One-step forming process for chrome concentrate powder extrusion pellets

Abstract

The present invention relates to the technical field of pellet preparation, and particularly relates to a one-step forming process for chrome concentrate powder extrusion pellets. The process comprises the following steps: weighing chrome concentrate powder, a composite chromium-containing viscous component, and water in a weight ratio, mixing the chrome concentrate powder and the composite chromium-containing viscous component in proportion, spraying water into the mixture, stirring evenly, and then cold-extruding the mixture into pellets, which are then naturally dried to obtain chrome concentrate powder pellets; the weight proportions of the chrome concentrate powder, the composite chromium-containing viscous component, and the water are as follows: 73-84 parts of chrome concentrate powder, 16-21 parts of the composite chromium-containing viscous component, and 4-6 parts of water; and the composite chromium-containing viscous component is composed of a wet-process nickel compound, chromium-containing dust removal ash powder, polymer water-absorbing resin powder, silica powder, bentonite, sodium carboxymethyl cellulose, and water. The chrome concentrate powder is prepared by one-step extrusion forming, which greatly reduces water consumption, does not require multiple grinding processes, has a short process flow, low energy consumption, uniform particle size, and more stable forming.

Description

Technical Field

[0001] The present application relates to the technical field of pellet preparation, and in particular to a one-step forming process for chromium concentrate powder extrusion pellets. Background Art

[0002] Chromium ore, a core raw material for chromium alloy smelting, is primarily lump ore due to its natural physical properties. Once placed in the furnace, lump ore maintains breathability, reduces sparks and dust emissions, thereby stabilizing furnace conditions and improving energy efficiency. However, with the scarcity of chromium ore resources, lump ore production is decreasing, its grade is declining, and its price is rising. In contrast, chromium ore fines (particle size <10mm) obtained through beneficiation are increasing. Chromium alloy manufacturers are gradually using fine ore to produce products such as ferrochrome, with many companies using almost half of their production. Conventional sintering processes require high-temperature consolidation at temperatures exceeding 1000°C to produce high-strength pellets. However, emerging cold-forming technologies achieve comparable mechanical strength through binder modification and low-temperature drying (typically <200°C). This innovative process not only eliminates the high-temperature sintering step, reducing energy consumption by over 30% and carbon emissions by 80%, but also reduces equipment investment and operating and maintenance costs, offering both economic benefits and environmental friendliness. For example, after a company adopted cold-setting pellets, the production cost per ton of ferrochrome dropped by 12% and dust emissions decreased by 65%, fully verifying the industrial promotion value of this technology.

[0003] In traditional pelletizing technology, chromium ore powder is first dried. The dried ferrochrome ore is then mixed with a binder in a specific ratio and dry-ground. The dry-ground mixture then enters the damp-grinding process. Before entering the damp-grinding mill, the mixture is pre-moistened with 6-7% water using an atomizing water sprayer. The damp-grinding process requires grinding the mixture to a -200 mesh size of ≥90%. The damp-grinded mixture is then conveyed to a disc pelletizer for pelletization. During the pelletizing process, 1-2% water is added to improve the quality and particle size of the raw balls.

[0004] The traditional process requires a multi-step process of drying - batching - grinding - pelletizing - drying. Multiple grinding and water addition are required during production. The process is long and complicated, and the energy consumption is high.

[0005] Prior art methods for pelletizing chromium ore powder primarily utilize a cold-pressing process: chromium ore powder is mixed with a binder and fed into a blender. After mixing, the mixture is transferred to a briquetting machine for pressing and then air-dried to produce chromium ore pellets. For example, Chinese patent document CN114592123B discloses a chromium ore pellet and its preparation method. This pelletization method utilizes an organic-inorganic composite binder to reduce the amount of inorganic binder used, thus minimizing the impact on the chromium ore grade, while also improving the strength and thermal stability of the pellets. One such pellet comprises, by weight, 85-95 parts chromium ore powder, 2-3 parts binder, and 2-3 parts water. The binder comprises, by weight, 6-7 parts of a silane-modified polyimide / bentonite composite material, 3-4 parts of a silane-modified epoxy resin, 0.01-0.03 parts of dibutyltin dilaurate, and 20-30 parts of tetrahydrofuran. In the chromium ore powder balls of the present invention, a silane-modified polyimide / bentonite composite material and a silane-modified epoxy resin are used as main raw materials of a binder. The bentonite is first intercalated with octadecyltrimethylammonium bromide to preliminarily expand the interlayer distance of the bentonite. Then, 4,4'-diaminodiphenyl ether and hexafluorodianhydride are used as monomers to insert polyimide into the bentonite interlayers through a solution polymerization in-situ intercalation method to obtain a polyimide / bentonite composite material. Finally, the polyimide is end-capped with γ-aminopropyltriethoxysilane to obtain a silane-modified polyimide / bentonite composite material. The bentonite and the silane-modified polyimide are compounded to prepare an organic-inorganic composite material, thereby reducing the amount of inorganic bentonite used. The organic components in the binder can be burned and removed during the smelting process, thereby reducing the amount of slag in the smelting process. In order to improve the strength of chrome ore powder balls, the present invention introduces silane groups into polyimide and epoxy resin respectively. After mixing the binder of the present invention with water, under the catalytic action of dibutyltin dilaurate, the silane groups in the silane-modified polyimide and the silane-modified epoxy resin will hydrolyze, thereby making the polyimide and the epoxy resin cross-linked and cured at room temperature, reducing the curing temperature and shortening the curing time; and the co-crosslinking of polyimide and epoxy resin improves the strength of chrome ore powder balls, which can effectively reduce the damage of the pellets during transportation and use. However, organic additives such as dibutyltin dilaurate, tetrahydrofuran, and silane-modified polyimide are needed in this process, and bentonite needs to be modified in a complicated manner. The process is complicated and the cost is high, which is not suitable for large-scale promotion.

