Composite binder for bentonite pelletizing and its pelletizing method

Abstract

The present application relates to the technical field of metallurgical pellet, and particularly relates to a composite binder for bentonite pelletizing and a pelletizing method thereof. The binder is composed of a cross-linking type bentonite-carboxymethyl cellulose sodium binder, sodium carbonate, polyacrylamide, explosion-proof fiber and magnesium oxide. The cross-linking type binder is obtained by bridging modification of sodium carboxymethyl cellulose with sodium trimetaphosphate and modification of sodium-based bentonite; the former is covalently modified by KH-560 and etherified by quaternary ammonium groups, and the latter is covalently modified by KH-550 and coordinated by citric acid. The system cooperatively constructs a three-dimensional hybrid network through covalent cross-linking, electrostatic anchoring and ionic complexation, chemically locks the interface, and effectively solves the problem of adhesion force attenuation caused by ion erosion and component migration in the process of green ball stacking.

Description

Technical Field

[0001] This invention relates to the field of metallurgical pelletizing technology, specifically a composite binder for bentonite pelletizing and a pelletizing method thereof. Background Technology

[0002] In the production of oxidized pellets, the combination of organic polymer binders and bentonite is an effective technical approach to reduce bentonite usage and improve the iron grade of the pellets. This composite system, through the interaction between the organic binder and montmorillonite, promotes uniform dispersion of iron ore particles, increases the contact area between particles, and thus enhances the strength of the green pellets.

[0003] However, during the wet stacking stage of green pellets, the existing sodium carboxymethyl cellulose-bentonite composite system suffers from insufficient interfacial bonding stability: the Ca in the pore solution... 2+ Mg 2+ The divalent cations compress the electrical double layer of montmorillonite and complex it with sodium carboxymethyl cellulose segments, leading to its desorption on the bentonite surface. Simultaneously, wet-dry cycling induces the migration of organic components to the pellet surface. The combined effect of these factors results in a continuous decline in interfacial adhesion, reduced green pellet stacking strength, and difficulty in meeting the stability requirements of the production process. Summary of the Invention

[0004] (1) Technical problems to be solved

[0005] The purpose of this invention is to provide a composite binder for bentonite pelletizing and a pelletizing method thereof, so as to overcome the problem that the interfacial adhesion between sodium carboxymethyl cellulose and bentonite continuously decreases during the wet stacking of green pellets in existing sodium carboxymethyl cellulose-bentonite composite binders, resulting in a decrease in the stacking strength of green pellets.

[0006] (2) Technical solution

[0007] To achieve the above objectives, on the one hand, the present invention provides a composite binder for bentonite pelletizing, comprising the following components by weight: 92-98 parts of cross-linked bentonite-sodium carboxymethyl cellulose binder, 2-5 parts of sodium carbonate, 0.8-1.5 parts of polyacrylamide, 0.2-0.6 parts of explosion-proof fiber, and 0.3-0.6 parts of magnesium oxide;

[0008] The cross-linked bentonite-sodium carboxymethyl cellulose binder is an organic-inorganic hybrid cross-linked complex obtained by bridging sodium carboxymethyl cellulose with sodium trimetaphosphate and modified sodium bentonite; the modified sodium carboxymethyl cellulose is obtained by covalently modifying sodium carboxymethyl cellulose with KH-560 and then etherifying it with 3-chloro-2-hydroxypropyltrimethylammonium chloride; the modified sodium bentonite is obtained by covalently modifying sodium bentonite with KH-550 and then coordinating it with citric acid.

[0009] The sodium-based bentonite has a montmorillonite content of not less than 85%; the sodium carboxymethyl cellulose has a viscosity of 300–800 mPa·s at 25°C in a 2% aqueous solution; the polyacrylamide is a nonionic polyacrylamide with a molecular weight of 8 million to 15 million; the explosion-proof fiber is a polypropylene fiber with a length of 3–6 mm and a diameter of 15–25 μm.

