent is at least one of magnesium oxide, magnesium hydroxide, magnesium carbonate, and lightly calcined magnesia powder; The polyacrylamide crosslinking network is formed by the polymerization of acrylamide monomers and a crosslinking agent; The crosslinking agent is N,N′-methylenebisacrylamide and / or ethylene glycol dimethacrylate; The preparation method of the functionalized core-shell structured binder for direct reduction of hydrogen-based pellets includes: Bentonite matrix, dispersing agent, and magnesium-containing grain boundary reinforcing agent were dispersed in water in a certain proportion to obtain a uniform slurry; cationic surfactants were added for intercalation and surface organic modification to obtain organic composite functional core powder. The organic composite functional core powder was dispersed in an organic solvent, and a vinyl-containing silane coupling agent was added under an inert atmosphere to carry out a reflux reaction to obtain a silanized modified core. The silanized modified core is dispersed in water and mixed with acrylamide monomer, crosslinking agent and water-soluble initiator to carry out free radical polymerization reaction to obtain the binder.

2. The functionalized core-shell structured binder for hydrogen-based direct reduction pellets according to claim 1, characterized in that, At least one of the following conditions must be met: A. The cationic surfactant comprises hexadecyltrimethylammonium bromide or hexadecylaminotrimethylammonium chloride; the amount of the cationic surfactant added is 30-60% of the mass of the bentonite matrix; B. The silane coupling agent includes at least one of vinyltrimethoxysilane, vinyltriethoxysilane, and γ-(methacryloyloxy)propyltrimethoxysilane; the mass ratio of the silane coupling agent to the organic composite functional core powder is 0.15-0.35:1; C. The mass ratio of the acrylamide monomer to the silanized modified core is 3-10:1; D. The amount of the crosslinking agent added is 0.2-1.0% of the mass of the acrylamide monomer; E. The water-soluble initiator includes at least one of ammonium persulfate, potassium persulfate, and azobisisobutyramidine hydrochloride; the amount of the water-soluble initiator added is 0.1-0.8% of the mass of the acrylamide monomer.

3. An oxidized pellet for direct hydrogen reduction, characterized in that, The raw materials for the oxidized pellets include the functionalized core-shell structure binder for direct hydrogen-based reduction pellets as described in claim 1; the reduction expansion rate of the oxidized pellets is less than 15%, and after isothermal reduction at 800-900℃ in pure hydrogen or a hydrogen-rich atmosphere for 30 minutes, its compressive strength is not less than 350N / pellet.

4. The oxidized pellets according to claim 3, characterized in that, The total amount of SiO2+Al2O3 introduced by the binder in the oxidized pellets is less than 0.5% of the total mass of the pellets.

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