[0006] Furthermore, the primary pelletizing binders used by cold-pressed pelletizing companies are inorganic binders such as bentonite and cement, and high-molecular-weight organic binders such as humic acid and starch. Due to the high coarse-grain content of the concentrate used in pelletizing, a high proportion of bentonite or cement is required to meet industrial production requirements. This introduces significant amounts of impurities such as aluminosilicates, significantly reducing the pellet grade. Furthermore, their low high-temperature strength leads to pulverization and cracking of the pellets during direct smelting. Organic binders have not been widely adopted for a number of reasons, including the following: 1) The binder's inherent viscosity makes it difficult to add or mix uniformly during industrial production; 2) The binder's poor pelletizing properties make it difficult to control pellet size and achieve a low pelletizing rate; 3) The binder's green pellets have poor thermal stability, resulting in a low cracking temperature and a high ore return rate, making industrial production difficult; 4) The finished pellets are weak and cannot meet blast furnace requirements; and 5) They are prohibitively expensive, resulting in poor economic returns. Moreover, the usage amount and method of cold-pressed pelletizing-related binders are mostly for other types of mineral powders such as iron ore powder, and are not applicable to chromium ore powder pellets.

[0007] In summary, in the chromium powder ore pelletizing process, there are problems such as multiple grinding and water addition in the process, high grinding cost, high water consumption, long process flow, high energy consumption, high amount of inorganic binder added and low ore grade, high amount of organic binder added and high cost, while the composite methods such as organic binder modification and compounding of inorganic binders improve the pelletizing quality, it also greatly increases the complexity of the process. There is still a lack of economical and effective process for the addition of binders and pelletizing process of chromium powder ore, the particle size of the prepared pellets is difficult to control, and there are still problems such as poor thermal stability, low bursting temperature, insufficient falling strength and compressive strength of the raw balls. A better chromium powder ore pelletizing process is yet to be provided. Summary of the Invention

[0008] To overcome the shortcomings of the existing technology, the present application provides a one-time forming process for chrome concentrate powder extrusion pellets. Chrome ore powder pellets are prepared by extruding chrome concentrate powder in one step, which greatly reduces water consumption and does not require multiple grinding processes. The process flow is short, the energy consumption is low, the particle size is uniform, and the forming is more stable.

[0009] The embodiment of the present application is implemented as follows:

[0010] The present application provides an example of a one-step molding process for chrome concentrate powder extrusion pellets, comprising the following steps: weighing chrome concentrate powder, a composite chromium-containing viscous component, and water in a weight ratio, mixing the chrome concentrate powder and the composite chromium-containing viscous component in proportion, spraying water into the mixture, stirring the mixture evenly, and then cold-extruding the mixture into pellets, which are then naturally dried to obtain chrome concentrate powder pellets; the weight parts of the chrome concentrate powder, the composite chromium-containing viscous component, and the water are as follows: 73-84 parts of chrome concentrate powder, 16-21 parts of the composite chromium-containing viscous component, and 4-6 parts of water;

[0011] The composite chromium-containing viscous component comprises: wet-process nickel compound, chromium-containing dust removal powder, polymer water-absorbing resin powder, silicon micropowder, bentonite, sodium carboxymethyl cellulose and water.

[0012] Optionally, the particle size of the chromium concentrate powder pellets is 20-50 mm; and the pressure range of the cold extrusion molding is 17-21 MPa.

[0013] Optionally, the composite chromium-containing viscous component is composed of: by weight, 50-58 parts of wet-process nickel compound, 21-28 parts of chromium-containing dust removal powder, 3-5 parts of polymer water-absorbing resin powder; 1-3 parts of silicon micropowder, 4-7 parts of bentonite, 0.5-1.5 parts of sodium carboxymethyl cellulose and 1-3 parts of water.

[0014] Optionally, the water content of the wet-process nickel compound is 12-25 wt %.

[0015] Optionally, the chromium-containing dust removal powder has a Cr2O3 content of 8-13 wt%, and a ferric oxide content of 14-21 wt%.

[0016] Optionally, the average mesh size of the polymer water-absorbing resin powder is 4-30 meshes, the particle size of the silicon micropowder is 70-80 meshes, and the SiO2 content is ≥85%.

[0017] Optionally, the bentonite is calcium-based bentonite and sodium-based bentonite, and the ratio of calcium-based bentonite to sodium-based bentonite is 2.3-2.5:1 based on the total mass of the bentonite.

[0018] Optionally, the preparation method of the composite chromium-containing viscous component includes: weighing and mixing the wet-process nickel compound, the chromium-containing dust removal powder, the polymer water-absorbing resin powder, the silicon micropowder, the bentonite, and the sodium carboxymethyl cellulose according to the composition ratio of the composite chromium-containing viscous component, spraying water and mixing evenly to prepare the composite chromium-containing viscous component.

[0019] Optionally, the preparation method of the composite chromium-containing adhesive component comprises:

[0020] S1, first mixing the wet-process nickel compound and the polymer water-absorbent resin powder for 10-15 minutes to obtain a first mixture;

[0021] S2. Add the chromium-containing dust removal powder to the first mixture and stir for 5-8 minutes to obtain a second mixture;

[0022] S3, adding the silicon powder to the second mixture, and spraying atomized water accounting for 40-60% of the total mass of the water added to the composite chromium-containing viscous component onto the surface of the silicon powder and mixing for 5-8 minutes to obtain a third mixture;

[0023] S4. Add the bentonite and the sodium carboxymethyl cellulose to the third mixture, and spray the remaining water at the same time until the mixture is evenly mixed to obtain a composite chromium-containing viscous component.

[0024] Optionally, in step S2, a variable magnetic field is applied during the stirring process of adding the chromium-containing dust removal powder to the first mixture; the magnetic field intensity is 0.3-0.5T.