[0010] Furthermore, the preparation method of the modified sodium carboxymethyl cellulose includes the following steps:

[0011] S11. Add anhydrous ethanol to the reactor, then add deionized water, and adjust the pH by adding acetic acid dropwise to obtain the first mixed solution; add KH-560 to the first mixed solution and stir to obtain a hydrolyzed KH-560 solution;

[0012] S12. Add sodium carboxymethyl cellulose powder to anhydrous ethanol, stir and swell to obtain sodium carboxymethyl cellulose suspension; add hydrolyzed KH-560 solution to sodium carboxymethyl cellulose suspension, adjust the pH of the system with sodium carbonate solution, heat and react to obtain the first dispersion;

[0013] S13. Adjust the pH of the first dispersion with sodium hydroxide solution; dissolve 3-chloro-2-hydroxypropyltrimethylammonium chloride in deionized water, and then add it dropwise to the adjusted first dispersion; after the addition is complete, control the system temperature at 60-65℃ and stir to obtain the first reaction suspension;

[0014] S14. After the reaction is complete, the first reaction suspension is washed with anhydrous ethanol, filtered and dried to obtain modified sodium carboxymethyl cellulose.

[0015] Furthermore, the mass ratio of KH-560 to sodium carboxymethyl cellulose is 1:3 to 1:2; the mass of 3-chloro-2-hydroxypropyltrimethylammonium chloride is 12% of the mass of sodium carboxymethyl cellulose.

[0016] Furthermore, the preparation method of the modified sodium-based bentonite includes the following steps:

[0017] S21. Add anhydrous ethanol and deionized water to the reactor, and add acetic acid dropwise to adjust the pH of the solution to obtain a second mixed solution; add KH-550 to the second mixed solution, stir to hydrolyze the solution, and obtain a hydrolyzed KH-550 solution;

[0018] S22. Sodium-based bentonite is added to an ethanol-water mixed solution and stirred to obtain a bentonite suspension; hydrolyzed KH-550 solution is added to the bentonite suspension, the pH is adjusted with acetic acid solution, and the reaction is heated to obtain a second dispersion;

[0019] S23. Cool the second dispersion to 45℃ and adjust the pH with 1mol / L dilute hydrochloric acid; dissolve citric acid in deionized water and then slowly add it to the adjusted second dispersion; keep the system temperature at 55℃ and stir to obtain the second reaction suspension;

[0020] S24. After the reaction is completed and cooled, the second reaction suspension is first washed with deionized water with pH adjusted to 6.0, then washed with anhydrous ethanol, filtered, dried, and ground to obtain modified sodium-based bentonite.

[0021] Furthermore, the mass ratio of KH-550 to sodium bentonite is 0.03 to 0.10:1; the mass of citric acid is 2.5% of the mass of sodium bentonite.

[0022] Furthermore, the preparation method of the cross-linked bentonite-sodium carboxymethyl cellulose binder includes the following steps:

[0023] S31. First, add the modified sodium bentonite to deionized water and stir to disperse it. Then, add the modified sodium carboxymethyl cellulose and continue stirring to obtain the third mixed solution.

[0024] S32. Add sodium trimetaphosphate to the third mixed solution, adjust the pH of the system with sodium carbonate solution; heat the reaction to obtain a cross-linked gel;

[0025] S33. After the reaction is complete, the cross-linked gel is spray-dried to obtain a cross-linked bentonite-carboxymethyl cellulose sodium binder.

[0026] Furthermore, the mass ratio of the modified sodium carboxymethyl cellulose to the modified sodium bentonite is 0.10 to 0.30:1; the amount of sodium trimetaphosphate added is 1% to 3% of the total mass of the modified sodium carboxymethyl cellulose and the modified sodium bentonite.

[0027] On the other hand, based on the same inventive concept, the present invention also provides a pelletizing method for a composite binder for bentonite pelletizing, which is used in the aforementioned composite binder for bentonite pelletizing, and includes the following steps:

[0028] S1. Preparation of binder: First, add cross-linked bentonite-carboxymethyl cellulose sodium binder, sodium carbonate, polyacrylamide and magnesium oxide into a double cone mixer or V-type mixer for dry mixing; then add explosion-proof fiber in batches and continue mixing to obtain a composite binder for bentonite pelletizing;

[0029] S2. Mixing the ingredients: Add the composite binder for bentonite pelletizing to the iron ore powder and dry mix to obtain the mixture;

[0030] S3. Grinding and pelletizing: Add the mixture to a grinding mill, add water and grind to obtain a ground mixture; add the ground mixture to a disc pelletizer or a cylindrical pelletizer to make pellets, adjust its moisture content, and obtain green pellets;

[0031] S4. Drying and calcining: The green pellets are fed into a chain grate machine-rotary kiln or belt calciner, and after drying, preheating, calcining and cooling processes, the oxidized pellets are obtained.

[0032] Furthermore, the amount of the composite binder for bentonite pelletizing added is 1.0% to 2.0% of the mass of the iron ore powder.

[0033] (3) Beneficial effects

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1. This invention upgrades the reversible physical adsorption interface between the organic and inorganic phases in the traditional system to a multi-layered chemical anchoring interface with covalent bonds as the main component and electrostatic anchoring and coordination complexation as the auxiliary components by KH-550 covalent modification of sodium carboxymethyl cellulose and quaternary ammonium group etherification modification, and KH-550 covalent modification and citric acid coordination modification of bentonite. This fundamentally eliminates the structural root cause of organic chain segment desorption caused by divalent cation erosion and component migration caused by wet-dry cycles, ensuring the continuous stability of the interfacial adhesion during the wet stacking of green pellets and improving the problem of continuous attenuation of the stacking strength of the existing sodium carboxymethyl cellulose-bentonite composite system.

[0036] 2. Based on the synergistic effect of silane covalent modification and citric acid coordination modification, sodium trimetaphosphate covalently bridges the two modified components, supplemented by strong electrostatic anchoring of quaternary ammonium groups on the montmorillonite surface, constructing a three-dimensional organic-inorganic hybrid cross-linked network, further locking the interfacial bonding state at the chemical structure level; simultaneously, citric acid exists in the binder system in the form of coordination anchoring or free dispersion, complexing free Ca in the pore solution. 2+ Mg 2+ By leveraging the metal ion sequestration function, the cross-linked network is indirectly protected from ion erosion, enabling the composite binder system to have stable resistance to ion erosion and component migration during green pellet stacking, thus fundamentally ensuring the strength stability of green pellet stacking. Attached Figure Description

[0037] Figure 1 This is a flowchart of the pelletizing method of the composite binder for bentonite pelletizing according to the present invention.

[0038] Figure 2 This is a physical image of the composite binder for bentonite pelletizing according to the present invention. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] This embodiment discloses a composite binder for bentonite pelletizing, comprising the following components by weight: 95 parts of cross-linked bentonite-sodium carboxymethyl cellulose binder, 3.5 parts of sodium carbonate, 1.2 parts of polyacrylamide, 0.4 parts of explosion-proof fiber, and 0.5 parts of magnesium oxide;

[0042] The cross-linked bentonite-sodium carboxymethyl cellulose binder is an organic-inorganic hybrid cross-linked complex obtained by bridging sodium carboxymethyl cellulose with sodium trimetaphosphate and modified sodium bentonite; the modified sodium carboxymethyl cellulose is obtained by covalently modifying sodium carboxymethyl cellulose with KH-560 and then etherifying it with 3-chloro-2-hydroxypropyltrimethylammonium chloride; the modified sodium bentonite is obtained by covalently modifying sodium bentonite with KH-550 and then coordinating it with citric acid.

[0043] The sodium-based bentonite has a montmorillonite content of not less than 85%; the sodium carboxymethyl cellulose has a viscosity of 300–800 mPa·s at 25°C in a 2% aqueous solution; the polyacrylamide is a nonionic polyacrylamide with a molecular weight of 8 million to 15 million; the explosion-proof fiber is a polypropylene fiber with a length of 3–6 mm and a diameter of 15–25 μm.

[0044] The preparation method of the modified sodium carboxymethyl cellulose includes the following steps:

[0045] S11. Add 95 mL of anhydrous ethanol to the reactor, then add 5 mL of deionized water, and adjust the pH to 4.5-5.0 by adding acetic acid dropwise to obtain the first mixed solution; take 3%-5% of the volume of the first mixed solution and slowly add KH-560 dropwise to the first mixed solution, stir at room temperature for 30-45 min to obtain the hydrolyzed KH-560 solution.

[0046] S12. Add 10g of sodium carboxymethyl cellulose powder to 100mL of anhydrous ethanol, stir and swell at room temperature for 30min to obtain a sodium carboxymethyl cellulose suspension; immediately add the hydrolyzed KH-560 solution (within 30min after preparation) to the sodium carboxymethyl cellulose suspension, adjust the pH of the system to 8.5-9.5 with sodium carbonate solution, raise the temperature to 70-80℃, stir and react for 4-5h to obtain the first dispersion;

[0047] S13. Adjust the pH of the first dispersion to 10.5–11.5 with sodium hydroxide solution; dissolve 1.2 g of 3-chloro-2-hydroxypropyltrimethylammonium chloride in 15 mL of deionized water, and then add it dropwise to the adjusted first dispersion; after the addition is complete, control the system temperature at 60–65 °C and stir the reaction for 2.0–2.5 h to obtain the first reaction suspension;

[0048] S14. After the reaction is complete, the first reaction suspension is washed four times with anhydrous ethanol, filtered, and dried under vacuum at 50°C to constant weight to obtain modified sodium carboxymethyl cellulose.