[0025] Beneficial effects include:

[0026] The present invention provides a one-step forming process for chromium concentrate powder extrusion pellets. By using a wet nickel compound as the main component of a composite chromium-containing viscous component, the function of water and a binder can be partially replaced, thereby reducing their usage content. At the same time, the chromium grade of the pellets is improved by resource utilization of the wet nickel compound, thereby reducing costs. By using chromium-containing dust removal ash with a coarser particle size than the wet nickel compound, the chromium-containing dust removal ash absorbs part of the water of the wet nickel compound through mixing, and the coarse particles are embedded in the wet nickel compound colloid, which is conducive to reducing the viscosity of the wet nickel compound, improving the miscibility, and improving the mixing uniformity. The porosity and particle size of the chromium-containing dust removal powder are between those of the wet-process nickel compound and the chromium concentrate powder, which can make the particle size distribution of the chromium-containing minerals in the pellets more dispersed, which is beneficial to improving the formation of stable mineral connections between the chromium-containing minerals, improving the pelletizing strength, improving the explosiveness of the pellets, while taking into account the air permeability of the pellets, etc., and is also beneficial to improving the grade of the chromium-containing pellets; by adding an appropriate amount of polymer water-absorbing resin powder, the water content and viscosity of the wet-process nickel compound are reduced, and the polymer water-absorbing resin powder swells when exposed to water and is embedded in the nickel-containing colloidal network of the wet-process nickel compound, physically dividing the continuous phase, thereby dispersing its overall adhesiveness into divided adhesive bodies, thereby It is beneficial to its bonding and uniform mixing with chrome concentrate powder, improving the quality of pellets. Its bonding properties are different from the adhesive properties of wet nickel compounds, thus providing different bonding properties for combining with chrome concentrate powder, enhancing the overall bonding properties of the composite chromium-containing adhesive component, and helping to improve the quality of pellets. The water absorption and expansion of the polymer water-absorbing resin powder (SAP) will form a slowly released water channel during the heating process, which can improve the possibility of raw ball bursting. The silicon micropowder makes the pellets have low and medium temperature strength, improves the thermal stability of the pellets, increases the thermal bursting temperature, reduces the generation of heating-induced cracks, reduces its viscosity, and enhances the colloid Strength; The lamellar structure and water swelling of bentonite can form an interpenetrating network with the wet-process nickel compound in the composite chromium-containing viscous component, and also reduce the excessive gelation of the wet-process nickel compound to a certain extent. At the same time, it can provide cross-space for silicon micropowder, high molecular water-absorbent resin powder, etc., which is conducive to the formation of cross-stable bonding between the composite chromium-containing viscous components and with chromium concentrate powder, and is conducive to the bonding with various components in the composite chromium-containing viscous component and chromium concentrate powder. When the organic bonding component is thermally decomposed, the quality of the pellets can still be ensured and the thermal cracking resistance can be improved; sodium carboxymethyl cellulose is conducive to enhancing the bonding performance of the composite chromium-containing viscous component.

[0027] The chromium ore raw material is directly chrome concentrate powder, eliminating the need for grinding. The chrome concentrate powder is mixed with a composite chromium-containing viscous component, added with a small amount of water, and pressurized to form pellets of the target size. This eliminates the need for multiple water-addition grinding processes, reducing grinding costs and conserving water. The process is short and requires only natural drying, eliminating the need for heating and drying, resulting in low energy consumption. The addition of the composite chromium-containing viscous component eliminates the need for specialized adhesives, reduces the amount of adhesive used, improves the chromium grade of the pellets, and provides excellent pelletizing properties. DETAILED DESCRIPTION

[0028] The technical solutions of the present invention will be described clearly and completely below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art, and unless specifically defined as herein, they will not be interpreted in an idealized or overly formal sense.

[0029] It will be understood by those skilled in the art that, unless otherwise stated, the singular forms "a," "an," "said," and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the stated features, integers, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The term "and / or" used herein includes all or any unit and all combinations of one or more associated listed items.

[0030] In the chromium powder ore pelletizing process, there are problems such as multiple grinding and water addition in the process, high grinding cost, high water consumption, long process flow, high energy consumption, high amount of inorganic binder added and low ore grade, high amount of organic binder added and high cost, while composite methods such as organic binder modification and compounding of inorganic binders improve the pelletizing quality, they also greatly increase the complexity of the process. There is still a lack of economical and effective process for the addition of binders and pelletizing process of chromium powder ore, the particle size of the prepared pellets is difficult to control, and there are still problems such as poor thermal stability, low bursting temperature, insufficient falling strength and compressive strength of the raw balls. Therefore, an embodiment of the present invention provides a one-time forming process for chromium concentrate powder extrusion pellets.

[0031] Exemplarily, a one-step molding process for chrome concentrate powder extrusion pellets is provided.

[0032] The following steps are involved:

[0033] Chrome concentrate powder, a composite chromium-containing viscous component, and water are weighed according to a weight ratio, mixed in proportion, sprayed with water, stirred evenly, and then cold-extruded to form pellets, which are naturally dried to obtain chrome concentrate powder pellets; the chrome concentrate powder pellets have a particle size of 20-50 mm; the cold extrusion molding pressure range is 17-21 MPa; the weight parts of the chrome concentrate powder, the composite chromium-containing viscous component, and water are as follows: 73-84 parts of chrome concentrate powder (optionally 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, etc.), 16-21 parts of the composite chromium-containing viscous component (optionally 16, 17, 18, 19, 20, 21, etc.), and 4-6 parts of water (optionally 4, 5, 6, etc.).

[0034] The chromium ore raw material is directly chrome concentrate powder, eliminating the need for grinding. The chrome concentrate powder is mixed with a composite chromium-containing viscous component, added with a small amount of water, and pressurized to form pellets of the target size. This eliminates the need for multiple water-addition grinding processes, reducing grinding costs and conserving water. The process is short and requires only natural drying, eliminating the need for heating and drying, resulting in low energy consumption. The addition of the composite chromium-containing viscous component eliminates the need for specialized adhesives, reduces the amount of adhesive used, improves the chromium grade of the pellets, and provides excellent pelletizing properties.