[0049] The mass ratio of KH-560 to sodium carboxymethyl cellulose is 1:3 to 1:2.

[0050] The preparation method of the modified sodium-based bentonite includes the following steps:

[0051] S21. Add 90 mL of anhydrous ethanol and 10 mL of deionized water to the reactor, and add acetic acid dropwise to adjust the pH of the solution to 5.0-6.0 to obtain a second mixed solution; add 0.5%-2% of the volume of the second mixed solution of KH-550 to the second mixed solution, and stir at room temperature for 30-60 min to hydrolyze to obtain a hydrolyzed KH-550 solution.

[0052] S22. Add 20g of sodium-based bentonite to 150mL of ethanol-water mixed solution (volume ratio 9:1), stir at room temperature for 30min to obtain a bentonite suspension; add hydrolyzed KH-550 solution to the bentonite suspension, adjust the pH of the system with acetic acid solution and maintain it at 6.0-7.5, raise the temperature to 75-85℃, stir the reaction for 3-4h to obtain a second dispersion;

[0053] S23. Cool the second dispersion to 45℃ and adjust the pH to 4.5-5.5 with 1mol / L dilute hydrochloric acid; dissolve 0.5g of citric acid in 10mL of deionized water and then slowly add it to the adjusted second dispersion; control the system temperature at 55℃ and stir the reaction for 2.5h to obtain the second reaction suspension.

[0054] S24. After the reaction is completed, cool to room temperature, wash the second reaction suspension twice with deionized water with pH adjusted to 6.0, then wash three times with anhydrous ethanol, filter, dry at 80℃ for 2 hours, grind and pulverize to obtain modified sodium-based bentonite.

[0055] The mass ratio of KH-550 to sodium bentonite is 0.03 to 0.10:1.

[0056] The preparation method of the cross-linked bentonite-sodium carboxymethyl cellulose binder includes the following steps:

[0057] S31. First, add the modified sodium bentonite to deionized water and stir to disperse for 15 minutes. Then, add the modified sodium carboxymethyl cellulose and continue stirring until uniform, so that the total solid content of the system is 10% to 20%, and obtain the third mixed solution.

[0058] S32. Add sodium trimetaphosphate to the third mixed solution, adjust the pH of the system to 9.5-10.0 with sodium carbonate solution; heat to 60-80℃, stir the reaction for 2-4 hours to obtain a cross-linked gel;

[0059] S33. After the reaction is complete, the cross-linked gel is spray-dried (inlet air temperature 160-175℃, outlet air temperature 80-90℃) to obtain cross-linked bentonite-carboxymethyl cellulose sodium binder.

[0060] The mass ratio of modified sodium carboxymethyl cellulose to modified sodium bentonite is 0.10 to 0.30:1; the amount of sodium trimetaphosphate added is 1% to 3% of the total mass of modified sodium carboxymethyl cellulose and modified sodium bentonite.

[0061] A pelletizing method using a composite binder for bentonite pelletizing includes the following steps:

[0062] S1. Preparation of binder: First, add cross-linked bentonite-sodium carboxymethyl cellulose binder, sodium carbonate, polyacrylamide and magnesium oxide into a double cone mixer or V-type mixer, and dry mix at 8-15 r / min for 5-8 min; then add explosion-proof fiber in 2-3 batches, and continue mixing for 5-8 min until the fiber is uniformly dispersed in the powder and there is no obvious fiber agglomeration, to obtain the composite binder for bentonite pelletizing;

[0063] S2. Mixing the ingredients: Add the composite binder for bentonite pelletizing to the iron ore powder and dry mix evenly to obtain the mixture;

[0064] S3. Grinding and pelletizing: Add the mixture to the grinding mill, adjust the moisture content of the mixture to 7.0% to 8.5%, grind for 5 to 10 minutes to obtain the ground mixture; add the ground mixture to the disc pelletizer or the cylindrical pelletizer to pelletize, pelletize for 10 to 15 minutes, adjust its moisture content to 8.0% to 9.0%, and obtain green pellets;

[0065] S4. Drying and Calcination: The green pellets are fed into a chain grate rotary kiln or belt calciner, and undergo drying (200-350℃), preheating (900-1050℃), calcination (1200-1280℃), and cooling processes to obtain the finished oxidized pellets. Figure 1 This is a flowchart illustrating the pelletizing method of the composite binder for bentonite pelletizing according to the present invention. Figure 2 This is a physical image of the composite binder for bentonite pelletizing according to the present invention.