[0035] Under pressure, loose powder particles, primarily chrome concentrate, shift, filling gaps and increasing packing density. Friction and geometrical resistance between particles are overcome by external forces, resulting in a denser packing. These forces force the particles to slide and roll, forming a more efficient packing structure (such as hexagonal close packing), significantly reducing porosity.

[0036] When the pressure exceeds the yield strength of the particles, they undergo plastic deformation, increasing the contact area and forming a mechanical interlock. Adding water reduces surface energy and promotes interparticle adhesion. After the water evaporates and then dries, it forms solid bridges, further increasing pellet strength. The composite chromium-containing adhesive component creates capillary forces at the contact points of the particles, enhancing temporary bonding. During the pressurization process, external forces drive the rearrangement and deformation of the particles, as well as the distribution of adhesive substances. A stable structure is formed through a combination of physical and chemical interactions. The composite chromium-containing adhesive component is squeezed into the interparticle gaps, evenly covering the surface and strengthening the bond. The composite chromium-containing adhesive component contains chromium-containing powders such as wet-process nickel compounds and chromium-containing dust removal ash. While providing a certain bonding effect and enhancing pelletizing performance, it also fully utilizes chromium resources, improving pellet quality, and promoting cost reduction. The aforementioned higher cold extrusion pressure improves pellet quality. Pressures below this range reduce pellet strength. Pressures above this range may result in overly dense pellets, which in turn may cause cracks during heating and hinder the increase in pellet burst temperature.

[0037] The composition of the composite chromium-containing viscous component includes: 50-58 parts (optionally 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, etc.) of wet nickel compound with a water content of 12-25wt% (optionally 12wt%, 14wt%, 16wt%, 18wt%, 21wt%, 23wt%, 24wt%, 25wt%, etc.), 21-28 parts (optionally 21 parts, 22 parts, 23 parts, 24 parts, 25 parts) of chromium-containing dust removal powder , 26 parts, 27 parts, 28 parts, etc.), 3-5 parts of polymer water-absorbing resin powder (optionally 3 parts, 4 parts, 5 parts, etc.); 1-3 parts of silica powder (optionally 1 part, 2 parts, 3 parts, etc.), 4-7 parts of bentonite (optionally 4 parts, 5 parts, 6 parts, 7 parts, etc.), 0.5-1.5 parts of sodium carboxymethyl cellulose (optionally 0.5 parts, 0.7 parts, 0.8 parts, 1.0 parts, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, 1.5 parts, etc.), and 1-3 parts of water (optionally 1 part, 2 parts, 3 parts, etc.). Wet-process nickel compound, chromium-containing dust removal ash powder, polymer water-absorbing resin powder, silica powder, bentonite, and sodium carboxymethyl cellulose are weighed and mixed according to the composition ratio of the above-mentioned composite chromium-containing viscous component, and water in the aforementioned ratio is sprayed in to prepare the composite chromium-containing viscous component. The stirring and mixing process can be performed using existing stirring and mixing equipment, which is not specifically limited here.

[0038] Wet-process nickel compounds are nickel compounds precipitated during hydrometallurgical refining processes. For example, precipitation is used in hydrometallurgy to produce nickel salts or intermediate products (such as nickel carbonate, nickel oxalate, and nickel hydroxide). These wet-process precipitates are typically very fine, sludge-like substances with high moisture content and high viscosity. Typically, these fine sludge-like substances are difficult to nucleate and grow into qualified green pellets in the pelletizing tray (or drum). Even if they do form, the green pellets are extremely weak. Directly utilizing these precipitates through cold pressing, due to their high moisture content, can lead to cracking and bursting during the drying process. While some precipitated nickel compounds from hydrometallurgical refining processes can be recycled back into the hydrorefining process for purification, certain limitations make recycling these precipitates expensive. It is beneficial to the characteristics of wet-process nickel compounds that they have high moisture content, high viscosity, and contain more chromium components, which can improve the grade of chromium balls. By using wet-process nickel compounds as the main component of the composite chromium-containing viscous component, the functions of water and binder can be partially replaced, and their usage content can be reduced. At the same time, by utilizing the resources of wet-process nickel compounds, the chromium grade of the pellets can be improved and the cost can be reduced.

[0039] The moisture content of the wet-process nickel compound should be controlled between 12-25wt%. Excessive moisture content results in high viscosity and excessive water content, making it difficult to mix evenly with other components and chrome concentrate. Mixing becomes difficult, resulting in excessive drying shrinkage, which can easily cause pellets to crack and produce varying strengths, hindering their usability. Excessive moisture content causes the wet-process nickel compound to disperse into ultrafine particles, blocking the gaps between the iron ore powder and disrupting capillary water channels, reducing the porosity of the green pellets and failing to achieve their adhesive properties. After mixing with chrome concentrate, the resulting pellets will either fail to bond or have low strength (such as compressive strength) and become loose. To mitigate the effects of impurities, the wet-process nickel compound is heat-treated to decompose and remove some sulfur, water (chemically bound and free water), possible carbonates, and volatiles.

[0040] Chromium-containing dust ash is the dust collected by dust collector during the smelting of ore-heat furnace. Optionally, the Cr2O3 content in the chromium-containing dust ash is between 8-13wt%, the ferric oxide content is 14-21wt%, and it also contains some MgO and CaO. If the dust ash is directly discharged without treatment, it will cause serious environmental pollution and waste of chromium resources. The particle size of the chromium-containing dust ash is between that of wet nickel compound and chromium concentrate powder, and it has a porous type. Compared with other substances, its composition is closer to that of wet nickel compound and chromium concentrate powder. The chromium-containing dust ash with a coarser particle size than that of wet nickel compound is used, and the chromium-containing dust ash is mixed with the chromium-containing dust ash. The chromium-containing dust removal ash absorbs part of the water in the wet-process nickel compound, and the coarse particles are embedded in the wet-process nickel compound colloid, which helps reduce the viscosity of the wet-process nickel compound, improve miscibility, and improve mixing uniformity. At the same time, the porosity and particle size of the chromium-containing dust removal ash are between that of the wet-process nickel compound and the chromium concentrate powder, which can make the particle size distribution of the chromium-containing minerals in the pellets more dispersed, which is conducive to improving the formation of stable mineral connections between chromium-containing minerals, increasing the pellet strength, improving the explosiveness of the pellets, and taking into account the air permeability of the pellets, which is also conducive to improving the grade of the chromium-containing pellets. The content of chromium-containing dust removal ash should not be too much, as too much will lead to an excessive reduction in the viscosity of the wet-process nickel compound and the compressive strength of the pellets; too little will reduce the improvement effect.

[0041] SAP is a cross-linked polymer that can quickly absorb hundreds of times its own weight in water, forming a gel. This gel retains water even under pressure, resulting in high water retention, high water absorption, and high expansion. SAPs manufactured by Wanhua Chemical are available. They are made by neutralizing acrylic acid and acrylamide with sodium hydroxide and potassium hydroxide, followed by polymerization with a crosslinker. The resulting polymer pellets are then cut and dried. The high water content and high viscosity of wet-process nickel compounds make them difficult to mix. By adding an appropriate amount of polymer water-absorbing resin powder, the water content and viscosity of the wet-process nickel compound can be reduced through its high water absorption. After the polymer water-absorbing resin powder expands in contact with water, it embeds into the nickel-containing colloidal network of the wet-process nickel compound, physically dividing the continuous phase, thereby dispersing its overall adhesiveness into segmented adhesive bodies, which facilitates its bonding and uniform mixing with the chrome concentrate powder and improves the quality of the pellets. The water-absorbing and swelling properties of the polymer water-absorbing resin powder (SAP) and the large number of water-absorbing groups after expansion can also enhance the bonding with the chrome concentrate powder during pelletization, thereby enhancing the bonding properties. Its bonding properties are different from those of the wet-process nickel compound, thus providing different bonding properties for combining with the chrome concentrate powder, enhancing the overall bonding properties of the composite chromium-containing adhesive component and improving the quality of the pellets. The water-absorbing and swelling properties of the polymer water-absorbing resin powder (SAP) form slowly released water channels during heating, which can reduce the possibility of raw pellets bursting. Its use also helps reduce the amount of inorganic binder used and improve the chromium content of the pellets. The SAP content should not be too high. Above the above range, the wet-process nickel compound's adhesive properties are severely reduced, hindering improvements in pellet bonding strength, pellet quality, and thermal cracking temperature. Below the above range, the wet-process nickel compound exhibits high adhesive properties and viscosity, making it difficult to mix evenly and affecting pellet quality.

[0042] Optionally, the average mesh size of the polymer water-absorbing resin powder is 4-30 meshes; appropriate particle size can achieve better embedding of the nickel-containing colloidal network of the wet-process nickel compound after water absorption and expansion, and the effect of physically dividing the continuous phase is conducive to obtaining a composite chromium-containing viscous component with good comprehensive performance and moderate viscosity; below the above particle size, the segmentation effect is poor; above the above particle size, excessive segmentation of the wet-process nickel compound causes a sharp drop in viscosity; both are not conducive to improving the overall viscosity of the composite chromium-containing viscous component and improving the quality of ball formation.

[0043] Silica powder, the particle size of silica powder is 70-80 mesh, and the SiO2 content is ≥85%. When silica powder comes into contact with water (such as free water in wet nickel compounds, a small amount of water sprayed in, etc.), silanol bonds Si-OH are generated on the surface of the powder, which is beneficial for its combination with chrome concentrate powder, making the pellets have improved wet strength. After the pellets are dried or heated, the Si-OH bonds are transformed into long silicon-oxygen chains in the form of Si-O-Si-O, which is beneficial for increasing the binding force between the ore particles and producing higher low-temperature dry strength. The highly active amorphous (non-crystalline) SiO2 in the silica powder can combine with the chromium-magnesium spinel (MgO) in the chrome concentrate at a high temperature above 400°C. O·Cr2O3) reacts with the chromium-containing viscous component, capturing MgO and forming a new high-temperature binder phase, magnesium silicate (MgO·SiO2). This imparts high intermediate-temperature strength to the pellets, thereby improving their thermal stability and raising their thermal cracking temperature. Furthermore, the low volume expansion of silicon powder reduces the occurrence of heat-induced cracks, thus improving the thermal stability of the pellets. Adding silicon powder to the wet-process nickel compound viscous colloid reduces its viscosity, enhancing its strength and thermal stability. Consequently, the addition of a small amount of silicon powder improves the bonding ability of the composite chromium-containing viscous component with the chromium concentrate powder, increasing bonding strength and the thermal cracking resistance of the pellets, thereby stabilizing the pellet quality. Excessive silicon powder addition requires more water, reduces pellet grade, and reduces air permeability. Excessive silicon powder addition is detrimental to improving the pellets' thermal stability and thermal cracking temperature.

[0044] Bentonite, a common inorganic binder for pellets, provides a foundation of stable bonding within the composite chromium-containing viscous component. Its lamellar structure and water-swelling properties allow it to form an interpenetrating network with the wet-process nickel compound within the composite chromium-containing viscous component, mitigating the excessive gelation of the wet-process nickel compound. Bentonite also provides cross-linking space for silica powder, polymer absorbent resin powder, and other components, fostering cross-linking and stable bonding within the composite chromium-containing viscous component and with chrome concentrate powder. This facilitates bonding with the various components within the composite chromium-containing viscous component and with chrome concentrate powder. This ensures pellet quality and improves thermal cracking resistance even when the organic binder decomposes under heat. The bentonite content should be neither too high, as this will affect pellet quality, nor too low, as this will compromise the foundation of stable bonding.

[0045] Optionally, calcium-based bentonite reduces the reduction expansion rate of the pellets, which is beneficial to the thermal stability of the pellets. Sodium-based bentonite has higher water absorption and expansion properties and better bonding properties. Based on the total mass of bentonite, the ratio of calcium-based bentonite to sodium-based bentonite is 2.3-2.5:1; thereby improving the thermal stability of the pellets and reducing thermal cracking, while taking into account the water absorption performance to ensure a strong bond with other components.