[0066] The amount of the composite binder used for bentonite pelletizing is 1.0% to 2.0% of the mass of iron ore powder.

[0067] It should be noted that after the composite binder for bentonite pelletizing is added to the iron ore powder, the powder undergoes limited swelling in the water during the grinding process (the covalent cross-linking network restricts its complete dissolution). Under the mechanical shearing action of the grinding mill, the swollen powder fully expands and is evenly dispersed between the mineral powder particles, forming an effective adhesive coating layer and exerting the pelletizing and bonding effect. In step S3, the rotation speed of the pelletizing disc is selected according to the diameter of the pelletizing disc: when the diameter of the pelletizing disc is 1.0 to 2.0 meters, the rotation speed is set to 18 to 22 r / min; when the diameter of the pelletizing disc is 2.0 to 3.0 meters, the rotation speed is set to 10 to 16 r / min; when the diameter of the pelletizing disc is greater than 3.0 meters, the rotation speed is set to 6 to 9 r / min; the inclination angle is 45° to 55°.

[0068] Example 2

[0069] This embodiment discloses a composite binder for bentonite pelletizing, comprising the following components by weight: 92 parts of cross-linked bentonite-sodium carboxymethyl cellulose binder, 2 parts of sodium carbonate, 0.8 parts of polyacrylamide, 0.2 parts of explosion-proof fiber, and 0.3 parts of magnesium oxide;

[0070] The remaining preparation steps and pelletizing methods are the same as in Example 1.

[0071] Example 3

[0072] This embodiment discloses a composite binder for bentonite pelletizing, comprising the following components by weight: 98 parts of cross-linked bentonite-sodium carboxymethyl cellulose binder, 5 parts of sodium carbonate, 1.5 parts of polyacrylamide, 0.6 parts of explosion-proof fiber, and 0.6 parts of magnesium oxide;

[0073] The remaining preparation steps and pelletizing methods are the same as in Example 1.

[0074] Comparative Example 1

[0075] This comparative example differs from Example 1 in that the modified sodium carboxymethyl cellulose is not etherified with 3-chloro-2-hydroxypropyltrimethylammonium chloride, but only covalently modified with KH-560. The preparation method is adjusted from Example 1 as follows: the first dispersion obtained in step S12 is directly subjected to washing, filtration, and drying in step S14.

[0076] The remaining preparation steps and pelletizing methods are the same as in Example 1.

[0077] Comparative Example 2

[0078] This comparative example differs from Example 1 in that the modified sodium carboxymethyl cellulose is not covalently modified with KH-560, but only etherified with 3-chloro-2-hydroxypropyltrimethylammonium chloride. The preparation method is adjusted from Example 1 as follows: 10g of sodium carboxymethyl cellulose powder is added to 100mL of anhydrous ethanol and stirred at room temperature for 30min to allow it to swell; the pH is adjusted to 10.5–11.0 with sodium hydroxide solution; 1.2g of 3-chloro-2-hydroxypropyltrimethylammonium chloride is dissolved in 15mL of deionized water and slowly added dropwise to the reaction system; the reaction is stirred at 60–65℃ for 3.5h; after the reaction, washing, filtration, and drying are performed according to step S14.

[0079] The remaining preparation steps and pelletizing methods are the same as in Example 1.

[0080] Comparative Example 3

[0081] This comparative example differs from Example 1 in that unmodified sodium carboxymethyl cellulose is used instead of modified sodium carboxymethyl cellulose.

[0082] The remaining preparation steps and pelletizing methods are the same as in Example 1.

[0083] Comparative Example 4

[0084] This comparative example differs from Example 1 in that the modified sodium-based bentonite in this comparative example is not coordinated with citric acid, but is only covalently modified with KH-550. The preparation method is adjusted from Example 1 as follows: the second dispersion obtained in step S22 is directly subjected to washing, filtration, drying, and grinding in step S24.

[0085] The remaining preparation steps and pelletizing methods are the same as in Example 1.

[0086] Comparative Example 5

[0087] This comparative example differs from Example 1 in that the modified sodium-based bentonite in this example is not covalently modified with KH-550, but only coordinated with citric acid. The preparation method is adjusted from Example 1 as follows: 20g of sodium-based bentonite is added to 150mL of an ethanol-water mixture and stirred at room temperature for 30min; the pH is adjusted to 6.0–6.5 with 1mol / L dilute hydrochloric acid; 0.5g of citric acid is dissolved in 10mL of deionized water and slowly added; the mixture is stirred at 55℃ for 2.5h; after the reaction, washing, filtration, drying, and grinding are performed according to step S24.

[0088] The remaining preparation steps and pelletizing methods are the same as in Example 1.

[0089] Comparative Example 6

[0090] This comparative example differs from Example 1 in that unmodified sodium-based bentonite is used instead of modified sodium-based bentonite.

[0091] The remaining preparation steps and pelletizing methods are the same as in Example 1.

[0092] Comparative Example 7

[0093] This comparative example differs from Example 1 in that, in the cross-linked bentonite-sodium carboxymethyl cellulose binder described in this comparative example, unmodified sodium carboxymethyl cellulose is used instead of modified sodium carboxymethyl cellulose, and unmodified sodium-based bentonite is used instead of modified sodium-based bentonite.

[0094] The remaining preparation steps and pelletizing methods are the same as in Example 1.

[0095] Comparative Example 8

[0096] This comparative example differs from Example 1 in that the cross-linked bentonite-carboxymethyl cellulose sodium binder described in this comparative example does not contain sodium trimetaphosphate. The preparation method is adjusted from Example 1 as follows: step S32 is omitted, and the third mixed solution obtained in S31 is directly subjected to subsequent spray drying.

[0097] The remaining preparation steps and pelletizing methods are the same as in Example 1.

[0098] Comparative Example 9

[0099] This comparative example differs from Example 1 in that it uses unmodified sodium carboxymethyl cellulose and unmodified sodium bentonite, and does not add sodium trimetaphosphate to replace the cross-linked bentonite-sodium carboxymethyl cellulose binder.

[0100] The remaining preparation steps and pelletizing methods are the same as in Example 1.

[0101] Comparative Example 10

[0102] This comparative example is based on Example 1, but unlike Example 1, no explosion-proof fibers are added in this comparative example.

[0103] The remaining preparation steps and pelletizing methods are the same as in Example 1.

[0104] Experimental verification:

[0105] 1. Preparation of green pellets: The iron ore powder used in the experiment was magnetite concentrate (total iron grade 65.2%, SiO2 content approximately 3.0%–4.5%, CaO content approximately 0.3%–1.0%, MgO content approximately 0.2%–1.0%, -0.074mm content 85%, moisture 8.0%). The composite binders obtained in Examples 1–3 and Comparative Examples 1–10 were added at 1.5% of the iron ore powder mass, dry-mixed evenly, and milled until the moisture content reached 7.8% ± 0.2%, milled for 8 min, and then pelletized in a pelletizing machine for 12 min. The moisture content of the green pellets was adjusted to 8.5% ± 0.2%, and green pellets with a diameter of 10–12 mm were sieved out. Sufficient quantities were taken for various determinations. Each sample group was prepared in triplicate.

[0106] 2. Drop intensity of raw balls (times / 0.5m)

[0107] Take 20 raw balls and drop them one by one from a height of 500mm onto a 10mm thick steel plate. Repeat this process until the raw balls break and record the number of times each ball falls.

[0108] 3. Compressive strength of green pellets (N / pellet)

[0109] Take 20 raw pellets and apply radial pressure at a constant rate (10 mm / min) using a particle strength tester, and record the maximum force during crushing.

[0110] 4. Bulb bursting temperature (°C)

[0111] Following the standard method: 50 green balls were placed in a basket and quickly immersed in a vertical tube furnace preheated to a constant temperature (hot air velocity 1.8 m / s). The furnace was kept at this temperature for 5 minutes, and any bursting was observed. In this experiment, "bursting" was defined as: the green ball exhibiting an audible cracking sound during the test, or having a visible through-crack (the crack penetrates more than 1 / 3 of the cross-sectional diameter) after removal, or the ball breaking into two or more pieces; meeting any of these conditions constituted bursting. The initial temperature was set at 300℃. If no bursting occurred, the temperature was increased by 15℃, and a new batch of green balls was used to repeat the test until bursting occurred. The temperature at which 50% of the green balls (i.e., 25 balls) burst was recorded as the bursting temperature, and the experiment was repeated three times.