[0046] Sodium carboxymethyl cellulose is an organic binder with long chains. While it weakens the adhesive properties of the wet-process nickel compound during thorough mixing with the other components, a small amount of this component is added to enhance the adhesive properties of the composite chromium-containing adhesive component. However, excessive addition should be avoided, as this can significantly affect the thermal stability of the pellets, leading to significant removal of the organic binder after heating.

[0047] Water, added by spraying or other means, can be used to adjust and improve local property changes caused by water absorption during the mixing process of silica powder and super absorbent resin. (For example, when silica powder is initially added, it has little contact with other components, absorbs insufficient water, and is difficult to mix. Spraying can be used to achieve preliminary hydration of the silica powder to enhance compatibility with other components and facilitate mixing.) This can affect the stirring and mixing effect. Avoid adding too much water, just enough to improve the effect.

[0048] Therefore, the composite chromium-containing sticky component can provide ball-forming viscosity, increase the comprehensive utilization of chromium-containing waste, improve the chromium grade, and reduce the amount of water required for ball forming. It only needs to be dried naturally without heating and drying, and has low energy consumption. When mixed with chromium concentrate powder, it can greatly reduce the amount of binder used and improve the quality of ball forming.

[0049] In some embodiments, the wet-process nickel compound and the polymer water-absorbent resin powder are first mixed for 10-15 minutes to obtain a first mixture. This allows the strong water absorption and expansion properties of the polymer water-absorbent resin powder to reduce the colloidal viscosity of the wet-process nickel compound with a high water content and improve its mixability.

[0050] Chromium-containing dust removal powder is added to the first mixture and stirred for 5-8 minutes to obtain a second mixture. By adding chromium-containing dust removal powder to the first mixture, the coarse particles of chromium-containing dust removal powder close to the wet-process nickel compound are facilitated to further reduce the colloidal viscosity of the wet-process nickel compound with a high water content, thereby facilitating further mixing.

[0051] Optionally, a variable magnetic field is applied during the stirring process of adding chromium-containing dust removal powder to the first mixture. The variable magnetic field promotes the migration of magnetizable substances (Fe3O4, FeCr2O4, Cr3O4, etc.) in the chromium-containing dust removal powder in the mixture, thereby improving the mixing effect; at the same time, the magnetic field induces metal ion oscillation and other effects, induces the activation of the interfaces between the various components, and can also accelerate the mixing process, thereby greatly improving the mixing uniformity rate of the mixture and achieving a better uniformity effect.

[0052] Optionally, the magnetic field strength is 0.3-0.5 T, thereby ensuring the magnetic field-enhanced mixing effect.

[0053] Silica powder is added to the second mixture, and atomized water accounting for 40-60% of the total mass of water added to the composite chromium-containing viscous component is sprayed on the surface of the silica powder and mixed for 5-8 minutes to obtain a third mixture. The addition of silica powder further improves the mixture. The sprayed water facilitates the contact between silica powder and water, and can generate silanol bonds Si-OH on the surface of the powder, which is beneficial to its compatibility and mixing with the mixture and improves the mixing effect.

[0054] Bentonite and sodium carboxymethyl cellulose are added to the third mixture, and the remaining water is sprayed in simultaneously until the mixture is uniformly mixed to obtain a composite chromium-containing adhesive component. Finally, bentonite and sodium carboxymethyl cellulose are added to adjust the overall adhesive properties of the composite chromium-containing adhesive component. The remaining water is sprayed in during the final mixing stage to achieve a cross-linked, stable network among the components in the mixture.

[0055] The features and performance of the present invention are further described in detail below with reference to the embodiments:

[0056] Example 1

[0057] A one-step forming process for chrome concentrate powder extrusion pellets comprises the following steps: weighing chrome concentrate powder, a composite chromium-containing viscous component, and water according to a weight ratio, mixing the chrome concentrate powder and the composite chromium-containing viscous component in proportion, spraying water into the mixture, stirring the mixture evenly, and then cold-extruding the mixture into pellets, which are then naturally dried to obtain chrome concentrate powder pellets; the weight ratios of the chrome concentrate powder, the composite chromium-containing viscous component, and the water are as follows: 83 parts of chrome concentrate powder, 20 parts of the composite chromium-containing viscous component, and 5 parts of water; the particle size of the chrome concentrate powder pellets is 30-40 mm; and the pressure range of the cold extrusion forming is 19 MPa.

[0058] The composite chromium-containing viscous component is composed, by weight, of 56 parts of a wet-process nickel compound, 24 parts of chromium-containing dust removal ash, 5 parts of a polymer water-absorbing resin powder, 2 parts of silica powder, 5 parts of bentonite, 1.3 parts of sodium carboxymethyl cellulose, and 2 parts of water. The moisture content of the wet-process nickel compound is 21% by weight. The chromium-containing dust removal ash contains 8-13% Cr2O3 and 14-21% ferric oxide. The polymer water-absorbing resin powder has an average mesh size of 21 mesh, the silica powder has a particle size of 70-80 mesh, and an SiO2 content of ≥85%. The bentonite is composed of calcium-based and sodium-based bentonite, with the ratio of calcium-based to sodium-based bentonite being 2.4:1, based on the total weight of the bentonite.

[0059] The preparation method of the composite chromium-containing adhesive component comprises:

[0060] S1. First, the wet-process nickel compound and the polymer water-absorbing resin powder are mixed for 13 minutes to obtain a first mixture.

[0061] S2. Add the chromium-containing dust removal powder to the first mixture and stir for 6 minutes to obtain a second mixture; apply a variable magnetic field during the stirring process; the magnetic field intensity is 0.4T.

[0062] S3. Add the silicon micropowder to the second mixture, and simultaneously spray atomized water accounting for 55% of the total mass of water added to the composite chromium-containing viscous component onto the surface of the silicon micropowder and mix for 7 minutes to obtain a third mixture.