[0112] 5. Compressive strength retention rate after 24 hours of stacking (%)

[0113] Take the same batch of green pellets and divide them into two groups. The initial compressive strength F0 of the first group is immediately measured. The second group is placed in a constant temperature and humidity chamber (30±1℃, relative humidity 95±2%), stacked for 24 hours, and then removed. The compressive strength is measured within 5 minutes to obtain F0. 24 Calculate the retention rate: ;where F0 and F 24 All values ​​are averages of 20 balls. The experiment was repeated 3 times.

[0114] 6. Compressive strength of finished pellets (N / pellet)

[0115] Green pellets were placed in a chain grate-rotary kiln simulation device and subjected to drying (280℃), preheating (950℃), roasting (1250℃), and cooling to obtain finished pellets. The radial compressive strength of 20 finished pellets was determined according to GB / T 14201. The roasting temperature of 1250℃ was selected in this experiment, which is the intermediate representative temperature of the roasting range (1200~1280℃) applicable to this invention and is consistent with the industrial production temperature of conventional magnetite concentrate pellets. In practical applications, the specific roasting temperature should be optimized within the range of 1200~1280℃ based on the characteristics of the ore and equipment conditions.

[0116] Table 1: Initial physical properties test results of green pellets:

[0117]

[0118] Table 2: Test results of the strength of green pellets after stacking and the compressive strength of finished pellets:

[0119]

[0120] As shown in Tables 1 and 2, the strength retention rates of green pellets in Examples 1-3 after 24 hours of stacking were higher than those in Comparative Examples 3, 6, and 9, verifying the core role of the dual-modification system and sodium trimetaphosphate crosslinking in constructing a covalent network for interfacial adhesion stability. The retention rates of Comparative Examples 1 and 2, and Comparative Examples 4 and 5, respectively, fell between those of their individual modifications and complete dual modifications, indicating that KH-560 modification and quaternization, and KH-550 modification and citric acid modification, each have synergistic complementary effects, and individual modifications cannot fully realize their potential. Comparative Example 8 demonstrates that sodium trimetaphosphate is indispensable as a cross-phase covalent bridging agent. Comparative Example 10, due to the lack of added explosion-proof fibers, had a low green pellet bursting temperature, resulting in partial bursting or internal microcrack initiation during the preheating stage. The intact pellets had many internal defects, leading to lower compressive strength in the finished pellets.

[0121] Finally, it should be noted that although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite binder for bentonite pelletization, characterized by, The product comprises the following components by weight: 92-98 parts of cross-linked bentonite-sodium carboxymethyl cellulose binder, 2-5 parts of sodium carbonate, 0.8-1.5 parts of polyacrylamide, 0.2-0.6 parts of explosion-proof fiber, and 0.3-0.6 parts of magnesium oxide; The cross-linked bentonite-sodium carboxymethyl cellulose binder is an organic-inorganic hybrid cross-linked complex obtained by bridging sodium carboxymethyl cellulose with sodium trimetaphosphate and modified sodium bentonite; the modified sodium carboxymethyl cellulose is obtained by covalently modifying sodium carboxymethyl cellulose with KH-560 and then etherifying it with 3-chloro-2-hydroxypropyltrimethylammonium chloride; the modified sodium bentonite is obtained by covalently modifying sodium bentonite with KH-550 and then coordinating it with citric acid. The sodium-based bentonite has a montmorillonite content of not less than 85%; the sodium carboxymethyl cellulose has a viscosity of 300–800 mPa·s at 25°C in a 2% aqueous solution; the polyacrylamide is a nonionic polyacrylamide with a molecular weight of 8 million to 15 million; the explosion-proof fiber is a polypropylene fiber with a length of 3–6 mm and a diameter of 15–25 μm.

2. A composite binder for the briquetting of bentonite according to claim 1, characterized in that, The preparation method of the modified sodium carboxymethyl cellulose includes the following steps: S11. Add anhydrous ethanol to the reactor, then add deionized water, and adjust the pH by adding acetic acid dropwise to obtain the first mixed solution; add KH-560 to the first mixed solution and stir to obtain a hydrolyzed KH-560 solution; S12. Add sodium carboxymethyl cellulose powder to anhydrous ethanol, stir and swell to obtain sodium carboxymethyl cellulose suspension; add hydrolyzed KH-560 solution to sodium carboxymethyl cellulose suspension, adjust the pH of the system with sodium carbonate solution, heat and react to obtain the first dispersion; S13. Adjust the pH of the first dispersion with sodium hydroxide solution; dissolve 3-chloro-2-hydroxypropyltrimethylammonium chloride in deionized water, and then add it dropwise to the adjusted first dispersion; after the addition is complete, control the system temperature at 60-65℃ and stir to obtain the first reaction suspension; S14. After the reaction is complete, the first reaction suspension is washed with anhydrous ethanol, filtered and dried to obtain modified sodium carboxymethyl cellulose.

3. A composite binder for the briquetting of bentonite according to claim 2, characterized in that, The mass ratio of KH-560 to sodium carboxymethyl cellulose is 1:3 to 1:2; the mass of 3-chloro-2-hydroxypropyltrimethylammonium chloride is 12% of the mass of sodium carboxymethyl cellulose.

4. A composite binder for the briquetting of bentonite according to claim 1, characterized in that, The preparation method of the modified sodium-based bentonite includes the following steps: S21. Add anhydrous ethanol and deionized water to the reactor, and add acetic acid dropwise to adjust the pH of the solution to obtain a second mixed solution; add KH-550 to the second mixed solution, stir to hydrolyze the solution, and obtain a hydrolyzed KH-550 solution; S22. Sodium-based bentonite is added to an ethanol-water mixed solution and stirred to obtain a bentonite suspension; hydrolyzed KH-550 solution is added to the bentonite suspension, the pH is adjusted with acetic acid solution, and the reaction is heated to obtain a second dispersion; S23. Cool the second dispersion to 45℃ and adjust the pH with 1mol / L dilute hydrochloric acid; dissolve citric acid in deionized water and then slowly add it to the adjusted second dispersion; keep the system temperature at 55℃ and stir to obtain the second reaction suspension; S24. After the reaction is completed and cooled, the second reaction suspension is first washed with deionized water with pH adjusted to 6.0, then washed with anhydrous ethanol, filtered, dried, and ground to obtain modified sodium-based bentonite.

5. A composite binder for the briquetting of bentonite according to claim 4, characterized in that, The mass ratio of KH-550 to sodium bentonite is 0.03 to 0.10:1; the mass of citric acid is 2.5% of the mass of sodium bentonite.

6. A composite binder for the briquetting of bentonite according to claim 1, characterized in that, The preparation method of the cross-linked bentonite-sodium carboxymethyl cellulose binder includes the following steps: S31. First, add the modified sodium bentonite to deionized water and stir to disperse it. Then, add the modified sodium carboxymethyl cellulose and continue stirring to obtain the third mixed solution. S32. Add sodium trimetaphosphate to the third mixed solution, adjust the pH of the system with sodium carbonate solution; heat the reaction to obtain a cross-linked gel; S33. After the reaction is complete, the cross-linked gel is spray-dried to obtain a cross-linked bentonite-carboxymethyl cellulose sodium binder.

7. A composite binder for the briquetting of bentonite according to claim 6, characterized in that, The mass ratio of modified sodium carboxymethyl cellulose to modified sodium bentonite is 0.10 to 0.30:1; the amount of sodium trimetaphosphate added is 1% to 3% of the total mass of modified sodium carboxymethyl cellulose and modified sodium bentonite.

8. A method of pelletizing a composite binder for bentonite pelletization, using a composite binder for bentonite pelletization according to any one of claims 1 to 7, characterized by, The method includes the following steps: S1. Preparation of binder: First, add cross-linked bentonite-carboxymethyl cellulose sodium binder, sodium carbonate, polyacrylamide and magnesium oxide into a double cone mixer or V-type mixer for dry mixing; then add explosion-proof fiber in batches and continue mixing to obtain a composite binder for bentonite pelletizing; S2. Mixing the ingredients: Add the composite binder for bentonite pelletizing to the iron ore powder and dry mix to obtain the mixture; S3. Grinding and pelletizing: Add the mixture to a grinding mill, add water and grind to obtain a ground mixture; add the ground mixture to a disc pelletizer or a cylindrical pelletizer to make pellets, adjust its moisture content, and obtain green pellets; S4. Drying and calcining: The green pellets are fed into a chain grate machine-rotary kiln or belt calciner, and after drying, preheating, calcining and cooling processes, the oxidized pellets are obtained.

9. A method of pelletizing a composite binder for bentonite pellets according to claim 8, characterized by, The amount of the composite binder used for bentonite pelletizing is 1.0% to 2.0% of the mass of iron ore powder.

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