[0063] S4. Add the bentonite and the sodium carboxymethyl cellulose to the third mixture, and spray the remaining water at the same time until the mixture is evenly mixed to obtain a composite chromium-containing viscous component.

[0064] The properties of the chrome concentrate powder pellets produced in the Examples and Comparative Examples were tested. Drop strength refers to the number of times a chrome concentrate powder pellet can be dropped freely from a height of 2.5 m onto a steel plate without breaking. Ten chrome concentrate powder pellets were tested in each group. Compressive strength is determined according to the national standard GB / T14201-93. The test results for the chrome concentrate powder pellets are as follows: compressive strength 23.2 MPa; drop strength 9 times; and burst temperature 841°C.

[0065] Example 2

[0066] The one-step pelletizing process for chrome concentrate powder extrusion is essentially the same as that of Example 1, with the primary difference being that the cold extrusion pressure range is 14 MPa. The test results for the chrome concentrate powder pellets are as follows: compressive strength 22.3 MPa; drop strength 8 times; and burst temperature 824°C.

[0067] Example 3

[0068] The one-step extrusion pelletizing process for chrome concentrate powder was essentially the same as that of Example 1, with the primary difference being that the cold extrusion pressure range was 25 MPa. The test results for the chrome concentrate powder pellets were as follows: compressive strength 23.7 MPa; drop strength 10 times; and burst temperature 819°C.

[0069] Example 4

[0070] The one-step pelletizing process for chrome concentrate powder extrusion was essentially the same as in Example 1, with the primary differences being: 45 parts of the wet-process nickel compound was used; the remaining components were increased proportionally. The following examples and comparative examples were modified in the same manner as in Example 1, with the added amounts being distributed proportionally to the remaining components. The chrome concentrate powder pellets were tested as follows: compressive strength 22.4 MPa; drop strength 8 times; and burst temperature 834°C.

[0071] Example 5

[0072] The one-step pelletizing process for chrome concentrate powder extrusion is essentially the same as in Example 1, with the main difference being the addition of 63 parts of wet nickel compound. The chrome concentrate powder pellets were tested as follows: compressive strength 22.7 MPa; drop strength 9 times; and burst temperature 837°C.

[0073] Example 6

[0074] The one-step pelletizing process for chrome concentrate powder extrusion is essentially the same as that of Example 1, with the main difference being that 17 parts of chromium dust removal powder is contained. The test results of the chrome concentrate powder pellets are as follows: compressive strength 22.5 MPa; drop strength 9 times; and burst temperature 836°C.

[0075] Example 7

[0076] The one-step pelletizing process for chrome concentrate powder extrusion is essentially the same as that of Example 1, with the main difference being that 31 parts of chromium dust removal powder is contained. The test results of the chrome concentrate powder pellets are as follows: compressive strength 21.6 MPa; drop strength 7 times; and burst temperature 819°C.

[0077] Example 8

[0078] The one-step pelletizing process for chrome concentrate powder extrusion is essentially the same as in Example 1, with the main difference being the addition of 2 parts of polymer water-absorbing resin powder. The test results for the chrome concentrate powder pellets are as follows: compressive strength 21.5 MPa; drop strength 7 times; and burst temperature 822°C.

[0079] Example 9

[0080] The one-step pelletizing process for chrome concentrate powder extrusion is essentially the same as in Example 1, with the main difference being the addition of 7 parts of polymer water-absorbing resin powder. The test results for the chrome concentrate powder pellets are as follows: compressive strength 21.2 MPa; drop strength 7 times; and burst temperature 808°C.

[0081] Example 10

[0082] The one-step pelletizing process for chrome concentrate powder extrusion was essentially the same as in Example 1, with the primary difference being the addition of 0.5 parts of silicon powder. The test results for the chrome concentrate powder pellets were as follows: compressive strength 22.8 MPa; drop strength 9 times; and burst temperature 836°C.

[0083] Example 11

[0084] The one-step pelletizing process for chrome concentrate powder extrusion is essentially the same as in Example 1, with the main difference being the addition of 3 parts bentonite. The test results for the chrome concentrate powder pellets are as follows: compressive strength 22.4 MPa; drop strength 8 times; and burst temperature 831°C.

[0085] Example 12

[0086] The one-step pelletizing process for chrome concentrate powder extrusion was essentially the same as in Example 1, with the main difference being the addition of 1.9 parts sodium carboxymethyl cellulose. The test results for the chrome concentrate powder pellets were as follows: compressive strength 22.9 MPa; drop strength 10 times; and burst temperature 823°C.

[0087] Example 13

[0088] The one-step pelletizing process for chrome concentrate powder extrusion was essentially the same as that in Example 1, with the primary difference being that the moisture content of the wet-process nickel compound was 10 wt%. Test results for the chrome concentrate powder pellets were as follows: compressive strength 21.3 MPa, drop strength 7 times, and burst temperature 801°C.

[0089] Example 14

[0090] The one-step pelletizing process for chrome concentrate powder extrusion was essentially the same as that in Example 1, with the primary difference being that the moisture content of the wet-process nickel compound was 28 wt%. Test results for the chrome concentrate powder pellets were as follows: compressive strength 22.9 MPa, drop strength 9 times, and burst temperature 835°C.

[0091] Example 15

[0092] The one-step pelletizing process for chrome concentrate powder extrusion is essentially the same as in Example 1, with the primary difference being that the bentonite is calcium-based. The test results for the chrome concentrate powder pellets are as follows: compressive strength 21.9 MPa; drop strength 8 times; and burst temperature 829°C.

[0093] Example 16

[0094] The one-step pelletizing process for chrome concentrate powder extrusion is essentially the same as that of Example 1, with the primary difference being that the bentonite is sodium-based bentonite. The test results for the chrome concentrate powder pellets are as follows: compressive strength 21.1 MPa; drop strength 7 times; and burst temperature 820°C.

[0095] Example 17

[0096] The one-step pelletizing process for chrome concentrate powder extrusion is essentially the same as in Example 1, with the primary difference being the simultaneous addition of the wet-process nickel compound, polymer water-absorbing resin powder, and chromium-containing dust removal ash powder. Test results for the chrome concentrate powder pellets are as follows: compressive strength 23.0 MPa; drop strength 9 times; and burst temperature 837°C.

[0097] Example 18

[0098] The one-step pelletizing process for chromium concentrate powder extrusion was essentially the same as in Example 1, with the primary difference being that no variable magnetic field was applied during the stirring process of the chromium-containing dust removal powder added to the first mixture. Testing results for the chromium concentrate powder pellets were as follows: compressive strength 22.8 MPa; drop strength 8 times; and burst temperature 833°C.

[0099] Example 19

[0100] The one-step pelletizing process for chrome concentrate powder extrusion was essentially the same as in Example 1, with the primary difference being the addition of silicon powder to the second mixture and the omission of water spraying. Test results for the chrome concentrate powder pellets were as follows: compressive strength 23.1 MPa; drop strength 9 times; and burst temperature 839°C.

[0101] Comparative Example 1

[0102] The one-step pelletizing process for chrome concentrate powder extrusion was essentially the same as in Example 1, with the primary difference being that no composite chromium-containing adhesive component was added, and bentonite was used as a binder. The test results for the chrome concentrate powder pellets were as follows: compressive strength 20.1 MPa; drop strength 5 times; and burst temperature 614°C.

[0103] Comparative Example 2

[0104] The one-step pelletizing process for chrome concentrate powder extrusion was essentially the same as in Example 1, with the primary difference being that the composite chromium-containing viscous component was omitted, while sodium carboxymethyl cellulose was added as a binder. The test results for the chrome concentrate powder pellets were as follows: compressive strength 19.2 MPa; drop strength 6 times; and burst temperature 594°C.

[0105] The above detailed description of the preferred embodiments of the present invention is only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some or all of the technical features therein can be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A one-step pelletizing process for chrome concentrate powder extrusion, characterized by: The following steps are involved: Chrome concentrate powder, a composite chromium-containing viscous component, and water are weighed in a weight ratio, mixed in proportion, sprayed with water, stirred evenly, and then cold-extruded to form pellets, which are then naturally dried to obtain chrome concentrate pellets; the weight ratios of the chrome concentrate powder, the composite chromium-containing viscous component, and water are as follows: 73-84 parts of chrome concentrate powder, 16-21 parts of the composite chromium-containing viscous component, and 4-6 parts of water; The composite chromium-containing viscous component comprises: wet-process nickel compound, chromium-containing dust removal powder, polymer water-absorbing resin powder, silicon micropowder, bentonite, sodium carboxymethyl cellulose and water.

2. The one-step forming process of chromium concentrate powder extrusion pellets according to claim 1, characterized in that: The particle size of the chromium concentrate powder pellets is 20-50 mm; the pressure range of the cold extrusion molding is 17-21 MPa.

3. The one-step forming process of chromium concentrate powder extrusion pellets according to claim 1, characterized in that: The composite chromium-containing viscous component comprises, by weight, 50-58 parts of wet-process nickel compound, 21-28 parts of chromium-containing dust removal powder, 3-5 parts of polymer water-absorbing resin powder, 1-3 parts of silicon micropowder, 4-7 parts of bentonite, 0.5-1.5 parts of sodium carboxymethyl cellulose and 1-3 parts of water.

4. The one-step forming process of chromium concentrate powder extrusion pellets according to claim 3, characterized in that: The water content of the wet-process nickel compound is 12-25 wt %.

5. The one-step forming process of chromium concentrate powder extrusion pellets according to claim 1, characterized in that: The chromium-containing dust removal powder has a Cr2O3 content of 8-13 wt%, and a ferric oxide content of 14-21 wt%.

6. The one-step forming process of chromium concentrate powder extrusion pellets according to claim 1, characterized in that: The average mesh size of the polymer water-absorbing resin powder is 4-30 meshes, the particle size of the silicon micropowder is 70-80 meshes, and the SiO2 content is ≥85%.

7. The one-step forming process of chromium concentrate powder extrusion pellets according to claim 1, characterized in that: The bentonite is calcium-based bentonite and sodium-based bentonite. Based on the total mass of the bentonite, the ratio of calcium-based bentonite to sodium-based bentonite is 2.3-2.5:

1.

8. The one-step forming process of chromium concentrate powder extrusion pellets according to claim 1, characterized in that: The preparation method of the composite chromium-containing viscous component comprises: weighing and mixing the wet-process nickel compound, the chromium-containing dust removal powder, the polymer water-absorbing resin powder, the silicon micropowder, the bentonite, and the sodium carboxymethyl cellulose according to the composition ratio of the composite chromium-containing viscous component, spraying water and mixing evenly to obtain the composite chromium-containing viscous component.

9. The one-step forming process of chromium concentrate powder extrusion pellets according to claim 8, characterized in that: The preparation method of the composite chromium-containing adhesive component comprises: S1, first mixing the wet-process nickel compound and the polymer water-absorbent resin powder for 10-15 minutes to obtain a first mixture; S2. Add the chromium-containing dust removal powder to the first mixture and stir for 5-8 minutes to obtain a second mixture; S3, adding the silicon powder to the second mixture, and spraying atomized water accounting for 40-60% of the total mass of the water added to the composite chromium-containing viscous component onto the surface of the silicon powder and mixing for 5-8 minutes to obtain a third mixture; S4. Add the bentonite and the sodium carboxymethyl cellulose to the third mixture, and spray the remaining water at the same time until the mixture is evenly mixed to obtain a composite chromium-containing viscous component.

10. The one-step forming process of chromium concentrate powder extrusion pellets according to claim 9, characterized in that: In step S2, the chromium-containing dust removal powder is added to the first mixture and a variable magnetic field is applied during stirring; the magnetic field intensity is 0.3-0.5T.